Drug Dosing: Obese Patients

A person exceeding the ideal body weight, IBW, by 20% is considered obese. It can be calculated using the following equations.

Typically, obesity is defined by the body mass index, which correlates strongly with total body fat.

Obesity can lead to hypertension, atherosclerosis, and coronary artery disease, all of which increase mortality rates.

Obese patients with excess body fat will have a smaller proportion of total body water, influencing the apparent volume of drug distribution.

Dosing in obese patients depends on the type of drug being administered.

For instance, polar drugs, such as gentamicin, distribute more into lean tissue than into adipose tissue. These drugs should be dosed based on IBW to avoid overdosing.

In contrast, non-polar drugs such as diazepam are distributed more in adipose tissues than lean tissues, necessitating larger doses based on total body weight.

Some amphiphilic drugs like lidocaine, which distribute equally in lean and adipose tissues, are dosed based on the patient’s total body weight.