Tacrolimus

tak-roe-lih′mus

Trade and Other Names: Protopic, FK506

Functional Classification: Immunosuppressant

Pharmacology and Mechanism of Action

Tacrolimus is a microbial product isolated from the organism Streptomyces tsukubaensis. Tacrolimus binds to an intracellular receptor and subsequently binds to calcineurin and inhibits the calcineurin pathway that stimulates the nuclear factor, NFAT. The action resembles that of cyclosporine (both drugs are calcineurin inhibitors), although the cellular receptors differ. By inhibiting the action of NFAT, tacrolimus decreases synthesis of inflammatory cytokines. In particular, synthesis of IL-2 is inhibited, which results in decreased activation of T lymphocytes. It is 10-100 times more potent than cyclosporine. Tacrolimus inhibits release of mast cell and basophil mediators and decreases inflammatory mediator expression.

Indications and Clinical Uses

Tacrolimus is used as an immunosuppressive drug to treat autoimmune disease, prevent organ transplant rejection, and treat atopic dermatitis. Most use in animals is with a topical formulation. It has been applied topically (ointment) for localized areas of atopic dermatitis. In some cases after resolution of lesions with systemic treatment with cyclosporine, isolated skin lesions are managed topically with tacrolimus ointment. There has been limited use for preventing renal transplant rejection in cats because the pharmacokinetics have been highly variable. A related drug, pimecrolimus, also has been used topically.

Instructions for Use

There are no reports of safe systemic doses used in dogs. Most use is topical. It can be used topically for immune-mediated skin lesions where local treatment can be used (e.g., on the bridge of the nose). It has also been applied topically for perianal fistula in addition to systemic prednisolone.

Patient Monitoring and Laboratory Tests

No specific monitoring is necessary with topical use.

Formulations Available

Tacrolimus is available in 0.1% and 0.03% topical ointment in 30-, 60-, and 100-g tubes.

Stability and Storage

Ointment is stable if stored in manufacturer’s original formulation. Compounded formulations of tacrolimus have been available from pharmacists, but the stability and potency of these formulations have not been evaluated. It is practically insoluble in water. When prepared in a suspension, it was stable for several weeks.

Small Animal Dosage

Dogs and Cats

Apply topical ointment (0.1%) to localized lesions on affected areas of skin. It has been used in dogs twice daily. For perianal fistula it has been applied twice daily.

Large Animal Dosage

No doses have been reported for large animals.

Regulatory Information

Do not administer to animals intended for food.

Tegaserod Maleate

teg-ah-ser’-odd mal’-ee-ate

Trade and Other Names: Zelnorm

Functional Classification: Gastrointestinal stimulant

Pharmacology and Mechanism of Action

Tegaserod maleate is an intestinal simulant that produces a prokinetic action to stimulate motility. It acts by binding to serotonin type-4 (5-HT₄) receptors and triggers the release of neurotransmitters that stimulate smooth muscle motility. Activation of 5-HT₄ receptors in the GI tract stimulates peristaltic reflex and intestinal secretion. In horses it has increased motility in the equine pelvic flexure and accelerated GI transit. In horses it has a 55% oral absorption rate and a half-life of approximately 2.7 hours.

Indications and Clinical Uses

Tegaserod has been withdrawn from the human market because of adverse effects but is still available from some sources. In people it was associated with an increased risk of cardiovascular adverse events, including heart attack, chest pain, and stroke. It had been used in people with irritable bowel syndrome (IBS) whose primary symptom is constipation. The only reported use in animals has been in horses to stimulate intestinal motility. It has increased GI transit in horses and stimulated motility in the large colon. The use in small animals is primarily anecdotal, and clinical use is not established.

Instructions for Use

Use in animals is based primarily from reports of use in horses.

Patient Monitoring and Laboratory Tests

No specific monitoring is necessary.

Formulations Available

Tegaserod meleate has been available in 2- and 6-mg tablets. However, after discontinuation from the human market, the availability has become more difficult. It is practically insoluble in water, but crushed tablets may be used in a suspension for oral administration to horses. It has also been dissolved in acetic acid and further diluted for IV administration.

Stability and Storage

Crushed tablets in water have been stable if administered shortly after mixing for horses.

Small Animal Dosage

Dogs and Cats

No doses have been reported for small animals. (Doses have been extrapolated from humans.)

