A 24 year-old male comes to the emergency room with fever, chills, weakness, chest pain with deep inspiration, persistent, productive cough with greenish sputum mixed with blood, and shortness of breath. On examination, his temperature is 103.5 °F, heart rate is 122 beats per minute (bpm), blood pressure is 100/71 mm Hg, and respiratory rate is 26 breaths per minute. He is alert and awake. Oral examination shows black staining on the teeth. Fundoscopic examination shows round, flame-shaped hemorrhages with a pale center in the posterior pole of the retina. Auscultation of lungs reveals inspiratory rales bilaterally. Cardiac examination shows tachycardia with a regular rhythm with a high pitched holosystolic murmur loudest in the fourth intercostal space at the left lower sternal border. There are splinter hemorrhages under the nails in both hands. He has bilateral axillary lymphadenopathy, hyperpigmentation and scarring over both forearms. When you ask him in a non-judgmental way, the patient reveals that he is a regular intravenous drug user. His laboratory tests are remarkable for leukocytosis, anemia, hematuria, elevated erythrocyte sedimentation rate, elevated C-reactive protein level, and elevated rheumatoid factor. Blood cultures were drawn and sent to the lab. Of the following, which is the next best step in the management of this patient?