Finasteride Topical Solution vs Finasteride Tablet
Oral Finasteride is a well-established and effective treatment for men with androgenic alopecia (AGA), but therapy is not always acceptable to patients due its side effects. The side effects which may be experienced from oral Finasteride include:
• Reduced sperm count
• Reduction in libido
• Erectile dysfunction
• Breast tenderness
This article will aim to evaluate:
• How researchers have tried to overcome the adverse effects and capitalise on hair gains,
• The efficacy and safety of topical Finasteride compared with oral Finasteride, and
• How system exposure can occur with topical Finasteride and how to avoid it.
What is Finasteride?
Finasteride is a competitive inhibitor of types II and III 5-alpha-reductase isoenzyme, resulting in inhibition of testosterone conversion to dihydrotestosterone (DHT). DHT is the most potent hormone among the androgens and is considered a pure androgen as it cannot convert into oestrogen. Research has shown that Finasteride reduces prostatic DHT levels by upwards of 90% and serum DHT levels by a staggering 70% by inhibiting the 5-alpha-reductase enzyme. The effects of Finasteride is also dose dependant.
"If you inhibit the conversion of testosterone to dihydrotestosterone, then men would have more testosterone, so isn't this a good thing?"
It's not quite so simple. Compared to testosterone, DHT has approximately double the binding affinity to the androgen receptor and a dissociation rate about five times slower (this means it hangs around for a lot longer). DHT plays a critical function in the sexual development of males and the role of DHT differs as males progress throughout adult life. In a perfect world, you want a nice balance of testosterone and dihydrotestosterone.
Figure 1 (below): How Finasteride works.
Due to the adverse effects of oral Finasteride, many researchers have embarked on new ventures to compare topical Finasteride with oral Finasteride. The first study on topical finasteride was completed in 1997 by Mazarella et al. as a single-blind, placebo-controlled study, including 28 males and 24 females patients with AGA for sixteen months. The Subjects were randomly split into two groups:
• Group 1 - Received 1.0 mL topical Finasteride 0.005% solution twice daily
• Group 2 - Received 1.0ml placebo twice daily Blood samples revealed no significant change in plasma levels of total testosterone, free testosterone, and DHT between the groups.
At sixth months, the researchers observed a significant decrease in the rate of hair loss in the topical Finasteride compared to the placebo group. The most recent study published in October 2021 involved 458 men (328 completed the study) over 24 weeks. This was a multi-centre, randomized, double-blind, placebo-controlled study in men with AGA. The experimental drug was topical Finasteride 0.25% w/w (concentration of 2.275 mg/mL) delivered using a spray applicator with a plastic cone that prevents product dispersion in the air. Each actuation delivers 50 µL of solution, equivalent to 0.114 mg of Finasteride.
The topical placebo containing the same excipients as the experimental solution was identical in appearance to the active treatment.
Oral Finasteride 1 mg was the reference drug for systemic exposure with the matching oral placebo an inert powder-filled capsule. The study concluded change from baseline in target area hair count (TAHC) at week 24 was numerically similar between topical and oral finasteride, however, lower systemic exposure and less impact on serum DHT concentrations was observed in favour of the topically applied solution.
How systemic exposure can occur with topical Finasteride
Systemic exposure to topical Finasteride can occur due to:
• Drawing too much into the dropper. Finasteride has a dose-dependant response curve so a little extra Finasteride can produce a big response,
• The strength/dose was too high for the individual,
• Formulation error,
• Changing the delivery vehicle - In the most recent study conducted, a topical spray was used containing Finasteride 2.275mg/ml but only 50 µL of solution was delivered due to air dispersion. If the same person applied the exact same dose in a topical solution, the systemic exposure would increase significantly due to the absence of air dispersion. Finally,
• The frequency - twice daily application has shown to have a larger impact on serum DHT and therefore daily application is preferred.
Can compounding pharmacies formulate a higher strength of Finasteride other than the 0.01% solution?
Of course! Compounding pharmacists can customise any strength that is on your prescription. It comes down to patient acceptability and safety profile.
Author: Helen Huynh B.Pharm MPS
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2) Caserini M1, Radicioni M, Leuratti C, et al. A novel finasteride 0.25% topical solution for androgenetic alopecia: pharmacokinetics and effects on plasma androgen levels in healthy male volunteers. Int J Clin Pharmacol Ther. 2014;52(10):842–9
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4)Pirracini, B et al (2021) Efficacy and safety of topical finasteride spray solution for male androgenetic alopecia: a phase III, randomized, controlled clinical trial. J Eur Acad Dermatol Venereol. 2021;Feb;36(2):286-294.