Animal and molecular pharmacology of mixed agonist-antagonist analgesic drugs.

1 The pharmacology of analgesic drugs with mixed agonist-antagonist action is reviewed in the light of the theory of drug action at single and multiple receptors. 2 Evidence for a heterogeneous population of opiate receptors in mammalian brain and in isolated tissue preparations is discussed. 3 The unusual pharmacological and pharmacokinetic profiles of the oripavine derivative buprenorphine are discussed in relation to the action of the drug at a molecular level.