Large Animal Dosage

0.27 mg/kg, PO, q12h.

Regulatory Information

Do not administer to animals intended for food.

Tamoxifen Citrate

tah-moks′ih-fen sih′trate

Trade and Other Names: Nolvadex

Functional Classification: Antiestrogen

Pharmacology and Mechanism of Action

Nonsteroidal estrogen receptor blocker. Tamoxifen also has weak estrogenic effects. Tamoxifen also may increase release of gonadotropin-releasing hormone (GnRH).

Indications and Clinical Uses

Tamoxifen is used as adjunctive treatment for certain tumors, especially estrogen-responsive tumors. The most common use in animals is adjunctive treatment for mammary neoplasia. In women it has been used to induce ovulation by stimulating release of GnRH from the hypothalamus.

Instructions for Use

Tamoxifen is often used with other anticancer drug protocols.

Patient Monitoring and Laboratory Tests

No specific monitoring is necessary.

Formulations Available

Tamoxifen is available in 10- and 20-mg tablets.

Stability and Storage

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

Small Animal Dosage

Veterinary dose not established but has been extrapolated from the human dose. Human dose is 10 mg q12h PO (approximately 0.14 mg/kg q12h).

Large Animal Dosage

No doses have been reported for large animals.

Regulatory Information

Do not administer to animals intended for food.

Taurine

tore′een

Trade and Other Names: Generic brands

Functional Classification: Nutritional supplement

Pharmacology and Mechanism of Action

Nutritional supplement. Taurine is a naturally occurring amino acid considered essential for cats. Deficiencies in animals may lead to blindness and heart disease. Taurine may have some cardiac inotropic effects.

Indications and Clinical Uses

Taurine is used in the prevention and treatment of ocular and cardiac disease (dilated cardiomyopathy) caused by taurine deficiency. Although current commercial diets have adequate amounts of taurine, it has been supplemented in dogs and cats with heart disease.

Instructions for Use

Routine supplementation with taurine may not be necessary in animals that are receiving a balanced diet. However, supplementation may be necessary in animals with diseases associated with taurine deficiency.

Patient Monitoring and Laboratory Tests

Taurine concentrations can be measured in some laboratories to detect deficiencies. Normal levels in plasma are 60-120 nmol/mL in dogs and cats or 200-350 nmol/mL in whole blood. Levels below 40 nmol/mL in plasma and 150 nmol/mL in whole blood are considered deficient.

Formulations Available

Taurine is available in powder or supplemented in some diets. Consult a compounding pharmacy for availability.

Stability and Storage

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

Small Animal Dosage

Dogs

• 500 mg/dog q12h PO.

Cats

• 250 mg/cat q12h PO.

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.

Tepoxalin

tep-oks′ah-lin

Trade and Other Names: Zubrin

Functional Classification: Anti-inflammatory

Pharmacology and Mechanism of Action

Tepoxalin is a nonsteroidal anti-inflammatory drug (NSAID). Like other drugs in this class, tepoxalin produces analgesic and anti-inflammatory effects by inhibiting the synthesis of prostaglandins. However, tepoxalin also inhibits the action of lipoxygenase (LOX) to decrease synthesis of inflammatory leukotrienes in dogs. This produces a “dual action” in dogs by inhibiting both prostaglandins and leukotrienes. Tepoxalin, using in vitro assays, is more cyclo-oxygenase-1 (COX-1) selective than COX-2 selective. It has not been established if the specificity for COX-1 or COX-2 is related to efficacy or safety. Tepoxalin forms an active metabolite after administration to dogs, cats, and horses. In dogs, tepoxalin has a half-life of 2 hours and the acid-metabolite has a half-life of 13 hours. It is highly protein bound. Feeding increases oral absorption in dogs.

Indications and Clinical Uses

Tepoxalin is used to decrease pain and inflammation. It has been used for the acute and chronic treatment of pain and inflammation in dogs. One of the most common uses is osteoarthritis, but it also has been used for pain associated with surgery. There is evidence that it was more effective than carprofen or meloxicam for reducing intra-articular inflammation in dogs and controlling synthesis of intra-articular PgE₂. Because of the dual action of tepoxalin, it has been investigated for treating other inflammatory conditions in dogs and cats. Studies available thus far to investigate the beneficial effect of dual inhibition by tepoxalin for other inflammatory diseases (for example, ocular inflammation, respiratory disease, or dermatitis) have had mixed results. Tepoxalin has been more effective than other drugs for ocular inflammation, but only partially effective for dermatitis, and not effective for respiratory disease. Use in large animals has not been reported.

