Drug Dosing in Obesity Reference Table

An evidence-based drug dosing resource

Dosing weight-based medications in obese patients can often be a tricky proposition. Most medications do not have guidelines for morbidly obesity, forcing clinicians to pursue in-depth literature searches in order to decide on a dose.

The purpose of this page is to serve as a dynamic, growing repository of evidence-based recommendations regarding medication dosing in obese patients. I would encourage you to examine each medication's cited references in order to form your own conclusions. As always, reasonable clinical judgment is required in conjunction with this information.

Lastly, if you have primary literature regarding obesity dosing for a medication that is not listed on this table, please contact me with the drug name and citation and I would be happy to add it to the list.

Drug Comments
A
Acyclovir 1
Amikacin 2
Atracurium 3
  • Dose using ideal body weight
  • The use of ideal body weight has been shown to be associated with a more predictable muscle strength recovery within 60 minutes and a lack of need for antagonism compared to total body weight
C
Colistin 4
  • Dose using ideal body weight
D
Dalteparin 5
  • Dose using total body weight
  • VTE prophylaxis: if BMI ≥ 40 mg/m2 increase dose by 30%
  • VTE treatment: once-daily dosing (200 units/kg daily) probably okay (unlike enoxaparin)
  • Anti-Xa level monitoring probably not necessary unless weight > 190 kg
Daptomycin 6,2
  • Dose using total body weight
Digoxin 7
Dobutamine 8
  • No kinetic data has been published -- titrate to goal MAP
Dopamine 8
  • No kinetic data has been published -- titrate to goal MAP
E
Enoxaparin 5
  • Dose using total body weight
  • VTE prophylaxis: if BMI ≥ 40 mg/m2 increase dose by 30%
  • VTE treatment: avoid once-daily dosing if BMI > 27 kg/m2 (eg, do not use 1.5 mg/kg daily)
  • Anti-Xa level monitoring probably not necessary unless weight > 190 kg
Epinephrine 8
  • No kinetic data has been published -- titrate to goal MAP
F
Fondaparinux 9
  • VTE prophylaxis: use standard dosing (2.5 mg daily)
  • In a study of patients with BMI > 40 kg/m2, 53% of patients of patients had anti-Xa levels were within or above target range
G
Gentamicin 2
H
Heparin (unfractionated)

10,11,12

  • Dose using adjusted body weight (preferred), ideal body weight, or actual body weight with a dosing cap
  • Studies have shown that using actual body weight (without a dose cap) is associated with a higher aPTT value
  • Heparin infusions should be titrated to an aPTT goal (usually every 6-8 hours until stable)
I
Immunoglobulin (IVIG) 13
  • Consider dosing using ideal body weight or adjusted body weight
  • Overall, there is a lack of data to support using a specific body weight metric -- these recommendations are based only on expert opinion
L
Levothyroxine

14

Linezolid

15

  • No dosing change for obesity is required
  • In a study of 20 obese patients, linezolid exposure (AUC) was no different between obese and non-obese patients
Lorazepam 16
  • For bolus doses, use total body weight
  • For continuous infusions, use ideal body weight
  • In obese patients, lorazepam volume of distribution increases proportionally to body weight. Therefore, doses based on total body weight are required to reach the same initial serum concentration
  • Once at goal sedation, continuous infusions should use ideal body weight because lorazepam clearance is not affected by total body weight.
M
Methylprednisolone

17

  • Dose using ideal body weight and consider less frequent dosing
  • In a study of 6 obese and non-obese patients, methylprednisolone volume of distribution was unaffected by body size, but clearance was significantly reduced in patients with obesity
Midazolam 16
  • For bolus doses, use total body weight
  • For continuous infusions, use ideal body weight
  • In obese patients, midazolam volume of distribution increases proportionally to body weight. Therefore, doses based on total body weight are required to reach the same initial serum concentration
  • Once at goal sedation, continuous infusions should use ideal body weight because midazolam clearance is not affected by total body weight.
N
Norepinephrine 8
  • No kinetic data has been published -- titrate to goal MAP
O
Oseltamivir 18,19
  • Use standard dosing (no adjustment for obesity)
P
Phenytoin 20,8
  • For loading doses, use the following equation for dosing weight: Dosing weight = Ideal + 1.33 * (Actual - Ideal)
  • Ideal body weight is calculated using the Devine equation
  • Obese patients will require more than their actual body weight for a phenytoin loading dose
Propofol 16
  • Dose using total body weight
  • For continuous infusions, titrate drip to desired sedation goal
  • Note that the cardiovascular effects of large propofol doses (hypotension) are poorly described and may be problematic
R
Rasburicase 21
  • Body weight does not strongly correlate to reduction in uric acid levels
  • Consider fixed, single doses irrespective of body weight
Remifentanil

