Application of two-point assay of digoxin serum concentration in studying population pharmacokinetics in Egyptian pediatric patients with heart failure: does it make sense?
Digoxin pharmacokinetics (PK) was studied among a selected group of Egyptian pediatric patients (n = 40) with an age range of 0.33 to 15 years. All the patients had heart failure and were maintained on i.v. digoxin (10 microg/kg/d in 2 equal doses). For population PK analysis, 2 serum samples of digoxin were taken per patient. From 30 patients' trough (before the next dose) and 4 hours postdose samples were obtained, while in the other 10 patients, 0.5- and 6-hour postdose samples were taken. Serum concentrations were measured by fluorescence polarization immunoassay. PK modeling was performed using NONMEM software on log-transformed serum digoxin data. The best structural covariate-free model was a linear 2-compartment model with an exponential error model for intersubject variability and an additive model for intrasubject variability. Serum creatinine (SCR) was a significant covariate for clearance. The final population PK parameters were CL (L/h) = 0.388 - [0.78 x (SCR-0.6)], V1 (L/kg) = 1.38, Q (L/h/kg) = 0.48, V2 (L/kg) = 9.11, where CL is the total body clearance, V1 and V2 are the apparent volumes of distribution in the central and peripheral compartments, and Q is intercompartment clearance. A bootstrap resampling for internal validation achieved excellent agreement with the original data sets for PK parameters. In conclusion, 2 points of digoxin concentration allow good regression analysis for clearance-covariate relationship. The inclusion of SCR into the final model might allow better selection of initial maintenance dose of the drug. A prospective study on larger sample size of pediatric patients is recommended for clinical validation of the final model.
el-Desoky
Ehab S
ES
Pharmacology Department, Faculty of Medicine, Assiut University, Assiut, Egypt. ehegypt@yahoo.com
Madabushi
Rajanikanth
R
Amry
Salah el-Din A
Sel-D
Bhattaram
Venkatesh Atul
VA
Derendorf
Hartmut
H
D000293:Adolescent; D002316:Cardiotonic Agents / Q000097:blood / Q000493:pharmacokinetics* / Q000627:therapeutic use; D002648:Child; D002675:Child, Preschool; D003404:Creatinine / Q000097:blood; D004077:Digoxin / Q000097:blood / Q000493:pharmacokinetics* / Q000627:therapeutic use; D016903:Drug Monitoring / Q000379:methods*; D004534:Egypt; D005260:Female; D016231:Fluorescence Polarization Immunoassay; D006333:Heart Failure / Q000188:drug therapy*; D006801:Humans; D007223:Infant; D007275:Injections, Intravenous; D008297:Male; D008657:Metabolic Clearance Rate
D002316:Cardiotonic Agents; D004077:Digoxin; D003404:Creatinine