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.

Pharmacokinetic Comparison of an Angiotensin II Receptor Antagonist, Telmisartan, in Japanese and Western Hypertensive Patients Using Population Pharmacokinetic Method

The objectives of this study were to develop a population pharmacokinetic (PPK) model for telmisartan based on the pooled data obtained from the different racial populations and then to identify the factors that affect the pharmacokinetics of telmisartan for the comparison between the regions. A PPK model was established based on the data of 1343 subjects in 12 clinical trials. The PK profiles of telmisartan were described with a 2-compartment model with first-order absorption. The obtained model could predict the observed plasma concentrations well. This PPK model suggested that CL/F was a function of age, dose, gender, race, alcohol consumption and liver function. A marked difference was observed in the plasma concentration profiles between Japanese and other countries' subjects. However, the effect of the factor "race" on CL/F was not large. In the present PPK model, "trial condition" affected all PK parameters except for V(2)/F. The condition differences were in food condition and formulation (Japanese: fed, capsule, US and EU: fasted, tablet). The extent of difference in the plasma concentration profiles simulated for Japanese and Caucasian using the PPK model under the same demographic condition was comparable with the results of the food effect study performed previously in Japan. The findings suggest that the difference in the plasma concentration profiles between Japanese and other countries' subjects was mainly due to the difference of food intake conditions under which the clinical trials were performed.

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.

Gene Expression Profile Revealed Different Effects of Angiotensin II Receptor Blockade and Angiotensin-Converting Enzyme Inhibitor on Heart Failure

Although recent clinical studies have indicated that angiotensin II receptor blocker is as effective in treating heart failure as an angiotensin-converting enzyme inhibitor, it is unknown whether their effects are different. Dahl salt-sensitive rats were treated with an angiotensin-converting enzyme inhibitor benazepril, and an angiotensin II receptor blocker candesartan from 11 weeks old. We examined cardiac geometry and function by echocardiography, and histology and gene expression by high-density oligonucleotide arrays using Affymetrix U34 (Affymetrix, Santa Clara, CA, U.S.A.). Dahl salt-sensitive rats fed a high salt diet showed a marked increase in blood pressure and developed concentric hypertrophy at 11 weeks, followed by left ventricle dilation and congestive heart failure by 20 weeks after birth. Although both medications had only a mild antihypertensive effect, they strongly suppressed the development of cardiac hypertrophy, fibrosis and heart failure to the same extent. Gene expression pattern examined by Affymetrix GeneChip (Affymetrix) is quite different between the two drug groups, indicating that angiotensin II receptor blocker and angiotensin-converting enzyme inhibitor prevent heart failure by different mechanisms.

Distinct populations of forebrain neural stem and progenitor cells can be isolated using side-population analysis

The absence of stem cell-specific markers has posed challenges to the identification and isolation of stem cells. We report the isolation of a discrete and highly enriched population of neural stem cells from clonally derived colonies of neural stem cell and progenitor cells (neurospheres) after exposure to the fluorescent DNA binding dye Hoeschst 33342 and subsequent analysis via dual wavelength flow cytometry. The low fluorescent side population comprised only 3.6% of all live cells sorted yet contained >99% of all the neural stem cells as assayed by the formation of neurospheres in culture. Most neurosphere-derived cells are progenitor cells, and these are found within the higher fluorescence (non-side population) fraction. The isolation of a highly enriched population of self-renewing, multipotential neural stem cells was seen from both adult- and embryonic-derived neurospheres; however, the relative percentage of cells comprising the side-population and the mechanism of dye efflux varied between adult and embryonic donor tissue. Combining the side-population analysis with markers recently shown to enrich for neural stem cells afforded no further enrichment in the case of peanut agglutinin expression and size criteria; however, when the side-population analysis was combined with Lewis X (LeX) expression, a slight enrichment was seen over side-population analysis alone.

