A Newly Developed HPLC-UV/Vis Method Using Chemical Derivatization with 2-Naphthalenethiol for Quantitation of Sulforaphane in Rat Plasma

Sulforaphane (SFN), a naturally occurring isothiocyanate, has received significant attention because of its ability to modulate multiple biological functions, including anti-carcinogenic properties. However, currently available analytical methods based on high-performance liquid chromatography (HPLC)-UV/Vis for the quantification of SFN have a number of limitations, e.g., low UV absorbance, sensitivity, or accuracy, due to the lack of a chromophore for spectrometric detection. Therefore, we here employed the analytical derivatization procedure using 2-naphthalenethiol (2-NT) to improve the detectability of SFN, followed by HPLC separation and quantification with UV/Vis detection. The optimal derivatization conditions were carried out with 0.3 M of 2-NT in acetonitrile with phosphate buffer (pH 7.4) by incubation at 37 °C for 60 min. Separation was performed in reverse phase mode using a Kinetex C18 column (150 mm × 4.6 mm, 5 μm) at a flow rate of 1 mL/min, with 0.1% formic acid as a mobile phase A, and acetonitrile/0.1% formic acid solution as a mobile phase B with a gradient elution, with a detection wavelength of 234 nm. The method was validated over a linear range of 10-2000 ng/mL with a correlation of determination (R2) > 0.999 using weighted linear regression analysis. The intra- and inter-assay accuracy (% of nominal value) and precision (% of relative standard deviation) were within ±10 and <15%, respectively. Moreover, the specificity, recovery, matrix effect, process efficiency, and short-term and long-term stabilities of this method were within acceptable limits. Finally, we applied this method for studying in vivo pharmacokinetics (PK) following oral administration of SFN at doses of 10 or 20 mg/kg. The Cmax (μg/mL), Tmax (hour), and AUC0-12h (μg·h/mL) of each oral dose were 0.92, 1.99, and 4.88 and 1.67, 1.00, and 9.85, respectively. Overall, the proposed analytical method proved to be reliable and applicable for quantification of SFN in biological samples.

In vivo pharmacokinetic study and oral glucose tolerance test of sulfoxide analogs of GPR40 agonist TAK-875

TAK-875 (compound 1) was the only GPR40 agonist with promising oral glucose-lowering effect, which entered phase III clinical trials. In previous studies, we successfully synthesized the TAK-875 sulfoxide analog 2, which was further separated to optically pure compounds 3 (S, S, 100.0% de) and 4 (R, S, 100.0% de). In vitro biological evaluation revealed that the sulfoxide analogs 3 and 4 possessed comparable GPR40 agonist activity to TAK-875. Herein, in order to further evaluate the druglikeness of TAK-875 sulfoxide analogs, the pharmacokinetic properties of compounds 2, 3, and 4 in rats were investigated and compared with that of TAK-875. The results showed that sulfoxide (2, 3, and 4) and sulfone (TAK-875) could be converted into each other in different degrees in vivo. Interestingly, compound 3 showed higher drug exposure calculated by the AUC sum of sulfoxide and sulfone in plasma than TAK-875, 2 and 4. In order to further investigate the in vivo glucose-lowering potency of sulfoxide analogs, asymmetric synthesis was carried out and led to two sulfoxides with moderate de values, 5 (S, S, 66.4% de) and 6 (R, S, 71.0% de). The following oral glucose tolerance test (OGTT) in rats showed that 5 (S, S, 66.4% de) had stronger glucose-lowering effect in vivo than 6 (R, S, 71.0% de) and TAK-875, which could be partly rationalized by the superior pharmacokinetic property of sulfoxide 3 (the main component of 5) relative to sulfoxide 4 (the main component of 6) and TAK-875.

Development and validation of a high throughput bioanalytical UPLC-MS/MS method for simultaneous determination of tamoxifen and sulphoraphane in rat plasma: Application to an oral pharmacokinetic study

Tamoxifen (TAM) is the choice of a drug approved by the Food and Drug Administration (FDA) for the treatment of estrogen-positive receptor (ER+) breast cancer. Sulphoraphane (SFN), a natural plant antioxidant compound, also acts on estrogen-positive breast cancer receptor. Thus, a combination of TAM with SFN is preferred as it helps to minimize the drug-related toxicity and increases the therapeutic efficacy by providing synergistic anticancer effects of both drugs. In the present study, a new simple, sensitive, precise, and selective UPLC-MS/MS method was developed for the simultaneous quantification of tamoxifen and sulphoraphane using propranolol as an internal standard (IS) in rat plasma. Chromatographic separation was achieved on reverse phase Acquity UPLC BEH C¹⁸ column (50 mm × 2.1 mm, i.d., 1.7 μm) with an isocratic mobile phase composed of solvent A (0.1% formic acid in acetonitrile) and B (0.1% formic acid in water) (80:20, v/v) at a flow-rate of 0.4 mL/min. The detection and quantification of analytes was performed on Waters Zspray^TM Xevo TQD using selected-ion monitoring operated under a positive electrospray ionization mode. The transitions were m/z = 372.0 [M+H]⁺ → 71.92 for tamoxifen, m/z = 177.9 [M+H]⁺ → 113.9 for sulphoraphane and m/z = 260.3 [M+H]⁺ → 116.1 for propranolol. The method was linear over the concentration range of 8-500 ng/mL (r² = 0.9996) for tamoxifen, 30-2000 ng/mL (r² = 0.9998) for sulphoraphane with insignificant matrix effect and high extraction recovery on spiked quality control (QC) samples. The intra- and inter-batch precisions and accuracy were within the acceptable limits, and both the analytes were found to be stable throughout the short term, long term and freeze thaw stability studies. The validated method was successfully applied for the simultaneous estimation of TAM and SFN in an oral pharmacokinetic study in female Wistar rats. This developed UPLC-MS/MS method could be a valuable tool for future pharmacokinetic interaction, therapeutic drug monitoring and pharmacokinetic characterization of novel formulations.

Enantioseparation, Stereochemical Assignment and Chiral Recognition Mechanism of Sulfoxide-Containing Drugs

The distinct pharmacodynamic and pharmacokinetic properties of enantiopure sulfoxide drugs have stimulated us to systematically investigate their chiral separation, stereochemical assignment, and chiral recognition mechanism. Herein, four clinically widely-used sulfoxide drugs were chosen and optically resolved on various chiral stationary phases (CSPs). Theoretical simulations including electronic circular dichroism (ECD) calculation and molecular docking were adopted to assign the stereochemistry and reveal the underlying chiral recognition mechanism. Our results showed that the sequence of calculated mean binding energies between each pair of enantiomers and CSP matched exactly with experimentally observed enantiomeric elution order (EEO). It was also found that the length of hydrogen bond might contribute dominantly the interaction between two enantiomers and CSP. We hope our study could provide a fresh perspective to explore the stereochemistry and chiral recognition mechanism of chiral drugs.

Biotransformation of pantoprazole by the fungusCunninghamella blakesleeana

To investigate the biotransformation of pantoprazole, a proton-pump inhibitor, by filamentous fungus and further to compare the similarities between microbial transformation and mammalian metabolism of pantoprazole, four strains of Cunninghamella (C. blakesleeana AS 3.153, C. echinulata AS 3.2004, C. elegans AS 3.156, and AS 3.2028) were screened for the ability to catalyze the biotransformation of pantoprazole. Pantoprazole was partially metabolized by four strains of Cunninghamella, and C. blakesleeana AS 3.153 was selected for further investigation. Three metabolites produced by C. blakesleeana AS 3.153 were isolated using semi-preparative HPLC, and their structures were identified by a combination analysis of LC/MS(n) and NMR spectra. Two further metabolites were confirmed with the aid of synthetic reference compounds. The structure of a glucoside was tentatively assigned by its chromatographic behavior and mass spectroscopic data. These six metabolites were separated and quantitatively assayed by liquid chromatography-ion trap mass spectrometry. After 96h of incubation with C. blakesleeana AS 3.153, approximately 92.5% of pantoprazole was metabolized to six metabolites: pantoprazole sulfone (M1, 1.7%), pantoprazole thioether (M2, 12.4%), 6-hydroxy-pantoprazole thioether (M3, 1.3%), 4'-O-demethyl-pantoprazole thioether (M4, 48.1%), pantoprazole thioether-1-N-beta-glucoside (M5, 20.6%), and a glucoside conjugate of pantoprazole thioether (M6, 8.4%). Among them, M5 and M6 are novel metabolites. Four phase I metabolites of pantoprazole produced by C. blakesleeana were essentially similar to those obtained in mammals. C. blakesleeana could be a useful tool for generating the mammalian phase I metabolites of pantoprazole.

