Topical Finasteride Solution - is twice daily dosing better?
Androgenic alopecia is a prevalent condition amongst men and women. Although the pattern of hair loss is different for men and women, there is one thing in common and that is follicle miniaturisation.
What is follicle miniaturisation?
Follicle miniaturisation is a term used to describe miniaturisation of the hair follicle gradually over time. As the hair follicles become miniaturised (smaller), the hairs become more fine through each new cycle and eventually becomes invisible.
Follicle miniaturisation occurs due to excess levels of a hormone called dihydrotestosterone (DHT). Both men and women of testosterone, just at different levels. Testosterone is converted to dihydrotestosterone (DHT) by an enzyme called 5-alpha reductase. Finasteride is one of the most potent inhibitors of 5-alpha reductase, thus helps to prevent follicle miniaturisation and hair loss.
However, too much Finasteride comes at a cost because a healthy amount of DHT is required for important body functions, especially in men.
Scalp DHT vs Serum DHT
Serum DHT refers to the levels found in the blood. Serum DHT therefore affects other body systems and functions.
Scalp DHT levels refers to the levels found in the scalp. Low DHT levels in the scalp reduces hair loss while high levels in the scalp causes hair loss. The goal of topical Finasteride is to reduce scalp DHT levels without affecting serum DHT.
When serum DHT levels are too low, systemic adverse effects can occur.
This article will focus on one of the most debatable topic: dosing schedule.
- How many times a day should I be applying topical finasteride?
- Is dosing finasteride twice daily better?
Keep in mind there is no right or wrong answer because it comes down to the daily exposure volume of Finasteride and also how fast you break down Finasteride which we will cover later.
How do drug companies determine how often a drug should be given?
The dosing schedule for medicines are determined by its half life (how long it takes to break down by half of its concentration).
The next step is to look at the patient's health e.g. their liver function, kidney function (and sometimes even ethnicity) because all of these factors affect how fast a drug is cleared from the body.
In a normal healthy person, we assume every organ is functioning properly and the drug clearance is normal. Given that Finasteride has a long half life and long tissue dissociation time, once daily dosing is theoretically, sufficient.
but ... what does the data show?
Before we go further, we have to remember the end goal is to grow hair and not have side effects.
In a systematic review published in 2018 by Lee et al, Lee concluded that plasma DHT levels decreased by 65-78% with the use of topical Finasteride 0.25% given twice daily and by 62-72% with oral Finasteride 1mg given once daily. The blood samples were taken at baseline (Day 0) and seven days later. Said differently, topical Finasteride 0.25% applied twice daily was found to reduce blood DHT levels similar to taking oral Finasteride 1mg once daily.
The results from once daily application was found to be more favourable.
You can read the full systematic review here.
If I am applying topical finasteride twice daily, am I using too much?
Not necessarily. If we look a little deeper, the total daily exposure is the driving force behind systemic reduction in DHT levels.
For example, applying 1ml of Finasteride 0.01% (equiv. Finasteride 0.1mg/ml) would give the same exposure volume as applying 2ml of Finasteride 0.005% (equiv. Finasteride 0.05mg/ml).
In the study by Lee et al above, Finasteride 0.25% is equiv. to Finasteride 2.5mg/ml. If the participants are applying a total of 2ml a day, then the total daily Finasteride exposure is 5mg per day.
Our take away
Finasteride 0.25% appears to be a small and insignificant number; and we believe this is where consumers get caught out.
In a hypothetical scenario, if another person were using Finasteride 0.025% 2ml daily, the total daily Finasteride exposure would be 0.5mg.
Finasteride dosing can be complex and should be tailored for the individual by a medical prescriber. Several factors will determine the total daily dose that is needed.
References:
- Lee, S et al. A Systematic Review of Topical Finasteride in the Treatment of Androgenic Alopecia in Men and Women. Journal of Drugs in Dermatology. (2018), v17:4.
- Martindale: The Complete Drug Reference. 34th Edition.
- MIMS Online 2024
