Do local injections of finasteride (5-alpha-reductase inhibitor) or dutasteride (5-alpha-reductase inhibitor) cause sexual side effects, and is there systemic absorption with these local injections or topical solutions?

From the Guidelines

Local injections of finasteride or dutasteride are likely to cause fewer sexual side effects compared to oral administration, but the risk cannot be completely eliminated due to potential systemic absorption. When these 5-alpha reductase inhibitors are administered locally (via injection or topical application), they aim to reduce systemic absorption while maintaining local effectiveness for conditions like androgenetic alopecia. The sexual side effects commonly reported with oral finasteride and dutasteride (including erectile dysfunction, decreased libido, and ejaculatory disorders) occur because these medications reduce dihydrotestosterone (DHT) throughout the body, including in genital tissues.

According to the study by 1, the adverse effects of 5-alpha reductase inhibitors include erectile dysfunction, decreased libido, and ejaculatory disorders, which are more common in the treatment arm compared to the placebo arm. The study found that the overall discontinuation or loss to follow-up rates for both the 5-ARI and placebo arms were approximately 15%, with a combined discontinuation and loss to follow-up rate specifically secondary to adverse events of approximately 6% in studies in both the 5-ARI and placebo patients.

Some small studies on topical finasteride have shown significantly lower serum DHT reduction compared to oral administration, suggesting reduced systemic effects 1. However, even topical formulations show some degree of systemic absorption, with studies detecting finasteride in plasma after topical application. The extent of systemic absorption from local injections specifically is not well-documented in large clinical trials, and individual responses may vary based on injection technique, dose, and individual metabolism.

Key points to consider:

• Local delivery of finasteride or dutasteride aims to minimize systemic effects by targeting specific areas while limiting systemic circulation.
• The risk of sexual side effects may be reduced with local administration, but it cannot be completely eliminated due to potential systemic absorption.
• Patients considering local administration should be aware of the potential risks and benefits, and individual responses may vary based on several factors.
• More research is needed to fully understand the effects of local injections of finasteride or dutasteride on sexual function and overall health.

From the FDA Drug Label

The most common side effects of dutasteride capsules include: trouble getting or keeping an erection (impotence)* a decrease in sex drive (libido)* ejaculation problems* enlarged or painful breasts.

The FDA drug label does not specifically address the question of local injection or topical solution of dutasteride or finasteride, and their potential for systemic absorption and sexual side effects. However, based on the information provided, dutasteride has been shown to cause sexual side effects, including:

• Impotence
• Decreased libido
• Ejaculation problems These side effects may persist after treatment discontinuation. There is no information provided about finasteride or local injection of these drugs. 2 2

From the Research

Sexual Side Effects of Finasteride and Dutasteride

• Finasteride and dutasteride, 5-α-reductase inhibitors, have been shown to produce an increase in the incidence of sexual dysfunction, including impotence, decreased libido, and ejaculation disorder 3.
• A systematic review and meta-analysis found that the use of 5α-reductase inhibitors carried a 1.57-fold risk of sexual dysfunction, with a relative risk of 1.66 for finasteride and 1.37 for dutasteride 4.
• Another study found that longer duration of 5α-RI exposure increased the risk of persistent erectile dysfunction (PED), independent of age and other known risk factors 5.
• A 5-year retrospective analysis found that dutasteride resulted in significantly more sexual side effects, including erectile dysfunction, ejaculatory dysfunction, and decreased libido, compared to finasteride 6.

Systemic Absorption of Local Injections or Topical Solutions

• There is no direct evidence in the provided studies regarding the systemic absorption of local injections or topical solutions of finasteride or dutasteride.
• However, the studies suggest that finasteride and dutasteride can cause sexual side effects when taken orally, which implies that systemic absorption of these drugs can occur 7, 3, 4, 5, 6.
• Further research is needed to determine the extent of systemic absorption of local injections or topical solutions of finasteride or dutasteride and their potential effects on sexual function.