Some of the views expressed in the following notes on newly approved products should be regarded as preliminary, as there may have been limited published data at the time of publication, and little experience in Australia of their safety or efficacy. However, the Editorial Executive Committee believes that comments made in good faith at an early stage may still be of value. Before new drugs are prescribed, the Committee believes it is important that more detailed information is obtained from the manufacturer's approved product information, a drug information centre or some other appropriate source.
Proscar (Merck Sharp & Dohme)
5 mg film coated tablets
Indication: benign prostatic hypertrophy
The development of benign prostatic hypertrophy is related to the production of dihydrotestosterone. This potent androgen is produced by the action of 5 alpha reductase on testosterone. Finasteride blocks this metabolism by inhibiting the enzyme.
A daily dose of 5 mg finasteride can reduce the size of the prostate gland and improve the flow of urine. These benefits may take several months to appear, and when treatment ceases, the volume of the prostate increases again, approaching pre-treatment size.
The bioavailability of the tablets is approximately 80% and absorption is complete after 8 hours. Plasma clearance is approximately 165 mL/minute giving a half-life of 6 hours. Finasteride is metabolised with a greater proportion of the two metabolites being excreted in the faeces. The company does not recommend different doses for elderly patients or those with renal insufficiency.
Adverse effects associated with inhibition of 5 alpha reductase are decreased libido, impotence and ejaculatory disorders. Treatment with finasteride decreases prostate specific antigen levels, even in the presence of prostate cancer.
It is not known if finasteride can mask a prostate cancer. Although the rate of cancer detection was not altered in clinical trials, will everyday patients be subjected to the same intensity of monitoring?
There are few data on long-term safety and efficacy. The optimum use of this drug is not yet clearly defined. At present, its use will be restricted to patients with symptomatic benign prostatic hypertrophy who cannot undergo surgery.
