Ketotifen is a Prodrug. Norketotifen is the active metabolite.

Axel Karl Gunnar Aberg, Nada Arulnesan, Gordon T Bolger, Vincent B Ciofalo, Kresimir Pucaj, Kristina Walle, Thomas Walle

Drug development research 2022 Apr

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Evaluation of the in vitro human liver microsome and hepatocyte metabolism of ketotifen demonstrated that norketotifen (NK) is the major demethylated hepatic metabolite of ketotifen. It is here reported that NK is completely devoid of the severe and dose-limiting sedative effects of ketotifen. Thus, while ketotifen is clinically dose-limited to 1 mg, bid, there are no dose-limiting sedative effects elicited by NK, even after the highest single-dose (16 mg) or after repeat-doses (8 mg × 7 days) in humans or after the highest doses given to dogs in repeat-dose toxicological studies (40 mg/kg × 14 days). In addition, NK-but not ketotifen-was found to express potent and dose-dependent inhibition of the release of the pro-inflammatory cytokine TNFα from activated human buffy coat preparations. Thus, when used as an anti-inflammatory drug, ketotifen is the sedating prodrug which is converted to NK a nonsedating metabolite with anti-inflammatory activity. © 2021 Wiley Periodicals, LLC.

Citation

Axel Karl Gunnar Aberg, Nada Arulnesan, Gordon T Bolger, Vincent B Ciofalo, Kresimir Pucaj, Kristina Walle, Thomas Walle. Ketotifen is a Prodrug. Norketotifen is the active metabolite. Drug development research. 2022 Apr;83(2):362-367