Acepromazine Maleate

ayss-proe′meh-zeen mal′ee-ate

Trade and other names: ACE, Aceproject, Aceprotabs, Atravet, and Promace; it sometimes is called acetylpromazine.

Functional classification: Tranquilizer, phenothiazine tranquilizer

Pharmacology and Mechanism of Action

Phenothiazine tranquilizer and sedative. Acepromazine inhibits central dopaminergic receptors to produce sedation and tranquilization. Acepromazine also has antimuscarinic action and blocks norepinephrine at adrenergic receptors (e.g., alpha-receptors). Because of the blockade of alpha-receptors on vascular smooth muscle it also produces vasodilation.

Indications and Clinical Uses

Acepromazine is used as a sedative, a tranquilizer, a preanesthetic, and an anesthetic adjunct. In small animals, acepromazine can produce antiemetic effects. For some indications, the administration also produces vasodilation. In horses for treatment of laminitis, it has increased the arterial digital blood flow after a dose of 0.02-0.04 mg/kg.

Precautionary Information

Adverse Reactions and Side Effects

Sedation and ataxia are common side effects. Extrapyramidal effects (involuntary muscle movements), twitching, dystonia, or Parkinson-like effects are rare but are possible with the administration of phenothiazines to animals. Phenothiazines may produce excessive vagal tone in some animals. This may be especially prominent in brachycephalic breeds. Administration of atropine may be used to treat the signs of high vagal tone. Because of alpha-adrenergic antagonism, hypotension is possible in animals. In horses, persistent penile prolapse has been reported from use. This effect in horses is unpredictable and apparently not related to dose.

Contraindications and Precautions

Use cautiously in animals that are prone to seizures. However, a risk of seizures in animals from administration of acepromazine may not be as much of a risk as once thought. Seizures were not reported to be a clinical problem in retrospective studies of patients who had seizures.

Do not use in animals that have problems with dystonia or that have had extrapyramidal effects from use of phenothiazines.

Phenothiazines can cause hypotension (via alpha-receptor blockade); therefore, use cautiously with other hypotensive drugs or in conditions that may exacerbate hypotension.

In pregnancy it produced only minor reduction in blood flow and oxygen delivery to the fetus when used in late pregnancy in cows.

Drug Interactions

Acepromazine may potentiate other drugs that cause vasodilation. Acepromazine may increase the risk of seizures if administered with other drugs that lower seizure threshold, but this may not be as much of a risk as once thought. Acepromazine has been used to sedate dogs for glucose tolerance testing (0.1 mg/kg), without adversely affecting the results.

Instructions for Use

Acepromazine can be administered PO, IV, or IM. When used with general anesthetics, lower doses of general anesthetics can be used, especially when administering barbiturates and inhalant anesthetics. Clinical signs from acepromazine administration are most prominent during the first 3-4 hours after administration but may persist for 7 hours.

Patient Monitoring and Laboratory Tests

Monitor blood pressure in animals susceptible to hypotension. Acepromazine does not affect adrenal function testing in dogs.

Formulations

Acepromazine is available in 5-, 10-, and 25-mg tablets and in a 10 mg/mL injection. Acepromazine oral granules and powder are available in Canada.

Stability and Storage

Store in a tightly sealed container, protected from light, and at room temperature. Stability of compounded formulations has not been investigated.

Regulatory Information

Withdrawal times: There are no withdrawal times established in the US. It has been estimated that for extralabel use, establish a withdrawal time of at least 7 days for meat and 48 hours for milk.

Canada: 7 days for meat; 48 hours for milk.

RCI Classification: 3

Acetaminophen

ah-seet-ah-mee′noe-fen

Trade and other names: Tylenol and generic brands

Functional classification: Analgesic

Pharmacology and Mechanism of Action

Analgesic drug. Exact mechanism of action is not known; however, acetaminophen probably inhibits centrally mediated pain transmission. The centrally mediated analgesia may occur via inhibition of COX-3, a variant of COX-1 found in the central nervous system. Other evidence indicates that acetaminophen may inhibit prostaglandins in some cells and tissue in which low concentrations of arachidonic acid are present. The site of acetaminophen action may be the peroxidase enzyme component of prostaglandin H₂ synthase. Therefore, COX inhibition may occur at site-specific tissues, sparing the gastrointestinal mucosa, platelets, and kidneys but acting centrally. Other evidence suggests that acetaminophen can stimulate inhibitory pain pathways mediated by serotonin (5-HT₃). This evidence suggests that acetaminophen may directly activate serotonin receptors.

In canine studies it has not produced anti-inflammatory action but has been effective as an analgesic agent.

Indications and Clinical Uses

Acetaminophen is used as an analgesic and for pain control in dogs. Do not use in cats. It is considered relatively weak as an analgesic. Often used in combination with an opiate (e.g., codeine).

Precautionary Information

Adverse Reactions and Side Effects

Acetaminophen is well tolerated in dogs at doses listed; however, high doses have caused liver toxicity. It causes severe toxicosis in cats because of their inability to excrete metabolites. Clinical signs of toxicity include methemoglobinemia, acute hepatic toxicosis, swelling of paws, and Heinz body anemia.

Contraindications and Precautions

Do not administer to cats. In people, toxic episodes are more likely when administered with drugs that alter the activity of hepatic drug enzymes. Such a reaction also is possible in animals.

In cats, treatment of intoxication requires prompt treatment with acetylcysteine (see monograph for acetylcysteine) and monitoring.

