S-Adenosylmethionine (SAMe)

ess′ah-den′oh-sill-meh-thye′oh-neen

Trade and Other Names: Denosyl, Denamarin, and SAMe

Functional Classification: Nutritional supplement

Pharmacology and Mechanism of Action

Nutritional supplement. S-Adenosylmethionine, usually abbreviated as SAMe, is found naturally and is formed from methionine and ATP. It has been associated with improvement in acetaminophen-induced hepatotoxicity in humans and has been beneficial according to isolated reports in veterinary medicine. It serves as a methyl donor, catalyzed by methyltransferase. It also is a substrate for a transsulfuration reaction in which demethylated SAMe is metabolized to glutathione (GSH). Glutathione may conjugate certain drug metabolites to enhance excretion. Cats and dogs have low levels of GSH, and SAMe may help restore GSH in animals that have been intoxicated and perhaps in animals that have liver disease. It is a methyl donor for neurotransmitter metabolism in the synthesis and turnover of biogenic monoamines (CNS neurotransmitters such as serotonin, dopamine, and norepinephrine). In dogs, the half-life after oral administration is approximately 2 hours.

Indications and Clinical Uses

SAMe has been used as a dietary supplement to support patients with hepatic disease. It may help restore hepatic GSH concentrations in deficient animals. It also has been administered to treat liver injury caused by intoxication of acetaminophen and other drugs that produce hepatotoxic oxidative drug injury. Another dietary supplement, silymarin (see monograph for silymarin), also known as “milk thistle” and silybin, has hepatic antioxidant properties and has been combined with SAMe for treatment in dogs in cats (Denamarin). Via the effect on neurotransmitter synthesis, SAMe has been used to improve cognitive function in dogs. In dogs older than 8 years, SAMe (18 mg/kg/day) improved age-related mental impairment compared to placebo. It has been used to treat arthritis in dogs, but there are no studies that have demonstrated effectiveness.

Instructions for Use

SAMe is a dietary supplement widely available without a prescription (OTC). Potency of formulations may vary. Absorption is decreased when given with a meal. Administer 30 minutes to 1 hour before feeding. To ensure passage into the stomach of cats, administer with water. Coated tablets (such as Denosyl) protect the active ingredient from moisture during storage and destruction by stomach acid. Do not break tablets or disrupt coating.

Patient Monitoring and Laboratory Tests

Monitor liver enzymes in animals being treated for toxicity.

Formulations

SAMe is widely available OTC in tablets and powder. The brand Denosyl is available in 90-, 225-, and 425-mg tablets. Veterinary formulations (e.g., Denamarin) may also contain silymarin (silybin) and vitamin E.

Stability and Storage

Store in a tightly sealed container, protected from light, and at room temperature. Do not disrupt coating on tablet.

Small Animal Dosage

Dogs

• 20 mg/kg per day, PO, or 90 mg (small dogs); 225 mg (medium dogs); and 425 mg (large dogs).

Cats

• 90 mg/cat/day PO, for cats up to 5 kg body weight.

Large Animal Dosage

No dose has been reported for large animals.

Regulatory Information

Because of low risk of harmful residues in food animals, no withdrawal time is suggested.

Selamectin

sel-ah-mek′tin

Trade and Other Names: Revolution

Functional Classification: Antiparasitic

Pharmacology and Mechanism of Action

Antiparasitic. Microfilaricide for heartworm prevention in dogs and cats. Selamectin is a semisynthetic avermectin. Avermectins (ivermectin-like drugs) and milbemycins (milbemycin, doramectin, and moxidectin) are macrocyclic lactones. Avermectins and macrocyclic lactones share similarities, including mechanism of action. These drugs are neurotoxic to parasites by potentiating glutamate-gated chloride ion channels in parasites. Paralysis and death of the parasite are caused by increased permeability to chloride ions and hyperpolarization of nerve cells. These drugs also potentiate other chloride channels, including ones gated by GABA. Mammals ordinarily are not affected because they lack glutamate-gated chloride channels, and there is a lower affinity for other mammalian chloride channels. Because these drugs ordinarily do not penetrate the blood–brain barrier, GABA-gated channels in the CNS of mammals are not affected. After topical application selamectin has high affinity for sebaceous glands and skin. The terminal half-life of selamectin is 11 days in dogs and 8 days in cats.

