Pro- and anticonvulsant effects of anesthetics (Part I).

Many inhaled anesthetics and intravenous analgesics have been alleged to produce both proconvulsant and anticonvulsant activity in humans. The reasons for these contrasting actions on the CNS are poorly understood at the present time. However, biologic variability plays an important role in determining individual patient's responses to anesthetic and analgesic drugs. In addition, variations in the responsiveness of inhibitory and excitatory neurons to the central depressant effects of these drugs could also explain these apparently conflicting data. Depending on the brain concentration, centrally active drugs may produce differing effects on the CNS inhibitory and excitatory neurotransmitter systems. The availability of increasingly powerful magnetic resonance imaging techniques to provide noninvasive information about tissue chemistry (e.g., neurotransmitters and citric acid cycle metabolites) and positron emission tomography to noninvasively evaluate CNS drug-receptor interactions should lead to a more in-depth understanding of the in vivo effects of anesthetics and analgesics on the CNS. In the second part of this review article, we discuss the pro- and anticonvulsant effects of the sedative-hypnotics, local anesthetics, and other anesthetic adjuvant drugs.