Dietary sodium, raised blood pressure and increased cardiovascular risk have well-known links, but many effervescent or soluble medicines contain large amounts of sodium. Researchers say people should be aware of the potential hazards of high sodium consumption and that the packaging should be labeled in the same way as food.
The research, published on the website of the BMJ, notes that patients taking the maximum doses of some medicines would exceed their recommended daily salt intake before they had even eaten anything.
And while doctors and health care providers will happily advise people to reduce the amount of salt they add to food, they do not always point out the hidden salt lurking in the pills and potions they prescribe.
The researchers, from the University of Dundee and University College London in the UK, argue that the public "should be warned about the potential dangers of high sodium intake from prescribed medicines," suggesting that the sodium-containing mixtures "be prescribed with caution only if the perceived benefits outweigh the risks."
Sparkling or still
For the study, Dr. Jacob George, from the University of Dundee, compared the risk of cardiovascular events - non-fatal heart attacks, non-fatal strokes and vascular deaths - for patients taking fizzy, soluble or dispersible versions of medications with patients taking non-sodium versions of the same drugs.
Using figures from the UK Clinical Practice Research Datalink (CPRD) database, the team analyzed the data of more than 1.2 million patients who were prescribed sodium-containing medications between January 1987 and December 2010.
On average, the patients were tracked for just over 7 years. During this time, more than 61,000 cardiovascular events occurred.
Even after factors that might affect the results - smoking, body mass index, alcohol consumption and a history of various chronic illnesses - were taken into account, patients taking the sodium-rich formulations had a 16% higher risk of a cardiovascular event than patients taking the non-sodium versions of the same medicines.
They also found that patients taking the high-sodium pills were seven times more likely to develop hypertension and experienced a 28% higher death rate than the other group.
The study authors acknowledge that there is still some controversy about the relationship between dietary salt and cardiovascular events, but they urge physicians to be more aware of the potential hazards of heavily salted medicines.
The researchers also call for "pharmaceutical innovation" to reduce the sodium content of drugs while preserving the effervescent, soluble or dispersible characteristics.
The study concludes:
"Sodium loaded effervescent, soluble, or dispersible tablets should be avoided in patients at risk of hypertension, and patients prescribed these drugs should be carefully monitored for the emergence of hypertension."