A 29-year-old male presents with 3 days of fever, headache, fatigue, decreased appetite, calf pain while walking, and cough. Physical exam: temperature 39.8°C, flushed face, conjunctival congestion, normal vision, bilateral inguinal lymphadenopathy, marked tenderness in gastrocnemius muscles, no meningeal signs or pathological reflexes. Liver palpable 1.5 cm below costal margin. WBC 12.7×10<sup>9</sup>/L (N 74%, L 21%, EOS 3%, M 2%). Frequently worked in rice paddies prior to illness. The drug of choice is: