Minoxidil

Minoxidil is a direct-acting arteriolar vasodilator (potassium channel opener). FDA-approved products are oral minoxidil tablets (originally Loniten) for hypertension and OTC topical minoxidil 2% solution and 5% solution and foam for hereditary hair loss. Lake Hills Pharmacy compounds minoxidil, pursuant to patient-specific prescriptions, in oral capsules and topical scalp solutions.

Drug class: vasodilator (potassium channel opener). Non-controlled.

Oral minoxidil tablets are labeled for severe hypertension that is symptomatic or associated with target-organ damage and not manageable with maximum therapeutic doses of a diuretic plus two other antihypertensive drugs. OTC topical minoxidil is labeled to regrow hair on the scalp in hereditary hair loss: 2% solution and 5% foam for women, 2% and 5% solution and 5% foam for men.

Prescribers use low-dose oral minoxidil and compounded topical concentrations off label for androgenetic alopecia and other hair loss.

Minoxidil is a prodrug converted by sulfotransferase to minoxidil sulfate, which opens ATP-sensitive potassium channels in vascular smooth muscle, causing hyperpolarization and arteriolar relaxation. The fall in peripheral resistance triggers reflex tachycardia, renin release and sodium and water retention. In hair follicles it prolongs the anagen phase and enlarges follicles; the exact mechanism is not fully defined.

Oral minoxidil is about 90% absorbed, with peak plasma levels within about 1 hour. It is not protein bound, is metabolized mainly by hepatic glucuronidation and is excreted in urine; it is removed by dialysis. The plasma half-life is about 4 hours, but the blood-pressure effect lasts much longer. After topical scalp use, only about 1 to 2% of the applied dose is absorbed systemically, and absorption increases with damaged skin, higher concentrations and penetration enhancers.

• Oral: pheochromocytoma; hypersensitivity to minoxidil.
• Topical (OTC labeling): do not use if there is no family history of hair loss, hair loss is sudden or patchy, or the cause is unknown; if the scalp is red, inflamed, infected, irritated or painful; or with other medicines on the scalp unless a prescriber directs. Not for use under age 18.

• Oral: salt and water retention and congestive heart failure; pericardial effusion and tamponade; reflex tachycardia and angina; too-rapid blood-pressure lowering can cause syncope or ischemic events; caution after recent myocardial infarction; hypertrichosis is common; ECG T-wave changes may occur; use lower doses in renal failure and dialysis.
• Topical: stop use and seek care for chest pain, rapid heartbeat, faintness, dizziness, sudden unexplained weight gain, or swelling of the hands or feet. Unwanted facial hair can result from transfer. Temporary shedding may occur at the start of treatment. Avoid eye contact. Hydroalcoholic solutions and foams are flammable.
• Pets: topical minoxidil is highly toxic to cats, even in small amounts from licking treated skin, bedding or spills.

• Guanethidine: profound orthostatic hypotension; labeling advises stopping guanethidine before oral minoxidil is started where possible.
• Other antihypertensives, vasodilators, nitrates and PDE5 inhibitors can add to the blood-pressure-lowering effect.
• Topical retinoids and other agents that disrupt the skin barrier may increase absorption of topical minoxidil.

Oral: fluid retention and edema, tachycardia, hypertrichosis, pericardial effusion, ECG changes, headache, rash and, rarely, Stevens-Johnson syndrome. Topical: scalp itching, dryness, scaling and redness, allergic or irritant contact dermatitis (often from propylene glycol), facial hypertrichosis, headache and dizziness.

Oral minoxidil crosses the placenta, and hypertrichosis and other effects have been reported in exposed newborns. Minoxidil passes into human milk; the oral minoxidil label states it should not be given to a nursing woman. Use in pregnancy only if the potential benefit justifies the potential risk to the fetus.

Oral: blood pressure, heart rate, body weight, edema and signs of pericardial effusion (dyspnea, chest pain, new murmur or rub), with echocardiography when effusion is suspected. Topical: scalp irritation, unwanted hair growth and cardiovascular symptoms.

• Loniten (minoxidil tablets) Prescribing Information, Pfizer.
• Minoxidil Tablets, USP Prescribing Information.
• Women's Rogaine (minoxidil topical solution 2% and topical aerosol 5%) Drug Facts label.
• Men's Rogaine (minoxidil topical solution 5%) Drug Facts label.