The hydroxylation of omeprazole correlates with S-mephenytoin metabolism: a population study

Effect of CYP2C19 genotypes on tamoxifen metabolism and early-breast cancer relapse

CYP2C19*2 and CYP2C19*17 might influence tamoxifen metabolism and clinical outcome. Our aim was to investigate the effect of CYP2C19 genotypes on tamoxifen concentrations and metabolic ratios (MRs) and breast cancer recurrence in a large cohort of Caucasian women. Genetic variants (CYP2D6 and CYP2C19 genotypes), tamoxifen and metabolites concentrations, baseline characteristics, and breast cancer recurrence from the CYPTAM study (NTR1509) were used. CYP2C19*2 and CYP2C19*17 genotypes were evaluated as alleles and as groups based on CYP2D6 genotypes (high, intermediate and low activity). Log-rank test and Kaplan–Meier analysis were used to evaluate differences in recurrence defined as relapse-free survival (RFS). Classification tree analyses (CTAs) were conducted to assess the levels of interactions per polymorphism (CYP2D6 and CYP2C19 genotypes) on endoxifen concentrations. No differences in mean concentrations and MRs were observed when comparing CYP2C19 genotypes (CYP2C19*1/*1; CYP2C19*1/*2; CYP2C19*2/*2; CYP2C19*1/*17; CYP2C19*17/*17; CYP2C19*2/*17). Only significant differences (p value < 0.05) in mean concentrations and MRs were observed when comparing tamoxifen activity groups (high, intermediate and low activity). A log-rank test did not find an association across CYP2C19 genotypes (p value 0.898). CTAs showed a significant relationship between CYP2D6 and endoxifen (p value < 0.0001), but no association with CYP2C19 genotypes was found. CYP2C19 polymorphisms do not have a significant impact on tamoxifen metabolism or breast cancer relapse.

Cardiac Arrest Associated with Combination Cisapride and Itraconazole Therapy

We report a case of cardiac arrest associated with cisapride in combination with itraconazole and provide a brief review of pertinent literature. Cisapride (Propulsid; Janssen Pharmaceuticals, Titusville, NJ), a gastrointestinal prokinetic drug, has recently been reported to prolong the QT interval. Itraconazole, an oral antifungal agent, is an inhibitor of cytochrome P450 (CYP3A4) metabolism and may elevate serum drug levels of compounds metabolized by this pathway. A 31-year-old woman had a witnessed cardiac arrest while taking the combination of cisapride and itraconazole. Following resucitation, the prolonged QT interval returned to normal after withdrawal of both agents. Echocardiography and cardiac catheterization were within normal limits; electrophysiologic testing failed to induce ventricular tachycardia/ventricular fibrillation. She has had no documented arrhythmias since the arrest. This combination can now be added to a growing list of drugs that may cause torsades de pointes and sudden cardiac death.

Voriconazole-induced Severe Hyperkalemia Precipitated by Multiple Drug Interactions

Voriconazole, a triazole antifungal agent used to treat serious fungal infections, has a pharmacokinetic characteristic of undergoing hepatic metabolism by the cytochrome P450 system. Few cases of hyperkalemia have been reported, which presented only when the serum voriconazole level was exceptionally elevated by drug-drug interactions. Additionally, azole antifungals may interfere with the biosynthesis of adrenal steroids and therefore can predispose patients to aldosterone deficiency. However, it is unclear whether voriconazole itself can induce hypoaldosteronism or hyperkalemia. Here, we report a case of voriconazole-induced hyperkalemia in a patient administered concurrent medications to treat comorbidities. Voriconazole was orally administered for pulmonary aspergillosis, and three episodes of severe hyperkalemia recurred, which improved with emergency treatment. In the first episode, renin-angiotensin-aldosterone system inhibitors were associated. We found that dronedarone might have increased the voriconazole level in the second episode. At that time, severe hypercalcemia was concurrent, which improved with acute hemodialysis and eliminating dronedarone. Finally, severe hyperkalemia recurred without concurrent medications known to interact with voriconazole. Upon switching from voriconazole to itraconazole, the hyperkalemia was resolved. Drug level monitoring is necessary when voriconazole is used. Genetic susceptibility, such as through CYP2C19 polymorphism, may be investigated for patients with adverse reactions to voriconazole.

Urine metabolic ratio of omeprazole in relation to CYP2C19 polymorphisms in Russian peptic ulcer patients

BACKGROUND

CYP2C19 is known to be the main enzyme of biotransformation of proton pump inhibitors (PPIs), whereas the CYP2C19 gene is highly polymorphic. Genotyping and phenotyping together represent more reliable data about patient's CYP2C19 activity.

PURPOSE

The aim of the study was to investigate the applicability of urine metabolic ratio of omeprazole for CYP2C19 phenotyping in Russian peptic ulcer patients with different CYP2C19 genotypes.

PATIENTS AND METHODS

A total of 59 patients (19 men and 40 women) aged 18-91 years (mean age 53.5±15.1 years) from four Moscow clinics who were diagnosed with an endoscopically and histologically proven peptic ulcer or had a history of endoscopically and histologically proven ulcers in the past were recruited. Peripheral venous blood (6 mL) was collected for DNA extraction, and real-time polymerase chain reaction was performed for the analysis of CYP2C19*2^G681A (rs4244285), CYP2C19*3^G636A (rs4986893) and CYP2C19*17^C-806T (rs12248560) polymorphisms. Urine samples of patients were collected in the morning between 6 am and 9 am, before food or drug intake, after at least 3 days of twice daily (b.i.d.) omeprazole intake. Omeprazole and 5-hydroxyomeprazole concentrations in the urine were measured using high-performance liquid chromatography with mass spectrometry.

RESULTS

Of the 59 patients, there were 27 (45.8%) extensive metabolizers (EMs; CYP2C19*1/*1), 16 (27.1%) ultrarapid metabolizers (UMs; CYP2C19*1/*17, CYP2C19*17/*17), 14 (23.7%) intermediate metabolizers (IMs; CYP2C19*1/*2, CYP2C19*2/*17, CYP2C19*3/*17) and two (3.4%) poor metabolizers (PMs; CYP2C19*2/*2). Median metabolic ratio (25%-75% percentiles) were 1.03 (0.69-1.36) for EMs, 1.95 (1.33-2.68) for UMs, 1.40 (0.78-2.13) for IMs+PMs and 1.26 (0.82-1.99) for the whole sample. A statistically significant difference in metabolic ratio (Mann-Whitney U test) was found between UMs and EMs (p=0.001) and in the multiple comparison Kruskal-Wallis test (p=0.005).

CONCLUSION

We found a connection between particular CYP2C19 genotypes and urine metabolic ratio of omeprazole in Russian peptic ulcer patients. This method needs to be improved as in our modification it worked mainly for UMs and did not differentiate all patients according to omeprazole biotransformation activity.

The influence of combination use of CYP450 inducers on the pharmacokinetics of voriconazole: a systematic review

WHAT IS KNOWN AND OBJECTIVES

Voriconazole is a triazole antifungal agent and is extensively metabolized via cytochrome P450 (CYP450); therefore, special precautions need to be taken when co-administered with a known CYP450 inducer, which may lead to treatment failure. The influence of some CYP450 inducers on the pharmacokinetics of voriconazole has been described in previous studies, but a systematic review was lacking. In this study, we carried out a systematic review to assess the influence of CYP450 inducers on the pharmacokinetic (PK) parameters of voriconazole.

METHODS

Pubmed, Embase, Cochrane Library, Clinicaltrials.gov and three Chinese databases (CNKI, CBM and WanFang) were searched through January 2016. Interventional and observational studies comparing the PK parameters of voriconazole used alone or with CYP450 inducers in healthy volunteers and patients were included. The outcomes included were the area under the plasma concentration-time curve (AUC), peak plasma concentrations (C_max ) and trough plasma concentrations (C_min ). The quality of the included studies was assessed using Cochrane's risk of bias tool, Newcastle-Ottawa Scale (NOS) and a modified risk of bias tool for pharmacokinetic before-and-after studies.

RESULTS AND DISCUSSION

Sixteen studies were included in this review: three randomized controlled trials (RCTs), five single-arm before-after studies (SBAs), six cohort studies and two case reports. All studies except case reports had moderate to high quality. Of the 11 inducers reviewed, efavirenz, ritonavir (chronic use), phenytoin, rifampin and rifabutin significantly decreased mean AUC and C_max of voriconazole; St John's wort significantly decreased only mean AUC; rifampin, rifabutin, phenobarbital and carbamazepine significantly decreased mean C_min . Etravirine and Ginkgo biloba did not reveal any such influence. The influence of glucocorticoids may depend on its type and dose.

WHAT IS NEW AND CONCLUSIONS

To conclude, the combination use of high-dose efavirenz, high-dose ritonavir, St John's wort, rifampin, phenobarbital, or carbamazepine with voriconazole is contraindicated as instructed in the drug label. Low-dose efavirenz, low-dose ritonavir, rifabutin and phenytoin may be used together with voriconazole provided TDM and dose adjustment of voriconazole. Moreover, this study shows there is low risk of drug-drug interactions when voriconazole is co-administered with etravirine or G. biloba; however, whether the use of glucocorticoids has a clinically significant effect on voriconazole still requires more evidence. This study also highlights the lack of clinical studies and future high-quality studies assessing the influence of CYP450 inducers on voriconazole. PK parameters and dosing optimization should be designed to provide a more definitive answer regarding the necessity of TDM and the recommendations for dose adjustment of voriconazole.

Addressing phenoconversion: the Achilles' heel of personalized medicine

Phenoconversion is a phenomenon that converts genotypic extensive metabolizers (EMs) into phenotypic poor metabolizers (PMs) of drugs, thereby modifying their clinical response to that of genotypic PMs. Phenoconversion, usually resulting from nongenetic extrinsic factors, has a significant impact on the analysis and interpretation of genotype-focused clinical outcome association studies and personalizing therapy in routine clinical practice. The high phenotypic variability or genotype-phenotype mismatch, frequently observed due to phenoconversion within the genotypic EM population, means that the real number of phenotypic PM subjects may be greater than predicted from their genotype alone, because many genotypic EMs would be phenotypically PMs. If the phenoconverted population with genotype-phenotype mismatch, most extensively studied for CYP2D6, is as large as the evidence suggests, there is a real risk that genotype-focused association studies, typically correlating only the genotype with clinical outcomes, may miss clinically strong pharmacogenetic associations, thus compromising any potential for advancing the prospects of personalized medicine. This review focuses primarily on co-medication-induced phenoconversion and discusses potential approaches to rectify some of the current shortcomings. It advocates routine phenotyping of subjects in genotype-focused association studies and proposes a new nomenclature to categorize study populations. Even with strong and reliable data associating patients' genotypes with clinical outcome(s), there are problems clinically in applying this knowledge into routine pharmacotherapy because of potential genotype-phenotype mismatch. Drug-induced phenoconversion during routine clinical practice remains a major public health issue. Therefore, the principal challenges facing personalized medicine, which need to be addressed, include identification of the following factors: (i) drugs that are susceptible to phenoconversion; (ii) co-medications that can cause phenoconversion; and (iii) dosage amendments that need to be applied during and following phenoconversion.

Rabeprazole: the role of proton pump inhibitors inHelicobacter pylorieradication

Proton pump inhibitors have become one of the cornerstones in the treatment of Helicobacter pylori infection. Rabeprazole (Pariet) is a substituted benzimidazole proton pump inhibitor with potent gastric acid suppression properties. Its high acid-base dissociation constant allows activation over a broader pH range, resulting in quick, irreversible binding to the H+/K+-ATPase pump, and a more rapid onset of action compared with omeprazole, lansoprazole and pantoprazole. Unlike other proton pump inhibitors, the metabolism of rabeprazole is primarily via a nonenzymatic reduction to the thioether derivative, and the cytochrome P450 isoenzyme 2C19 is only partly involved in its metabolism. The effect of genetic polymorphism in cytochrome P450 isoenzyme 2C19 on the pharmacokinetics and pharmacodynamics of rabeprazole is therefore limited. In humans, once-daily dosing of 5-40 mg of rabeprazole inhibits gastric acid secretion in a dose-dependent manner. In vitro studies have shown that rabeprazole possesses more potent antibacterial properties against the growth of H. pylori than other proton pump inhibitors. Furthermore, its thioether derivative has more potent inhibitory in vitro activity against the growth and motility of clarithromycin-resistant H. pylori than other proton pump inhibitors or commonly used antimicrobials. Despite these inherent favorable characteristics of rabeprazole, randomized controlled trials have largely shown equivalence amongst proton pump inhibitors when used with two antibiotics in the eradication of H. pylori, with cure rates of 75-89% on an intent-to-treat basis. However, rabeprazole appears to consistently achieve such comparable eradication rates even when used at reduced doses (10 mg twice daily) as part of clarithromycin-based triple therapy.

