A 28-year-old man presents to the clinic for evaluation of painful urination and cloudy-color penile discharge. The symptoms started 2 days ago and are not associated with any other symptoms. His past medical history is not significant and he is not on any medications.His physical examination is completely normal except for a purulent discharge that can be expressed from his penis. A swab of the fluid reveals Gram-negative diplococci within neutrophils. Which of the following is the most appropriate treatment?