Review Question - QID 108807

The most likely diagnosis in this patient is genital herpes. Acyclovir is the first-line treatment in genital herpes but can lead to crystalline nephropathy if the patient is not adequately hydrated.

The presence of painful erosive vesicular lesions and lymphadenopathy is most consistent with genital herpes caused by herpes simplex virus (HSV). Acyclovir is the first-line treatment for HSV. Acyclovir is a guanosine analog that requires activation (phosphorylation) by a virus-specific thymidine kinase. The selective toxicity of acyclovir is explained by the fact that most herpesviridae have this kinase, but human cells do not, making acyclovir non-toxic to human cells. Acyclovir, which is rapidly filtered by the glomeruli and secreted by the renal tubules, has low solubility in urine. As a result, acyclovir levels in the renal tubules can rise rapidly, leading to intratubular crystal deposition. Adequate hydration will reduce the urine concentration of acyclovir and prevent crystalline nephropathy from occurring.

Incorrect Answers:
Answer 1: Gingival hyperplasia has been associated with phenytoin and cyclosporine.

Answer 2: Pulmonary fibrosis has been associated with methotrexate and bleomycin.

Answer 3: Deafness (ototoxicity) has been associated with cisplatin, aminoglycosides, and loop diuretics.

Answer 5: Photosensitivity is known to be caused by tetracyclines, fluoroquinolones, and isotretinoin.

Bullet Summary:
Acyclovir is a guanosine analog used to treat infections with herpes simplex virus. It is important to ensure that patients taking acyclovir are adequately hydrated to prevent medication-induced crystal nephropathy.