Applications of CYP450 testing in the clinical setting

Interindividual variability in drug response is a major clinical problem. Polymedication and genetic polymorphisms modulating drug-metabolising enzyme activities (cytochromes P450, CYP) are identified sources of variability in drug responses. We present here the relevant data on the clinical impact of the major CYP polymorphisms (CYP2D6, CYP2C19 and CYP2C9) on drug therapy where genotyping and phenotyping may be considered, and the guidelines developed when available. CYP2D6 is responsible for the oxidative metabolism of up to 25% of commonly prescribed drugs such as antidepressants, antipsychotics, opioids, antiarrythmics and tamoxifen. The ultrarapid metaboliser (UM) phenotype is recognised as a cause of therapeutic inefficacy of antidepressant, whereas an increased risk of toxicity has been reported in poor metabolisers (PMs) with several psychotropics (desipramine, venlafaxine, amitriptyline, haloperidol). CYP2D6 polymorphism influences the analgesic response to prodrug opioids (codeine, tramadol and oxycodone). In PMs for CYP2D6, reduced analgesic effects have been observed, whereas in UMs cases of life-threatening toxicity have been reported with tramadol and codeine. CYP2D6 PM phenotype has been associated with an increased risk of toxicity of metoprolol, timolol, carvedilol and propafenone. Although conflicting results have been reported regarding the association between CYP2D6 genotype and tamoxifen effects, CYP2D6 genotyping may be useful in selecting adjuvant hormonal therapy in postmenopausal women. CYP2C19 is responsible for metabolising clopidogrel, proton pump inhibitors (PPIs) and some antidepressants. Carriers of CYP2C19 variant alleles exhibit a reduced capacity to produce the active metabolite of clopidogrel, and are at increased risk of adverse cardiovascular events. For PPIs, it has been shown that the mean intragastric pH values and the Helicobacter pylori eradication rates were higher in carriers of CYP2C19 variant alleles. CYP2C19 is involved in the metabolism of several antidepressants. As a result of an increased risk of adverse effects in CYP2C19 PMs, dose reductions are recommended for some agents (imipramine, sertraline). CYP2C9 is responsible for metabolising vitamin K antagonists (VKAs), non-steroidal anti-inflammatory drugs (NSAIDs), sulfonylureas, angiotensin II receptor antagonists and phenytoin. For VKAs, CYP2C9 polymorphism has been associated with lower doses, longer time to reach treatment stability and higher frequencies of supratherapeutic international normalised ratios (INRs). Prescribing algorithms are available in order to adapt dosing to genotype. Although the existing data are controversial, some studies have suggested an increased risk of NSAID-associated gastrointestinal bleeding in carriers of CYP2C9 variant alleles. A relationship between CYP2C9 polymorphisms and the pharmacokinetics of sulfonylureas and angiotensin II receptor antagonists has also been observed. The clinical impact in terms of hypoglycaemia and blood pressure was, however, modest. Finally, homozygous and heterozygous carriers of CYP2C9 variant alleles require lower doses of phenytoin to reach therapeutic plasma concentrations, and are at increased risk of toxicity. New diagnostic techniques made safer and easier should allow quicker diagnosis of metabolic variations. Genotyping and phenotyping may therefore be considered where dosing guidelines according to CYP genotype have been published, and help identify the right molecule for the right patient.

Influence of Azimilide on CYP2C19-Mediated Metabolism

The purpose of this study was to assess the influence of multiple-dose oral administration of azimilide dihydrochloride on CYP2C19-mediated metabolism. A two-period, randomized crossover study was conducted in 40 healthy male subjects who were phenotyped as extensive CYP2C19 metabolizers. Oral doses of placebo or 125 mg of azimilide dihydrochloride were administered every 12 hours for 3 days, followed by every 24 hours for 5 days; 20 mg omeprazole was coadministered on Day 8. Blood or plasma samples were obtained over 24 hours and analyzed for azimilide or omeprazole/5-hydroxyomeprazole using high-performance liquid chromatography with tandem mass spectrometry. Data were analyzed using "noncompartmental" analysis. Azimilide blood concentrations observed in this study were similar to those previously observed at steady state in patients. Based on AUC(m)/AUC(p) for omeprazole, azimilide does not significantly inhibit CYP2C19-mediated metabolism (90% confidence interval [CI] = 104%-111%). For 5-hydroxyomeprazole, no significant changes in pharmacokinetics were observed. For omeprazole, a statistically significant decrease ( approximately 12%) was observed for AUC. However, this change was small and is not expected to be clinically important since the CI was contained within those used to establish bioequivalence. These results indicate that azimilide does not inhibit CYP2C19-mediated metabolism. Since this isozyme had the lowest in vitro IC(50) values for the cytochrome P450s most commonly involved with the metabolism of drugs (CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4), azimilide-related drug interactions mediated via these isozymes are not anticipated.

CYP2C19- and CYP3A4-Dependent Omeprazole Metabolism in West Mexicans

Omeprazole has been used as a drug probe for CYP2C19, but no systematic data are available for Mexican populations. The aim of this study was to evaluate the phenotype frequencies of the CYP2C19 polymorphism in West Mexicans. Besides omeprazole, sulfone was measured to evaluate CYP3A4 after administration of the 20-mg dose to 127 healthy volunteers. Logarithms of metabolic indexes of omeprazole/hydroxyomeprazole for CYP2C19 and omeprazole/omeprazole sulfone for CYP3A4 had trimodal distributions. Five subjects (4%) had a log CYP2C19 metabolic index below -0.9, suggesting an ultra-extensive phenotype. Poor metabolizers (log metabolic index > 0.6) were 6%. For CYP3A4, 11 subjects (9%) were below -0.3 of the log metabolic index. The log metabolic index of omeprazole/omeprazole sulfone was above the antimode of 0.6 for 11% of this population. The mean log metabolic index of CYP3A4 extensive metabolizers (80%) was 0.166, which seems to be higher than the data described for Caucasians and lower than that for Asians.

Clinical Application of CYP2C19 Pharmacogenetics Toward More Personalized Medicine

More than 30 years of genetic research on the CYP2C19 gene alone has identified approximately 2,000 reference single nucleotide polymorphisms (rsSNPs) containing 28 registered alleles in the P450 Allele Nomenclature Committee and the number continues to increase. However, knowledge of CYP2C19 SNPs remains limited with respect to biological functions. Functional information on the variant is essential for justifying its clinical use. Only common variants (minor allele frequency >5%) that represent CYP2C19*2, *3, *17, and others have been mostly studied. Discovery of new genetic variants is outstripping the generation of knowledge on the biological meanings of existing variants. Alternative strategies may be needed to fill this gap. The present study summarizes up-to-date knowledge on functional CYP2C19 variants discovered in phenotyped humans studied at the molecular level in vitro. Understanding the functional meanings of CYP2C19 variants is an essential step toward shifting the current medical paradigm to highly personalized therapeutic regimens.

Induction of CYP2C19 and CYP3A activity following repeated administration of efavirenz in healthy volunteers

Drug-drug interactions involving efavirenz are of major concern in clinical practice. We evaluated the effects of multiple doses of efavirenz on omeprazole 5-hydroxylation (CYP2C19) and sulfoxidation (CYP3A). Healthy volunteers (n = 57) were administered a single 20 mg oral dose of racemic omeprazole either with a single 600 mg oral dose of efavirenz or after 17 days of administration of 600 mg/day of efavirenz. The concentrations of racemic omeprazole, 5-hydroxyomeoprazole (and their enantiomers), and omeprazole sulfone in plasma were measured using a chiral liquid chromatography-tandem mass spectrometry method. Relative to single-dose treatment, multiple doses of efavirenz significantly decreased (P < 0.0001) the area under the plasma concentration-time curve from 0 to infinity (AUC(0-∞)) of racemic-, R- and S-omeprazole (2.01- to 2.15-fold) and the corresponding AUC(0-∞) metabolic ratio (MR) for 5-hydroxyomeprazole (1.36- to 1.44-fold) as well as the MR for omeprazole sulfone (∼2.0) (P < 0.0001). The significant reduction in the AUC of 5-hydroxyomeprazole after repeated efavirenz dosing suggests induction of sequential metabolism and mixed inductive/inhibitory effects of efavirenz on CYP2C19. In conclusion, efavirenz enhances omeprazole metabolism in a nonstereoselective manner through induction of CYP3A and CYP2C19 activity.

