Erythromycin-induced digoxin toxicity

Effects of medicines used to treat gastrointestinal diseases on the pharmacokinetics of coadministered drugs: a PEARRL Review

OBJECTIVES

Drugs used to treat gastrointestinal diseases (GI drugs) are widely used either as prescription or over-the-counter (OTC) medications and belong to both the 10 most prescribed and 10 most sold OTC medications worldwide. The objective of this review article is to discuss the most frequent interactions between GI and other drugs, including identification of the mechanisms behind these interactions, where possible.

KEY FINDINGS

Current clinical practice shows that in many cases, these drugs are administered concomitantly with other drug products. Due to their metabolic properties and mechanisms of action, the drugs used to treat gastrointestinal diseases can change the pharmacokinetics of some coadministered drugs. In certain cases, these interactions can lead to failure of treatment or to the occurrence of serious adverse events. The mechanism of interaction depends highly on drug properties and differs among therapeutic categories. Understanding these interactions is essential to providing recommendations for optimal drug therapy.

SUMMARY

Interactions with GI drugs are numerous and can be highly significant clinically in some cases. While alterations in bioavailability due to changes in solubility, dissolution rate, GI transit and metabolic interactions can be (for the most part) easily identified, interactions that are mediated through other mechanisms, such as permeability or microbiota, are less well-understood. Future work should focus on characterising these aspects.

Erythromycin infusion prior to endoscopy for acute nonvariceal upper gastrointestinal bleeding: a pilot randomized controlled trial

BACKGROUND/AIMS

The aim of this study was to compare the effects of erythromycin infusion and gastric lavage in order to improve the quality of visualization during emergency upper endoscopy.

METHODS

We performed a prospective randomized pilot study. Patients presented with hematemesis or melena within 12 hours and were randomly assigned to the erythromycin group (intravenous infusion of erythromycin), gastric lavage group (nasogastric tube placement with gastric lavage), or erythromycin + gastric lavage group (both erythromycin infusion and gastric lavage). The primary outcome was satisfactory visualization. Secondary outcomes included identification of a bleeding source, the success rate of hemostasis, duration of endoscopy, complications related to erythromycin infusion or gastric lavage, number of transfused blood units, rebleeding rate, and bleeding-related mortality.

RESULTS

A total of 43 patients were randomly assigned: 14 patients in the erythromycin group; 15 patients in the gastric lavage group; and 14 patients in the erythromycin + gastric lavage group. Overall satisfactory visualization was achieved in 81% of patients: 92.8% in the erythromycin group; 60.0% in the gastric lavage group; and 92.9% in the erythromycin + gastric lavage group, respectively (p = 0.055). The identification of a bleeding source was possible in all cases. The success rate of hemostasis, duration of endoscopy, and number of transfused blood units did not significantly differ between groups. There were no complications. Rebleeding occurred in three patients (7.0%). Bleeding-related mortality was not reported.

CONCLUSIONS

Intravenous erythromycin infusion prior to emergency endoscopy for acute nonvariceal upper gastrointestinal bleeding seems to provide satisfactory endoscopic visualization.

[Promotility drugs use in critical care: indications and limits?]

Enteral feeding is often limited by gastric and intestinal motility disturbances in critically ill patients, particularly in patients with shock. So, promotility agents are frequently used to improve tolerance to enteral nutrition. This review summaries the pathophysiology, presents the available pharmacological strategies, the clinical data, the counter-indications and the principal limits. The clinical data are poor. No study demonstrates a positive effect on clinical outcomes. Metoclopramide and erythromycin seems to be the more effective. Considering the risk of antibiotic resistance, the first line use of erythromycin should be avoided in favor of metoclopramide.

Role of p-glycoprotein inhibition for drug interactions: evidence from in vitro and pharmacoepidemiological studies

OBJECTIVES

We determined in vitro the potency of macrolides as P-glycoprotein inhibitors and tested in hospitalised patients whether coadministration of P-glycoprotein inhibitors leads to increased serum concentrations of the P-glycoprotein substrates digoxin and digitoxin.

METHODS

In vitro, the effect of macrolides on polarised P-glycoprotein-mediated digoxin transport was investigated in Caco-2 cells. In a pharmacoepidemiological study, we analysed the serum digoxin and digitoxin concentrations with and without coadministration of P-glycoprotein inhibitors in hospitalised patients.

RESULTS

All macrolides inhibited P-glycoprotein-mediated digoxin transport, with concentrations producing 50% inhibition (IC(50)) values of 1.8, 4.1, 15.4, 21.8 and 22.7 micromol/L for telithromycin, clarithromycin, roxithromycin, azithromycin and erythromycin, respectively. Coadministration of P-glycoprotein inhibitors was associated with increased serum concentrations of digoxin (1.3 +/- 0.6 vs 0.9 +/- 0.5 ng/mL, p < 0.01). Moreover, patients receiving macrolides had higher serum concentrations of cardiac glycosides (p < 0.05).

CONCLUSION

Macrolides are potent inhibitors of P-glycoprotein. Drug interactions between P-glycoprotein inhibitors and substrates are likely to occur during hospitalisation.

