Cisapride: a potential model substrate to assess cytochrome P4503A4 activity in vivo.
OBJECTIVE
Cisapride was compared with midazolam in vivo to determine its potential applicability as a cytochrome P450 (CYP) 3A4 "probe." As well, we evaluated whether cisapride was transported by P-glycoprotein.


METHODS
Bidirectional transport assays were conducted in LLC-PK1 cells and the derivative cell line L-MDR1 to determine whether cisapride was a substrate for P-glycoprotein. A pharmacokinetic study was also conducted in 17 healthy adults (n = 8 women) who received intravenous midazolam (0.025 mg/kg), oral midazolam (0.15 mg/kg), and oral cisapride (0.07 mg/kg) in a randomized crossover design. Plasma concentrations were quantitated from repeated after-dosing blood samples by HPLC with ultraviolet detection for midazolam and HPLC with tandem mass spectrometry detection for cisapride and norcisapride. Pharmacokinetic parameters were determined by noncompartmental methods. Both linear and nonlinear regression analyses were used to examine the association between the apparent plasma clearance of midazolam and cisapride and the cisapride/norcisapride plasma concentration ratios.


RESULTS
Although not a substrate for P-glycoprotein, cisapride inhibited P-glycoprotein with an apparent inhibition constant (K(i)) of 16.1 micromol/L. Linear correlations between cisapride clearance and both intravenous and oral midazolam clearance (P =.01, r(2) = 0.43 and P =.001, r(2) = 0.46, respectively) were found. Cisapride/norcisapride plasma concentration ratios at 8 hours (P =.001, r(2) = 0.90) and 12 hours (P =.001, r(2) = 0.96), as well as cisapride plasma concentrations at these time points, were shown to accurately predict the area under the plasma concentration versus time curve for cisapride.


CONCLUSIONS
CYP3A4 activity reflected by the total body clearance after oral administration of cisapride should be independent of transport by P-glycoprotein. Concordance between the pharmacokinetics for cisapride and midazolam support the applicability of oral cisapride as a pharmacologic substrate to assess total CYP3A4 activity in vivo. Cisapride plasma concentration ratios at 8 or 12 hours after a single oral cisapride dose may prove useful as a single-point determination to reflect the area under the plasma concentration versus time curve and the plasma clearance of cisapride and, as well, total CYP3A4 activity in vivo.
Lowry
Jennifer A
JA
Division of Pediatric Clinical Pharmacology and Medical Toxicology, Children's Mercy Hospitals and Clinics, 2401 Gillham Road, Kansas City, MO 64108, USA.
Kearns
Gregory L
GL
Abdel-Rahman
Susan M
SM
Nafziger
Anne N
AN
Khan
Irim S
IS
Kashuba
Angela D M
AD
Schuetz
Erin G
EG
Bertino
Joseph S
JS
van den Anker
John N
JN
Leeder
J Steven
JS
D018435:ATP Binding Cassette Transporter, Subfamily B / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000284:Administration, Oral; D000293:Adolescent; D000328:Adult; D000818:Animals; D019540:Area Under Curve; D002851:Chromatography, High Pressure Liquid; D020117:Cisapride / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000097:blood / Q000493:pharmacokinetics*; D018592:Cross-Over Studies; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D005260:Female; D006801:Humans; D007262:Infusions, Intravenous; D018374:LLC-PK1 Cells / Q000187:drug effects; D008297:Male; D013058:Mass Spectrometry; D008874:Midazolam / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics; D008875:Middle Aged; D008954:Models, Biological; D012044:Regression Analysis; D013552:Swine
D018435:ATP Binding Cassette Transporter, Subfamily B; C072044:norcisapride; D003577:Cytochrome P-450 Enzyme System; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D008874:Midazolam; D020117:Cisapride