minoxidil (Loniten, Rogaine)
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Introduction
Tradename: Loniten.
Indications
- management of severe hypertension
- symptomatic hypertension
- associated end-organ damage
- used with loop diuretic to prevent fluid retention
- prevention & reversal of male pattern baldness
Contraindications
Caution:
- coronary artery disease
- recent myocardial infarction
- pulmonary hypertension
- renal insufficiency
- congestive heart failure
Dosage
- start 5 mg PO QD
- increase every 3 days
- average effective dose: 10-40 mg/day
- max: 100 mg/day
- androgenetic alopecia: 2.5 mg/day
Tabs: 2.5 mg, 10 mg.
Topical agent: Tradename Rogaine.
Packaging: solution 2%.
Pharmacokinetics
- oral bioavailability is 90%
- onset of hypotensive effect (oral): 30 minutes
- peak hypotensive effect (oral): within 2-8 hours
- duration of action: up to 2-5 days
- an average of 7 days for maximum effect
- plasma protein binding is negligible
- metabolized by liver to glucuronide derivative
- excreted in the urine
elimination via kidney
Adverse effects
- common (> 10%)
- hypertrichosis*, transient EKG T-wave changes, reflex tachycardia, palpitations, congestive heart failure, edema 2 less common (1-10%)
- fluid & electrolyte imbalance (Na+ retention & H2O retention resulting in edema)
- uncommon (< 1%)
- rash, thrombocytopenia, leukopenia, breast tenderness, angina, pericardial effusion#, pericardial tamponade, dizziness, headache, coarsening of facial features, Stevens-Johnson syndrome, sunburn, weight gain
* hypertrichosis commonly occurs within 1-2 months of therapy
# increased risk of pericardial effusion with renal insufficiency
Drug interactions
- guanethidine in combination may result in profound orthostatic hypotension; discontinue guanethidine 1-3 weeks prior to starting minoxidil or initiate therapy in hospital
Mechanism of action
- potent vasodilator
- reduces peripheral vascular resistance (decreases afterload)
- reflex tachycardia may occur
- lowers blood pressure
- greater effect on arterioles than veins
More general terms
References
- ↑ The Pharmacological Basis of Therapeutics, 9th ed. Gilman et al, eds. Permagon Press/McGraw Hill, 1996
- ↑ Drug Information & Medication Formulary, Veterans Affairs, Central California Health Care System, 1st ed., Ravnan et al eds, 1998
- ↑ Kaiser Permanente Northern California Regional Drug Formulary, 1998