Shelf life Studies of Pralidoxime Chloride Solution in Autoinjector Cartridges Stored at Room Temperature

The pralidoxime chloride (PAM) cartridge in a reusable autoinjector consists of 300 mg/mL of pralidoxime chloride in 2.2 mL solution with a shelf life of one year. The present study is aimed at evaluating the antidotal efficacy of PAM filled in the cartridges at (stored at room temperature of 25–35°C) different time points using three different methods to determine the shelf life. The study showed that administration of atropine sulfate or freshly prepared pralidoxime chloride alone did not offer appreciable protection as measured by Protection Index (PI) against either diisopropylphosphorofluoridate (DFP) or dichlorvos (DDVP) in male mice. The combined treatment of atropine sulfate and samples of pralidoxime chloride, one after the other but close in time, showed far better protection. Atropine sulfate antagonizes the actions of acetylcholine and PAM reactivates the inhibited acetylcholinesterase (AChE) enzyme. In the case of DDVP, treatment with atropine sulfate and all the samples of pralidoxime chloride (freshly prepared, and 3, 6, 12, 24 and 36 months old) offered a PI of 26.9. On the other hand, DFP intoxication and subsequent treatment with atropine sulfate and all the samples of PAM showed varying PI. It was observed that maximum PI (38.3) could be achieved with 12 months old PAM sample compared to freshly prepared solution. Minimum PI (13.3) was observed with 36 months old PAM sample. This decrease in PI can not be attributed to the less percent reactivation (91.3%) of isopropyl methyl phosphonofluoridate (Sarin) inhibited electric eel AChE by PAM, as both the parameters i.e. PI (26.9) of DDVP and estimation of active PAM (99.5±5.9%) are not in agreement. We assume that the said change may be due to biological variation and high toxicity of DFP (4 times more toxic than that of DDVP). It may be concluded that (i) Pralidoxime chloride filled and stored in autoinjector cartridges has storage stability of more than 2 years, (ii) it also has an appreciable activity in terms of protection index, percent reactivation of sarin inhibited electric eel acetylcholinesterase and (iii) estimation of active PAM for three years.