The oldest Anesthetics group
Also used as SedatoHypnotics
Drugs:
- Long acting: SedatoHypnotics and Anticonvulsives
- Not used for anesthesia
- Phenobarbital
- Short acting (30min): Euthanasia and Anticonvulsives
- Ultrashort acting (3-5min): Anesthetics
- Thiopental: Also used for Euthanasia
- Metohexital: Can be readministered
Effects:
GABAa Agonists in the brain: immediate loss of consciousness but no analgesia
Excellent muscle relaxation
Pharmacokinetics:
- Very lipophilic
- Cross BBB very fast
- Redistribution from the brain to the fat tissue and muscles (Decreased effects from redistribution, not metabolism) > Patient can wake up
- No readministration of Thiopental or high risk of overdose
- Greyhounds and lean dog breeds are more sensitive to Thiopental as they have less fat for brain redistribution
- Metohexital can be readministered as it is less lipophilic
- No readministration of Thiopental or high risk of overdose
- Slow liver metabolism
- Phenobarbital: CYP450 induction (Not in cats): Need for dose increase for liver metabolized drugs
- Excretion by the kidney
Side effects: Very dangerous
Respiratory depression: Inhibition of respiratory centers of the brain
Circulatory depression > Hypotension > Tachycardia: Not for Dehydrated / Hypovolemic patients
Excitation
Tissue irritation: Only slow IV administration