Indications and Clinical Uses

Selamectin is approved for prevention of heartworms; control of fleas, mites, and ticks in dogs; and prevention of heartworms, control of fleas, mites, hookworms, and roundworms in cats.

Instructions for Use

Apply as indicated on product label to skin of dogs and cats.

Patient Monitoring and Laboratory Tests

Monitor heartworm status in animals.

Formulations

Selamectin is available in 60- and 120-mg/mL topical solution.

Stability and Storage

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

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).

Selegiline Hydrochloride

se-leh′jeh-leen hye-droe-klor′ide

Trade and Other Names: Anipryl (also known as deprenyl and l-deprenyl), Eldepryl (human preparation), and Emsam transdermal patch

Functional Classification: Dopamine agonist

Pharmacology and Mechanism of Action

Dopamine agonist. Selegiline has been known by many names. Selegiline hydrochloride is the official USP drug name, but most clinicians know it by the older name, l-deprenyl. (l-deprenyl is distinguished from its steroisomer d-deprenyl.) A related drug is rasagiline. Selegiline has been used in humans for treatment of Parkinson’s disease and occasionally for Alzheimer’s disease with the trade name Eldepryl. (Efficacy for Alzheimer’s disease has not been established.)

The veterinary formulation is approved for treatment of Cushing’s disease in dogs and canine cognitive dysfunction. The action of selegiline is to inhibit MAO type B (and other MAOs at higher doses). The proposed mechanism of action is to inhibit the metabolism of dopamine in the central nervous system. The action for pituitary-dependent hyperadrenocorticism may be through increased dopamine levels in the brain, which decreases ACTH release, resulting in lower cortisol levels. Secondary effects are related to inhibition of the metabolism of phenylethylamine. (Phenylethylamine in laboratory animals produces amphetamine-like effects.) Two active metabolites are l-amphetamine and l-methamphetamine, but it is not known to what extent these contribute to pharmacologic effects. In horses, the metabolism to amphetamine-like metabolites is low.

Indications and Clinical Uses

In dogs, selegiline is approved to control clinical signs of pituitary-dependent hyperadrenocorticism (PDH; Cushing’s disease) and to treat cognitive dysfunction in older dogs. However, the efficacy for Cushing’s disease may not be as high as for other drugs such as mitotane or trilostane. Selegiline effects may be limited PDH caused by lesions of the pars intermedia and may not be effective for other forms of PDH (most cases of canine PDH have lesions of the pars distalis). It may improve some clinical signs without lowering cortisol levels in dogs with PDH administered 1.0 mg/kg once daily. For canine cognitive dysfunction (dementia) in old dogs, treatment with selegiline inhibits MAO type B and increases dopamine concentrations in the brain, which restores dopamine and balance and may improve cognitive ability. It has been administered to some older cats with age-related behavior problems, but clinical results in cats have not been reported. It does not appear to produce any clinical effects in horses from oral administration.

Precautionary Information

Instructions for Use

Dose titration to effect. Start with low dose and increase gradually until clinical effect is observed. The transdermal patch for humans has not been evaluated for animals.

Patient Monitoring and Laboratory Tests

No specific monitoring is required. Serum cortisol testing is not valuable for evaluating efficacy.

Formulations

Selegiline is available in 2-, 5-, 10-, 15-, and 30-mg tablets for animals; 5-mg tablets or capsules for humans; and 20-, 30-, and 40-cm² transdermal patch (EmSam) for humans.

Stability and Storage

Stable if stored in manufacturer’s original formulation.

Small Animal Dosage

Dogs

• Begin with 1 mg/kg q24h PO. If there is no response within 2 months, increase dose to maximum of 2 mg/kg q24h PO.

Cats

• 0.25-0.5 mg/kg q12-24h PO.

Large Animal Dosage

No dose has been reported for large animals. In preliminary studies in which selegiline was administered at a dose of 30 mg/horse PO or IV, there were no observed effects on behavior or locomotor activity.

