Anticholinergic drugs can induce a delirium characterized by confusion, disorientation, visual hallucinations, and memory disturbance. They can also produce general distress related to their common peripheral side effects of dry mouth, delayed gastrointestinal transit time producing constipation and sometimes even toxic megacolon, and impairment of urination. Antiparkinsonian agents, tricyclic antidepressants, and antihistamines, especially when combined with anticholinergic antipsychotics such as chlorpromazine, thioridazine, and clozapine. The elderly are particularly vulnerable.
There are some studies that raise the possibility that anticholinergic agents may interfere with or reduce the efficacy of antipsychotics on positive symptoms of schizophrenia.¹
For these reasons, it may be best to keep the anticholinergic load as low as possible in antipsychotic-treated patients. For example, use of low to moderate doses of Parkinsonism-producing antipsychotics may enable discontinuation or avoidance of antiparkinsonians.
Recommendation #155
