A 61-year-old patient weighing 90 kg is prescribed ethambutol 2200 mg daily. Given the dosing range of 15-25 mg/kg/day, this dose is:

A 61-year-old patient weighing 90 kg is prescribed ethambutol 2200 mg daily. Given the dosing range of 15-25 mg/kg/day, this dose is:

• A. At the low end
• B. At the middle
• C. Above the range
• D. At the high end of the range

Answer: (D)

Dosing ethambutol is done in mg per kilogram of body weight per day, so you convert the daily amount to mg/kg to see where it falls. For this patient: 2200 mg per day divided by 90 kg equals about 24.4 mg/kg/day. The stated dosing range is 15–25 mg/kg/day, so 24.4 mg/kg/day is within the range and near the upper limit. In fact, the maximum daily dose for this patient would be 25 mg/kg/day × 90 kg = 2250 mg, so 2200 mg is just under that top value. This is why it’s described as at the high end of the range. Clinically, dosing stays within this upper range to balance efficacy with the risk of adverse effects, such as optic neuritis, which is monitored during therapy.

Dosing ethambutol is done in mg per kilogram of body weight per day, so you convert the daily amount to mg/kg to see where it falls.

For this patient: 2200 mg per day divided by 90 kg equals about 24.4 mg/kg/day. The stated dosing range is 15–25 mg/kg/day, so 24.4 mg/kg/day is within the range and near the upper limit. In fact, the maximum daily dose for this patient would be 25 mg/kg/day × 90 kg = 2250 mg, so 2200 mg is just under that top value. This is why it’s described as at the high end of the range. Clinically, dosing stays within this upper range to balance efficacy with the risk of adverse effects, such as optic neuritis, which is monitored during therapy.