Haematological changes in dogs with prolonged administration of high doses of sulphamethoxazole/trimethoprim

Sulphamethoxazole/trimethoprim (SMX/T) is an antimicrobial agent that has been used for decades against both Gram-positive and Gram-negative bacteria as well as protozoa. It is particularly used as prophylaxis against Pneumocystis carinii pneumonia (PCP) in patients with acquired immune-deficiency syndrome (AIDS). Its use in dogs with associated adverse reactions has necessitated an experimental study that may enhance clinical management of the toxicities. The study aimed to determine the effects of prolonged treatment with high doses of sulphamethoxazole/trimethoprim on the haematological profile of dogs. Dogs were given SMX/T at 30, 60 and 120 mg/kg body weight at 12-h intervals for 21 days. The packed cell volume (PCV), haemoglobin concentration (HbC), red blood cell (RBC) count and total and differential white blood cell (WBC) counts were performed using standard techniques. Data generated was analysed by one-way analysis of variance (ANOVA). Alopecia, epistaxis and skin eruptions were seen at the dose of 120 mg/kg. There were also dose-dependent decreases in the PCV and RBC count. HbC was significantly (p < 0.05) lower than the control only at the dose of 120 mg/kg. Total WBC count was significantly (p < 0.05) lower than the control only on day 7 of treatment at 30, 60 and 120 mg/kg. Beyond day 7, the white cell response, total and differential WBC counts, were fluctuating with significant depression at the dose of 120 mg/kg. Increase in dose and prolonged use of SMX/T in the dogs decreased the haematological parameters and increased the occurrence of toxic reactions and may outweigh the benefits of treatment with the drug in recommended cases.