Precautionary Information

Instructions for Use

Rapidly dissolving tablets can be administered with or without food. In some animals, it is helpful to wet the tablet before placing on the animal’s tongue. Long-term studies have not been completed in cats; only single-dose studies have been reported in which a dose of 10 mg/kg did not produce adverse effects.

Patient Monitoring and Laboratory Tests

Monitor GI signs for evidence of diarrhea, GI bleeding, or ulcers. Because of risk of renal injury, monitor renal parameters (water consumption, BUN, creatinine, and urine-specific gravity) periodically during treatment.

Formulations

Tepoxalin is available in 30-, 50-, 100-, and 200-mg tablets (rapidly dissolving).

Stability and Storage

Store in a tightly sealed container, protected from light, and at room temperature. Shelf life is 2 years if maintained in manufacturer’s original packaging.

Large Animal Dosage

No doses have been reported for large animals.

Regulatory Information

Do not administer to animals that produce food.

Terbinafine Hydrochloride

ter-bin′ah-feen hye-droe-klor′ide

Trade and Other Names: Lamisil

Functional Classification: Antifungal

Pharmacology and Mechanism of Action

Antifungal drug. Terbinafine belongs to the allylamine group of antifungal drugs. It acts on ergosterol biosynthesis by targeting fungal squalene epoxidase (SE). SE is a membrane-bound enzyme and is involved in the conversion of squalene into squalene 2,3-epoxide, which is subsequently converted into lanosterol and ergosterol. Terbinafine is selective for fungal SE. Terbinafine is active against dermatophytes. After administration, concentrations persist in hair for much longer than in plasma or other body fluids. For example, concentrations were maintained in cat hair for more than 5 weeks after treatment.

Indications and Clinical Uses

Terbinafine is indicated for treatment of dermatophyte infections in dogs, cats, birds, and some exotic animals. For dermatophytes in animals, the doses necessary for efficacy are much higher than those used in people. Although there has been experience with using terbinafine in animals—primarily for dermatophytes—there is no evidence that terbinafine is more effective than other oral antifungal agents. In dogs it has been used for Malassezia yeast infections. Treatment of infections in horses with terbinafine has not been successful probably because of poor absorption.

Instructions for Use

Treatment of dogs and cats requires much higher doses compared to doses used in people.

Patient Monitoring and Laboratory Tests

No specific monitoring is necessary.

Formulations

Terbinafine is available in 250-mg tablets, 1% topical solution, and 1% topical cream.

Stability and Storage

Store in a tightly sealed container, protected from light, and at room temperature. Terbinafine is slightly soluble in water and alcohol. When suspensions have been prepared from crushed tablets in a vehicle (Ora-Sweet) it was stable for 42 days.

Small Animal Dosage

Dogs

• 30-40 mg/kg q24h PO (with food) for 2-3 weeks.

Cats

• 30-40 mg/kg/day PO for at least 2 weeks.

Large Animal Dosage

There are no effective doses reported for large animals. It is not effective for horses.

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).

Terbutaline Sulfate

ter-byoo′tah-leen sul′fate

Trade and Other Names: Brethine and Bricanyl

Functional Classification: Bronchodilator, beta agonist

Pharmacology and Mechanism of Action

Beta₂-adrenergic agonist. Bronchodilator. Stimulates beta₂ receptors to relax bronchial smooth muscle. Terbutaline is more beta₂ specific than drugs such as isoproterenol. Other beta₂-specific drugs include albuterol and metaproterenol. In addition to the beta₂ effects to relax bronchial smooth muscle and relieve bronchospasm, the beta₂-agonists also may inhibit release of inflammatory mediators, especially from mast cells.

Indications and Clinical Uses

Terbutaline, like other beta₂-agonists, is indicated in animals with reversible bronchoconstriction, such as cats with bronchial asthma. It also has been used in dogs to relieve bronchoconstriction and in animals with bronchitis and other airway diseases. Use in animals has been primarily derived from empirical use and experience in humans. There are no well-controlled clinical studies or efficacy trials to document clinical effectiveness. Albuterol injection may be used as an alternative for terbutaline injection (4 mcg/kg bolus, up to 8 mcg/kg as needed). Terbutaline is not absorbed by the oral route in horses; therefore, it is not effective in horses for oral administration. Clenbuterol usually is the drug of choice for horses.