Mechanistic and anti-proliferative studies of two novel, biologically active bis-benzimidazoles

We have previously synthesised a number of novel head-to-head bis-benzimidazole derivatives that are structurally related to the fluorochrome, Hoechst 33258, and which possess strong affinity for A:T sites in the minor groove of duplex DNA. Initial studies revealed these compounds to exhibit potent antiproliferative activity against a range of ovarian cell lines and to inhibit transcription in an in vitro setting. In this study, we have examined their cellular behaviour in detail and have shown that two of these compounds (ABA13 and ABA833) potently inhibit the proliferation of a range of human tumour cell lines, and show some specificity towards breast carcinoma cell lines. In most of the cell lines investigated, ABA833 was the more potent of the two compounds. Flow cytometric analysis revealed that ABA13 and ABA833 (50-500 nM) induced an S phase block and increased the pre-G1 population in MCF-7 and MDA 468 human breast cancer cells. An increase in the pre-G1 population of RKO colon carcinoma cells was seen only at 500 nM with ABA833, reflecting the reduced sensitivity of this cell line to the bis-benzimidazoles in comparison to the breast cancer cell lines. Mechanistic studies revealed that neither ABA13 or ABA833 act as topoisomerase I (topo I) or topoisomerase II (topo II) poisons in plasmid or kinetoplast DNA (kDNA) relaxation assays, but both compounds do inhibit the catalytic activity of these enzymes. Drug uptake studies showed that reduced sensitivity of MCF-7adr and RKO cells compared with MCF-7 to both ABA13 and ABA833 correlated with a markedly reduced intracellular drug accumulation.

Center specificity in the limited sampling model (LSM): can the LSM developed from healthy subjects be extended to disease states?

BACKGROUND AND OBJECTIVES

Area under the curve (AUC) can be related to the therapeutic or toxic effect of a drug. In order to accurately measure AUC, multiple blood samples are required, but in a clinical setting, frequent blood sampling from the patients is time-consuming and expensive. The limited sampling model (LSM) is one of the approaches that is gaining popularity due to its simplicity for the estimation of AUC using 1 - 3 samples. Despite its simplicity, the LSM has some shortcomings. One of the major drawbacks of the LSM is that the LSM developed under a given condition may not be extended to other conditions. For example, the LSM developed from healthy subjects may not be extended to disease states such as renal or hepatic impairment or vice versa. This characteristic of the LSM can be referred to as "center-specific". In this investigation, the LSM developed from the healthy subjects was used to predict AUC in patients with renal or hepatic impairment.

METHODS

Two sets of simulated plasma concentration versus time data for 2 antihypertensive drugs and measured plasma concentration versus time data for 2 representative drugs (A and B) were used in the analysis.

RESULTS AND CONCLUSION

The results of the study indicate that the LSM developed from healthy subjects is inadequate to predict AUC in patients with hepatic or renal impairment, indicating center specificity of the LSM.

Combined Raman and continuous-wave-excited two-photon fluorescence cell imaging

We demonstrate a confocal optical microscope that combines cw two-photon-excited fluorescence microscopy with confocal Raman microscopy. With this microscope fast image acquisition with fluorescence imaging can be used to select areas of interest for subsequent chemical analysis with spontaneous Raman imaging. The distribution of the UV-absorbing fluorophore Hoechst 33342 in the apoptotic HeLa cells is measured in the combined cw two-photon-excited fluorescence and Raman microscopy modes. The 647-nm line of a Kr-ion laser is used to excite both the Raman scattering and the two-photon-excited fluorescence emission. The lateral and axial resolutions in the two imaging modes are compared by use of the Gaussian beam approximation and backprojection of the focal volume through the confocal pinhole.

Altered pharmacokinetics and excessive hypotensive effect of candesartan in a patient with the CYP2C9*1/*3 genotype

An 89-year-old man with severe hypertension (190/82 mm Hg) and chronic heart failure (New York Heart Association class II) despite treatment with benidipine, doxazosin mesylate (INN, doxazosin), and furosemide was given oral candesartan cilexetil (4 mg/d), an angiotensin II type 1 receptor blocker metabolized via cytochrome p450 (CYP) 2C9. Two days later, he started to have severe dizziness and returned to the hospital on the fourth day without taking any of his medications. The blood pressure 30 hours after the last dose of candesartan was 126/64 mm Hg. Polymorphism analysis revealed the heterozygous poor metabolizer genotype CYP2C9*1/*3. The area under the concentration-time curve and the mean residence time of candesartan were both increased 2.5-fold, and the oral clearance of candesartan was 48% lower than that of the average elderly Japanese patient with hypertension. These results suggest that the CYP2C9*1/*3 genotype could be associated with decreased clearance and increased plasma concentration of candesartan, potentially enhancing its hypotensive effect.

