0
Get Alert
Please Wait... Processing your request... Please Wait.
You must sign in to sign-up for alerts.

Please confirm that your email address is correct, so you can successfully receive this alert.

1
Letter to the Editor   |    
Benztropine Equivalents for Antimuscarinic Medication
JOSE de LEON, M.D.
Am J Psychiatry 2005;162:627-627. doi:10.1176/appi.ajp.162.3.627

To the Editor: Michael J. Minzenberg, M.D., et al. (1) are to be congratulated for developing a benztropine equivalent table, as we previously did (2), by reviewing in vitro studies and asking experienced clinicians. However, measuring serum antimuscarinic activity may provide better knowledge (3).

The in vitro literature (1, 2) suggests that haloperidol has negligible antimuscarinic binding activity (10 g of haloperidol equals 1 mg of benztropine) (2). Although our senior pharmacologist also concluded that the clinical antimuscarinic binding activity of haloperidol was negligible (2), the psychiatrists working with Dr. Minzenberg et al. proposed that 13 mg of haloperidol equals 1 mg of benztropine (1). Our recent study (3) also suggested that haloperidol probably has negligible antimuscarinic clinical activity. The mean serum antimuscarinic activity in pmol/ml in 16 patients taking haloperidol was 0.40 (95% confidence interval [CI]=0.30–0.51). This low serum antimuscarinic activity appeared to represent nonspecific antimuscarinic binding (the "noise" of the measuring system) since haloperidol levels (or doses) were not correlated with serum antimuscarinic activity.

Clozapine differs in that its in vitro tables suggest that 1 mg of benztropine equals 15 mg (2) or 8 mg (1) of clozapine; the clinical tables suggest that 1 mg of benztropine equals 375 mg (2) or 85 mg (1) of clozapine. Our recent study agreed that clozapine probably has important antimuscarinic activity (3). The mean serum antimuscarinic activity in 20 patients taking antiparkinsonian medications with mean doses of two benztropine equivalents was approximately 1 pmol/ml (1.05, 95% CI=0.66–1.44) (3). The antimuscarinic activity of 100 mg/day of clozapine in 17 patients was approximately 1 pmol/ml (1.38, 95% CI=0.83–1.93). The mean antimuscarinic activity of 300 mg/day of clozapine in 25 patients was approximately 2 pmol/ml (1.91, 95% CI=1.42–2.40). The mean antimuscarinic activity of 600 mg/day of clozapine in 27 patients was approximately 3 pmol/ml (2.81, 95% CI=2.16–3.46).

To estimate clozapine equivalence, one can approximate that 1 benztropine equivalent equals 0.5 pmol/ml of serum antimuscarinic activity. Using the serum muscarinic activity data of the three clozapine doses, one can estimate that 1 mg of benztropine equals 50 mg of clozapine (obtained from the 100-mg data) to 75 mg of clozapine (obtained from the 300-mg data) to 100 mg of clozapine (obtained from the 600-mg data). Thus, the clozapine equivalent of 1 mg/day of benztropine ranges from 50 to 100 mg/day of clozapine. The misleading fact that clozapine is an agonist for some muscarinic receptors, the M4, and may cause hypersalivation instead of dry mouth may confound clinicians.

Minzenberg MJ, Poole JH, Benton C, Vinogradov S: Association of anticholinergic load with impairment of complex attention and memory in schizophrenia. Am J Psychiatry  2004; 161:116–124
[PubMed]
[CrossRef]
 
de Leon J, Canuso C, White AO, Simpson GM: A pilot effort to determine benztropine equivalents of anticholinergic medications. Hosp Community Psychiatry  1994; 45:606–607
[PubMed]
 
de Leon J, Odom-White A, Josiassen RC, Diaz FJ, Cooper TB, Simpson GM: Serum muscarinic activity during clozapine treatment. J Clin Psychopharmacol  2003; 23:336–341
[PubMed]
[CrossRef]
 
+

References

Minzenberg MJ, Poole JH, Benton C, Vinogradov S: Association of anticholinergic load with impairment of complex attention and memory in schizophrenia. Am J Psychiatry  2004; 161:116–124
[PubMed]
[CrossRef]
 
de Leon J, Canuso C, White AO, Simpson GM: A pilot effort to determine benztropine equivalents of anticholinergic medications. Hosp Community Psychiatry  1994; 45:606–607
[PubMed]
 
de Leon J, Odom-White A, Josiassen RC, Diaz FJ, Cooper TB, Simpson GM: Serum muscarinic activity during clozapine treatment. J Clin Psychopharmacol  2003; 23:336–341
[PubMed]
[CrossRef]
 
+
+

CME Activity

There is currently no quiz available for this resource. Please click here to go to the CME page to find another.
Submit a Comments
Please read the other comments before you post yours. Contributors must reveal any conflict of interest.
Comments are moderated and will appear on the site at the discertion of APA editorial staff.

* = Required Field
(if multiple authors, separate names by comma)
Example: John Doe



Related Content
Books
The American Psychiatric Publishing Textbook of Psychopharmacology, 4th Edition > Chapter 34.  >
The American Psychiatric Publishing Textbook of Psychopharmacology, 4th Edition > Chapter 34.  >
The American Psychiatric Publishing Textbook of Psychopharmacology, 4th Edition > Chapter 34.  >
The American Psychiatric Publishing Textbook of Psychopharmacology, 4th Edition > Chapter 34.  >
The American Psychiatric Publishing Textbook of Psychopharmacology, 4th Edition > Chapter 34.  >
Topic Collections
Psychiatric News
PubMed Articles