For gentamicin and tobramycin, trough levels should be < 1 mcg / mL (< 2.09 micromol / L for gentamicin and < 2.14 micromol / L for tobramycin) at 18 to 24 hours after the first dose with once / day dosing and between 1 and 2 mcg / mL (between 2.09 and 4.18 micromol / L for gentamicin and between 2.14 and 4.28 micromol / L for tobramycin) with traditional intermittent dosing.