A-Z Drug Facts > Minoxidil

Minoxidil

Pronouncation: (min-OX-ih-dill)
Class: Peripheral vasodilator, Dermatological agent

Trade Names:
Minoxidil
- Tablets 2.5 mg
- Tablets 10 mg

Trade Names:
Minoxidil for Men
- Topical solution 2%

Trade Names:
Rogaine
- Solution 2%

APO-Gain Topical Solution (Canada)

Pharmacology

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Directly dilates vascular smooth muscle by mechanism possibly related to blockade of calcium uptake or stimulation of catecholamine release; reduces elevated systolic and diastolic BP by decreasing peripheral arteriolar resistance; triggers sympathetic, vagal inhibitory and renal homeostatic mechanisms including increased renin release, which results in increased cardiac rate and output and fluid retention; stimulates hair growth by unknown mechanism but likely is related to its arterial vasodilating action.

Pharmacokinetics

Absorption

At least 90% is absorbed. T _max is 1 h.

Distribution

0% is protein bound.

Metabolism

Approximately 90% is primarily metabolized by glucuronic acid conjugation.

Elimination

Primary route of excretion is urine. Mean t _½ is 4.2 h. Hemodialysis does not remove minoxidil or its metabolites.

Onset

Onset is 30 min.

Peak

Time to peak is 2 to 3 h.

Duration

Duration is approximately 75 h.

Indications and Usage

Oral

Management of severe hypertension associated with target organ damage in patients who have failed to respond to max doses of a diuretic plus 2 other antihypertensive drugs.

Topical

Treatment of androgenic alopecia.

Unlabeled Uses

Treatment of alopecia areata (topical).

Contraindications

Pheochromocytoma; standard considerations.

Dosage and Administration

Adults and children older than 12 yr of age

PO 5 mg/day initially. If necessary, can increase to 10, 20, and then 40 mg/day in single or divided doses (max, 100 mg/day).

Children younger than 12 yr of age

PO 0.2 mg/kg/day as single dose initially. May increase in 50% to 100% increments until optimal BP control is achieved (usually 0.25 to 1 mg/kg/day; max, 50 mg/day).

Adults

Topical Apply 1 mL to affected scalp areas morning and evening (max, 2 mL/day).

Storage/Stability

Store at room temperature (59° to 86°F) in tightly closed container.

Drug Interactions

Guanethidine

May result in profound orthostatic hypotensive effects; discontinue guanethidine before minoxidil therapy.

Topical corticosteroids or retinoids, petrolatum

May enhance cutaneous drug absorption of topically applied minoxidil.

Laboratory Test Interactions

None well documented.

Adverse Reactions

Cardiovascular

Changes in T-waves (60%); pericardial effusion leading to tamponade (3%); edema, chest pain, BP changes, palpitations, heart rate changes (topical); tachycardia, edema, angina, rebound hypertension following withdrawal (systemic).

CNS

Headache; dizziness, faintness (topical); fatigue (systemic).

Dermatologic

Hypertrichosis (80%); irritant or allergic dermatitis, eczema, local erythema, pruritus, dry scalp, exacerbation of hair loss, alopecia (topical).

GI

Diarrhea; nausea; vomiting.

Hematologic

Hct, Hgb, and RBC counts may fall but return to normal (7%, systemic); thrombocytopenia, leukopenia (rare).

Miscellaneous

Temporary edema (7%); breast tenderness (less than 1%); darkening of skin (systemic).

Precautions

Warnings Serious adverse reactions may occur including pericardial effusion, occasionally progressing to tamponade, which can exacerbate angina pectoris. When first administering minoxidil, hospitalize and monitor patients with malignant hypertension and those patients already receiving guanethidine to avoid too rapid or large orthostatic decreases in BP.

Pregnancy

Category C .

Lactation

Excreted in breast milk. In general, breast-feeding should not be undertaken.

Children

Safety and efficacy not established.

Elderly

Use with caution because of the greater frequency of decreased hepatic, renal, or cardiac function, and concomitant diseases or other drug therapy.

Hypersensitivity

Can occur and is manifested by rash, bullous eruptions, and Stevens-Johnson syndrome.

Renal failure or dialysis

Patients may require smaller doses and should have close medical supervision to prevent exacerbation of renal failure or precipitation of cardiac failure.

Abnormal scalp

Use of topical form of drug may result in increased absorption and systemic effects; avoid use on scalps with decreased integrity.

ECG changes

T-wave changes may occur; significance unknown.

Fluid/electrolytes imbalance

Sodium and water retention occur, leading to edema and possible CHF.

Heart disease

Patients may be predisposed to CV adverse reactions.

Pericardial effusion

Has occurred rarely, sometimes with tamponade.

Severe hypertension

Too rapid BP correction can precipitate syncope, cerebrovascular accidents, MI, and ischemia of special sense organs with resulting loss of vision or hearing. Patients should be hospitalized to monitor carefully.

Tachycardia

Can be prevented by concomitant use of beta-blocker or other agent.

Overdosage

Symptoms

Exaggerated hypotension, fluid retention, tachycardia.

Patient Information

• Advise patient not to change dose without health care provider direction.
• Tell patient that diuretic and beta-blocker are necessary to enhance effectiveness and to decrease adverse reactions of minoxidil.
• Instruct patient to notify health care provider of heart rate at least 20 beats/min over normal, rapid weight gain of more than 5 lb, unusual swelling, breathing difficulty, angina symptoms, dizziness, or lightheadedness.
• Tell patient to report the following symptoms to health care provider: skin irritation, diarrhea, vomiting, rash, or other bothersome physical complaints.
• Warn patient taking oral form that enhanced growth and darkening of fine body hair may occur. It may take 1 to 6 mo to return to pretreatment appearance.
• Inform patient using topical form that 4 mo of continuous use is required before hair growth is seen and that stopping treatment will lead to hair loss within a few mo.
• Advise patient using topical form that more frequent applications or use of larger doses will not enhance hair growth and may lead to adverse reactions.
• Inform patient using topical form to expect initial hair growth to be soft, downy, colorless, and barely visible and that after further treatment new hair should match other scalp hair.
• Tell patient using topical form not to use it in conjunction with other topical scalp medications, to apply drug only to healthy areas of scalp, not to use if scalp becomes irritated or sunburned, and not to use it on other parts of body.
• For topical application; instruct patient to dry head and scalp before application and to wash hands after application.
• Explain that product contains significant amount of alcohol as base. Caution patient to avoid having topical form coming into contact with eyes, mucous membranes or sensitive skin areas. If accidental contact occurs, instruct patient to rinse area with large amounts of cool tap water and to notify health care provider.

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