A population-based assessment of the potential interaction between serotonin-specific reuptake inhibitors and digoxin

Digoxin Use and Associated Adverse Events Among Older Adults

BACKGROUND

Over the past 2 decades, guidelines for digoxin use have changed significantly. However, little is known about the national-level trends of digoxin use, hospitalizations for toxicity, and subsequent outcomes over this time period.

METHODS

To describe digoxin prescription trends, we conducted a population-level, cohort study using data from IQVIA, Inc.'s National Prescription Audit (2007-2014) for patients aged ≥65 years. Further, in a national cohort of Medicare fee-for-service beneficiaries aged ≥65 years in the United States, we assessed temporal trends of hospitalizations associated with digoxin toxicity and the outcomes of these hospitalizations between 1999 and 2013.

RESULTS

From 2007 through 2014, the number of digoxin prescriptions dispensed decreased by 46.4%; from 8,099,856 to 4,343,735. From 1999 through 2013, the rate of hospitalizations with a principal or secondary diagnosis of digoxin toxicity decreased from 15 to 2 per 100,000 person-years among Medicare fee-for-service beneficiaries. In-hospital and 30-day mortality rates associated with hospitalization for digoxin toxicity decreased significantly among Medicare fee-for-service beneficiaries; from 6.0% (95% confidence interval [CI], 5.2-6.8) to 3.7% (95% CI, 2.2-5.7) and from 14.0% (95% CI, 13.0-15.2) to 10.1% (95% CI, 7.6-13.0), respectively. Rates of 30-day readmission for digoxin toxicity decreased from 23.5% (95% CI, 22.1-24.9) in 1999 to 21.7% (95% CI, 18.0-25.4) in 2013 (P < .05).

CONCLUSION

While digoxin prescriptions have decreased, it is still widely prescribed. However, the rate of hospitalizations for digoxin toxicity and adverse outcomes associated with these hospitalizations have decreased. These findings reflect the changing clinical practice of digoxin use, aligned with the changes in clinical guidelines.

Evaluation of P-Glycoprotein Inhibitory Potential Using a Rhodamine 123 Accumulation Assay

In vitro evaluation of P-glycoprotein (P-gp) inhibitory potential is now a regulatory issue during drug development, in order to predict clinical inhibition of P-gp and subsequent drug-drug interactions. Assays for this purpose, commonly based on P-gp-expressing cell lines and digoxin as a reference P-gp substrate probe, unfortunately exhibit high variability, raising thus the question of developing alternative or complementary tests for measuring inhibition of P-gp activity. In this context, the present study was designed to investigate the use of the fluorescent dye rhodamine 123 as a reference P-gp substrate probe for characterizing P-gp inhibitory potential of 16 structurally-unrelated drugs known to interact with P-gp. 14/16 of these P-gp inhibitors were found to increase rhodamine 123 accumulation in P-gp-overexpressing MCF7R cells, thus allowing the determination of their P-gp inhibitory potential, i.e., their half maximal inhibitor concentration (IC50) value towards P-gp-mediated transport of the dye. These IC50 values were in the range of variability of previously reported IC50 for P-gp and can be used for the prediction of clinical P-gp inhibition according to Food and Drug Administration (FDA) criteria, with notable sensitivity (80%). Therefore, the data demonstrated the feasibility of the use of rhodamine 123 for evaluating the P-gp inhibitory potential of drugs.

Clinically relevant drug interactions in anxiety disorders

OBJECTIVE

Certain drugs used in the treatment of patients with anxiety disorders can interact with other psychotropic drugs and with pharmacological treatments for physical illnesses. There is a need for an updated comparative review of clinically relevant drug interactions in this area.

DESIGN

Relevant literature on drug interactions with medications used in the treatment of anxiety disorders was identified through a search in MEDLINE and EMBASE.