Neurokinin 1 Receptor Antagonists: Correlation between in Vitro Receptor Interaction and in Vivo Efficacy

We compared the neurokinin 1 receptor (NK(1)R) antagonists aprepitant, CP-99994 [(2S,3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine], and ZD6021 [3-cyano-N-((2S)-2-(3,4-dichlorophenyl)-4-[4-[2-(methyl-(S)-sulfinyl)phenyl]piperidino]butyl)-N-methyl]napthamide]] with respect to receptor interactions and duration of efficacy in vivo. In Ca(2+) mobilization assays (fluorometric imaging plate reader), antagonists were applied to human U373MG cells simultaneously with or 2.5 min before substance P (SP). In reversibility studies, antagonists were present for 30 min before washing, and responses to SP were repeatedly measured afterward. The compounds were administered i.p. to gerbils, and the gerbil foot tap (GFT) response was monitored at various time points. The NK(1)R receptor occupancy for aprepitant was determined in striatal regions. Levels of compound in brain and plasma were measured. Antagonists were equipotent at human NK(1)R and acted competitively with SP. After preincubation, aprepitant and ZD6021 attenuated the maximal responses, whereas CP-99994 only shifted the SP concentration-response curve to the right. The inhibitory effect of CP-99994 was over within 30 min, whereas for ZD6021, 50% inhibition still persisted after 60 min. Aprepitant produced maximal inhibition lasting at least 60 min. CP-99994 (3 micromol/kg) inhibited GFT by 100% 15 min after administration, but the effect declined rapidly together with brain levels thereafter. The efficacy of ZD6021 (10 micromol/kg) lasted 4 h and correlated well with brain levels. Aprepitant (3 micromol/kg) inhibited GFT and occupied striatal NK(1)R by 100% for >48 h despite that brain levels of compound were below the limit of detection after 24 h. Slow functional reversibility is associated with long-lasting in vivo efficacy of NK(1)R antagonists, whereas the efficacy of compounds with rapid reversibility is reflected by their pharmacokinetics.

Assessment of the main metabolism pathways for the flukicidal compound triclabendazole in sheep

Triclabendazole (TCBZ) is an halogenated benzimidazole (BZD) compound worldwide used to control immature and adult stages of the liver fluke Fasciola hepatica. The purpose of this investigation was to characterize in vitro the patterns of hepatic and ruminal biotransformation of TCBZ and its metabolites in sheep. TCBZ parent drug was metabolized into its sulphoxide (TCBZSO), sulphone (TCBZSO2) and hydroxy derivatives by sheep liver microsomes. The same microsomal fraction was also able to oxidize TCBZSO into TCBZSO2 and hydroxy-TCBZSO (HO-TCBZSO). TCBZ sulphoxidation was significantly (P < 0.001) inhibited after inactivation of the flavin-monooxygenase (FMO) system (77% inhibition) as well as in the presence of the FMO substrate methimazole (MTZ) (71% inhibition). TCBZ sulphoxidative metabolism was also reduced (24% inhibition, P < 0.05) by the cytochrome P450 inhibitor piperonyl butoxide (PB). The rate of TCBZSO conversion into TCBZSO2 was also significantly inhibited by PB (55% inhibition), MTZ (52% inhibition) and also following FMO inactivation (58% inhibition). The data reported here indicate that the FMO is the main enzymatic pathway involved in TCBZ sulphoxidation (ratio FMO/P450 = 3.83 +/- 1.63), although both enzymatic systems participate in a similar proportion in the sulphonation of TCBZSO to form the sulphone metabolite (ratio FMO/P450 = 1.31 +/- 0.23). Additionally, ketoconazole (KTZ) did not affect TCBZ sulphoxidation but decreased (66% inhibition, P < 0.05) the formation of TCBZSO2. Similarly, inhibition of TCBZSO2 production was observed after incubation of TCBZSO in the presence of KTZ and erythromycin (ETM). Conversely, thiabendazole (TBZ) and fenbendazole (FBZ) did not affect the oxidative metabolism of both incubated substrates. The sheep ruminal microflora was able to reduce the sulphoxide (TCBZSO) into the parent thioether (TCBZ). The ruminal sulphoreduction of the HO-TCBZSO derivative into HO-TCBZ was also demonstrated. The rate of sulphoreduction of HO-TCBZSO was significantly (P < 0.05) higher than that observed for TCBZSO. The metabolic approach tested here contributes to the identification of the different pathways involved in drug biotransformation in ruminant species. These findings on the pattern of hepatic and ruminal biotransformation of TCBZ and its main metabolites are a further contribution to the understanding of the pharmacological properties of widely used anthelmintics in ruminants. Comprehension of TCBZ metabolism is critical to optimize its flukicidal activity.

Lansoprazole regimens that sustain intragastric pH > 6.0: an evaluation of intermittent oral and continuous intravenous infusion dosages

BACKGROUND

Orally and intravenously administered proton pump inhibitors have been shown to reduce rebleeding rates, surgery and transfusion requirement.

AIM

To compare lansoprazole intravenous and orally disintegrating tablet (Prevacid SoluTab) regimens with a pantoprazole intravenously administered regimen in sustaining intragastric pH >6.0.

METHODS

Two similarly designed three-way, randomized crossover studies each enrolled 36 Helicobacter pylori-negative healthy volunteers. Study 1 regimens included intravenously administered bolus followed by 24-h continuous infusion (lansoprazole 90 mg, 6 mg/h; lansoprazole 120 mg, 6 mg/h; pantoprazole 80 mg, 8 mg/h). Study 2 regimens included intravenous bolus followed by lansoprazole orally disintegrating tablet or intravenous continuous infusion for 24 h (lansoprazole 90 mg, lansoprazole orally disintegrating tablet 60 mg every 6 h; lansoprazole 120 mg, 9 mg/h; pantoprazole 80 mg, 8 mg/h). Percentage of time pH >6.0 was assessed with 24-h intragastric pH monitoring.

RESULTS

All regimens produced comparable gastric acid suppression. In both studies, regimens superior to pantoprazole included lansoprazole 90 mg, 6-mg/h; lansoprazole 90 mg, lansoprazole orally disintegrating tablet 60 mg q.d.s. and lansoprazole 120 mg, 9 mg/h (P < or = 0.013). The lansoprazole 120-mg, 6-mg/h regimen (P = 0.082) was not superior to pantoprazole in percentage of time intragastric pH >6.0. Mild reaction at the intravenous injection site was the most frequently reported adverse event.

CONCLUSIONS

The intravenous bolus and continuously infused lansoprazole or intravenous bolus and intermittent lansoprazole orally disintegrating tablet regimens are as effective as intravenous pantoprazole in sustaining intragastric pH >6.0.

Intravenous proton pump inhibitors

Intravenous (IV) administration of a proton pump inhibitor (PPI) is a faster way to achieve gastric acid suppression than oral administration of the same agent. Peak suppression after IV administration occurs within hours, compared with several days later after oral administration. Thus the IV route of administration offers a faster onset of gastric suppression, achievement of intragastric pH closer to neutrality, and better bioavailability. The PPIs that have IV formulations in the United States (esomeprazole, lansoprazole, and pantoprazole) are approved for different indications; the key differences among them relate to their ability to reach specific gastric pH, time to maintain a specific gastric pH, and ease of use of the IV formulation (eg, reconstitution, requirement of inline filters, infusion times).

Pharmacokinetic Differences between Pantoprazole Enantiomers in Rats

PURPOSE

The purpose of this study was to quantitatively clarify the contribution of the absorption, protein binding, and metabolism of cytochrome P450 enzymes to the enantioselective pharmacokinetics of pantoprazole enantiomers in rats.

METHODS

The enantioselective pharmacokinetics of pantoprazole enantiomers was estimated by an oral administration of racemic pantoprazole to rats. The pharmacokinetic differences between pantoprazole enantiomers were evaluated by the experiments of the in situ perfusion into rat small intestine, the protein binding, and the in vitro metabolism in rat liver microsomes of pantoprazole enantiomers.

RESULTS

The mean area under the curve value of S-pantoprazole was 1.5 times greater than that of R-pantoprazole after administration of racemic pantoprazole to rats (20 mg/kg, p.o.). There were significant differences in k(e) (p < 0.05), t1/2 (p < 0.01), and mean residence time (p < 0.01) values between the two enantiomers. In the in situ absorption study, the absorption rate constants were of no significant differences between the two enantiomers. The mean unbound fraction of R-pantoprazole was slightly greater than that of S-pantoprazole. The intrinsic clearance (CLint) of the formation of the 5'-O-demethyl metabolite from S-pantoprazole was 4-fold lower than that from R-pantoprazole. However, the CLint value for the sulfone and 6-hydroxy metabolites from S-pantoprazole was higher than that from R-pantoprazole. The sum of the CLint of the formation of all three metabolites was 3.06 and 4.82 mL/min/mg protein for S- and R-pantoprazole, respectively.