Regulatory Information

Do not administer to animals intended for food.

RCI Classification: 2

Senna

sen′na

Trade and Other Names: Senokot

Functional Classification: Laxative

Pharmacology and Mechanism of Action

Laxative. Senna acts via local stimulation or via contact with intestinal mucosa.

Indications and Clinical Uses

Senna is indicated for treatment of constipation.

Instructions for Use

Doses and indications are not well established for veterinary medicine. Use is strictly based on anecdotal experience.

Patient Monitoring and Laboratory Tests

No specific monitoring is necessary.

Formulations

Senna is available in granules in concentrate or syrup.

Stability and Storage

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

Small Animal Dosage

Dogs

• Syrup: 5-10 mL/dog/day PO.

• Granules: 1/2 to 1 tsp/dog/day PO.

Cats

• Syrup: 5 mL/cat q24h.

• Granules: 1/2 tsp/cat q24h (with food).

Large Animal Dosage

No doses have been reported for large animals.

Regulatory Information

Because of low risk of harmful residues in animals intended for food, no withdrawal time is suggested.

Sevoflurane

see-voe-floo′rane

Trade and Other Names: Aerrane

Functional Classification: Anesthetic

Pharmacology and Mechanism of Action

Inhalant anesthetic. Like other inhalant anesthetics, the mechanism of action is uncertain. Sevoflurane produces a generalized, reversible depression of the CNS. The inhalant anesthetics vary in their solubility in blood, their potency, and the rate of induction and recovery. Those with low blood/gas partition coefficients are associated with the most rapid rates of induction and recovery. Sevoflurane has a vapor pressure of 160 mm Hg (at 20°C), a blood/gas partition coefficient of 0.65, and a fat/blood coefficient of 48. Sevoflurane is similar to isoflurane in many respects, except that it has lower solubility, resulting in faster induction and recovery times.

Indications and Clinical Uses

Sevoflurane is used as an inhalant anesthetic. There are not any significant advantages over the use of isoflurane and it is more expensive than isoflurane. It has a minimum alveolar concentration (MAC) value of 2.58%, 2.36%, and 2.31% in cats, dogs, and horses, respectively. Sevoflurane, like other inhalant anesthetics, can be used with preanesthetics, opioids, alpha-2 agonists, and tranquilizers.

Instructions for Use

Use of inhalant anesthetics requires careful monitoring. Dose is determined by depth of anesthesia.

Patient Monitoring and Laboratory Tests

Carefully monitor patient’s heart rate and rhythm and respiratory rate during use.

Formulations

Sevoflurane is available in a 100-mL bottle.

Stability and Storage

Sevoflurane is highly volatile and should only be stored in approved containers.

Small Animal Dosage

• Induction: 8%; maintenance: 3%-6%

Large Animal Dosage

Horses

MAC value: 2.31.

Regulatory Information

No withdrawal times are established for animals intended for food. Clearance is rapid and short withdrawal times are suggested. For extralabel use withdrawal interval estimates, contact FARAD at 1-888-USFARAD (1-888-873-2723).

Sildenafil Citrate

sill-den’-ah-fil

Trade and Other Names: Viagra, Revatio

Functional Classification: Vasodilator

Pharmacology and Mechanism of Action

Vasodilator. Sildenafil is a vasodilator, specific for phosphodiesterase V. Sildenafil and similar drugs act to increase cyclic GMP by inhibiting its breakdown by phosphodiesterase-V (PDE-V). There are two important locations of phosphodiesterase V: (1) vascular smooth muscle of the lungs, and (2) corpus cavernosum. The second effect produces the desired clinical effects that have caused the popularity in human medicine. The effect on vascular smooth muscle of the lungs produces vasodilation of the pulmonary vascular bed in patients with pulmonary hypertension. Other drugs that have been used for this effect are tadalafil (Cialis) at a dose of 1-2 mg/kg q12h PO in dogs.

Indications and Clinical Uses

Sildenafil and related drugs are used in people for treating erectile dysfunction via the effect on the corpus cavernosum. This effect has not been explored in veterinary medicine. The use in veterinary medicine has been limited to the treatment of pulmonary arterial hypertension. In dogs sildenafil produced improvement in patients with pulmonary hypertension.

