Quantification of doxazosin in human plasma using hydrophilic interaction liquid chromatography with tandem mass spectrometry.

Hydrophilic interaction LC with MS/MS (HILIC-MS/MS) was described as a rapid, sensitive, and selective method for the quantification of doxazosin in human plasma. Doxazosin and cisapride (internal standard) were extracted from human plasma with ethyl acetate at alkaline pH and analyzed on an Atlantis HILIC Silica column with the mobile phase of ACN/ammonium formate (100 mM, pH 4.5) (93:7 v/v). The analytes were detected using an ESI MS/MS in the selective-reaction-monitoring mode. The standard curve was linear (r = 0.9994) over the concentration range of 0.2-50 ng/mL. The LOQ for doxazosin was 0.2 ng/mL using 100 microL plasma sample. The CV and relative error for intra- and interassay at four QC levels were 3.7-8.7% and 0.0-9.8%, respectively. The matrix effect for doxazosin and cisapride were practically absent. The recoveries of doxazosin and cisapride were 67.4 and 61.7%, respectively. This method was successfully applied to the pharmacokinetic study of doxazosin in humans.

Characterization of dual layered pellets for sustained release of poorly water-soluble drug.

The aim of this study was to develop pellet formulations that could be used to improve the dissolution and bioavailability of a poorly water-soluble model drug, cisapride. Six different types of pellets were prepared by coating sugar spheres in a fluidized bed coater. When the sugar spheres were single layered containing cisapride and solubilizer such as polysorbate 80, the resulting pellets provided an instant release of cisapride in the simulated gastric fluid. Dissolution tests carried out in the simulated intestinal fluid showed that there were negligible amounts of cisapride released, regardless of the pellet formulation. To succeed in attaining dissolution and the sustained release of cisapride at a neural pH, the single layered pellets were coated again with a coating suspension containing Eudragit RS 30D and L 30D. Scanning electron microscopy revealed that the dual layered pellets had a crack-free and spherical surface. Interestingly, the dual layered pellets provided the sustained release of cisapride in both the simulated gastric and intestinal fluids. The composition and components of the dual layers were found to be key parameters affecting the pattern of cisapride dissolution. Significant improvement in the bioavailability of cisapride was achieved when the dual layered pellets were administered orally to dogs. Overall, these results suggest that the dual layered pellets have potential as a sustained release dosage form for poorly water-soluble drugs.

A novel predictive pharmacokinetic/pharmacodynamic model of repolarization prolongation derived from the effects of terfenadine, cisapride and E-4031 in the conscious chronic av node--ablated, His bundle-paced dog.

INTRODUCTION: Terfenadine, cisapride, and E-4031, three drugs that prolong ventricular repolarization, were selected to evaluate the sensitivity of the conscious chronic atrioventricular node--ablated, His bundle-paced Dog for defining drug induced cardiac repolarization prolongation. A novel predictive pharmacokinetic/pharmacodynamic model of repolarization prolongation was generated from these data. METHODS: Three male beagle dogs underwent radiofrequency AV nodal ablation, and placement of a His bundle-pacing lead and programmable pacemaker under anesthesia. Each dog was restrained in a sling for a series of increasing dose infusions of each drug while maintained at a constant heart rate of 80 beats/min. RT interval, a surrogate for QT interval in His bundle-paced dogs, was recorded throughout the experiment. RESULTS: E-4031 induced a statistically significant RT prolongation at the highest three doses. Cisapride resulted in a dose-dependent increase in RT interval, which was statistically significant at the two highest doses. Terfenadine induced a dose-dependent RT interval prolongation with a statistically significant change occurring only at the highest dose. The relationship between drug concentration and RT interval change was described by a sigmoid E(max) model with an effect site. Maximum RT change (E(max)), free drug concentration at half of the maximum effect (EC(50)), and free drug concentration associated with a 10 ms RT prolongation (EC(10 ms)) were estimated. A linear correlation between EC(10 ms) and HERG IC(50) values was identified. DISCUSSION: The conscious dog with His bundle-pacing detects delayed cardiac repolarization related to I(Kr) inhibition, and detects repolarization change induced by drugs with activity at multiple ion channels. A clinically relevant sensitivity and a linear correlation with in vitro HERG data make the conscious His bundle-paced dog a valuable tool for detecting repolarization effect of new chemical entities.