CONCLUSIONS

This study suggests that the enantioselective pharmacokinetics of pantoprazole enantiomers in rats is probably ascribable to their enantioselective metabolism, which is contributed by all the three metabolic pathways, including sulfoxide oxidation, 4'-O-demethylation, and 6-hydroxylation.

Pharmacokinetics and pharmacodynamics of pantoprazole in clinically normal neonatal foals

REASONS FOR PERFORMING STUDY

Proton pump inhibitors (PPIs) are a mainstay of treatment for acid-related ulceration in man and horses. Currently, only an oral preparation of omeprazole is approved for use in horses in the USA. Intravenous administration of a PPI would provide a useful therapeutic alternative for those foals in which oral medication is not feasible.

OBJECTIVE

To investigate the pharmacokinetics and pharmacodynamics of pantoprazole following i.v. or intragastric administration in healthy neonatal foals.

METHODS

Seven healthy foals age 6-12 days at the start of the study were evaluated. Treatments included no drug administration, i.v. pantoprazole (1.5 mg/kg bwt) and intragastric pantoprazole (1.5 mg/kg bwt). Intragastric pH was recorded for 24 h after drug administration for pharmacodynamic evaluation. Plasma pantoprazole concentrations were measured using high-performance liquid chromatography.

RESULTS

Plasma concentrations of pantoprazole were detectable at the 5 min sampling point following i.v. or intragastric administration. Bioavailability of intragastric-administered pantoprazole was 41%. Baseline mean hourly pH was 1.5-6.1. There was a statistically significant increase in mean hourly pH relative to untreated foals 2-24 h after i.v. or intragastric pantoprazole administration.

CONCLUSIONS

Based on these data, i.v. or intragastric administration of pantoprazole results in a significant, prolonged increase in intragastric pH.

POTENTIAL RELEVANCE

The i.v. formulation of pantoprazole may provide a clinically useful alternative means of acid suppression in foals unable to tolerate enteral administration of a PPI, such as those with pyloric outflow obstruction.

Pharmacokinetic interactions between omeprazole/pantoprazole and clarithromycin in health volunteers

The association omeprazole/clarithromycin is of current wide use in the treatment of Helicobacter pylori associated gastroduodenal ulcer. This combination may result in increased levels of omeprazole with potential interactions with commonly associated drugs. Kinetic/metabolic changes occurring after omeprazole/clarithromycin were compared to those occurring after pantoprazole/clarithromycin in healthy volunteers. Eight healthy volunteers, all males, age 25-34 years, all EM for CYP2C19, participated in a randomized, double blind crossover study in two periods of 7 days, separated by a 14-day washout. In each treatment period, subjects took either omeprazole 20mg b.i.d. together with clarithromycin 500 mg b.i.d., or pantoprazole 40 mg b.i.d. with the same dose of the antibiotic. The pharmacokinetic parameters of omeprazole and pantoprazole were compared to those after intake of both agents alone. Kinetics of unchanged clarithromycin was evaluated at the end of the two periods. The mean value of the area under the plasma concentration versus time curve (AUC) of unchanged omeprazole increased almost two-fold after concomitant administration of clarithromycin; the average 5-OH-omeprazole AUC was instead significantly reduced by 42%. Omeprazole clearance and volume of distribution were reduced significantly by 75 and 56%, respectively, after administration of the drug with clarithromicyn. No significant changes of the kinetic of pantoprazole and metabolites were observed. Kinetics of clarithromycin did not differ after the two associated treatments. The administration of clarithromycin with two different proton pump inhibitors indicates that the antibiotic can markedly increase omeprazole, not pantoprazole, levels. This observation may result in a better therapeutic response to omeprazole, but it may also potentially affect either the metabolism of CYP3A4 substrates or interfere with the absorption of drugs requiring an intact gastric digestion system.

Simultaneous Determination of Pantoprazole and Its Two Metabolites in Dog Plasma by HPLC

A simple and sensitive high-performance liquid chromatography (HPLC) method is developed and validated for simultaneous determination of pantoprazole and its two metabolites (pantoprazole sulfone and pantoprazole thioether) in dog plasma and applied to a pharmacokinetic study in Beagle dogs. Following a protein precipitation procedure, the samples are separated using reversed-phase HPLC (C18) by a gradient of acetonitrile and ammonium acetate (pH 6.0) at a flow rate of 1.0 mL/min and quantitated using UV detection at 290 nm. Omeprazole is selected as the internal standard. The method has a lower limit of quantitation of 0.025 microg/mL for pantoprazole and its two metabolites, using 0.1-mL aliquots of plasma. The linear calibration curves are obtained in the concentration range of 0.025-10.0 microg/mL for three analytes. The intra- and interrun precision (relative standard deviation), calculated from quality control (QC) samples, is less than 13% for three analytes. The accuracy determined from QC samples is between -6.4% and 12%.

Differences in binding properties of two proton pump inhibitors on the gastric H+,K+-ATPase in vivo

Restoration of acid secretion after treatment with covalently-bound proton pump inhibitors may depend on protein turnover and on reversal of inhibition by reducing agents such as glutathione. Glutathione incubation of the H(+),K(+)-ATPase isolated from omeprazole or pantoprazole-treated rats reversed 88% of the omeprazole inhibition but none of the pantoprazole inhibition. The present study was designed to measure binding properties of omeprazole or pantoprazole in vivo. Rats were injected with (14)C-omeprazole or (14)C-pantoprazole after acid stimulation. The specific binding to the gastric H(+),K(+)-ATPase was measured at timed intervals as well as reversal of binding by glutathione reduction. The stoichiometry of omeprazole and pantoprazole binding to the catalytic subunit of the H(+),K(+)-ATPase was 2 moles of inhibitor per mole of the H(+),K(+)-ATPase phosphoenzyme. Omeprazole bound to one cysteine between transmembrane segments 5/6 and one between 7/8, pantoprazole only to the two cysteines in the TM5/6 domain. Loss of drug from the pump was biphasic, the fast component accounted for 84% of omeprazole binding and 51% of pantoprazole binding. Similarly, only 16% of omeprazole binding but 40% of pantoprazole binding was not reversed by glutathione. The residence time of omeprazole and pantoprazole on the ATPase in vivo depends on the reversibility of binding. Binding of pantoprazole at cysteine 822 is irreversible whereas that of omeprazole at cysteine 813 and 892 is reversible both in vivo and in vitro. This is consistent with the luminal exposure of cysteine 813 and 892 and the intra-membranal location of cysteine 822 in the 3D structure of the H(+),K(+)-ATPase.

Excretion of pantoprazole in human breast

OBJECTIVE

To measure the amount of pantoprazole in human milk following its oral administration to a breast-feeding mother and to estimate human exposure.

STUDY DESIGN

One woman was studied over a 24-hour interval after oral administration of 40-mg pantoprazole. Serial plasma and milk samples were collected over 24 hours, and pantoprazole concentrations were measured by high-performance liquid chromatography. A milk/plasma ratio of 0.022 was observed at tmax, 2 hours after dose administration. Infant exposure was measured as maximum concentration in milk multiplied by an estimated maximum consumption of 200 mL at this time.

RESULTS

The relative infant dose was estimated to be 7.3 microg of pantoprazole, which is equivalent to 0.14% of the weight-normalized dose received by the mother. Because pantoprazole is unstable in acidic pH, the systemic dose received by the infant is expected to be lower if the ingested pantoprazole is exposed to acid in the infant's stomach. The mother detected no adverse events in the infant.

CONCLUSION

These limited data show that pantoprazole is minimally excreted into breast milk. While it is not known if pantoprazole affects breast milk production, women who are breast-feeding do not have to stop breastfeeding when taking pantoprazole chronically.

[Studies on chiral inversion of dextropantoprazole in human]

AIM

To study the chiral inversion of dextropantoprazole in human.

METHODS

Three healthy Chinese male volunteers after an oral dose of 40 mg dextropantoprazole. An HPLC method was developed and used to determine the total plasma concentrations of each enantiomer. The ratios of the enantiomers in plasma samples were measured on a Chiral-AGP column. The plasma concentration of each enantiomer was then calculated using the ratios of enantiomers and total concentrations of the two enantiomers previously measured.