Drug Interactions

In people, other drugs (especially alcohol) will increase risk of hepatotoxicosis. It is not known if other drugs increase this risk in animals.

Instructions for Use

Many non-prescription (OTC) formulations are available. Acetaminophen with codeine may have greater analgesic efficacy in some animals. See other entries for formulations that contain codeine.

Patient Monitoring and Laboratory Tests

Monitor liver enzyme levels periodically to look for evidence of hepatotoxicity. In cats that have received acetaminophen, there is a high risk of toxicity and careful monitoring of liver enzymes and blood cell parameters is needed. Many human hospitals and some diagnostic laboratories can measure acetaminophen concentrations in plasma. In people, treatment is initiated if plasma/serum concentrations are above 200 mcg/mL 4 hours after ingestion.

Formulations

Acetaminophen is available in 120-, 160-, 325-, and 500-mg tablets.

Stability and Storage

Acetaminophen is stable in aqueous solutions. Maximum stability is at pH of 5-7.

Small Animal Dosage

Dogs

• 15 mg/kg q8h PO.

Cats

• Contraindicated.

Large Animal Dosage

Calves

50 mg/kg PO, followed by 30 mg/kg PO q6h.

No other doses have been reported for large animals.

Regulatory Information

No regulatory information is available. For extralabel use withdrawal interval estimates, contact FARAD at 1-888-USFARAD (1-888-873-2723).

RCI Classification: 4

Acetaminophen + Codeine

ah-seet-ah-mee′noe-fen + koe′deen

Trade and other names: Tylenol with codeine and many generic brands

Functional classification: Analgesic, opioid

Pharmacology and Mechanism of Action

Analgesic agent. Exact mechanism of action for acetaminophen is not known; however, as discussed previously, a centrally mediated mechanism is likely, either via inhibition of central prostaglandin synthesis or effects on serotonergic inhibitory pain pathways. In this formulation, the opiate codeine is added to enhance analgesia. Effects of codeine are not established in animals. Systemic absorption of codeine from oral administration is small in dogs, and codeine may play only a minor role in analgesia.

Indications and Clinical Uses

Acetaminophen + Codeine is used for analgesia in dogs (e.g., postoperative use). Codeine or codeine with acetaminophen is indicated for treatment of moderate pain.

Codeine formulations have also been used as an antitussive. Despite the widespread use of codeine in humans, the efficacy in animals for its antitussive use or analgesic use has not been established.

Oral absorption of codeine in dogs is low. Because codeine is converted to morphine (10% of dose) for its activity and the duration of morphine is short in dogs, the clinical effectiveness of codeine in dogs may be questionable.

Precautionary Information

Adverse Reactions and Side Effects

Acetaminophen + Codeine is well tolerated in dogs at doses listed; however, high doses have caused liver toxicity.

Contraindications and Precautions

Do not administer to cats because acetaminophen is known to be toxic to cats. Codeine is a Schedule II controlled substance.

Drug Interactions

In people, other drugs (especially alcohol) will increase risk of hepatotoxicity. It is not known if other drugs increase this risk in animals, but consider this possibility when administering other drugs that may affect hepatic metabolism (see Appendix F).

Instructions for Use

Many generic preparations are available. Consider that other ingredients may be present in some combination tablets (e.g., ibuprofen or caffeine).

Patient Monitoring and Laboratory Tests

Monitor liver enzyme levels periodically to look for evidence of hepatotoxicity caused by acetaminophen.

Formulations

Acetaminophen + Codeine is available in oral solution and tablets. A variety of formulations are available (e.g., 300-mg acetaminophen plus 15-, 30-, or 60-mg codeine).

Stability and Storage

Acetaminophen is stable in aqueous solutions. Maximum stability is at pH of 5-7.

Small Animal Dosage

Dogs

Follow dosing recommendations for codeine. Administer dose to deliver doses of codeine equivalent to 0.5-1.0 mg/kg q4-6h PO.

Cats

• Contraindicated.

Large Animal Dosage

No dose has been reported for large animals.

Regulatory Information

Acetaminophen + Codeine is a Schedule III drug controlled by DEA. Do not administer to animals intended for food.

Acetazolamide

ah-seet-ah-zole′a-mide

Trade and other names: Diamox

Functional classification: Diuretic

Pharmacology and Mechanism of Action

Carbonic anhydrase inhibitor. Acetazolamide, like other carbonic anhydrase inhibitors, produces a diuresis through inhibition of the uptake of bicarbonate in proximal renal tubules via enzyme inhibition. This action results in loss of bicarbonate in the urine and a diuresis. The action of carbonic anhydrase inhibitors results in urine loss of bicarbonate, alkaline urine, and water loss.

Indications and Clinical Uses

Acetazolamide is rarely used as a diuretic any longer. There are more potent and effective diuretic drugs available such as the loop diuretics (furosemide).

Acetazolamide, like other carbonic anhydrase inhibitors, is used primarily to lower intraocular pressure in animals with glaucoma. Methazolamide is used more often than acetazolamide for this purpose, and other treatment regimens are now used more often than carbonic anhydrase inhibitors.

Acetazolamide, like other carbonic anhydrase inhibitors, is sometimes used to produce more alkaline urine for management of some urinary calculi.