Roadmap to risk evaluation and mitigation strategies (REMS) success

Medical safety-related risk management is a rapidly evolving and increasingly important aspect of drug approval and market longevity. To effectively meet the challenges of this new era, we describe a risk management roadmap that proactively yet practically anticipates risk-management requirements, provides the foundation for enduring yet appropriately flexible risk-management practices, and leverages these techniques to efficiently and effectively utilize risk evaluation and mitigation strategies (REMS)/risk minimization programs as market access enablers. This fully integrated risk-management paradigm creates exciting opportunities for newer tools, techniques, and approaches to more successfully optimize product development, approval, and commercialization, with patients as the ultimate beneficiaries.

Pharmacokinetics and safety of 14 days intravenous voriconazole in allogeneic haematopoietic stem cell transplant recipients

BACKGROUND

Voriconazole is used to manage invasive fungal diseases in recipients of an allogeneic haematopoietic stem cell transplant (HSCT) after myeloablative treatment. Little is known about the pharmacokinetics (PK) of voriconazole in this population, who also receive cyclosporine A.

METHODS

Patients admitted for an allogeneic HSCT were eligible for the study. Voriconazole was given intravenously at 6 mg/kg twice daily on day 1, then 4 mg/kg twice daily until the day of transplant to reach steady-state conditions and then continued for a further week during which cyclosporine A was administered. Blood samples were drawn on the day of HSCT and daily for the next 14 days. PK curves were determined on days 7 and 14. PK parameters were calculated using non-compartmental analysis. CYP2C19*2 and CYP2C19*3 polymorphisms were also determined.

RESULTS

Ten patients were fully evaluable. Median AUC(0-12) of voriconazole on the day of HSCT was 33.81 mg.h/L [interquartile range (IQR) 20.59-39.39] and 25.61 mg.h/L (IQR 22.48-38.65) 1 week later. AUC(0-12) of voriconazole on both days was similar to data reported for healthy volunteers. Trough levels were <1.0 mg/L for 3 of 10 patients on the day of HSCT and for 4 of 10 patients 1 week later. No difference in clearance of voriconazole was found between CYP2C19 extensive metabolizers (n = 4) and carriers of one non-functional allele (n = 6).

CONCLUSIONS

Exposure and clearance of voriconazole in recipients of an allogeneic HSCT are similar to those of healthy volunteers though there was high intra- and inter-individual variation in drug exposures which may have implications for similar patient populations.

Management of invasive aspergillosis in patients with COPD: rational use of voriconazole

Invasive pulmonary aspergillosis (IPA) is an important cause of mortality in patients with hematologic malignancies. The reported incidence of IPA in the context of chronic obstructive pulmonary disease (COPD) seems to increase. Approximately 1%-2% of overall fatal cases of IPA occur in COPD patients. The combination of factors such as lung immune imbalance, long-term corticosteroid use, increasing rate of bacterial exacerbations over time, and malnutrition are responsible for the emergence of IPA in these patients. The diagnosis of IPA is difficult to establish, which explains the delay in implementing accurate antifungal therapy and the high mortality rate. Persistent pneumonia nonresponsive to appropriate antibiotic treatment raises the concern of an invasive fungal infection. Definite diagnosis is obtained from tissue biopsy evidencing Aspergillus spp. on microscopic examination or in culture. Culture and microscopy of respiratory tract samples have a sensitivity and specificity of around 50%. Other diagnostic tools can be useful in documenting IPA: computed tomography (CT) scan, nonculture-based tests in serum and/or in bronchoalveolar lavage such as antibody/antigen tests for Aspergillus spp. More recent tools such as polymerase chain reaction or [1-->3]-beta-D-glucan have predictive values that need to be further investigated in COPD patients. Antifungal monotherapy using azole voriconazole is recommended as a first-line treatment of IPA. This review assesses the use of voriconazole in COPD patients.

CYP2C19 pharmacogenetics in advanced cancer: compromised function independent of genotype

CYP2C19 is a drug-metabolising enzyme involved in the metabolism of a number of chemotherapeutic agents including cyclophosphamide. Variants of the CYP2C19 gene result in a loss of function polymorphism, which affects approximately 3% of the Caucasian population. These individuals are poor metabolisers (PM) of a wide range of medications including omeprazole (OMP). In healthy subjects PM can be identified through homozygous variant genotype. However, a discordance between CYP2C19 genotype and phenotype has been reported previously in a small study of cancer patients. To investigate whether CYP2C19 activity was decreased in patients with advanced cancer, CYP2C19 genotype was determined in 33 advanced cancer patients using PCR-RFLP analysis for the two important allelic variants (*2,681G>A and *3,636G>A) and the activity of the enzyme was evaluated using the CYP2C19 probe drug OMP. The activity of the drug-metabolising enzyme CYP2C19 was severely compromised in advanced cancer patients, resulting in a PM status in 37% of the patients who had normal genotype. This is significantly (P<0.0005) higher than that would be predicted from the genotypic status of these patients. There was no evidence of a correlation between compromised CYP2C19 activity and any of the proinflammatory cytokines or acute phase response proteins studied. However, there was preliminary evidence of an association between PM status and low body mass (P=0.03). There is increasing interest in using pharmacogenetics to 'individualise medicine', however, the results of this study indicate that in a cancer population genotyping for CYP2C19 would significantly underestimate the number of phenotypic PM of drugs, such as cyclophosphamide, which may be metabolised by this enzyme.

Endocrine and metabolic manifestations of invasive fungal infections and systemic antifungal treatment

Systemic fungal infections are increasingly reported in immunocompromised patients with hematological malignancies, recipients of bone marrow and solid organ allografts, and patients with AIDS. Mycoses may infiltrate endocrine organs and adversely affect their function or produce metabolic complications, such as hypopituitarism, hyperthyroidism or hypothyroidism, pancreatitis, hypoadrenalism, hypogonadism, hypernatremia or hyponatremia, and hypercalcemia. Antifungal agents used for prophylaxis and/or treatment of mycoses also have adverse endocrine and metabolic effects, including hypoadrenalism, hypogonadism, hypoglycemia, dyslipidemia, hypernatremia, hypocalcemia, hyperphosphatemia, hyperkalemia or hypokalemia, and hypomagnesemia. Herein, we review how mycoses and conventional systemic antifungal treatment can affect the endocrine system and cause metabolic abnormalities. If clinicians are equipped with better knowledge of the endocrine and metabolic complications of fungal infections and antifungal therapy, they can more readily recognize them and favorably affect outcome.

CYP2C19 GENOTYPE AND OMEPRAZOLE HYDROXYLATION PHENOTYPE IN CHINESE LI POPULATION

1. CYP2C19 is a polymorphism of cytochrome P450, which is responsible for the metabolism of many drugs. The genetic polymorphism shows interethnic variation and it has been demonstrated that the frequency of poor metabolizers (PM) and the distribution of alleles of CYP2C19 vary among Chinese ethnic nationalities. The aim of the present study was to investigate the incidence of CYP2C19 polymorphism in the Chinese Li population. 2. One hundred and sixty-five unrelated healthy Li subjects were identified with respect to CYP2C19 by genotype and phenotype analysis. A polymerase chain reaction-restriction fragment length polymorphism method was performed for genotyping. The plasma concentrations of omeprazole and 5-hydroxyomeprazole were assayed by reversed-phase high-performance liquid chromatography and the omeprazole hydroxylation index (HI) was determined. 3. The frequency distribution of omeprazole HI is bimodal and the antimode for HI was estimated to be 5.6. The prevalence of phenotypic PM in the Li population was 16.6% (13.7-19.5; 95% CI). Genotype analysis revealed that the frequencies of the CYP2C19*1, *2 and *3 alleles in the Li population were 0.617 (0.590-0.644; 95% CI), 0.353 (0.327-0.379; 95% CI) and 0.031 (0.021-0.041; 95% CI), respectively. The frequency of genotypic PM was 14.7% (11.9-17.5; 95% CI), which almost agreed with the frequency of phenotypic PM. Omeprazole HI was significantly different among the different genotype groups (P < 0.05). 4. The present study revealed that the incidence of the CYP2C19*1, *2 and *3 alleles in Chinese Li population is different to that in other ethnic populations of China. There was an obvious relationship between CYP2C19 genotype and omeprazole hydroxylation phenotype, and about 90% of phenotypic PM can be explained by the CYP2C19*2 and *3 alleles.

