<p>Possible increase in difficulty in producing anaesthesia in patients taking alcohol or CNS depressants. Additive action with other CNS depressants including sedatives, hypnotics, nitrous oxide or alcohol. Increased hypotension and excitatory effects with phenothiazine antipsychotics. Increased hypnotic effect with antipsychotic. Decreased requirement of thiopental sodium with metoclopramide, sulfisoxazole, aspirin, meprobamate, probenecid and other highly protein bound drugs.</p>