Health Canada is warning that two popular medications used to treat baldness and enlarged prostates may put men at an increased risk of a serious form of prostate cancer, known as high-grade prostate cancer.
The agency warned Monday that finasteride and dutasteride can increase the risk for high-grade prostate cancer, an aggressive type of prostate cancer that grows and spreads more quickly than low-grade cancers.
The warning comes after Health Canada reviewed two large international clinical trials that, ironically, were designed to provide evidence to support using finasteride and dutasteride to prevent prostate cancer.
Health Canada advised doctors and the public Monday that high-grade prostate cancer is rare, "and the increased risk seen with finasteride and dutasteride drugs is still considered very small."
Nevertheless, the agency said that new warnings about the risk are now being added to the labels for finasteride and dutasteride products.
Finasteride is available under the brand names Proscar (5 mg finasteride), Propecia (1 mg finasteride), and their generic equivalents, all of which contain "finasteride" in their name. Propecia is used for the treatment of male pattern hair loss while the higher-dose Proscar is used in the treatment of benign prostatic hyperplasia (BPH), or a non-cancerous enlarged prostate.
Dutasteride is available under the brand names Avodart and Jalyn (a combination drug product containing dutasteride and tamsulosin).
The new safety information is based on Health Canada's review of the Prostate Cancer Prevention Trial (PCPT), and the Reduction by Dutasteride of Prostate Cancer Events (REDUCE) trial.
The trials showed that the long-term daily use over four years of 5-mg finasteride and dutasteride in men aged 50 years and older was associated with a small but statistically significant increased risk of high-grade prostate cancer.
The 1 mg finasteride strength (Propecia) was not included in these trials but "a potential risk has not been ruled out," the agency said.
Both trials showed that the possible benefits of these drugs in preventing low-grade prostate cancer are small relative to the risk of developing high-grade prostate cancer.
Last August, Health Canada warned that finasteride might put men at a slightly increased risk of breast cancer.
It said that breast cancer has been reported in a small number of patients worldwide taking both the 1 mg and 5 mg formulations, though most of the reports have been in association with the 5mg formulation.
The labelling for generic finasteride has been updated to include information about the breast cancer risk.