Evaluation of the activity of CYP2C19 in Gujrati and Marwadi subjects living in Mumbai (Bombay)

Background

Inherited differences in the metabolism and disposition of drugs, and genetic polymorphisms in the targets of drug therapy (e.g., receptors), can greatly influence efficacy and toxicity of medications. Marked interethnic differences in CYP2C19 (a member of the cytochrome P-450 enzyme superfamily catalyzing phase I drug metabolism) which affects the metabolism of a number of clinically important drugs have been documented. The present study evaluated the activity of CYP2C19 in normal, healthy Gujrati and Marwadi subjects by phenotyping (a western Indian population).

Methods

All subjects received 20 mg of omeprazole, which was followed by blood collection at 3 hrs to estimate the metabolic ratio of omeprazole to 5-hydroxyomeprazole. The analysis was done by HPLC.

Results

It was seen that 10.36% of this population were poor metabolizers(PM) whereas 89.63% were extensive metabolizers(EM).

Conclusion

A genotyping evaluation would better help in identifying population specific genotypes and thus help individualize drug therapy.

Lopinavir/ritonavir induces the hepatic activity of cytochrome P450 enzymes CYP2C9, CYP2C19, and CYP1A2 but inhibits the hepatic and intestinal activity of CYP3A as measured by a phenotyping drug cocktail in healthy volunteers

OBJECTIVE

The effect of lopinavir/ritonavir (LPV/r) administration on cytochrome P450 (CYP) enzyme activity was quantified using a phenotyping biomarker cocktail. Changes in CYP2C9, CYP2C19, CYP3A, CYP1A2, N-acetyltransferase-2 (NAT-2), and xanthine oxidase (XO) activities were evaluated using warfarin (WARF) + vitamin K, omeprazole (OMP), intravenous (IV) and oral (PO) midazolam (MDZ), and caffeine (CAF).

DESIGN

: Open-label, multiple-dose, pharmacokinetic study in healthy volunteers.

METHODS

Subjects (n = 14) simultaneously received PO WARF 10 mg, vitamin K 10 mg, OMP 40 mg, CAF 2 mg/kg, and IV MDZ 0.025 mg/kg on days (D) 1 and 14, and PO MDZ 5 mg on D2 and D15. LPV/r (400/100 mg twice daily) was administered on D4-17. CYP2C9 and CYP2C19 activities were quantified by S-WARF AUC0-inf and OMP/5-hydroxy OMP ratio, respectively. CYP1A2, NAT-2, and XO activities were quantified by urinary CAF metabolite ratios. Hepatic and intestinal + hepatic CYP3A activities were quantified by IV (CL) and PO (CL/F) MDZ clearance, respectively.

RESULTS

After LPV/r therapy, CYP2C9, CYP2C19, and CYP1A2 activity increased by 29%, 100%, and 43% (P = 0.001, 0.046, and 0.001), respectively. No changes were seen in NAT-2 or XO activity. Hepatic and intestinal + hepatic CYP3A activity decreased by 77% (P < 0.001) and 92% (P = 0.001), respectively.

CONCLUSION

LPV/r therapy results in modest induction of CYP1A2 and CYP2C9 and potent induction of CYP2C19 activity. Increasing doses of concomitant medications metabolized by these enzymes may be necessary. LPV/r inhibited intestinal CYP3A to a greater extent than hepatic CYP3A activity. Doses of concomitant CYP3A substrates should be reduced when combined with LPV/r, although intravenously administered compounds may require less of a relative dose reduction than orally administered compounds.

Papel del polimorfismo genético CYP2C19 en los efectos adversos a fármacos y en el riesgo para diversas enfermedades

There are a great number of polymorphic genes in the human genome. Many of them codify enzymes that metabolizes drugs and xenobiotic agents, including carcinogens. Among the better known of them, there are a number of isozymes of the microsomal oxidative system (CYP3A4, CYP2C9, CYP2C19 y CYP2D6). This article reviews the following issues: a) frequency of presentation of the "poor metabolizer" genotype and/or phenotype for substrates of CYP2C19; b) role of CYP2C19 polymorphism on the metabolism of some drugs (mephenytoine and other antiepileptic drugs, proton pump inhibitors, several antidepressants and anxyolitics, the antimalaria aggent proguanyl, and propranolol, among others, use this metabolic pathway), and c) possible role of CYP2C19 polymorphism in the risk for development of neoplasia and other diseases (systemic lupus erythematosus, psoriasis, hip osteonecrosis, Alzheimer's disease, amyotrophic lateral sclerosis, essential tremor).

The effect of aging on the relationship between the cytochrome P450 2C19 genotype and omeprazole pharmacokinetics

BACKGROUND AND OBJECTIVE

The metabolic activity of cytochrome P450 (CYP) 2C19 is genetically determined, and the pharmacokinetics of omeprazole, a substrate for CYP2C19, are dependent on the CYP2C19 genotype. However, a discrepancy between the CYP2C19 genotype and omeprazole pharmacokinetics was reported in patients with liver disease or advanced cancer. The objective of the present study was to evaluate the effect of aging on the relationship between the CYP2C19 genotype and its phenotype.

METHODS

Twenty-eight elderly and 23 young Japanese volunteers were enrolled after being genotyped. Each subject received a single intravenous dose of omeprazole (10 mg and 20 mg for the elderly and the young groups, respectively) and blood samples were obtained up to 6 hours after dose administration to determine the plasma concentrations of omeprazole and its metabolites, 5-hydroxyomeprazole and omeprazole sulfone. Pharmacokinetic parameters were obtained by noncompartmental analysis. Linear regression models were used to examine the joint effects of covariates such as genotype, age, etc., on the pharmacokinetic parameters, and the pharmacokinetic parameters showing statistical significance were compared by ANOVA.

RESULTS

There were significant differences between genotypes in the area under the plasma concentration-time curve of the young group and the elderly group. The number of mutation alleles and age were significant covariates for systemic clearance (CL), but age was the only significant covariate for volume of distribution at steady state (Vss). There were significant age- and genotype-related differences and a significant age x genotype interaction in CL (20.6+/-11.0/12.7+/-4.0/3.2+/-1.0 and 5.4+/-4.0/3.7+/-1.4/2.1+/-0.7 L/h for homozygous extensive metabolisers [EMs]/heterozygous EMs/poor metabolisers [PMs] of the young and the elderly groups, respectively). In Vss, a significant difference was found between the young and the elderly groups (219+/-115 and 107+/-44.5 mL/kg, respectively), but not between three genotypes (178+/-142, 173+/-79 and 110+/-51 mL/kg for homozygous EMs, heterozygous EMs and PMs, respectively).

