Drug Interactions and Antipsychotic Agents
Most antipsychotics are metabolized by hepatic microsomal oxidases (cytochrome P450 system). The major isoenzyme sys-tems involved are CYP1A2, CYP2C19, CYP2D6 and CYP3A4 (Ereshefsky, 1996). Induction or inhibition of these enzymes by other drugs may occasionally produce clinically important drug interactions (Burns, 2001). Table 77.6 summarizes clinically significant pharmacokinetic drug interactions involving second-generation antipsychotic drugs.
There are other common interactions that will concern clinicians. Antacids can decrease the absorption of the antip-sychotic agent from the gut. Antipsychotic medications can antagonize the effects of dopamine agonists or levodopa when these drugs are used to treat parkinsonism. Antipsychotic agents may also enhance the effects of central nervous system depressants such as analgesics, anxiolytics and hypnotics. If patients require preanesthetic medication or general anesthet-ics, the doses of these drugs may need to be reduced (Marder, 1997).