22,2,8

Rocuronium 23
S
Succinylcholine

16,24

  • Dose using total body weight
  • Obese patients may have increased pseudocholinesterase activity, which metabolizes succinycholine
  • This recommendation is only based on expert opinion -- there is nearly no compelling evidence
T
Tigecycline 25
  • Drug pharmacokinetics are not impacted by obesity
Tinzaparin 5
  • Dose using total body weight
  • VTE prophylaxis: if BMI ≥ 40 mg/m2 increase dose by 30%
  • VTE treatment: once-daily dosing (175 units/kg daily) probably okay (unlike enoxaparin)
  • Anti-Xa level monitoring probably not necessary unless weight > 190 kg
Tobramycin 2
V
Vancomycin 2,26
  • Dose using toal body weight
  • Vancomycin dose should be adjusted based on vancomycin trough levels once at steady state (usually 3-4 doses)
Vecuronium 16
  • Dose using ideal body weight
  • Although volume of distribution and clearance are unchanged in obese patients, doses using actual body weight may have prolonged neuromuscular blockade.
Voriconazole 27
  • Dose using lean body weight (LBW 2005 equation)
  • LBW2005 correlates to AUC better than total body weight, although both are poor predictors of voriconazole levels due to a high degree of interpatient variability (R2 < 0.50)
  • Voriconazole dose should be adjusted based on voriconazole trough levels once at steady state (usually 5-7 days of therapy)
W
Warfarin 28
  • Hospitalized obese patients had a higher discharge warfarin dose versus non-obese patients (6.7 ± 0.7 vs. 4.4 ± 0.5 mg per day) and had a longer median time to therapeutic INR (10 vs. 6 days)

About This Calculator

Ideal Body Weight (Devine 1974) 29

Although this equation lacks scientific basis, its easy of use at the bedside and extensive use for a variety of medical applications has made it the standard method for estimating lean body mass. Note that you may use the Ideal Body Weight online calculator, or use the equations below:

$$ \\Ideal\;BW\;(men)\; = 50 + 2.3*(height\;over\;60\;inches) \\Ideal\;BW\;(women)\; = 45.5 + 2.3*(height\;over\;60\;inches)$$

Lean Body Weight (LBW2005) 30

LBW2005 is an accurate, validated method of measuring the lean mass of an obese patient. The equation is less commonly used than the Devine 1974 equation,29 but is more accurate. Note that you may use the LBW2005 online calculator, or use the equations below:

$$ \\ LBW2005\;(men) = \frac{9.27*10^3*ActualBW}{6.68*10^3+(216*BMI)} \\ LBW2005\;(women) = \frac{9.27*10^3*ActualBW}{8.78*10^3+(244*BMI)}$$

Adjusted body weight

In obese patients, the use of ideal body weight underdoses patients, but the use of actual body weight overdoses patients. With these circumstances, an adjustment factor (usually 40%) is often used to estimate the proportion of adipose tissue that distributes a given medication. Note that you may use the adjusted body weight online calculator, or use the equations below:

$$ \\AdjustedBW\; = IdealBW + (0.4*(ActualBW - IdealBW))$$

References and Additional Reading

  1. Acyclovir [package insert]. Bedford (OH): Bedford Laboratories; 2005. DailyMed Monograph.
  2. Pai MP, Bearden DT. Antimicrobial dosing considerations in obese adult patients. Pharmacotherapy. 2007;27(8):1081-91. PMID 17655508.
  3. van Kralingen S, van de Garde EM, Knibbe CA, et al. Comparative evaluation of atracurium dosed on ideal body weight vs. total body weight in morbidly obese patients. Br J Clin Pharmacol. 2011;71(1):34-40. PMID 21143499.
  4. Garonzik SM, Li J, Thamlikitkul V, et al. Population pharmacokinetics of colistin methanesulfonate and formed colistin in critically ill patients from a multicenter study provide dosing suggestions for various categories of patients. Antimicrob Agents Chemother. 2011 Jul;55(7):3284-94. PMID 21555763.
  5. Nutescu EA, Spinler SA, Wittkowsky A, et al. Low-molecular-weight heparins in renal impairment and obesity: available evidence and clinical practice recommendations across medical and surgical settings. Ann Pharmacother. 2009;43(6):1064-83. PMID 19458109.
  6. Dvorchik BH, Damphousse D. The pharmacokinetics of daptomycin in moderately obese, morbidly obese, and matched nonobese subjects. J Clin Pharmacol. 2005;45(1):48-56. PMID 15601805.
  7. Abernethy DR, Greenblatt DJ, Smith TW. Digoxin disposition in obesity: clinical pharmacokinetic investigation. Am Heart J. 1981;102(4):740-4. PMID 7282520.
  8. Erstad BL. Dosing of medications in morbidly obese patients in the intensive care unit setting. Intensive Care Med. 2004;30(1):18-32. PMID 14625670.
  9. Martinez L, Burnett A, Borrego M, et al. Effect of fondaparinux prophylaxis on anti-factor Xa concentrations in patients with morbid obesity. Am J Health Syst Pharm. 2011;68(18):1716-22. PMID 21880887.
  10. Barletta JF, DeYoung JL, McAllen K, et al. Limitations of a standardized weight-based nomogram for heparin dosing in patients with morbid obesity. Surg Obes Relat Dis. 2008;4(6):748-53. PMID 18586569.
  11. Yee WP, Norton LL. Optimal weight base for a weight-based heparin dosing protocol. Am J Health Syst Pharm. 1998;55(2):159-62. PMID 9465981.
  12. Myzienski AE, Lutz MF, Smythe MA. Unfractionated heparin dosing for venous thromboembolism in morbidly obese patients: case report and review of the literature. Pharmacotherapy. 2010;30(3):324. PMID 20180615.
  13. UK Department of Health. Clinical Guidelines for Immunoglobulin Use. 2nd ed, updated 15 November 2011. Available at GOV.UK.
  14. Santini F, Pinchera A, Marsili A, et al. Lean body mass is a major determinant of levothyroxine dosage in the treatment of thyroid diseases. J Clin Endocrinol Metab. 2005 Jan;90(1):124-7. PMID 15483074.
  15. Bhalodi AA, Papasavas PK, Tishler DS, et al. Pharmacokinetics of intravenous linezolid in moderately to morbidly obese adults. Antimicrob Agents Chemother. 2013;57(3):1144-9. PMID 23254421.
  16. Casati A, Putzu M. Anesthesia in the obese patient: pharmacokinetic considerations. J Clin Anesth. 2005;17(2):134-45. PMID 15809132.
  17. Dunn TE, Ludwig EA, Slaughter RL, et al. Pharmacokinetics and pharmacodynamics of methylprednisolone in obesity. Clin Pharmacol Ther. 1991;49(5):536-49. PMID 1827621.
  18. Thorne-Humphrey LM, Goralski KB, Slayter KL, et al. Oseltamivir pharmacokinetics in morbid obesity (OPTIMO trial). J Antimicrob Chemother. 2011;66(9):2083-91. PMID 21700623.
  19. Pai MP, Lodise TP Jr. Oseltamivir and oseltamivir carboxylate pharmacokinetics in obese adults: dose modification for weight is not necessary. Antimicrob Agents Chemother. 2011;55(12):5640-5. PMID 21930881.
  20. Abernethy DR, Greenblatt DJ. Phenytoin disposition in obesity. Determination of loading dose. Arch Neurol. 1985;42(5):468-71. PMID 3994563.
  21. Trifilio SM, Pi J, Zook J, et al. Effectiveness of a single 3-mg rasburicase dose for the management of hyperuricemia in patients with hematological malignancies. Bone Marrow Transplant. 2011;46(6):800-5. PMID 20818444.
  22. Egan TD, Huizinga B, Gupta SK, et al. Remifentanil pharmacokinetics in obese versus lean patients. Anesthesiology. 1998;89(3):562-73. PMID 9743391.
  23. Meyhoff CS, Lund J, Jenstrup MT, et al. Should dosing of rocuronium in obese patients be based on ideal or corrected body weight? Anesth Analg. 2009;109(3):787-92. PMID 19690247.
  24. Lemmens HJ, Brodsky JB. The dose of succinylcholine in morbid obesity. Anesth Analg. 2006;102(2):438-42. PMID 16428539.
  25. Pai MP. Serum and urine pharmacokinetics of tigecycline in obese class III and normal weight adults. J Antimicrob Chemother. 2014 Jan;69(1):190-9. PMID 23883872.
  26. Rybak MJ, Lomaestro BM, Rotschafer JC, et al. Therapeutic monitoring of vancomycin in adults summary of consensus recommendations from the American Society of Health-System Pharmacists, the Infectious Diseases Society of America, and the Society of Infectious Diseases Pharmacists. Pharmacotherapy. 2009;29(11):1275-9. PMID 19873687.
  27. Pai MP, Lodise TP. Steady-state plasma pharmacokinetics of oral voriconazole in obese adults. Antimicrob Agents Chemother. 2011;55(6):2601-5. PMID 21422207.
  28. Wallace JL, Reaves AB, Tolley EA, et al. Comparison of initial warfarin response in obese patients versus non-obese patients. J Thromb Thrombolysis. 2013 Jul;36(1):96-101. PMID 23015280.
  29. Devine BJ. Gentamicin therapy. Drug Intell Clin Pharm. 1974;8:650–655.
  30. Janmahasatian S, Duffull SB, Ash S, et al. Quantification of lean bodyweight. Clin Pharmacokinet. 2005;44(10):1051-65. PMID 16176118.

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