Instructions for Use

The use in veterinary medicine has been based on studies in dogs with pulmonary hypertension. The dosages and clinical use are based on these limited reports.

Patient Monitoring and Laboratory Tests

No specific monitoring is necessary, but monitor the patient’s cardiovascular function (blood pressure and heart rate) in animals at risk for cardiovascular complications.

Formulations

Sildenafil is available as 20-, 25-, 50-, and 100-mg tablets.

Stability and Storage

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

Small Animal Dosage

Dogs

• 2 mg/kg q12h, PO. Dose interval may range from 8 to 24 hours, and doses as high as 3 mg/kg have been administered to some dogs.

Cats

• 1 mg/kg q8h, PO.

Large Animal Dosage

No dose has been reported for large animals.

Regulatory Information

No withdrawal times are established for animals intended for food. For extralabel use withdrawal interval estimates, contact FARAD at 1-888-USFARAD (1-888-873-2723).

Silymarin

sill-ih-mare′in

Trade and Other Names: Silybin, Marin, Milk Thistle, and generic brands

Functional Classification: Hepatic protectant

Pharmacology and Mechanism of Action

Silymarin contains silybin as the most active ingredient. It is also known as milk thistle, from which it is derived. Silymarin is a mixture of antihepatotoxic flavonolignans (derived from the plant silybum). Silymarin has three components that are considered flavonolignans: silidianin, silcristin, and silybin (which is the major component and also called silymarin and silibinin). Silymarin has been used for the treatment of a variety of liver disorders in humans. The mechanism of silymarin’s action is thought to be as an antioxidant inhibiting both peroxidation of lipid membranes and glutathione oxidation. Experimental data have supported the hepatoprotective properties of silymarin as an antioxidant and a free radical scavenger.

Indications and Clinical Uses

Silymarin has been used to treat hepatic disease, including hepatotoxic reactions in people and animals. In cats it may provide antioxidant activity. Silymarin is used as a complementary treatment in canine and feline liver disease. However, there is no scientific information on the oral absorption, correct dose, or evidence of efficacy of silymarin treatment. Silymarin can be used with S-adenosylmethionine (SAMe). There are preparations that include both silymarin and SAMe (Denamarin).

Instructions for Use

Silymarin is a dietary supplement, and forms available may vary in potency and stability.

Patient Monitoring and Laboratory Tests

Monitor liver enzymes in animals being treated for toxicity.

Formulations

Silymarin tablets are widely available OTC. Commercial veterinary formulations (Marin) also contain zinc and vitamin E in a phosphatidylcholine complex in tablets for dogs and cats. The combination of Denamarin contains both silymarin and SAMe.

Stability and Storage

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

Small Animal Dosage

Dogs and Cats

• 5-15 mg/kg PO, once daily. Some sources recommend a higher dose of a minimum of 30 mg/kg PO per day.

Large Animal Dosage

No dose has been reported for large animals.

Regulatory Information

Because of low risk of harmful residues in animals intended for food, no withdrawal time is suggested.

Sodium Bicarbonate

Trade and Other Names: Baking soda, Soda mint, Citrocarbonate, and Arm & Hammer pure baking soda

Functional Classification: Alkalinizing agent

Pharmacology and Mechanism of Action

Alkalizing agent. Antacid. It increases plasma and urinary concentrations of bicarbonate. One gram sodium bicarbonate is equal to 12 mEq sodium and bicarbonate ions; 3.65 g sodium bicarbonate is equal to 1 g sodium.

Indications and Clinical Uses

Sodium bicarbonate is a typical alkalinizing solution. It is the most frequent alkalinizing solution used for intravenous therapy of systemic acidosis and to treat severe hyperkalemia. When adding to fluid therapy, the goal is to maintain PaCO₂ within 37-43 mm Hg. It also has been administered to alkalize urine.

Precautionary Information

Adverse Reactions and Side Effects

Adverse effects have been attributed to alkalizing activity. Hypokalemia may occur with excessive administration. Hyperosmolality, hypernatremia, paradoxical CNS, and intracellular acidosis may occur.

