Magnesium Citrate

Trade and other names: Citroma, CitroNesia, and Citro-Mag (Canada)

Pharmacology and Mechanism of Action

Saline cathartic. Acts to draw water into the small intestine via an osmotic effect. Fluid accumulation produces distension, which promotes bowel evacuation.

Indications and Clinical Uses

Magnesium citrate is administered orally for constipation and bowel evacuation prior to certain procedures. It also may be used to promote intestinal clearance of an ingested toxin. It is prompt in its cathartic action.

Instructions for Use

Magnesium citrate is commonly used to evacuate the bowel prior to surgery or diagnostic procedures. Doses are empirical and extrapolated from other species. Onset of action is rapid.

Patient Monitoring and Laboratory Tests

No specific monitoring is necessary. However, monitor magnesium concentrations in patients if repeated treatments or high doses are administered.

Formulations

Magnesium citrate is available in a 6% oral suspension.

Stability and Storage

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

Small Animal Dosage

Dogs and Cats

• 2-4 mL/kg/day PO.

Large Animal Dosage

Horses and Cattle

• 2-4 mL/kg once PO.

Regulatory Information

No regulatory information is available. Because of low risk of residues, no withdrawal times are suggested.

Magnesium Hydroxide

Trade and other names: Milk of Magnesia, Carmilax, and Magnalax

Functional classification: Laxative

Pharmacology and Mechanism of Action

Saline cathartic. Magnesium hydroxide acts to draw water into the small intestine via an osmotic effect. Fluid accumulation produces distension, which promotes bowel evacuation.

Indications and Clinical Uses

Magnesium hydroxide is used for constipation and bowel evacuation prior to certain procedures. It is commonly used to evacuate the bowel prior to surgery or diagnostic procedures. Onset of action is rapid. Magnesium hydroxide also is used as an oral antacid to neutralize stomach acid. In large animals it is used as an antacid and mild cathartic. In cattle, approximately 1 g/kg as a single dose significantly increases rumen pH and decreases rumen microbial activity.

Instructions for Use

Administer to patients only if they are properly hydrated.

Patient Monitoring and Laboratory Tests

Monitor electrolytes with chronic use.

Formulations

Magnesium hydroxide is available as an oral liquid 400 mg/5 mL (Milk of Magnesia) OTC. Milk of Magnesia is approximately 400 mg per 1 teaspoon. It is also available as a 27-g bolus for cattle and sheep and as a powder 310-360 g/lb (approximately 745 g/kg). As a powder, 1.0 pounds of powder is equivalent to 1 gallon of Milk of Magnesia and three 27-g boluses are equal to 1 quart of Milk of Magnesia.

Stability and Storage

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

Small Animal Dosage

Dogs

• Antacid: 5-10 mL/dog q4-6h PO.

• Cathartic: 15-50 mL/dog q24h PO.

Cats

• Antacid: 5-10 mL/cat q4-6h PO.

• Cathartic: 2-6 mL/cat q24h.

Regulatory Information

Withdrawal time for animals intended for food: 12-24 hours (milk) depending on the product.

Magnesium Sulfate

Trade and other names: Epsom salts

Functional classification: Laxative, antiarrhythmic

Pharmacology and Mechanism of Action

Saline cathartic and antiarrhythmic. Magnesium sulfate when administered orally acts to draw water into the small intestine via an osmotic effect. Fluid accumulation produces distension, which promotes bowel evacuation. It is used as a replacement for magnesium in patients who are deficient. When used as an antiarrhythmic it serves as a source of magnesium for treating refractory arrhythmias because in animals with hypomagnesemia it acts as a cofactor for the Na/K ATPase pump. It also may block calcium channels.

Indications and Clinical Uses

Magnesium sulfate is used for constipation and bowel evacuation prior to certain procedures. An injectable solution of magnesium sulfate is used to treat refractory arrhythmias in patients who are critically ill. In horses magnesium sulfate is administered for ventricular tachycardia that is not responsive to other drugs. In cattle, magnesium sulfate is used to treat hypomagnesemia, especially in dairy cattle.

