If TBW is greater than 120% of IBW, adjusted body weight (ABW) should be used to calculate doses: IBW in kg (males): 50 + (2.3 × inches above 60 inches) IBW in kg (females): 45.5 + (2.3 × inches above 60 inches) ABW in kg: IBW + [0.4 × (TBW - IBW)] In patients with normal renal function, once / day dosing is Gentamicin or tobramycin: 5 mg / kg (7 mg / kg if patients are critically ill) every 24 hours Amikacin: 15 mg / kg every 24 hours If patients respond to the 7-mg / kg dose of gentamicin or tobramycin clinically and renal function continues to be normal, the once / day dose can be reduced to 5 mg / kg after the first few days of treatment.