Precautionary Information

Adverse Reactions and Side Effects

Acetazolamide can potentially produce hypokalemia in some patients. Significant bicarbonate loss can occur with repeated administration. In dogs, a respiratory reaction has been observed, which is attributed to respiratory acidosis.

Contraindications and Precautions

Do not use in patients with acidemia. Use cautiously in any animal sensitive to sulfonamides.

Drug Interactions

Acetazolamide will produce alkaline urine, which may affect clearance of some drugs. Alkaline urine may potentiate the effects of some antibacterial drugs (e.g., macrolides and quinolones).

Instructions for Use

Acetazolamide, in combination with other agents, is usually used to decrease intraocular pressure in the treatment of glaucoma. Acetazolamide has been used to produce alkaline urine to prevent formation of some urinary calculi. However, unless there is supplementation with bicarbonate, the urine alkalinization will not be sustained with repeated administration.

Patient Monitoring and Laboratory Tests

Monitor patient’s ocular pressure when used to treat glaucoma.

Formulations

Acetazolamide is available in 125- and 250-mg tablets.

Stability and Storage

Stable if stored in tight containers. Compounded solutions are stable at least 60 days.

Small Animal Dosage

Dogs

• Glaucoma: 5-10 mg/kg q8-12h PO.

• Other diuretic uses: 4-8 mg/kg q8-12h PO.

Cats

• 7 mg/kg, q8h, PO.

Large Animal Dosage

No dose has been reported for large animals.

Regulatory Information

No regulatory information is available. For extralabel use withdrawal interval estimates, contact FARAD at 1-888-USFARAD (1-888-873-2723).

RCI Classification: 4

Acetylcysteine

ah-see-til-sis′tay-een

Trade and other names: Mucomyst and Acetadote. Also referred to as N-acetylcysteine.

Functional classification: Mucolytic, antidote

Pharmacology and Mechanism of Action

Acetylcysteine decreases viscosity of secretions and is used as a mucolytic agent in eyes and in bronchial nebulizing solutions. Acetylcysteine is a sulfhydryl compound and acts to increase synthesis of glutathione in the liver. Glutathione subsequently acts as an antioxidant and facilitates conjugation to toxic metabolites, particularly the toxic metabolites of acetaminophen. The antioxidant effects also have been used to treat conditions associated with oxidative stress.

Indications and Clinical Uses

As a donator of the sulfhydryl group, it is used as an antidote for intoxications (e.g., acetaminophen toxicosis in cats). When treating poisoning, it is important that acetylcysteine be administered as soon as possible for optimum effectiveness. Acetylcysteine also has been used to prevent contrast medium-induced nephropathy. Acetylcysteine has been used as a treatment of oxidative stress because it is a scavenger of hydroxyl radicals and hypochlorous acid. Acetylcysteine will reduce cerebral edema.

Precautionary Information

Adverse Reactions and Side Effects

None reported in animals. Allergic reactions have been reported in people, which resemble anaphylactic reactions when it is given IV. These reactions are manifest as skin reactions, bronchospasm, tachycardia, and hypotension.

Contraindications and Precautions

Acetylcysteine may cause sensitization with prolonged topical administration. It may react with certain materials in nebulizing equipment.

Drug Interactions

Acetylcysteine acts to donate sulfhydryl groups and may facilitate drug conjugation.

Instructions for Use

Available as agent for decreasing viscosity of respiratory secretions, but most common use is as a treatment for intoxications. In cats, acetylcysteine is used to treat acetaminophen toxicosis. When treating an intoxication, doses are listed here, but consult a poison control center for specific guidelines. For treatment of oxidative stress, constant rate infusions have been used in which 50 mg/kg is diluted 1 : 4 in saline solutions and administered IV over the course of 1 hour.

Patient Monitoring and Laboratory Tests

When used to treat acetaminophen toxicity, monitor CBC and liver enzyme concentrations.

Formulations

Acetylcysteine is available in a 20% solution (200 mg/mL).

Stability and Storage

Acetylcysteine is unstable in air and easily oxidizes. It should be protected from light. Discard open vials after 96 hours.

Large Animal Dosage

No dose has been reported for large animals.

Regulatory Information

No regulatory information is available. However, because it is short-acting and is used primarily for treatment of intoxications, no withdrawal time is suggested. For further information contact FARAD at 1-888-USFARAD (1-888-873-2723).

Acyclovir

ay-sye′kloe-veer

Trade and other names: Zovirax and generic brands

Functional classification: Antiviral

Pharmacology and Mechanism of Action

Antiviral drug. Acyclovir is a synthetic purine analogue (acyclic nucleoside analogue). It has antiviral activity against herpes virus. The action is related to the affinity for the enzyme thymidine kinase (TK). However, resistance among some virus forms is possible because of changes in TK or in the DNA polymerase. It is used for treatment of various forms of herpes virus infection in humans and also has been used for treatment of viral infections in animals. However, feline herpes virus 1 (FHV1) is resistant to acyclovir and valciclovir, and studies are lacking on the susceptibility of other herpes viruses. The half-life is 9.6 hours for horses, 2.3 hours for dogs, and 2.6 hours for cats. By comparison, the half-life in humans is 2.5 hours. Unfortunately, it is not absorbed orally in horses (less than 3%), and there are little data to confirm oral absorption in other species. In humans, oral absorption is only 10%. Other forms (e.g., pro-drugs and related compounds) are better absorbed in people, but these have been expensive to use in animals. Information on these drugs (penciclovir, valacyclovir, and famciclovir) can be found in other monographs.