RESULTS

The AUC0-t of levopantoprazole was only 1.5% of the total AUC0-t of enantiomers.

CONCLUSION

The chiral inversion from dextropantoprazole to levopantoprazole does not occur in the three healthy Chinese male volunteers after an oral dose of 40 mg dextropantoprazol.

Acute Interstitial Nephritis Due to Pantoprazole

OBJECTIVE:

To describe what is believed, as of November 4, 2003, to be the first case published in the literature of acute interstitial nephritis (AIN) due to pantoprazole.

CASE SUMMARY:

A 77-year-old white woman presented to the hospital with elevated serum creatinine, oliguria for the past 24 hours, arthralgia, fatigue, fever, and bilateral flank pain. The patient had initiated treatment with oral pantoprazole 40 mg/d for gastroesophageal reflux 2 months prior to admission. After 5 weeks of therapy, she stopped taking pantoprazole due to general malaise. Upon admission, all home medications, including pantoprazole, were reinitiated based on the patient's medication list. Serum creatinine increased to 6.1 mg/dL on day 4 of admission from a baseline of 1.0 mg/dL. Pantoprazole therapy was promptly discontinued, and prednisone 40 mg/d was initiated. Urinalysis revealed eosinophils, and a subsequent renal biopsy confirmed a diagnosis of AIN. The serum creatinine level gradually declined over 2 weeks, and the patient was discharged home with a serum creatinine level of 1.6 mg/dL. The Naranjo probability scale suggests a highly probable relationship between AIN and pantoprazole therapy in this patient.

DISCUSSION:

Drug hypersensitivity reactions are the most common cause of AIN. There have been several reported cases of omeprazole-induced AIN. Although there are very few prospective data on the efficacy of treatment of drug-induced AIN, corticosteroids may have a role in recovery of renal function. Prednisone doses of 1 mg/kg/d have been suggested.

CONCLUSIONS:

Physicians should be aware that drug-induced AIN can be associated with proton-pump inhibitors. Early detection of this rare adverse reaction may prevent acute renal insufficiency.

The comparative metabolism of triclabendazole sulphoxide by triclabendazole-susceptible and triclabendazole-resistant Fasciola hepatica

Benzimidazole anthelmintics are widely used against nematode, cestode and trematode parasites. The drugs undergo several enzyme-mediated reactions within the host animal that produce a number of metabolites. Although it has been shown that certain helminths, including Fasciola hepatica, can metabolise albendazole, nothing is known regarding the ability of the liver fluke to metabolise triclabendazole, which is the major flukicidal compound currently on the market. In the current study, adult triclabendazole-susceptible flukes were treated with triclabendazole sulphoxide in vitro, and the metabolism of the drug was monitored by high performance liquid chromatography. The data show that F. hepatica can metabolise triclabendazole sulphoxide into its relatively inert sulphone metabolite. Parallel experiments using triclabendazole-resistant flukes showed that the conversion of triclabendazole sulphoxide to triclabendazole sulphone was on average 20.29% greater in the resistant flukes compared with the susceptible flukes. The results are discussed with regard to the mechanism of triclabendazole resistance in F. hepatica.

Proton pump inhibitors in pediatrics: relevant pharmacokinetics and pharmacodynamics

A marked discordance between the disposition of proton pump inhibitors (PPIs) in plasma and the kinetics of effect suggests the need for new approaches to characterize the clinical pharmacology of PPIs in infants and children. An assessment of pharmacokinetics and pharmacodynamics must take into account the genetic polymorphism of CYP2C19 and the impact of ontogeny on the activity of this and other enzymes (e.g., CYP3A4) which affect the biotransformation of the PPIs and, thus, their plasma clearance. In addition, the potential effects of extemporaneous formulations of the drugs on their rate and extent of absorption must be considered. Because of the apparent safety of PPIs and a well-demonstrated dose-response-effect relationship in adults, pediatric pharmacokinetic data and an exposure correlate, such as the dose-area-under-the-plasma-concentration-versus-time-curve relationship, can be used as a bridge to determine pediatric dosing.

Oral bioavailability of pantoprazole suspended in sodium bicarbonate solution

The bioavailability of pantoprazole when administered as a suspension in sodium bicarbonate solution and as the oral tablet was studied. In an open-label, randomized, two-period crossover study, healthy fasting subjects received either one enteric-coated 40-mg pantoprazole tablet by mouth with 240 mL of water or 20 mL of a suspension prepared from one crushed pantoprazole tablet and 840 mg of sodium bicarbonate solution and administered via a nasogastric tube. Treatments were separated by a 48-hour washout period. Blood samples were collected at intervals up to 24 hours after drug administration for measurement of pantoprazole concentration by high-performance liquid chromatography (HPLC) and estimation of pharmacokinetic values. A separate study was conducted to determine pantoprazole's stability in the suspension for up to three months at 25, 5, and -20 degrees C; concentrations were measured by HPLC. Twelve subjects completed the study. The suspension yielded pantoprazole Cmax values similar to those of the tablet formulation, but the drug was 25% less bioavailable. There was no lag time for the suspension. The suspension was stable for up to two weeks at 5 degrees C and up to three months at -20 degrees C. A suspension of pantoprazole in sodium bicarbonate solution yielded a Cmax similar to that of the tablet formulation, and the drug was quickly absorbed. However, bio-availability was slightly lower with the suspension than with the tablet.

The clinical importance of proton pump inhibitor pharmacokinetics

Achieving the optimal clinical response for patients with upper gastrointestinal peptic disease is important. This response depends on the pathology treated as well as on the choice of proton pump inhibitor. Here, we identify factors in specific disease therapy and proton pump inhibitor (PPI) pharmacokinetic and pharmacodynamic characteristics that help us achieve this goal. These include differences in PPI bioavailability and acid-suppressive effects. Available data indicate that PPIs appear to have similar potency on a milligram basis, and that omeprazole and lansoprazole are more frequently double dosed than pantoprazole. The lower propensity for double dosing with pantoprazole may also result in lower medication acquisition costs and a reduction in physician visits due to ineffective therapy with the standard dosing of these other agents.

Pantoprazole: an update of its pharmacological properties and therapeutic use in the management of acid-related disorders

Pantoprazole (Protonix) is an irreversible proton pump inhibitor (PPI) that reduces gastric acid secretion. In combination with two antimicrobial agents (most commonly metronidazole, clarithromycin or amoxicillin) for 6-14 days, pantoprazole 40 mg twice daily produced Helicobacter pylori eradication rates of 71-93.8% (intent-to-treat [ITT] or modified ITT analysis) in patients without known antibacterial resistance. Pantoprazole-containing triple therapy was at least as effective as omeprazole- and similar in efficacy to lansoprazole-containing triple therapy in large trials. In the treatment of moderate to severe gastro-oesophageal reflux disease (GORD), oral pantoprazole 40 mg/day was as effective as other PPIs (omeprazole, omeprazole multiple unit pellet system, lansoprazole and esomeprazole) and significantly more effective than histamine H(2)-antagonists. Pantoprazole 20 mg/day provided effective mucosal healing in patients with GORD and mild oesophagitis. Intravenous pantoprazole 40 mg/day can be used in patients who are unable to take oral medication. Oral pantoprazole 20-40 mg/day for up to 24 months prevented relapse in most patients with healed GORD. According to preliminary data, oral pantoprazole 20 or 40 mg/day was effective at healing and preventing non-steroidal anti-inflammatory drug (NSAID)-related ulcers, and intravenous pantoprazole was at least as effective as intravenous ranitidine in preventing ulcer rebleeding after endoscopic haemostasis. Oral or intravenous pantoprazole up to 240 mg/day maintained target acid output levels in most patients with hypersecretory conditions, including Zollinger-Ellison syndrome. Oral and intravenous pantoprazole appear to be well tolerated in patients with acid-related disorders in short- and long-term trials. Tolerability with oral pantoprazole was similar to that with other PPIs or histamine H(2)-antagonists in short-term trials. Formal drug interaction studies have not revealed any clinically significant interactions between pantoprazole and other agents. In conclusion, pantoprazole is an effective agent in the management of acid-related disorders. As a component of triple therapy for H. pylori eradication and as monotherapy for the healing of oesophagitis and maintenance of GORD, pantoprazole has shown similar efficacy to other PPIs and greater efficacy than histamine H(2)-antagonists. Limited data suggest that it is also effective in Zollinger-Ellison syndrome and in preventing ulcer rebleeding. Pantoprazole is well tolerated with minimal potential for drug interactions. The availability of pantoprazole as both oral and intravenous formulations provides flexibility when the oral route of administration is not appropriate. Thus, pantoprazole is a valuable alternative to other PPIs in the treatment of acid-related disorders.

