T
Tacrolimus
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.
Precautionary Information
Adverse Reactions and Side Effects
There may be a slight burning or pruritic sensation with initial topical application. These reactions are mild and decrease as the skin heals. With systemic administration, dogs may show GI signs, which include diarrhea, intestinal discomfort, vomiting, intestinal intussusception, and intestinal injury. Tacrolimus is minimally absorbed systemically from topical application.
Contraindications and Precautions
Tacrolimus is a potent immunosuppressant. Use cautiously in animals prone to infection. Pet owners should be cautioned about skin contact when handling the medication for their pets.
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.
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.
Tegaserod Maleate
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.
Precautionary Information
Adverse Reactions and Side Effects
Adverse cardiovascular events have been responsible for its withdrawal in humans. However, adverse effects have not been reported in animals.
Contraindications and Precautions
Do not use in animals with intestinal obstruction. Tegaserod is not absorbed from rectal administration in horses.
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.
Tamoxifen Citrate
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.
Precautionary Information
Adverse Reactions and Side Effects
Adverse effects have not been thoroughly documented in animals. However, in people, tamoxifen has been reported to cause increased tumor pain.
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).
Taurine
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.
Tepoxalin
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
Adverse Reactions and Side Effects
GI problems are the most often adverse effects associated with tepoxalin and can include vomiting, diarrhea, nausea, ulcers, and erosions of the GI tract. Both acute and long-term safety and efficacy have been established for dogs. In field trials, vomiting was the most often reported adverse effect. In studies performed in dogs, dogs have tolerated 10 times and 30 times the labeled dose. Renal effects and bleeding studies have been performed on healthy dogs. Tepoxalin in these studies was not shown to adversely affect bleeding times or renal function. Nevertheless, renal toxicity, especially in dehydrated animals or animals with preexisting renal disease, has been shown for some NSAIDs. Toxicity studies have not been performed in cats, but single doses of 10 mg/kg to a small group of cats did not produce adverse effects.
Contraindications and Precautions
Dogs and cats with preexisting GI problems or renal problems may be at a greater risk of adverse effects from NSAIDs. Safety in pregnancy is not known, but adverse effects have not been reported.
Drug Interactions
Do not administer with other NSAIDs or with corticosteroids. Corticosteroids have been shown to exacerbate the GI adverse effects. Some NSAIDs may interfere with the action of diuretic drugs and angiotensin-converting enzyme (ACE) inhibitors. However, in experimental studies in dogs, tepoxalin combined with an ACE inhibitor did not produce adverse renal effects.
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.
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.
Terbinafine Hydrochloride
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.
Precautionary Information
Adverse Reactions and Side Effects
Vomiting has been the most common adverse effect. Nausea and anorexia also are possible. Liver enzymes may be elevated in some animals. Hepatotoxicity is possible, but it has not been reported from use in animals. Facial pruritus has been observed in some treated cats. In people, a persistent taste disturbance, gastrointestinal problems, and headache have been reported.
Instructions for Use
Treatment of dogs and cats requires much higher doses compared to doses used in people.
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.
Large Animal Dosage
There are no effective doses reported for large animals. It is not effective for horses.
Terbutaline Sulfate
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.
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.
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)
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.
Precautionary Information
Adverse Reactions and Side Effects
Adverse effects are caused by excessive androgenic action of testosterone. Prostatic hyperplasia is possible in male dogs. Masculinization can occur in female dogs. Hepatopathy is more common with oral methylated testosterone formulations than with injected formulations.
Contraindications and Precautions
Use cautiously in patients with hepatic disease. Do not administer to pregnant animals. This drug has potential for abuse in humans for anabolic uses.
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.
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.
Large Animal Dosage
There are no large animal formulations available, except for implants for calves. Do not administer injections to animals intended for food.
Tetracycline, Tetracycline Hydrochloride
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.
Precautionary Information
Adverse Reactions and Side Effects
Tetracyclines in general may cause renal tubular necrosis at high doses. Tetracyclines can affect bone and teeth formation in young animals. Tetracyclines have been implicated in drug fever in cats. Hepatotoxicity may occur at high doses in susceptible individuals.
Contraindications and Precautions
Do not use in young animals because it can affect bone and teeth formation.
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.
Thenium Closylate
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).
Stability and Storage
Store in a tightly sealed container, protected from light, and at room temperature.
Theophylline
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.
Large Animal Dose
Thiabendazole
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.
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.
Thiacetarsemide Sodium
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.
Precautionary Information
Adverse Reactions and Side Effects
Adverse effects are common, especially anorexia, vomiting, and hepatic injury. Pulmonary thromboembolism may occur as a consequence of heartworm kill.
Contraindications and Precautions
Its use is not recommended in cats unless they can be carefully monitored. Cats are less susceptible to arsenical toxicity than dogs, but they are more prone to pulmonary thromboembolism. If cats are treated, they should be confined under close observation for 3-4 weeks.
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.
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.
Thiamine Hydrochloride
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.
Precautionary Information
Adverse Reactions and Side Effects
Adverse effects are rare because water soluble vitamins are easily excreted.
Contraindications and Precautions
Administer solutions of vitamin B1 very slowly IV, if at all. Rapid intravenous administration has caused anaphylactic reactions.
Instructions for Use
Vitamin B supplements are administered often in combination with other B vitamins as vitamin B complex solutions.
Formulations
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.
Thioguanine
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.
Precautionary Information
Adverse Reactions and Side Effects
Adverse effects, as with any anticancer drug, are expected. Adverse effects from thioguanine may be similar to those observed from mercaptopurine. Immunosuppression and leukopenia are common.
Stability and Storage
Store in a tightly sealed container, protected from light, and at room temperature.
Thiopental Sodium
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.
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.
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