Drug interactions with digoxin

Impact of Abnormal Potassium on Arrhythmia Risk During Pediatric Digoxin Therapy

Digoxin is used in children with heart failure and tachyarrhythmia. Its use in patients with single ventricle anatomy has increased following evidence of improved interstage survival after the Norwood procedure. Digoxin has a narrow therapeutic window and may alter serum potassium balance, inducing arrhythmias. We hypothesized digoxin use in the setting of abnormal serum potassium levels is associated with arrhythmias. We reviewed all patients ≤ 18 years who received digoxin while admitted at our institution from 2014 to 2021. Admissions < 2 nights were excluded. We compared patients with a hemodynamically significant arrhythmia to those without. We performed adjusted mixed-effects logistic regression with arrhythmia as the outcome variable and potassium status as the predictor variable; adjusting for weight, route of digoxin administration, digoxin indication, serum creatinine, and number of interacting drugs prescribed. Abnormal potassium was defined as serum levels < 3.5 mmol/L or > 6.0 mmol/L. There were 268 encounters in 171 patients. Potassium levels were abnormal in 75.5% of patients who experienced an arrhythmia during digoxin administration, compared to 42.6% who did not (p < 0.001). Odds of arrhythmia was 138% higher in patients with abnormal potassium receiving digoxin (AOR = 2.38, 95% CI 1.07-5.29, p = 0.03). Receiving intravenous digoxin was also associated with a 7.35 odds of cardiac arrhythmia (AOR 7.35, p = 0.006, 95% CI 1.79-30.26). Odds of arrhythmia is increased during digoxin administration when pediatric patients have abnormal potassium levels. Vigilant attention to potassium levels is essential to prevent adverse outcomes during digoxin therapy.

Drug Interactions Affecting Antiarrhythmic Drug Use

Antiarrhythmic drugs (AAD) play an important role in the management of arrhythmias. Drug interactions involving AAD are common in clinical practice. As AADs have a narrow therapeutic window, both pharmacokinetic as well as pharmacodynamic interactions involving AAD can result in serious adverse drug reactions ranging from arrhythmia recurrence, failure of device-based therapy, and heart failure, to death. Pharmacokinetic drug interactions frequently involve the inhibition of key metabolic pathways, resulting in accumulation of a substrate drug. Additionally, over the past 2 decades, the P-gp (permeability glycoprotein) has been increasingly cited as a significant source of drug interactions. Pharmacodynamic drug interactions involving AADs commonly involve additive QT prolongation. Amiodarone, quinidine, and dofetilide are AADs with numerous and clinically significant drug interactions. Recent studies have also demonstrated increased morbidity and mortality with the use of digoxin and other AAD which interact with P-gp. QT prolongation is an important pharmacodynamic interaction involving mainly Vaughan-Williams class III AAD as many commonly used drug classes, such as macrolide antibiotics, fluoroquinolone antibiotics, antipsychotics, and antiemetics prolong the QT interval. Whenever possible, serious drug-drug interactions involving AAD should be avoided. If unavoidable, patients will require closer monitoring and the concomitant use of interacting agents should be minimized. Increasing awareness of drug interactions among clinicians will significantly improve patient safety for patients with arrhythmias.

Drug-drug interactions mediated through P-glycoprotein: clinical relevance and in vitro-in vivo correlation using digoxin as a probe drug

The clinical pharmacokinetics and in vitro inhibition of digoxin were examined to predict the P-glycoprotein (P-gp) component of drug-drug interactions. Coadministered drugs (co-meds) in clinical trials (N = 123) resulted in a small, <or=100% increase in digoxin pharmacokinetics. Digoxin is likely to show the highest perturbation, via inhibition of P-gp, because of the absence of metabolic clearance. In vitro inhibitory potency data (concentration of inhibitor to inhibit 50% P-gp activity; IC(50)) were generated using Caco-2 cells for 19 P-gp inhibitors. Maximum steady-state inhibitor systemic concentration [I], [I]/IC(50) ratios, hypothetical gut concentration ([I(2)], dose/250 ml), and [I(2)]/IC(50) ratios were calculated to simulate systemic and gut-based interactions and were compared with peak plasma concentration (C(max))(,i,ss)/C(max,ss) and area under the curve (AUC)(i)/AUC ratios from the clinical trials. [I]/IC(50) < 0.1 shows high false-negative rates (24% AUC, 41% C(max)); however, to a limited extent, [I(2)]/IC(50) < 10 is predictive of negative digoxin interaction for AUC, and [I]/IC(50) > 0.1 is predictive of clinical digoxin interactions (AUC and C(max)).

