INTERACTIONS BETWEEN ANTIPSYCHOTIC AND ANTIHYPERTENSIVE DRUGS

OBJECTIVE: TO provide a comprehensive review of the pharmacokinetic and pharmacodynamic interactions between antipsychotics and antihypertensives and to provide recommendations for the selection of antihypertensives in patients receiving antipsychotic therapy. DATA SOURCES: A MEDLINE search of the English-language literature was used to identify pertinent human and animal studies, reviews, and case reports. STUDY SELECTION: All available sources were reviewed. DATA EXTRACTION: Background information was obtained from comprehensive reviews. Individual case reports were assimilated, and pertinent data were extracted. DATA SYNTHESIS: Because hypertension is common in patients with psychiatric illness and antihypertensive agents are used for a multiplicity of indications, significant numbers of patients receive concurrent therapy with antihypertensives and antipsychotics. Many antipsychotics may block the antihypertensive efficacy of guanethidine and related drugs. The interaction between clonidine and antipsychotics is defined less clearly. Limited data suggest possible additive hypotensive effects when chlorpromazine and methyldopa are given in combination. Increased plasma concentrations of thioridazine with a resultant increase in adverse effects have been reported when propranolol or pindolol are added to the regimen. A similar increase in chlorpromazine concentrations has been reported when propranolol was added. Although there are no reports documenting an interaction between a calcium-channel antagonist and an antipsychotic, the possible inhibition of oxidative metabolism of antipsychotics, additive calcium-blocking activity, and additive pharmacodynamic effects are theorized. Hypotension and postural syncope were reported in a patient given therapeutic dosages of chlorpromazine and captopril, and in 2 patients when clozapine was added to enalapril therapy. CONCLUSIONS: No antipsychotic-antihypertensive combination is absolutely contraindicated, but no combination should be considered to be completely without risk. Antihypertensives with no centrally acting activity, such as diuretics, may be the least likely to result in adverse reactions. The combination of the beta-antagonists propranolol or pindolol with thioridazine or chlorpromazine should be avoided if possible. Scrupulous patient monitoring for attenuated or enhanced activity of either agent is essential whenever antipsychotics and antihypertensives are given concurrently.