Lower body weight and female gender: Hyperphosphatemia risk factors after sodium phosphate preparations

Casais et al have reported an inverse correlation between serum phosphate and body weight after administration of sodium phosphate at a dose of 60 g. Our group has already described the relationship between body weight and hyperphosphatemia with these preparations, although our study was not quoted by Casais. We performed a pharmacokinetic study involving 13 volunteers who were divided into two groups on the basis of body weight: group I consisting of seven women with a median weight of 60 kg and group II consisting of five men and one woman with a median weight of 119.2 kg. Group I developed higher peak phosphate levels and maintained these levels above the subjects in Group II for a prolonged time period despite adequate hydration being ensured with frequent monitoring of weight, fluid intake and total body weight. Our study demonstrated that adequate hydration does not protect against the secondary effects of hyperphosphatemia. In the study by Casais et al, 66% of the study subjects were women, the correlation between serum phosphate and gender in their data also appears to be important. Women are at higher risk of acute phosphate nephropathy due to a diminished volume of distribution of the high dose of ingested phosphate. Decreased volume of distribution in women is due to diminished body weight. This is further compounded by decreased creatinine clearance in females.