Source:http://www4.wiwiss.fu-berlin.de/dailymed/resource/drugs/51
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MINOXIDIL (Tablet)
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Patients over 12 years of age: The recommended initial dosage of minoxidil tablets is 5 mg of minoxidil given as a single daily dose. Daily dosage can be increased to 10, 20 and then to 40 mg in single or divided doses if required for optimum blood pressure control. The effective dosage range is usually 10 to 40 mg per day. The maximum recommended dosage is 100 mg per day.<br/>Patients under 12 years of age: The initial dosage is 0.2 mg/kg minoxidil as a single daily dose. The dosage may be increased in 50 to 100% increments until optimum blood pressure control is achieved. The effective dosage range is usually 0.25 mg to 1 mg/kg/day. The maximum recommended dosage is 50 mg daily .<br/>Dose frequency: The magnitude of within-day fluctuation of arterial pressure during therapy with minoxidil is directly proportional to the extent of pressure reduction. If supine diastolic pressure has been reduced less than 30 mm Hg, the drug need be administered only once a day; if supine diastolic pressure has been reduced more than 30 mm Hg, the dailydosage should be divided into two equal parts.<br/>Frequency of dosage adjustment: Dosage must be titrated carefully according to individual response. Intervals between dosage adjustments normally should be at least 3 days since the full response to a given dose is not obtained for at least that amount of time. Where a more rapid management of hypertension is required, dose adjustments can be made every 6 hours if the patient is carefully monitored.<br/>Concomitant therapy: Diuretic and beta-blocker or other sympathetic nervous system suppressant.<br/>Diuretics: Minoxidil must be used in conjunction with a diuretic in patients relying on renal function for maintaining salt and water balance. Diuretics have been used at the following dosages when starting therapy with minoxidil: hydrochlorothiazide (50 mg, b.i.d.) or other thiazides at equieffective dosage; chlorthalidone (50 to 100 mg, once daily); furosemide (40 mg, b.i.d.). If excessive salt and water retention results in a weight gain of more than 5 pounds, diuretic therapy should bechanged to furosemide; if the patient is already taking furosemide, dosage should be increased in accordance with the patient's requirements.<br/>Beta-blocker or other sympathetic nervous system suppressants: When therapy with minoxidil is begun, the dosage of a beta-adrenergic receptor blocking drug should be the equivalent of 80 to 160 mg of propranolol per day in divided doses. If beta-blockers are contraindicated, methyldopa (250 to 750 mg, b.i.d.) may be used instead. Methyldopa must be given for at least 24 hours before starting therapy with minoxidil because of the delay in the onset of methyldopa's action. Limited clinical experience indicates that clonidine may also be used to prevent tachycardia induced by minoxidil; the usual dosage is 0.1 to 0.2 mg twice daily. Sympathetic nervous system suppressants may not completely prevent an increase in heart rate due to minoxidil but usually do prevent tachycardia. Typically, patients receiving a beta-blocker prior to initiation of therapy with minoxidil have a bradycardia and can be expected to have an increase in heart rate toward normal when minoxidil is added. When treatment with minoxidil and beta-blocker or other sympathetic nervous system suppressant are begun simultaneously, their opposing cardiac effects usually nullify each other, leading to little change in heart rate.
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Minoxidil tablets contain minoxidil, an antihypertensive peripheral vasodilator. Minoxidil occurs as a white to off-white, odorless crystalline powder that is soluble in alcohol and propylene glycol; sparingly soluble in methanol; slightly soluble in water; practically insoluble in chloroform, acetone and ethyl acetate. The chemical name for minoxidil is 2,4-pyrimidinediamine, 6-(1-piperidinyl)-,3-oxide. The structural formula is represented below: Minoxidil tablets for oral administration contain either 2.5 mg or 10 mg of minoxidil. Inactive ingredients: colloidal silicon dioxide, anhydrous lactose, magnesium stearate, microcrystalline cellulose, sodium starch glycolate.
