Background In hospital, continuous intravenous drug administration to patients for 24 hours is common. In some wards, such as intensive care units, these infusions may be kept beyond 24 hours.

Purpose We aimed to assess pH variation of morphine 10 and 100 µg/mL and 10% dextrose solutions stored in three types of 50 mL polypropylene syringes for 72 hours.

Material and methods Three solutions: (A) 10 µg/mL morphine and (B) 100 µg/mL morphine in water for injection, and C) 10% dextrose were prepared and divided in triplicate in two types of syringes: (1) polypropylene syringes unprotected from light (UPLS) and (2) light shielded polypropylene syringes (LSS). LSS came from two different companies, manufacturer 1 (LSS-1) and manufacturer 2 (LSS-2). Syringes were stored in a climatic chamber (daylight, 30±2°C, RH 65±5%) over the full duration of the study. The pH of solutions in UPLS, LSS-1 and LSS-2 was measured at T0, 24 hours and 72 hours. At each point time, the pH of each syringe was performed in triplicate.

Results The pH of the 10% dextrose solution varied from T0 to T72: UPLS, 4.05±0.01 to 4.10±0.20; LSS-1, 4.23±0.08 to 6.12±0.08; and LSS-2, 4.09±0.02 to 4.14±0.02 (p<0.05). The pH of 10 µg/mL morphine in water for injection varied from T0 to T72: UPLS, 4.02±0.05 to 4.08±0.02; LSS-1, 4.12±0.04 to 4.82±0.07; and LSS-2, 3.93±0.05 to 3.98±0.01 (p<0.05). The pH of 100 µg/mL morphine in water for injection varied from T0 to T72: UPLS, 3.90±0.02 to 3.98±0.05; LSS-1, 3.98±0.04 to 5.56±0.11; and LSS-2, 3.95±0.01 to 3.99±0.02 (p<0.05).

Conclusion The pH of identical drug solutions varied depending on the type of syringe in which they are stored. The pH values of solutions stored in LSS-1 were modified more than in UPLS and LSS-2. This phenomenon could be a serious problem in unbuffered solutions of drugs which are stable only in a defined range of pH, administered continuously over several days.

No conflict of interest