Instructions for Use

Magnesium sulfate when used as a laxative is administered for its prompt action to evacuate bowel prior to surgery or diagnostic procedures. Onset of action is rapid. For use in cattle (hypomagnesemia) an initial dose can be administered IV, followed by an SQ dose to produce a sustained effect. Monitor animals for hypocalcemia, which can occur simultaneously.

Patient Monitoring and Laboratory Tests

Monitor magnesium and calcium concentrations. Normal magnesium concentrations in animals are 1.32-2.46 mEq/L. Many cattle also have hypocalcemia.

Formulations

Magnesium sulfate is available as solid crystals in generic preparations. Solution for injection is 12.5% mEq/mL. Intravenous and subcutaneous solutions for cattle are usually 1.5-4 g/L.

Stability and Storage

Crystals are stable if stored in a dry container. Store injectable solutions at room temperature, in a tightly sealed vial, protected from light.

Regulatory Information

No regulatory information is available. Because of low risk of residues, no withdrawal times are suggested.

Mannitol

man′ih-tole

Trade and other names: Osmitrol

Functional classification: Diuretic

Pharmacology and Mechanism of Action

Hyperosmotic diuretic. Mannitol occurs naturally as a sugar in fruits and vegetables. As an osmotic diuretic, mannitol is freely filtered by the glomerulus, but it is not reabsorbed by the renal tubule. Therefore it increases osmolality of the urine. The osmotic effect inhibits reabsorption of fluid from the renal tubules, and this produces a natriuretic effect and strong diuresis. Reabsorption of sodium chloride and solutes also is inhibited. Mannitol, compared to other diuretic drugs, produces a more profound diuretic effect, which can potentially cause excessive fluid loss in a patient. After intravenous administration, mannitol increases the plasma osmolality, which draws fluid from tissues to plasma, which is helpful for treating tissue edema (e.g., cerebral edema). It reduces intracranial pressure. It is also used as an antiglaucoma agent because it lowers intraocular pressure when administered IV.

Indications and Clinical Uses

Mannitol is administered IV for treatment of cerebral edema, acute glaucoma, and conditions associated with tissue edema. Mannitol also has been used to promote urinary excretion of certain toxins and in the management of anuric or oliguric renal failure.

Instructions for Use

Use only in animals in which fluid and electrolyte balance can be monitored.

Patient Monitoring and Laboratory Tests

Monitor hydration and electrolyte balance in treated animals. Monitor intraocular pressure when treating acute glaucoma.

Formulations

Mannitol is available in a 5%, 10%, 15%, 20%, and 25% solution for injection. The 25% solution is equivalent to 1 g in 4-mL vials.

Stability and Storage

Once solutions are prepared, discard unused portions. If solutions are chilled, crystals may form.

Large Animal Dosage

• 0.25-1 g/kg (20% solution) IV administered over 1 hour.

Regulatory Information

No regulatory information is available. Because of low risk of residues, no withdrawal times are suggested.

Marbofloxacin

mar-boe-floks′ah-sin

Trade and other names: Zeniquin and Marbocyl (European name)

Functional classification: Antibacterial

Pharmacology and Mechanism of Action

Fluoroquinolone antimicrobial. Marbofloxacin acts via inhibition of DNA gyrase in bacteria to inhibit DNA and RNA synthesis. Marbofloxacin is a bactericidal with a broad spectrum of activity. Sensitive bacteria include Staphylococcus, Escherichia coli, Proteus, Klebsiella, and Pasteurella. Pseudomonas aeruginosa is moderately sensitive but requires higher concentrations. Some methicillin-resistant Staphylococcus also may be resistant to fluoroquinolones. Marbofloxacin has poor activity against streptococci and anaerobic bacteria.

Indications and Clinical Uses

Marbofloxacin, like other fluoroquinolones, is used to treat susceptible bacteria in a variety of species. Marbofloxacin is registered for use in dogs and cats. Infections treated with marbofloxacin include skin and soft tissue infections, bone infections, UTIs, pneumonia, and infections caused by intracellular organisms. Marbofloxacin has been effective for some bloodborne pathogens such as Mycoplasma haemofelis, in cats at a dose of 2.75 mg/kg q24h PO for 14 days. Marbofloxacin also has been used in horses to treat infections caused by susceptible bacteria. In dogs the half-life is 7-9 hours, but it has been longer in some studies. In horses the half-life has varied from 4.7 to 7.6 hours, depending on the study. Volume of distribution in these species is 1.2 to 2 L/kg. Oral absorption is close to 100% in small animals and approximately 60% in horses.