RESULTS

Drug interactions involving medications used to treat anxiety disorders may be pharmacokinetic, such as enzyme inhibition or induction in the cytochrome P450 system and transporter-mediated drug interactions, or pharmacodynamic, such as additive effects in causing drowsiness or additive effects at neurotransmitter receptors. Certain selective serotonin reuptake inhibitors (fluoxetine, fluvoxamine, and paroxetine) are particularly liable to be potentially involved in untoward pharmacokinetic interactions.

CONCLUSIONS

The potential for drug interactions with medications used in anxiety disorders should be the cause of clinical concern, particularly in elderly individuals. However, the liability for harmful drug interactions may be anticipated, and the risk reduced. Although not all interactions are clinically relevant, careful monitoring of clinical response and possible interactions is essential.

Different effects of the selective serotonin reuptake inhibitors fluvoxamine, paroxetine, and sertraline on the pharmacokinetics of fexofenadine in healthy volunteers

Although the interaction between selective serotonin reuptake inhibitors (SSRIs) and other drugs is important in the treatment of depression, there have been few studies of SSRIs concerning transporter-mediated interactions in humans. The objective of this study was to evaluate the in vivo effects of commonly used SSRIs on the pharmacokinetics of fexofenadine, a P-glycoprotein substrate.Twelve healthy volunteers (3 females and 9 males) were enrolled in this study. Each subject received a 60-mg dose of fexofenadine orally at baseline. Afterward, they were randomly assigned to receive 3 treatments with a 60-mg dose of fexofenadine after a 7-day treatment with fluvoxamine (50 mg/d), paroxetine (20 mg/d), or sertraline (50 mg/d), with 2-week intervals between the agents.Fluvoxamine pretreatment significantly increased the maximum plasma concentration, the area under the concentration time curves, and the 24-hour urinary fexofenadine excretion by 66% (P = 0.004), 78% (P = 0.029), and 78% (P < 0.001), respectively, without prolonging its elimination half-life. Paroxetine extended the elimination half-life of fexofenadine by 45% (P = 0.042), and it increased the 24-hour urinary fexofenadine excretion by 55% (P = 0.002). Sertraline did not alter any of the pharmacokinetic parameters of fexofenadine.This is the first report of the different effects of 3 commonly used SSRIs on fexofenadine pharmacokinetics in humans. Our 7-day, repeated-dose clinical study in healthy volunteers indicates that fluvoxamine and paroxetine, but not sertraline, may impact the patient exposure to fexofenadine, which is likely the result of P-glycoprotein inhibition in the small intestine and/or the liver.

Exposure to sennoside-digoxin interaction and risk of digoxin toxicity: a population-based nested case-control study

AIMS

Digoxin is an important medication for heart failure (HF) patients and sennosides are widely used to treat constipation. Recently, safety concerns have been raised about a possible interaction between sennosides and digoxin, an issue that has not been studied empirically. This study therefore aimed to evaluate whether exposure to sennoside-digoxin interaction is associated with an increased risk of digoxin toxicity.

METHODS AND RESULTS

This was a population-based nested case-control study that analysed data obtained from the Taiwan National Health Insurance Research Database between 1 January 2001 and 31 December 2004. All HF patients treated with digoxin for the first time were included as the study cohort. Of these, cases were identified as subjects hospitalized for digoxin toxicity (International Classification of Diseases, Ninth Revision, Clinical Modification, ICD-9-CM 972.1), and matched to randomly selected controls. Use of sennosides was compared between the two groups. Odds ratios (ORs) were employed to quantify the risk associated with exposure to sennoside-digoxin interaction by conditional logistic regression. The study cohort comprised 222,527 HF patients, of whom 524 were identified as cases and 2,502 as matched controls. Use of sennosides during the 14 days preceding the index date was found to be associated with a 1.61-fold increased risk of digoxin toxicity [95% confidence interval (CI) = 1.15, 2.25]. Additionally, a greater risk was observed for sennosides prescribed at an average daily dose ≥ 24 mg (adjusted OR = 1.93; 95% CI = 1.27, 2.94).

