Evaluation of Synergistic Anti-plasmodial Activity of Tamarindus indica and Hibiscus sabdariffa Extracts Against Clinical Isolates of Plasmodium falciparum: In-Vitro and Ex-Vivo protocols

Abstract

Malaria caused by Plasmodium falciparum remains a major global health burden and serious health challenge, exacerbated by increasing resistance to conventional antimalarial drugs. This study evaluated the in vitro and ex vivo anti-plasmodial activity of Tamarindus indica (Tamarind) and Hibiscus sabdariffa (Zobo) extracts, individually and in combination, against clinical isolates of P. falciparum. Aqueous extracts were prepared and screened for phytochemical constituents, followed by dose-dependent schizont maturation assays and growth kinetic analyses. Results demonstrated that phytochemical screening confirmed the presence of flavonoids, tannins, alkaloids, and saponins, which likely contribute to the observed bioactivity. While T. indica exhibited potent anti-plasmodial activity with an IC₅₀ of 3.8 ± 0.96 µg/mL, approaching that of quinine (2.5 ± 0.74 µg/mL), while H. sabdariffa showed moderate activity (IC₅₀ = 13.5 ± 0.99 µg/mL). The combined extract improved efficacy relative to H. sabdariffa alone (IC₅₀ = 5.2 ± 0.99 µg/mL), but combination index analysis (CI = 1.61) revealed an antagonistic interaction. Growth kinetic studies indicated that untreated parasites exhibited a typical exponential replication with a doubling time of 17.5 hours, whereas extract-treated cultures showed prolonged lag phases, suppressed exponential growth, and early transition to decline phases. Notably, H. sabdariffa alone demonstrated a paradoxical increase in parasite viability at higher concentrations, suggesting potential metabolic or protective effects on parasite survival. However, T. indica demonstrates strong antimalarial potential, while the combination with H. sabdariffa does not confer synergistic benefit. These findings highlight the importance of rigorous interaction studies in plant-based combination therapies for malaria.