minoxidil
Loniten

Available forms
Available by prescription only
Tablets: 2.5 mg, 10 mg

Indications and dosages
 Severe hypertension. Adults and children older than age 12: Initially, 2.5 to 5 mg P.O. as a single daily dose. Dose may be increased at 3-day intervals (minimum) to 10 mg, 20 mg, and then 40 mg. If rapid control is needed, dose may be adjusted q 6 hours. Effective dosage range is usually 10 to 40 mg daily in one to two divided doses. Maximum dose is 100 mg/day.
Children younger than age 12: 0.2 mg/kg (maximum 5 mg) as an initial single daily dose. If necessary, dose is increased after at least a 3-day interval in increments of 50% to 100% until optimal response is attained. Effective dosage range is usually 0.25 to 1 mg/kg daily in one or two doses. If rapid control is needed, dose may be adjusted q 6 hours. Maximum dose is 50 mg/day.

Pharmacodynamics
Antihypertensive action: Drug produces its antihypertensive effect by a direct vasodilating effect on vascular smooth muscle; the effect on resistance vessels (arterioles and arteries) is greater than that on capacitance vessels (venules and veins).

Pharmacokinetics
Absorption: Absorbed rapidly and almost completely from the GI tract.
Distribution: Distributed widely into body tissues; it isn’t bound to plasma proteins.
Metabolism: About 90% of a given dose is metabolized.
Excretion: Excreted primarily in urine. Average plasma half-life is 4 1/4 hours.

Contraindications and precautions
Contraindicated in patients hypersensitive to drug and in those with pheochromocytoma. Use cautiously in patients with impaired renal function or dissecting aortic aneurysm or after acute MI.

Interactions
Drug-drug. Diuretics, hypotensive drugs, nitrates: Increases hypotensive effects. May be used to therapeutic advantage.
Guanethidine: May cause profound orthostatic hypotension. Discontinue guanethidine 1 to 3 days before starting minoxidil.

Adverse reactions
CNS: headache.
CV: edema, tachycardia, pericardial effusion and tamponade, heart failure, ECG changes, rebound hypertension.
GI: nausea, vomiting.
Metabolic: weight gain.
Respiratory: pulmonary edema.
Skin: rash, Stevens-Johnson syndrome.
Other: hypertrichosis, gynecomastia, breast tenderness.

Effects on lab test results
• May increase BUN, creatinine, and alkaline phosphatase levels.
• May decrease hemoglobin and hematocrit.

Overdose and treatment
Evidence of overdose includes hypotension, tachycardia, headache, and skin flushing.
 After acute ingestion, empty stomach by induced emesis or gastric lavage, and give activated charcoal to reduce absorption. Further treatment is usually symptomatic and supportive. Administer normal saline solution I.V. to maintain blood pressure. Avoid sympathomimetics, such as epinephrine and norepinephrine, because of their excessive cardiac stimulating action.

Special considerations
• Drug usually is given with other antihypertensives, such as diuretics, beta blockers, or sympathetic nervous system suppressants.
• Patients with renal impairment or a need for dialysis may need smaller maintenance dosages. Because minoxidil is removed by dialysis, it’s recommended that, on the day of dialysis, the drug be given immediately after dialysis if dialysis is at 9 a.m.; if dialysis is after 3 p.m., the daily dose is given at 7 a.m. (8 hours before dialysis).
• After blood pressure is stabilized, reevaluate patient every 3 to 6 months.
• Monitor blood pressure and pulse after administration.
• Assess intake, output, and body weight for sodium and water retention.
• Monitor patient for heart failure, pericardial effusion, and cardiac tamponade; have phenylephrine, dopamine, and vasopressin on hand to treat hypotension.
Breast-feeding patients
• Drug appears in breast milk. An alternative to breast-feeding is recommended during therapy.
Pediatric patients
• Because of limited experience in children, use drug and adjust dosage cautiously.
Geriatric patients
• These patients may be sensitive to antihypertensive effects of drug. Dosage adjustment may be needed because of altered drug clearance. Monitor orthostatic blood pressure in geriatric patients.

Patient education
• Explain that drug is usually taken with other antihypertensives; emphasize importance of taking drug as prescribed.
• Caution patient to report these cardiac symptoms promptly: increased heart rate (more than 20 beats per minute over normal), rapid weight gain, shortness of breath, chest pain, severe indigestion, dizziness, light-headedness, or fainting.
• Tell patient to call for instructions before taking OTC cold preparations.
• Advise patient that hypertrichosis will disappear 1 to 6 months after stopping drug.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use