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.

Effects of AT1 Receptor Block Begun Late in Life on Normal Cardiac Aging in Rats

The goal of this study was to determine how short-term (12 weeks) angiotensin type I (AT1) block begun late in life affects aspects of myocardial biology and physiologic function altered by normal aging. Exercise capacity, myocardial morphology, histopathology, and coronary vascular function (degree of coronary vasodilation in response to adenosine) were evaluated in 53 Fischer 344 rats. Adult (6 months of age) and old (21 months of age) rats were studied after 12 weeks of either control drinking water, a low dose of candesartan that did not significantly lower blood pressure (1 mg/kg/d), or a high dose of candesartan (10 mg/kg/d). Significant age-associated changes in exercise capacity (38% decrease), coronary dilation in response to adenosine (41% decrease), and histopathology occurred but were not affected by candesartan treatment. Age-associated myocardial hypertrophy occurred as indicated by an increase in heart weight-to-tibia length ratio from 0.27 g/cm +/- 0.01 in the adult controls to 0.34 g/cm +/- 0.02 in the old controls (P < 0.05). This hypertrophy in the aged hearts was significantly attenuated by both low-dose (0.30 g/cm +/- 0.01) and high-dose (0.29 g/cm +/- 0.01) candesartan (P < 0.05). Echocardiographic measurements indicate that the candesartan-induced decrease in hypertrophy occurred concomitantly with slight decreases in septal wall thickness and left ventricular (LV) chamber diameter. It is concluded that short-term AT1 block, even when initiated late in life, can decrease age-associated LV hypertrophy independent of blood pressure-lowering effects.

Blood Pressure- and Pulse Pressure-Lowering Effects, Trough:Peak Ratio and Smoothness Index of Telmisartan Compared with Lisinopril

OBJECTIVE

To compare lisinopril with telmisartan, in regard to: 1) their effect on blood pressure (BP) and pulse pressure (PP), and 2) the duration and the homogeneity of their antihypertensive effect.

PATIENTS AND METHODS

A randomized, open-label, crossover, comparative study of telmisartan 80 mg versus lisinopril 20 mg was conducted in 32 untreated hypertensive patients using clinic and 24-hour ambulatory BP measurements. Trough: peak ratio (TPR) and smoothness index (SI) were calculated for each drug.

RESULTS

Using both measurement techniques no difference was detected between the 2 drugs in their effects either on BP (mean difference in 24-hour systolic BP 1.2 +/- 7.1 mm Hg, 95% confidence intervals -1.4, 3.8, and diastolic 0.7 +/- 5.1, -1.2, 2.5) or on PP (0.5 +/- 3.5, -0.7, 1.8). There was no difference between the TPR and the SI values of telmisartan (TPR 0.85/0.61 for systolic/diastolic BP and SI 1.46/1.2) and lisinopril (TPR 0.74/0.64 and SI 1.3/1.17).

CONCLUSIONS

These data suggest that telmisartan is as effective as lisinopril in reducing BP and PP. Both drugs seem to provide smooth and sustained effects throughout the full 24-hour period.

Determination of dissociation constants of labile drug compounds by capillary electrophoresis

The utility of capillary electrophoresis (CE) for determination of the negative logarithm of dissociation constants (pK(a)) of labile compounds was investigated. In this study pyridinyl-methyl-sulfinyl-benzimidazoles (PMSB's), which have both an acidic and a basic pK(a), were selected as a first set of model drug compounds. This is a group of compounds that are known to degrade in aqueous solutions under neutral and acidic conditions which thus may impair their pK(a) determination when using common batch techniques based on spectrophotometry or potentiometry. An additional set of model drug compounds, benzenesulfonic acid phenethyloxy-phenyl esters (BSAP's), which are labile at high pH, were also studied. It is demonstrated that pK(a) values can be determined with high precision and accuracy by CE for both these sets of model compounds because decomposition products and impurities can be sufficiently separated from the main component. Based on the results in this study, a general strategy is proposed and discussed for determination of pK(a) for labile compounds. Key steps comprise use of a stabilizing sample diluent, injection by electromigration, short analysis time, and characterization of the main component by UV-Vis spectra.

