Background: Antituberculosis drugs (ATD) potentially cause hepatotoxicity and pre-treatment with Kleinhovia hospita extract has been shown to reduce ATD-induced hepatotoxicity. Objective: This study aimed to investigate the possible adverse effects of co-administration of ATD and Kleinhovia extract on hematology profiles and electrolyte balance in rats. Materials and Methods: Male Wistar rats were divided into four treatment groups. Group I only received suspending agent as placebo (n=6); group II was treated with ATD tablet 89 mg/kg (n=7); group III received 250 mg/kg Kleinhovia extract and ATD (n=7); group IV received 500 mg/kg Kleinhovia extract and ATD (n=7). The extract was given 3 hours before ATD administration. Blood samples were taken from rat lateral veins after 28 days of treatment and analyzed to obtain complete blood counts and electrolyte levels. Results: ATD treatment in rats did not alter electrolyte balance but led to significantly reduced mean corpuscular volume (MCV) and increased mean corpuscular hemoglobin concentration (MCHC) compared to placebo group (p<0.05). ATD also lowered mean platelet volume (MPV), platelet distribution width (PDW) and platelet large cell ratio (P-LCR). Rats received ATD and Kleinhovia extract 250 mg/kg had similar alteration in their hematological indices with those treated with ATD only, meanwhile extract 500 mg/kg further reduced the PDW and P-LCR (p<0.05). Conclusion: ATD administration for 28 days in rats did not affect electrolyte level but may trigger some variations in red blood cell and platelet sizes. Co-administration with Kleinhovia extract at 500 mg/kg dose could signify the alteration of platelet size and distribution.

Key words: Antituberculosis, Kleinhovia hospita, blood cell counts, electrolyte level