Barbiturates

Barbiturates are derivatives of barbituric acid that are used therapeutically as anticonvulsants and sedatives. Barbiturates are also the primary component of most euthanasia solutions. Most barbiturate poisonings in companion animals are the result of accidental ingestion of human or veterinary prescription products, although ingestion of illicit medications, iatrogetic overdoses, accidental injection of euthanasia solutions, and ingestion of meat from carcasses euthanized with barbiturate – based solutions are other means of exposure.

Kinetics:

Barbiturates are well absorbed orally.

Highly lipid – soluble barbiturates rapidly distribute throughout the body, including the CNS, and then are  very rapidly redistributed into fat and total body water, which terminates their anesthetic effect.

 Barbiturates undergo hepatic metabolism, and metabolites as well as parent compound are eliminated in the urine.

Mechanism of Action :

In the CNS, barbiturates stimulate γ – aminobutyric acid (GABA), an inhibitory neurotransmitter, receptors and inhibit glutamate, a stimulatory neurotransmitter, receptors, causing CNS depression. Some of the CNS depressive effects of barbiturates relate to their inhibition of the release of other neurotransmitters such as norepinephrine and acetylcholine. Very high doses of barbiturates depress respiration and cardiac contractility, leading to respiratory depression and hypotension.

Clinical Signs:

The clinical effects of barbiturates relate to CNS depression, so the signs that can be seen include lethargy, ataxia, weakness, disorientation, recumbency, coma, respiratory depression, tachycardia or bradycardia, hypothermia, and death.

Diagnosis:

History ,clinical signs

Blood, urine, stomach content, and feces can be analyzed by most veterinary diagnostic laboratories for the presence of barbiturates.

Treatment:

1. Minimize absorption of the drug and provide symptomatic and supportive care to animals experiencing CNS depression.
2. Emesis may be induced followed by administration of activated charcoal and monitoring in hospital for 4 – 6 hours. Animals that present with severe CNS depression should not have vomiting induced due to the risk of aspiration; in these patients, gastric lavage should be considered.

• Activated charcoal administration should be repeated every 12 hours until the animals are ambulatory.

1. Animals experiencing severe coma will need intensive supportive care. Endotracheal tube placement may be indicated in those animals with severe coma and subsequent respiratory depression; in some cases mechanical ventilation may be necessary.
2. Oxygen and intravenous fl uids should be administered,