Precautionary Information

Adverse Reactions and Side Effects

Excessive beta-adrenergic stimulation from terbutaline 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 hyperglycemia. Treatment consists of KCl supplement at a rate of 0.5 mEq/kg/hr.

Contraindications and Precautions

Administer cautiously to animals with cardiac disease, particularly animals that may be susceptible to tachyarrhythmias. Do not use late in gestation unless the intended effect is to delay uterine contractions.

Drug Interactions

Use cautiously with other drugs that may stimulate the heart and cause tachycardia.

Instructions for Use

May be administered PO, IM, or SQ. Terbutaline (and other beta₂-agonists) have also been used in people to delay labor (dose in people is 2.5 mg q6h PO). Other beta₂-agonists used in animals for relief of bronchoconstriction include albuterol and salmeterol. Animals with acute bronchoconstriction also may benefit from corticosteroid treatment and oxygen therapy. Caution should be used when administering repeated subcutaneous doses. The maximum subcutaneous dose in people is 500 mcg/person (0.5 mg) within a 4-hour period.

Patient Monitoring and Laboratory Tests

Monitor heart rate in animals during treatment. Monitor potassium concentration if high doses are administered.

Formulations

Terbutaline is available in 2.5- and 5-mg tablets and 1-mg/mL (equivalent to 0.82 mg/mL) injections.

Stability and Storage

Store in a tightly sealed container, protected from light, and at room temperature. Terbutaline sulfate is soluble in water. Solutions may be subject to degradation. Observe for color change, and discard if solution turns a dark color. Suspensions have been prepared from tablets in syrup and stable for 55 days.

Large Animal Dosage

Horses

• Not absorbed orally. Use IV for treatment of chronic recurrent airway obstruction (RAO): 2-5 mcg/kg q6-8h IV, or as needed.

Regulatory Information

Terbutaline has similar properties as clenbuterol and should not be administered to animals intended for food.

RCI Classification: 3

Testosterone

tess-toss′ter-one

Trade and Other Names: Testosterone cypionate ester: Andro-Cyp, Andronate, Depo-Testosterone, and generic brands and testosterone propionate ester: Testex and Malogen (in Canada)

Functional Classification: Hormone

Pharmacology and Mechanism of Action

Testosterone ester for injection is available in two forms: testosterone cypionate and testosterone propionate. It is used to supplement testosterone in deficient animals. It will also produce anabolic effects. Testosterone esters are administered IM to avoid first-pass effects that occur from oral administration. Esters in oil are absorbed more slowly from intramuscular injections. Esters are then hydrolyzed to free testosterone. Other agents with more specific anabolic activity include boldenone, oxymetholone, nandrolone, stanozolol, and methyltestosterone.

Indications and Clinical Uses

Anabolic agents have been used for reversing catabolic conditions, increasing weight gain, increasing muscling in animals, and stimulating erythropoiesis. Testosterone and other anabolic agents have also been abused in people for athletic performance.

Instructions for Use

Use of testosterone androgens has not been evaluated in clinical studies in veterinary medicine. Use is based primarily on experimental evidence or experiences in people.

Patient Monitoring and Laboratory Tests

Monitor hepatic enzymes in treated patients periodically.

Formulations

Testosterone cypionate ester is available in 100- and 200-mg/mL injections. Testosterone propionate ester is available in 100-mg/mL injections.

Stability and Storage

Testosterone is insoluble in water but soluble in oils and ethanol. Protect from light, heat, and freezing. When mixed with oil, it has been stable for 60 days.

Small Animal Dosage

Dogs and Cats

• Testosterone cypionate ester: 1-2 mg/kg q2-4weeks IM.

• Testosterone propionate ester: 0.5-1 mg/kg 2-3 times/week IM.

Large Animal Dosage

There are no large animal formulations available, except for implants for calves. Do not administer injections to animals intended for food.

Regulatory Information

Testosterone is a Schedule III controlled drug.

