Refining the in vitro and in vivo critical parameters for P-glycoprotein, [I]/IC50 and [I2]/IC50, that allow for the exclusion of drug candidates from clinical digoxin interaction studies.
The objective of this work was to further investigate the reasons for disconcordant clinical digoxin drug interactions (DDIs) particularly for false negative where in vitro data suggests no P-glycoprotein (P-gp) related DDI but a clinically relevant DDI is evident. Applying statistical analyses of binary classification and receiver operating characteristic (ROC), revised cutoff values for ratio of [I]/IC(50) < 0.1 and [I(2)]/IC(50) < 5 were identified to minimize the error rate, a reduction of false negative rate to 9% from 36% (based on individual ratios). The steady state total C(max) at highest dose of the inhibitor is defined as [I] and the ratio of the nominal maximal gastrointestinal concentration determined for highest dose per 250 mL volume defined [I(2)](.) We also investigated the reliability of the clinical data to see if recommendations can be made on values that would allow predictions of 25% change in digoxin exposure. The literature derived clinical digoxin interaction studies were statistically powered to detect relevant changes in exposure associated with digitalis toxicities. Our analysis identified that many co-meds administered with digoxin are cardiovascular (CV) agents. Moreover, our investigations also suggest that the presence of CV agents may alter cardiac output and/or kidney function that may act alone or are additional components to enhance digoxin exposure along with P-gp interaction. While we recommend digoxin as the probe substrate to define P-gp inhibitory potency for clinical assessment, we observed high concordance in P-gp inhibitory potency for calcein AM as a probe substrate.
Cook
Jack A
JA
Departments of Clinical Pharmacology, Pharmacokinetics, Groton/New London, Connecticut, Sandwich, UK.
Feng
Bo
B
Fenner
Katherine S
KS
Kempshall
Sarah
S
Liu
Ray
R
Rotter
Charles
C
Smith
Dennis A
DA
Troutman
Matthew D
MD
Ullah
Mohammed
M
Lee
Caroline A
CA
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D002986:Clinical Trials as Topic; D004077:Digoxin / Q000378:metabolism*; D004347:Drug Interactions; D006801:Humans; D020128:Inhibitory Concentration 50; D004364:Pharmaceutical Preparations / Q000378:metabolism*
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D004364:Pharmaceutical Preparations; D004077:Digoxin