Indications and Clinical Uses

Acyclovir is an antiviral drug. The use in veterinary medicine is limited because the activity against some viruses (e.g., FHV1) is either poor or unknown. In cats, acyclovir had poor absorption and produced toxicity. Acyclovir is able to inhibit replication of equine herpes virus (EHV1) in vitro. However, acyclovir oral absorption in horses was poor and inconsistent and intravenous treatment is needed for treatment of EHV1 infection.

Precautionary Information

Adverse Reactions and Side Effects

The most serious adverse effect in humans is acute renal insufficiency. This may be prevented by slow intravenous infusion and proper hydration. Phlebitis can occur with intravenous administration. No adverse effects were identified in limited studies performed in horses. In cats, significant adverse effects have been observed, which included myelosuppression, hepatotoxicity, and nephrotoxicity.

Contraindications and Precautions

Do not use in animals with compromised renal function.

Drug Interactions

Do not mix with biological solutions (e.g., blood products). Do not mix with fluids that contain bacteriostatic preservatives. Do not use with other nephrotoxic drugs.

Instructions for Use

To prepare injectable formulation, dilute each vial with 10 or 20 mL of water to make 50 mg/mL. Do not use bacteriostatic water that contains benzyl alcohol or parabens. Further dilute solution to at least 100 mL to a concentration of 7 mg/mL or less.

Patient Monitoring and Laboratory Tests

Monitor BUN and creatinine during use. In horses, doses should be administered to maintain plasma concentrations above 0.3 mcg/mL.

Formulations

Acyclovir is available in 400- and 800-mg tablets, 200-mg capsules, 1-g and 500-mg vials for injection (50 mg/mL), and 40-mg/mL oral suspension.

Stability and Storage

After reconstitution of solution, at 50 mg/mL, it is stable for 12 hours at room temperature. More dilute solutions are stable for 24 hours. If refrigerated, a precipitate will form, which should be redissolved at room temperature before use. Store tablets and capsules in a tightly sealed container, protected from light, and at room temperature.

Small Animal Dosage

Dogs and Cats

• Systemic doses have not been determined. Doses have been extrapolated from human use: 3 mg/kg PO 5 times daily for 10 days, up to 10 mg/kg PO 5 times daily for 10 days. Alternatively 10-20 mg/kg IV q8h (slow infusion for 1 hour).

Large Animal Dosage

Horses

• 10 mg/kg q12h IV infused over one hour. Even after 20 mg/kg, oral acyclovir is not absorbed in horses well enough for systemic treatment.

Regulatory Information

Because of mutagenicity, it should not be administered to animals intended for food.

Aglepristone

Trade and other names: Alizine

Functional classification: Hormone, antiprogestin

Pharmacology and Mechanism of Action

Aglepristone (RU 46534) is a synthetic steroid antiprogestin related to mifepristone (RU 38486). It has an affinity for progesterone receptors that is three times that of progesterone, without producing the same effects as progesterone. When administered, it binds to progesterone receptors to produce an antiprogestin effect and to interrupt and terminate pregnancy.

Indications and Clinical Uses

Aglepristone has also been used to terminate pregnancy in animals, treat mammary hyperplasia in cats, induce parturition in dogs and cats, and treat pyometra.

Precautionary Information

Adverse Reactions and Side Effects

After termination of pregnancy in dogs, mucoid discharge may be observed. Other side effects include slight depression, transient anorexia, and mammary gland congestion. Otherwise, there have been no significant adverse effects reported in animals.

Contraindications and Precautions

Aglepristone will terminate pregnancy. It should be handled with caution by women. Owners should be cautioned about risks during pregnancy.

Drug Interactions

No drug interactions are reported in animals.

Instructions for Use

For treatment of pyometra, it should be administered on days 1, 2, 7, and 14 by SQ injection.

Patient Monitoring and Laboratory Tests

No specific monitoring is necessary.

Formulations

Aglepristone is not available in the US at this time. In some European countries it is available as a 30-mg/mL injection.

Stability and Storage

Store at room temperature protected from light.

Small Animal Dosage

Dogs

• Terminate pregnancy: Two doses of 10 mg/kg (0.33 mL/kg) once daily for 2 days.

Cats

• Treatment of pyometra: 10 mg/kg SC, on days 1, 2, 7, and 14.

Large Animal Dosage

Large Animals

No large animal doses are available.

Regulatory Information

Do not administer to food-producing animals.

Albendazole

al-ben′dah-zole

Trade and other names: Valbazen

Functional classification: Antiparasitic

Pharmacology and Mechanism of Action

Benzimidazole antiparasitic drug. Albendazole binds to intracellular beta-tubulin in parasites and prevents the microtubule formation for cell division.

Indications and Clinical Uses

Albendazole is used to treat a variety of intestinal helminth parasites. It has been used for treating parasitic infections of the respiratory tract, including Capillaria aerophilia, Paragonimus kellicotti, Aelurostrongylus abstrusus, Filaroides spp., and Oslerus osleri. It is also effective for treatment of Giardia in small animals. However, because albendazole has been associated with bone marrow suppression in dogs and cats, other drugs have been used for Giardia.

