Dosing of antimicrobials in obesity

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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
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
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

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)

Further Reading

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