Practical application of guinea pig telemetry system for QT evaluation.

The purpose of this study was to evaluate a telemetry system for examining QT evaluation in the conscious free-moving guinea pig using 10 reference compounds whose effects on human QT interval are well established: 8 positive references (bepridil, terfenadine, cisapride, haloperidol, pimozide, quinidine, E-4031 and thioridazine), and 2 negative references (propranolol and nifedipine). Pharmacokinetic experiments were also performed for the 8 positive references. Telemetry transmitters were implanted subcutaneously in male Hartley guinea pigs, and the RR and QT intervals were measured. All 8 positive references prolonged QTc (QTc = k x QT/RR(1/2)) 10% or more during the 60 min observation period. When the values of the QTc changes were plotted against the serum concentrations, the resulting curves exhibited an anticlockwise hysteresis loop for all 8 references. In guinea pigs treated with haloperidol, changes of the T-wave shape from positive to flat were observed. The 2 negative references did not prolong the QTc. These findings suggest that the present telemetry guinea pig model is useful for QT evaluation in the early stages of drug development, because of the small body size of guinea pigs and their action potential configuration, which is similar to that of humans.

Liquid chromatographic determination including simultaneous "on-cartridge" separation of ranitidine cisapride drug combinations from paediatric plasma samples using an automated solid-phase extraction procedure.

HPLC methodology was investigated for the simultaneous determination of cisapride and ranitidine in small volume paediatric plasma samples. Such a simultaneous determination proved difficult due to the small sample volumes, the low concentrations of the drugs and the different log P values of the two compounds. The two drugs and their respective internal standards were separated "on-cartridge" using HLB Solid Phase Extraction cartridges and the samples quantified by individual HPLC methodologies. The technique has been applied successfully to 60 paediatric plasma samples containing both cisapride and ranitidine.

Cisapride disposition in neonates and infants: in vivo reflection of cytochrome P450 3A4 ontogeny.

BACKGROUND: Cisapride, a prokinetic agent and substrate for cytochrome P450 (CYP) 3A4, has been used to treat neonates and infants with feeding intolerance and apnea or bradycardia associated with gastroesophageal reflux. At age 1 month, CYP3A4 activity has been reported to be only 30% to 40% of adult activity. This known developmental delay in the expression of CYP3A4 prompted us to conduct a classical open-label pharmacokinetic study of cisapride in neonates and young infants. METHODS: A total of 35 infants with a postconceptional age of 28 to 54 weeks at the time of the study received a single oral cisapride dose (0.2 mg/kg) at a postnatal age of 4 to 102 days, followed by repeated (n = 7) blood sampling over a 24-hour period. Cisapride and norcisapride were quantitated from plasma by HPLC-tandem mass spectrometry and pharmacokinetic data determined (n = 32) by noncompartmental methods. RESULTS: The pharmacokinetic parameters (mean +/- SD) were as follows: time to reach peak plasma concentration (t(max)), 4.4 +/- 2.8 hours (range, 0.9-12 hours); peak plasma concentration (C(max)), 29.3 +/- 16.6 ng/mL (range, 5.2-71.7 ng/mL); elimination half-life (t(1/2)), 10.7 +/- 3.7 hours (range, 1.9-18.1 hours); apparent total body clearance (Cl/F), 0.62 +/- 0.43 L. h(-1). kg(-1) (range, 0.2-1.9 L. h(-1). kg(-1)); and apparent volume of distribution (VD(ss)/F), 9.0 +/- 7.1 L/kg (range, 2.2-30.5 L/kg). The apparent renal clearance (CL(R)) of cisapride in infants (n = 28) was estimated to be 0.003 +/- 0.003 L. h(-1). kg(-1). Substratification of the population based on postconceptional age demonstrated the following findings for cisapride: (1) The mean (+/-SD) C(max) for cisapride was higher in the oldest postconceptional age category (44.5 +/- 19.6 ng/mL) than the middle and youngest categories (23.4 +/- 11.7 ng/mL and 30.0 +/- 17.5 ng/mL, respectively); (2) the t(max) for cisapride was shortest in the oldest postconceptional age category (2.2 +/- 1.1 hours) compared with the middle and youngest categories (4.4 +/- 3.3 hours and 5.0 +/- 2.6 hours, respectively); (3) the CL/F for cisapride in the youngest postconceptional age group was significantly lower (0.45 +/- 0.26 L. h(-1). kg(-1), P <.05) than in the middle and oldest categories (0.75 +/- 0.46 L. h(-1). kg(-1) and 0.85 +/- 0.69 L. h(-1). kg(-1), respectively); (4) a positive linear correlation was found between postconceptional age and the apparent terminal elimination rate constant (lambda(z)) for cisapride (P <.001, r(2) = 0.47) but not with CL/F. For norcisapride, the mean apparent C(max) was highest and the t(max) was shortest in the oldest postconceptional age group, although no association between postconceptional age and the norcisapride/cisapride area under the curve ratio was observed. All infants tolerated a single dose of cisapride well without significant alteration in QTc. CONCLUSIONS: (1) In neonates and infants, cisapride absorption and metabolism to its primary metabolite, norcisapride, were developmentally dependent; (2) approximately 99% of cisapride CL/F in neonates and young infants was nonrenal in nature; (3) CL/F of cisapride in neonates and infants noted in this study was reduced compared with data from older children and adults, likely as a result of developmental reductions in CYP3A4 activity; (4) as reflected by the correlation between postconceptional age and lambda(z), a rapid increase in total CYP3A4 activity occurs in the first 3 months of life.

