A 4-year-old patient presents to the nurse practitioner for complaints of periumbilical pain, nausea, abdominal distention, and diarrhea. Exam and stool results reveal giardiasis. Treatment should include:

Rationale: A. Sulfamethoxazole is not the treatment of choice for Giardia lamblia infections. B. Metronidazole is the first-line treatment for giardiasis in children. It is effective in eradicating the protozoal infection, alleviating symptoms such as diarrhea, abdominal pain, and nausea, and preventing transmission. Pediatric dosing should be weight-based, typically for 5–7 days. C. Fluconazole (Diflucan) is an antifungal agent and not effective against protozoal infections like giardiasis. D. Erythromycin/sulfisoxazole acetyl (Pediazole) is an antibiotic combination used for bacterial infections, not protozoal infections.