The clinical impact of reported variance in potency of antipsychotic agents

Abstract

There is significant disagreement on the clinical equivalence (or potency) of antipsychotic agents, with up to 500% variance reported in texts. To address the extent and consequences of these discrepancies, we took a random sample of 18 common psychiatry, psychopharmacology and pharmacology texts for antipsychotic equivalence tables. We found a marked variation in stated equivalences for the majority of antipsychotics. Most affected were the high potency (haloperidol, fluphenazine) and newer (molindone) drugs, which had a 500% variance. This variation inadvertently contributes to the misuse of these agents. For instance, high-potency antipsychotics are prescribed in far larger doses than necessary, leading to decreased efficacy and increased side effects. Steps to simplify and rationalize the use of these agents are recommended.

International Consensus Study of Antipsychotic Dosing

“…Broadly representative and plausible recommendations of clinically equivalent doses for antipsychotic drugs are needed to guide clinical dosing decisions, design of research studies, and interpretation of research findings (2,4,5,(22)(23)(24)(25). Accordingly, this study employed a Delphi, two-stage, international survey of experienced and expert clinical and research colleagues to gain consensus estimates of clinically equivalent doses (compared to oral olanzapine or short-acting injectable haloperidol as standards).…”

“…It would be desirable to base such potency comparisons on randomized, especially head-tohead, comparisons of a range of antipsychotics at several fixed doses, and across various diagnostic, illness severity, comorbidity, and demographic variables. Uncertainties about clinically equivalent doses of antipsychotics probably contribute to apparent variance in efficacy and tolerability in clinical practice and to inconsistent findings among experimental clinical trials (4,5,(22)(23)(24)(25). Uncertainties about clinically equivalent doses of antipsychotics probably contribute to apparent variance in efficacy and tolerability in clinical practice and to inconsistent findings among experimental clinical trials (4,5,(22)(23)(24)(25).…”

The pharmacological treatment of schizophrenia in Chinese patients: a comparison of prescription patterns between 1996 and 1999

“…First, adequacy of pharmacotherapy is measured against guidelines and standard textbook recommendations, rather than the characteristics of the particular patient population under review. Second, the conversion of different antipsychotics into CPZ equivalents is an approximation lacking objective, scientifically sound and widely accepted standard conversion values, particularly for atypi­cal agents [15]. Repeated surveys of the same locality using the same conversion table mitigate these shortcomings, and may reveal favourable developments or undesirable trends in prescribing practices [6–9].…”

An Audit of Outpatient Antipsychotic Usage in the Three Health Sectors of Auckland, New Zealand

“…The concept of chlorpromazine equivalence is controversial but useful where aggregated data is represented to show broad trends across patient groups. Although the CPZe derivation differs by up to 500% in the literature [12], for the typical antipsychotics conversion data related to dopamine (D2) affinity and therapeutic response is commonly available. The introduction of the atypical antipsychotics required new equivalence estimates.…”