Precautionary Information

Adverse Reactions and Side Effects

Leukopenia and thrombocytopenia are possible in dogs and cats. Albendazole has an affinity for rapidly dividing cells and may cause toxicity to bone marrow and intestinal epitheliulm. High doses have been associated with bone marrow toxicity (J Am Vet Med Assoc, 213: 44-46, 1998) in dogs and cats, and it should be used cautiously in small animals. In other species, at approved doses, there is a wide margin of safety. Adverse effects can include anorexia, lethargy, and bone marrow toxicity.

Contraindications and Precautions

Adverse effects are more likely when administered for longer than 5 days. Avoid high doses. Pregnancy caution: Do not use during first 45 days of pregnancy.

Drug Interactions

No drug interactions are reported in animals.

Instructions for Use

Used primarily as antihelmintic but also has demonstrated efficacy for giardiasis.

Patient Monitoring and Laboratory Tests

Monitor CBC in animals experiencing signs suspicious of adverse effects. If high doses are accidentally administered to small animals, CBC should be examined for evidence of suppression.

Formulations

Albendazole is available in a 113.6-mg/mL suspension and 300-mg/mL paste.

Stability and Storage

Store in a tightly sealed container, protected from light, and at room temperature. Stability of compounded formulations has not been investigated.

Small Animal Dosage

• Anthelmintic dose: 25-50 mg/kg q12h PO for 3 days.

• Respiratory parasites: 50 mg/kg q24h PO for 10-14 days.

• Giardia: 25 mg/kg q12h PO for 2 days.

Birds

50-100 mg/kg once per day for 2-9 days.

Regulatory Information

Cattle withdrawal time: 27 days meat. Do not use in lactating dairy cattle. Sheep withdrawal time: 7 days meat.

Albuterol Sulfate

al-byoo′ter-ole sul′fate

Trade and other names: Proventil, Ventolin, and Torpex equine inhaler. Also known as Salbutamol outside the US.

Functional classification: Bronchodilator, beta-agonist

Pharmacology and Mechanism of Action

Beta₂-adrenergic agonist. Albuterol stimulates beta₂-receptors to relax bronchial smooth muscle. It may also inhibit release of inflammatory mediators, especially from mast cells. This mechanism of action has been beneficial to relax bronchial smooth muscle to relieve bronchospasm and bronchoconstriction.

Indications and Clinical Uses

Albuterol is indicated in a variety of airway diseases for bronchodilation. Except for equine use, doses are primarily derived from extrapolation of human dose. Efficacy studies for small animal use are not reported. Onset of action is 15-30 minutes, and duration of action may be as long as 8 hours.

Albuterol is used as an inhaler (Torpex) in horses for treatment of airway disease. It provides immediate relief of bronchospasm and bronchoconstriction in horses.

Precautionary Information

Adverse Reactions and Side Effects

Excessive beta-adrenergic stimulation at high doses results in tachycardia and muscle tremors. Arrhythmias are possible with high doses. All beta₂-agonists will inhibit uterine contractions at the end of gestation in pregnant animals. High doses of beta₂-agonists can lead to hypokalemia because they stimulate Na⁺-K⁺-ATPase and increase intracellular K⁺, while decreasing serum K⁺ and producing hykperglycemia. Treatment consists of KCl supplement at a rate of 0.5 mEq/kg/hr.

Contraindications and Precautions

Avoid use in pregnant animals. IM or SQ injections can be painful.

Drug Interactions

All beta-agonists will interact with, and potentiate other drugs that act on, beta-adrenergic receptors.

Instructions for Use

Administration to horses requires an adaptor to facilitate a metered-dose inhaler. For horses, each valve actuation (puff) of the device delivers 120 micrograms of albuterol sulfate. One dose is three puffs, totaling 360 micrograms. For injection, dilute solution to 0.01 mg/mL (10 mcg/mL) before injection and further dilute to 50/50 with saline or 5% dextrose before injection. When used for bronchoconstriction, it is helpful for acute exacerbations, used intermittently, with other drugs (e.g., corticosteroids) administered for maintenance.

Patient Monitoring and Laboratory Tests

Monitor heart rate and rhythm in animals with cardiovascular disease. Monitor potassium concentrations for evidence of hypokalemia if high doses are administered. Monitor glucose for evidence of hyperglycemia.

Formulations

Albuterol is available in 2-, 4-, and 5-mg tablets and 2-mg/5-mL syrup. Solutions for inhalation are 0.83 mg/mL and 5 mg/mL. Equine formulation contains 6.7 grams of formulated albuterol sulfate in a pressurized aluminum canister. This formulation delivers 120 micrograms of albuterol sulfate. One dose is three puffs, totaling 360 micrograms.

Stability and Storage

Store in well-closed containers and protected from light. Aqueous solutions are stable if kept at an acidic pH (2.2-5).

Small Animal Dosage

Dogs and Cats

• 20-50 mcg/kg q6-8h, oral, up to a maximum of 100 mcg/kg q6h.

Large Animal Dosage

Horses

• 120-mcg albuterol per actuation. Administer 3 actuations, up to a maximum of 6, actuations per each dose four times daily.

• Foals: 0.01-0.02 mg/kg, q8-12h, PO.

Regulatory Information

Do not administer to animals intended for food.

When treating horses, allow 48 hours or longer for urine clearance in performance animals that may be tested.

