MINOXIDIL

MINOXIDIL
(mi-nox'i-dill)
Rogaine
Classifications: nonnitrate vasodilator; antihypertensive;
Therapeutic: antihypertensive; nonnitrate vasodilator

Prototype: Hydralazine
Pregnancy Category: C

Availability

2.5 mg, 10 mg tablets; 2% solution

Action

Direct-acting vasodilator similar to other drugs of this class, but hypotensive effect is more pronounced. Appears to act by blocking calcium uptake through cell membrane. Reduces elevated systolic and diastolic blood pressures in supine and standing positions, by decreasing peripheral vascular resistance.

Therapeutic Effect

Effective as an antihypertensive agent. It increases heart rate and cardiac output. Topical minoxidil reverses balding to some degree.

Uses

Treat severe hypertension that is symptomatic or associated with damage to target organs and is not manageable with maximum therapeutic doses of a diuretic plus two other antihypertensive drugs. Used with a diuretic to prevent fluid retention and a beta adrenergic blocking agent (e.g., propranolol) or an alpha-adrenergic agonist (e.g., clonidine or methyldopa) to prevent tachycardia. (Topical) to treat alopecia areata and male pattern alopecia.

Contraindications

Pheochromocytoma; acute MI, dissecting aortic aneurysm, valvular dysfunction, heart failure; CVA; pulmonary hypertension. Severe renal failure Clcr <10 mL/min, pregnancy (category C), children.

Cautious Use

Severe renal impairment; recent MI (within preceding month); coronary artery disease, chronic CHF.

Route & Dosage

Hypertension
Adult: PO 5 mg/d, increased q3–5d up to 40 mg/d in single or divided doses as needed (max: 100 mg/d)
Child: PO 0.2 mg/kg/d (max: 5 mg/d) initially, gradually increased to 0.25–1 mg/kg/d in divided doses (max: 50 mg/d)

Alopecia
Adult: Topical Apply 1 mL of 2% solution to affected area b.i.d.

Administration

Oral
  • Dose increments are usually made at 3–5 d intervals. If more rapid adjustment is necessary, adjustments can be made q6h with careful monitoring.
Topical
  • Do not apply topical product to an irritated scalp (e.g., sunburn, psoriasis).
  • Store at 15°–30° C (59°–86° F) in tightly covered container unless otherwise directed.

Adverse Effects (≥1%)

CV: Tachycardia, angina pectoris, ECG changes, pericardial effusion and tamponade, rebound hypertension (following drug withdrawal); edema, including pulmonary edema; CHF (salt and water retention). Skin: Hypertrichosis, transient pruritus, darkening of skin, hypersensitivity rash, Stevens-Johnson syndrome. With topical use: itching, flushing, scaling, dermatitis, folliculitis. Body as a Whole: Fatigue.

Diagnostic Test Interference

Hct, Hgb, and erythrocyte count usually decrease (about 7%) during early therapy; serum alkaline phosphatase, BUN, and creatinine may increase during early therapy.

Interactions

Drug: Epinephrine, norepinephrine cause excessive cardiac stimulation; guanethidine causes profound orthostatic hypotension.

Pharmacokinetics

Absorption: Readily absorbed from GI tract. Onset: 30 min PO; at least 4 mo topical. Peak: 2–8 h PO. Duration: 2–5 d PO; new hair growth will remain 3–4 mo after withdrawal of topical. Distribution: Widely distributed including into breast milk. Metabolism: In liver. Elimination: 97% in urine and feces. Half-Life: 4.2 h.

Nursing Implications

Assessment & Drug Effects

  • Take BP and apical pulse before administering medication and report significant changes. Consult physician for parameters.
  • Lab tests: Periodic serum electrolytes.
  • Do not stop drug abruptly. Abrupt reduction in BP can result in CVA and MI. Keep physician informed.
  • Monitor fluid and electrolyte balance closely throughout therapy. Sodium and water retention commonly occur. Consult physician regarding sodium restriction. Monitor potassium intake and serum potassium levels in patient on diuretic therapy.
  • Monitor I&O and daily weight. Report unusual changes in I&O ratio or daily weight gain, greater than 1 kg (2 lb).
  • Observe patient daily for edema and auscultate lungs for rales. Be alert to signs and symptoms of CHF (see Appendix F).
  • Observe for symptoms of pericardial effusion or tamponade. Symptoms are similar to those of CHF, but additionally patient may have paradoxical pulse (normal inspiratory reduction in systolic BP may fall as much as 10–20 mm Hg).

Patient & Family Education

  • Learn about usual pulse rate and count radial pulse for one full minute before taking drug. Report an increase of 20 or more bpm.
  • Notify physician promptly if the following S&S appear: Increase of 20 or more bpm in resting pulse; breathing difficulty; dizziness; light-headedness; fainting; edema (tight shoes or rings, puffiness, pitting); weight gain, chest pain, arm or shoulder pain; easy bruising or bleeding.
  • Be aware of possibility of hypertrichosis: Elongation, thickening, and increased pigmentation of fine body hair, especially of face, arms, and back. Develops 3–9 wk after start of therapy and occurs in approximately 80% of patients; reversible within 1–6 mo after drug withdrawal.
  • Report any dermatologic adverse effects or any other adverse effect promptly to physician.
  • Schedule follow-up examinations for q4–6mo.
  • Comply strictly with regular regimen; maximizes chance of at least some hair regrowth.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

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