High performance liquid chromatographic determination, pharmacokinetic and comparative bioavailability studies of cisapride.

A sensitive and specific reversed phase HPLC method was developed to quantitate plasma levels of cisapride in order to conduct comparative bioavailability studies. The drug and internal standard was extracted from plasma with heptane-isoamyl alcohol (95:5 v/v) and back extracted with sulfuric acid. The acidic layer was then re-extracted with the same extracting solvent. The separated organic layer was evaporated to dryness under nitrogen and the residue reconstituted with acetonitrile. Analysis was performed on a C-8 Sil-X-10 HPLC column, with a mobile phase of acetonitrile, water, and triethylamine (75:25:0.01) and UV detection at 215 nm. The standard curve covering the concentration range 5-160 ng/ml was linear (r(2)=0.9992), relative errors were within +/-10% and the CV% ranged from 1.34 to 11.82. The in vivo study was carried out in 12 healthy volunteers according to a single dose, two-sequence, cross over randomized design. The bioavailability was compared using the total area under the plasma level versus time curve (AUC(0-34,) AUC(0- infinity )), peak plasma concentration (C(max)) and time to C(max) (T(max)). No statistically significant difference was found between the AUC(0- infinity ) or C(max) values of the test (cisapride) and reference (Propulsid). It was, therefore, concluded that the generic cisapride was bioequivalent with the innovator formulation.

Cisapride: a potential model substrate to assess cytochrome P4503A4 activity in vivo.

OBJECTIVES: 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.

Expression of the ether-a-go-go (ERG) potassium channel in smooth muscle of the equine gastrointestinal tract and influence on activity of jejunal smooth muscle.

OBJECTIVE: To determine whether ether-a-go-go (ERG) potassium channels are expressed in equine gastrointestinal smooth muscle, whether ERG channel antagonists affect jejunal muscle contraction in vitro, and whether plasma cisapride concentrations in horses administered treatment for postoperative ileus (POI) are consistent with ERG channels as drug targets. SAMPLE POPULATION: Samples of intestinal smooth muscle obtained from 8 horses free of gastrointestinal tract disease and plasma samples obtained from 3 horses administered cisapride for treatment of POI. PROCEDURE: Membranes were prepared from the seromuscular layer of the duodenum, jejunum, ileum, cecum, large colon, and small colon. Immunoblotting was used to identify the ERG channel protein. Isolated jejunal muscle strips were used for isometric stress response to ERG channel blockers that included E-4031, MK-499, clofilium, and cisapride. Plasma concentrations of cisapride were determined in 3 horses administered cisapride for treatment of POI after small intestinal surgery. RESULTS: Immunoblotting identified ERG protein in all analyzed segments of the intestinal tract in all horses. The selective ERG antagonist E-4031 caused a concentration-dependent increase in jejunal contraction. Clofilium, MK-499, and cisapride also increased jejunal contraction at concentrations consistent with ERG channel block; effects of E-4031 and cisapride were not additive. Peak plasma cisapride concentrations in treated horses were consistent with ERG block as a mechanism of drug action. CONCLUSIONS AND CLINICAL RELEVANCE: The ERG potassium channels modulate motility of intestinal muscles in horses and may be a target for drugs. This finding may influence development of new prokinetic agents and impact treatment of horses with POI.

In vitro effects of cisapride, metoclopramide and bethanechol on smooth muscle preparations from abomasal antrum and duodenum of dairy cows.

The objective of this study was to investigate the effects of cisapride (CIS), metoclopramide (MET) and bethanechol (BET) on contractility parameters from smooth muscle preparations of the abomasal antrum and proximal duodenum of cows. Smooth muscle preparations were harvested shortly post-mortem from 42 healthy dairy cows, and concentration-response curves were performed by cumulative application of the drugs. Cisapride and MET did not have any significant effect on the contractility parameters studied, while BET induced a significant, concentration-dependent increase in basal tone (BT), mean amplitude (Amean), and area under the curve (AUC) in smooth muscle preparations from the abomasal antrum, but not from the duodenum. The effect of BET on BT was more pronounced in specimens with longitudinal orientation while the maximal obtainable effect (Vm) in Amean was more pronounced in circular-oriented preparations. Atropine (1 x 10-5 m) significantly inhibited the effect of BET, whereas pre-incubation with hexamethonium or tetrodotoxin (TTX) had no effect, suggesting that the effect was mediated by cholinergic receptors on the smooth muscle. The results may be relevant to diseases or disorders associated with gastric emptying and gastric hypomotility. Further investigations are warranted to investigate the potential ability of BET to enhance abomasal emptying of adult dairy cows.

Population pharmacokinetics of cisapride in neonates.

OBJECTIVES: We conducted a population pharmacokinetic analysis of cisapride in neonates to study whether metabolic immaturity in this population may lead to increased concentrations. METHODS: Cisapride was administered orally in 91 neonates at the dose of 0.2 mg/kg four times a day. Plasma concentrations were measured using a validated HPLC method. A one-compartment model with first-order absorption was fitted to the data using NONMEM software. RESULTS: One to seven plasma samples were obtained from neonates aged 7-123 days. Cisapride concentrations ranged from 5.5 ng/mL to 172 ng/mL and were not higher than those reported in adults. The absorption constant rate was fixed to 2.5 h-1. Clearance (CL/F) and volume of distribution (V/F) both significantly correlated to weight (WT), but addition of this covariate in V/F did not improve the objective function after it was added in the CL/F covariate model. Prematurity, postnatal age, or coadministered drugs did not affect cisapride clearance. Final population pharmacokinetic parameters (interindividual variability) were: V/F=17,200 mL (90.4%) and CL/F=3.91 x WT(3/4) mL/h (36.3%). CONCLUSIONS: Our finding that cisapride clearance is primarily influenced by weight is in agreement with current recommendations of weight-adjusted doses. This study indicates that no clinically relevant maturational changes in cisapride clearance have to be considered during the first quadrimester of life.

Cisapride plasma levels and corrected QT interval in infants undergoing routine polysomnography.