RCI Classification: 3

Alendronate

ah-len′droe-nate

Trade and other names: Fosamax

Functional classification: Antihypercalcemic

Pharmacology and Mechanism of Action

Bisphosphonate drug. Drugs in this class include pamidronate, risedronate, zolendronate, and etidronate. This is a group of drugs characterized by a germinal bisphosphonate bond. They slow the formation and dissolution of hydroxyapatite crystals. Their clinical use is in their ability to inhibit bone resorption. These drugs decrease bone turnover by inhibiting osteoclast activity, retarding bone resorption, and decreasing the rate of osteoporosis. Alendronate is 100-1000 times more potent than older drugs such as etidronate. Unfortunately, alendronate is poorly absorbed orally (3%-7%), and use of oral formulations in animals may not be effective. In dogs, half-life in plasma is short (1-2 hours), but there is prolonged update bone in which the half-life is 300 days.

Indications and Clinical Uses

Alendronate, like other bisphosphonate drugs, is used in people to treat osteoporosis and treatment of hypercalcemia of malignancy.

In animals, alendronate is used to decrease calcium in conditions that cause hypercalcemia, such as cancer and vitamin D toxicosis. It may be helpful for managing neoplastic complications associated with pathologic bone resorption. It also may provide pain relief in patients with pathologic bone disease. Most experimental work performed in dogs has been performed with pamidronate rather than alendronate.

Precautionary Information

Adverse Reactions and Side Effects

No serious adverse effects have been identified; however, use in animals has been uncommon. In people, esophageal injury and erosion are important problems.

When administering to animals, ensure that the entire medication is swallowed and followed with water.

Contraindications and Precautions

Do not administer with foods or medications containing calcium. Food will decrease absorption.

Drug Interactions

Do not mix with a solution containing calcium (e.g., Lactated Ringer’s solution). Do not give with foods containing calcium.

Instructions for Use

When administering oral medication, ensure that the drug is not trapped in the esophagus. Food will significantly reduce oral absorption. Wait at least 30 minutes before feeding.

Patient Monitoring and Laboratory Tests

Monitor serum calcium and phosphorus.

Formulations

Alendronate is available in 5-, 10-, 35-, 40-, and 70-mg tablets.

Stability and Storage

Store in a tightly sealed container, protected from light, and at room temperature.

Small Animal Dosage

Dogs

• 0.5-1 mg/kg q24h PO.

Large Animal Dosage

No dose has been reported for large animals.

Regulatory Information

Withdrawal times are not established for animals that produce food. For extralabel use withdrawal interval estimates, contact FARAD at 1-888-USFARAD (1-888-873-2723).

Alfaxalone

Al-FAX-ah-lone

Trade and other names: Alfaxan (previous name was alphaxalone)

Functional classification: Anesthetic agent

Pharmacology and Mechanism of Action

Alfaxalone is chemically alfaxalone-2-hydroxypropyl-beta-cyclodextrin (HPCD). It is a synthetic neuroactive steroid that interacts with GABA receptors in the central nervous system to produce anesthesia and muscle relaxation. Alfaxalone is related to an older formulation (Saffan) first introduced in 1971, which was alfaxalone plus alfadolone in a combination of neurosteroids. This older formulation was in a castor oil formulation that induced mast cell degranulation and histamine release and produced swollen extremities, anaphylactic reactions, and other signs of histamine release. This new formulation (Alfaxan) overcomes the formulation issue by usine a cyclodextrin solubilizing vehicle. The half-life is short in animals (less than 1 hour) but it exhibits nonlinear pharmacokinetics and may be eliminated slower with high doses.

Indications and Clinical Uses

Alfaxalone is used as a general anesthetic agent. It can be injected directly into the cephalic vein or delivered via constant rate infusion. If injected directly, administer over 60 seconds to allow enough time to cross the blood–brain barrier. It has been used safely with other anesthetic agents (e.g., propofol), and in combination with premedications (e.g., opiates, atropine, phenothiazines, benzodiazepines, and NSAIDs).

Precautionary Information

Adverse Reactions and Side Effects

As an anesthetic agent, CNS depression, respiratory depression, and some blood pressure decrease are expected after administration. At constant rate infusion doses >0.1 mg/kg/min it will produce noticable hypotension and hypoventilation.

Drug Interactions

No drug interactions are reported in animals. However, do not mix with other drugs in the same syringe unless specific compatibility information is available.

Instructions for Use

For induction of anesthesia, use with appropriate monitoring equipment and ventilatory support.

Patient Monitoring and Laboratory Tests

Monitor character and depth of anesthesia during use. Monitor blood pressure and respiratory rate during infusions.

Formulations

Alfaxalone is not available in the US at this time.

Stability and Storage

Store at room temperature protected from light.

Large Animal Dosage

Large Animals

No large animal doses are available.

Regulatory Information

Do not administer to food-producing animals.

Allopurinol

al-oh-pyoo′rih-nole

Trade and other names: Lopurin, Zyloprim, and Allopur (Europe)

Functional Classification: Anti-inflammatory

Pharmacology and Mechanism of Action

Purine analogue. Allopurinol decreases the production of uric acid by inhibiting enzymes responsible for uric acid synthesis. The other use of allopurinol is treating leishmaniasis. In parasites, allopurinol is metabolized to products that disrupt RNA synthesis and interfere with protein synthesis. Allopurinol does not eliminate Leishmania or cure the disease, but it may improve cutaneous lesions and induce remission.