RCI Classification: 4

Tetracycline, Tetracycline Hydrochloride

tet-rah-sye′kleen

Trade and Other Names: Panmycin, Duramycin powder, and Achromycin V

Functional Classification: Antibacterial

Pharmacology and Mechanism of Action

Tetracycline antibiotic. Mechanism of action of tetracyclines is to bind to 30S ribosomal subunit and inhibit protein synthesis. The action is time-dependent and against some bacteria is bacteriostatic. Tetracycline, like other tetracyclines, has a broad spectrum of activity including bacteria, some protozoa, Rickettsiae, and Ehrlichiae. Resistance is common. Tigecycline is a new tetracycline that has improved activity against bacteria that are resistant to other drugs. However, there are no reports of the use of tigecycline in animals.

Indications and Clinical Uses

Tetracyclines are used to treat a variety of infections, including soft tissue infections, pneumonia, and UTIs. Other drugs in this group that are used more frequently in animals for treatment include oxytetracycline, minocycline, and doxycycline. Consult sections containing those drugs for a more complete list of clinical use and indications.

Instructions for Use

Pharmacokinetic and experimental studies have been conducted in small animals but not in clinical studies. Use of tetracyclines in small animals has primarily been replaced by doxycycline. The most common oral tetracycline in horses is doxycycline or minocycline.

Patient Monitoring and Laboratory Tests

Susceptibility testing: CLSI break point for sensitive organisms ≤2 mcg/mL for streptococci and ≤4 mcg/mL for other organisms. However, on the basis of plasma concentrations achieved, 1 mcg/mL or less should be used for animals. Tetracycline is used as a marker to test susceptibility for other drugs in this class such as doxycycline, minocycline, and oxytetracycline. When using tetracycline to test for susceptibility to oxytetracycline in pathogens from cattle, use a break point of ≤2 mcg/mL for susceptible bacteria. When using tetracycline to test for susceptibility to oxytetracycline in pathogens from swine, use a break point of ≤0.5 mcg/mL for susceptible bacteria.

Formulations

Tetracycline is available in 250- and 500-mg capsules, 500-mg calf bolus, 100-mg/mL oral suspension, and 25 and 324 g/lb of powder.

Stability and Storage

Store in a tightly sealed container, protected from light, and at room temperature. Tetracycline has poor aqueous solubility. However, tetracycline hydrochloride is more soluble (100 mg/mL). The pH of tetracycline hydrochloride solution is approximately 2.0. It will decompose if kept at alkaline pH. Tetracycline hydrochloride is unstable, and compounded preparations are better prepared from tetracycline base as a suspension. Tetracycline will darken with exposure to light. Protect from freezing.

Small Animal Dosage

Dogs and Cats

• 15-20 mg/kg q8h PO.

• 4.4-11 mg/kg q8h IV or IM.

• Rickettsial infection (dogs): 22 mg/kg q8h for 14 days PO.

Large Animal Dosage

Calves and Pigs

For treatment of enteritis and pneumonia: 11 mg/kg q12h administered in the water or as a bolus. When administered in the water, the dose may actually vary among animals, depending on their water intake.

Regulatory Information

Cattle and pig withdrawal times: 5 days meat for oral powder; 18 days meat; 72 hours milk when used as intrauterine bolus in cattle; and 12, 14, and 24 days when oral tablets are used, depending on product (check label).

Thenium Closylate

thee′nee-um kloe′sill-ate

Trade and Other Names: Canopar

Functional Classification: Antiparasitic

Pharmacology and Mechanism of Action

Antiparasitic drug. Thenium is an antiparasitic drug with action specific for hookworms.

Indications and Clinical Uses

Thenium closylate is used to treat adult forms of the species Ancylostoma caninum and Uncinaria stenocephala (hookworms).

Instructions for Use

Tablet is bitter if coating is broken.

Patient Monitoring and Laboratory Tests

Monitor fecal samples for evidence of parasites.

Formulations

Thenium closylate is available in 500-mg tablets (veterinary preparation).

Stability and Storage

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

Small Animal Dosage

• Dogs weighing >4.5 kg: 500 mg PO once and repeat in 2-3 weeks.

• Dogs weighing 2.5-4.5 kg: 250 mg (half tablet) twice a day PO for 1 day; repeat in 2-3 weeks.

Large Animal Dosage

No doses have been reported for large animals.

Regulatory Information

Do not administer to animals intended for food.

