Digoxin-quinidine Interaction Research Articles

The effect of digoxin dosage on the digoxin-quinidine interaction in the bile duct-cannulated rat.

Pretreating anaesthetized bile duct-cannulated rats with 9 mg kg-1 quinidine significantly decreased the cumulative biliary excretion of digoxin and its metabolites after 10 or 100 micrograms kg-1 [3H]digoxin, although the effect was more marked in animals receiving the high dose of digoxin. In contrast, however, although quinidine pretreatment raised plasma radioactivity levels by 50-80% in animals given the higher dose of digoxin, no significant effect on circulating plasma levels was observed in rats receiving 10 micrograms kg-1 digoxin. Generally, quinidine had no statistically significant effect on other aspects of digoxin disposition, although with both digoxin doses there were trends towards a reduction in the direct intestinal secretion and urinary excretion of digoxin-derived radioactivity with an increase in tissue levels of radioactivity (apart from the small intestine wall where concentrations were reduced). The radioactivity in the bile after 100 or 10 micrograms kg-1 digoxin comprised about 25 and 33% of digoxin and digoxigenin bis-digitoxoside, respectively, as well as appreciable amounts of the monodigitoxoside and a highly polar component. This metabolite profile was unaffected by quinidine. The influence of cardiac glycoside dosage shown by the present work indicates that the digoxin-quinidine interaction and possibly analogous interactions involving other cardiac glycosides, may not always be readily detectable from plasma concentration data.

PH-dependent bidirectional transport of weakly basic drugs across Caco-2 monolayers: implications for drug-drug interactions.

The purpose of this study was to investigate the pH-dependent passive and active transport of weakly basic drugs across the human intestinal epithelium. The bidirectional pH-dependent transport of weak bases was studied in Caco-2 cell monolayers in the physiologic pH range of the gastrointestinal tract. A net secretion of atenolol and metoprolol was observed when a pH gradient was applied. However, the bidirectional transport of both compounds was equal in the nongradient system. Hence, at lower apical than basolateral pH a change in passive transport caused by an imbalance in the concentration of the uncharged drug species resulted in a "false" asymmetry (efflux ratio). Furthermore, a mixture of pH-dependent passive and active efflux was found for the P-glycoprotein (P-gp, MDR1, ABCB1) substrates, talinolol and quinidine, but not for the neutral drug, digoxin. However, the clinically important digoxin-quinidine interaction depended on the presence of a pH gradient. Hence, the degree of interaction depends on the amount of quinidine available at the binding site of the P-gp. Active efflux of weak bases can only be accounted for when the fraction of unionized drug species is equal in all compartments because the transport is biased by a pH-dependent passive component. However, this component may take part in vivo and contribute to drug-drug interactions involving P-gp.

P-glycoprotein: a defense mechanism limiting oral bioavailability and CNS accumulation of drugs.

Transport by ATP-dependent efflux pumps such as P-glycoprotein is an increasingly recognized determinant of drug disposition. P-glycoprotein does not only contribute to multidrug resistance (MDR) in tumor cells, it is also expressed in normal tissues with excretory function such as liver, kidney and intestine. Apical expression of P-glycoprotein in such tissues results in reduced drug absorption from the gastrointestinal tract and enhanced drug elimination into bile and urine. Moreover, expression of P-glycoprotein in the endothelial cells of the blood-brain barrier prevents entry of certain drugs into the central nervous system. Human P-glycoprotein has been shown to transport a wide range of structurally unrelated drugs such as digoxin, quinidine, cyclosporine and HIV-1 protease inhibitors. Drug administration to P-glycoprotein knock-out and control mice provided data on the importance of P-glycoprotein for absorption after oral administration and penetration through the blood-brain barrier. Moreover, P-glycoprotein knock-out mice were used to identify inhibition of P-glycoprotein-mediated transport as a mechanism for drug interactions such as the digoxin-quinidine interaction. Studies in humans indicate a particular importance of intestinal P-glycoprotein for bioavailability of the immunosuppressant cyclosporine. Moreover, induction of intestinal P-glycoprotein by rifampin has now been identified as the major underlying mechanism of reduced digoxin plasma concentrations during concomitant rifampin therapy. In summary, P-glycoprotein functions as a defense mechanism, which determines bioavailability and CNS concentrations of drugs. Modification of P-glycoprotein function is an important underlying mechanism of drug interactions in humans. However, disposition of a drug and its metabolites frequently is not only determined by P-glycoprotein, but also by drug-metabolizing enzymes and possibly by drug transporters other than P-glycoprotein [e.g. members of the MRP family (MRP = multidrug resistance-associated proteins)].

