At last week’s HNE northern ICU antimicrobial stewardship teleconference, discussion centred around how to dose a large patient. eTG indicates that actual body weight is used to calculate the dosage. Edition 15 also brings in a routine recommendation for a single loading dose of vancomycin- 25-30mg/kg in those with sepsis. There were misgivings about using an actual body weight (250kg!) to arrive at the dose. I referred the issue to Hunter Drug Information Service (HDIS) and to the eTG reviewer who dealt with the vancomycin dosing (Jason Roberts) for their views.
From HDIS (Ms Felicity Prior, pharmacist, Director HDIS and Dr Ian Whyte, clinical pharmacologist)
It appears that total body weight (TBW) is used for calculating such doses, and I attach a paper that you might be interested in (abstract below). Ian would not be unhappy in giving such a large dose as 6.25 g. However there may be some issues with administration (calculated to be given over 10.4 hours!).
TCIWorks® does include a model for vancomycin which we have been keen to validate, but we’ve been unable to get any patient data to date. If you are able to provide us with the patient’s MRN we are happy to use the dose prediction program to monitor their progress and provide dose adjustments.
From Jason Roberts (eTG, edition 15 reviewer/contributor)
In practice , we use total body weight dosing all the time for vancomycin (the only antibiotic where it really applies in obesity) and in this person I would have used 30mg/kg probably as an 8-hour infusion.
The PK supports it and it works. I have never observed any nephrotoxicity in these patients either.
Altered vancomycin pharmacokinetics in obese and morbidly obese
patients: what we have learned over the past 30 years. J Antimicrob Chemother 2012; 67: 1305–1310 Abstract-
Vancomycin was the first glycopeptide antibiotic introduced into clinical practice. Despite the numerous benefits of vancomycin, clinicians have struggled to dose vancomycin successfully in obese patients to achieve a therapeutic concentration for optimal bacterial killing. Owing to the hydrophilicity of vancomycin and the increase in both adipose tissue and muscle mass associated with obesity, the volume of distribution of vancomycin
in obese patients is likely to be altered compared with non-obese patients. In addition to an increase in body mass, obesity is associated with an increase in certain circulating proteins, which results in altered free serum vancomycin concentration. Another alteration that occurs in obesity is increased blood flow secondary to increased cardiac output and blood volume, resulting in increased vancomycin clearance in obese patients. Vancomycin pharmacokinetics in the obese population remain an area of much debate, one that requires continued research given the rising number of obese patients in both the USA and worldwide.