Indications and Clinical Uses

Allopurinol is indicated to decrease formation of uric acid uroliths in at-risk animals. Allopurinol also is used to treat clinical signs associated with leishmaniasis. When used for leishmaniasis it is administered with pentavalent antimonial compounds such as meglumine antimonite (Glutamine) or sodium stibogluconate (Pentosan). With chronic treatment, allopurinol will produce progressive remission and improvement in clinical signs associated with leishmaniasis, which include decreasing the damaging effects of Leishmania on the animal’s kidneys by decreasing proteinuria and preventing deterioration of GFR.

Precautionary Information

Adverse Reactions and Side Effects

Allopurinol may cause skin reactions (hypersensitivity). In dogs that were treated for leishmaniasis for several months, no adverse effects were reported.

Contraindications and Precautions

No contraindications reported for animals.

Drug Interactions

Allopurinol may inhibit drug metabolism of certain drugs. Do not use with azathioprine because it interferes with xanthine oxidase, an important enzyme for metabolizing azathioprine, and will enhance toxicity.

Instructions for Use

In people, allopurinol is used primarily for treating gout.

In animals, it is used to decrease formation of uric acid uroliths and for treating signs associated with leishmaniasis. No single drug or combination is completely effective for treating leishmaniasis, but allopurinol will improve skin lesions. Allopurinol is usually administered with other drugs for leishmaniasis. For example, it has been administered with either amphotericin B or pentavalent antimonial compounds such as meglumine antimonite (Glutamine) or sodium stibogluconate (Pentosan).

Patient Monitoring and Laboratory Tests

Dose adjustments for treating leishmaniasis are based on monitoring clinical signs. Allopurinol will not cure the underlying disease, but it will decrease some clinical signs.

Formulations

Allopurinol is available in 100- and 300-mg tablets.

Stability and Storage

Store in well-closed containers at room temperature. Allopurinol is stable for at least 60 days in compounded formulations. Maximum stability in solutions at pH of 3-3.4.

Large Animal Dosage

Horses

• 5 mg/kg PO.

Regulatory Information

No regulatory information is available. For extralabel use withdrawal interval estimates, contact FARAD at 1-888-USFARAD (1-888-873-2723).

Alprazolam

al-pray′zoe-lam

Trade and other names: Xanax and Niravam

Functional classification: Tranquilizer, CNS depressant

Pharmacology and Mechanism of Action

Benzodiazepine. Central-acting central nervous system (CNS) depressant. Mechanism of action appears to be via potentiation of GABA-receptor mediated effects in CNS. A drug that has similar effects is diazepam.

Indications and Clinical Uses

Alprazolam is used to treat behavior problems in dogs and cats, particularly those associated with anxiety. Alprazolam has been used in dogs for the short-term treatment of anxiety states, such as noise phobias and thunderstorm phobia. For thunderstorm phobia, it may be more effective if combined with long-term clomipramine treatment.

Precautionary Information

Adverse Reactions and Side Effects

Sedation is the most common side effect, but alprazolam may also cause paradoxical excitement in dogs. It also causes polyphagia. In cats, idiopathic fatal hepatic necrosis has been reported from diazepam, but this has not been reported from alprazolam, probably because of differences in metabolism. Alprazolam is not as extensively metabolized as diazepam. Chronic administration in any species may lead to dependence and a withdrawal syndrome if discontinued.

Contraindications and Precautions

No serious contraindications. In rare individuals, benzodiazepines have caused paradoxical excitement.

Drug Interactions

Other drugs may decrease hepatic metabolism (e.g., ketoconazole, chloramphenicol, and itraconazole).

Instructions for Use

Use in animals has been primarily derived from empirical use. There are no well-controlled clinical studies or efficacy trials to document clinical effectiveness. Duration of effect is only 2-3 hours in many dogs. Therefore, if needed, more frequent administration may be required.

When treating thunderstorm phobia, it is helpful in some dogs to administer 0.02 mg/kg of clomipramine 1 hour before a storm, in addition to alprazolam.

The Niravam tablets (see formulation section) are rapidly dissolving and may be easier to administer to animals that are difficult to medicate. Tablets easily dissolve on the tongue without requiring water and can be cut for accurate dosing.

Patient Monitoring and Laboratory Tests

Monitor hepatic enzymes in animals with chronic use.

Formulations

Alprazolam is available in 0.25-, 0.5-, 1-, and 2-mg tablets and 1- and 2-mg scored tablets.

Rapidly dissolving tablets (Niravam) are available in 0.25, 0.5, 1, and 2 mg that can be cut for accurate dosing.

Stability and Storage

Store in a tightly sealed container, protected from light, and at room temperature. Drug is stable in some compounded formulations for 60 days.

Large Animal Dosage

No dose has been reported for large animals.

Regulatory Information

No regulatory information is available. For extralabel use withdrawal interval estimates, contact FARAD at 1-888-USFARAD (1-888-873-2723).

RCI Classification: 2

Altrenogest

al-tren′-oh-jest

Trade and other names: Regu-Mate, Matrix

Functional classification: Hormone

Pharmacology and Mechanism of Action

Altrenogest is an active synthetic progestin hormone. As a progesterone agonist, it is primarily used to suppress estrus in animals. Suppression of estrus allows for a predictable occurrence of estrous activity after the drug is discontinued. Therefore, it is used to induce a normal cycle of estrous activitiy to facilitate scheduled breeding. When treatment is initiated, 95% of the mares will have an estrous cycle suppressed in 3 days.