BACKGROUND: Reported QTc prolongation associated with cardiac arrhythmia in a small number of children undergoing cisapride therapy and lack of pharmacokinetic correlation provided the impetus for this prospective study. The authors evaluated the relation between cisapride plasma concentrations, the electrocardiographic QT interval, and cardiac rhythm in infants undergoing routine 8-hour polysomnography. METHODS: A total of 211 infants were enrolled: 84 (17 born prematurely) undergoing cisapride therapy for at least 4 days for suspected gastroesophageal reflux and 127 controls (10 born prematurely), aged between 1 week and 13.5 months. Infants underwent continuous bipolar limb lead I recording during routine 8-hour polysomnography. QT intervals and heart rate were measured at hourly intervals. The morning after polysomnography, 12-lead electrocardiography was performed (1 hour after cisapride administration). Cisapride plasma concentrations were determined immediately before and 1 to 2 hours after administration. Serum electrolyte concentrations were measured. RESULTS: The administered cisapride dose ranged from 0.35 to 1.55 (mean, 0.81, median 0.79) mg. kg-1. d-1. Cisapride plasma concentrations were significantly higher in infants younger than 3 months of age. Cisapride-treated infants younger than 3 months of age had longer QTc intervals compared with age-matched controls. Heart rate was similar for cisapride-treated and control infants. No arrhythmia or atrioventricular conduction abnormalities were observed. CONCLUSIONS: At comparable doses of cisapride and comparable plasma concentrations, the QTc was significantly higher in infants younger than 3 months of age. This confirms age-dependent cisapride pharmacokinetics in the first 10 to 12 weeks strongly correlated with changes in body weight and may also suggest an altered ability of infants younger than 3 months of age to metabolize cisapride. The clinical significance and risk of the increased QTc interval is unclear. Cisapride should be judiciously prescribed in infants younger than the age of 3 months and electrocardiography should be performed before and during therapy.

Cisapride raises the bioavailability of paracetamol by inhibiting its glucuronidation in man.

The effect of cisapride on plasma concentrations of paracetamol was investigated with respect to hepatic metabolism. Paracetamol (1 g) together with cisapride (7.5 mg) or placebo was orally administered to five healthy male volunteers. Venous blood samples were taken before and after administration. Plasma paracetamol and its glucuronide and sulfate conjugates were measured by HPLC. The pharmacokinetic variables were calculated from the plasma concentration-time curves of each volunteer. The area under the plasma paracetamol concentration-time curve from 0 to 180 min (mean +/- s.d.) increased from 1875.0 +/- 112.8 micrg min mL(-1) (placebo coadministration) to 2238.8 +/- 125.8 microg min mL(-1) (cisapride coadministration) (P < 0.01). The mean maximum plasma paracetamol concentration(18.2 microg mL(-1))with placebo was reached 30 min after administration, whereas mean maximum plasma paracetamol concentration (21.2 microg mL(-1)) with cisapride occurred 45 min after administration. The plasma paracetamol concentrations with cisapride were significantly greater at 45 to 120 min after administration compared with placebo. Plasma paracetamol glucuronide conjugate concentrations with cisapride were decreased at 15 to 60 min compared with placebo (P< 0.05), whereas plasma paracetamol sulfate conjugate concentrations did not change significantly. Hence the coadministration of paracetamol with cisapride reduced plasma paracetamol glucuronide concentrations and increased plasma paracetamol concentrations, presumably due to inhibition of paracetamol metabolism via paracetamol glucuronyltransferase. Thus, care is necessary when paracetamol and cisapride are coadministered.

Red wine-cisapride interaction: comparison with grapefruit juice.

OBJECTIVES: Our objective was to compare the interactions of red wine and grapefruit juice with cisapride. METHODS: The oral pharmacokinetics of cisapride, its norcisapride metabolite, and electrocardiographic QTc interval were determined over a 24-hour period after administration of cisapride 10 mg with 250 mL grapefruit juice, red wine (cabernet sauvignon), or water in a randomized 3-way crossover study in 12 healthy men. RESULTS: The cisapride area under the concentration-time curve (AUC) and the maximum plasma drug concentration after single-dose administration (C(max)) with grapefruit juice were 151% (P <.01) and 168% (P <.001), respectively, of those with water. The increase in cisapride AUC and C(max) was variable among individuals; however, cisapride AUC and C(max) were enhanced by the same proportion. The time to reach maximum concentration after drug administration (t(max)) and the apparent elimination half-life (t((1/2)) for cisapride and the pharmacokinetics of norcisapride were not altered. Norcisapride/cisapride ratios were reduced. Cisapride AUC and C(max) with red wine were 115% (difference not statistically significant) and 107% (difference not statistically significant), respectively, of those with water. The cisapride t(max) was slightly longer. Cisapride t((1/2)) and norcisapride pharmacokinetics were not different. The norcisapride/cisapride ratio at cisapride C(max) was lower. One subject had a doubling in cisapride AUC and C(max) and a decrease in norcisapride/cisapride ratios with red wine and also had the largest interaction with grapefruit juice. QTc interval was unchanged in all treatment groups and individuals. CONCLUSIONS: A single glass of grapefruit juice produced an individual-dependent variable increase in the systemic availability of cisapride by inhibition of intestinal cytochrome P450 3A4 (CYP3A4) activity. The identical volume of red wine caused only minor changes in cisapride pharmacokinetics despite some inhibition of CYP3A4 in most individuals. However, even this amount of red wine may cause a marked interaction similar to that for grapefruit juice in individuals with a preexisting high intestinal CYP3A4 content.

Liquid chromatographic method with electrochemical detection for determination of cisapride in serum.

A sensitive liquid chromatographic (LC) method using electrochemical detection was developed for the identification and quantitation of cisapride in serum. The serum samples were deproteinized by a simple acetonitrile precipitation technique followed by n-hexane extraction. Cisapride in the deproteinized serum was separated by an isocratic elution with an ODS Hypersil LC column (150 x 4.6 mm) using a mobile phase consisting of 0.05M Na2HPO4-acetonitrile (60 + 40), pH 8.4. Cisapride eluted from the column was detected by a Coulochem II electrochemical detector. The precision of this assay method was determined by intra- and inter-day analyses of cisapride-free fetal bovine serum samples that were spiked with 25, 50, and 100 ng/mL cisapride. For the intra-day assay, recoveries were 94.3 +/- 1.4, 90.1 +/- 2.9, and 103.2 +/- 9.2%, respectively. This electrochemical detection LC method could be very useful in monitoring plasma levels of cisapride.

Influence of coadministration of fluoxetine on cisapride pharmacokinetics and QTc intervals in healthy volunteers.

STUDY OBJECTIVE: To evaluate the effect of fluoxetine on the pharmacokinetics and cardiovascular safety of cisapride at steady state in healthy men. DESIGN: Open-label, three-phase, sequential study. SETTING: Clinical research center. SUBJECTS: Twelve healthy male volunteers. INTERVENTIONS: Each subject was treated according to the following sequence: baseline; phase 1 (days 1-6): cisapride 10 mg 4 times/day; washout (days 7-13); phase 2 (days 14-44): fluoxetine 20 mg/day; and phase 3 (days 45-52): cisapride 10 mg 4 times/day (days 45-51) plus fluoxetine 20 mg/day (days 45-52). MEASUREMENTS AND MAIN RESULTS: Blood samples were drawn and 12-lead electrocardiograms performed at specified time points after the last morning dose of cisapride in phases 1 and 3. Blood samples also were taken before morning doses on the 3rd, 4th, and 5th days of phases 1 and 3. Electrocardiograms were done at baseline and on the last day of the washout period and phase 2. Coadministration of fluoxetine significantly decreased cisapride plasma concentrations. There were no clinically significant changes in corrected QT intervals during administration of cisapride alone or with fluoxetine. Cisapride was well tolerated when administered alone or with fluoxetine. CONCLUSION: Cisapride can be administered safely to patients receiving low therapeutic dosages of fluoxetine.

Stereoselective determination of cisapride, a prokinetic agent, in human plasma by chiral high-performance liquid chromatography with ultraviolet detection: application to pharmacokinetic study.