Novel method for the isolation and characterisation of the putative prostatic stem cell

BACKGROUND

Prostate stem cells, responsible for the development, maturation, and function of the prostate, have been implicated in the aetiology of both benign prostate hyperplasia (BPH) and prostate cancer (CaP). However, research has been hampered by the lack of a definitive stem cell marker. We have adapted the protocol for differential Hoechst 33342 uptake by hemopoietic stem cells to enable isolation of putative stem cells from the prostate.

METHODS

Prostate epithelial cells isolated from prostate tissue obtained from patients with BPH after transurethral resection of the prostate were stained with Hoechst 33342. The Hoechst 33342 Red/Blue flow cytometry profile was then determined. Hoechst 33342 and Pyronin Y staining was used to determined the cell cycle status.

RESULTS

A verapamil-sensitive side population (SP) can be isolated from primary prostate tissue accounting for 1.38% +/- 0.07% of prostate epithelial cells. Cell cycle analysis of this SP population revealed that the majority of SP cells are in either G0 (12.38 +/- 0.31%) or G1 (63.19 +/- 2.13%).

CONCLUSIONS

The Hoechst 33342 dye efflux protocol can be adapted for the isolation of a SP from primary prostate tissue.

Flibanserin, a potential antidepressant drug, lowers 5-HT and raises dopamine and noradrenaline in the rat prefrontal cortex dialysate: role of 5-HT(1A) receptors

(1) Using in vivo intracerebral microdialysis in conscious, freely moving rats, we examined the effect of flibanserin, a potential antidepressant drug with high affinity for human 5-HT(1A) receptors and four-50-fold lower affinity for 5-HT(2A) and D(4) receptors, on basal extracellular concentrations of serotonin (5-hydroxytryptamine, 5-HT), dopamine (DA) and noradrenaline (NA) in selected regions of the rat brain. (2) Flibanserin at 3 and 10 mg kg(-1) significantly reduced extracellular 5-HT in the prefrontal cortex (by 30 and 45%) and dorsal raphe (35 and 44%), but had no effect on extracellular 5-HT in the ventral hippocampus. The 3 and 10 mg kg(-1) doses raised extracellular NA to a similar extent in the prefrontal cortex (47 and 50%). In all, 10 mg kg(-1) raised extracellular DA in the prefrontal cortex (63%) whereas 3 mg kg(-1) had no significant effect. (3) Pretreatment with the selective 5-HT(1A) receptor antagonist WAY100,635 (0.3 mg kg(-1)) 30 min before 10 mg kg(-1) flibanserin completely antagonized the latter's effects on extracellular 5-HT, DA and NA in the prefrontal cortex. WAY100,635 by itself had no effect on cortical extracellular monoamines. (4) The results show that the stimulation of 5-HT(1A) receptors plays a major role in the effect of flibanserin on brain extracellular 5-HT, DA and NA.

In-vitro metabolism of the new anxiolytic agent, RWJ-50172, in rat hepatic S9 fraction and microbial transformation in fungi, Cunninghamella sp

The in-vitro biotransformation of the anxiolytic agent, RWJ-50172 was studied after incubation with rat hepatic S9 fraction in the presence of an NADPH-generating system, and incubating with Cunninghamella echinulata in soy-bean medium. Unchanged RWJ-50172 (80% of the sample in rat; 86% in fungi) plus 6 metabolites (M1-M6) were profiled, quantified and tentatively identified on the basis of API-MS/MS data. The metabolic pathways for RWJ-50172 are proposed, and the four metabolic pathways are: pyrido-oxidation (pathway A), phenylhydroxylation (B), dehydration (C) and reduction (D). Pathway A formed hydroxy-pyrido-RWJ-50172 (M1, 10% of the sample in both rat and fungi) as the only major metabolite, which further dehydrated to form dehydro-RWJ-50172 in trace quantities in rat. Pathway B produced hydroxyphenyl-RWJ-50172 (M2) in small amounts (4%) in rat, and in conjunction with step A formed dihydroxy-RWJ-50172 as a trace metabolite in rat. Step D produced a minor benzimidazole-reduced metabolite in fungi. RWJ-50172 is substantially metabolized by this rat hepatic S9 fraction and fungi.