Pharmacokinetic and pharmacodynamic drug interactions between digoxin and macrogol 4000, a laxative polymer, in healthy volunteers

AIMS

The aim of this study was to examine the bioequivalence between a single oral dose of digoxin administered alone and with a coadministration of macrogol 4000 (a laxative polymer) in 18 healthy volunteers.

METHODS

This was an open, randomised, two-way cross-over study, with a single dose oral administration of 0.5 mg digoxin administered alone or in combination with macrogol 4000, 20 g day-1 during 8 days. Pharmacokinetics of digoxin, heart rate and PR ECG interval at rest were assessed.

RESULTS

Macrogol 4000 coadministration was associated with a 30% decrease of digoxin AUC and a 40% decrease in its Cmax (P<0.05). Digoxin tmax and t1/2,z were not significantly altered. Heart rate and PR interval did not differ during the two therapeutic sequences, digoxin alone and digoxin in combination.

CONCLUSIONS

Macrogol 4000 coadministration interacts with single-dose digoxin pharmacokinetics. This is most likely due to a reduction of the intestinal absorption of digoxin. However, there was no consequence of this interaction on heart rate and AV conduction.

Effect of multiple doses of losartan on the pharmacokinetics of single doses of digoxin in healthy volunteers

1. Losartan (DuP 753, MK-954) is a novel, potent and highly selective AT1 angiotensin II receptor antagonist. The effect of multiple oral doses of losartan on digoxin pharmacokinetics was evaluated in healthy male subjects. 2. In a double-blind and randomized fashion, subjects received 50 mg losartan or placebo once daily for 15 days in each period. At least 7 days elapsed between the two treatment periods. On days 4 and 11 of each period, subjects also received a single 0.5 mg dose of digoxin intravenously and orally respectively. 3. Eleven of 13 subjects completed the study. Side effects were mild and transient (12 out of 13 subjects reported at least one adverse experience). During the study, no laboratory abnormalities were noted. 4. Multiple oral doses of losartan (50 mg daily) did not affect the pharmacokinetic parameters of 0.5 mg of digoxin i.v. AUC(0.48h) of immunoreactive digoxin during losartan 28.8 +/- 2.9 vs 28.5 +/- 3.9 ng ml-1 h during placebo; not significant, and 96 h urinary excretion [% dose] during losartan 54.0 +/- 7.2 vs 51.9 +/- 6.5% during placebo; not significant). Geometric mean ratios (90% confidence interval) for AUC and urinary excretion were respectively, 1.03 (0.98, 1.08) and 1.09 (0.98, 1.21). 5. Multiple oral doses of losartan did not affect the pharmacokinetic parameters of oral digoxin AUC(0.48 h) during losartan 23.6 +/- 3.7 ng ml-1 h vs 22.4 +/- 2.6 ng ml-1 h during placebo; not significant, Cmax 3.5 +/- 0.7 ng ml-1 with vs 3.1 +/- 0.5 ng ml-1 without losartan; not significant and tmax 0.6 +/- 0.2 h with vs 0.9 +/- 0.7 h without losartan; not significant, and 96 h urinary excretion [% dose] during losartan 51.2 +/- 6.3 vs 46.3 +/- 2.4% during placebo; not significant). Geometric mean ratios (90% confidence interval) for AUC and urinary excretion were respectively, 1.06 (0.98, 1.14) and 1.12 (0.97, 1.28). 6. We conclude that multiple oral doses of losartan (50 mg daily) do not alter the pharmacokinetics of immunoreactive digoxin, following either intravenous or oral digoxin. Furthermore, the co-administration of digoxin with losartan is well tolerated by healthy male volunteers.

Pharmacokinetic interactions with digoxin

Numerous pharmacological agents have been shown to produce clinically significant pharmacokinetic interactions with digoxin. Drugs which reduce digoxin absorption include the antacids aluminium hydroxide, magnesium hydroxide and magnesium trisilicate, the antidiarrhoeals kaolin and pectin, the hypocholesterolaemic agent cholestyramine and the chemotoxins cyclophosphamide, vincristine and bleomycin. Certain antibiotics including sulphasalazine, neomycin and aminosalicylic acid reduce digoxin absorption while others, including erythromycin and tetracycline, increase the bioavailability of digoxin in some patients. Capsule preparations of digoxin in solution are less subject to several of the interactions which affect the absorption and bioavailability of digoxin tablets. Various drugs induce alterations in the volume of distribution and clearance of digoxin. Cardiac patients receiving digoxin therapy are particularly prone to interactions with commonly co-administered medications such as the antiarrhythmics quinidine and amiodarone, the calcium channel blockers verapamil and nifedipine, and possibly some vasodilating agents. Studies of digoxin interactions have yielded discrepant results, indicating the need for careful analysis of investigational design before arriving at clinical conclusions.

