Adverse reactions with hydralazine are usually reversible when dosage is reduced. However, in some cases it may be necessary to discontinue the drug. The following adverse reactions have been observed, but there has not been enough systematic collection of data to support an estimate of their frequency.

Common: Headache, anorexia, nausea, vomiting, diarrhea, palpitations, tachycardia, angina pectoris
Less Frequent: Digestive: constipation, paralytic ileus.
• Cardiovascular: hypotension, paradoxical pressor response, edema.
• Respiratory: dyspnea
• Neurologic: peripheral neuritis, evidenced by paresthesia, numbness, and tingling, dizziness, tremors, muscle cramps, psychohc reactions characterized by depression, disorientation, or anxiety.
• Genitourinary: difficulty in urination
• Hematologic: blood dyscrasias, consisting of reduction in hemoglobin and red cell count, leukopenia, agranulocytosis, purpura, lymphadenopathy, splenomegaly
• Hypersensitivity Reactions: rash, urticaria, pruritis, fever, chills, arthralgia, eosinophilia, and rarely, hepatitis.
• Other: nasal congestion, flushing, lacrimation, conjunctivitis.

MAO inhibitors should be used with caution in patients receiving hydralazine.

When other potent parental antihypertensive drugs, such as diazoxide, are used in combination with hydralazine, patients should be continuously observed for several hours for any excessive fall in blood pressure. Profound hypotensive episodes may occur when diazoxide infection and hydralazine are used concomitantly.

Beta-blockers (metoprolol, propranolol) serum concentrations and pharmacologic effects may be increased. Monitor cardiovascular status.

Propranolol increases hydralazine's serum concentrations. Acebutolol, atenolol, and nadolol (low hepatic clearance or no first-pass metabolism) are unlikely to be affected.

NSAIDs may decrease the hemodynamic effects of hydralazine; avoid use if possible or closely monitor cardiovascular status at the end of drug interactions

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