Dosing of antimicrobials in obesity

From IDWiki

Calculating Body Weight

Weight-based dosing can use total body weight (TBW) in some instances, but often requires adjustments.

Statistic Equation Notes
Body mass index (BMI) (kg/m2) kg and m
Body surface area (BSA) (m2) kg and cm
Ideal body weight (IBW) (kg) male: Failed to parse (unknown function "\small"): {\displaystyle 50 + 2.3 \times \small{\text{(inches over 5 ft)}}} in inches
female: Failed to parse (unknown function "\small"): {\displaystyle 45.5 + 2.3 \times \small{\text{(inches over 5 ft)}}}
Adjusted body weight (ABW) (kg) C = 0.3 to 0.4
Lean body weight (LBW) (kg) male:
female:

Calculating CrCl

Salazer-Cocoran equation is more reliable in obesity but requires both height and weight.

Antibiotics

β-lactams

Penicillins

Drug Usual Dose Obesity Notes
Amoxicillin 250-500 mg q8h 1 g PO q8h
Ampicillin 1-2 g q4-6h 2 g IV q4h
Nafcillin 2 g IV q4h
Piperacillin-tazobactam 4.5 g IV q8h (q6h for Pseudomonas) Prolonged infusion

Cephalosporins

Drug Usual Dose Obesity Notes
Cephalexin 500-1000 g PO qid 1000 g PO qid
Cefazolin 1-2 g IV q8h 2-3 g IV q6-8h once ≥120 kg
Cefipime 2 g IV q8h 2 g IV q8h prolonged infusion
Ceftazidime 1-2 g IV q8h 2 g IV q8h prolonged infusion
Ceftazidime-avibactam Usual dose
Ceftolozane-tazobactam Usual dose
Ceftaroline Consider q8h

Carbapenems

Drug Usual Dose Obesity Notes
Doripenem Consider extended infusion
Ertapenem 1 g IV q24h Usual dose
Imipenem Usual dose
Meropenem 500 mg q6h (1 g IV q8h for febrile neutropenia) Consider prolonged infusion

Quinolones

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

Macrolides

Drug Usual Dose Obesity Notes

Tetracyclines

Drug Usual Dose Obesity Notes

Aminoglycosides

Drug Usual Dose Obesity Notes
Amikacin 15 mg/kg Use ABW0.4 Use Hartford nomogram with a (halved) random level
Gentamicin 7 mg/kg Use ABW0.4 Use Hartford nomogram with a random level
Tobramycin 7 mg/kg Use ABW0.4 Use Hartford nomogram with a random level

Others

Drug Usual Dose Obesity Notes
Aztreonam 2 g IV q6-8h
Colistin 5 mg CBA/kg IBW x1 loading (max 300 mg) followed by 5 mg/kg/day divided q8h Use IBW Max 360 mg daily (nephrotoxicity)
Polymyxin B Use ABW0/4 Max 200 mg or 2 MU daily (toxicity)
Clindamycin 300-450 mg PO q6-8h
600-900 mg IV q8h
600 mg IV q6h
900 mg IV q8h
450-600 mg PO q6h
600-900 mg PO q8h
Max 2700 mg daily, or 4800 mg daily IV if life-threatening
Dalbavancin Usual dose
Daptomycin 4-6 mg/kg q24h Use ABW0.4
Linezolid 600 mg PO/IV q12h Usual dose
Oritavancin Usual dose
TMP-SMX 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