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

Antibiotics

β-lactams

Penicillins

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

Cephalosporins

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

Carbapenems

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

Quinolones

Drug	Usual Dose	Obesity	Max dose
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

Macrolides

Drug	Usual Dose	Obesity	Max dose

Tetracyclines

Drug	Usual Dose	Obesity	Max dose

Aminoglycosides

Drug	Usual Dose	Obesity	Max dose
Amikacin		Use ABW0.4
Gentamicin		Use ABW0.4
Tobramycin		Use ABW0.4

Others

Drug	Usual Dose	Obesity	Max dose
Aztreonam		2 g IV q6-8h
Colistin		Use IBW	360 mg daily (nephrotoxicity)
Polymyxin B		Use ABW0/4	200 mg or 2 MU daily (toxicity)
Ceftaroline		Consider 18h
Clindamycin		600 mg IV q6h 900 mg IV q8h 450-600 mg PO q6h 600-900 mg PO q8h	2700 mg daily; or 4800 mg daily IV if life-threatening
Dalbavancin		Usual dose
Daptomycin		Use ABW0.4
Linezolid	600 mg PO/IV q12h	Usual dose
Oritavancin		Usual dose
Cotrimoxazole	Up to 320 mg(TMP) PO q12h 8-10 mg(TMP)/kgABW in divided doses	Consider ABW0.4 when doing high dose
Telavancin		Usual dose
Tigecycline		Usual dose
Vancomycin	20-25 mg/kg load (max 2.5 g) 10-15 mg/kg q12h (maintenance)	Use TBW; or 25-30 mg/kg load and 15 mg/kg q12h with ABW0.4

Further Reading

• Comprehensive Guidance for Antibiotic Dosing in Obese Adults. Pharmacotherapy. 2017;37(11):1415-1431. doi: 10.1002/phar.2023