Digoxin (Page 4 of 8)

5.8 Reduced Efficacy In Patients With Hypocalcemia

Hypocalcemia can nullify the effects of digoxin in humans; thus, digoxin may be ineffective until serum calcium is restored to normal. These interactions are related to the fact that digoxin affects contractility and excitability of the heart in a manner similar to that of calcium.

5.9 Altered Response in Thyroid Disorders and Hypermetabolic States

Hypothyroidism may reduce the requirements for digoxin.

Heart failure and/or atrial arrhythmias resulting from hypermetabolic or hyperdynamic states (e.g., hyperthyroidism, hypoxia, or arteriovenous shunt) are best treated by addressing the underlying condition. Atrial arrhythmias associated with hypermetabolic states are particularly resistant to digoxin treatment. Patients with beri beri heart disease may fail to respond adequately to digoxin if the underlying thiamine deficiency is not treated concomitantly.

6 ADVERSE REACTIONS

The following adverse reactions are included in more detail in the Warnings and Precautions section of the label:

  • Cardiac arrhythmias [see Warnings and Precautions (5.1, 5.2)]
  • Digoxin Toxicity [see Warnings and Precautions (5.3)]

6.1 Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in clinical practice.

In general, the adverse reactions of Digoxin Tablets are dose-dependent and occur at doses higher than those needed to achieve a therapeutic effect. Hence, adverse reactions are less common when Digoxin Tablets are used within the recommended dose range, is maintained within the therapeutic serum concentration range, and when there is careful attention to concurrent medications and conditions.

In the DIG trial (a trial investigating the effect of digoxin on mortality and morbidity in patients with heart failure), the incidence of hospitalization for suspected digoxin toxicity was 2% in patients taking Digoxin Tablets compared to 0.9% in patients taking placebo [see Clinical Studies (14.1)].

The overall incidence of adverse reactions with digoxin has been reported as 5 to 20%, with 15 to 20% of adverse events considered serious. Cardiac toxicity accounts for about one-half, gastrointestinal disturbances for about one-fourth, and CNS and other toxicity for about one-fourth of these adverse events.

Gastrointestinal: In addition to nausea and vomiting, the use of digoxin has been associated with abdominal pain, intestinal ischemia, and hemorrhagic necrosis of the intestines.

CNS: Digoxin can cause headache, weakness, dizziness, apathy, confusion, and mental disturbances (such as anxiety, depression, delirium, and hallucination).

Other: Gynecomastia has been occasionally observed following the prolonged use of digoxin. Thrombocytopenia and maculopapular rash and other skin reactions have been rarely observed.

To report SUSPECTED ADVERSE REACTIONS, contact West-Ward Pharmaceutical Corp. at 1-877-233-2001, or the FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.

7 DRUG INTERACTIONS

Digoxin has a narrow therapeutic index, increased monitoring of serum digoxin concentrations and for potential signs and symptoms of clinical toxicity is necessary when initiating, adjusting, or discontinuing drugs that may interact with digoxin. Prescribers should consult the prescribing information of any drug which is co-prescribed with digoxin for potential drug interaction information.

7.1 P-Glycoprotein (PGP) Inducers/Inhibitors

Digoxin is a substrate of P-glycoprotein. Drugs that induce or inhibit P-glycoprotein in intestine or kidney have the potential to alter digoxin pharmacokinetics.

7.2 Pharmacokinetic Drug Interactions

NA – Not available/reported
Digoxin concentrations increased greater than 50%
Digoxin Serum Concentration Increase Digoxin AUC Increase Recommendations
Amiodarone 70% NA Measure serum digoxin concentrations before initiating concomitant drugs. Reduce digoxin concentrations by decreasing dose by approximately 30-50% or by modifying the dosing frequency and continue monitoring.
Captopril 58% 39%
Clarithromycin NA 70%
Dronedarone NA 150%
Gentamicin 129 to 212% NA
Erythromycin 100% NA
Itraconazole 80% NA
Nitrendipine 57% 15%
Propafenone NA 60 to 270%
Quinidine 100% NA
Ranolazine 50% NA
Ritonavir NA 86%
Tetracycline 100% NA
Verapamil 50 to 75% NA
Digoxin concentrations increased less than 50%
Atorvastatin 22% 15% Measure serum digoxin concentrations before initiating concomitant drugs. Reduce digoxin concentrations by decreasing the dose by approximately 15-30% or by modifying the dosing frequency and continue monitoring.
Carvedilol 16% 14%
Diltiazem 20% NA
Indomethacin 40% NA
Nefazodone 27% 15%
Nifedipine 45% NA
Propantheline 24% 24%
Quinine NA 33%
Saquinavir 27% 49%
Spironolactone 25% NA
Telmisartan 20 to 49% NA
Tolvaptan 30% NA
Trimethoprim 22 to 28% NA
Digoxin concentrations increased, but magnitude is unclear
Alprazolam, azithromycin, cyclosporine, diclofenac, diphenoxylate, epoprostenol, esomeprazole, ibuprofen, ketoconazole, lansoprazole, metformin, omeprazole, rabeprazole, Measure serum digoxin concentrations before initiating concomitant drugs. Continue monitoring and reduce digoxin dose as necessary.
Digoxin concentrations decreased
Acarbose, activated charcoal, albuterol, antacids, certain cancer chemotherapy or radiation therapy, cholestyramine, colestipol, extenatide, kaolin-pectin, meals high in bran, metoclopramide, miglitol, neomycin, penicillamine, phenytoin, rifampin, St. John’s Wort, sucralfate, sulfasalazine Measure serum digoxin concentrations before initiating concomitant drugs. Continue monitoring and increase digoxin dose by approximately 20-40% as necessary.
No significant Digoxin exposure changes
Please refer to section 12 for a complete list of drugs which were studied but reported no significant changes on digoxin exposure. No additional actions are required.

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