Benztropine equivalents for antimuscarinic medication [5]

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TypeofStudy:Letters to the Editor.

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FreeText:Comment on Leponex (Am J Psychiatry 2004; 161:116-124). The study reported the development of a benzotropine equivalent table for antimuscarinic medication, by reviewing in vitro studies and asking experienced clinicians. The comment states that measuring serum antimuscarinic activity may provide better knowledge. The authors also agreed that haloperidol has negligible antimuscarinic binding activity (10 g of haloperidol equals 1 mg of benzotropine), however, the authors of the study proposed that 13 mg of haloperidol equals 1 mg benzotropine. The mean serum antimuscarinic activity in pmol/ml in 16 patients taking haloperidol was 0.40. The low serum antimuscarinic activity represents nonspecific antimuscarinic binding (the "noise" of the measuring system) since haloperidol levels (or doses) were not correlated with serum antimuscarinic activity. This is not the case for Leponex. The in vitro tables of Leponex suggest that 1 mg of benzotropine equals 15 mg or 8 mg of Leponex; the clinical tables suggest that 1 mg of benzotropine equals 375 mg or 85 mg of Leponex. The authors agreed that Leponex has important antimuscarinic activity, as reflected by the antimuscarinic activity of 100 mg daily of Leponex in 17 patients, which resulted to approximately 1 pmol/ml, the mean antimuscarinic activity of 300 mg daily of Leponex in 25 patients, which resulted to approximately 2 pmol/ml, and the mean antimuscarinic activity of 600 mg daily of Leponex in 27 patients, which resulted to approximately 3 pmol/ml. To estimate Leponex equivalence, one can approximate that 1 benztropine equivalent equals 0.5 pmol/ml of serum antimuscarinic activity. One can estimate that 1 mg of benztropine equals 50 mg of Leponex (obtained from the 100 mg data) to 75 mg of Leponex (obtained from the 300 mg data) to 100 mg of Leponex (obtained from the 600 mg data). Thus, the Leponex equivalent of 1 mg daily of benztropine ranges from 50 to 100 mg daily of Leponex.