INFLUENCE OF ANTIPARKINSONIAN DRUGS ON PLASMA-LEVEL OF NEUROLEPTICS

Abstract

Interaction between various neuroleptics and antiparkinsonian drugs was analyzed by measuring the neuroleptic plasma level before and after withdrawal of antiparkinsonian drugs. The population completing the study consisted of 32 chronic schizophrenics treated with chlorpromazine (8), levomepromazine (14), thioridazine (6) or haloperidol (4). Twenty-five received benztropine; 4, trihexyphenidyl; and 3, procyclidine. During the first 4 wk patients remained on neuroleptics and antiparkinsonians, the latter being withdrawn during the 5th wk and the neuroleptics alone being administered during the following 16 wk. The plasma level of neuroleptics was assayed by GLC, once weekly in the morning at 2 different times. Analysis of variance showed a significant difference in neuroleptic plasma level when patients took neuroleptics only vs. the period they had received neuroleptics and antiparkinsonians. The multiple comparison based on Studentized range Q0.05 revealed a significant progressive increase of neuroleptic plasma level during 12 wk after withdrawal of antiparkinsonian drugs after which a plateau was reached. The hypothetical mechanisms of action of antiparkinsonians on neuroleptic plasma level are discussed.