CONCLUSION

The combined use of sennosides and digoxin was found to be associated with a modest increased risk of digoxin toxicity in HF patients.

Risk of digoxin intoxication in heart failure patients exposed to digoxin-diuretic interactions: a population-based study

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT * Increased frequency of electrolyte abnormalities and cardiac arrhythmias among patients exposed to digoxin-diuretic interactions has been well-documented in numerous descriptive studies. * Nonetheless, a clear causal relationship has not been established in these studies. WHAT THIS STUDY ADDS * The risks of digoxin intoxication associated with use of digoxin in combination with any diuretic use, types of diuretics, combinations of diuretics, and individual diuretics were quantified using a population-based nested case-control study design. * The combined therapy of digoxin with any diuretic is associated with a 3.08-fold increase in the risk of digoxin intoxication. * Regarding diuretic class, the risk carried by loop diuretics is greater than that of thiazides or potassium-sparing diuretics, and the risk varies with different combinations of diuretic classes and individual diuretics. AIMS To quantify the digoxin intoxication risk associated with exposure to digoxin-diuretic interactions, and evaluate whether the risk varies by diuretic type, individually or in combination. METHODS This was a population-based nested case-control study in which data from the National Health Insurance Research Database (NHIRD) in Taiwan were analysed. RESULTS The study cohort comprised 154 058 heart failure (HF) patients taking digoxin between 2001 and 2004, in whom digoxin intoxication requiring a hospitalization (ICD-9 code 972.1) occurred in 595 cases. A total of 28 243 matched controls were also selected for analysis. Cases were 3.08 times (adjusted OR 3.08, 95% CI 2.50, 3.79) more likely to have been prescribed diuretic medication in the previous month than controls. Regarding the class of diuretics, loop diuretics carried the greatest risk (adjusted OR 2.97, 95% CI 2.35, 3.75), followed by thiazides (OR 2.36, 95% CI 1.70, 3.29) and potassium-sparing diuretics (OR 1.72, 95% CI 0.83, 3.56). The risk was also observed to vary with different combinations of diuretics, and the loops/thiazides/potassium-sparing diuretics combination carried the greatest risk (adjusted OR 6.85, 95% CI 4.93, 9.53). Among the individual diuretics examined, hydrochlorothiazide carried the greatest risk (adjusted OR 4.63, 95% CI 2.50, 8.57). CONCLUSIONS This study provided empirical evidence that digoxin-diuretic interactions increased the risk of hospitalization for digoxin intoxication in HF patients. The risk was particularly high for concomitant use of digoxin with a combination of loop diuretics, thiazide and potassium-sparing diuretics. The combined use of digoxin and diuretics should be avoided if possible.

Citalopram versus other antidepressants for late-life depression: a systematic review and meta-analysis

OBJECTIVE

To determine the efficacy and tolerability of citalopram when compared to other antidepressants for late-life depression (LLD).

METHODS

We searched electronic databases and trial registries to identify randomized controlled trials comparing citalopram to other antidepressants for LLD. Study quality was assessed using the Cochrane collaboration risk of bias tool. We summarized the efficacy of citalopram compared to other antidepressants by examining rates of depression remission, depression response and change in depression symptom scores. Medication tolerability was assessed through trial withdrawals due adverse events and withdrawals due to any cause. We used meta-analysis to determine the odds ratios (OR) of efficacy and tolerability outcomes for citalopram compared to other antidepressants.

RESULTS

Seven studies comparing citalopram (N = 647) to other antidepressants (N = 641) for LLD were identified including four studies with tricyclic comparators and three studies with non-tricyclic comparators. Most of the studies had methodological limitations that placed them at risk for potential bias. The majority of studies reported no significant differences between citalopram and comparator medications for depression efficacy or tolerability outcomes. Meta-analysis did not find any significant differences between citalopram and other antidepressants for depression remission [OR = 0.84; 95%CI: 0.56-1.28] or for trial withdrawals due to adverse effects [OR = 0.70; 95%CI: 0.48-1.02].

