TERBUTALINE SULFATE

Chemistry - A synthetic sympathomimetic amine, terbutaline sulfate occurs as a slightly bittertasting, white to gray-white, crystalline powder that may have a faint odor of acetic acid. One gramis soluble in 1.5 ml of water or 250 ml of alcohol. The commercially available injection has its pHadjusted to 3-5 with hydrochloric acid.

Storage, Stability, Compatibility

Terbutaline tablets should be stored in tight containers atroom temperature (15-30°C). Tablets have an expiration date of 3 years beyond the date of manufacture. Terbutaline injection should be stored at room temperature (15-30°C), and protected fromlight. The injection has an expiration date of 2 years after the date of manufacture.
Terbutaline injection is stable over a pH range of 1-7. Discolored solutions should not be used. Itis compatible with D5W and aminophylline.

Pharmacology - TERBUTALINE SULFATE

Terbutaline stimulates beta-adrenergic receptors found principally in bronchial, vascular, and uterine smooth muscles (beta2) and bronchial and vascular smooth muscle relaxationoccurs with resultant reduced airway resistance. At usual doses it has little effect on cardiac (beta1)receptors and usually does not cause direct cardiostimulatory effects. Occasionally, a tachycardiadevelops which may be a result of either direct beta stimulation or a reflex response secondary toperipheral vasodilation. Terbutaline has virtually no alpha-adrenergic activity.

Uses, Indications

Terbutaline is used as a bronchodilating agent in the adjunctive treatment ofcardiopulmonary diseases (including tracheobronchitis, collapsing trachea, pulmonary edema, andallergic bronchitis) in small animals.
It has been used occasionally in horses for its bronchodilating effects, but adverse effects havelimited its use in this species. A related compound, clenbuterol, has been used to a much greaterextent for treating bronchoconstriction in the horse, but it is not available commercially in the
United States.
Oral and intravenous terbutaline has been used successfully (in humans) in the inhibition ofpremature labor symptoms.

Pharmacokinetics - TERBUTALINE SULFATE

The pharmacokinetics of this agent have apparently not been thoroughlystudied in domestic animals. In humans, only about 33-50% of an oral dose is absorbed; peakbronchial effects occur within 2-3 hours and activity persists for up to 8 hours. Terbutaline is wellabsorbed following SQ administration with an onset of action occurring within 15 minutes, peakeffects at 30-60 minutes, and a duration of activity for up to 4 hours.
Terbutaline is distributed into milk, but at levels of approximately 1% of the oral dose given to themother. Terbutaline is principally excreted unchanged in the urine (60%), but is also metabolized inthe liver to an inactive sulfate conjugate.
Contraindications/Precautions - Terbutaline is contraindicated in patients hypersensitive to it.
One veterinary school formulary (Schultz 1986) states that terbutaline is contraindicated in dogsand cats with heart disease, especially with CHF or cardiomyopathy. It should be used with cautionin patients with diabetes, hyperthyroidism, hypertension, seizure disorders, or cardiac disease(especially with concurrent arrhythmias).

Adverse Effects, Warnings

Most adverse effects are dose-related and are those that would beexpected with sympathomimetic agents, including increased heart rate, tremors, CNS excitement(nervousness) and dizziness. These effects are generally transient and mild and do not requirediscontinuation of therapy. After parenteral injection in horses, sweating and CNS excitation havebeen reported.
Transient hypokalemia has been reported in humans receiving beta-adrenergic agents. If an animalis susceptible to developing hypokalemia, it is suggested that additional serum potassiummonitoring be done early in therapy.
Overdosage - Symptoms of significant overdose after systemic administration may include arrhythmias (bradycardia, tachycardia, heart block, extrasystoles), hypertension, fever, vomiting, mydriasis, and CNS stimulation. If a recent oral ingestion, it should be handled like other overdoses(empty gut, give activated charcoal and a cathartic) if the animal does not have significant cardiac or CNS effects. If cardiac arrhythmias require treatment, a beta blocking agent (e.g., propranolol) canbe used, but may precipitate bronchoconstriction.

Drug Interactions

Use of terbutaline with other sympathomimetic amines may increase therisk of developing adverse cardiovascular effects. Beta-adrenergic blocking agents (e.g., propranolol) may antagonize the actions of terbutaline. Tricyclic antidepressants or monoamineoxidase inhibitors may potentiate the vascular effects of terbutaline. Use with inhalation anesthetics (e.g., halothane, isoflurane, methoxyflurane), may predispose the patient to ventriculararrhythmias, particularly in patients with preexisting cardiac disease¯use cautiously. Use withdigitalis glycosides may increase the risk of cardiac arrhythmias.