VPT 321: Veterinary Neuropharmacology (2+1)

PHARMACOKINETICS OF BARBITURATES

• Absorption—readily absorbed from GI tract when given orally
• Distribution – Cross BBB. High levels reached in brain, liver and kidney. Lipid soluble and redistribute to muscle leading to decrease  in plasma level of barbiturate.
• Large store in adipose tissue.
• Animal seems to recover once the plasma level goes down
• Then sedate and drowsy as the drug keeps coming back to circulation from storage resulting in  long periods of CNS depression
• Repeated doses end up in  cumulation.
• Once stores are saturated can cause severe depression of CVS and respiration
• Excretion – renal, after oxidation in hepatic and extra-hepatic sites
• Barbiturates – known inducers of microsomal enzymes. Induces its own metabolism resulting in tolerance to the effects. Tolerance disappears after withdrawal of the drug.
• Cats are sensitive to the respiratory depression and dogs to the CVS depression of barbiturates
• Antidote – Bemegride. a CNS stimulant