Oral Minoxidil After Bariatric Surgery: What Patients and Prescribers Need to Know

What is the short answer?

The tablet is a direct-acting peripheral arteriolar vasodilator indicated for hypertension that is symptomatic or associated with target organ damage and not controlled by a diuretic plus two other antihypertensives [1]. The label states that use of minoxidil tablets, in any formulation, to promote hair growth is not an approved indication [1].

Randomized hair-loss trials studied oral minoxidil at 1 mg/day and at 5 mg/day [4][5]. An observational series studied 0.25 mg/day together with spironolactone 25 mg [6]. The label's usual hypertension range is 10 to 40 mg/day [1].

In a retrospective 1404-patient low-dose study (943 women, 461 men) with no control group, there were no life-threatening adverse effects, but lightheadedness occurred in 1.7%, fluid retention in 1.3%, tachycardia in 0.9% and periorbital edema in 0.3% [3].

Does bariatric surgery change absorption?

The label gives the picture without reference to surgery: at least 90% absorbed, peak plasma levels within the first hour, average half-life 4.2 hours, and about 90% metabolized mainly by glucuronide conjugation, not by a named CYP enzyme [1]. It also states minoxidil does not bind to plasma proteins [1].

A modeling study of five other drugs (simvastatin, omeprazole, diclofenac, fluconazole and ciprofloxacin) found that changes in bioavailability after RYGB, sleeve gastrectomy, biliopancreatic diversion with duodenal switch and jejunoileal bypass depended on the drug's solubility, permeability and gut-wall metabolism, and on the operation performed [7]. Minoxidil was not among the drugs modeled, so that study does not show what happens to minoxidil absorption [7].

What does the label warn about?

The tablet carries a boxed warning for pericardial effusion, occasionally progressing to tamponade, and for exacerbation of angina [1]. The label says it should usually be given with a beta blocker and a diuretic [1]. At antihypertensive doses, reversible edema developed in about 10% of non-dialysis patients, pericardial effusion in about 3%, and hypertrichosis in about 80% [1].

At 5 mg/day or less, a meta-analysis of uncontrolled studies found no significant mean change in systolic blood pressure (-0.13 mm Hg) or diastolic blood pressure (-1.25 mm Hg), a heart-rate increase of 2.67 beats/min, and hypotensive symptoms in 5.0% [2]. The label says body weight should be monitored closely [1].

What about nutrition?

The American Society for Metabolic and Bariatric Surgery micronutrient guideline addresses thiamine (B1), B12, folate, iron, vitamins A, E and K, calcium, vitamin D, copper and zinc after weight-loss surgery [8]. A review of iron deficiency and hair loss found that some studies link iron deficiency to alopecia areata, androgenetic alopecia, telogen effluvium and diffuse hair loss while others do not, and it found insufficient evidence to recommend universal screening or iron supplementation without anemia [9].