CONCLUSIONS

Currently there are few studies directly comparing citalopram to other antidepressants for LLD. The small number of studies and methodological issues in many studies limit any conclusions about the relative efficacy and tolerability of citalopram compared to other antidepressants. Well-designed studies comparing citalopram to other antidepressants for LLD are required.

In vitro and in vivo evaluation of the effects of duloxetine on P-gp function

OBJECTIVE

To evaluate the effect of duloxetine (DLX) on the P-glycoprotein (P-gp) function in vitro and in vivo.

METHOD

In vitro experiment was conducted using the Caco-2 cell, a human colon cancer cell line that naturally expresses the P-gp and P-gp function was evaluated by monitoring whether DLX affect the accumulation of Rhd123. In vivo study was conducted by quantitating the effect of orally administered DLX on the bioavailability of talinolol.

RESULTS

In the in vitro study, incubation of Caco-2 cell with DLX caused a concentration-dependent increase in the accumulation of Rhd123. In the in vivo study, co-administration of DLX increased the bioavailability of talinolol. The ratio (90% confidence intervals) of AUC(0-60), AUC(0-∞), and C(max) (talinolol alone versus talinolol plus DLX) were 0.87(0.77-1.06), 0.85(0.74-1.01), 0.87 (0.68-1.12).

CONCLUSION

Our results suggest that DLX could inhibit the function of P-gp in vitro and in vivo, and caution should be exercised when DLX is to be co-administered with drugs that are P-gp substrate.

Selective serotonin reuptake inhibitors and breast cancer mortality in women receiving tamoxifen: a population based cohort study

OBJECTIVE

To characterise whether some selective serotonin reuptake inhibitor (SSRI) antidepressants reduce tamoxifen's effectiveness by inhibiting its bioactivation by cytochrome P450 2D6 (CYP2D6).

DESIGN

Population based cohort study.

PARTICIPANTS

Women living in Ontario aged 66 years or older treated with tamoxifen for breast cancer between 1993 and 2005 who had overlapping treatment with a single SSRI.

MAIN OUTCOME MEASURES

Risk of death from breast cancer after completion of tamoxifen treatment, as a function of the proportion of time on tamoxifen during which each SSRI had been co-prescribed.

RESULTS

Of 2430 women treated with tamoxifen and a single SSRI, 374 (15.4%) died of breast cancer during follow-up (mean follow-up 2.38 years, SD 2.59). After adjustment for age, duration of tamoxifen treatment, and other potential confounders, absolute increases of 25%, 50%, and 75% in the proportion of time on tamoxifen with overlapping use of paroxetine (an irreversible inhibitor of CYP2D6) were associated with 24%, 54%, and 91% increases in the risk of death from breast cancer, respectively (P<0.05 for each comparison). By contrast, no such risk was seen with other antidepressants. We estimate that use of paroxetine for 41% of tamoxifen treatment (the median overlap in our sample) would result in one additional breast cancer death within five years of cessation of tamoxifen for every 19.7 (95% confidence interval 12.5 to 46.3) patients so treated; the risk with more extensive overlap would be greater.

CONCLUSION

Paroxetine use during tamoxifen treatment is associated with an increased risk of death from breast cancer, supporting the hypothesis that paroxetine can reduce or abolish the benefit of tamoxifen in women with breast cancer.

Using prescription registries to define continuous drug use: how to fill gaps between prescriptions

Pharmacoepidemiological studies often use prescription registries to assess patients' drug episodes. The databases usually provide information on the date of the redemption of the prescription as well as on the dispensed amount, and this allows us to define episodes of drug use. However, when patients take less medication than prescribed, apparent gaps between prescriptions occur, and most studies handle this issue by allowing for small gaps when defining continuous drug use. This paper argues that it becomes crucial whether gaps are 'filled' prospectively or retrospectively. In the latter case the inferred exposure status depends on the patient's future dispensing behaviour and this can lead to severe bias in the findings of the study. In this paper we investigate this potential bias in a study of the risk of acute myocardial infarction (AMI) for women using hormone therapy (HT), and we show that the retrospective exposure definition introduces an artificially protective effect of HT.