Inhibition of P-glycoprotein-mediated drug transport: A unifying mechanism to explain the interaction between digoxin and quinidine [seecomments

Although quinidine is known to elevate plasma digoxin concentrations, the mechanism underlying this interaction is not fully understood. Digoxin is not extensively metabolized, but it is known to be transported by the drug efflux pump P-glycoprotein, which is expressed in excretory tissues (kidney, liver, intestine) and at the blood-brain barrier. Accordingly, we tested the hypothesis that inhibition of P-glycoprotein-mediated digoxin transport by quinidine contributes to the digoxin-quinidine interaction. First, we demonstrated active transcellular transport of both digoxin and quinidine in cultured cell lines that express P-glycoprotein in a polarized fashion. In addition, 5 micromol/L quinidine inhibited P-glycoprotein-mediated digoxin transport by 57%. Second, the effect of quinidine on digoxin disposition was studied in wild-type and in mdr1a(-/-) mice, in which the gene expressing the major digoxin-transporting P-glycoprotein has been disrupted. Because the in vitro data showed that quinidine itself is a P-glycoprotein substrate, quinidine doses were reduced in mdr1a(-/-) mice to produce plasma concentrations similar to those in wild-type control animals. Quinidine increased plasma digoxin concentrations by 73.0% (P=0.05) in wild-type animals, compared with 19.5% (P=NS) in mdr1a(-/-) mice. Moreover, quinidine increased digoxin brain concentrations by 73.2% (P=0.05) in wild-type animals; by contrast, quinidine did not increase digoxin brain concentrations in mdr1a(-/-) mice but rather decreased them (-30.7%, P<0.01). Quinidine and digoxin are both substrates for P-glycoprotein, and quinidine is a potent inhibitor of digoxin transport in vitro. The in vivo data strongly support the hypothesis that inhibition of P-glycoprotein-mediated digoxin elimination plays an important role in the increase of plasma digoxin concentration occurring with quinidine coadministration in wild-type mice and thus support a similar mechanism in humans.

Quinidine enhances digitalis toxicity at therapeutic serum digoxin levels

To determine the effect of the digoxin-quinidine interaction on rate of in-hospital digitalis toxicity. This was a prospective observational study over 9 months, set in two general medical wards. We studied consecutive patients (n = 141) who were receiving digoxin. Measurements included digitalis toxicity, defined by ECG criteria and resolution after stopping digoxin; all additional medications (including antiarrhythmics) continued. The observer was "blinded" to serum digoxin level and to concomitant drugs. Digitalis toxicity rates were as follows: digoxin alone, 4.9% (5 of 101 patients); with amiodarone or verapamil, 5.0% (1 of 20 patients); with quinidine, 50% (10 of 20 patients) (p < 0.01). No toxicity was seen at digoxin levels < 1.0 ng/ml. Toxicity at 1.0 to 2.0 ng/ml was as follows: digoxin alone, 1 of 41 patients; with quinidine, 4 of 15 patients (p = 0.014). Toxicity was similar at levels > 2.0 ng/ml: 4 of 8 patients and 7 of 11 patients, respectively. Independent relative risks and 95% confidence intervals (CI) of digitalis toxicity were as follows: serum digoxin, 9.1 (95% CI, 2.9 to 13.0); concurrent quinidine, 24.3 (95% CI, 3.4 to 124). There was a significant (p < 0.01) interaction between concurrent quinidine, serum digoxin of 1.0 to 2.0 ng/ml, and digitalis toxicity. The digoxin-quinidine interaction significantly increases digitalis toxicity, even in the therapeutic range of serum digoxin levels.

