Pharmacokinetics of ranitidine in morbidly obese women

The pharmacokinetics of a single dose of ranitidine 50 mg iv were determined in ten normal-weight and ten morbidly obese (greater than 90 percent ideal body weight) age-matched female subjects. No significant difference between normal and obese subjects was found in ranitidine peak serum concentration, volume of distribution, clearance, and elimination rate constant. Ranitidine volume of distribution and clearance were significantly smaller in the obese subjects per kilogram of total body weight (1.45 vs. 0.80 L/kg and 0.59 vs. 0.33 L/h/kg, respectively; p less than 0.001) but not when normalized to ideal body weight (1.65 vs. 1.45 L/kg and 0.68 vs. 0.59 L/h/kg). We conclude that obese patients receiving ranitidine therapy should be treated with standard dosages or dosages based on ideal body weight.