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1. General Pharmacologic Properties: Minoxidil is an orally effective direct acting peripheral vasodilator that reduces elevated systolic and diastolic blood pressure by decreasing peripheral vascular resistance. Microcirculatory blood flow in animals is enhanced or maintained in all systemic vascular beds. In man, forearm and renal vascular resistance decline; forearm blood flow increases while renal blood flow and glomerular filtration rate are preserved. Because it causes peripheral vasodilation, minoxidil elicits a number of predictable reactions. Reduction of peripheral arteriolar resistance and the associated fall in blood pressure trigger sympathetic, vagal inhibitory, and renal homeostatic mechanisms, including an increase in renin secretion, that lead to increased cardiac rate and output and salt and water retention. These adverse effects can usually be minimized by concomitant administration of a diuretic and a beta-adrenergic blocking agent or other sympathetic nervous system suppressant. Minoxidil does not interfere with vasomotor reflexes and therefore does not produce orthostatic hypotension. The drug does not enter the central nervous system in experimental animals in significant amounts, and it does not affect CNS function in man.<br/>2. Effects on Blood Pressure and Target Organs: The extent and time-course of blood pressure reduction by minoxidil do not correspond closely to its concentration in plasma. After an effective single oral dose, blood pressure usually starts to decline within one-half hour, reaches a minimum between 2 and 3 hours and recovers at an arithmetically linear rate of about 30%/day. The total duration of effect is approximately 75 hours. When minoxidil is administered chronically, once or twice aday, the time required to achieve maximum effect on blood pressure with a given daily dose is inversely related to the size of the dose. Thus, maximum effect is achieved on 10 mg/day within 7 days, on 20 mg/day within 5 days, and on 40 mg/day within 3 days. The blood pressure response to minoxidil is linearly related to the logarithm of the dose administered. The slope of this log-linear dose-response relationship is proportional to the extent of hypertension and approaches zero at a supine diastolic blood pressure of approximately 85 mm Hg. When used in severely hypertensive patients resistant to other therapy, frequently with an accompanying diuretic and beta-blocker, minoxidil tablets usually decreased the blood pressure and reversed encephalopathy and retinopathy.<br/>3. Absorption and Metabolism: Minoxidil is at least 90% absorbed from the GI tract in experimental animals and man. Plasma levels of the parent drug reach maximum within the first hour and decline rapidly thereafter. The average plasma half-life in man is 4.2 hours. Approximately 90% of the administered drug is metabolized, predominantly by conjugation with glucuronic acidat the N-oxide position in the pyrimidine ring, but also by conversion to more polar products. Known metabolites exert much less pharmacologic effect than minoxidil itself; all are excreted principally in the urine. Minoxidil does not bind to plasma proteins, and its renal clearance corresponds to the glomerular filtration rate. In the absence of functional renal tissue, minoxidil and its metabolites can be removed by hemodialysis.<br/>4. Cardiac Lesions in Animals: Minoxidil produces several cardiac lesions in animals. Some are characteristic of agents that cause tachycardia and diastolic hypotension (beta-agonists like isoproterenol, arterial dilators like hydralazine) while others are produced by a narrower range of agents with arterial dilating properties. The significance of these lesions for humans is not clear, as they have not been recognized in patients treated with oral minoxidil at systemically active doses, despite formal review of over 150 autopsies of treated patients. Autopsies of over 150 patients who died of various causes after receiving minoxidil for hypertension have not revealed the characteristic hemorrhagic (especially atrial) lesions seen in dogs and minipigs. While areas of papillary muscle and subendocardial necrosis were occasionally seen, they occurred in the presence of known pre-existing coronary artery disease and were also seen in patients never exposed to minoxidil in another series using similar, but not identical, autopsy methods.
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Minoxidil tablets are available as follows: Minoxidil tablets 2.5 mg are round, scored, white and debossedon one side andon the reverse side. Bottles of 100 NDC 53489-386-01Bottles of 250 NDC 53489-386-03Bottles of 500 NDC 53489-386-05Bottles of 1000 NDC 53489-386-10 Minoxidil tablets 10 mg are round, scored, white and debossedon one side andon the reverse side.Bottles of 100 NDC 53489-387-01Bottles of 250 NDC 53489-387-03Bottles of 500 NDC 53489-387-05Bottles of 1000 NDC 53489-387-10 Store at controlled room temperature 15��- 30��C (59��- 86��F). DISPENSE IN TIGHT, LIGHT-RESISTANT CONTAINER.
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WARNINGS: Minoxidil tablets contain the powerful antihypertensive agent, minoxidil, which may produce serious adverse effects. It can cause pericardial effusion, occasionally progressing to tamponade, and angina pectoris may be exacerbated. Minoxidil should be reserved for hypertensive patients who do not respond adequately to maximum therapeutic doses of a diuretic and two other antihypertensive agents. In experimental animals, minoxidil caused several kinds of myocardial lesions as well as other adverse cardiac effects (see Cardiac Lesions in Animals). Minoxidil must be administered under close supervision, usually concomitantly with therapeutic doses of a beta-adrenergic blocking agent to prevent tachycardia and increased myocardial workload. It must also usually be given with a diuretic, frequently one acting in the ascending limb of the loop of Henle, to prevent serious fluid accumulation. Patients with malignant hypertension and those already receiving guanethidine (see Warnings) should be hospitalized when minoxidil is first administered so that they can be monitored to avoid too rapid, or large orthostatic, decreases in blood pressure.