Regeneration of ganglion cell axons into a peripheral nerve graft alters retinal expression of glial markers and decreases vulnerability to re-axotomy

PURPOSE

To compare the effect of cutting the optic nerve versus replacing the cut optic nerve with a peripheral nerve (PN) graft on retinal glial markers, and to determine whether the PN graft can stabilize regenerating retinal ganglion cells (RGCs), thus preventing their death following re-axotomy.

METHODS

Retinas harvested after ganglion cell regeneration into a sciatic nerve graft were compared to untreated control retinas and retinas obtained following optic nerve axotomy. Glial-specific proteins such as glial fibrillary acidic protein (GFAP), Bcl-2 and complement-3 receptor (Ox-42) were examined using immunohistochemistry. Ganglion cells that survived the second axotomy were quantified on retinal flat mounts by retrograde labeling from the graft.

RESULTS

GFAP expression in astrocytes and Muller cells was elevated in axotomized retinas when compared to controls, and an additional up-regulation in Muller cells was found in retinas following ganglion cell regeneration. Increased GFAP expression in retinas containing regenerated neurons was accompanied by increased Bcl-2 expression with latter being confined to Muller cells. Moreover, re-axotomy of the regenerated axons within the graft did not result in significant retrograde degeneration of RGCs within 28 days.

CONCLUSIONS

The data suggest that the graft stabilizes the regenerating RGCs to an extent reminiscent of peripheral neurons, a process that may involve the interaction between neuronal and glial elements.

Involvement of the ubiquitin-proteasome system in the early stages of wallerian degeneration

Local axon degeneration is a common pathological feature of many neurodegenerative diseases and peripheral neuropathies. While it is believed to operate with an apoptosis-independent molecular program, the underlying molecular mechanisms are largely unknown. In this study, we used the degeneration of transected axons, termed "Wallerian degeneration," as a model to examine the possible involvement of the ubiquitin proteasome system (UPS). Inhibiting UPS activity by both pharmacological and genetic means profoundly delays axon degeneration both in vitro and in vivo. In addition, we found that the fragmentation of microtubules is the earliest detectable change in axons undergoing Wallerian degeneration, which among other degenerative events, can be delayed by proteasome inhibitors. Interestingly, similar to transected axons, degeneration of axons from nerve growth factor (NGF)-deprived sympathetic neurons could also be suppressed by proteasome inhibitors. Our findings suggest a possibility that inhibiting UPS activity may serve to retard axon degeneration in pathological conditions.

Age-related changes in pharmacokinetics and pharmacodynamics of lerisetron in the rat: a population pharmacokinetic model

BACKGROUND

The importance of studying the effects of age on the pharmacokinetics and pharmacodynamics of lerisetron - a new 5-hydroxytryptamine-3 (serotonin) receptor antagonist - comes from the facts that lerisetron will be administered to patients that are being treated with cytotoxic drugs and that the elderly frequently suffer from neoplastic diseases.

OBJECTIVE

The present study was designed to explore the effects of age on the pharmacokinetics and pharmacodynamics of lerisetron by using an aged rat model. A mixed-effects population study was carried out in order to analyze the sparse data and to create covariate models which could be used to derive dosage recommendations.

METHODS

Fischer 344 rats (n = 44) were divided into three groups, depending on their age: 5, 13, and 25 months. Blood samples were collected before administration of 200 micro g/kg of lerisetron for measurements of albumin, alpha(1)-acid glycoprotein, and unbound fraction of lerisetron. The lerisetron plasma concentrations were measured by high-performance liquid chromatography. A two-compartment model was fitted to the data using the nonlinear mixed-effects computer program WinNonMix. The population analysis was performed with the complete set of the collected data, and the potential sources of variability in the population parameters were investigated. Additionally, a pharmacodynamic study was performed. The effect of lerisetron (inhibition of the von Bezold-Jarisch reflex) was evaluated in young, adult, and senescent Fischer 344 rats.

RESULTS

The mean values of the individual Bayes estimates of the parameters showed a decrease in total clearance and distribution volume of the central compartment in old rats. The lerisetron free (unbound) fraction remained unchanged among the groups, and there were no significant differences in alpha(1)-acid glycoprotein levels. The concentration-effect relationship was best described by a sigmoid E(max) model. Since the drug concentration in plasma at half-maximal effect (EC(50)) decreased in old rats, an increased sensitivity to the effect of lerisetron in old animals could be expected.