Precautionary Information

Instructions for Use

At the low range of the approved label dose, marbofloxacin is active against most susceptible bacteria. Within the approved dose range, higher doses are needed for organisms with higher minimum inhibitory concentration (MIC) values. Doses published for European use are lower than US approved doses, but there is no evidence that this has affected efficacy. For example, successful treatment of pyoderma in European studies has been accomplished with doses of 2.0 mg/kg once daily, but in the US the lowest dose is 2.75 mg/kg once daily.

Patient Monitoring and Laboratory Tests

Susceptibility testing: CLSI break points for sensitive organisms in dogs and cats are ≤1.0 mcg/mL. If other fluoroquinolones are used to test susceptibility to marbofloxacin, results will be similar. However, marbofloxacin is slightly more active than other veterinary quinolones against Pseudomonas aeruginosa, and the human drug ciprofloxacin is more active.

Formulations

Marbofloxacin is available in 25-, 50-, 100-, and 200-mg tablets. Injectable marbofloxacin (Marbocyl) is approved in other countries but not in the US.

Stability and Storage

Store in a tightly sealed container, protected from light, and at room temperature. Do not compound with ingredients that may chelate with quinolones, such as iron or calcium.

Small Animal Dosage

Dogs

• 2.75-5.5 mg/kg once-daily PO.

Cats

• 2.75-5.5 mg/kg once-daily PO.

Large Animal Dosage

Horses

• 2 mg/kg once-daily IV or PO for treatment of susceptible gram-negative bacteria. (IV formulation not available in the US.) An oral dose of 2 mg/kg may not be sufficient for treating other bacteria that cause infections in horses, including gram-positive cocci. However, higher doses have not been tested.

Regulatory Information

Marbofloxacin is prohibited from use in animals intended for food. There are no withdrawal times established because it should not be administered to animals that produce food.

Maropitant citrate

mar-op’-i-tent

Trade and other names: Cerenia

Functional classification: Antiemetic

Pharmacology and Mechanism of Action

Maropitant is an antiemetic from the same group as the human drug aprepitant (Emend). These drugs act as an antiemetic by blocking the neurokinin-1 (NK₁) receptor (also known as Substance P). It has less affinity for other neurokinin receptors (NK₂ and NK₃). Although NK₁ receptors are involved in other physiologic and behavioral responses, at doses used to control vomiting there were no adverse effects associated with blockade of other receptors. Neurokinin-1 is a neurotransmitter to simulate vomiting from the emetic center. Maropitant can inhibit vomiting that is stimulated from both central and peripheral sources mediated by other neurotransmitters such as acetylcholine, histamine, dopamine, and serotonin. In dogs, the half-life was 4 to 8 hours, depending on the dose. Dose-dependent pharmacokinetics occur with the clearance decreasing and half-life increasing with doses above 2 mg/kg. Because of nonlinear pharmacokinetics, accumulation is possible with repeated dosing. Oral absorption is 24% at 2 mg/kg and 37% at 8 mg/kg in dogs. Pharmacokinetics are not affected by feeding. In cats the clearance is much lower than in dogs, and the half-life is longer than in dogs at 13-17 hours. In cats, it has nearly complete SQ absorption and 50% oral absorption.

Indications and Clinical Uses

Maropitant is approved for use as an antiemetic in dogs to inhibit vomiting from both central and peripheral sources. It has been effective to inhibit vomiting from chemotherapy, gastrointestinal disease, toxins, renal disease, vestibular stimuli (motion sickness), and circulating stimuli via the chemoreceptor trigger zone. After SQ injection it has a rapid onset and a duration of 24 hours. Although not approved for cats, it has been used safely and effectively in cats to treat vomiting from a variety of sources, such as motion sickness and stimulation by emetogenic agents, with a duration of action of 24 hours.

