Abstract
Despite the frequency of acute poisoning in normal children by oral or rectal phosphosoda laxatives, the rate of clearance of the resultant high level of phosphorus and the rationale for therapy are defined incompletely.
1 Pharmacokinetic analysis has been made of plasma inorganic phosphate (P i) in an infant after ingestion of phosphosoda laxative and of data reported for four comparable poisonings in healthy infants to provide a nomogram which predicts the decline in P i in paediatric phosphate poisoning.
2 Clearance of Pi is exponential; it directly correlates with and approaches the glomerular filtration rate.
3 After single oral or rectal overdoses, plasma Pi at diagnosis is 4-20 mmoul and has a half-life of 5-11 h that appears independent of therapy. The time for plasma Pi to return to normal can be calculated from the initial Pi as t = (In 5/P i )/0.1292.
4 Neuromuscular and cardiac abnormalities relate to the low serum calcium; the increase of total serum calcium during recovery from phosphate poisoning is linear but is accelerated by intravenous (i.v.) calcium salt. Continued i.v. calcium therapy may be required since restoration of plasma calcium is often delayed.
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