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

Penicillins

Drug	Usual Dose	Obesity	Max dose
Amoxicillin		1 g PO q8h	No data
Ampicillin		2 g IV q4h

Cephalosporins

Drug	Usual Dose	Obesity	Max dose
Cefazolin	1-2 g IV q8h	2-3 g IV q6-8h	No data; 12 g daily

Further Reading

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