Sertraline and its metabolite desmethylsertraline, but not bupropion or its three major metabolites, have high affinity for P-glycoprotein

The ATP-binding cassette (ABC) transporter protein subfamily B1 line (ABCB1) transporter P-glycoprotein (P-gp) plays an important role in the blood-brain barrier limiting a broad spectrum of substrates from entering the central nervous system. In the present study, the transport activity of P-gp for sertraline, desmethylsertraline, bupropion, and the major metabolites of bupropion, threo-amino alcohol (TB), erythro-amino alcohol (EB), and hydroxy metabolite (HB) was studied using an ATPase assay in expressed human P-gp membranes by measuring concentrations of inorganic P(i) in expressed human P-gp membranes. Verapamil was included as a positive control. The Michaelis-Menten equation was used for characterizing the kinetic data. Sertraline and desmethylsertraline showed high affinity for P-gp. The V(max)/K(m) values of sertraline (1.6 min(-1) x 10(-3)) and desmethylsertraline (1.4 min(-1) x 10(-3)) were comparable with that of verapamil (1.7 min(-1) x 10(-3)). Bupropion and its three metabolites showed very weak affinity for P-gp, with V(max)/K(m) values lower than 0.01 min(-1) x 10(-3). The results of the present study indicate that sertraline and desmethylsertraline have high affinity for P-gp, whereas bupropion and its three major metabolites TB, EB, and HB have very weak affinity for P-gp. These findings may help to explain observed drug-drug interactions among antidepressants.

A systematic review on the application of pharmacoepidemiology in assessing prescription drug-related adverse events in pediatrics

OBJECTIVES

To conduct a systematic review of recent case-control and cohort studies in assessing adverse drug events (ADEs) among pediatric patients aged between 0 and 18 years; to establish strengths and limitations of pharmacoepidemiology when applied in evaluating pediatric drug safety; and to identify areas of pediatric drug safety that may be suitable for future pharmacoepidemiological investigations.

METHODS

A PubMed search was conducted using a list of keywords representing drugs, adverse drug events, case control and cohort studies, and pediatric population. Selection criteria were used to extract relevant studies published from 1/1 2000 to 7/1 2006.

RESULTS

Twenty-seven studies met our criteria. Of them, 12 used a prospective cohort design. The others were either case-control (seven) or retrospective cohort (eight) studies, based on the analysis of existing databases. More than half of the studies included more than 500 subjects. Inclusion and exclusion criteria for participants in these studies were generally not very stringent. The subjects closely resembled patients in the real-world settings. The length of study follow-up ranged from 1 day to 40 years. In eight studies, the length of follow-up surpassed 5 years. Potential confounding factors were taken into consideration in all of the studies. But the database-based studies generally failed to control for some important clinical variables such as disease severity. Misclassification of drug exposures also occurred in some of these studies.

CONCLUSIONS

Despite some limitations, pharmacoepidemiology proves to be useful for assessing ADEs in pediatrics. With appropriate study design, this methodology can bolster our understanding about the safety of pediatric drug use. Several areas of pediatric drug safety may especially be suitable for future pharmacoepidemiological investigations. These areas include the safety of polypharmacy, long-term drug effects, and off-label drug use.

The Prevalence of Potential Drug-Drug Interactions in Patients with Heart Failure at Hospital Discharge

BACKGROUND/OBJECTIVE

Pharmacotherapy for heart failure is complex and, due to polypharmacy, is associated with a large risk of potential drug-drug interactions (DDIs). The objective of the present study was to assess the prevalence of potential DDIs in the medication of hospitalised heart failure patients and to evaluate their clinical relevance.

