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Pharmacologic class: Peripheral vasodilator
Therapeutic class: Antihypertensive
Pregnancy risk category C
Relaxes vascular smooth muscles of arteries and arterioles, causing peripheral vasodilation and decreasing peripheral vascular resistance. These actions decrease blood pressure and increase heart rate, stroke volume, and cardiac output.
Injection: 20 mg/ml
Tablets: 10 mg, 25 mg, 50 mg, 100 mg
Indications and dosages
Adults: Initially, 10 mg P.O. q.i.d. After 2 to 4 days, may increase to 25 mg P.O. q.i.d. for remainder of first week; may then increase further to 50 mg P.O. q.i.d., up to 300 mg/day. Once maintenance dosage is established, may give in two daily doses.
Children: Initially, 0.75 mg/kg/day P.O. in four divided doses; may increase gradually over 3 to 4 weeks to 7.5 mg/kg or 200 mg/day
Neonates: 0.5 mg/kg P.O., I.M., or I.V. q 4 to 6 hours
• Hypersensitivity to drug or tartrazine
• Coronary artery disease
• Mitral valvular rheumatic heart disease
Use cautiously in:
• suspected CV or cerebrovascular disease, severe renal or hepatic disease
• pregnant or breastfeeding patients
• Administer oral form with food.
☞ Inject I.V. form slowly over 1 minute. Monitor blood pressure response continuously.
• Draw up and use parenteral drug immediately; solution changes color after contact with metal needle.
CNS: dizziness, drowsiness, headache, peripheral neuritis
CV: tachycardia, angina, orthostatic hypotension, arrhythmias
EENT: lacrimation, nasal congestion
GI: nausea, vomiting, diarrhea, constipation, anorexia
Metabolic: sodium retention
Musculoskeletal: joint pain, arthritis
Skin: rash, blisters, flushing, pruritus, urticaria
Other: chills, fever, lymphadenopathy, edema, lupuslike syndrome
Drug-drug. Antihypertensives, nitrates: additive hypotension
Epinephrine: reduced pressor response to epinephrine
Metoprolol, propranolol: increased blood levels of both drugs
MAO inhibitors: increased hypotension
Drug-diagnostic tests. Coombs' test: positive result
Granulocytes, hemoglobin, neutrophils, platelets, red blood cells, white blood cells: decreased levels
Drug-behaviors. Alcohol use: additive hypotensive response
• Monitor CBC, lupus erythematosus cell studies, and antinuclear antibody titers before and periodically during therapy.
• Monitor blood pressure, pulse rate and regularity, and daily weight.
• To avoid rapid blood pressure drop, taper dosage gradually before discontinuing.
☞ Assess for lupuslike signs and symptoms, including joint pain, fever, myalgia, pharyngitis, and splenomegaly.
• Watch for peripheral neuritis. If it occurs, expect to give pyridoxine.
• Tell patient to take tablets with food.
• Instruct patient to move slowly when rising (especially in morning on awakening), to avoid dizziness from sudden blood pressure decrease.
☞ Instruct patient to immediately report fever, muscle and joint aches, or sore throat.
• Tell patient to report chest pain or numbness or tingling of hands or feet.
• To minimize GI upset, advise patient to eat small, frequent meals.
• Caution patient not to discontinue drug abruptly, because severe hypertension may result.
• As appropriate, review other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, and behaviors mentioned above.