CONCLUSION

The elderly EMs showed wide variance in the in vivo CYP2C19 activity and were phenotypically closer to the elderly PMs than the young EMs were to the young PMs. Some of the elderly homozygous EMs, as well as heterozygous EMs, have a metabolic activity similar to PMs, and the CYP2C19 genotype may therefore not be as useful as phenotyping in the elderly.

Possible Interethnic Differences in Omeprazole Pharmacokinetics

BACKGROUND AND OBJECTIVE

Considerable ethnic differences have been reported in the incidence of the poor metaboliser (PM) genotype of cytochrome P450 (CYP) 2C19. The frequency of this genotype was found to be much higher in Oriental persons (13-23%) than in American or European populations (3-5%). There are, however, no valid data published for Arabic subjects. The present study was conducted to evaluate pharmacokinetic parameters of omeprazole after a single dose in healthy Jordanian Arabic subjects and to compare the results with data published for other populations.

METHODS

Seventy-four healthy male Jordanian Arabic volunteers contributed to the study, which was performed at Al Essra Hospital in Amman, Jordan. After an overnight fast, omeprazole was administered as a single Losec 20mg capsule. A total of 20 blood samples were collected over a 10-hour period after administration. Omeprazole pharmacokinetic parameters were determined from the plasma concentration-time profiles using the WinNonlin software. Kolmogorov-Smirnov's test and probit plots of omeprazole area under the plasma concentration-time curve (AUC) data were used to analyse the frequency distribution of phenotypic data.

RESULTS

The mean pharmacokinetic parameters and their corresponding coefficient of variation (CV%) for peak plasma concentration (Cmax), AUC from time zero to infinity (AUCinfinity), time to reach Cmax (tmax), apparent oral clearance (CL/F) and elimination half-life (t(1/2)) were 314.96 ng/mL (56%), 923.2 ng . h/mL (108.6%), 2.1h (44%), 0.66 L/h/kg (92%) and 1.5 h (56.6%), respectively. Interindividual differences in the current study were high for all pharmacokinetic parameters, yet comparable to CVs reported in nonphenotyped subjects identified within other ethnic groups (40.3-159% for AUC and 39-48.2% for Cmax). The frequency distribution of all parameters, particularly the AUC, was shown to be trimodal. This has proposed the presence of three distinct phenotypes, designated as extensive metabolisers (EMs), slow-extensive metabolisers (SEMs), and PMs, with corresponding frequency of 36.5%, 39.2% and 24.3%, respectively. After stratification, the relative mean AUCs of omeprazole in EMs, SEMs and PMs were 1 : 2.7 : 9.3 (all p < 0.001). Accordingly, the CL/F of omeprazole showed a ratio of 9.8 : 3.6 : 1 for three phenotype groups, respectively. For other pharmacokinetic parameters including Cmax, t1/2, AUC normalised for bodyweight (AUCN), Cmax/dose and AUC/dose, there were also significant differences between the three groups.

CONCLUSIONS

The current pharmacokinetic study revealed that the majority of the Jordanian Arabics seemed to be more properly classified within the EM phenotype. More specifically, the observed metabolic rates of heterozygous and homozygous Jordanian Arabic EMs were more comparable to those of Caucasian EMs than Oriental EMs. Consequently, higher dosage requirements can be expected among most of the Jordanian Arabics. Yet, the incidence of PMs is significant and they seemed to exhibit a similar pharmacokinetic pattern to Chinese PMs in terms of long-term exposure (clearance and AUC) as well as short-term exposure (Cmax) parameters, after adjustment for dose and bodyweight. Therefore, further clinical application of CYP2C19 polymorphism is anticipated in Jordanian Arabic mixed population, particularly if long-term use of omeprazole is intended.

Effects of enzyme inducers and inhibitors on the pharmacokinetics of intravenous omeprazole in rats

A series of experiments using various inducers and inhibitors of the hepatic microsomal cytochrome P450 (CYP) isozymes were conducted to find CYP isozymes responsible for the metabolism of omeprazole in male Sprague-Dawley rats. Omeprazole, 20 mg/kg, was administered intravenously. In rats pretreated with SKF 525-A (a nonspecific CYP isozyme inhibitor in rats), the time-averaged nonrenal clearance (Cl(nr)) was significantly slower (77.1% decrease) than that in untreated rats. This indicated that omeprazole is metabolized via CYP isozymes in rats. Hence, rats were pretreated with various enzyme inducers and inhibitors. In rats pretreated with 3-methylcholanthrene and dexamethasone (main inducers of CYP1A1/2 and 3A1/2 in rats, respectively), the Cl(nr) values were significantly faster (43.8% and 26.3% increase, respectively). In rats pretreated with troleandomycin and quinine (main inhibitors of CYP3A1/2 and 2D1 in rats, respectively), the Cl(nr) values were significantly slower (20.9% and 12.9% decrease, respectively). However, the Cl(nr) values were not significantly different in rats pretreated with orphenadrine, isoniazid and sulfaphenazole (main inducers of CYP2B1/2 and 2E1, and a main inhibitor of 2C11, respectively, in rats) compared with those of respective control rats. The above data suggested that omeprazole could be mainly metabolized via CYP1A1/2, 3A1/2 and 2D1 in male rats.

Cytochrome P450 mRNA expression in peripheral blood lymphocytes as a predictor of enzyme induction

OBJECTIVE

Previous reports have supported the concept that messenger ribonucleic acid (mRNA) concentrations for cytochrome P450 (CYP) enzymes in peripheral blood mononuclear cells may be predictive of systemic enzyme activity. We investigated whether changes in mRNA expression for CYP1A2,CYP2C19, CYP2D6 and CYP3A4 in peripheral blood lymphocytes (PBLs) may serve as surrogate markers for changes in CYP enzyme activity following the administration of rifampin.

METHODS

On day 1 and day 9 of the study, 12 healthy volunteers were administered caffeine 100 mg, debrisoquine 10 mg and omeprazole 40 mg orally, along with midazolam 0.025 mg/kg intravenously. Blood samples and urine were collected for 8 h after drug administration. The subjects took rifampin 300 mg (n = 6) or 600 mg (n = 6) daily on days 2-8. Total RNA was isolated from PBLs on day 1 and day 9, and mRNA expression for the CYP enzymes and hGAPDH were determined by means of quantitative, real-time, reverse-transcriptase polymerase chain reaction. CYP1A2 activity was estimated by calculating the plasma paraxanthine to caffeine AUC ratio (caffeine metabolic ratio; CMR), CYP2C19 activity by the 2-h omeprazole hydroxylation index (HI), CYP2D6 activity by the urinary debrisoquine recovery ratio (DBRR) and CYP3A4 activity by midazolam clearance.

