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Laxative phosphate poisoning: pharmacokinetics of serum phosphorus
Insights
Acute phosphate poisoning in children from laxatives is common. This study provides a nomogram to predict phosphorus decline and a formula to calculate recovery time, aiding treatment decisions.
Area of Science:
- Pediatric Toxicology
- Clinical Pharmacology
- Nephrology
Background:
- Acute poisoning from phosphosoda laxatives in children presents a frequent clinical challenge.
- Understanding phosphorus clearance and therapeutic strategies for hyperphosphatemia in pediatric poisoning remains incomplete.
Observation:
- Pharmacokinetic analysis of plasma inorganic phosphate (Pi) was performed in an infant and four other reported cases of phosphosoda laxative poisoning.
- Plasma Pi levels at diagnosis ranged from 4-20 mmol/l with a half-life of 5-11 hours, independent of therapy.
Findings:
- A nomogram was developed to predict the decline of plasma Pi in pediatric phosphate poisoning.
- Pi clearance is exponential and correlates with glomerular filtration rate.
- A formula, t = (ln 5/Pi)/0.1292, calculates the time for plasma Pi to normalize.
Implications:
- Neuromuscular and cardiac complications are linked to hypocalcemia during phosphate poisoning.
- Intravenous calcium salt administration accelerates serum calcium normalization.
- Sustained intravenous calcium therapy may be necessary due to delayed serum calcium restoration.
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. Pharmacokinetic analysis has been made of plasma inorganic phosphate (Pi) 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 Pi in paediatric phosphate poisoning. Clearance of Pi is exponential; it directly correlates with and approaches the glomerular filtration rate. After single oral or rectal overdoses, plasma Pi at diagnosis is 4-20 mmol/l 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 = (ln 5/Pi)/0.1292. 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.