minoxidil

minoxidil

(mi nox' i dill)

Topical:

Rogaine, Rogaine Extra Strength

Pregnancy Category C

Drug classes

Antihypertensive

Vasodilator

Therapeutic actions

Acts directly on vascular smooth muscle to cause vasodilation, reducing elevated systolic and diastolic BP; does not interfere with CV reflexes; does not usually cause orthostatic hypotension but does cause reflex tachycardia and renin release, leading to sodium and water retention; mechanism in stimulating hair growth is not known, possibly related to arterial dilation.

Indications

·        Severe hypertension that is symptomatic or associated with target organ damage and is not manageable with maximum therapeutic doses of a diuretic plus two other antihypertensive drugs; use in milder hypertension not recommended

·        Topical use (when compounded as a 1%–5% lotion or 1% ointment): Alopecia areata and male pattern alopecia

Contraindications and cautions

·        Contraindicated with hypersensitivity to minoxidil or any component of the topical preparation (topical); pheochromocytoma (may stimulate release ofcatecholamines from tumor); acute MI; dissecting aortic aneurysm; lactation.

·        Use cautiously with malignant hypertension; CHF (use diuretic); angina pectoris (use a beta-blocker); pregnancy.

Available forms

Tablets—2.5, 10 mg; topical 2%, 5%

Dosages

ADULTS AND PATIENTS > 12 YR

Oral

·        Monotherapy: Initial dosage is 2.5–5 mg/day PO as a single dose. Daily dosage can be increased to 10, 20, then 40 mg in single or divided doses. Effective range is usually 10–40 mg/day PO. Maximum dosage is 100 mg/day. If supine diastolic BP has been reduced less than 30 mm Hg, administer the drug only once a day. If reduced more than 30 mm Hg, divide the daily dosage into two equal parts. Dosage adjustment should normally be at least at 3-day intervals; in emergencies, q 6 hr with careful monitoring if possible.

·        Concomitant therapy with diuretics: Use minoxidil with a diuretic in patients relying on renal function for maintaining salt and water balance; the following diuretic dosages have been used when starting minoxidil therapy: Hydrochlorothiazide, 50 mg bid; chlorthalidone, 50–100 mg daily; furosemide, 40 mg bid. If excessive salt and water retention result in weight gain > 5 lb, change diuretic therapy to furosemide; if patient already takes furosemide, increase dosage.

·        Concomitant therapy with beta-adrenergic blockers or other sympatholytics: The following dosages are recommended when starting minoxidil therapy:Propranolol, 80–160 mg/day; other beta-blockers, dosage equivalent to the above; methyldopa 250–750 mg bid (start methyldopa at least 24 hr beforeminoxidil); clonidine, 0.1–0.2 mg bid.

Topical

Apply 1 mL to the total affected areas of the scalp twice daily. The total daily dosage should not exceed 2 mL. Twice daily application for > 4 mo may be required before evidence of hair regrowth is observed. Once hair growth is realized, twice daily application is necessary for continued and additional hair regrowth. Balding process reported to return to untreated state 3–4 mo after cessation of the drug.

PEDIATRIC PATIENTS < 12 YR

Experience is limited, particularly in infants; use recommendations as a guide; careful adjustment is necessary. Initial dosage is 0.2 mg/kg/day PO as a single dose. May increase by 50%–100% increments until optimum BP control is achieved. Effective range is usually 0.25–1 mg/kg/day; maximum dosage is 50 mg daily. Experience in children is limited; monitor carefully.

GERIATRIC PATIENTS OR PATIENTS WITH IMPAIRED RENAL FUNCTION

Smaller doses may be required; closely supervise to prevent cardiac failure or exacerbation of renal failure.

