Dr. med. Dirk Manski

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Finasteride: Treatment of Benign Prostate Hyperplasia

Mechanism of Action of Finasteride

Finasteride is a selective competitive inhibitor of 5α-reductase type 2 of the prostate, seminal vesicles and skin. The inhibition lowers the concentration of dihydrotestosterone (DHT) in the prostate. Since DHT causes the androgenic effect in the prostate, the inhibition of 5α-reductase leads to a reduction in prostate volume. Furthermore, finasteride is used to treat male pattern baldness.

Indications for Finasteride

Finasteride is indicated in lower urinary tract symptoms or bleeding due to benign prostate hyperplasia. Finasteride should be used from a prostate volume of >40 ml.

The consequence of finasterid treatment is the shrinkage of the prostate, improvement of LUTS and IPSS score, improved urinary flow and the risk reduction for urinary retention, gross hematuria or the need for TURP (5% vs. 10%) after 5 years of treatment (McConnell et al, 1998).

Pharmacokinetics of Finasteride

After metabolization, the metabolites are excreted via the urine and stool. No dosage reduction is necessary in renal insufficiency (GFR >9 ml/min). Experiences in dialysis patients are not available.

Side Effects of Finasteride

PSA concentration:

Reduction by 50% after treatment over 6 month. PSA should be measured after several month of treatment with finasteride and the new PSA concentration should be considered for prostate cancer screening. The ratio fPSA/tPSA is not affected.

Prostate cancer:

In long-term randomized studies with 5$\alpha$-reductase inhibitors to treat benign prostate hyperplasia, the incidence of prostate cancer was reduced (compared to placebo). For finasteride, the reduction of prostate cancer incidence was shown in one randomized study. However, the rate of undifferentiated tumors was higher in the verum group.

Sexual side effects:

Often reduced ejaculate volume, decreased libido, gynecomastia (2%), erectile dysfunction (<2%). The risk for infertility (reduced sperm count) is controversial. Libido loss and erectile dysfunction may be permanently disturbed in some patients on long-term use (Traish et al, 2011) and are sometimes referred to as post-finasteride syndrome.

Further side effects:

Rare allergic skin reactions. Unknown frequency or isolated cases: breast cancer, depression.

Drug Interactions with Finasteride

No important drug interactions are known.

Contraindications of Finasteride

Dosage of Finasteride

5 mg 1–0–0 p.o. for treatment of BPH. For treatment of male pattern baldness: 1~mg 1-0-0 p.\,o.

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