Health Implications of Drug Interactions

The awareness of the digoxin-quinidine interaction in the mid-70s led to increased interest in drug interactions. Much has been published on the subject in the form of interaction reports, handbooks, lists, cards, discs etc. However, only a few interactions in the literature have clinical significance and can be remembered by thinking in terms of groups, pharmacokinetics and probabilities. It is important to realise that drugs in a given class will have similar properties. Thus, phenylbutazone, like any other nonsteroidal anti-inflammatory drug (NSAID), is likely to potentiate the effects of warfarin. A knowledge of drug pharmacokinetics is also essential; a highly protein-bound drug may displace another when they are administered together. Remembering those drugs which induce liver enzyme formation will prevent their co-administration with drugs which have a critical dose-range. If a general practitioner can remember the few drugs in clinical practice with a narrow therapeutic index, he can consult a handbook before anything else is prescribed. Some interactions will rarely be encountered in daily general practice, i.e. those associated with tuberculosis treatment or anesthetic agents. Other interactions, e.g. the interaction between antihypertensive treatment and over-the-counter medication containing phenylpropanolamine, are more common. While most drug interactions can be avoided by thinking in terms of groups, pharmacokinetics and probabilities, some learning by rote is required, e.g. the potential for heart failure with concomitant beta-blocker and nifedipine therapy. In general, a schematic approach using thinking in terms of groups, pharmacokinetics and probabilities will prevent most clinically significant drug interactions; the rest can be avoided by consulting appropriate handbooks and specialists.

Effect of milrinone on steady-state digoxin levels in congestive heart failure

A variety of cardioactive agents have been shown to affect the pharmacokinetics of digoxin and thereby alter serum digoxin levels. Since the first reports describing the digoxin-quinidine interaction, 1,2 numerous agents have been shown to increase serum digoxin levels. 3–6 Milrinone is a nonglycoside, noncatecholamine inotropic agent currently undergoing investigation for the treatment of congestive heart failure. Because many patients receive digoxin for the treatment of heart failure, we attempted to determine retrospectively if milrinone significantly affects steady-state digoxin levels in a heart failure population.

Digoxin quinidine interaction: A pharmacokinetic study in the isolated perfused rat liver

Digoxin-quinidine interaction was studied in the experimental model of isolated perfused rat liver. Neither digoxin nor quinidine were toxic to the isolated rat liver. The clearance of digoxin and quinidine by the liver was directly related to the rate of bile flow and the size of the initial dose of digoxin. In the presence of quinidine, after initial doses of digoxin of 0.5 and 1 μg, the concentration of digoxin in the perfusate was increased 2.5 and 3-fold. Its excretion in the bile was reduced by 45% and 20.5%, respectively (all comparisons, p<0.01). Digoxin concentration in the liver tissue was calculated and found to be appreciably elevated in the presence of quinidine. A reduction of about 30% (p<0.05) in the excretion of quinidine in the bile was observed in the presence of digoxin. Thus, a competition of digoxin and quinidine for biliary excretion was demonstrated as an underlying cause for digoxin-quinidine interaction in the isolated perfused rat liver.

Reduction of Digoxin Effect During the Digoxin-Quinidine Interaction

Reduction of Digoxin Effect During the Digoxin-Quinidine Interaction

Reduction of digoxin effect during the digoxin-quinidine interaction.

The effects of the digoxin-quinidine interaction on cardiac function was examined in healthy subjects. Our results indicate that while serum digoxin levels were elevated, the improved cardiac function due to digoxin declined during combined therapy. Our data also provide an alternate explanation for the changes previously interpreted as "enhanced digitalis effects" during the interaction.

Biological model for the study of the digoxin-quinidine drug interaction

Biological model for the study of the digoxin-quinidine drug interaction

Digoxin-quinidine interaction in patients with chronic renal failure.

We evaluated the effect of quinidine on digoxin pharmacokinetic in six patients with severe renal failure. Quinidine reduced the total body clearance of digoxin from 1.87 to 1.06 l/hour (p less than 0.001), and prolonged the digoxin half-life of elimination from 5.20 to 9.61 days (p less than 0.01). The digoxin volume of distribution was unchanged. Renal clearance of digoxin was negligible; thus, the decrease in total body clearance was due to a decrease in the nonrenal clearance of digoxin. The mean trough serum concentrations of quinidine ranged from 1.0 to 3.0 micrograms/ml. We conclude that in patients with chronic renal failure, the dose of digoxin should be decreased by 50% if quinidine therapy is initiated.

Digoxin-quinidine interaction in renal failure patients on hemodialysis: Insight into mechanism

Digoxin-quinidine interaction in renal failure patients on hemodialysis: Insight into mechanism

Digoxin-quinidine interaction in unanesthetized guinea pigs.

The clinically relevant interaction between quinidine (3 mg/kg) and digoxin (0.6 mg/kg plus 20 microCi 3H-digoxin) was investigated using unanesthetized and unrestrained guinea pigs for in vivo pharmacokinetic and tissue disposition studies. Quinidine caused a significant elevation of plasma levels of digoxin as early as 5 min after injection, and the increase persisted for at least 8 h. A significant decrease in the volume of distribution for digoxin from 3.6 to 2.7 liters/kg (20%) was observed in quinidine-treated animals. No change was noted in the dominant elimination half-life of digoxin in quinidine-treated animals. The decreased volume of distribution appeared to be due to displacement of digoxin from tissue stores by quinidine as evidenced by decreased tissue to plasma ratios for kidney (41%), intestine (41%), fat (33%), lung (31%), left ventricle (27%), liver (24%), left atrium (22%), right ventricle (21%), right atrium (18%), pancreas (12%), and bladder (-4%) samples.

Digoxin-quinidine interaction in the dog.

In seven healthy dogs, digoxin was given as an oral loading dose (0.05 mg/kg/day) on the first day, followed by an oral maintenance dose (0.02 mg/kg/day) during the next 14 days. On the sixth day of digoxin treatment, oral quinidine (200 mg b.i.d.) was added until the tenth day. Plasma concentrations of digoxin and quinidine were measured; in three of the seven dogs ECG and physical signs of digitalis toxicity were evaluated. The average steady state plasma concentration of digoxin increased significantly (P less than 0.01) during quinidine administration (from 1.4 to 2.3 ng/ml). On the days that digoxin was administered without quinidine, none of the dogs vomited nor was anorectic; the PQ-interval increased significantly (P less than 0.01) between 0.01 and 0.03 s. When quinidine was added, vomiting and anorexia occurred but no further increases in the PQ-interval were seen.

Digoxin-quinidine interaction in patients with renal failure.

Investigations were performed in order to study whether or not quinidine would exert similar effects on the serum digoxin concentration in patients with renal failure as in normal subjects. Fourteen out of fifteen patients showed a significant increase of the serum digoxin level after four days of quinidine application. This indicates, that the quinidine effect is not solely caused by a decrease of the renal digoxin clearance, although nine patients, not being hemodialysed, revealed a correlation between their creatinine clearance and the rise of the serum digoxin concentration after quinidine. As however, the patients on hemodialysis did not show higher digoxin levels than those treated conservatively, it is suggested that the degree of the uremic intoxication might be responsible for the observed correlation.

Effect of quinidine on positive inotropic action of digoxin

To determine whether digoxin-quinidine interaction alters the inotropic effect of the glycoside, the response of peak isometric force and maximal rate of force development (dF/dt) in isolated feline right ventricular papillary muscles to digoxin and quinidine alone, and in various combinations, was examined. The administration of 1.3 or 2.6 × 10 −5M of quinidine after 2 × 10 −7M of digoxin resulted in an increase in contractile performance in each animal. Although 1.3 × 10 −5M of quinidine alone produced a positive inotropic effect, 2.6 × 10 −5M of quinidine produced no such effect. Because myocardial digoxin content has been reported to decline after administration of quinidine these results suggest that the increase in contractile performance when quinidine was administered after digoxin is due to displacement of digoxin from less to more active myocardial sites. The administration of 2 or 4 × 10 −7M of digoxin after 2.6 × 10 −5M of quinidine resulted in a minimal increase in force and rate of force development. A similar inhibition of the inotropic effect of digoxin was found in rabbit papillary muscles pretreated with quinidine. Inhibition was not limited to digoxin because pretreatment of muscles with quinidine also inhibited the inotropic effect of acetylstrophanthidin. Thus, quinidine has diametrically opposite effects on digitalis-induced inotropy dependent on the sequence with which the drugs are administered.

