Mirtazapine-induced hyponatremia in an elderly hospice patient

Mirtazapine Risk of Hyponatremia and Syndrome of Inappropriate Antidiuretic Hormone Secretion in Adult and Elderly Patients: A Systematic Review

Hyponatremia is the most common fluid and electrolyte imbalance in hospitalized patients. Among hyponatremia causes, syndrome of inappropriate antidiuretic hormone secretion is a condition characterized by excessive release of antidiuretic hormone from the pituitary gland or nonpituitary sources. One of the most common drugs associated with hyponatremia is selective serotonin reuptake inhibitors, especially in elderly patients. Therefore, distinct therapeutic alternatives are essential for patients having risk factors for hyponatremia or syndrome of inappropriate antidiuretic hormone secretion development. 

The present article aims to review the available literature evaluating mirtazapine-induced hyponatremia or syndrome of inappropriate antidiuretic hormone secretion in adult or elderly patients in order to determine the incidence of these adverse effects and analyze the existence of any correlation between the administered dose of mirtazapine and serum sodium levels. A systematic search was conducted, using key terms from the research topic, their synonyms, and Boolean/logic operators. From this evidence pool, inclusion and exclusion criteria were applied. We abstracted population characteristics and clinical endpoints. Relevant data from selected studies was abstracted and subject to statistical analysis. 

A total sample size of 30,851 patients treated with mirtazapine was included. Mirtazapine-induced hyponatremia incidence was 3.26% (95% CI 3.06-3.45%), with the syndrome of inappropriate antidiuretic hormone secretion (SIADH) the most probable underlying cause. Among case series and case reports evaluated (n=7), hyponatremia and SIADH were more frequent in female patients (71.4%) and the most frequent clinical manifestations included confusion (57%), somnolence (42%), and altered speech (28%). Mean serum sodium levels were (117 mEq/L, ranging from 113-130 mEq/L). The average time lapse between mirtazapine administration and clinical findings was 34 days. The Spearman's rank correlation coefficient between mirtazapine dosage and serum sodium levels was -0.3181 with a p-value >0.05. 

In conclusion, mirtazapine presents a moderate risk of hyponatremia and should be considered as an alternative therapy in patients requiring antidepressants with risk factors for this preventable adverse effect. 

Identifying predictive clinical characteristics of the treatment efficacy of mirtazapine monotherapy for major depressive disorder

BACKGROUND

Mirtazapine, which is classified as a noradrenergic and specific serotonergic antidepressant, is widely prescribed for the treatment of major depressive disorder. The potential predictive factors of the efficacy of mirtazapine and the tolerability based on the incidence of oversedation and jitteriness/anxiety syndrome were evaluated.

PATIENTS AND METHODS

Patients with major depressive disorder were retrospectively investigated. Study subjects comprised 68 patients with depression who received mirtazapine as an initial antidepressant at the Department of Psychiatry of the Tokyo Women's Medical University Hospital from September 2009 to March 2013. The efficacy of mirtazapine monotherapy was evaluated based on the Clinical Global Impression Improvement score. Clinical characteristics were compared between remission and nonremission groups to determine the factors predicting the efficacy. Moreover, discontinuation rates due to adverse effects, including oversedation and jitteriness/anxiety syndrome, were examined, and the effects of confounding factors were evaluated.

RESULTS

The remission rate of mirtazapine monotherapy was 36.8% among the 68 enrolled subjects. The mean final doses in the remission and nonremission groups were 27.6±13.5 mg and 26.0±14.1 mg, respectively, and there was no significant difference between them. Multiple logistic analyses revealed that the absence of guilt (odds ratio [OR] =0.15; 95% CI [1.66-37.24], P=0.006) and the presence of psychomotor retardation (OR =4.30; 95% CI [1.30-16.60], P=0.016) were significantly related to the efficacy of mirtazapine monotherapy. The discontinuation rates due to oversedation and jitteriness/anxiety syndrome were 13.2% and 11.8%, respectively. Age did not differ significantly between patients with or without oversedation or jitteriness/anxiety syndrome (P=0.078 and P=0.579, respectively).

CONCLUSION

The absence of guilt and the presence of psychomotor retardation may predict the efficacy of mirtazapine, and mirtazapine may be tolerable for all ages.

Antidepressants and the risk of hyponatremia: a class-by-class review of literature

BACKGROUND

Antidepressant-induced hyponatremia can cause significant morbidity and mortality. It is mostly associated with the use of selective serotonin reuptake inhibitors (SSRIs), but its frequency and class specificity are uncertain.

OBJECTIVES

To determine the relationship between hyponatremia and antidepressants and to define the incidence and odds ratios for antidepressant classes.

METHODS

A review of the literature prior to March 2013 was performed using Web of Science and PubMed by employing combinations of search strings "antidepressants" and antidepressant class and generic drug names with "hyponatr(a)emia," "SIADH," or "inappropriate ADH."

RESULTS

Overall, 21 effect studies and more than 100 case reports were considered, most concerning SSRIs. Because of variations in study designs, populations, and cutoff values, incidence rates diverged between 0.06% and 40% for SSRIs and 0.08% and 70% for venlafaxine. Although based on less solid evidence, incidence figures for mirtazapine and tricyclic antidepressants were lower. Regarding classes, odds ratios for SSRIs (1.5-21.6) were consistently higher than for tricyclic antidepressants (TCAs) (1.1-4.9). The risks associated with monoamine oxidase inhibitors, reboxetine, and bupropion could not be established owing to insufficient information. Patient risk factors included older age (odds ratios = 6.3) and concomitant use of (thiazide) diuretics (odds ratios = 11.2-13.5).