Concise Review: Clinical Relevance of Drug–Drug and Herb–Drug Interactions Mediated by the ABC Transporter ABCB1 (MDR1, P‐glycoprotein)

The importance of P-glycoprotein (P-gp) in drug-drug interactions is increasingly being identified. P-gp has been reported to affect the pharmacokinetics of numerous structurally and pharmacologically diverse substrate drugs. Furthermore, genetic variability in the multidrug resistance 1 gene influences absorption and tissue distribution of drugs transported. Inhibition or induction of P-gp by coadministered drugs or food as well as herbal constituents may result in pharmacokinetic interactions leading to unexpected toxicities or undertreatment. On the other hand, modulation of P-gp expression and/or activity may be a useful strategy to improve the pharmacological profile of anticancer P-gp substrate drugs. In recent years, the use of complementary and alternative medicine (CAM), like herbs, food, and vitamins, by cancer patients has increased significantly. CAM use substantially increases the risk for interactions with anticancer drugs, especially because of the narrow therapeutic window of these compounds. However, for most CAMs, it is unknown whether they affect metabolizing enzymes and/or drug transporter activity. Clinically relevant interactions are reported between St John's wort or grapefruit juice and anticancer as well as nonanticancer drugs. CAM-drug interactions could explain, at least in part, the large interindividual variation in efficacy and toxicity associated with drug therapy in both cancer and noncancer patients. The study of drug-drug, food-drug, and herb-drug interactions and of genetic factors affecting pharmacokinetics and pharmacodynamics is expected to improve drug safety and will enable individualized drug therapy. Disclosure of potential conflicts of interest is found at the end of this article.

Effect of macrolide antibiotics on uptake of digoxin into rat liver

The objective of this study was to examine the effect of macrolide antibiotics, clarithromycin, erythromycin, roxithromycin, josamycin and azithromycin, on the hepatic uptake of digoxin. The uptake of [(3)H]digoxin was studied in rats in vivo, using the tissue-sampling single-injection technique, and in isolated rat hepatocytes in vitro. The uptake of [(3)H]digoxin into rat hepatocytes was concentration-dependent with a Michaelis constant (K(m)) of 445 nM. All the macrolide antibiotics inhibited the uptake of [(3)H]digoxin into rat hepatocytes in a concentration-dependent manner. However, clarithromycin did not affect the in vivo hepatic uptake of digoxin in rats. The in vivo permeability-surface area product of digoxin for hepatic uptake (PS(inf)) was estimated to be 12.5 ml/min/g liver from the present in vitro data, which is far larger than the hepatic blood flow rate (1.4 ml/min/g liver). Macrolide antibiotics at clinically relevant concentrations inhibit digoxin uptake by rat hepatocytes in vitro, but not in vivo, probably because hepatic uptake of digoxin in rats is blood flow-limited. Clinically observed digoxin-macrolide interaction in humans could be due to macrolide inhibition of hepatic digoxin uptake, if the uptake is permeation-limited.

Comparative safety of the different macrolides

The macrolides are generally well tolerated when used for the treatment of acute infections. Even when given long term for prophylaxis, there are few discontinuations due to side-effects. There are isolated reports of QT(c) prolongation in patients treated with erythromycin and other 14-membered-ring macrolides. Since the 14-membered-ring macrolides are metabolized by P450 isoenzymes, there is the potential for interaction with other therapeutic agents also metabolized in this way. Pharmacokinetic studies have demonstrated interactions between either erythromycin or clarithromycin and cyclosporin, cisapride, pimozide, disopyramide, astemizole, carbamazepine, midazolam, digoxin, hydroxymethylglutaryl-coenzyme A reductase inhibitors (i.e. 'statins') and warfarin. In patients receiving such concurrent therapy, azithromycin may be superior to erythromycin and clarithromycin.

Pharmacokinetic aspects of treating infections in the intensive care unit: focus on drug interactions