Pharmacokinetics of digoxin in patients subjected to the quinidine-digoxin interaction.

1 This study was designed to evaluate pharmacokinetically the digoxin-quinidine interaction in patients with atrial fibrillation. 2 Five patients on maintenance digoxin therapy were given [3H]-digoxin as a single i.v. dose before and during quinidine therapy and the elimination of [3H]-digoxin from plasma and excretion in urine were determined. 3 The mean steady state plasma concentration of digoxin increased from 0.7 to 1.3 nmol/l after quinidine administration. 4 The apparent volume of distribution of digoxin decreased on the average 38%. Renal clearance and the total body clearance of digoxin decreased 51 and 56% respectively (mean values). Also non renal clearance was reduced. The fraction of digoxin excreted unmetabolised in urine did not change during quinidine treatment. The mean elimination half life of digoxin increased from 49 to 72 h during quinidine. 5 In two patients the DC-shock did not cause a conversion to sinus rhythm. However, the quinidine induced changes in the pharmacokinetics of digoxin in these patients did not differ from the others. 6 Quinidine appears to decrease the amount of digoxin distributed to body tissue(s). In addition, the reduction of renal clearance of digoxin and the observed unchanged clearance of creatinine suggests an inhibition of the renal secretion of digoxin.

The digoxin-quinidine interaction: serum protein binding unlikely to be involved.

British Journal of Clinical PharmacologyVolume 11, Issue 1 p. 94-96 Free Access The digoxin-quinidine interaction: serum protein binding unlikely to be involved. B Fichtl, B FichtlSearch for more papers by this authorW Doering, W DoeringSearch for more papers by this author B Fichtl, B FichtlSearch for more papers by this authorW Doering, W DoeringSearch for more papers by this author First published: January 1981 https://doi.org/10.1111/j.1365-2125.1981.tb01111.xCitations: 2AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume11, Issue1January 1981Pages 94-96 ReferencesRelatedInformation

Further insights into digoxin-quinidine interaction: Lack of correlation between serum digoxin concentration and inotropic state of the heart

The digoxin-quinidine interaction was studied in nine healthy human subjects aged 26 to 31 years. A single oral dose (400 mg) of quinidine sulfate administered to subjects taking digoxin resulted in a mean (± standard error of the mean) increase within 1 to 6 hours in the serum digoxin concentration of 0.12 ± 0.01 ng/ ml (p <0.0001), an increase of 21 percent. Continued quinidine administration for 24 hours resulted in a 59 percent increase in the mean serum digoxin concentration from 0.68 ± 0.04 to 1.04 ± 0.06 ng/ ml (alpha = 0.05). At the same time, however, systolic time intervals demonstrated a lengthening of the mean left ventricular ejection time index from 406 ± 4 to 419 ± 2 ms (alpha = 0.05) and the mean Q−S 2 Index from 524 ± 6 to 532 ± 7 ms (difference not significant [NS]). When compared with the shortening of these intervals predicted from the digoxin dose-response curve if digoxin were the only variable, the lengthening actually observed for both intervals was highly significant. The negative inotropic effect of quinidine administration alone was assessed with systolic time intervals in four subjects. The left ventricular ejection time index lengthened from 419 ± 3 to 425 ± 6 ms (NS) and the Q−S 2 index from 541 ± 6 to 550 ± 7 ms (NS). Therefore, the lengthening of these intervals in subjects taking digitalis after the addition of quinidine represents more than just the negative inotropic effect of quinidine, and occurs despite the increase in serum digoxin concentration. The results of this study support the view that quinidine displaces digoxin from tissue-binding sites as a major mechanism of the interaction. Furthermore, it appears that quinidine may specifically displace digoxin from cardiac-binding sites. These results raise important questions concerning the recommendation to reduce the maintenance digoxin dose when concomitant quinidine therapy is initiated.