Chemical Properties
Yellowish-white, hygroscopic powder.
Definition
A rapidly acting barbiturate administered
intravenously for general anesthesia and hypnosis.
Commonly known as “truth serum.”
Brand name
Thiopental is BAN.
Hazard
May cause respiratory failure; use onlywith
physician in attendance.
Description
Thiopental sodium , the sodium
salt of 5-ethyl-5-(1-methylbutyl)thiobarbituric
acid, a yellowish-white,
crystalline, slightly bitter powder, is very soluble
in water and soluble in alcohol. The compound
is hygroscopic and has a weak unpleasant
odor. The free acid forms colorless crystals, mp
158 – 159 ?C.A10%solution of the sodium salt
has a pH of 10.6.
Pharmacokinetics
Thiopental is highly bound to albumin, and free drug availability is increased
in hypoproteinaemia. Protein binding is decreased by alkalaemia,
hyperventilation and some drugs that occupy the same albumin binding
sites, thereby increasing unbound thiopental concentrations. Metabolism
occurs predominantly in the liver, and the metabolites are excreted by the
kidneys. Only a small proportion is excreted unchanged in the urine. The
terminal elimination half-life is approximately 11.5h (longer in the elderly).
Elimination after an infusion is a zero-order process with 10%–15% of the
remaining drug metabolised each hour. Up to 30% of the original dose may
remain in the body at 24h, and a hangover effect is common. Accumulation
may result if further doses of thiopental are administered within 1–2 days.
Clinical Use
Thiopental sodium is a short-acting intravenous
anesthetic used for brief surgical procedures
and induction of anesthesia. It is a potent,rapidly effective hypnotic. Sleep ensues within
30 – 60 s. A disadvantage is the lengthy hangover.
In the United States and Great Britain it is
the most widely used injection anesthetic. Abuse
can lead to addiction.
Veterinary Drugs and Treatments
Because of its rapid action and short duration, in young, healthy
animals, thiopental is excellent induction agent (rapid IV bolus)
for general anesthesia with other anesthetics or as the sole anesthetic
agent for very short procedures. In sick or debilitated animals,
thiopental may be used in a more cautious manner (IV, slowly to
effect).
