The Physical Compatibility of Clinically Used Concentrations of Diltiazem Hydrochloride With Heparin Sodium

Background: Acute treatment of atrial fibrillation often requires concomitant intravenous (IV) continuous infusions of unfractionated heparin and diltiazem. Concomitantly infusing these medications through the same IV line minimizes multiple IV sites. Diltiazem and heparin visual compatibility have been previously investigated but with limited drug dwell times and differing drug concentrations leading to inconsistent published results. Objective: To investigate the physical compatibility of diltiazem hydrochloride at concentrations of 5 and 1 mg/mL combined with an equal volume of heparin sodium 100 units/mL. Methods: Using a 0.22-µm filter, 15 mL of heparin sodium were placed into a polyvinyl chloride infusion bag followed by 15 mL of either diltiazem hydrochloride 5 or 1 mg/mL. Admixtures were prepared in triplicate. Each admixture was investigated for visual precipitation, spectrophotometric absorbance, and pH change at baseline and 1, 5, 8, and 24 hours after mixing. Physical incompatibility was determined by visual observation, increased spectrophotometric absorbance, and demonstrative pH changes. Results: Each diltiazem 5 mg/mL admixture exhibited a slight haze and enhanced absorbance readings indicating turbidity while none revealed a demonstrative pH change. None of the diltiazem 1 mg/mL assessments revealed visual precipitation or suggested turbidity. Only one pH reading at 5 hours revealed a demonstrative change from baseline. Conclusions: Our findings indicate that infusing diltiazem hydrochloride 5 mg/mL with heparin sodium 100 units/mL in the same IV line cannot be advocated. In contrast, our findings suggest that heparin sodium 100 units/mL infused with diltiazem hydrochloride 1 mg/mL is physically compatible but chemical stability was not assessed.