Finasteride is a specific inhibitor of type 2 5alpha-reductase, the enzyme that catalyses the conversion of testosterone to dihydrotestosterone.
Based on studies conducted in subjects with androgen insensitivity and congenital 5alpha-reductase deficiency, androgenic alopecia is induced by an excessive activity of intrafollicular receptors for androgens, due to or local factors (e.g. an increase in the number of receptors or an increase in local testosterone production) or systemic factors (e.g. an increase in circulating androgens). The areas most affected by hair loss are those associated with a greater density of androgen receptors, in particular for dihydrotestosterone which has an affinity for these receptors 5 times higher than testosterone.
Well absorbed after oral administration, regardless of the presence of food, finasteride has a bioavailability of 80%. It is metabolised in the liver and excreted in the urine and faeces, with a half-life of 5-6 hours.
Oral administration of finasteride represents an alternative to the use of topical minoxidil in the treatment of alopecia.
Various clinical studies have confirmed the effectiveness of the drug. Subjects with mild to moderate vertex alopecia were treated with finasteride 1 mg / day or placebo for up to two years. More than half of the men treated with finasteride obtained results considered satisfactory, with an increase in the number, thickness and length of hair, while in 90% of cases there was an arrest of the fall.
In the two-year studies, the number of hairs remained stable among the men who continued the treatment for the second year, while in the group who took the placebo during the second year, the hair started falling out again. Therefore, if the results are positive, the drug must be taken indefinitely.
A long-term placebo study, lasting a total of 5 years, initially enrolled 1,553 men aged 18 to 41 years with mild to moderate vertex alopecia (779 treated with finasteride and 774 with placebo). After the first 12 months, patients were asked to continue the treatment they were receiving, assessing their willingness to continue up to 5 years each year. Patients treated with finasteride (279) maintained or increased the number of hairs per cm 2 they had at the start of the study in 65% of cases, while those who continued the placebo treatment (15) for the most part continued to lose hair.
The effect of finasteride may not be evident for 4-6 months. If beyond this period of time there are no appreciable results, the treatment must be suspended.
The drug’s efficacy in later stage alopecia and bitemporal recession has not been demonstrated.
In a study comparing topical minoxidil, minoxidil induced faster initial improvement while finasteride was modestly more effective with continued treatment. The efficacy of the two drugs was found to be comparable as regards the arrest of the fall.
Some small studies have evaluated the efficacy of finasteride in the treatment of androgenetic alopecia in women. 2 studies conducted respectively on 136 and 137 postmenopausal patients with androgenetic alopecia, randomized to finasteride 1 mg / day or placebo for 1 year, concluded that finasteride is ineffective in reducing hair loss and slowing its progressive thinning. . 1 open-label 1-year study was conducted in a total of 48 premenopausal women with androgenetic alopecia to evaluate the efficacy of finasteride (5 mg / day) vs. flutamide (250 mg / day), vs. cyproterone acetate (50 mg / day + ethinyl estradiol, sequentially) vs. no treatment. While flutamide induced a modest improvement in alopecia at 1 year,.
The incidence of undesirable effects was similar to placebo except for the effects on the sexual sphere; decreased libido, difficulty in erection, decreased ejaculate volume were in fact more frequent in subjects treated with finasteride than placebo (4.2% vs 2.2%).
Contraindications and warnings
Finasteride is teratogenic in animals (genitourinary abnormalities in male offspring). It is therefore contraidicated in women and pregnant women or women of childbearing age should not even handle broken or crushed tablets.
The drug reduces the blood level of prostate specific antigen (PSA) by up to 50%; this must be taken into account when reading the results of this examination.
No clinically significant interactions with other drugs were found.
Dosage and method of administration
The dosage is 1 mg per day orally. There is no evidence that increasing the dosage increases the drug’s effectiveness. The application of a topical formulation (0.05%), while lowering the concentration of serum dihydrotestosterone, was not able to induce hair regrowth.