Contraindications and Precautions

Do not administer to animals with hypocalcemia (may exacerbate tetany). Do not administer to animals with excessive chloride loss because of vomiting. Do not administer to animals with alkalosis. Administration of sodium bicarbonate may increase risk of hypernatremia, paradoxical CNS acidosis, and hyperosmolality.

Drug Interactions

Sodium bicarbonate should not be mixed with drugs that require an acidic medium for stability and solubility. Such drugs may include solutions containing hydrochloride (HCl) salts. When mixing intravenous solutions, do not mix bicarbonate with solutions containing calcium (chelation may result). When administered orally, interaction may occur to decrease absorption of other drugs (partial list includes anticholinergic drugs, ketoconazole, fluoroquinolones, and tetracyclines).

Instructions for Use

When used for systemic acidosis, doses should be adjusted on the basis of blood gas measurements or assessment of acidosis. The following equation may be used to estimate requirement:

Initially, administer 25%-50% of this dose in intravenous fluids over 20-30 minutes. In calves or neonates, use a factor of 0.5 instead of 0.3. Twelve mEq of bicarbonate = 1 g of sodium bicarbonate. Note: 1.4% solution = 0.17 mEq/mL and provides 13 g of bicarbonate per L. 8.5 % solution = 1 mEq/mL of NaHCO₃. One teaspoon of baking soda is approximately 2 g of NaHCO₃. When used during cardiac resuscitation, caution is advised because of risk of hyperosmolality, hypernatremia, and paradoxical CNS acidosis.

Patient Monitoring and Laboratory Tests

Monitor acid–base status.

Formulations

Sodium bicarbonate is available in 325-, 520-, and 650-mg tablets. Per teaspoonful (3.9 g) of Citrocarbonate, there is 780 mg sodium bicarbonate and 1.82 grams sodium citrate. It is also available in injections of various strengths: 4.2% is 0.5 mEq/mL (11.5 mg/mL sodium) and 8.4% is 1 mEq/mL (23 mg/mL sodium).

Stability and Storage

Store in a tightly sealed container at room temperature. Alkaline solution with pH of 7-8.5. Do not mix with acid solutions. Sodium bicarbonate is soluble in water. If exposed to air, it may decompose to sodium carbonate, which is more alkaline.

Large Animal Dosage

• Metabolic acidosis: 0.5-1 mEq/kg IV slowly. Other doses should be calculated based on base deficits. Oral doses vary. Ten to 12 grams of sodium bicarbonate may be given orally to adult large animals (horses and cattle) and 2-5 grams to calves, foals, and pigs.

Regulatory Information

Because of low risk of harmful residues in animals intended for food, no withdrawal time is suggested.

Sodium Chloride 0.9%

Trade and Other Names: Normal saline and generic brands

Functional Classification: Fluid replacement

Pharmacology and Mechanism of Action

Sodium chloride is used for intravenous infusion as replacement fluid. It is not a suitable maintenance solution. Sodium chloride (0.9%) contains 154 mEq/L sodium and 154 mEq/L chloride. See Appendix for comparison to other fluid solutions.

Indications and Clinical Uses

Sodium chloride is used for intravenous fluid supplementation. However, it is not a balanced electrolyte solution and should not be used for maintenance. It also is frequently used as a vehicle to deliver intravenous medications via constant rate infusion (CRI).

Patient Monitoring and Laboratory Tests

Monitor hydration status and serum electrolytes, particularly potassium.

Formulations

Sodium chloride 0.9% is available in a 500- and 1000-mL infusion.

Stability and Storage

Store in a tightly sealed container at room temperature.

Regulatory Information

Because of low risk of harmful residues in animals intended for food, no withdrawal time is suggested.

Sodium Chloride 7.2%

Trade and Other Names: Hypertonic saline solution and HSS

Functional Classification: Fluid replacement

Pharmacology and Mechanism of Action

Concentrated sodium chloride used for acute treatment of hypovolemia. Hypertonic saline solution causes rapid expansion of plasma volume and may improve microvascular blood flow. Hypertonic saline solution contains 2566 mOsm/L, 1232 mEq/L sodium, and 1232 mEq/L chloride.

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