Doesn't the dosing schedule for isotretinoin for treating acne vulgaris

Isotretinoin therapy should be initiated at a dose of 0.5 mg/kg/d for 4 weeks and increased as tolerated until a cumulative dose of 120-150 mg/kg is achieved.

contradict the following evidence for multiple courses? Even if a patient has achieved acne clearance (meaning absence of primary acne lesions especially inflammatory ones (multiple and/or deep comedones may require adjunctive therapy)), why not continue for another 6 months? To wit, aren't multiple courses of therapy the same as exceeding the maximum dosage?

Aug 21 2019 PRODUCT MONOGRAPH on Accutane, Hoffmann-La Roche Limited, p. 13 of 36.

Effects of multiple courses of Accutane on the developing musculoskeletal system are unknown. There is some evidence that long-term, high-dose, or multiple courses of therapy with isotretinoin have more of an effect than a single course of therapy on the musculoskeletal system.

3 doctors also allege the efficacy in multiple courses of Epuris.

The therapeutic response to isotretinoin is dose-related and varies between patients. This necessitates individual adjustment of dosage according to the response of the condition and the patient’s tolerance of the drug. In most cases, complete or near-complete suppression of acne is achieved with a single 12 to 16 week course of therapy. If a second course of therapy is needed, it can be initiated eight or more weeks after completion of the first course, since experience has shown that patients may continue to improve while off the drug.


I think you're asking if multiple courses will exceed the maximally recommended cumulative dose of 120-150 mg/kg though that is not steadfast as your reference also says

One recent study of 116 patients found that a cumulative dose of 220 mg/kg or more may result in lower relapse rates, but confirmation will require study in larger populations.278

However, the half life of isotretinoin is

The half life is 22 hours and the bioavailability is 25%.

So, once a course of treatment has finished, and a delay is instituted to allow the drug to clear from the system, another course of treatment can be instituted.

Further courses of therapy are usually successful when required. There are no reports of cumulative toxicity from using repeat courses and tachyphylaxis has not been noted.

In other words, the cumulative dose refers to a single treatment course and not a combination of all treatment courses.


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