Evaluation of the antidiarrheal activity of the leaf extract of Parquetina nigrescens and formulation into oral suspensions

PURPOSE: Parquetina nigrescens (Pn) extract was evaluated for safety and antidiarrheal activity, formulated into stable suspensions, and characterized. METHODS: Acute toxicity of the extract based on Organization for Economic Cooperation and Development-423 guidelines was performed. The antidiarrheal effects of the extract on castor oil-induced diarrhea in four groups of Wistar rats were determined. The first and second groups received 5 and 200 mg/kg body weight (bw) of the extract, while the third and fourth groups received normal saline (5 mg/kg bw) and loperamide (5 mg/kg bw) as negative and positive controls, respectively. Pn extract was used at 1.25% w/v to formulate structured vehicle (carboxylmethylcellulose, polyvinylpyrrolidone and tragacanth) suspensions. The suspensions were tested for pharmacological activity and characterized. RESULTS: Acute toxicity gave a lethal dose 50 (LD50) that is greater than 300 and less than 2,000 mg/kg bw. A reduction in intestinal transit by 0.14 and 0.15% at 5 and 200 mg/kg of the extract was achieved as compared to an inhibition of 0.12% by 5 mg/kg loperamide. There was a dose-dependent decrease in the frequency of watery stool passed in castor oil-induced rats by 35.29% and 64.70% at 5 and 200 mg/kg, respectively. All the suspensions inhibited diarrhea, exhibiting a dose-dependent pattern and remained stable after 4 weeks. Their pH values ranged from 4.60±2.73 to 4.73±1.91, while viscosity ranged from 3.50±1.23 to 6.75±1.24 Pas at 60 rpm. CONCLUSION: The results suggest that Pn possesses significant antidiarrheal activity. Suspensions of Pn were successfully formulated in structured vehicles and were effective in the control of diarrhea in Wistar rats.