Precautionary Information

Adverse Reactions and Side Effects

Maropitant may cause slight pain or irritation from SQ injection. It has been recognized that the pain is caused by alteration of the formulation, which may occur when the injectable formulation is stored at room temperature. The cyclodextrin complex of maropitant is preserved at cold temperatures and is more stable and intact when the formulation is refrigerated. Therefore, the adverse event associated with a painful injection can be reduced if injectable maropitant is stored in the refrigerator before use. Safety studies have been conducted with maropitant in both preclinical and clinical trials. In experimental dogs it was safe at 3× and 5× the labeled dose. Adverse effects observed in trials included excess salivation and muscle tremors. In cats it has been well-tolerated at high doses (of a factor of 10×) and was safe at 5 mg/kg for 15 consecutive days.

Contraindications and Precautions

There is accumulation after repeated doses and decreased clearance with higher doses. Therefore, because of accumulation, it should not be administered for more than 5 consecutive days. Allow a 2-day washout period before instituting another course of treatment. Take care to identify any underlying disease whenever possible instead of relying on maropitant to control the clinical signs. Maropitant effects and pharmacokinetics are not affected by renal disease.

Drug Interactions

Single doses have been administered in an IV line, but precipitation may be observed if mixed with alkalinizing solutions. Maropitant is an NK₁ inhibitor. Other neurokinin receptors are affected by a lesser degree. Because of the unique mechanism of action, drug interactions have not been identified. Maropitant has been used safely with other drugs, including anesthetics and anticancer agents. Maropitant is highly protein bound, but it is not known if there are protein-binding interactions with other drugs.

Instructions for Use

Clinical trials in dogs have outlined the appropriate protocols for use of maropitant. It has been effective for a wide range of causes of vomiting in dogs. In cats, although not approved, it has been effective for a variety of causes of vomiting, including motion sickness and stimulation from emetogenic agents. The effective dose in cats is 1 mg/kg regardless of cause.

Patient Monitoring and Laboratory Tests

Monitor for clinical signs and disease that may be a cause for the vomiting. Other specific monitoring and tests are not needed to use maropitant safely.

Formulations

Maropitant is available in 16-, 24-, 60-, or 160-mg tablets and a 10-mg/mL injectable solution.

Stability and Storage

Store in a tightly sealed container, protected from light. The injectable formulation can be stored at room temperature and in the refrigerator, but as noted earlier, pain from injection can be reduced if formulation is stored in the refrigerator. Discard vial after 28 days of first use.

Large Animal Dosage

No large animal doses have been identifed.

Regulatory Information

No regulatory information is available for food animals. There are no withdrawal times established, and it is not recommended to be administered to animals that produce food.

MCT Oil

Trade and other names: Medium chain triglycerides (MCT) oil

Functional classification: Nutritional supplement

Pharmacology and Mechanism of Action

MCT oil supplements triglycerides in animals.

Indications and Clinical Uses

MCT oil is used to treat lymphangiectasia and as a component of enteral feeding formulas.

Instructions for Use

Results of clinical trials using MCT oil have not been reported. Many enteral feeding formulas contain MCT oil (many polymeric formulations).

Patient Monitoring and Laboratory Tests

No specific monitoring is necessary.

Formulations

MCT is available as an oral liquid.

Stability and Storage

Store in a tightly sealed container, protected from light, at room temperature, and in a cool place. Do not store in a plastic container. It may be mixed with fruit juices or food products prior to administration.

Small Animal Dosage

• 1-2 mL/kg daily in food.

Large Animal Dosage

No large animal doses have been reported.

Regulatory Information

No regulatory information is available. Because of low risk of residues, no withdrawal times are suggested.

Mebendazole

meh-ben′dah-zole

Trade and other names: Telmintic, Telmin, Vermox (human preparation), and generic brands

Functional classification: Antiparasitic

Pharmacology and Mechanism of Action

Benzimidazole antiparasitic drug. Like other benzimidazoles, mebendazole produces a degeneration of the parasite microtubule and irreversibly blocks glucose uptake in parasites. Inhibition of glucose uptake causes depletion of energy stores in the parasite, eventually resulting in death. However, there is no effect on glucose metabolism in mammals.

