Finasteride Switching Protocols: How to Transition From or To Other Drugs in Class

What makes a finasteride switch different from other drug swaps

Finasteride and dutasteride act on the same enzyme, 5-alpha reductase, which converts testosterone to dihydrotestosterone. Finasteride is a competitive inhibitor of the type II isozyme with roughly 100-fold selectivity over type I; type II accounts for about two-thirds of circulating DHT and type I for about one-third [2]. Dutasteride inhibits both isozymes [3].

The difference in depth of DHT suppression between the two drugs is measurable. In a 24-week randomized trial of 399 men with benign prostatic hyperplasia, dutasteride 0.5 mg lowered serum DHT by 94.7% and finasteride 5 mg by 70.8%, with wider variation on finasteride [3]. At the scalp, a 42-day biopsy study of 249 men with androgenetic alopecia found scalp DHT fell 64.1% on finasteride 1 mg and serum DHT fell 71.4% [5].

Is there a protocol for switching from finasteride to dutasteride?

In the EPICS trial, men randomized to finasteride 5 mg or dutasteride 0.5 mg for 48 weeks could then enter an optional 24-month open-label phase in which all received dutasteride 0.5 mg once daily [1]. The trial also compared the two drugs when each was taken continuously [1].

For hair, a network meta-analysis of 23 studies found dutasteride 0.5 mg daily produced the greatest 24-week increase in total hair count and beat finasteride 1 mg daily by a mean difference of 7.1 hairs per cm2 (95% CI 5.1 to 9.3) [6]. A direct randomized comparison of 416 men aged 21 to 45 assigned dutasteride at 0.05, 0.1, 0.5 or 2.5 mg, finasteride 5 mg, or placebo for 24 weeks; dutasteride 2.5 mg was superior to finasteride at 12 and 24 weeks [7]. The 416-man trial compared dutasteride doses with finasteride 5 mg, which is five times the 1 mg Propecia dose [7][2].

For BPH, the EPICS trial randomized 813 men to dutasteride 0.5 mg and 817 to finasteride 5 mg for 12 months and found no significant difference between them in prostate volume reduction, AUA symptom index scores or maximum urinary flow, with a similar percentage of adverse events [1].

The labels also cover PSA interpretation on finasteride. The Proscar label states that finasteride lowers PSA by approximately 50% within six months, that a new PSA baseline should be established at least six months after starting, and that an isolated PSA in a man treated six months or more should be doubled for comparison with normal ranges [8]. The Propecia label reports mean PSA falling from 0.7 to 0.5 ng/mL at month 12 in men aged 18 to 41, and states that any confirmed increase from the lowest value on treatment should be evaluated even if the number is still in the normal range [2].

Is there a protocol for switching from dutasteride to finasteride?

We found no label or trial that gives one. What is documented is finasteride's own behavior: mean terminal half-life about 5 to 6 hours in men aged 18 to 60 and about 8 hours in men over 70, while the type II enzyme complex turns over slowly, with a half-life of roughly 30 days, so the effect on DHT outlasts the drug's time in blood [2].

On tolerability, a meta-analysis of 15 randomized placebo-controlled trials in 4,495 men with androgenetic alopecia found a 1.57-fold relative risk of sexual dysfunction with 5-alpha reductase inhibitors (95% CI 1.19 to 2.08); for finasteride 1 mg alone the relative risk was 1.66 (1.20 to 2.30) and for dutasteride 0.5 mg it was 1.37 (0.81 to 2.32), which did not reach statistical significance [9].

What happens when finasteride is stopped?

The Propecia label is direct: continued use is recommended to sustain benefit, and withdrawal of treatment leads to reversal of effect within 12 months [2]. In the three 12-month controlled trials in men aged 18 to 41 (945 on finasteride, 934 on placebo), drug-related decreased libido occurred in 1.8% versus 1.3%, erectile dysfunction in 1.3% versus 0.7% and ejaculation disorder in 1.2% versus 0.7%; 3.8% versus 2.1% reported one or more of these (p=0.04), 1.2% versus 0.9% discontinued for them, and resolution occurred in men who stopped and in most who continued [2]. The postmarketing section also lists sexual dysfunction that continued after discontinuation, described as voluntary reports of uncertain frequency [2]. Safety reporting in this literature has been criticized: a review of 34 finasteride trials for hair loss found none had adequate safety reporting [10].

For anyone staying on treatment, the label for finasteride 1 mg describes one tablet once daily, with or without food [2].

Should the switch be to minoxidil instead?

One 12-month randomized trial of 450 Chinese men with male pattern hair loss reported improvement in 80.5% of those on finasteride, 59% on 5% topical minoxidil and 94.1% on the two together; adverse reactions were reported in 1.8% of the finasteride group and 6.1% of the minoxidil group [4]. A separate meta-analysis of randomized trials found 1 mg finasteride and topical minoxidil each superior to placebo for hair outcomes in men [11].

Is there a topical or injectable finasteride to switch to?

No. Drugs@FDA lists only oral finasteride tablets, and no topical or injectable finasteride is FDA-approved [12].