Alternate day infusion of calcium and phosphate in very low birth weight infants: wasting of the infused mineral.

ABSTRACT

Very low birth weight infants require greater intakes of calcium and phosphate than can be supplied simultaneously in parenteral nutrition. We investigated the biochemical effects and retention of calcium and phosphate when each was administered for 24 h on an alternate day schedule as part of total parenteral nutrition. Serum and urine were collected during a 24 h basal period and during randomly ordered 24 h infusions of either calcium or phosphate in 14 infants during the first week of life. In general, the urinary excretion of the infused mineral (calcium or phosphorus) increased during the 24 h period of its infusion. The serum phosphorus level fluctuated widely from day to day while the serum calcium level did not change. During the 24 h infusion of phosphate, phosphate retention was 67.9 +/- 7.4% and, during the 24 h infusion of calcium, calcium retention was 72.5 +/- 4.3%. However, ongoing excretion of each mineral on the day it was not infused meant that 48.3% of the 48 h phosphate intake and 42.2% of the 48 h calcium intake were lost in the urine. We conclude that excessive amounts of the administered mineral were excreted and that alternate day infusion of calcium and phosphate is an unsatisfactory method for providing these minerals. Attainment of sufficient retentions of calcium and phosphate will require development of novel methods of simultaneous administration which provide calcium and phosphate in high concentrations.