Hyperphosphataemia and Hypocalcaemia Induced by Hypertonic Phosphate Enema - An Experimental Study and Review of the Literature

Abstract

1 The study objective was to determine the hyperphosphataemic and hypocalcaemic effect of hypertonic phosphate enema. The study was conducted in a department of Internal Medicine at a University Medical Center.

2 Fourteen patients were studied. Patients' mean age (± s.d.) was 78.5 ± 9 years. The creatinine clearance was 48.2 ± 17.4 ml min^-1 (mean ± s.d.).

3 500 ml (approx. 7 ml kg^-1) of Fleet enema (FE - Na₂HPO₄.7H ₂O 224 mmol l^-1 and NaH₂PO₄.H ₂O 1160 mmol l^-1) were administered to each patient. Blood was drawn before FE administration and ½, 1, 3, 5, 12 and 24 h thereafter. Serum was analysed for levels of inorganic phosphorus and for calcium.

4 The serum inorganic phosphorus level rose from 1.01 ± 0.3 mmol l^-1 to 1.4 ± 0.5 mmol l^-1 (P = 0.001) 1 h after FE was administered. Serum calcium decreased from 2.32 ± 0.12 mmol l^-1 to 2.12 ± 0.1 mmol l^-1 ( P < 0.001) 12 h after FE was administered.

5 We conclude that FE carries a potential risk for acutely ill elderly patients. To avoid untoward effects due to hyperphosphataemia and hypocalcaemia, the phosphate load must be adjusted to the patient's renal function, i.e. enema volume is to be lowered when phosphate concentration is high, so that if renal function is compromised the amount of phosphate absorbed does not exceed renal excretion capacity.