Design, synthesis, and SAR of tachykinin antagonists: modulation of balance in NK(1)/NK(2) receptor antagonist activity

Through optimization of compounds based on the dual NK(1)/NK(2) antagonist ZD6021, it was found that alteration of two key regions could modulate the balance of NK(1) and NK(2) potency. Substitution of the 2-naphthalene position in analogues of ZD6021 resulted in increased NK(1) potency and thus afforded NK(1) preferential antagonists. Alterations of the piperidine region could then increase NK(2) potency to restore dual NK(1)/NK(2) selectivity. Through these efforts, three novel receptor antagonists from a single chemically related series were identified; two are dual NK(1)/NK(2) antagonists, and the third is an NK(1) preferential antagonist. In this paper, the factors affecting the balance of NK(1) and NK(2) selectivity in this series are discussed and the in vitro and in vivo properties of the novel antagonists are described.

Proton pump inhibitors: an update

Since their introduction in the late 1980s, proton pump inhibitors have demonstrated gastric acid suppression superior to that of histamine H2-receptor blockers. Proton pump inhibitors have enabled improved treatment of various acid-peptic disorders, including gastroesophageal reflux disease, peptic ulcer disease, and nonsteroidal antiinflammatory drug-induced gastropathy. Proton pump inhibitors have minimal side effects and few significant drug interactions, and they are generally considered safe for long-term treatment. The proton pump inhibitors omeprazole, lansoprazole, rabeprazole, and the recently approved esomeprazole appear to have similar efficacy.

Acid suppression in healthy subjects following lansoprazole or pantoprazole

AIM

To compare the effect of lansoprazole, 30 mg once daily, with that of pantoprazole, 40 mg once daily, for the inhibition of gastric acid secretion.

METHODS

Two randomized, single-blind, two-way, crossover studies were conducted in 74 healthy male volunteers. Lansoprazole, 30 mg, or pantoprazole, 40 mg, was administered once daily for five consecutive days with at least a 2-week washout period between regimens. Ambulatory 24-h intragastric pH was recorded at baseline and on days 1 and 5 of each crossover treatment period.

RESULTS

On day 1 in both studies, lansoprazole, 30 mg, produced significantly higher mean 24-h intragastric pH values when compared to pantoprazole, 40 mg (3.78 vs. 3.08, P < 0.001, and 3.97 vs. 3.20, P < 0.001, in the first and second studies, respectively). In both studies, lansoprazole, 30 mg, produced significantly greater proportions of time that the intragastric pH was above 3, 4 and 5 when compared with pantoprazole, 40 mg (P < 0.005 in all comparisons). By treatment day 5 in the first study, lansoprazole, 30 mg, continued to produce a higher mean 24-h intragastric pH (4.15 vs. 3.91, P=0.014) and a significantly greater percentage of time that the intragastric pH was above 4 (63% vs. 56%, P=0.017) and 5 (41% vs. 30%, P < 0.001) when compared with pantoprazole, 40 mg. In the second study, the effects on intragastric pH were comparable between the two treatment groups. Headache was the most commonly reported adverse experience (nine lansoprazole-treated subjects, seven in the first study and two in the second study; six pantoprazole-treated subjects, five in the first study and one in the second study).

CONCLUSIONS

Lansoprazole, 30 mg once daily, produces a faster onset and greater degree of acid inhibition than pantoprazole, 40 mg once daily. The implications for these differences on symptom relief and healing of erosive oesophagitis should be explored.

Relative efficacies of gastric proton-pump inhibitors on a milligram basis: desired and undesired SH reactions. Impact of chirality

Gastric proton-pump inhibitors (PPIs) are prodrugs. Their acid activation at pH 1.0 inside the canaliculus of a parietal cell should be fast relative to their serum elimination rate. Actually, all PPIs display chemical activation half-lives at pH 1.0 of a few minutes at the most, while being eliminated from serum with a half-life of about 1 h. This is the main reason they show similar antisecretory efficacies on a milligram basis. It is in line with about 5% to 15% higher healing rates in GERD, DU and GU when 40 mg is compared to 20 mg of either omeprazole or pantoprazole. The comparably large biological variation between patient samples explains why some studies show statistically significant differences between the two doses, while others do not. However, it would matter to the individual patient if s/he was the one additionally healed by a 40 mg dose within a defined treatment period. Chemical activation of PPI prodrugs is unwanted in weakly acidic tissue compartments such as lysosomes or secretory granules. However, the ratio of the serum elimination half-life (availability at the target) to the chemical activation half-life at a critical pH 5.0 is reversed only with pantoprazole. when compared to pH 1.0 (i.e. the ratio is < 1 at pH 5.0 and > 1.0 at pH 1.0). This is the basis of the high pH selectivity of pantoprazole. In contrast, rabeprazole is activated at pH 5.0 almost as quickly as it is at pH 1.0 and much faster than it is eliminated from serum. This unwanted reactivity of rabeprazole at pH 5.0 does not contribute to the antisecretory action at pH 1.0 and results in poor pH selectivity. Omeprazole and lansoprazole lie in between, as they are activated, at pH 5.0, about as quickly as they are eliminated from serum. The above activation rates refer to room temperature. At 37 degrees C. the activation rates of all PPIs further increase, by about the same factor of between 3 and 4. This renders their differential pH selectivities even more critical for drug safety. Biological consequences have been reported in the literature. It has been claimed that a dose of 40 mg of the S-enantiomer of omeprazole (esomeprazole) results in 10%-15% higher healing rates in GERD patients, compared to 20 mg omeprazole racemate. The same difference is found when the two doses of omeprazole racemate are compared to each other. This is not surprising, as the chiral PPI prodrug is converted by acid into an achiral cyclic sulfenamide which only then reacts with the proton pump. There is therefore no pharmacodynamic argument in favour of any single enantiomer formulation of any PPI. Moreover, potential pharmacokinetic differences between the enantiomers seem to be of little if any importance in the patient.

Enantiomeric determination of pantoprazole in human plasma by multidimensional high-performance liquid chromatography

Multidimensional HPLC is a powerful tool for the analysis of samples of a high degree of complexity. This work reports the use of multidimensional HPLC by coupling a RAM column with a chiral polysaccharide column to the analysis of Pantoprazole in human plasma by direct injection. The enantiomers from the plasma samples were separated with high resolution on a tris(3,5-dimethoxyphenylcarbamate) of amylose phase after clean-up by a RAM BSA octyl column. Water was used as solvent for the first 5 min in a flow-rate of 1.0 ml/min for the elution of the plasmatic proteins and then acetonitrile-water (35:65 v/v) for the transfer and analysis of pantoprazole enantiomers, which were detected by UV at 285 nm. Analysis time was 28 min with no time spent on sample preparation. A good linear relationship was obtained in the concentration range of 0.20 to 1.5 microg/ml for each enantiomer. Inter and intra-day precision and accuracy were determined by one low (0.24 microg/ml), one medium (0.70 microg/ml) and one high (1.3 microg/ml) plasma concentration and gave a C.V. varying from 1.80 to 8.43% and accuracy from 86 to 92%. Recoveries of pantoprazole enantiomers were in the range of 93.7-101.2%. The validated method was applied to the analysis of the plasma samples obtained from ten Brazilian volunteers who received an 80 mg oral dose of racemic pantoprazole and was able to quantify the enantiomers of pantoprazole in all clinical samples analyzed.

Discovery of novel, orally active dual NK1/NK2 antagonists

Exploration of the SAR around selective NK2 antagonists, SR48968 and ZD7944, led to the discovery that naphth-1-amide analogues provide potent dual NK1 and NK2 antagonists. ZD6021 inhibited binding of [3H]-NKA or [3H]-SP to human NK1 and NK2 receptors, with high-affinity (K(i)=0.12 and 0.62nM, respectively). In functional assays ZD6021 had, at 10(-7)M, in human pulmonary artery pK(B)=8.9 and in human bronchus pK(B)=7.3, for NK1 and NK2, respectively. Oral administration of ZD6021 to guinea pigs dose-dependently attenuated ASMSP induced extravasation of plasma proteins, ED(50)=0.5mg/kg, and NK2 mediated bronchoconstriction, ED(50)=13mg/kg.

Pharmacokinetics of pantoprazole in patients with moderate and severe hepatic dysfunction

BACKGROUND

Patients with impaired hepatic function usually require gastric acid-suppressant therapy but are at increased risk for drug interactions and may require dosage adjustments. The proton pump inhibitor pantoprazole is rapidly absorbed and eliminated, primarily by cytochrome P450 (CYP) 2C19 isozymes.

