Thiopental (Pentothal®)
By: Dr. Nicholas Dodman

Overview

Thiopental is a rapidly acting, ultra-short duration, intravenous anesthetic that is used for induction of anesthesia prior to inhalation maintenance or as sole agent for minor procedures.

Thiopental is approved by the Food and Drug Administration (FDA) for use in humans and many species of domestic animals.

Due to potential for abuse and misuse, thiopental is a controlled substance.

Thiopental is a prescription drug should only be administered by a veterinarian in a veterinary setting.

Brand Names or Other Names

This drug is registered for use in humans and animals.

Human formulations: Pentothal® (Abbott), Thiopental Sodium® (IMS) and generic equivalents

Veterinary formulations: Pentothal® (Abbott) and generic equivalents

Uses of Thiopental

Thiopental is used to induce anesthesia. It is also used to maintain anesthesia for short, non-painful procedures.

Precautions and Side Effects

While generally safe and effective when administered by a veterinarian, thiopental causes some unwanted side effects.

Thiopental should not be used in animals with known hypersensitivity or allergy to the drug.

Thiopental should not be used in animals with severe cardiovascular compromise, such as shock, head trauma, intracranial space-occupying lesions, or liver disease.

Thiopental should be used with caution in animals with kidney disease.

Thiopental should not be used to induce or maintain anesthesia in sight hounds because of their reduced ability to metabolize the drug (prolonged recovery and associated complications).

Thiopental may interact with other medications. Consult with your veterinarian to determine if other drugs your pet is receiving might interact with thiopental. Such drugs include Ringer's solution, Lactated Ringers, amikacin, atropine, benzylquinamide, cephapyrin, chlorpromazine, codeine, dimenhydrinate, diphenhydramine, ephedrine, glycopyrrolate, hydromorphone, insulin, levorphanol, meperidine, metaraminol, morphine, norepinephrine, penicillin G, prochlorperazine, promazine, promethazine, succinylcholine, and tetracycline. In general, drugs with an acidic pH should not be mixed with (alkaline) thiopental solutions

If inadvertently injected perivascularly (outside of the vein); thiopental may cause a skin slough due to the solution's high alkalinity.

How Thiopental is Supplied

Thiopental is supplied as a pale yellow powder for reconstitution with sterile water to make an injectable solution. Various amounts of thiopental powder are available in this form: 250 mg, 400 mg, 500 mg, 1 g, 2.5 g, and 5 g. Sterile water is added to make either a 2.0% or 2.5% solution (containing 20 and 25mg/mL, respectively).

Dosing Information

Thiopental should only be administered to an animal by a licensed veterinarian.

The drug is titrated intravenously to effect. A typical dose range in unpremedicated, healthy dogs is 5 to 12.5 mg per pound (10 to 25 mg/kg). The dose for cats is 4.5 mg to 5.5 mg per pound (9 to 11 mg/kg) intravenously.

Different premedicants affect the dose rate of thiopental. Xylazine premedication reduces the dose to about 1/3 of the calculated dose. Premedication with a phenothiazine, such as acepromazine, approximately halves the computed dose. Narcotic premedication alone does not cause a marked reduction in the induction dose of thiopental, though some downward adjustment in dose may be required.

Whatever the anticipated dose, it is normal practice, in healthy animals, to give approximately half of the computed dose relatively rapidly, with the remainder of the dose being given more slowly and to effect. Normally, an interval of 20 to 30 seconds is sufficient for thiopental's effects to become apparent.

The amount of thiopental required depends on the precise use to which it is being put, the clinical response of the patient to the medication, and the development of any adverse effects.

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