Pharmacokinetic drug interactions between digoxin and antiarrhythmic agents and calcium channel blocking agents: an appraisal of study methodology

While preliminary screening for interactions between new cardiovascular pharmacotherapeutic agents and digoxin can be efficiently and safely conducted in normal healthy volunteers, it is particularly important to detect and quantify drug interactions in patients with varying degrees of cardiac, hepatic and/or renal dysfunction. Much of the previously published literature provides only minimal data to guide clinical practice because of limitations of study design including sample size and measurement techniques. Important factors that determine the ability of a particular study design to detect a drug interaction with digoxin include the accuracy and precision of the assay method for serum digoxin concentrations, intrasubject and intersubject variability in serum digoxin concentration, and sample size. The format of the trial (chronic versus single digoxin dosing in cardiac patients; chronic versus single digoxin dosing in normal subjects) and the method of assessment of alterations in digoxin handling (formal determination of digoxin clearance, comparison of multiple or single digoxin measurements during various phases of trial) also impact greatly on the clinical relevance of such investigations. Guidelines for future studies of drug interactions with digoxin in cardiac patients are proposed with particular emphasis on laboratory methods; measurement techniques during baseline, placebo, and active drug phases; calculation of the statistical power of the study; time course of the trial; and assessment of the clinical significance of the findings.

The effect of dietary fiber on the bioavailability of digoxin in capsules

Sixteen healthy volunteers were regularly given 0.4 mg of digoxin daily as two capsules with breakfast. After ten days during which breakfast was supplemented with 11 g of bran fiber, steady-state predose mean serum digoxin was lower (0.89 +/- 0.19 versus 0.84 +/- 0.18 ng/mL, P less than .05) and mean 24-hour area under curve determination was lower (30.5 +/- 6.1 versus 28.4 +/- 6.0 ng X hr/mL, P less than .05) than during the control period without bran. Height and time of peak serum digoxin, and 24-hour urinary digoxin were not significantly different. The 6 to 7% reduction in digoxin absorption from capsules is less than that reported from tablets and is probably clinically unimportant.

A steady-state evaluation of the effects of propantheline bromide and cholestyramine on the bioavailability of digoxin when administered as tablets or capsules

Drug interactions can profoundly alter the absorption of digoxin in tablet form. This study evaluated whether digoxin solution in capsules, a new dosage form with 90% to 100% bioavailability, would reduce such alterations, specifically those caused by cholestyramine and propantheline bromide. The investigation used a six-treatment, steady-state, balanced, incomplete block design with 18 healthy adults studied for four continuous two-week treatment periods. Treatments were either two 0.25 mg digoxin tablets or two 0.20 mg digoxin capsules administered alone, with propantheline, 15 mg qid, or with cholestyramine, 8 g qd. Bioavailability was determined from steady-state, 24-hour area under the serum concentration-time curve (AUC, ng X h/mL) and from 0- and 24-hour trough serum digoxin concentrations (ng/mL). The AUCs for tablets alone, with cholestyramine, and with propantheline were 32.8 +/- 13.3 (+/- SD), 22.4 +/- 12.1, and 40.6 +/- 13.9, respectively, while corresponding values for capsules were 31.7 +/- 9.3, 24.7 +/- 7.9, and 35.9 +/- 12.8. The trough concentrations for tablets alone, with cholestyramine, and with propantheline were 0.88 +/- 0.47, 0.61 +/- 0.38, and 1.09 +/- 0.35, respectively; trough concentrations for capsules were 0.77 +/- 0.28, 0.74 +/- 0.28, and 0.96 +/- 0.48, respectively. The only significant differences in AUC were seen when comparing tablets alone versus tablets with cholestyramine (P less than .0005) and tablets with propantheline (P less than .01). A significant finding was also observed when comparing trough concentrations for tablets alone versus tablets with cholestyramine (P less than .005).(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetic interactions between digoxin and other drugs

Drug interactions with digoxin are important because of this agent's narrow therapeutic index. Among the drugs that can decrease digoxin bioavailability are cholestyramine, antacid gels, kaolin-pectate, certain antimicrobial drugs and cancer chemotherapeutic agents. In selected patients, antibiotics may enhance digoxin bioavailability by eliminating intestinal flora that metabolize digoxin. Antiarrhythmic drugs, such as quinidine and amiodarone, can markedly increase steady state serum digoxin levels. Certain calcium channel blocking drugs, particularly verapamil, have a similar effect. Potassium-sparing diuretic drugs, such as spironolactone, can alter digoxin pharmacokinetics. Indomethacin may decrease renal excretion of digoxin in preterm infants. Finally, rifampin, an antibiotic used in the treatment of tuberculosis, may lower steady state serum digoxin levels in patients with severe renal disease. Physicians must maintain constant vigilance whenever medications are added to or withdrawn from a therapeutic regimen that includes digoxin.