With a Giardia lamblia diagnosis, which medication would the NP most likely prescribe?

Metronidazole is the drug of choice for treating Giardia lamblia infections due to its effectiveness in targeting anaerobic bacteria and certain parasites. Giardia lamblia is a protozoan parasite responsible for giardiasis, which often presents with gastrointestinal symptoms. Metronidazole works by inhibiting nucleic acid synthesis and disrupting the DNA of the organism, thereby eliminating the infection.

While the other medications listed may be effective against different types of infections, they are not the primary choice for treating giardiasis. Erythromycin is primarily an antibiotic effective against a variety of bacterial infections but not indicated for Giardia. Ampicillin is also an antibiotic used for certain bacterial infections, and trimethoprim-sulfamethoxazole is typically used for a range of bacterial infections and some other protozoal infections, but not as a first-line treatment for Giardia. Therefore, the selection of metronidazole for Giardia lamblia highlights its specific efficacy against this parasite, making it the most appropriate medication in this scenario.