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Action/Kinetics:
Decreases elevated BP by decreasing peripheral resistance by a direct effect. Causes increase in renin secretion, increase in cardiac rate and output, and salt/water retention. Does not cause orthostatic hypotension.
Onset: 30 min.
Peak plasma levels: reached within 60 min;
plasma t
1/2: 4.2 hr.
Duration: 24-48 hr. Ninety percent absorbed from GI tract; excretion: renal (90% metabolites). The time needed to reach the maximum effect is inversely related to the dose.
Uses:
Severe hypertension not controllable by the use of a diuretic plus two other antihypertensive drugs. Usually taken with at least two other antihypertensive drugs (a diuretic and a drug to minimize tachycardia such as a beta-adrenergic blocking agent). Can produce severe side effects; reserve for resistant cases of hypertension. Close medical supervision required, including possible hospitalization during initial administration. Topically to promote hair growth in balding men.
Contraindications:
Pheochromocytoma. Within 1 month after a MI. Dissecting aortic aneurysm.
Special Concerns:
Safe use during lactation not established. Use with caution and at reduced dosage in impaired renal function. Geriatric clients may be more sensitive to the hypotensive and hypothermic effects of minoxidil; also, may be necessary to decrease the dose due to age-related decreases in renal function. BP controlled too rapidly may cause syncope, stroke, MI, and ischemia of affected organs. Experience with use in children is limited.
Side Effects:
CV: Edema,
pericardial effusion that may progress to tamponade (acute compression of heart caused by fluid or blood in pericardium), CHF, angina pectoris, changes in direction of T waves, increased HR. In children, rebound hypertension following slow withdrawal.
GI: N&V.;
CNS: Headache, fatigue.
Hypersensitivity: Rashes, including bullous eruptions and
Stevens-Johnson syndrome.
Hematologic: Initially, decrease in hematocrit, hemoglobin, and erythrocyte count but all return to normal. Rarely, thrombocytopenia and leukopenia.
Other: Hypertrichosis (enhanced hair growth, pigmentation and thickening of fine body hair 3-6 weeks after initiation of therapy), breast tenderness, darkening of skin.
Laboratory Test Alterations:
Nonspecific changes in ECG.
Alkaline phosphatase, serum creatinine, and BUN.
Overdose Management:
Symptoms: Excessive hypotension.
Treatment: Give NSS IV (to maintain BP and urine output). Vasopressors, such as phenylephrine and dopamine, can be used but only in underperfusion of a vital organ.
Drug Interactions:
Concomitant use with guanethidine may result in severe hypotension.
How Supplied:
Tablet: 2.5 mg, 10 mg
Dosage
?Tablets
Hypertension.
Adults and children over 12 years, Initial: 5 mg/day. For optimum control, dose can be increased to 10, 20, and then 40 mg in single or divided doses/day. Do not exceed 100 mg/day.
Children under 12 years: Initial, 0.2 mg/kg/day. Effective dose range: 0.25-1.0 mg/kg/day. Dosage must be titrated to individual response. Do not exceed 50 mg/day.