OBJECTIVE

This study sought to determine whether dosage adjustment of pantoprazole is required in patients with moderate or severe hepatic impairment by comparing the pharmacokinetic profile of pantoprazole in such patients with that in healthy slow metabolizers of pantoprazole, in whom no dosage adjustment is required.

METHODS

Patients with moderate (Child-Pugh class B) and severe (Child-Pugh class C) hepatic impairment received oral pantoprazole 40 mg once daily on days 1 through 4 and then on alternate days (days 6 and 8). Serial blood samples were collected on days 4 and 8 for analyses of plasma pantoprazole concentrations. Pharmacokinetic data were compared between the 2 groups with hepatic impairment and against historical data from 17 healthy subjects who were genetically slow CYP2C19 metabolizers of pantoprazole.

RESULTS

Twenty-two patients participated in the study, 13 in the Child-Pugh class B group and 9 in the Child-Pugh class C group. No clinically significant differences in pantoprazole pharmacokinetics were noted between the patients with hepatic impairment and the healthy slow metabolizers of pantoprazole on days 4 and 8. Pantoprazole was well tolerated. Four Child-Pugh class B patients and 3 Child-Pugh class C patients reported > or = 1 adverse event. Adverse events were generally mild or moderate, and were similar to those reported in healthy subjects. Two patients discontinued the study because of severe events related to their underlying disease.

CONCLUSIONS

The pharmacokinetics and tolerability of pantoprazole were similar in patients with moderate hepatic impairment, patients with severe hepatic impairment, and healthy slow metabolizers of pantoprazole, in whom no dosage adjustment is required. Thus, no dosage adjustment of pantoprazole is required in patients with hepatic impairment, regardless of its severity. However, caution should be exercised when giving pantoprazole to patients with severe hepatic impairment.

Effects on 24-hour intragastric pH: a comparison of lansoprazole administered nasogastrically in apple juice and pantoprazole administered intravenously

OBJECTIVE

To compare the 24-h intragastric pH effects of lansoprazole, 30 mg administered nasogastrically, with pantoprazole, 40 mg administered i.v.

METHODS

Healthy adults were enrolled in an open label, two-way crossover, single-center study. Thirty milligrams of lansoprazole (administered nasogastrically in apple juice) or pantoprazole (i.v.) were administered once daily at 8:00 AM for 5 consecutive days with at least a 2-wk washout period between the regimens. Ambulatory 24-h intragastric pH was monitored at baseline and on days 1 and 5 of each treatment period. Blood specimens were collected on days I and 5 for pharmacokinetic parameter determinations.

RESULTS

Thirty-three adults completed both crossover periods, with the exception of one patient with a zero lansoprazole plasma concentration on day 1 of period 2. Lansoprazole, 30 mg per nasogastric tube, produced significantly higher mean 24-h intragastric pH values relative to pantoprazole, 40 mg i.v., on both day 1 (3.05 vs 2.76, p < 0.002) and day 5 (3.65 vs 3.45, p = 0.024). Lansoprazole sustained the intragastric pH above 3 (days 1 and 5), 4, and 5 (day 1) significantly longer relative to pantoprazole. Lansoprazole's time to the maximum observed concentration and area under the plasma concentration-time curve over the 24-h time interval increased significantly from day I to day 5 (1.7 h vs 2.0 h and 1865 ng x h/ml vs 2091 ng x h/ml, respectively), and a significant increase in half-life relative to day 1 (0.96 h) was observed on day 5 (1.03 h) during pantoprazole treatment.

CONCLUSION

Lansoprazole, 30 mg administered nasogastrically, effectively controls intragastric pH and is an alternative to i.v. pantoprazole in patients who are unable to swallow solid dosage formulations.

Pantoprazole

The pharmacology, pharmacokinetics, clinical efficacy, adverse effects, and dosage and administration of pantoprazole are reviewed. Pantoprazole is a gastric hydrogen-potassium adenosine triphosphatase (H+/K(+)-ATPase) inhibitor. It shares the same core structure as other currently available proton-pump inhibitors (PPIs). The FDA-labeled indication is the short-term treatment of erosive esophagitis. PPIs act by selectively inhibiting H+/K(+)-ATPase in the secretory canaliculus of the stimulated parietal cell. Understanding the pharmacodynamics of PPIs is more relevant than knowing their pharmacokinetics, since the duration of action depends on the rate of de novo proton-pump regeneration, not the duration of drug circulation in the body. Pantoprazole is well absorbed, undergoes little first-pass metabolism, and has an absolute bioavailability of approximately 77%. Pantoprazole has been evaluated in more than 100 clinical trials involving more than 11,000 patients. It is effective in treating erosive esophagitis and duodenal and gastric ulcers. It is also effective as adjunctive treatment with antimicrobials in patients infected with Helicobacter pylori. Pantoprazole has been shown to control acid production in Zollinger-Ellison syndrome. Pantoprazole is well tolerated. The most commonly reported adverse effects are headache, diarrhea, and abdominal pain. The recommended oral dosage for erosive esophagitis is 40 mg once a day for up to eight weeks. The recommended i.v. dose is 40 mg given over 15 minutes once a day in patients with gastroesophageal reflux disease who are unable to take oral medication. Pantoprazole appears to be as safe and effective as other PPIs in acid-related disorders.

Shortcomings of the first-generation proton pump inhibitors

Proton pump inhibitors (PPIs) are widely prescribed for the treatment of gastro-oesophageal reflux disease (GORD) as well as gastric and duodenal ulcers, and these agents are now considered the drugs of choice for managing such acid-related disorders. Despite their well-documented efficacy and safety, first-generation PPIs (omeprazole, pantoprazole and lansoprazole) have notable limitations. These drugs exhibit substantial interpatient variability in pharmacokinetics and may have significant interactions with other drugs. The time of dosing and ingestion of meals may also influence the pharmacokinetics of these agents as well as their ability to suppress gastric acid secretion. First-generation PPIs also have a relatively slow onset of pharmacological action and may require several doses to achieve maximum acid suppression and symptom relief, possibly limiting their usefulness in on-demand GORD therapy. First-generation PPIs may also fail to provide 24-h suppression of gastric acid, and noctural acid breakthrough can occur even with twice-daily dosing. Both first- and second-generation PPIs may be associated with adverse events consequent to gastric acid suppression, but newer PPIs have the potential to overcome some critical pharmacokinetic, pharmacodynamic, and clinical limitations of the first-generation drugs.

Stereoselective pharmacokinetics of pantoprazole, a proton pump inhibitor, in extensive and poor metabolizers of S-mephenytoin

Pantoprazole, a proton pump inhibitor, is administered as a racemic mixture. To determine the role of cytochrome P450 (CYP) 2C19 in the stereoselective metabolism of pantoprazole, we investigated the pharmacokinetic disposition of (+)- and (-)-pantoprazole in 7 extensive metabolizers and 7 poor metabolizers of S-mephenytoin. All of the subjects received an oral 40-mg dose of racemic pantoprazole as the enteric-coated formulation. In the extensive metabolizers, the mean clearance of (-)-pantoprazole was only slightly lower than that of (+)-pantoprazole and no significant differences in the other pharmacokinetic parameters between (+)- and (-)-pantoprazole were observed. The mean (+)/(-) ratios for maximum concentration, area under the plasma concentration-time curve from 0 to infinity, and elimination half-life were 0.94, 0.82, and 0.90, respectively. In contrast, in the poor metabolizers, the clearance values of both enantiomers were significantly lower than those in the extensive metabolizers, and a significant difference in pharmacokinetics between (+)- and (-)-pantoprazole was observed. The mean elimination half-life for (+)-pantoprazole was 3.55-fold longer than that of (-)-pantoprazole, and the mean maximum concentration and area under the plasma concentration-time curve from 0 to infinity for (+)-pantoprazole were 1.31- and 3.59-fold greater, respectively, than those for (-)-pantoprazole. These results indicate that the stereoselective metabolism of pantoprazole depends on S-mephenytoin 4'-hydroxylase (CYP2C19). The metabolism of (+)-pantoprazole was impaired to a greater extent than (-)-pantoprazole in the poor metabolizers.

