Drug-induced hyponatraemia and possible related signals: Analysis of 659 cases reported to the Spanish Pharmacovigilance System and disproportionality analysis.

Introduction: Hyponatraemia has negative effects on cognitive function and gait stability and is a risk factor for osteoporosis, falls, fractures and hospital mortality. Acute hyponatraemia can lead to neurological dysfunction due to cerebral oedema. Its rapid correction can also be fatal, leading to osmotic demyelination syndrome. For some antiepileptics, thiazides, benzodiazepines or antidepressants this reaction is widely described. Knowing which drugs are most likely to cause hyponatraemia will allow early detection and prevention of its complications, as well as individualising the prescription of these drugs according to the patient's characteristics.

Objective: The main objectives are to identify potential new safety signals related to hyponatraemia and to analyse the cases of hyponatraemia reported to the Spanish Pharmacovigilance System for Medicines for Human Use (SEFV-H).

Method: A disproportionality and a descriptive analysis of individual case safety reports (ICSR) was performed in the SEFV-H database (FEDRA).

Results: Six hundred and fifty-nine cases of suspected drug-induced hyponatraemia were found (0.6% of the total database). Over the 5 years period studied, there was a 57% increase in the number of hyponatraemia reports in Spain. Most of the reported cases were serious (93%). Patients were most often women (63.7%) and elderly (71.9%). The time to onset ranged from 1 to 7030 days (median, 79 days) and approximately 70% of the total occurred within the first year of treatment. Five hundred and forty-six patients (82.9%) showed complete recovery after the withdrawal of the suspected medicine. Diuretics (reported in 57.7% of the cases), antidepressants (in 25%), drugs acting on renin angiotensin system (in 24%) and antiepileptics (in 20.2%) were the most frequent involved drugs. Disproportionate reporting has been found for almost all the substances most frequently reported, higher for amiloride and oxcarbazepine. Regarding new safety signals, the Reporting Odds Ratio (ROR) (95% CI) was found to be statistically significant for valsartan [7.7 (5.1-11.5)], olmesartan [7.3 (4.7-11.1)], amlodipine [3.4 (2.1-5.4)], pregabalin [2.5 (1.4-4.5)], irbesartan [18.6 (9.6-35.9)], paliperidone [2.7 (1.3-5.7)], ritonavir [2.4 (1.1-5.5)], atosiban [29.7 (8.6-102.2)], melphalan [9.7 (3.5-26.8)] and clozapine [4.4 (1.6-11.8)]. These active ingredients do not include this reaction on their SPC and comply with the EMA criteria for a safety signals.

Conclusion: There are increasing reports of drug-induced hyponatraemia. It can be serious and seems to most often affect women over 65 years of age who take more than 1 medication. The time to onset varies and can be very long, so patient monitoring should be continuous throughout treatment. Hydrochlorothiazide is the drug with the highest number of reported cases in our setting. In terms of disproportionate reporting, diuretics leads the list, followed by antiepileptics as oxcarbazepine and eslicarbazepine. Safety signals were found for several drugs, more plausibly for pregabalin and paliperidone, thus a possible association between these drugs and hyponatraemia/SIAD is identified. This signal must be further studied. Meanwhile healthcare professionals should pay attention to this possibility. The reporting of suspected ADRs is essential to understand the risks associated with medicines once they are on the market.