Hydralazine hydrochloride is available as a 20-mg/mL injection solution in 1-mL single-dose vials.923 Each mL contains hydralazine hydrochloride 20 mg, methylparaben 0.65 mg and propylparaben 0.35 mg as preservatives, and propylene glycol 103.6 mg in water for injection.923 The pH may have been adjusted with hydrochloric acid and/or sodium hydroxide.923
pH
From 3.4 to 4.4.923
Hydralazine hydrochloride may be administered intramuscularly or as a rapid direct intravenous injection; the manufacturer states the drug should not be added to infusion solutions.923
Hydralazine hydrochloride in intact vials should be stored at controlled room temperature.923 Refrigeration of the intact containers may result in precipitation or crystallization.593 The solution should be used immediately after the vial is opened.923
Hydralazine hydrochloride is a colorless solution.923 Contact with metal may result in discoloration of the solution.923 One report indicated a pink discoloration in prefilled syringes when the hydralazine hydrochloride had been drawn up through filter needles (Monoject) with a stainless steel filter and stored for up to 12 hours. The reaction is not specific to any one metal. Consequently, contact with metal parts should be minimized, and hydralazine hydrochloride should be prepared just prior to use.906 Discolored solutions should be discarded.923
pH Effects
Hydralazine hydrochloride exhibits maximum stability at pH 3.5 and is stable over the pH range of 3 to 5. It undergoes more rapid decomposition as the pH becomes alkaline.106; 466
Light Effects
Exposure to light increases the rate of hydralazine hydrochloride decomposition during long-term storage. At a concentration of 0.35 mg/mL in sodium chloride 0.9% in glass bottles, 10% decomposition was calculated to occur in 14.4 weeks in the dark and 12.3 weeks under fluorescent light. In PVC containers, decomposition occurs more rapidly; a 10% loss was calculated to occur in 12.8 weeks in the dark and 9.9 weeks under fluorescent light.1561
Sorption
Hydralazine hydrochloride 27 mg/L in sodium chloride 0.9% in PVC bags exhibited approximately 10% loss in 1 week at 15 to 20°C due to sorption.536 However, no loss due to sorption occurred during a 7-hour simulated infusion through an infusion set consisting of a cellulose propionate burette chamber and 170 cm of PVC tubing.606
Hydralazine hydrochloride was shown not to exhibit sorption to polyethylene tubing, Silastic tubing, and polypropylene syringes.606
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