We have developed a simple, sensitive, specific and reproducible stereoselective high-performance liquid chromatography technique for analytical separation of cisapride enantiomers and measurement of cisapride enantiomers in human plasma. A chiral analytical column (ChiralCel OJ) was used with a mobile phase consisting of ethanol-hexane-diethylamine (35:64.5:0.5, v/v/v). This assay method was linear over a range of concentrations (5-125 ng/ml) of each enantiomer. The limit of quantification was 5 ng/ml in human plasma for both cisapride enantiomers, while the limit of detection was 1 ng/ml. Intra- and inter-day C.V.s did not exceed 15% for all concentrations except at 12.5 ng/ml for EII (+)-cisapride, which was approximately 20 and 19%, respectively. The clinical utility of the method was demonstrated in a pharmacokinetic study of normal volunteers who received a 20 mg single oral dose of racemic cisapride. The preliminary pharmacokinetic data obtained using the method we describe here provide evidence for the first time that cisapride exhibits stereoselective disposition.

The involvement of flavin-containing monooxygenase but not CYP3A4 in metabolism of itopride hydrochloride, a gastroprokinetic agent: comparison with cisapride and mosapride citrate.

The goals of the present study were to identify the enzyme responsible for metabolism of itopride hydrochloride (itopride) and to evaluate the likelihood of drug interaction involving itopride. In human liver microsomes, the involvement of flavin-containing monooxygenase in N-oxygenation, the major metabolic pathway of itopride, was indicated by the following results: inhibition by methimazole and thiourea, heat inactivation, and protection against heat inactivation by NADPH. When the effects of ketoconazole on the metabolism of itopride, cisapride, and mosapride citrate (mosapride) were examined using human liver microsomes, ketoconazole strongly inhibited the formation of the primary metabolites of cisapride and mosapride, but not itopride. Other cytochrome P450 (CYP) 3A4 inhibitors, cimetidine, erythromycin, and clarithromycin, also inhibited the metabolism of cisapride and mosapride. In an in vivo study, itopride (30 mg/kg), cisapride (1.5 mg/kg), or mosapride (3 mg/kg) was orally administered to male rats with or without oral pretreatment with ketoconazole (120 mg/kg) twice daily for 2 days. The ketoconazole pretreatment significantly increased the area under the serum concentration curve and the maximum serum concentration of cisapride and mosapride but had no significant effect on the pharmacokinetics of itopride. In addition, itopride did not inhibit five specific CYP-mediated reactions of human liver microsomes. These results suggest that itopride is unlikely to alter the pharmacokinetics of other concomitantly administered drugs.

Repeated consumption of grapefruit juice considerably increases plasma concentrations of cisapride.

BACKGROUND: Grapefruit juice increases the bioavailability of several drugs that are metabolized during first pass by CYP3A4. In this study, the effect of grapefruit juice on the pharmacokinetics of orally administered cisapride was investigated. METHODS: In a randomized, two-phase crossover study, 10 healthy volunteers took either 200 mL double-strength grapefruit juice or water three times a day for 2 days. On day 3, each subject ingested 10 mg cisapride with either 200 mL grapefruit juice or water, and an additional 200 mL was ingested 1/2 hour and 1 1/2 hours after cisapride administration. Timed blood samples were collected for 32 hours after cisapride intake, and a standard 12-lead ECG was recorded before the administration of cisapride and 2, 5, 8, and 12 hours later. RESULTS: The mean peak plasma concentration of cisapride was increased by 81% (range, 38% to 138%; P < .01) and the total area under the plasma cisapride concentration-time curve by 144% (range, 65% to 244%; P < .01) by grapefruit juice. The time of the peak concentration of cisapride was prolonged from 1.5 to 2.5 hours (P < .05) and the elimination half-life from 6.8 to 8.4 hours (P < .05) by grapefruit juice. ECG tracings did not show any significant differences in the QTc interval between the grapefruit juice and control phases. CONCLUSIONS: Grapefruit juice significantly increases plasma concentrations of cisapride, probably by inhibition of the CYP3A4-mediated first-pass metabolism of cisapride in the small intestine. Concomitant use of high amounts of grapefruit juice and cisapride should be avoided, at least in patients with risk factors for cardiac arrhythmia.