Theophylline

thee-off′ih-lin

Trade and Other Names: Many generic brands and theophylline sustained release.

Functional Classification: Bronchodilator

Pharmacology and Mechanism of Action

Methylxanthine bronchodilator. Nonselective phosphodiesterase (PDE) inhibitor. Phosphodiesterase is the enzyme that converts cyclic adenosine monophosphate (cyclic AMP) to inactive forms. Therapeutic effects may be caused by cyclic AMP or antagonism of adenosine. There appears to be anti-inflammatory action and bronchodilating action. Sustained-release preparations are used to decrease frequency of administration. Oral theophylline is well-absorbed orally in dogs, cats, and horses with bioavailability exceeding 90%. After absorption, theophylline has a half-life in dogs, cats, and horses of 5-6 hours, 14-18 hours, and 12-15 hours, respectively. Some oral formulations contain aminophylline, and theophylline is the active component of aminophylline.

Indications and Clinical Uses

Theophylline is administered for inflammatory airway disease in cats, dogs, and horses. Use in animals has been primarily derived from empirical use, some experimental models, and experience in humans. There are no well-controlled clinical studies or efficacy trials to document clinical effectiveness. It has been used to control clinical signs of reversible airway constriction, such as seen with feline asthma. In dogs, the uses include collapsing trachea, bronchitis, and other airway diseases. In horses, it will relieve signs of recurrent airway obstruction (heaves), but the IV dose may cause adverse effects in horses. Other drugs (e.g., clenbuterol, albuterol) are often used for this condition in horses. It has not been effective for respiratory diseases in cattle. In dogs and cats, human-labeled extended-release tablets and capsules may be used twice daily in dogs and once daily in cats to achieve effective blood concentrations.

Precautionary Information

Adverse Reactions and Side Effects

Adverse effects include nausea, vomiting, and diarrhea. With high doses, tachycardia, excitement, tremors, and seizures are possible. Cardiovascular and CNS adverse effects appear to be less frequent in dogs than people. Overdoses can cause hypokalemia.

Contraindications and Precautions

Administer with caution to patients with cardiovascular disease or patients with seizure disorders.

Drug Interactions

Use cautiously with other phosphodiesterase inhibitors such as pentoxifylline, sildenafil (Viagra), and pimobendan. Many drugs will inhibit the metabolism of theophylline and potentially increase concentrations. Drugs responsible include cimetidine, erythromycin, fluoroquinolones, and propranolol. Some drugs will decrease concentrations by increasing metabolism. Such drugs include phenobarbital and rifampin.

Instructions for Use

Adjust dose to maintain therapeutic blood levels. Older slow-release and extended-release formulations are no longer available. Pharmacokinetic studies have established doses for human-labeled tablets and capsules in dogs and cats. These formulations have produced the most consistent plasma concentrations from oral dosing.

Patient Monitoring and Laboratory Tests

Plasma concentrations of theophylline should be monitored in patients receiving chronic therapy to maintain plasma concentrations between 10 and 20 mcg/mL. Regularly monitor plasma concentrations in patients receiving chronic treatment. Peak-trough concentration measurements are encouraged.

Formulations

Theophylline is available in 100-, 125-, 200-, 250-, and 300-mg tablets; 27-mg/5-mL (5.3-mg/mL) oral solution or elixir; and injection in 5% dextrose. Theophylline extended release is available in 100-, 200- and 300-mg tablets (Theochron). However, availability of various sizes of extended-release formulations may vary. The manufacturers have discontinued other extended-release formulations such as Slo-Bid and Theo-Dur.

Stability and Storage

Store in a tightly sealed container, protected from light, and at room temperature. Theophylline is slightly soluble in water (8 mg/mL). Theophylline has been mixed with some oral liquids and found to be stable if administered shortly after mixing. When using the slow-release tablets or capsules in dogs and cats, do not disrupt coating on formulation.

