Abstract
The protective and therapeutic effects of the H 1–antihistamine chlorpheniramine against an acute poisoning induced by organophosphorus insecticide dichlorvos in a 7–14 days old chicks model were evaluated and compared with that of the standard antidote atropine. Chlorpheniramine or atropine at 20 mg/kg, intramuscularly (i.m.) given immediately after oral dichlorvos dosing increased the LD 50 value of dichlorvos (10.85 mg/kg, orally) in the chicks by 77 and 123 %, respectively. Chlorpheniramine at 20 mg/kg, i.m. given immediately after dichlorvos (12 mg/kg, orally) significantly delayed the onset of acute signs, time of death, decreased toxicity score and increased the percentages of survivors (62.5 %) during 2 and 24 h after dichlorvos dosing. The antidotal effect of chlorpheniramine and atropine groups at a dose of 20 mg/kg, i.m. given immediately after oral dichlorvos were close to each other in delaying the onset signs of poisoning and time of death. They also significantly increased the percentages of survivors and decreased of toxicity scores. Chlorpheniramine at 20 mg/kg, i.m. significantly decreased plasma (34%) and brain (52%) cholinesterase activities in comparison with the control group. Dichlorvos dosing at 8 mg/kg, orally significantly reduced plasma (83%) and brain (93%) cholinesterase activities in comparison with the control and chlorpheniramine groups. Chlorpheniramine given after dichlorvos dosing significantly protected the plasma and brain cholinesterase from further decreased in its activities caused by dichlorvos dosing by 29 and 41%, respectively. In conclusion, the study suggests that chlorpheniramine have a protective and therapeutic effects in case of dichlorvos poisoning in chicks resembling that of atropine.
Highlights
Chlorpheniramine is an H1–receptor antagonist [1,2,3,4]
Intramuscular injection of chlorpheniramine at a dose of 20 mg/kg immediately after oral dosing with dichlorvos increased the oral 24 h LD50 value of dichlorvos to become 19.16 mg/kg with an increased in a protection ratio to reach 1.77 (77 %) (Table 1)
Atropine when given by intramuscular route at a dose of 20 mg/kg immediately after oral dosing with dichlorvos increased the 24 h LD50 value of dichlorvos to be 24.22 mg/kg, orally and a protection ratio increased to became 2.23 (123 %) (Table 1)
Summary
Chlorpheniramine is an H1–receptor antagonist [1,2,3,4]. H1–receptor blockers are previously known to inhibit erythrocyte cholinesterase in vitro and plasma cholinesterase in vitro and in vivo in experimental animals (mice and horses) [5,6,7]. Chlorpheniramine is a commonly used antihistamine in human with antimuscarinic property that resemble that of the standard antidote atropine, since atropine is the drug of choice in treatment and preventing anticholinesterase poisoning [2,3,4]. Dichlorvos is an organophosphorus insecticide used in the fields of veterinary, public health and agriculture [19,20,21]. It induces cholinergic nervous system hyperstimulation in mammals by inhibiting the physiological activity of acetylcholinesterase irreversibly by combining with the esteratic site of this enzyme with strong covalent bond leading to subsequent accumulation of acetylcholine at peripheral and central nervous system [19,22]
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