Soru

A 28-year-old man comes to the clinic because of a 5-day history of right knee pain and swelling. He reports that the knee feels stiff and is difficult to bend. He also notes a gritty sensation in both eyes and mild burning upon urination for the past two days. One month ago, he had an episode of severe diarrhea with abdominal cramping that resolved without treatment after a week. His temperature is $37.2^\circ\text{C}$ ($99.0^\circ\text{F}$), blood pressure is $122/78\text{ mm Hg}$, and pulse is $84/\text{min}$. Physical examination shows a swollen, warm, and tender right knee with a moderate effusion. Conjunctival injection is present bilaterally. Arthrocentesis of the right knee yields synovial fluid with a leukocyte count of $18,000/\text{mm}^3$ and no crystals. Gram stain of the fluid is negative. Which of the following is the most appropriate next step in the management of this patient's joint condition?