Regulatory Information

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

RCI Classification: 3

Thiabendazole

thye-ah-ben′dah-zole

Trade and Other Names: Omnizole, Equizole, TBZ, and Thibenzole

Functional Classification: Antiparasitic

Pharmacology and Mechanism of Action

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

Indications and Clinical Uses

Availability of commercial forms of thiabendazole has been limited. In horses, thiabendazole has been used for control of large and small strongyles; Strongyloides; and pinworms of the genera Strongylus, Cyathostomum, Cylicobrachytus and related genera Craterostomum, Oesophagodontus, Poteriostomum, and Oxyuris. In ruminants it has been used for infections of GI roundworms in sheep and goats (Trichostrongylus spp. Haemonchus spp., Ostertagia spp., Cooperia spp., Nematodirus spp., Bunostomom spp., Strongyloides spp., Chabertia spp., Oesophagostomum spp., Trichostrongylus colubriformis and T. axei, and Ostertagia spp.).

Instructions for Use

Thiabendazole is ordinarily administered to horses and cattle. Experience in small animals is limited.

Patient Monitoring and Laboratory Tests

Monitor fecal samples for evidence of intestinal parasites.

Formulations Available

Thiabendazole is available in paste, pellets, and solution for oral administration and premix for feeds. Some formulations are no longer commercially available.

Stability and Storage

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

Small Animal Dosage

Dogs

• 50 mg/kg q24h for 3 days; repeat in 1 month.

• Treating respiratory parasites: 30-70 mg/kg q12h PO.

Cats

• Strongyloides spp: 125 mg/kg q24h for 3 days.

Regulatory Information

Withdrawal time for milk: 96 hours.

Sheep and goat withdrawal time (meat): 30 days.

Cattle withdrawal time (meat): 3 days.

Pig withdrawal time (meat): 30 days.

Thiacetarsemide Sodium

thye-ass-et-ars′ah-mide soe-dee-um

Trade and Other Names: Caparsolate

Functional Classification: Antiparasitic

Pharmacology and Mechanism of Action

Organic arsenical that produces toxicity in parasites such as adult heartworms.

Indications and Clinical Uses

Thiacetarsemide is used for treatment of adult heartworm infections. Caparsolate is no longer recommended as an adulticide heartworm treatment by the American Heartworm Society. Caparsolate is less effective in cats than in dogs, with a higher incidence of adverse reactions. In dogs, melarsomine is considered safer and has replaced thiacetarsemide for routine treatment.

Instructions for Use

Thiacetarsemide is administered via four injections over 2 days; however, if severe adverse effects are observed, discontinue regimen. Extravasation can result in skin slough. It is recommended to substitute melarsomine for thiacetarsemide, if possible, for treating heartworm disease.

Patient Monitoring and Laboratory Tests

Monitor renal and hepatic function.

Formulations

Thiacetarsemide is available in 10-mg/mL injections. There are no longer commercial supplies of thiacetarsemide, and its availability is uncertain.

Stability and Storage

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

Small Animal Dosage

Dogs

• 2.2 mg/kg IV twice daily for 2 days.

Cats

• Not recommended, unless the cat can be closely supervised. Dose is 2.2 mg/kg twice daily IV for 2 consecutive days.

Large Animal Dosage

No doses have been reported for large animals.

Regulatory Information

Do not administer to animals intended for food.

Thiamine Hydrochloride

thye′ah-min hye-droe-klor′ide

Trade and Other Names: Vitamin B₁, Bewon, and generic brands

Functional Classification: Vitamin

Pharmacology and Mechanism of Action

Vitamin B₁ is used for treatment of vitamin deficiency. Vitamin B complex often contains thiamine (B₁), riboflavin, niacinamide, and cyanocobalamin B₁₂.

Indications and Clinical Uses

Thiamine is used to provide Vitamin B₁ supplementation or to treat vitamin B₁ deficiency.

Instructions for Use

Vitamin B supplements are administered often in combination with other B vitamins as vitamin B complex solutions.

Patient Monitoring and Laboratory Tests

No specific monitoring is necessary.

Formulations

Thiamine is available in 250-mcg/5-mL elixir, 5- to 500-mg tablets, and 100- and 500-mg/mL injections.

Vitamin B complex aqueous solutions for injection usually contain 12.5 mg/mL of vitamin B₁.

Stability and Storage

Store in a tightly sealed container, at room temperature, protected from light. When mixed with other solutions (e.g., fluid solutions), incompatibility may result.

Small Animal Dosage

Dogs

• 10-100 mg/dog/day PO.

• 12.5-50 mg/dog/day IM or SQ.

Cats

• 5-30 mg/cat/day PO, up to a maximum dose of 50 mg/cat/day.

• 12.5-25 mg/cat/day IM or SQ.

Regulatory Information

Withdrawal time for animals intended for food: 0 days.

Thioguanine

thye-oh-gwah′neen

Trade and Other Names: Generic brands

Functional Classification: Anticancer agent

Pharmacology and Mechanism of Action

Anticancer agent. Antimetabolite of purine analogue type. Thioguanine inhibits DNA synthesis in cancer cells.

Indications and Clinical Uses

Thioguanine is used in some anticancer protocols. It is not commonly used in animals. Use in animals has been primarily derived from empirical use and experience in humans. There are no well-controlled clinical studies or efficacy trials to document clinical effectiveness.

Instructions for Use

Thioguanine may be combined with other agents for treatment of cancer.

Patient Monitoring and Laboratory Tests

Monitor CBC to screen for evidence of bone marrow toxicity.

Formulations

Thioguanine is available in 40-mg tablets.

Stability and Storage

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

Small Animal Dosage

Dogs

• 40 mg/m² q24h PO.

Cats

• 25 mg/m² q24h PO for 1-5 days, then repeat every 30 days.

Large Animal Dosage

No dose has been reported for large animals.

Regulatory Information

Withdrawal times are not established for animals that produce food. This drug should not be used in animals intended for food because it is an anticancer agent.

Thiopental Sodium

thye-oh-pen′tahl soe′dee-um

Trade and Other Names: Pentothal

Functional Classification: Anesthetic, barbiturate

Pharmacology and Mechanism of Action

Ultrashort-acting barbiturate. Anesthesia is produced by CNS depression without analgesia. Anesthesia is terminated by redistribution in the body.

Indications and Clinical Uses

Thiopental is used primarily for induction of anesthesia or for short duration of anesthesia (10-15-minute procedures). It induces a rapid, smooth, and generally excitement-free induction. It can be administered intravenously, with prior premedication of other anesthetic adjuncts such as tranquilizers and sedatives (e.g., alpha-2 agonists, phenothiazines, and opiates).

Precautionary Information

Adverse Reactions and Side Effects

The most common effect is transient apnea and respiratory depression. Other adverse effects are related to the anesthetic effects of the drug. Thiopental may cause cardiovascular depression with a slight decrease in stroke volume and little change in cardiac output or blood pressure. Premedication will reduce the risk of cardiovascular events. Supplementation with oxygen during induction also will decrease cardiovascular events. Overdoses are caused by rapid or repeated injections. Avoid extravasation outside of the vein.

Contraindications and Precautions

Use carefully in patients with respiratory or cardiac disease. Do not use unless there is an ability to monitor and maintain respiration.

Drug Interactions

Thiopental is compatible with other anesthetics. However, use of other sedatives and anesthetics will lower dose of thiopental. Thiopental has been combined with propofol in a 1:1 mixture without loss of effectiveness. This mixture of 1:1 2.5% thiopental and propofol has been used to induce anesthesia in dogs.

Instructions for Use

Therapeutic index is low. Use only in patients in which it is possible to monitor cardiovascular and respiratory functions. Thiopental is often administered with other anesthetic adjuncts.

Patient Monitoring and Laboratory Tests

Monitor cardiovascular and respiratory function during anesthesia with thiopental.

Formulations

Thiopental is available in 250-mg to 10-g vials (mix to desired concentration).

Stability and Storage

Thiopental, when prepared properly, is chemically stable and resists bacterial growth for up to 4 weeks when refrigerated. Thiopental has a pH of 10-11 and should not be mixed with acidifying solutions. If mixed with other drugs, the alkalinity may affect their stability. Propofol has been mixed with thiopental sodium in a 1:1 mixture and they are physically and chemically compatible if used promptly.

Small Animal Dosage

Dogs

• 10-25 mg/kg IV (to effect).

Cats

• 5-10 mg/kg IV (to effect).

Large Animal Dosage

Cattle

• Induction: 6-12 mg/kg IV (to effect).

Pigs

• 10-20 mg/kg IV (to effect).

Regulatory Information

Extralabel use: Establish a withdrawal time of at least 1 day for meat and 24 hours for milk.

Pig withdrawal time (meat): 0 days.

Schedule II controlled drug.

RCI Classification: 2

Thiotepa

thye-oh-tep′ah

Trade and Other Names: Thioplex and generic brands

Functional Classification: Anticancer agent

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