Protocol for Stability Study
Three formulations were evaluated for compatibility and stability. These were prepared, using aseptic technique, from the commercially available gentamicin (40 mg/mL) and trisodium citrate (46.7% for injection, diluted with water). Formulation A consisted of gentamicin 2.5 mg/mL, formulation B consisted of sodium citrate 40 mg/mL, and formulation C consisted of both gentamicin and sodium citrate at concentrations of 2.5 and 40 mg/mL, respectively. A 30-mL volume of each formulation was prepared, and 5-mL aliquots of each formulation were packaged into six 5-mL polyethylene syringes. The syringes were closed with luer-lock syringe tips and were stored at room temperature in a plastic bin with an opaque, snug-fitting lid.
On days 0, 7, 14, 28, 42, 56, and 112, a sample of about 0.8 mL was withdrawn from each of 4 randomly selected syringes for each formulation. These samples were placed in 1.8-mL screw-top cryovials and stored at —20°C until analysis. Both gentamicin and citrate have been shown to be stable for 6 months when frozen and stored at -20°C. For gentamicin analysis, the samples were diluted 1:1 with water to give a nominal concentration of 250 g/mL; phenylisocyanate derivatives were prepared from 0.5-mL volumes of these solutions, as previously described, and analyzed by means of HPLC. For citrate analysis, samples were diluted 1:25 with water to generate a nominal concentration of 1600 |ig/mL, and these solutions were analyzed by HPLC. The concentration of gentamicin and citrate was quantified with reference to standards analyzed concurrently with the samples. At the time of analysis, all samples, standards, and a blank were coded and analyzed in random order.
At the start and finish of the study, the pH of the formulations was assessed using a pH meter (Accumet Basic AB15, Fisher Scientific, Nepean, Ontario). Colour and clarity were assessed visually. canadian antibiotics
Statistical analyses were performed with SigmaStat (SPSS Inc, Chicago, Illinois) and Excel 2000 (Microsoft) software. All statistical analyses were performed at the 95% significance level, and data are presented as means ± SD, unless indicated otherwise. Linear regression models were constructed to estimate the amount, with 95% confidence intervals (CIs), of gentamicin and citrate remaining at the end of the 112-day observation period. In each model, the independent variable was time, and the dependent variables were the concentrations of gentamicin and citrate. Analysis of variance (ANOVA) was used to test changes in concentration over time.