Pharmacodynamic modeling of pantoprazole's irreversible effect on gastric acid secretion in humans and rats

The relationship between the pharmacokinetics of pantoprazole, an irreversible proton pump inhibitor, and its effect on gastric acid secretion was evaluated in humans and rats. Pantoprazole pharmacokinetics were studied in 6 rats (5 mg/kg, i.v.) and 22 healthy volunteers (10 to 80 mg, i.v. and oral). Gastric acid secretion under maximum pentagastrin stimulation was measured after i.v. administration of placebo or pantoprazole in 31 rats (0.12 to 1.15 mg/kg) for 4 hours and in 31 subjects (20 to 120 mg) for 24 hours. Pantoprazole has short half-lives of 0.5 hours in rats and 0.8 hours in humans. After administration of the highest dose, acid secretion was fully inhibited within 1 hour and for the whole observation period in both species. An irreversible pharmacodynamic response model was successfully developed and validated. The apparent reaction rate constants of pantoprazole with the proton pumps were 0.691 L/mg/h in rats and 0.751 L/mg/h in humans, and the apparent recovery rates of the pumps were 0.053 h-1 and 0.031 h-1, respectively. The maximum inhibition and the overall effect of pantoprazole are related to exposure, and the onset is related to initial pantoprazole concentrations. It was concluded that this irreversible response model accurately describes the effect of i.v. and oral pantoprazole on gastric secretion and may be used to predict effects under other dosage regimens.

Bioavailability of a crushed pantoprazole tablet after buffering with sodium hydrogencarbonate or magaldrate relative to the intact enteric coated pantoprazole tablet

The aim of this study was to determine the bioavailability of orally administered, crushed pantoprazole tablets after buffering with either 1.4% sodium hydrogencarbonate or 1600 mg magaldrate relative to the intact enteric coated pantoprazole tablet. A single dose, three-period crossover study was performed with 18 healthy male volunteers. The crushed pantoprazole suspension, together with either sodium hydrogencarbonate or magaldrate, was administered via a nasogastral tube. Tmax of crushed pantoprazole was earlier as compared to the intact tablet (0.5 h vs. 3 h) and Cmax was approximately 10% higher due to faster absorption. The bioavailability of the crushed pantoprazole tablet relative to the intact pantoprazole tablet was 93% when using sodium hydrogencarbonate as the buffering agent, and 88% when using magaldrate. Based on the internationally approved confidence intervals for AUC (0.80-1.20) and Cmax (0.70-1.43), the crushed tablet buffered with sodium hydrogencarbonate was shown to be bioequivalent with the intact tablet (point estimates for AUC or Cmax: 0.93 or 1.10). For the crushed tablet buffered with magaldrate (point estimates for AUC or Cmax: 0.88 or 1.12) bioequivalence with the intact tablet could not be formally demonstrated, although the lower confidence limit for AUC of 0.78 was only slightly below the lower limit of the equivalence range of 0.80.

Clinical experience with pantoprazole in gastroesophageal reflux disease

BACKGROUND

Pantoprazole is a new proton pump inhibitor indicated for the treatment of erosive esophagitis associated with gastroesophageal reflux disease (GERD) and is available in both oral and intravenous (IV) formulations.

OBJECTIVE

This paper reviews the pharmacologic properties of pantoprazole and summarizes the findings from clinical studies of this drug.

METHODS

This review was compiled from the published literature, abstracts from clinical trials, and data on file with the manufacturer of pantoprazole.

RESULTS

Pantoprazole selectively accumulates in the acidic environment of gastric parietal cells and acts at the final step of acid secretion by binding 2 key cysteine residues of the proton pump involved in gastric acid production. The bioavailability of pantoprazole is not altered by concomitant administration of food or antacids or with repeated dosing. Both oral and IV formulations of pantoprazole exhibit linear pharmacokinetics. Several clinical trials have proved pantoprazole superior to histamine-2-receptor antagonists (H2RAs) in reducing acid secretion and elevating gastric pH levels. Pantoprazole has been shown to be more effective than ranitidine (P < 0.05), famotidine (P < 0.001), and nizatidine (P < 0.05), and at least as effective as omeprazole, in healing erosive esophagitis and relieving associated symptoms of GERD, including regurgitation. Pantoprazole is also more effective than the H2RA nizatidine for the treatment of nighttime heartburn (P < 0.05). Studies have shown pantoprazole to be well tolerated; adverse events, including headache, diarrhea, flatulence, abdominal pain, eructation, nausea, and rash, occurred in < or = 6% of patients. The oral and IV formulations of pantoprazole are equally potent in inhibiting gastric acid secretion; thus, switching between formulations requires no dosage adjustments. Special patient populations, including the elderly and patients with renal or mild to moderate hepatic impairment, can take pantoprazole without an adjustment in dosage.

CONCLUSIONS

Because of its unique pharmacokinetic properties, mechanism of action, and reduced potential for producing cytochrome P-450-based drug interactions, pantoprazole in both oral and IV formulations is effective over a full 24 hours and is well tolerated in a variety of patient types.

A comparative pharmacodynamic study of IY-81149 versus omeprazole in patients with gastroesophageal reflux disease

OBJECTIVE

To evaluate and compare the pharmacodynamic effects of IY-81149 and omeprazole on gastric pH in patients with gastroesophageal reflux disease.

METHODS

Sixty male and female volunteers with gastroesophageal reflux disease were enrolled in a double-blind, two-way, crossover, dose-ranging study. Subjects were randomized into three groups, with each group comparing the effect of one of three doses of IY-81149 (5, 10, or 20 mg) with 20 mg omeprazole. IY-81149 and omeprazole were administered once daily for 5 days. Continuous 24-hour pH measurements were performed before the first dose (baseline) and after the fifth dose in both periods. Gastric acid suppression was evaluated on the basis of the following parameters: AUC(0-24), median pH in a 24-hour interval (pHmedian), and the percent time in a 24-hour interval in which the gastric pH was greater than 4 (tpH > 4). The truncated AUC parameters AUC(0-8), AUC(8-16), and AUC(16-24) were also calculated. The effects of IY-81149 and omeprazole on gastric pH were compared by use of analyses of covariance. The dose-response relationship for IY-81149 was also evaluated.

RESULTS

There were no statistically significant differences between 5 mg IY-81149 and 20 mg omeprazole in terms of AUC(0-24), pHmedian, tpH, 4, AUC(0-8), and AUC(8-16). IY-81149, at 10 mg, produced a significantly greater gastric acid suppression than omeprazole on the basis of the values of AUC(0-24), pHmedian, tpH > 4, AUC(8-16), and AUC(16-24). Administration of 20 mg IY-81149 produced a significantly greater gastric acid suppression on the basis of all parameters. All doses of IY-81149 were more effective than omeprazole during 16 to 24 hours after the dose was administered.

CONCLUSIONS

Administration of 10 and 20 mg IY-81149 produced a statistically significantly greater and prolonged suppression of gastric pH than 20 mg omeprazole.

Differential stereoselective pharmacokinetics of pantoprazole, a proton pump inhibitor in extensive and poor metabolizers of pantoprazole--a preliminary study

Pantoprazole (PAN) is a proton pump inhibitor that is administered as a racemic mixture. The pharmacokinetics of PAN enantiomers were investigated in extensive metabolizers (EMs) and apparent poor metabolizers (PMs) of PAN who received a single, 40, 60, or 80 mg oral dose of racemic PAN as enteric-coated formulation. In the EMs, the serum concentrations of (-)-PAN were slightly higher than those of (+)-PAN at each dose level. The (+)/(-) ratios for the area under the concentration-time curve (AUC) and the half-life were 0.58-0.89 and 0.62-0.88, respectively. In the PMs, the serum concentrations and both enantiomers were much higher than those in the EMs at each dose level and significant differences in pharmacokinetics of (+)- and (-)-PAN were observed. The half-lives for (+)-PAN were 2.67-3.77 times longer than those for (-)-PAN. The AUCs for (+)-PAN were 2.65-3.45 times greater than those for (-)-PAN. Therefore, the metabolism of (+)-PAN is impaired to a greater extent than (-)-PAN in the PMs, which resulted in the stereoselective disposition of PAN in the PMs. It has been suggested that the EMs and the PMs of PAN could be differentiated by determining the (+)/(-) enantiomer ratio in serum at one time point, possibly 2-6 h after oral dosing, because the (+)/(-) enantiomer ratios in the PMs were opposite those in the EM subjects.