Pharmacokinetic interactions involving anti-infective drugs may be important in the intensive care unit (ICU). Although some interactions involve absorption or distribution, the most clinically relevant interactions during anti-infective treatment involve the elimination phase. Cytochrome P450 (CYP) 1A2, 2C9, 2C19, 2D6 and 3A4 are the major isoforms responsible for oxidative metabolism of drugs. Macrolides (especially troleandomycin and erythromycin versus CYP3A4), fluoroquinolones (especially enoxacin, ciprofloxacin and norfloxacin versus CYP1A2) and azole antifungals (especially fluconazole versus CYP2C9 and CYP2C19, and ketoconazole and itraconazole versus CYP3A4) are all inhibitors of CYP-mediated metabolism and may therefore be responsible for toxicity of other coadministered drugs by decreasing their clearance. On the other hand, rifampicin is a nonspecific inducer of CYP-mediated metabolism (especially of CYP2C9, CYP2C19 and CYP3A4) and may therefore cause therapeutic failure of other coadministered drugs by increasing their clearance. Drugs frequently used in the ICU that are at risk of clinically relevant pharrmacokinetic interactions with anti-infective agents include some benzodiazepines (especially midazolam and triazolam), immunosuppressive agents (cyclosporin, tacrolimus), antiasthmatic agents (theophylline), opioid analgesics (alfentanil), anticonvulsants (phenytoin, carbamazepine), calcium antagonists (verapamil, nifedipine, felodipine) and anticoagulants (warfarin). Some lipophilic anti-infective agents inhibit (clarithromycin, itraconazole) or induce (rifampicin) the transmembrane transporter P-glycoprotein, which promotes excretion from renal tubular and intestinal cells. This results in a decrease or increase, respectively, in the clearance of P-glycoprotein substrates at the renal level and an increase or decrease, respectively, of their oral bioavailability at the intestinal level. Hydrophilic anti-infective agents are often eliminated unchanged by renal glomerular filtration and tubular secretion, and are therefore involved in competition for excretion. Beta-lactams are known to compete with other drugs for renal tubular secretion mediated by the organic anion transport system, but this is frequently not of major concern, given their wide therapeutic index. However, there is a risk of nephrotoxicity and neurotoxicity with some cephalosporins and carbapenems. Therapeutic failure with these hydrophilic compounds may be due to haemodynamically active coadministered drugs, such as dopamine, dobutamine and furosemide, which increase their renal clearance by means of enhanced cardiac output and/or renal blood flow. Therefore, coadministration of some drugs should be avoided, or at least careful therapeutic drug monitoring should be performed when available. Monitoring may be especially helpful when there is some coexisting pathophysiological condition affecting drug disposition, for example malabsorption or marked instability of the systemic circulation or of renal or hepatic function.

Effect of clarithromycin on renal excretion of digoxin: interaction with P-glycoprotein

We present a digoxin-clarithromycin interaction in two patients in whom digoxin concentrations were unexpectedly increased. The ratio of renal digoxin clearance to creatinine clearance in one patient was lower during the concomitant administration of clarithromycin (0.64 and 0.73) than that after cessation of clarithromycin administration (1.30 +/- 0.20; mean +/- SD). Because P-glycoprotein could play an important role in the renal secretion of digoxin, we hypothesized that clarithromycin decreases renal digoxin excretion by inhibiting P-glycoprotein-mediated transport. Digoxin transport was evaluated with use of a kidney epithelial cell line, which expresses the human P-glycoprotein on the apical membrane by transfection with MDR1 complementary deoxyribonucleic acid. Clarithromycin inhibited the transcellular transport of digoxin from the basolateral to the apical side in a concentration-dependent manner and concomitantly increased the cellular accumulation of digoxin. These results suggest that clarithromycin may inhibit the P-glycoprotein-mediated tubular secretion of digoxin, and this interaction mechanism may contribute to an increase in the serum digoxin concentration.

Macrolide antibacterials. Drug interactions of clinical significance

Macrolide antibiotics can interact adversely with commonly used drugs, usually by altering metabolism due to complex formation and inhibition of cytochrome P-450 IIIA4 (CYP3A4) in the liver and enterocytes. In addition, pharmacokinetic drug interactions with macrolides can result from their antibiotic effect on microorganisms of the enteric flora, and through enhanced gastric emptying due to a motilin-like effect. Macrolides may be classified into 3 different groups according to their affinity for CYP3A4, and thus their propensity to cause pharmacokinetic drug interactions. Troleandomycin, erythromycin and its prodrugs decrease drug metabolism and may produce drug interactions (group 1). Others, including clarithromycin, flurithromycin, midecamycin, midecamycin acetate (miocamycin; ponsinomycin), josamycin and roxithromycin (group 2) rarely cause interactions. Azithromycin, dirithromycin, rikamycin and spiramycin (group 3) do not inactivate CYP3A4 and do not engender these adverse effects. Drug interactions with carbamazepine, cyclosporin, terfenadine, astemizole and theophylline represent the most frequently encountered interactions with macrolide antibiotics. If the combination of a macrolide and one of these compounds cannot be avoided, serum concentrations of concurrently administered drugs should be monitored and patients observed for signs of toxicity. Rare interactions and those of dubious clinical importance are those with alfentanil and sufentanil, antacids and cimetidine, oral anticoagulants, bromocriptine, clozapine, oral contraceptive steroids, digoxin, disopyramide, ergot alkaloids, felodipine, glibenclamide (glyburide), levodopa/carbidopa, lovastatin, methylprednisolone, phenazone (antipyrine), phenytoin, rifabutin and rifampicin (rifampin), triazolam and midazolam, valproic acid (sodium valproate) and zidovudine.

The rational pharmacology of digoxin

Although digoxin remains one of the most widely prescribed drugs in the United States, potential pharmacodynamic and pharmacokinetic interactions between this compound and other drugs, diseases, and events commonly encountered in the perioperative period remain largely unappreciated. Furthermore, the therapeutic benefit of discontinuing or initiating digoxin treatment preoperatively remains unclear. We present a basic review of current knowledge regarding digoxin pharmacology and examine those concepts from the perspective of clinical anesthesiologists.