Minoxidil

Pronunciation: min-OX-i-dil
Class: Peripheral vasodilator, Dermatological agent

Trade Names

Minoxidil
- Tablets 2.5 mg
- Tablets 10 mg

Rogaine for Men
- Topical foam 5%
- Topical solution 2%
- Topical solution 5%

Rogaine for Women
- Topical solution 2%

APO-Gain Topical Solution (Canada)

Pharmacology

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 can remove minoxidil and 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 Foam (men only) Apply ½ capful 2 times/day to scalp in hair loss area. Solution (regular strength [2%] or extra strength [5%] for men) 1 mL 2 times/day directly onto scalp in area of hair thinning/loss. Solution (2% for women) 1 mL 2 times/day onto scalp in area of hair thinning/loss.

Storage/Stability

Store at room temperature (68° to 77°F) in tightly closed container.

Drug Interactions

Guanethidine

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

Petrolatum, retinoids , or topical corticosteroids

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%); BP changes, chest pain, heart rate changes (topical).

CNS

Dizziness, faintness (topical).

Dermatologic

Hypertrichosis (80%); rashes, including bullous eruptions and Stevens-Johnson syndrome, scalp irritation or redness (topical).

GI

Nausea, vomiting.

Genitourinary

Breast tenderness (less than 1%).

Hematologic

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

Lab Tests

Increased BUN and serum creatinine (7%); increased alkaline phosphatase.

Metabolic-Nutritional

Sudden weight gain.

Miscellaneous

Temporary edema (7%); swelling of the hands or feet (topical).

Precautions

Warnings

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


Monitor

Because of possible salt and water retention, closely monitor body weight. Monitor fluid and electrolytes; observe patients for pericardial effusion.


Pregnancy

Category C .

Lactation

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

Children

Limited data available.

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. Hospitalize patients to monitor carefully.

Tachycardia

Can be prevented by concomitant use of a beta-blocker or other sympathetic nervous system suppressant agents.

Overdosage

Symptoms

Exaggerated hypotension, fluid retention, tachycardia.

Patient Information

  • Advise patient not to change dose without health care provider direction.
  • Tell patient that a diuretic and a beta-blocker are necessary to enhance effectiveness and decrease adverse reactions of minoxidil.
  • Instruct patient to notify health care provider of angina symptoms, breathing difficulty, dizziness, heart rate at least 20 beats/min over normal, light-headedness, rapid weight gain of more than 5 lb, or unusual swelling.
  • Tell patient to report the following symptoms to health care provider: diarrhea, rash, skin irritation, vomiting, 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 months of continuous use is required before hair growth is seen and that stopping treatment will lead to hair loss within a few months.
  • 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 it 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.

Copyright © 2009 Wolters Kluwer Health.

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