Indications and Clinical Uses

Mebendazole is used in horses for treatment of infections caused by large roundworms (Parascaris equorum), large strongyles (Strongylus edentatus, S. equinus, and S. vulgaris), small strongyles, and mature and immature (fourth larval stage pinworms [Oxyuris equi]). In dogs it has been used for treatment of infections of roundworms (Toxocara canis), hookworms (Ancylostoma caninum and Uncinaria stenocephala), whipworms (Trichuris vulpis), and tapeworms (Taenia pisiformis).

Instructions for Use

The powder for horses may be sprinkled directly on the horse’s grain or dissolved in 1 L of water and administered via stomach tube. For dogs, it may be added directly to its food.

Patient Monitoring and Laboratory Tests

No specific monitoring is necessary.

Formulations

Mebendazole is available in 40- or 166.7-mg/g powder, 200-mg/g equine paste, 33.3-mg/mL solution, and 100-mg chewable tablets (human preparation).

Some equine formulations contain 83.3 mg mebendazole plus 375 mg trichlorfon in each gram of powder.

Stability and Storage

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

Small Animal Dosage

Dogs

• 22 mg/kg (mixed with food) q24h for 3 days. May be repeated in 3 weeks.

Large Animal Dosage

Horses

• 8.8 mg/kg PO.

Regulatory Information

Do not administer to horses intended for food.

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).

Meclizine

mek′lih-zeen

Trade and other names: Antivert, Bonine, Meclozine (British name), and generic brands

Functional classification: Antiemetic

Pharmacology and Mechanism of Action

Antiemetic. Antihistamine. Like other antihistamines, it blocks the effect of histamine on the H₁ receptor. However, it also has central anticholinergic actions, which may be responsible for the central-acting antiemetic properties.

Indications and Clinical Uses

Meclizine is used to treat vomiting. It may suppress the chemoreceptor trigger zone. It also is used for treatment of motion sickness. Use in animals has been primarily derived from empirical use. There are no well-controlled clinical studies or efficacy trials to document clinical effectiveness. Other drugs with proven efficacy (e.g., maropitant) are often used instead of meclizine for vomiting.

Instructions for Use

Results of clinical studies in animals have not been reported. Use in animals is based on experience in people or anecdotal experiences in animals.

Patient Monitoring and Laboratory Tests

No specific monitoring is necessary.

Formulations

Meclizine is available in 12.5-, 25-, and 50-mg tablets.

Stability and Storage

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

Large Animal Dosage

No large animal doses have been reported.

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).

Meclofenamate Sodium, Meclofenamic Acid

mek′loe-fen′am-ate soe-dee′um, mek′loe-fen-am′ik ass′id

Trade and other names: Arquel and Meclofen

Functional classification: Nonsteroidal anti-inflammatory drug (NSAID)

Pharmacology and Mechanism of Action

Meclofenamate is also known as meclofenamic acid and is related to tolfenamic acid, which is approved in some countries for animals. Meclofenamate and other NSAIDs have produced analgesic and anti-inflammatory effects by inhibiting the synthesis of prostaglandins. The enzyme inhibited by NSAIDs is the cyclo-oxygenase enzyme (COX). The COX enzyme exists in two isoforms: COX-1 and COX-2. COX-1 is primarily responsible for synthesis of prostaglandins important for maintaining a healthy GI tract, renal function, platelet function, and other normal functions. COX-2 is induced and responsible for synthesizing prostaglandins that are important mediators of pain, inflammation, and fever. Meclofenamic acid is a balanced COX-1/COX-2 inhibitor.

Indications and Clinical Uses

Meclofenamate is used in animals for treatment of pain and inflammation. The most common use has been musculoskeletal inflammation. Use in animals has diminished because of decreased availability and increased popularity of other drugs.

Precautionary Information

Adverse Reactions and Side Effects

Adverse effects have not been reported in animals, but adverse effects common to other NSAIDs are possible. These side effects are generally GI in nature (e.g., gastritis, gastric ulcers).

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