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In the book Kaplan and Sadock's synopsis of psychiatry:

Clozapine. Clozapine (Clozaril) levels are trough levels determined in the morning before administration of the morning dose of medication. A therapeutic range for clozapine has not been established; however, a level of 100 mg/mL is widely considered to be the minimum therapeutic threshold. At least 350 mg/mL of clozapine is considered to be necessary to achieve therapeutic response in patients with refractory schizophrenia. The likelihood of seizures and other side effects increases with clozapine levels greater than 1,200 mg/mL or doses greater than 600 mg per day or both. Clozapine is a common cause of a leukopenia in psychiatry. When moderate to severe leucopenia develops, clozapine treatment must be interrupted, but patients may be retreated with clozapine in the future.

What is "mL" here?

Sadock, B. J., & Sadock, V. A. (2011). Kaplan and Sadock's synopsis of psychiatry: Behavioral sciences/clinical psychiatry. Lippincott Williams & Wilkins.

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(edit, actually found the book text on Google books and paid a bit more attention to the context; the book is Kaplan & Sadock's Concise Textbook of Clinical Psychiatry by Sadock, Sadock, and Ruiz, and you can find the specific passage by searching for the quoted text)

This book is talking about plasma concentrations of drugs. Based on the actual plasma concentrations for clozapine with typical doses, this looks like just an error or typo: mL means milliliters, but these numbers would be more appropriate if they were in nanograms rather than milligrams, milligrams is several orders of magnitude too high and well beyond the solubility of clozapine in water.

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  • $\begingroup$ Indeed, from a review paper, "The lowest effective clozapine levels ranged from 250 to 550 µg/L, while the recommended upper limit to prevent toxicity varied from 600 to 2000 µg/L [0.002 mg/mL].". That is a big error. :O $\endgroup$
    – Steven Jeuris ♦
    Oct 23, 2018 at 10:48
  • $\begingroup$ The book I found states "A therapeutic range for clozapine has not been established; however, a level of 100 nanograms per milliliter (ng/mL) is widely considered to be a minimum therapeutic threshold." This is not the same book the OP listed though, but based on it (Kaplan & Sadock's Concise Textbook of Clinical Psychiatry). Maybe they corrected it here, or it was an erroneous copy/paste/typo of the OP. $\endgroup$
    – Steven Jeuris ♦
    Oct 23, 2018 at 10:55
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    $\begingroup$ @StevenJeuris Might be correct in an earlier or later version but the one on Google Books I link to shows the same error as OP. $\endgroup$
    – Bryan Krause ♦
    Oct 23, 2018 at 14:30
  • $\begingroup$ Well, that only further confirms your answer! :) $\endgroup$
    – Steven Jeuris ♦
    Oct 23, 2018 at 14:49

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