Stereoselective chiral inversion of pantoprazole enantiomers after separate doses to rats

(+/-)-Pantoprazole ((+/-)-PAN), (+/-)-5-(difluoromethoxy)-2-[[3.4-dimethoxy-2-pyridinyl)methyl]sul finyl]- 1H-benzimidazole) is a chiral sulfoxide that is used clinically as a racemic mixture. The disposition kinetics of (+)-PAN and (-)-PAN given separately has been studied in rats. Serum levels of (+)- and (-)-PAN and its metabolites, pantoprazole sulfone (PAN-SO2), pantoprazole sulfide (PAN-S), 4'-O-demethyl pantoprazole sulfone (DMPAN-SO2), and 4'-O-demethyl pantoprazole sulfide (DMPAN-S) were measured by HPLC. Following single intravenous or oral administration, both enantiomers were rapidly absorbed and metabolized, resulting in similar serum concentrations, suggesting that the two enantiomers have approximately the same disposition kinetics. The major metabolite of both (+)- and (-)-PAN was PAN-SO2, while DMPAN-SO2 was also detected as a minor metabolite. Serum levels of PAN-S and DMPAN-S could not be quantified after intravenous or oral administration of either enantiomer. Significant chiral inversion occurred after intravenous and oral administration of (+)-PAN. The AUCs of (-)-PAN after intravenous and oral dosing of (+)-PAN were 36.3 and 28.1%, respectively of those of total [(+) + (-)] PAN. In contrast, the serum levels of (+)-PAN were below quantitation limits after intravenous or oral administration of (-)-PAN. Therefore, chiral inversion was observed only after administration of (+)-PAN, supporting the hypothesis that stereoselective inversion from (+)-PAN to (-)-PAN occurs in rats.

Lack of a pharmacokinetic interaction between lansoprazole or pantoprazole and theophylline

AIM

To study the potential pharmacokinetic interaction between lansoprazole or pantoprazole and theophylline at steady state.

METHODS

Theophylline 200 mg extended-release formulation was administered twice daily on days 1-11 to 30 healthy, non-smoking males. On days 5-11, 15 subjects received concomitant lansoprazole 30 mg once daily (o.d.) and 15 subjects received concomitant pantoprazole 40 mg o.d.

RESULTS

No significant changes in the steady-state theophylline maximum plasma concentration (Cmax), time to Cmax (Tmax), minimum plasma concentration (Cmin), area under the plasma concentration-time curve over the 12-h dosing interval (AUC0-12), or apparent total oral clearance (CL/F) were observed within the two treatment groups when theophylline was administered alone or in combination with lansoprazole or pantoprazole. In addition, no significant differences in the changes of steady-state theophylline pharmacokinetics from day 4 to day 11 were noted between the two treatment groups. Treatment with theophylline in combination with either lansoprazole or pantoprazole was well tolerated. All adverse events were transient and rated mild to moderate in severity.

CONCLUSION

Co-administration of either lansoprazole or pantoprazole in healthy subjects does not significantly affect the steady-state pharmacokinetics of theophylline at the therapeutic doses tested.

Metabolism of ethyl methyl sulphide and sulphoxide in rat microsomal fractions

1. Gas chromatographic (GC) methods for the analysis of ethyl methyl sulphide (EMS) and its corresponding sulphoxide (EMSO) and sulphone (EMSO2) in rat microsomes and aspects of the in vitro metabolism of EMS and EMSO are described. 2. EMS and the internal standard (dimethyl sulphide) were extracted by a headspace procedure and separated satisfactorily using a column packed with 4% Carbowax 20 M/0.8% KOH on Carbopack B. EMSO, EMSO2 and the internal standard n-propyl sulphone were separated satisfactorily using a 2-m column packed with 10% Carbowax 20 M on Chromosorb W. 3. Under the optimum conditions (incubation of 10 min and microsomal protein content of approximately 4 mg/ml), 10% of the initial EMS concentration (2.5 mM) was converted to the corresponding sulphoxide in rat liver microsomal incubations. However, < 0.1% of the sulphone was detected when rat liver microsomes were incubated with EMS. Similarly, 2.5% of the initial EMSO concentration (2.5 mM) was converted to the corresponding sulphone by rat liver microsomes (approximately 4 mg/ml protein) during an incubation of 30 min. However, no EMS was detected after incubation with EMSO under these conditions. 4. The estimated apparent Vmax and Km for the sulphoxidation of EMS were 3.8+/-0.02 nmol/mg protein/min and 1.9+/-0.10 mM respectively. Vmax1, Vmax2 and Km1 and Km2 for the S-oxidation of EMSO were 0.5+/-0.01 and 0.2+/-0.01 nmol/mg protein/min and 0.7+/-0.02 and 0.1+/-0.00 mM respectively. 5. Studies with selective inducers and inhibitors of microsomal monooxygenases indicated that the sulphoxidation of EMS is mediated mainly by FMO, whereas both FMO and cytochrome P450 are involved in the S-oxidation of EMSO.

Relative efficacies of gastric proton pump inhibitors: their clinical and pharmacological basis

The present review will verify by intra-study rank orders, and their comparison between studies, that the different gastric proton pump inhibitors (PPIs) display similar dose-response relationships with similar potencies and efficacies on a milligram basis, i.e., at the same milligram doses. This is in line with their basic pharmacology which suggests that, primarily, the serum AUCs of the free pro-drugs and their chemical activation half lives at pH 1 relative to their serum elimination half lives determine the efficacies of PPIs. According to the literature, these drug characteristics are similar for all PPIs. Although PPIs have been introduced into the therapy of acute peptic ulcer disease at different daily, oral doses of 20 mg (omeprazole and rabeprazole), 30 mg (lansoprazole) and 40 mg (pantoprazole), the data suggest that the optimal dose of lansoprazole, omeprazole and pantoprazole, with respect to the acute treatment of peptic ulcers and moderate to severe gastroesophageal reflux disease (GERD), is about 30-40 mg daily. The data base of rabeprazole appears to be too small at present to make any definite statement. Lower daily doses of the PPIs of about 15-20 mg are sufficient in less severe cases of GERD and in maintenance therapy. It appears that different dose recommendations were based on different strategies to balance optimal drug dosage and safety, rather than on real differences in milligram-related efficacies.

Pantoprazole lacks induction of CYP1A2 activity in man

OBJECTIVE

This drug-drug interaction study investigated the potential influence of the proton pump inhibitor pantoprazole on the CYP1A2 activity as assessed by urinary excretion of caffeine metabolites.

SUBJECTS, MATERIALS AND METHODS

12 healthy, non-smoking volunteers underwent two treatment periods of 7 days each in randomized order with once-daily oral intake of 40 mg pantoprazole (test) or placebo (reference). On days 6 and 7 of both periods, 200 mg caffeine was administered two hours after pantoprazole intake, i.e. at the expected t(max) of pantoprazole serum concentrations. Urinary excretion of the caffeine metabolites 1X, 1U, AFMU, 17U was measured up to 8 hours after caffeine intake. In accordance with recent guidelines on drug-drug interactions, lack of interaction was handled as an equivalence problem.

RESULTS

Point estimate and 90% confidence intervals (CI) of the respective ratios test/reference were 0.91 (0.81, 1.03) for (1X + 1U + AFMU)/17U, indicative for CYP1A2 activity, 1.03 (0.94, 1.13) for AFMU/1X (N-acetyl transferase activity) and 1.01 (0.94, 1.09) for 1U/1X (xanthine oxidase activity).

CONCLUSION

Pantoprazole does not induce CYP1A2 activity, consistent with previous findings following theophylline administration, nor does it have any influence on N-acetyl-transferase or xanthine oxidase activity.

Comparison of the pharmacodynamics and pharmacokinetics of pantoprazole (40 mg) as compared to omeprazole MUPS (20 mg) after repeated oral dose administration

The effects on intragastric p11 and gastrin secretion of once daily pantoprazole (40 mg) and a new formulation omeprazole (20 mg) in a Multiple Unit Pellet System (MUPS) were investigated during two treatment periods of 7 days each in a randomized crossover study with 16 healthy Helicobacter pylori-negative male volunteers. Intragastric pH was measured using continuous 24 hour pH-metry on days 1 and 7. The results were compared to the baseline curves obtained before each treatment period. On day 1, pantoprazole raised the intragastric pH significantly higher and more quickly than omeprazole MUPS (pH median 1.9 vs. 1.6, baseline pH 1.4). After 7 days, the 24 h gastric pH medians were still in favor of pantoprazole (pH 3.0 vs. 2.8). With respect to the basal gastrin concentration, both treatments resulted in similar increases. For pantoprazole, no differences were observed in AUC and Cmax after single and repeated dosing. However, the new omeprazole MUPS formulation still showed the well-known effect of initial low bioavailability increasing after repeated dosing. Pantoprazole and omeprazole were well tolerated. There seems to be no advantage in the new omeprazole formulation compared with the conventional capsule with regard to bioavailability and increase in intragastric pH. The results of this study confirm former results in which pantoprazole (40 mg) was shown to be significantly superior to omeprazole (20 mg) in elevating intragastric pH.