Minoxidil: An Underused Vasodilator for Resistant or Severe Hypertension

Domenic A. Sica, MD

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Pharmacokinetics

Minoxidil is completely and rapidly absorbed from the gastrointestinal tract, although its absorption can be delayed in the setting of advanced renal failure.[9] Minoxidil is primarily metabolized by hepatic glucuronidation to an active metabolite, which is renally cleared.[10] Because minoxidil localizes to compartments other than the intravascular space, such as arterial smooth muscle cells and the myocardium, its volume of distribution typically extends beyond that of total body water.[11] Minoxidil is minimally protein bound, making it freely available for dialysis.[12] The plasma elimination half-life of minoxidil is in the order of 3-4 hours. This differs noticeably from the duration of its hypotensive effect, which in some patients may endure for as long as 72 hours. It is the latter effect that supports its once-daily dosing, although there is considerable interindividual variability in the frequency with which dosing must occur.[13,14] Although there appears to be a relationship between the dose of minoxidil and the degree of BP reduction, there is a more limited correlation between plasma minoxidil levels and its BP-reducing ability.

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