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| Other names | Minoxidil sulphate; Minoxidil sulfate ester; Minoxidil sulphate ester; Minoxidil N-O-sulfate; Minoxidil N-O-sulphate; U-58838 |
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| ECHA InfoCard | 100.163.834 |
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| Formula | C9H15N5O4S |
| Molar mass | 289.31 g·mol−1 |
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Minoxidil sulfate, also known as minoxidil sulfate ester or minoxidil N-O-sulfate, is an active metabolite of minoxidil (Rogaine, Loniten, others) and is the active form of this agent.[1][2] Minoxidil acts as a prodrug of minoxidil sulfate.[1] Minoxidil sulfate is formed from minoxidil via sulfotransferase enzymes, with the predominant enzyme responsible, at least in hair follicles, being SULT1A1.[1][2] Minoxidil sulfate acts as a potassium channel opener, among other actions, and has vasodilating, hypotensive, and trichogenic or hypertrichotic (hair growth-promoting) effects.[1][3] Its mechanism of action in terms of hair growth is still unknown, although multiple potential mechanisms have been implicated.[1]
Minoxidil sulfate is a sulfate ester of minoxidil, not a sulfate salt of the compound.[3] However, minoxidil sulfate forms an inner salt, which makes it more hydrophobic than minoxidil.[3] This is in contrast to most sulfate esters, which are usually more hydrophilic than their non-ester forms.[3] The bioactivation of minoxidil into minoxidil sulfate is very unusual and is among the only known instances of sulfation producing a more active drug form.[3][4] Normally, sulfation tends to inactivate drugs by reducing their biological activity and increasing their excretion.[3][4]
Minoxidil sulfate is highly unstable in aqueous solutions and alcohol-containing solvents, with a half-life of 6 hours in aqueous solutions and a further much lower half-life in alcohol-containing solvents.[3] This has served as a limiting factor in its potential pharmaceutical use and therapeutic effectiveness.[5] Moreover, minoxidil sulfate has a 40% higher molecular weight than minoxidil, and this may reduce its absorption into the scalp.[5] In any case, a minoxidil sulfate-based topical formulation has been investigated for the treatment of scalp hair loss.[6][5] Additionally, minoxidil-sulfate-based topical formulations appear to be available for medical use in some parts of the world, for instance in Brazil.[5][7]