<p>The study aimed to evaluate the drug resistance of <i>Eimeria</i> spp. in Vietnam to toltrazuril and sulfaclozine, and their effects on intestinal recovery. A total of 100 twelve-day-old chicks were randomly assigned to four groups: a negative control, a positive control, an <i>Eimeria</i>-infected group treated with toltrazuril, and an <i>Eimeria</i>-infected group treated with sulfaclozine. Treatments were administered from day 12 to day 21 of age. At day 14, all groups except NG were orally challenged with 2 × 10⁴ sporulated oocysts of <i>Eimeria</i> spp. The anticoccidial index, percentage of optimal anticoccidial activity, and reduction of lesion score, which reflect overall efficacy, performance, and intestinal damage, consistently indicated resistance for both toltrazuril and sulfaclozine, whereas reduction of oocyst production indicated sensitivity. However, based on an integrated assessment in which severe resistance is defined when resistance was detected in three or all four indexes, the <i>Eimeria</i> isolate was classified as exhibiting severe resistance to both drugs. Nevertheless, sulfaclozine treatment was associated with significantly improved body weight gain and reduced microscopic lesion scores. Given that oocyst output was comparable between the treated groups, these effects may not be directly attributable to inhibition of <i>Eimeria</i> development, but rather to host-related responses during intestinal recovery. The upregulation of Claudin family gene expression observed in the sulfaclozine-treated group may suggest a possible association with modulation of intestinal epithelial responses. This study emphasizes the importance of considering drug-resistance patterns when designing alternative strategies for coccidiosis control in poultry.</p>