STUDY DESIGN/METHODS

The medication of 400 patients was retrospectively analysed for potential DDIs at hospital admission and discharge using a computerised drug interaction program. Main inclusion criteria were the diagnosis of heart failure and a minimum of two drug prescriptions at discharge.

RESULTS

In the study population of 400 heart failure patients (median age 79 years, 55.5% men), the median number of drugs per patient was lower at admission than at discharge (6 [interquartile range {IQR} 4-9] vs 8 [IQR 6-10]; p < 0.001). At hospital admission, a total of 863 potential DDIs were detected in 272 patients (68.0%; 95% CI 63.4, 72.6). At discharge, 1171 potential DDIs were detected in 355 patients (88.8%; 95% CI 85.7, 91.8). This corresponds with a significant increase in the median number of potential DDIs per patient from admission to discharge (1.5 [IQR 0-3] vs 3 [IQR 1-4]; p < 0.001). Of the 1171 potential DDIs at discharge, 432 (36.9%) were prevalent at admission and 739 (63.1%) resulted from a medication change during the hospital stay. Of these 739 new potential DDIs, the severity of the potential adverse effect was rated as 'major' in 190 (25.7%) patients, 'moderate' in 482 (65.2%) and 'minor' in 67 (9.1%). The 190 potential DDIs with major severity were recorded in a total of 145 patients (36.3%; 95% CI 31.5, 41.0%). Hyperkalaemia was the most prevalent potential adverse effect of major severity (n = 93) and the combination of an ACE inhibitor with a potassium-sparing diuretic was recorded in 64 (16.0%) patients.

CONCLUSIONS

The study shows that hospitalisation of patients with heart failure results in an increase in the number of drugs prescribed per patient and, thereby, also in the number of potentially interacting drug combinations per patient. Although electronic drug interaction programs are a valuable tool to check for potential DDIs, the clinical relevance of most potential DDIs can only be judged by assessment of the individual patient.

Dose-dependent interaction of paroxetine with risperidone in schizophrenic patients

Augmentation with paroxetine (10-40 mg/d) for antipsychotic treatment may improve the negative symptoms in schizophrenic patients but involves a risk of drug-drug interaction. We studied the effects of paroxetine on plasma concentrations of risperidone and 9-hydroxyrisperidone and their clinical symptoms in risperidone-treated patients. Twelve schizophrenic inpatients with prevailingly negative symptoms receiving risperidone 4 mg/d were, in addition, treated with incremental doses of paroxetine for 12 weeks (10, 20, and 40 mg/d for 4 weeks each). Plasma concentrations of risperidone and 9-hydroxyrisperidone were quantified with liquid chromatography-mass spectrometry mass-mass spectrometry together with clinical assessments before and after each phase of the 3 paroxetine doses. Risperidone concentrations during coadministration of paroxetine 10, 20, and 40 mg/d were 3.8-fold (95% confidence interval, 3.2-5.8, P < 0.01), 7.1-fold (95% confidence interval, 5.3-16.5, P < 0.01), and 9.7-fold (95% confidence interval, 7.8-22.5, P < 0.01) higher than that before paroxetine coadministration, respectively. Active moiety (risperidone plus 9-hydroxyrisperidone) concentration was not increased during the paroxetine 10 mg/d (1.3-fold, not significant) or 20 mg/d (1.6-fold, not significant), but were significantly increased by 1.8-fold (95% confidence interval, 1.4-2.7, P < 0.05) during the paroxetine 40 mg/d. Significant improvement in negative symptoms was observed from 10 to 40 mg/d of paroxetine, whereas scores in extrapyramidal side effects during 20 and 40 mg/d of paroxetine were significantly higher than baseline score. This study indicates that paroxetine increases plasma risperidone concentration and active moiety concentration in a dose-dependent manner. Low-dose coadministration of paroxetine with risperidone may be safe and effective in the treatment of schizophrenic patients with negative symptoms.