The temporal relation between soluble paracetamol administration and the development of hypernatremia, in the presence of stable renal function, suggests that our patient may have incurred soluble paracetamol-induced hypernatremia.
Elderly patients constitute a high percentage of the total inpatient population. Renal function in older people usually falls with increasing age, compromising the handling of solutes and electrolytes by the kidneys . Hypernatremia, defined as a serum sodium concentration over 145 mmol/L, is associated with a high mortality in elderly people (42-75%), especially when acquired acutely in hospital -. Morbidity in survivors is high, with neurological deficits if hypernatremia is severe. It is therefore of paramount importance for health-care professionals to recognise, prevent, and treat the cause of hypernatremia early.
High sodium intake has been an especial cause of concern in the elderly, as chronic excess sodium intake has been positively linked with hypertension and associated co-morbidities. Current WHO guidelines stipulate that the daily intake of sodium should not exceed 2 g, which is equivalent to 5 gm of sodium chloride . Considering that a tablet of soluble paracetamol (Panadol) contains 18.6 mmol (427 mg) of sodium , 8 tablets of soluble paracetamol a day will equate to 148.8 mmol (3.4 gm) of sodium or 8.7 gm of salt, which exceeds WHO guidelines. Soluble co-codamol (manufactured by Neolab) contains 19.1 mmol (438 mg) of sodium per tablet , which corresponds to a maximum of 8.9 gm of sodium chloride per day. Several frequently used over the counter medications, such as antacids and laxatives, also contain generous amounts of sodium. For example, Alka Seltzer Effervescent Antacid tablets contain 19.4 mmol (445 mg) of sodium per tablet (maximum of 8 a day). Movicol, a commonly used laxative, contains 8.1 mmol (187 mg) of sodium per sachet . A list of high sodium preparations has been compiled by UK medicines information pharmacists and is available on the National Electronic Library for Medicines website .
Various cases of hypernatremia due to excessive oral sodium consumption have been described. These include cases due to co-codamol , sodium phosphate , and soluble paracetamol . There have also been reports of hypertension in patients taking long-term soluble paracetamol . Even after accounting for underreporting of hypernatremia secondary to excessive sodium consumption, such cases are rare. However, in all these cases hypernatremia developed in patients with renal insufficiency, and several have been described in children. This suggests that there are homoeostatic mechanisms for maintaining serum sodium, which can be overcome when renal handling of solute load is compromised. In our patient, poor oral intake was a further contributory factor.
Both health-care professionals and patients should be aware of this pitfall. Care should be taken when prescribing for patients in whom high sodium consumption is contraindicated, especially those with hypertension, heart failure, hypernatremia, or renal insufficiency. Moreover, drug manufacturers should clearly communicate salt concentrations to all parties concerned.