Pharmacokinetics

Route	Onset	Peak	Duration
Oral	30 min	2–3 hr	75 hr

Metabolism: Hepatic; T_1/2: 4.2 hr

Distribution: Crosses placenta; enters breast milk

Excretion: Urine

Adverse effects

·        CNS: Fatigue, headache

·        CV: Tachycardia (unless given with beta-adrenergic blocker or other sympatholytic drug), pericardial effusion and tamponade; changes in direction and magnitude of T-waves; cardiac necrotic lesions (reported in patients with known ischemic heart disease, but risk of minoxidil-associated cardiac damage cannot be excluded)

·        Dermatologic: Temporary edema, hypertrichosis (elongation, thickening, and enhanced pigmentation of fine body hair occurring within 3–6 wk of starting therapy; usually first noticed on temples, between eyebrows and extending to other parts of face, back, arms, legs, scalp); rashes including bullous eruptions;Stevens-Johnson syndrome; darkening of the skin

·        GI: Nausea, vomiting

·        Hematologic: Initial decrease in Hct, Hgb, RBC count

·        Local: Irritant dermatitis, allergic contact dermatitis, eczema, pruritus, dry skin/scalp, flaking, alopecia (topical use)

·        Respiratory: Bronchitis, upper respiratory tract infection, sinusitis (topical use)

Interactions

Drug-drug

·        Risk of profound orthostatic hypotension if given with guanethidine; stop guanethidine; if not possible, hospitalize patient

Nursing considerations

Assessment

·        History: Hypersensitivity to minoxidil or any component of the topical preparation; pheochromocytoma; acute MI, dissecting aortic aneurysm; malignant hypertension; CHF; angina pectoris; lactation, pregnancy

·        Physical: Skin color, lesions, hair, scalp; P, BP, orthostatic BP, supine BP, perfusion, edema, auscultation; bowel sounds, normal output; CBC with differential, renal function tests, urinalysis, ECG

Interventions

·        Apply topical preparation to affected area; if fingers are used to facilitate drug application, wash hands thoroughly afterward.

·        Do not apply other topical drugs, including topical corticosteroids, retinoids, and petrolatum or agents known to enhance cutaneous drug absorption.

·        Do not apply topical preparation to open lesions or breaks in the skin, which could increase risk of systemic absorption.

·        WARNING: Arrange to withdraw oral drug gradually, especially from children; rapid withdrawal may cause a sudden increase in BP (rebound hypertension has been reported in children, even with gradual withdrawal; use caution and monitor BP closely when withdrawing from children).

·        Arrange for echocardiographic evaluation of possible pericardial effusion; more vigorous diuretic therapy, dialysis, other treatment (including minoxidilwithdrawal) may be required.

Teaching points

Oral

·        Take this drug exactly as prescribed. Take all other medications that have been prescribed. Do not discontinue any drug or reduce the dosage without consulting your health care provider.

·        You may experience these side effects: Enhanced growth and darkening of fine body and face hair (do not discontinue medication without consulting health care provider); GI upset (eat frequent small meals).

·        Report increased heart rate of > 20 beats per minute over normal (your normal heart rate is ___ beats per minute); rapid weight gain of more than 5 pounds; unusual swelling of the extremities, face, or abdomen; difficulty breathing, especially when lying down; new or aggravated symptoms of angina (chest, arm, or shoulder pain); severe indigestion; dizziness, light-headedness, or fainting.

Topical

·        Apply the prescribed amount to affected area twice a day. If using the fingers to facilitate application, wash hands thoroughly after application. It may take 4 months or longer for any noticeable hair regrowth to appear. Response to this drug is very individual. If no response is seen within 4 months, consult with your health care provider about efficacy of continued use.

·        Do not apply more frequent or larger applications. This will not speed up or increase hair growth but may increase side effects.

·        If one or two daily applications are missed, restart twice-daily applications, and return to usual schedule. Do not attempt to make up missed applications.

·        Do not apply any other topical medication to the area while you are using this drug.

·        Do not apply to any sunburned, broken skin or open lesions; this increases the risk of systemic effects. Do not apply to any part of the body other than the scalp.

·        Twice daily use of the drug will be necessary to retain or continue the hair regrowth.

Adverse effects in Italic are most common; those in Bold are life-threatening.