Which antifungal drug is used topically to treat fungal infections like athlete’s foot?

Choice A reason: Penicillin antibiotics, like amoxicillin, inhibit bacterial cell wall synthesis and are not associated with photosensitivity. Their side effects include allergic reactions and gastrointestinal upset. Photosensitivity requires drugs that absorb UV light, altering skin response, which is not a mechanism of penicillin’s action on bacterial peptidoglycan.

Choice B reason: Cephalosporins, similar to penicillins, target bacterial cell walls and are not commonly linked to photosensitivity. Their side effects include hypersensitivity and gastrointestinal issues. Unlike drugs that cause phototoxic reactions by absorbing UV light, cephalosporins lack chromophores that trigger skin photosensitivity, making this incorrect.

Choice C reason: Tetracyclines, like doxycycline, are known to cause photosensitivity by forming phototoxic compounds under UV light exposure. These compounds generate reactive oxygen species, damaging skin cells and causing exaggerated sunburn or rashes. Patients must avoid sun exposure and use sunscreen to prevent this adverse effect during therapy.

Choice D reason: Vancomycin, used for gram-positive infections, inhibits cell wall synthesis but is not associated with photosensitivity. Its primary side effects include nephrotoxicity and red man syndrome. It does not absorb UV light or form phototoxic metabolites, making it an unlikely cause of skin reactions to sunlight.

Choice A reason: Tetracyclines, like doxycycline, cause photosensitivity by forming phototoxic compounds under UV light, leading to severe sunburn or rashes. Avoiding sunlight and tanning beds prevents skin damage, as tetracycline’s protein synthesis inhibition does not mitigate its phototoxic effects, making this the correct instruction.

Choice B reason: Taking tetracycline only until feeling better is incorrect, as incomplete treatment promotes bacterial resistance. Tetracyclines require a full course to eradicate infection, preventing survival of resistant mutants, which could worsen infections like acne or respiratory infections, making this an unsafe instruction.

Choice C reason: Milk and cheese reduce, not increase, tetracycline levels by chelating the drug, forming insoluble complexes that decrease absorption. This interaction lowers efficacy, requiring tetracycline to be taken away from dairy, making this statement incorrect for patient education.

Choice D reason: Antacids reduce tetracycline absorption by chelating with divalent cations (e.g., calcium, magnesium), forming insoluble complexes. This decreases efficacy, not gastrointestinal distress. Taking tetracycline away from antacids ensures proper absorption, making this statement incorrect and potentially harmful.