Effect of plantain on therapeutic drug monitoring of digoxin and thirteen other common drugs.
BACKGROUND
Plantain, a herbal remedy, has been reported to interfere with therapeutic drug monitoring of digoxin. We evaluated three commercially available plantain products for potential interference with therapeutic drug monitoring of digoxin and 13 other common drugs.


METHODS
Dry content of plantain capsule or plantain leaf was extracted with either methanol or ethanol:water (60:40 by volume), added to drug-free serum and apparent digoxin was measured by both fluorescence polarization immunoassay and microparticle enzyme immunoassay. Using immunoassays, we also measured apparent concentrations of 13 other drugs (tobramycin, procainamide, tricyclic antidepressants, quinidine, carbamazepine, phenytoin, theophylline, valproic acid, amikacin, gentamycin, phenobarbital, salicylate and acetaminophen [paracetamol]) due to the presence of plantain. In separate experiments, a serum pool prepared from patients receiving digoxin was further supplemented with plantain and observed digoxin values were compared with original digoxin concentration. The presence of any cardiac glycoside in plantain was also investigated using thin layer chromatography (TLC).


RESULTS
We observed no apparent digoxin in the presence of plantain in serum. Moreover, when aliquots of digoxin serum pool were supplemented with various amounts of plantain, the observed digoxin concentrations in the presence of plantain compared well with original digoxin concentration. TLC analysis did not show the presence of either digoxin or digitoxin in plantain products studied. Moreover, plantain did not affect immunoassay results of the 13 other drugs studied.


CONCLUSIONS
The plantain products studied did not interfere with therapeutic drug monitoring of digoxin as well as 13 other commonly monitored drugs.
Dasgupta
Amitava
A
Department of Pathology and Laboratory Medicine, University of Texas-Houston Medical School, 6431 Fannin, MSB 2.292, TX, USA. Amitava.Dasgupta@uth.tmc.edu
Davis
Bonnette
B
Wells
Alice
A
D002301:Cardiac Glycosides / Q000627:therapeutic use*; D002316:Cardiotonic Agents / Q000627:therapeutic use*; D002855:Chromatography, Thin Layer; D004077:Digoxin / Q000627:therapeutic use*; D004347:Drug Interactions; D016903:Drug Monitoring; D016231:Fluorescence Polarization Immunoassay; D006801:Humans; D007118:Immunoassay; D010943:Plantago / Q000378:metabolism*
D002301:Cardiac Glycosides; D002316:Cardiotonic Agents; D004077:Digoxin