Hydrochlorothiazide and risk of hearing disorder: a case series

Hydrochlorothiazide is a thiazide diuretic that is used in the treatment of hypertension and edema either as the sole therapeutic agent or in combination with other drugs [1, 2]. To the best of our knowledge, there are no published articles or case reports that associate hydrochlorothiazide (HCTZ) and hearing disorder or ototoxicity. HCTZ has only been associated with vertigo and there are also reports of tinnitus when combined with amiloride [3]. The summary of product characteristics (SPC) of HCTZ found on the webpage of the European Medicines Agency (EMA) [4], Medicines and Healthcare Products Regulatory Agency (MHRA) [5], US Food and Drug Administration (FDA) [6] and others [7] do not mention ototoxicity or hearing disorder as an adverse effect. Ototoxicity is defined by the toxic capacity of certain drugs or toxins relative to the inner ear structures, particularly to the cochlea and the vestibular cells, or the acoustic nerve [8, 9]. The symptoms of cochleotoxicity range from mild tinnitus to total hearing loss and vestibulotoxicity may range from mild imbalance to total incapacitation [10].

Even though HCTZ is not known to cause hearing disorder, the Eritrean Pharmacovigilance Centre received two cases of hearing disorder, including irreversible deafness, associated with the use of HCTZ. The objective of this study is, therefore, to assess the causal association between HCTZ and hearing loss through data mining on the WHO global adverse drug reaction database, VigiBase™.

Data was retrieved from the WHO global adverse drug reaction database, VigiBase™, which is developed and maintained by the Uppsala Monitoring Centre (UMC), Sweden. The database captures adverse drug reaction reports submitted from National Pharmacovigilance Centres of more than 120 countries. A search on VigiBase™ was made on August 6, 2017 using “hydrochlorothiazide” as drug substance, and “ototoxicity” [preferred term (PT)], “hearing decreased” [high-level term (HLT)], and “vestibular disorder” (HLT) as reaction terms [World Health Organization Adverse Reaction Terminology (WHO-ART)]. All relevant information like the reaction outcome, seriousness, information component (IC), outcome of rechallenge/dechallenge, and patients’ background characteristics were extracted using VigiLyze™, a tool developed by the UMC for data mining and analysis of adverse drug reactions (ADR) in VigiBase™. IC value is a measure of disproportionality of drug ADR in VigiBase™ [11, 12]. A positive IC value indicates that a particular drug ADR pair is reported more often than expected, based on all the reports in VigiBase™. The results generated were then exported to an Excel spreadsheet for descriptive analysis. Potential duplicate cases were eliminated using VigiMatch™, a tool developed by the UMC.

The series of cases were then subjected to Austin Bradford-Hill criteria [13] to assess the causal association between HCTZ and hearing disorder. Using Bradford-Hill criteria, strength of association, consistency of cases, specificity of the association, temporal relationship, dose–response relationship, biological plausibility, experimental evidence, coherence, and analogy of the association was assessed in case series. Expectedness or labeledness of the adverse effect was assessed through thorough literature review including the SPCs.

The Eritrean Pharmacovigilance Centre has received two cases of HCTZ-associated hearing disorder. In both cases, HCTZ was the sole suspect with no other concomitants. The causality assessment using Naranjo adverse drug reaction probability scale [14] was found to be “probable” for both cases.

In this case series assessment, the relationship of HCTZ and hearing disorder was assessed using Austin Bradford-Hill criteria (Table 3). The wide geographic distribution of the case reports, the plausible time relationship, the positive dechallenge and rechallenge reported in some cases, cases with hearing loss manifested on the second day following administration of HCTZ with no concomitants, and the irreversible deafness observed shortly after overdose intake of HCTZ supports a causal association.

Although the availability of multiple co-reported drugs and reactions in many of the cases make the association nonspecific, in 28% of the cases, HCTZ was reported as the only suspected drug with no other concomitants.

Even though drug-induced hearing disorder is dose and duration related [15], 75% of the cases were manifested at normal therapeutic daily dose (12.5–50 mg/day) a few days after intake of HCTZ. This suggests that HCTZ-related hearing loss can occur even at normal dose; especially when administered with other ototoxic drugs.

It should, however, be noted that the association of HCTZ and hearing disorder can be affected by many confounders like age, the disease itself (hypertension), and other drugs taken concomitantly like acetylsalicylic acid (ASA) [16]. As the median age of the cases was 64 years, hearing disorder could be assumed as age related. On the other hand, age-related hearing loss is characterized by progressive (irreversible), symmetrical, and sensory neural hearing loss [17]; thus reversibility of the cases in 66.7% shows that the effect of age was not remarkable. Even though hypertension is known to cause sensory neural hearing loss [18], which usually is irreversible, the effect of the disease seems insignificant as outcome was reversible in the majority of the cases. ASA is also well known to cause reversible hearing loss, but the number of patients taking ASA in our study was small (3.9%); suggesting a minimal potential contribution. Similarly, the effect of other concurrently used drugs could not be ruled out due to the nature of the study. The effect of heredity, environmental or occupational hazards like noise pollution were also left as residual confounders. Taking into account the inherent limitation of spontaneous reporting, similar cases might be underreported, which can understate the association. Another limitation of the study is that, as we had no denominator data, the incidence of the potential risk cannot be estimated.

From this case series assessment, it can be concluded that there is a suggestive causal association between HCTZ and hearing disorder. As it may cause irreversible hearing loss, this association warrants further study to substantiate the safety signal through epidemiologic studies. Taking into consideration the impact of hearing loss, difficulty in communication, loss of balance, incapacity, dependency and accidents, healthcare professionals should be cautious in prescribing ototoxic drugs concomitantly with HCTZ. Besides, they should also advise patients to avoid or minimize over-the-counter drugs, which are believed to be ototoxic like NSAIDS. We also recommend healthcare professionals to do routine hearing assessment for patients taking HCTZ.