Which of the following is a topical ocular drug example?

Proparacaine 0.5% is the correct answer as it is a topical ocular anesthetic specifically designed for use in the eye. Proparacaine works by temporarily blocking the sensation in the cornea and is commonly used in ophthalmic procedures to facilitate discomfort during examinations and surgeries. Its formulation is designed for direct application to the eye, which aligns perfectly with what is classified as a topical ocular drug.

On the other hand, the other options do not serve this specific purpose. Ibuprofen is an oral nonsteroidal anti-inflammatory drug (NSAID) used primarily for pain and inflammation, not formulated for topical or ocular use. Amoxicillin is an antibiotic commonly administered orally or through injection for bacterial infections, and likewise, it does not have an ocular formulation. Metformin is an oral medication used in the management of type 2 diabetes and is also not related to ocular or topical applications. Each of these medications serves distinct therapeutic purposes that do not involve direct application to the eyes.