Stability and sorption of calcitriol in plastic tuberculin syringes

The stability of commercially formulated calcitriol 1 and 2 micrograms/mL and calcitriol formulation subsequently diluted to 0.5 microgram/mL in 0.9% sodium chloride injection, 5% dextrose injection, or water for injection was evaluated after eight hours' storage in polypropylene syringes. The apparent affinities of calcitriol for polypropylene and polyvinyl chloride were also examined. Three calcitriol 0.5 microgram/mL solutions (diluted in 0.9% sodium chloride injection, 5% dextrose injection, or water for injection) and aqueous calcitriol formulations, 1 and 2 micrograms/mL, were placed in 1-mL polypropylene tuberculin syringes and assayed by high-performance liquid chromatography initially and after two, four, and eight hours' storage under room light at ambient temperature. Samples of calcitriol 2 micrograms/mL were also exposed to polypropylene or polyvinyl chloride at room temperature for 20 days. The remaining calcitriol concentrations were determined and apparent calcitriol polymer/water partition coefficients were calculated. Calcitriol concentrations did not change substantially during the eight-hour stability study. The mean apparent polymer/water partition coefficient for polyvinyl chloride was 66 times that for polypropylene, indicating that calcitriol has a definite affinity for polyvinyl chloride but no similar affinity for polypropylene. Aqueous calcitriol solution 1 or 2 micrograms/mL or 0.5 microgram/mL in 0.9% sodium chloride injection, 5% dextrose injection, or water for injection, when stored in polypropylene syringes exposed to ambient temperature and room light, appears to be stable for eight hours. Calcitriol appears to have greater affinity for polyvinyl chloride than for polypropylene.