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, the hairs become more fine to the point where it becomes invisible and eventually falls out completely.
Follicle miniaturisation occurs due to excess levels of a hormone called dihydrotestosterone (DHT). Testosterone is converted to dihydrotestosterone by an enzyme called 5-alpha reductase. Finasteride is one of the most potent inhibitors of 5-alpha reductase, thus helps to reduce follicle miniaturisation and hair loss.
However, too much Finasteride comes at a cost. DHT is required for important body functions, especially in men. Serum DHT refers to the levels found in the blood.
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 levels.
When serum DHT levels are reduced, systemic adverse effects can occur.
This article will focus on one of the most debatable topic: dosing schedule.
- Isn't twice daily dosing 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 dosed?
The dosing schedule for medicines are determined by its half life (how long it takes to break down by half of its concentration). This is often referred to as the drugs' pharmacokinetics.
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. This is often referred to as pharmacodynamics.
In a normal healthy person, we assume the pharmacodynamics are constant (no variables) so the pharmacokinetics becomes the determining factor. 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.
The results from once daily application was found to be more favourable.
You can read the full systematic review here.
If I am applying 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).
Finasteride dosing can be complex and should tailored for the individual by a medical prescriber and 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
