Intramuscular ophthalmic homatropine vs. atropine to prevent lethality in rates with dichlorvos poisoning.

Most hospitals lack a sufficient supply of atropine to treat, simultaneously, patients poisoned with multiple organophosphorous compound (OC) or nerve agent. The presence of a ubiquitous alternate antidote would prove useful if mass poisoning occurred. Our objective was to evaluate the effect of ophthalmic homatropine (Isopto Homatropine 5%) on survivability in a rat model of significant, acute OC poisoning. Sprague-Dawley rats were randomized to one of five pre-treatment groups (N = 10 per group). Prior to experimentation, animals were pre-treated with intramuscular (IM) injections of either atropine 5 mg/kg, atropine 10 mg/kg, homatropine 10 mg/kg, or homatropine 20 mg/kg. The control group received 0.3 mL normal saline IM. Five minutes later, 25 mg/kg of dichlorvos was subcutaneously administered. Mortality rates were compared using Fisher's Exact test. Kaplan-Meier survival curves with Logrank analysis was also performed. If alive at 120 minutes, survival was assumed, and the study was terminated. All rats pre-treated with normal saline, atropine 5 mg/kg, and homatropine 10 mg/kg died. Survival in the homatropine (20 mg/kg) and atropine (10 mg/kg) groups was 30% and 40% respectively. Times to death ranged between 4 and 12 minutes. Overall comparison of time to death revealed a statistically significant improvement for groups pre-treated with homatropine (20 mg/kg) and atropine (10 mg/kg). Pre-treatment with homatropine (20 mg/kg) was comparable with atropine (10 mg/kg) in preventing lethality in this rat model of acute OC poisoning.