Dexamethasone phosphate stability and contamination of solutions stored in syringes

The stability of 10 mg/mL dexamethasone sodium phosphate injection was evaluated using a validated, stability-indicating liquid chromatographic method during 91 days storage in glass and 55 days storage in plastic syringes with rubber plungers. The presence of accelerators, commonly used in the manufacture of rubber, mercaptobenzothiazole (MBT), tetramethyl thiuram disulfide (TMTD) and tetraethyl thiuram disulfide (TETD), was monitored on day 101 and after 18 months storage. During the 91-day study period there was no significant trend for dexamethasone phosphate concentrations in Glaspak syringes to decrease in solutions stored at room temperature or 4 degrees C. The concentration remaining in each syringe on the final day of analysis was greater than 95% of the initial concentration. In Monject plastic syringes there was no significant decrease in the dexamethasone phosphate concentration over 35 days with 1 mL syringes or 55 days with 3 mL syringes at either room temperature or 4 degrees C. The concentration remaining in each syringe on the final day of analysis was greater than 93% of the initial concentration. Analysis of samples for leachates on day 101 failed to demonstrate any contamination. However, re-analysis of the syringes following 18 months storage indicated contamination by a number of compounds. The results indicate that sorption of dexamethasone phosphate to the syringe barrel or plunger did not occur to a clinically important degree. We conclude that dexamethasone phosphate solutions (10 mg/mL) stored at 4 degrees C or 23 degrees C for up to 91 days in Glaspak syringes or 55 days in plastic Monject syringes will retain more than 93% of the initial dexamethasone concentration. Furthermore after 101 days there was no measurable contamination of the dexamethasone phosphate solution, although after 18 months considerable contamination was observed.