CONCLUSION

Hyponatremia is a potentially dangerous side effect of antidepressants and is not exclusive to SSRIs. Current evidence suggests a relatively higher risk of hyponatremia with SSRIs and venlafaxine, especially when combined with patient risk factors, warranting clinicians to be aware of this complication. The risks associated with mirtazapine are moderate, supporting this antidepressant as an alternative treatment for patients with (an increased risk of) hyponatremia.

Variation in the CYP2D6 gene is associated with a lower serum sodium concentration in patients on antidepressants

AIM

To study the effect of the CYP2D6*4 polymorphism on serum sodium concentration in users of antidepressants [selective serotonin reuptake inhibitors and tricyclic antidepressants (TCAs)].

METHODS

In this population-based cohort study, all subjects in the Rotterdam Study were included who used an antidepressant at baseline and from whom a blood sample was available in which CYP2D6 genotype and serum sodium concentration could be determined (n= 76). Multivariate linear regression was used to study the association between CYP2D6*4 and serum sodium concentration.

RESULTS

CYP2D6 poor metabolizers (PMs) (*4/*4) had a significantly lower mean serum sodium concentration in comparison with CYP2D6 extensive metabolizers (EMs) (*1/*1) [difference -3.9 mmol l(-1); 95% confidence interval (CI) -0.86, -7.03; P= 0.013]. In CYP2D6*4 heterozygotes (*1/*4) serum sodium concentration was 1.7 mmol l(-1) (95% CI -3.48, 0.18) lower compared with CYP2D6 EMs, but this difference was not statistically significant (P= 0.077).

CONCLUSIONS

The serum sodium concentration in PMs was lower in users of an antidepressant, especially in TCA users. Therefore CYP2D6 PMs might be at increased risk of developing symptoms of hyponatraemia.

Pathoetiological model of delirium: a comprehensive understanding of the neurobiology of delirium and an evidence-based approach to prevention and treatment

Delirium is the most common complication found in the general hospital setting. Yet, we know relatively little about its actual pathophysiology. This article contains a summary of what we know to date and how different proposed intrinsic and external factors may work together or by themselves to elicit the cascade of neurochemical events that leads to the development delirium. Given how devastating delirium can be, it is imperative that we better understand the causes and underlying pathophysiology. Elaborating a pathoetiology-based cohesive model to better grasp the basic mechanisms that mediate this syndrome will serve clinicians well in aspiring to find ways to correct these cascades, instituting rational treatment modalities, and developing effective preventive techniques.

Hyponatremia associated with tolterodine therapy

PURPOSE

The case of a patient who developed hyponatremia after recent initiation of tolterodine is reported.

SUMMARY

An 86-year-old woman arrived at the hospital due to an acute change in her mental status. The patient's daughter found her mother slumped over and stated that she was unresponsive for approximately four minutes. The admitting diagnosis was transient ischemic attack or syncope. Baseline laboratory tests revealed an abnormal basic metabolic panel, including a serum sodium concentration of 125 mmol/L and a serum chloride concentration of 88 mmol/L. The results of a complete blood count and thyroid function tests were within normal limits. Unsuccessful attempts at sodium correction included initial fluid restriction and, later, the administration of 0.9% sodium chloride injection over 24 hours. Physiological causes of hyponatremia were ruled out. The attending physician and team pharmacist reviewed the patient's medication profile for potential causes of hyponatremia. Hydrochlorothiazide, a home medication for the patient, was discontinued at hospital admission and ruled out as a cause of her hyponatremia. A documented association between lisinopril, mirtazapine, or omeprazole and hyponatremia exists in various case reports. However, per the patient's primary care physician, tolterodine was the only modification of an otherwise stable medication profile at an outpatient office visit approximately four weeks prior to admission. Once tolterodine was discontinued, the patient's hyponatremia quickly resolved. Tolterodine was discontinued on hospital day 5, and the hyponatremia was corrected by the next day.

CONCLUSION

An 86-year-old woman developed hyponatremia after recent initiation of tolterodine therapy.

Medical costs of abnormal serum sodium levels

An abnormal serum sodium level is the most common electrolyte disorder in the United States and can have a significant impact on morbidity and mortality. The direct medical costs of abnormal serum sodium levels are not well understood. The impact of hyponatremia and hypernatremia on 6-mo and 1-yr direct medical costs was examined by analyzing data from the Integrated HealthCare Information Services National Managed Care Benchmark Database. During the period analyzed, there were 1274 patients (0.8%) with hyponatremia (serum sodium <135 mmol/L), 162,829 (97.3%) with normal serum sodium levels, and 3196 (1.9%) with hypernatremia (>145 mmol/L). Controlling for age, sex, region, and comorbidities, hyponatremia was a significant independent predictor of costs at 6 mo (41.2% increase in costs; 95% confidence interval, 30.3% to 53.0%) and at 1 yr (45.7% increase; 95% confidence interval, 34.2% to 58.2%). Costs associated with hypernatremia were not significantly different from those incurred by patients with normal serum sodium. In conclusion, hyponatremia is a significant independent predictor of 6-mo and 1-yr direct medical costs.