January 21, 2015
Extreme Obesity Affects How Some Drugs Are
Distributed, Eliminated 

Leiden, The Netherlands—Extreme obesity is rarely taken into account when prescribing and dispensing medications, according to a new Dutch study, but that oversight could have detrimental effects.

The article, published recently in the journal Annual Review of Pharmacology and Toxicology, argues that more information is needed on how obesity affects the distribution and elimination of drugs.

Lead author Catherijne Knibbe of Leiden University points out that, as a rule, patients with extreme obesity require individualized dosing because of the physical changes they have undergone.

The study notes that obesity can lead to an enlarged heart, wider blood vessels, and a larger blood volume. That, in turn, can lead to effects such as an increase in blood flow through the liver, which can hasten the elimination rate of certain drugs. Altered body composition in the obese also might lead to a significantly different distribution of the drug throughout the body.

“Obese patients are often prescribed a standard drug dose, or doctors and pharmacists tend to automatically assume that these people need a higher dose,” Knibbe said. “However, that is not necessarily the case. Moreover, a higher dose can also be harmful. For example, obese people are more likely to suffer from sleep apnea: they do not breathe well when they sleep. We have to think carefully before giving these patients a higher dose of sedatives or morphine.”

Knibbe, a clinical pharmacologist, said she does research at St. Antonius Hospital in Nieuwegein, Utrecht, to gain insight into how drugs are distributed and eliminated from obese patients.

After administering the usual dose, blood samples are taken from the patient to help derive the optimal dosage.

As an example, Knibbe mentions a study she conducted with the drug cefazolin, an antibiotic that is prescribed to prevent wound infections. The standard dose is 2 grams, which was administered to normal weight patients and to obese patients.

The concentration of the drug in the blood did not differ significantly between the two groups. In the skin, however, where wound infections are likely to occur, the concentration of the drug was more than 30% lower in obese patients than in nonobese patients, she said, adding, “This means that a standard dose of this drug may potentially be less effective in these patients.”

U.S. Pharmacist Social Connect