What is the recommended dose of ethambutol for a 74 kg patient with disseminated tuberculosis?

Ethambutol Dosing for 74 kg Patient with Disseminated Tuberculosis

For a 74 kg patient with disseminated tuberculosis, administer ethambutol 1,200 mg orally once daily (approximately 16.2 mg/kg), which falls within the CDC-recommended range of 15-20 mg/kg per day. 1, 2

Standard Dosing Regimen

• The CDC recommends 15-20 mg/kg per day as a single daily dose for all forms of tuberculosis, including disseminated disease. 1, 2
• For a 74 kg patient, the weight-based dosing table specifies 1,200 mg daily for patients in the 56-75 kg weight range, delivering 16.0-21.4 mg/kg. 1, 2
• The maximum dose should not exceed 2.5 g per day regardless of weight. 1, 2
• Ethambutol must be administered as part of a multi-drug regimen with isoniazid, rifampin, and pyrazinamide—never as monotherapy. 2, 3

Treatment Duration for Disseminated TB

• Standard disseminated tuberculosis requires a 6-month treatment regimen unless there is central nervous system involvement, which extends treatment to 12 months. 2
• A lumbar puncture is mandatory in disseminated (miliary) tuberculosis to rule out meningeal involvement, as this determines whether 6-month or 12-month therapy is needed. 2
• The FDA label specifies that therapy should continue until bacteriological conversion has become permanent and maximal clinical improvement has occurred. 3

Critical Monitoring Requirements

Baseline visual acuity testing using a Snellen chart and Ishihara color discrimination tests must be performed before starting ethambutol. 1, 2

• At each monthly visit, specifically question the patient about visual disturbances including blurred vision, scotomata, or changes in color perception. 1, 2
• Monthly visual acuity and color discrimination testing is recommended for patients receiving doses >15-25 mg/kg, those on treatment >2 months, or any patient with renal insufficiency. 1
• Instruct the patient to contact you immediately if any vision changes occur, and discontinue ethambutol immediately and permanently if visual toxicity develops. 1

Key Safety Considerations

• The primary concern is dose-related retrobulbar neuritis manifesting as decreased visual acuity or red-green color discrimination affecting one or both eyes. 1, 2
• At the recommended 15 mg/kg daily dose, the risk of ocular toxicity is minimal—no difference in visual acuity prevalence was found compared to regimens without ethambutol. 1, 2
• The risk of optic toxicity increases substantially at doses >30 mg/kg per day (18% of patients) and in patients with renal insufficiency. 1
• Peripheral neuritis is a rare adverse effect, and cutaneous reactions requiring discontinuation occur in only 0.2-0.7% of patients. 1

Dose Adjustments for Renal Impairment

• For creatinine clearance <70 mL/min, adjust the dose or dosing interval. 1, 2
• For end-stage renal disease or hemodialysis patients, administer 15-20 mg/kg three times weekly by directly observed therapy (DOT) after dialysis. 1, 2
• Ethambutol is cleared primarily by the kidneys, making dose adjustment critical in renal dysfunction to prevent drug accumulation and increased toxicity risk. 1

Common Pitfalls to Avoid

• Do not use ethambutol as monotherapy—this increases the risk of acquired drug resistance. 2, 3
• Do not skip baseline visual testing, as this eliminates your ability to detect drug-induced changes versus pre-existing visual impairment. 1
• Do not continue ethambutol if visual symptoms develop—permanent blindness can occur if the drug is not stopped immediately. 1
• Do not use standard dosing in patients with renal insufficiency without adjustment, as this significantly increases toxicity risk. 1