Antimicrobial and Antidiarrheal Activities of Pterocarpus santalinoides Stem Bark Extract in Rat Models

Background and Objective: Diarrhea remains a major health challenge, often linked to microbial infections and managed using synthetic drugs that may cause side effects or resistance. This study aimed to evaluate the antimicrobial and antidiarrheal activities of Pterocarpus santalinoides stem bark ethanolic extract in albino rat models to validate its traditional use. Materials and Methods: The antimicrobial activity was assessed using the agar well diffusion method to measure zones of inhibition against S. typhi, E. coli, S. dysenteriae, S. aureus, and C. jejuni. The minimum inhibitory concentration (MIC) was determined via doubling dilution (1000-62.25 mg/mL). Ciprofloxacin served as a positive control. The antidiarrheal potential was tested in rats using castor oil-induced diarrhea and charcoal meal motility models. Four rat groups (n = 5 per group) were treated with distilled water, 0.5 mg/kg loperamide, and 500 or 1000 mg/kg extract. Acute toxicity (LD ) was also determined. Data were analyzed using appropriate statistical tests at p<0.05 significance. Results: The extract showed significant (p<0.05) antimicrobial activity with inhibition zones at 1000 mg/mL measuring 25.00±1.00 mm (S. typhi), 15.67±0.78 mm (E. coli), 9.00±1.00 mm (S. dysenteriae), 16.67±0.58 mm (S. aureus), and 12.67±0.58 mm (C. jejuni). The MIC was 62.25 mg/mL for S. typhi and 250 mg/mL for the other pathogens. In the castor oil model, extract-treated groups had significantly reduced stool frequency and severity, and decreased intestinal motility in the charcoal test. Loperamide showed the highest reduction, but extract effects were comparable Conclusion: Pterocarpus santalinoides stem bark extract exhibits notable antimicrobial and antidiarrheal activities, supporting its traditional use as an alternative remedy for infectious diarrhea. Further studies are recommended to isolate active compounds and assess long-term safety.