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There have been only a few instances of deliberate or accidental overdosage with minoxidil tablets. One patient recovered after taking 50 mg of minoxidil together with 500 mg of a barbiturate. When exaggerated hypotension is encountered, it is most likely to occur in association with residual sympathetic nervous system blockade from previous therapy (guanethidine-like effects or alpha-adrenergic blockage), which prevents the usual compensatory maintenance of blood pressure. Intravenous administration of normal saline will help to maintain blood pressure and facilitate urine formation in these patients. Sympathomimetic drugs such as norepinephrine or epinephrine should be avoided because of their excessive cardiac stimulating action. Phenylephrine, angiotensin II, vasopressin, and dopamine all reverse hypotension due to minoxidil, but should only be used if underperfusion of a vital organ is evident. Radioimmunoassay can be performed to determine the concentration of minoxidil in the blood. At the maximum adult dose of 100 mg/day, peak blood levels of 1641 ng/mL and 2441 ng/mL were observed in two patients, respectively. Due to patient-to-patient variation in blood levels, it is difficult to establish an overdosage warning level. In general, a substantial increase above 2000 ng/mL should be regarded as overdosage, unless the physician is aware that the patient has taken no more than the maximum dose. Oral LDin rats has ranged from 1321-3492 mg/kg; in mice, 2456-2648 mg/kg.
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minoxidil
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MINOXIDIL (Tablet)
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1. Salt and Water Retention (see WARNINGS: Concomitant use of Adequate Diuretic is Required) - Temporary edema developed in 7% of patients who were not edematous at the start of therapy. 2. Pericarditis, Pericardial Effusion and Tamponade . 3. Dermatologic - Hypertrichosis - Elongation, thickening, and enhanced pigmentation of fine body hair are seen in about 80% of patients taking minoxidil tablets. This develops within 3 to 6 weeks after starting therapy. It is usually first noticed on the temples, between the eyebrows, between the hairline and the eyebrows, or in the side-burn area of the upper lateral cheek, later extending to the back, arms, legs, and scalp. Upon discontinuation of minoxidil, new hair growth stops, but 1 to 6 months may be required for restoration to pretreatment appearance. No endocrine abnormalities have been found to explain the abnormal hair growth; thus, it is hypertrichosis without virilism. Hair growth is especially disturbing to children and women and such patients should be thoroughly informed about this effect before therapy with minoxidil is begun. Allergic - Rashes have been reported, including rare reports of bullous eruptions, and Stevens-Johnson Syndrome. 4. Hematologic - Thrombocytopenia and leukopenia (WBC<3000/mm) have rarely been reported. 5. Gastrointestinal - Nausea and/or vomiting has been reported. In clinical trials the incidence of nausea and vomiting associated with the underlying disease has shown a decrease from pretrial levels. 6. Miscellaneous - Breast tenderness - This developed in less than 1 % of patients. 7. Altered Laboratory Findings - (a) ECG changes - Changes in direction and magnitude of the ECG T-waves occur in approximately 60% of patients treated with minoxidil. In rare instances a large negative amplitude of the T-wave may encroach upon the S-T segment, but the S-T segment is not independently altered. These changes usually disappear with continuance of treatment and revert to the pretreatment state if minoxidil is discontinued. No symptoms have been associated with these changes, nor have there been alterations in blood cell counts or in plasma enzyme concentrations that would suggest myocardial damage. Long-term treatment of patients manifesting such changes has provided no evidence of deteriorating cardiac function. At present the changes appear to be nonspecific and without identifiable clinical significance. (b) Effects of hemodilution - hematocrit, hemoglobin and erythrocyte count usually fall about 7% initially and then recover to pretreatment levels. (c) Other - Alkaline phosphatase increased varyingly without other evidence of liver or bone abnormality. Serum creatinine increased an average of 6% and BUN slightly more, but later declined to pretreatment levels.
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Minoxidil tablets contain the powerful antihypertensive agent, minoxidil, which may produce serious adverse effects. It can cause pericardial effusion, occasionally progressing to tamponade, and angina pectoris may be exacerbated. Minoxidil should be reserved for hypertensive patients who do not respond adequately to maximum therapeutic doses of a diuretic and two other antihypertensive agents. In experimental animals, minoxidil caused several kinds of myocardial lesions as well as other adverse cardiac effects (see Cardiac Lesions in Animals). Minoxidil must be administered under close supervision, usually concomitantly with therapeutic doses of a beta-adrenergic blocking agent to prevent tachycardia and increased myocardial workload. It must also usually be given with a diuretic, frequently one acting in the ascending limb of the loop of Henle, to prevent serious fluid accumulation. Patients with malignant hypertension and those already receiving guanethidine (see Warnings) should be hospitalized when minoxidil is first administered so that they can be monitored to avoid too rapid, or large orthostatic, decreases in blood pressure.
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Because of the potential for serious adverse effects, minoxidil tablets are indicated only in the treatment of hypertension that is symptomatic or associated with target organ damage and is not manageable with maximum therapeutic doses of a diuretic plus two other antihypertensive drugs. At the present time use in milder degrees of hypertension is not recommended because the benefit-risk relationship in such patients has not been defined. Minoxidil reduced supine diastolic blood pressure by 20 mm Hg or to 90 mm Hg or less in approximately 75% of patients, most of who had hypertension that could not be controlled by other drugs.
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MINOXIDIL
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