RESULTS

Median midazolam clearance (0.362 to 0.740 l/kg/h), omeprazole HI (0.752 to 0.214), CMR (0.365 to 0.450) and DBRR (0.406 to 0.479) all changed significantly following rifampin, consistent with the expected enzyme induction. CYP1A2,CYP2D6 and CYP3A4 mRNA content were measurable in all samples. CYP2C19 mRNA was inconsistently detectable. There were no significant correlations between changes in enzyme activity and mRNA expression by Spearman's rank order correlation.

CONCLUSION

The results do not support the use of mRNA expression assays for CYP1A2, CYP2C19, CYP2D6 and CYP3A4 enzymes in PBLs as surrogates for quantifying changes in systemic enzyme activity in the setting of enzyme induction.

Validation of an assay for voriconazole in serum samples using liquid chromatography-tandem mass spectrometry

A simple and rapid liquid chromatography tandem mass spectrometry (HPLC-MS/MS) method for the analysis of voriconazole has been developed. For comparison, serum voriconazole was measured using HPLC and bioassay. For the HPLC-MS/MS assay, samples were prepared in a deep-well block by adding 10 microL of serum to 40 microL of 0.1 M zinc sulfate solution. Proteins were precipitated by adding 100 microL acetonitrile containing ketoconazole as internal standard. After vigorous mixing and centrifugation, 3 microL of the supernatant was injected into the HPLC-MS/MS system. An HPLC system was used to elute a C18 cartridge (2 mm x 4 mm) at 0.6 mL/min with a step gradient of 50% to 100% methanol containing 2 mM ammonium acetate and 0.1% (vol/vol) formic acid. The column was maintained at 55 degrees C, and the retention times were voriconazole 1.50 minutes and ketoconazole 1.47 minutes. Cycle time was 3 minutes, injection to injection. The analytes were monitored using a tandem mass spectrometer operated in multiple reaction monitoring mode using the following transitions: voriconazole m/z 350.0 > 224.1 and ketoconazole m/z 531.1 > 489.1. Within- and between-batch CVs were < 5% and < 8%, respectively, over the range 0.38 to 15.3 mg/L. The lower limit of quantification was 0.1 mg/L. Regression analysis showed HPLC-MS/MS = 1.06 +/- 0.02 (HPLC-UV) - 0.07 +/- 0.1, R2 = 0.95, n = 99.

The effect of the CYP2C19 genotype on the hydroxylation index of omeprazole in South Indians

To investigate the relationship between CYP2C19 genotypes and the hydroxylation index (HI) of omeprazole in the South Indian population. Healthy unrelated South Indian subjects (n=300) were separated into three groups based on their CYP2C19 genotypes. They were administered a single oral dose of 20 mg omeprazole, and venous blood was collected 3 h later. Plasma was assayed using reversed-phase high-performance liquid chromatography, and the omeprazole HI was calculated. The means of HIs in individuals with CYP2C19*1/*1 (n=124), *1/*2 (n=129) and *2/*2,*2/*3 (n=47) were 2.4, 5.3 and 22.5, respectively, and were found to be significantly different between any two groups (P<0.0001). A good correlation was established between CYP2C19 genotype and omeprazole HI (r=0.54, 95% CI 0.45-0.62; P<0.0001). Of the 300 subjects, 42 (14.0%; 95% CI 10.1-17.9) were phenotypic poor metabolizers (PMs), but only 33 of them had two mutant alleles and the remaining 9 PMs had at least one wild-type allele. Among the 258 extensive metabolizers, 14 had two mutant alleles. The prevalence of PMs in the South Indian population was 14.0%, which is similar to that in North Indians and Orientals but significantly higher than in Caucasians and Africans. A genotype-phenotype relationship was established between the CYP2C19 genotype and HI of omeprazole, but 7.7% of subjects deviated from expected genotype-phenotype associations. This could be due to an additional mutation, either in the exons/introns or in the 5'-regulatory region of the CYP2C19 gene.

Differences in drug pharmacokinetics between East Asians and Caucasians and the role of genetic polymorphisms

Interethnic variability in pharmacokinetics can cause unexpected outcomes such as therapeutic failure, adverse effects, and toxicity in subjects of different ethnic origin undergoing medical treatment. It is important to realize that both genetic and environmental factors can lead to these differences among ethnic groups. The International Conference on Harmonization (ICH) published a guidance to facilitate the registration of drugs among ICH regions (European Union, Japan, the United States) by recommending a framework for evaluating the impact of ethnic factors on a drug's effect, as well as its efficacy and safety at a particular dosage and dosage regimen. This review focuses on the pharmacokinetic differences between East Asians and Caucasians. Differences in metabolism between East Asians and Caucasians are common, especially in the activity of several phase I enzymes such as CYP2D6 and the CYP2C subfamily. Before drug therapy, identification of either the genotype and/or the phenotype for these enzymes may be of therapeutic value, particularly for drugs with a narrow therapeutic index. Furthermore, these differences are relevant for international drug approval when regulatory agencies must decide if they accept results from clinical trials performed in other parts of the world.

Safety and Potential of Drug Interactions of Caspofungin and Voriconazole in Multimorbid Patients

Due to their broad antimycotic spectrum and the relatively low rate of side effects, the two antifungals caspofungin and voriconazole are considered as attractive therapeutic alternatives to amphotericin B. However, treatment of severe mycotic infections in patients taking co-medication is associated with the risk of severe adverse drug interactions. The risk of such interactions is increased if voriconazole and, much less pronounced caspofungin, are co-administered with drugs which have an inducing or inhibiting effect on the CYP 450 system, primarily on the isoenzymes CYP2C19, CYP2C9 and CYP3A4. This review provides a comprehensive overview on the potential drug interactions of caspofungin and voriconazole in multimorbid patients.

Genetic polymorphism of cytochrome P450 2C19 in healthy Malaysian subjects

AIMS

Impaired S-mephenytoin 4'-hydroxylation is a well-described genetic polymorphism affecting drug metabolism in humans. Although ethnic differences in its distribution of polymorphism has been described, it is not known whether there is an ethnic heterogeneity of the structure and expression of the CYP2C19 enzyme in the Malaysian population.

METHODS

Study subjects were 142 healthy, unrelated Malaysians aged 18-29 years. Baseline omeprazole and 2-h postingestion omeprazole and 5'-hydroxyomeprazole concentrations were measured for CYP2C19 phenotype determination. Identification of CYP2C19 genotypes was performed with the use of polymerase chain reaction.

RESULTS

Phenotyping of CYP2C19 revealed that the prevalence of poor metabolizers (PMs) in the Malaysian population was 14.1%, whereas prevalence of PMs in genotyping was 12.6%. The PM genotypic prevalence rate was 5.6% in Malays, 19.1% in Chinese and 10.0% in Indian subjects. There were significant differences in PM genotypic prevalence rates among the three primary ethnic groups (P < or = 0.05).

CONCLUSIONS

Phenotyping and genotyping revealed significant differences in the prevalence rates among the three ethnic groups in Malaysia, with Chinese recording highest prevalence.

