Drug Interactions between lofexidine and sodium nitrite

MONITOR CLOSELY: Coadministration with antihypertensive agents, diuretics, vasodilators, or phosphodiesterase-5 (PDE5) inhibitors may potentiate the hypotensive effect of sodium nitrite. Since sodium nitrite can cause serious hypotension and methemoglobin formation, patients may be at increased risk for complications related to inadequate perfusion and oxygenation. In healthy volunteers, oral doses of 120 to 180 mg caused minimal cardiovascular changes when subjects were maintained in the horizontal position. However, subjects exhibited tachycardia and hypotension with syncope within minutes after being placed in the upright position. A wide range of methemoglobin concentrations may occur following sodium nitrite administration. Methemoglobin concentrations as high as 58% have been reported after administration of two 300 mg doses to an adult. There have been reports of severe hypotension, methemoglobinemia, cardiac dysrhythmias, coma, and death in patients without life-threatening cyanide poisoning but who were treated with injection of sodium nitrite at dosages less than twice those recommended for the treatment of cyanide poisoning.

MANAGEMENT: Sodium nitrite should be used with caution and close monitoring in the presence of concomitant antihypertensive agents, diuretics, vasodilators, or PDE5 inhibitors. Hemodynamics should be monitored during and after administration of sodium nitrite, and the infusion rate decreased if significant hypotension occurs. In addition, methemoglobin levels should be monitored and oxygen administered during treatment whenever possible.