Effect of vehicle ionic strength on sorption of nitroglycerin to a polyvinyl chloride administration set

The nitroglycerin sorptive properties of a polyvinyl chloride i.v. administration set were studied, and the role played by the admixture vehicle in this process was explored. Admixtures of nitroglycerin 0.4 mg/mL were prepared in sterile water for injection, 5% dextrose injection, Ringer's injection, and 0.25%, 0.9%, and 5% sodium chloride injection. Each admixture was divided into two 500-mL sterile glass containers, and flow through the administration set at 100 mL/hr was begun. Samples of effluent were collected at intervals beginning 10 minutes after the start of the infusion and ending at 180 minutes. Nitroglycerin depletion from solution and uptake by the set was determined by an ultraviolet spectrophotometric assay. Initially, the degree of nitroglycerin loss to the set was greatest for dextrose admixtures, intermediate for water admixtures, and least for sodium chloride admixtures. Losses of about 40% were observed during the first 10 minutes; between 15 and 20 minutes, the stated pattern of drug sorption was reversed, with sodium chloride admixtures now showing the greatest loss of nitroglycerin. The availability of nitroglycerin was an inverse function of increasing ionic strength during the three-hour observation period. Nitroglycerin availability in admixtures in contact with a polyvinyl chloride administration set was dependent on the ionic strength of the vehicle and the time points in the infusion period at which measurements were made.