Tailoring treatment: patients who are obese

Last updated: Tuesday, June 20, 2017

Question
You are covering the acute medical admissions unit and you’re asked by a registrar about the dose of chloramphenicol in a patient with severe community acquired pneumonia. He would normally prescribe 1 gram four times a day according to the hospital guidelines but the patient is 178 kg. Does the dose need to be adjusted in view of the patient’s weight?

Outcome
After a quick check of your hospital guidelines and the patient’s medical history you are reassured that chloramphenicol is a suitable antibiotic. You then search your general and specialist resources but they have no guidance specifically for dosing chloramphenicol in patients who are obese. You turn to your medicines information pharmacist who points you towards some theoretical considerations around antibiotic dosing in obesity.

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You look at the pharmacokinetic profile of chloramphenicol and establish that it might be expected to have a higher volume of distribution compared to a patient of a healthy weight, but that it’s not an exact science. Discussing your findings with your microbiology pharmacist, you conclude that this ultimately is a balance of risk versus benefit. If you use 1 gram four times a day as per the hospital policy there is a risk that the patient will be under-dosed and not respond to treatment. If you use a higher dose the patient’s pneumonia may be treated effectively but they may be at an increased risk of side effects. In the absence of any guidance, together you decide that since the dose of chloramphenicol may be doubled in severe infections that it would be reasonable to use 2 grams four times a day for this specific patient, reviewing and reducing the dose as they improve. Your hospital pathology department is also able to process chloramphenicol blood samples and so you advise the registrar that therapeutic drug monitoring may be prudent.