DIGOXIN injection drug interactions
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Abdurahman Khalil, M.D. [2]
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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
Pharmacokinetic interactions have been observed and reported primarily when digoxin is co-administered by oral route. There are very few studies that have evaluated the drug interaction when digoxin is administered via IV route. The magnitude of digoxin exposure change through IV route is generally lower than that through oral route. Table below provides available interaction data using digoxin IV formulation (NA means not available).
7.3 Potentially Significant Pharmacodynamic Drug Interactions
Because of considerable variability of pharmacodynamic interactions, the dosage of digoxin should be individualized when patients receive these medications concurrently.
7.4 Drug/Laboratory Test Interactions
Endogenous substances of unknown composition (digoxin-like immunoreactive substances [DLIS]) can interfere with standard radioimmunoassays for digoxin. The interference most often causes results to be falsely positive or falsely elevated, but sometimes it causes results to be falsely reduced. Some assays are more subject to these failings than others. Several LC/MS/MS methods are available that may provide less susceptibility to DLIS interference. DLIS are present in up to half of all neonates and in varying percentages of pregnant women, patients with hypertrophic cardiomyopathy, patients with renal or hepatic dysfunction, and other patients who are volume-expanded for any reason. The measured levels of DLIS (as digoxin equivalents) are usually low (0.2 to 0.4 ng/mL), but sometimes they reach levels that would be considered therapeutic or even toxic.
In some assays, spironolactone, canrenone, and potassium canrenoate may be falsely detected as digoxin, at levels up to 0.5 ng/mL. Some traditional Chinese and Ayurvedic medicine substances like Chan Su, Siberian Ginseng, Asian Ginseng, Ashwagandha, or Dashen can cause similar interference.
Spironolactone and DLIS are much more extensively protein-bound than digoxin. As a result, assays of free digoxin levels in protein-free ultrafiltrate (which tend to be about 25% less than total levels, consistent with the usual extent of protein binding) are less affected by spironolactone or DLIS. It should be noted that ultrafiltration does not solve all interference problems with alternative medicines. The use of an LC/MS/MS method may be the better option according to the good results it provides, especially in terms of specificity and limit of quantization.
References
http://dailymed.nlm.nih.gov/dailymed/lookup.cfm?setid=58f45aba-ff6f-43cc-bb88-be40a9f7beda