CONCLUSION

Both pharmacokinetic changes (decreased volume of distribution and clearance and increased elimination half-life) and pharmacodynamic alterations (decrease in total and unbound EC(50)) may be responsible for the different responses to lerisetron observed in old rats.

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.

Time-dependent amplified pharmacokinetic and pharmacodynamic responses of rabeprazole in cytochrome P450 2C19 poor metabolizers

STUDY OBJECTIVES

To determine the pharmacokinetic and pharmacodynamic rationale for the optimum regimen of rabeprazole in the treatment of Helicobacter pylori infection in patients who are cytochrome P450 (CYP) 2C19 poor metabolizers or extensive metabolizers.

DESIGN

Prospective, multiple-dose pharmacokinetic and pharmacodynamic study.

SETTING

University-affiliated medical center in Taiwan.

SUBJECTS

Twelve healthy volunteers (aged 20-30 yrs) who were identified as CYP2C19 poor metabolizers (six subjects) or extensive metabolizers (six).

INTERVENTION

Each subject received rabeprazole 20 mg twice/day for 3 consecutive days and once/day on the fourth day.

MEASUREMENTS AND MAIN RESULTS

Pharmacokinetic and pharmacodynamic parameters were compared between CYP2C19 poor and extensive metabolizers on day 1 and day 4 of dosing. The mean +/- SD values of area under the concentration-time curve of rabeprazole and rabeprazole thioether were significantly higher in poor metabolizers than in extensive metabolizers on day 1 (5357 +/- 883 vs 1131 +/- 512 ng x hr/ml and 1703 +/- 432 vs 561 +/- 358 ng x hr/ml, respectively; p<0.001) and on day 4 (5601 +/- 669 vs 1619 +/- 778 ng x hr/ml and 1914 +/- 378 vs 511 +/- 360 ng x hr/ml, respectively; p<0.001). However, no significant difference was noted between day 1 and day 4 of dosing within the same genotype groups. Only CYP2C19 poor metabolizers had significantly higher plasma gastrin levels on day 4 compared with those levels on day 1 (p<0.05). The pharmacokinetic-pharmacodynamic relationship of rabeprazole appears to be time dependent.

CONCLUSION

The pharmacokinetic and pharmacodynamic data suggest that CYP2C19 poor metabolizers might be subject to advantageous conditions, especially after day 4, for treating H. pylori infection with rabeprazole.

Calcium-dependent potassium channels as a target protein for modulation of the blood-brain tumor barrier

Even though the blood-brain tumor barrier (BTB) is more permeable than the blood-brain barrier (BBB), the BTB still significantly restricts the delivery of anticancer drugs to brain tumors. Brain tumor capillaries that form the BTB, however, express certain unique protein markers that are absent or barely detectable in normal brain capillaries. We were able to biochemically modulate one such protein marker, the calcium-dependent potassium (K(Ca)) channel, by using a specific K(Ca) channel agonist, NS-1619, to obtain sustained enhancement of selective drug delivery, including molecules of varying sizes, to tumors in rat syngeneic and xenograft brain tumor models. Immunolocalization and potentiometric studies showed increased K(Ca) channel distribution on tumor cells compared with normal cells, suggesting that tumor cell-specific signals might induce overexpression of K(Ca) channels in capillary endothelial cells, leading to increased BTB permeability. We also demonstrated that the cellular mechanism for K(Ca) channel-mediated BTB permeability increase is due to accelerated formation of pinocytotic vesicles, which can transport therapeutic molecules across the BTB. This concept was investigated by using NS-1619 to facilitate increased delivery of carboplatin to brain tumor leading to enhanced survival in rats with brain tumors. Additionally, we showed that K(Ca) channel modulation resulted in enhanced permeability to macromolecules, including Her-2 monoclonal antibody and green fluorescent protein-adenoviral vectors, in a human, primary brain-tumor xenograft model. Therefore, K(Ca) channels are a potential, promising target for biochemical modulation of BTB permeability to increase antineoplastic drug delivery selectively to brain tumors.

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.