Background: Asthma is a chronic inflammatory respiratory disease affecting over 300 million individuals globally, with limited treatment efficacy and significant adverse effects associated with conventional pharmacotherapy. Plant-based therapeutic agents have emerged as promising alternatives warranting systematic evaluation. Objective: This study evaluated the anti-asthmatic, antihistaminic, and bronchoprotective potential of ethanolic leaf extract of Caesalpinia pulcherrima (Caesalpiniaceae) through complementary in vitro and in vivo approaches in guinea pig models. Methods: In vitro antihistaminic activity was assessed using histamine-induced contraction in isolated guinea pig ileum preparations, with responses compared against chlorpheniramine maleate (standard control). In vivo bronchoprotective efficacy was evaluated in an acute histamine aerosol-induced bronchospasm model in guinea pigs. Test groups received vehicle (0.1% carboxymethyl cellulose), chlorpheniramine maleate (2 mg/kg), or ethanolic leaf extract (200 and 400 mg/kg, p.o.). Preconvulsive dyspnoea time (PCT) was measured at baseline, 1 hour, 4 hours, and 24 hours post-drug administration. Percentage protection was calculated and analyzed. Results: In vitro studies demonstrated dose-dependent inhibition of histamine-induced ileal contractions by the extract, achieving 74.05% inhibition at maximum histamine concentration (3.2 ml), comparable to chlorpheniramine effects. In vivo studies showed significant bronchoprotection with peak efficacy at 4 hours post-administration; the 400 mg/kg extract dose yielded 67.44% protection versus 73.73% for chlorpheniramine maleate. The 400 mg/kg extract group exhibited preconvulsive dyspnoea time of 21.50 ± 0.43 seconds at 4 hours, significantly extended compared to vehicle control (p<0.001), demonstrating protection comparable to the standard antihistamine. Conclusion: Ethanolic leaf extract of Caesalpinia pulcherrima demonstrates significant antihistaminic activity and bronchoprotective efficacy in guinea pig models of acute histamine-induced bronchospasm, providing pharmacological validation of its ethnomedicinal use in respiratory disorders. The findings support further mechanistic investigation and phytochemical characterization to identify active constituents and elucidate molecular pathways underlying these therapeutic effects.

Zenodo (CERN European Organization for Nuclear Research) 2026 Open access