Indications and Clinical Uses

Altrenogest is indicated to suppress estrus in animals to facilitate induction of normal estrous cycle activity. It is used in mares to facilitate scheduled breeding activity. It is also used to suppress estrous behavior in performance horses. When treatment is discontinued, mares exhibiting regular estrous cycles return to estrus within 4 to 5 days following treatment and continue to cycle normally.

In swine altrenogest is used for synchronization of estrus in sexually mature gilts that have had at least one estrous cycle. Do not use in gilts having a previous or current history of uterine inflammation (i.e., acute, subacute, or chronic endometritis).

Precautionary Information

Contraindications and Precautions

Do not administer to pregnant animals. Humans handling altrenogest, particularly women, should wear gloves and avoid contact because altrenogest can be absorbed in humans through intact skin. Altrenogest should not be used in mares or in gilts with a previous history of uterine problems (metritis).

Instructions for Use

Administer altrenogest 1 dose daily for 15 days, orally on grain or directly on the horse’s tongue. In pigs administer as a top dressing or with feed.

Patient Monitoring and Laboratory Tests

Monitor for signs of estrous activity. Monitor CBC in cases of overdose.

Formulations

Altrenogest is available in an oil solution of 0.22% (2.2 mg/mL).

Stability and Storage

Store in well-closed containers at room temperature.

Small Animal Dosage

• No dose available.

Regulatory Information

Do not use in horses intended for food. In pigs, gilts must not be slaughtered for human consumption for 21 days after the last treatment. Do not administer to other food-producing animals.

Aluminum Hydroxide and Aluminum Carbonate

ah-loo′mih-num hye-droks′ide, ah-loo′mih-num kar′boe-nate

Trade and other names: Aluminum hydroxide gel (Amphogel) and aluminum carbonate gel (Basalgel)

Functional classification: Antacid

Pharmacology and Mechanism of Action

Aluminum is an antacid and phosphate binder in intestine. It is used in both the aluminum hydroxide and aluminum carbonate formulations.

Indications and Clinical Uses

A common use of aluminum hydroxide is for its antacid properties to treat or manage gastrointestinal ulcers. Also, it is used as a phosphate binder. It is indicated in animals with hyperphosphatemia associated with chronic renal failure, often in combination with phosphorus-restricted diets. Because of the decreased availability of products containing aluminum, other drugs are used to decrease hyperphosphatemia in patients, such as calcium carbonate and calcium citrate.

Precautionary Information

Adverse Reactions and Side Effects

These aluminium-containing compounds are generally safe. However, there has been some concern expressed that these drugs may increase the systemic levels of aluminum, which may lead to some forms of aluminum toxicoses. The evidence for this as a clinical problem in veterinary medicine is lacking.

Contraindications and Precautions

Aluminum decreases oral absorption of some drugs (e.g., fluoroquinolones, tetracyclines). If fluoroquinolone antimicrobials are used concurrently, separation of oral doses should be considered.

Drug Interactions

Aluminum will bind and chelate some drugs and prevent the gastrointestinal absorption. Drugs bound to aluminum include tetracyclines and quinolone antibiotics.

Instructions for Use

Antacid doses are designed to neutralize stomach acid, but duration of acid suppression is short. Although aluminum hydroxide is often used to prevent hyperphosphatemia, this drug may not be available in some pharmacies. A substitute for this indication is calcium citrate or calcium carbonate.

Patient Monitoring and Laboratory Tests

Phosphate plasma levels should be monitored to determine success of therapy.

Formulations

Aluminum hydroxide gel is available in a 64-mg/mL oral suspension and 600-mg tablet. Aluminum carbonate gel is available in capsules (equivalent to 500 mg aluminum hydroxide). Note: Products containing aluminum may no longer be available from many sources.

Stability and Storage

Store in a tightly sealed container, protected from light, and at room temperature.

Large Animal Dosage

Horses

• Antacid: 60 mg/kg q8h PO.

Regulatory Information

No regulatory information is available. Residues from administration to food-producing animals ordinarily are not a concern. However, for extralabel use withdrawal interval estimates, contact FARAD at 1-888-USFARAD (1-888-873-2723).

Amantadine

ah-man′tah-deen

Trade and other names: Symmetrel and generic brands

Functional classification: Antiviral

Pharmacology and Mechanism of Action

Amantadine is an antiviral drug. The action against viruses is not entirely known. For treating other conditions in people (Parkinson’s disease) its effects are attributed to an increase in dopamine in the central nervous system (CNS). However it also is an N-methyl-D-aspartate (NMDA) receptor antagonist. As an NMDA antagonist, it will decrease tolerance to other analgesic drugs (e.g., opiates), but it probably does not possess many analgesic properties when used alone. Pharmacokinetics have not been investigated for veterinary uses, but this drug is completely absorbed from oral administration in people and crosses the blood–brain barrier.

Indications and Clinical Uses

Amantadine is an antiviral drug used to treat influenza infections in people. It also is used in people to treat Parkinson’s disease and extrapyramidal reactions, especially those that are drug induced. It also has been used to manage muscular weakness in humans with multiple sclerosis. However, its use in veterinary medicine has primarily been for treating pain in dogs and cats. It is used for treating pain when other drugs have been ineffective or when it is desirable to use in combination with multiple drugs in multimodal therapy analgesic protocols.

Precautionary Information

Adverse Reactions and Side Effects

Toxicity has not been seen in dogs and cats until doses are exceeded by at least two times. Rarely, the side effects of anxiety states and dry mouth have been observed. Dizziness, confusion, and other CNS disturbances have been reported in people.

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