Dosing of antimicrobials in obesity

Calculating Body Weight

Statistic	Equation (Male)	Equation (Female)	Notes
Body mass index (BMI) (kg/m²)	weight, kg / (height, m)²
Body surface area (BSA) (m²)	(height, cm × weight, kg / 3600)^1/2
Ideal body weight (IBW) (kg)	50 + 2.3 × (inches over 5 ft)	45.5 + 2.3 × (inches over 5 ft)
Adjusted body weight (ABW) (kg)	IBW + C × (TBW - IBW)		C = 0.3 to 0.4
Lean body weight (LBW) (kg)	9270 × TBW / 6680 + 216 x BMI	9270 × TBW / 8780 + 244 x BMI
Fat-free weight (FFW) (kg)	0.00139 × (height, cm)² - 0.0801 × R + 0.187 × TBW + 39.83	0.00151 × (height, cm)² - 0.0344 × R + 0.14 × TBW - (0.158 × age) + 20.387	R = resistance

Drug	Usual Dose	Obesity	Max dose
Amoxicillin		1 g PO q8h	No data
Ampicillin		2 g IV q4h
Nafcillin		2 g IV q4h	No data
Piperacillin-tazobactam	4.5 g IV q6-8h	Prolonged infusion	18 g daily

Drug	Usual Dose	Obesity	Max dose
Cefazolin	1-2 g IV q8h	2-3 g IV q6-8h	No data; 12 g daily
Cephalexin	500-1000 g PO qid	1000 g PO qid	No data
Cefipime	2 g IV q8h	2 g IV q8h prolonged infusion	2 g IV q8h prolonged infusion
Ceftazidime	2 g IV q8h	2 g IV q8h prolonged infusion	2 g IV q8h prolonged infusion
Ceftazidime-avibactam		Usual dose
Ceftolozane-tazobactam		Usual dose

Drug	Usual Dose	Obesity
Doripenem		Consider extended infusion
Ertapenem	1 g IV q24h	Usual dose
Imipenem
Meropenem		Consider prolonged infusion

Drug	Usual Dose	Obesity
Ciprofloxacin	500-750 mg PO q12h or 400 mg IV q6-8h	400 mg IV q8h or 750 mg PO q12h
Levofloxacin	750 mg PO q24h	Consider up to 1000 mg PO q24h
Moxifloxacin		Usual dose

Drug	Usual Dose	Obesity	Max dose

Drug	Usual Dose	Obesity	Max dose

Drug	Obesity	Max dose
Aztreonam	2 g IV q6-8h
Colistin	Use IBW	360 mg daily (nephrotoxicity)
Polymyxin B	Use ABW_0/4	200 mg or 2 MU daily (toxicity)