Spironolactone, with the trade name, Aldactone, was originally developed in the early 1970's as a competitive antagonist of aldosterone for the treatment of hyperaldosteronism, edema (water retention), and hypokalemia (low potassium). Aldosterone, secreted by the adrenal glands, was traditionally believed to act only on the kidneys to increase sodium and bicarbonate retention, promote potassium and hydrogen excretion, and exert a role in water retention. This latter property allows for the use of spironolactone as a diuretic, often abused by bodybuilders to achieve a more defined look prior to a competition.
Spironolactone has a chemical structure similar to other steroids but with a lactone substituent at C-17. It has excellent oral bioavailability of 90%, a limited first pass effect, and a steady state half-life of approximately 1.4 hours. Canrenoate and canrenone are its principal pharmacologically active metabolites. Spironolactone acts not only to competitively inhibit aldosterone but also reacts with testosterone and progesterone receptors causing side effects of impotence, gynecomastia and menstrual irregularities. A selective aldosterone receptor blocker, eplerenone, is currently in development. The most serious adverse effect of spironolactone is hyperkalemia (dangerously elevated levels of potassium).
As we noted, it has a structure similar enough to testosterone to bind to the testosterone receptor. However, instead of activating it as androgens do, it antagonizes the receptor, acting as an antiandrogen. Dihydrotestosterone, the 5-alpha reduced metabolite of testosterone, is believed to play a major role in androgenic alopecia, or male pattern baldness. By blocking the binding of DHT to androgen receptors in the scalp, spironolactone may help prevent or treat AA.
DHT is also responsible for hirsutism (excess body hair ) in women. Oral sprironolactone has proven effective in treating this condition. Interestingly, on study looked at the activity of the enzyme 5-alpha reductase (which converts T to DHT) in the genital skin of hirsute women. When exposed to spironolactone in vitro, there was a marked reduction in 5 alpha reductase activity (1). So besides blocking the binding of DHT to the androgen receptor, it is possible that spironolactone helps prevent AA by lowering the conversion rate of T to DHT in the scalp.
Oral spironolactone is a viable option for the treatment of hirsuitism in women, who may not be so concerned about antagonizing the male sex hormone testosterone. However, most men would consider blocking testosterone throughout the body using oral spironolactone an unacceptable treatment for hair loss.
This has led to experimentation with topical delivery of spironolactone to the scalp and skin to treat hairloss and acne, respectively, with some success being reported (2). In one study a 5% solution of topical spironolactone applied to the skin of human males showed a significant drop in DHT binding. Although not tested on the scalp, these results do suggest that spironolactone applied topically could potentially prevent male pattern hair loss or even promote hair regrowth.
Physicians are hesitant to prescribe topical spironolactone to patients with AA out of fear of side effects, and for lack of concrete studies proving the effectiveness of spironolactone in preventing hair loss. This has certainly not stopped individuals from experimenting on their own with topical spironolactone, with many reporting success rates comparable to finasteride. Case studies support the anecdotal evidence that spironolactone promotes the regrowth of scalp hair (3).
In summary, spironolactone applied topically to the scalp or skin appears to show promise in the treatment of male pattern baldness as well as acne. It appears to be devoid of systemic antiandrogenic effects, which is the primary motivation for using the compound topically as opposed to systemically.
Some physicians who prescribe topical spironolactone report that results are comparable to those seen with finasteride used at 1 mg daily (4), but without the side effects associated with finasteride use.
(1) Serafini PC, Catalino J, Lobo RA. The effect of spironolactone on genital skin 5 alpha-reductase activity. J Steroid Biochem. 1985 Aug;23(2):191-4 (2) Califano L, Cannavo S, Siragusa M, Girardi R. [Experience in the therapy of acne with topical administration of spironolactone as an antiandrogen] Clin Ter. 1990 Nov 15;135(3):193-9. (3) Bou-Abboud CF, Nemec F, Toffel F. Reversal of andro-genetic alopecia in a male. A spironolactone effect? Acta Derm Venereol. 1990;70(4):342-3. (4)
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