Thiopental is a thiobarbiturate used for intravenous induction of general anesthesia. A single administration can produce a brief hypnotic effect as drug redistributes away from the brain. Its veterinary role has declined with wider use of other induction agents, but it remains relevant to selected short anesthetic procedures and protocols.
Thiopental enhances GABA-A-receptor-mediated inhibition, increasing chloride conductance and reducing neuronal excitability. At greater exposure it produces broader central nervous system depression. Rapid brain entry causes loss of consciousness, while redistribution to muscle and other tissues terminates much of the initial hypnotic effect. Its anesthetic action is primarily hypnosis rather than intrinsic analgesia.
Overdose produces respiratory and cardiovascular depression. Stop injection, maintain oxygenation/ventilation and support circulation; extravasation causes additional local tissue damage.
Titrate intermittent IV increments to effect and monitor ventilation, oxygenation and cardiovascular status.
Typical reported reconstitution concentrations are 2.5% for small animals and 2.5-5% for large animals. Refrigerated chemical stability is not a substitute for aseptic in-use limits.
Equine combination alternative: thiopental 1 g per 90 kg as 10% solution over 20 seconds, 15 minutes after xylazine 0.22 mg/kg IV or acepromazine 0.05 mg/kg IV. Cattle/horses premedicated with guaifenesin have received 5.5 mg/kg IV or 8.8-11 mg/kg after tranquilization; preserve the premedication context.
