A 52-year-old African American man comes to the physician because of foggy vision in both eyes. He denies any headache, nausea, or vomiting. He was diagnosed with extensive cellulitis and osteomyelitis of the right foot 4 weeks ago and has been taking oral linezolid. His other medical problems include sarcoidosis, pulmonary hypertension, lower extremity venous stasis, deep vein thrombosis, type 2 diabetes for 5 years, hypertension, and chronic kidney disease.
His medications include warfarin, prednisone (10 mg/day) , insulin, hydralazine, clonidine, metoprolol, valsartan, and furosemide. He has been compliant with his medication regimen. He quit smoking 7 years ago and denies the use of alcohol or illicit drugs. He is allergic to vancomycin.
His temperature is 36.7 C (98 F) , blood pressure is 150/90 mm Hg, and pulse is 72 /min. His BMI is 32 kg/m². Visual acuity is 20/400 in both eyes with considerable optic disc edema, hyperemia, and reduced color perception. A right carotid bruit is present. Examination shows jugular venous distention, a few fine crackles in all lung fields, normal first and second heart sounds, and a palpable liver 2 cm below the costal margin. Bilateral 1+ pitting lower extremity edema to the mid shin and a resolving right leg cellulitis is present.
Which of the following is the most immediate next step in management?

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11ec193a_9898_5394_853d_4185d31def17_MD0002_00 This patient's bilateral ophthalmological complaints while on prolonged linezolid treatment is most consistent with drug-induced optic neuropathy. Linezolid is active against most gram-positive bacteria including streptococci, vancomycin-resistant enterococci (VRE), and methicillin-resistant Staphylococcus aureus (MRSA). The main indications of linezolid are skin and soft tissue infections and pneumonia. The long-term use of linezolid has been associated with bone marrow suppression, peripheral neuropathy, and optic neuropathy. Both the peripheral and optic neuropathy may be irreversible, possibly due to mitochondrial toxicity. Guidelines recommend no more than 28 days of linezolid therapy with a weekly CBC to monitor for possible bone marrow suppression. Periodic eye and neurological examinations are recommended in patients requiring > 4 weeks of linezolid. Patients developing optic neuropathy (such as this one) should discontinue linezolid. (Choice A) This patient's unilateral carotid artery stenosis is less likely to present with bilateral changes in vision. (Choice C) Sarcoidosis typically causes anterior uveitis and patients usually present with a red eye. Optic neuropathy can also be seen with sarcoidosis. The optic disc may have a nodular appearance (granulomatous infiltration). However, this patient is on prednisone, which makes a sarcoid flare less likely. (Choices D & E) An ESR measurement and a temporal artery biopsy are helpful for the diagnosis of giant-cell arteritis. This patient does not have any systemic symptoms to suggest these diagnoses. Also, the patient is already on prednisone which makes it even less likely. Educational objective: Linezolid-induced optic neuropathy usually occurs after long-term use (> 4 weeks). Patients should receive periodic eye and neurological examinations to document early findings and discontinue the drug if present. __________ References: Linezolid-associated peripheral and optic neuropathy, lactic acidosis, and serotonin syndrome. (http://www.ncbi.nlm.nih.gov/pubmed/17655517) Linezolid-associated toxic optic neuropathy. (http://www.ncbi.nlm.nih.gov/pubmed/16505322) Drug-induced optic neuropathies. (http://www.ncbi.nlm.nih.gov/pubmed/18174968)

A 52-Year-Old African American Man Comes to the Physician Because