Lack of weight-based dose dependency and intraindividual variability of omeprazole for CYP2C19 phenotyping

To determine if dose dependency occurs with 2 weight-based single doses of omeprazole in a phenotyping study, as well as to quantitate 3-month intraindividual variability of CYP2C19 activity, 24 Caucasian subjects with body weights from 45 to 66 kg and 67 to 90 kg received single oral 30-mg and 40-mg doses of omeprazole, respectively. Female subjects were phenotyped during the mid-follicular and mid-luteal phases of their menstrual cycles for 3 complete cycles. Male subjects were phenotyped every 14 days for 12 weeks. Subjects with a body weight between 45 and 66 kg received an additional 40-mg omeprazole single dose on visit 7. The 2-hour postdose plasma concentration ratio of omeprazole to 5-hydroxyomeprazole was used as a measure of CYP2C19 activity. The percent coefficient of variation (CV%) of omeprazole phenotyping ranged from 6.3% to 51.3% (median = 18.5%, interquartile range = 14.8%-23.5%). Weight-based single doses of omeprazole for CYP2C19 phenotyping did not exhibit dose dependency. Therefore, a weight-based approach may improve the quantitation of omeprazole/metabolites.

Pharmacogenetics and herb???drug interactions

OBJECTIVE

Ginkgo biloba was found to exert a significant inductive effect on CYP2C19 activity. This study was designed to investigate the potential herb-drug interaction between G. biloba and omeprazole, a widely used CYP2C19 substrate, in subjects with different CYP2C19 genotypes.

METHODS

Eighteen healthy Chinese subjects previously genotyped for CYP2C19 were selected. All subjects received a single omeprazole 40 mg at baseline and then at the end of a 12-day treatment period with G. biloba (140 mg, bid). Multiple blood samples were collected over 12 h, and 24 h urine was collected post omeprazole dosing. Plasma and urine concentrations of omeprazole and its metabolites, 5-hydroxyomeprazole and omeprazole sulfone, were determined, and their pharmacokinetics calculated non-compartmentally.

RESULTS

Plasma concentrations of omeprazole and omeprazole sulfone were significantly decreased, and 5-hydroxyomeprazole significantly increased following G. biloba administration in comparison to baseline. A significant decrease in the ratio of area under the plasma concentration-time curve (AUC) of omeprazole to 5-hydroxyomeprazole was observed in the homozygous extensive metabolizers, heterozygous extensive metabolizers, and poor metabolizers, respectively. The decrease was greater in PMs than EMs. No significant changes in the AUC ratios of omeprazole to omeprazole sulfone were observed. Renal clearance of 5-hydroxyomeprazole was significantly decreased after G. biloba, but the change was not significantly different among the three genotype groups.

CONCLUSION

Our results show that G biloba can induce omeprazole hydroxylation in a CYP2C19 genotype-dependent manner and concurrently reduce the renal clearance of 5-hydroxyomeprazole. Co-administration of G. biloba with omeprazole or other CYP2C19 substrates may significantly reduce their effect, but further studies are warranted.

Omeprazole treatment: genotoxicity biomarkers, and potential to induce CYP1A2 activity in humans

Omeprazole is one of the most used acid-suppressing medications. This fact emphasizes the questions concerning the safety of this compound. Healthy volunteers (n=33) were included in this prospective study. All study subjects were analysed for their CYP2C19 genotype. Of the 33 individuals, 24 were homozygous for the wild type CYP2C19*1 allele, 7 were heterozygous for the CYP2C19*2 variant allele, and 2 were homozygous for the CYP2C19*2 variant allele. Before and after 14 days of omeprazole treatment at a daily dose of 20 mg, one blood sample was taken from each individual to determine five cytogenetic biomarkers of genotoxicity: chromosome aberrations, micronuclei, proliferating rate index, sister chromatid exchanges, and mitotic index. The only significant change was that of a weak increase in micronuclei count after treatment in relation to baseline values (day 0) (P = 0.026). To assess the potential of omeprazole to induce P450 CYP1A2, the urinary ratio AFMU+1X+1U/17U in the interval of 4-5 hours after caffeine intake was calculated twice (days 0 and 15), using the caffeine test in 27 of the 33 individuals. This result suggests that omeprazole does not increase CYP1A2 activity after 14 days of treatment.

Adverse reactions to voriconazole

Voriconazole is a new antifungal agent effective in the treatment of invasive aspergillosis. Interpatient variation in plasma concentrations is considerable--more than 100-fold. We describe 3 patients with diverse manifestations of toxicity (e.g., hallucinations, hypoglycemia, electrolyte disturbance, and pneumonitis) possibly attributable to high voriconazole concentrations. Measurement of plasma concentrations could be helpful in optimizing voriconazole dosages.

Omeprazole as a CYP2C19 marker in Chinese subjects: assessment of its gene-dose effect and intrasubject variability

The objective of this study was to determine the reliability of omeprazole as a marker for CYP2C19 activity in Chinese subjects. In 27 healthy male Chinese subjects, the CYP2C19 phenotype was first determined with the standard mephenytoin hydroxylation index (HI) method. Subsequently, the subjects were randomized in a three-way crossover manner to receive an oral 40-mg dose from each of three omeprazole formulations (as part of a bioequivalence study). Multiple blood samples were obtained over 12 hours, and plasma concentrations of omeprazole, 5-hydroxyomeprazole, and omeprazole sulfone were determined by a high-performance liquid chromatography (HPLC) method. Individual CYP2C19 genotype was determined by the polymerase chain reaction/restriction fragment length polymorphism method. To assess the specificity for CYP2C19 activity, the hydroxylation metabolic ratio (MR) of omeprazole (AUC(omeprazole)/AUC(5-hydroxyomeprazole)) was compared to mephenytoin HI and related to CYP2C19 genotype status. The inter- and intrasubject variabilities of MR were also calculated, and their magnitudes were compared. The intersubject MR varied more than 20 fold. Among the subjects, there was a gene-dose effect, and the mean MR was 1.76, 3.45, and 33.08, respectively, in the homozygous extensive metabolizers (wt/wt, n = 9), heterozygous extensive metabolizers (wt/m1 or wt/m2, n = 10), and poor metabolizers (m1/m1 or m1/m2, n = 7). However, the coefficients of variation for intrasubject MR only ranged from 4.5% to 33.7% over the three periods with the three formulations. The phenotype based on MR was concordant with HI. In view of the clear gene-dose effect, concordance with mephenytoin HI, and low intrasubject variability, omeprazole MR following a 40-mg oral dose can be considered as a specific and sensitive marker for CYP2C19 activity in Chinese subjects.

A simplified analytical method for a phenotyping cocktail of major CYP450 biotransformation routes

An efficient, fast and reliable analytical method was developed for the simultaneous evaluation of the activities of five major human drug metabolising cytochrome P450 (1A2, 2C9, 2C19, 2D6 and 3A4) with a cocktail approach including five probe substances, namely caffeine, flurbiprofen, omeprazole, dextromethorphan and midazolam. All substances were administered simultaneously and a single plasma sample was obtained 2h after the administration. Plasma samples were handled by liquid-liquid extraction and analysed by gradient high performance liquid chromatography (HPLC) coupled to UV and fluorescence detectors. The chromatographic separation was achieved using a Discovery semi-micro HS C18 HPLC column (5 microm particle size, 150 mm x 2.1 mm i.d.) protected by a guard column (5 microm particle size, 20 mm x 2.1 mm i.d.) The mobile phase was constituted of a methanol, acetonitrile and 20mM ammonium acetate (pH 4.5) with 0.1% triethylamine mixture and was delivered at a flow rate of 0.3 mL min(-1). All substances were separated simultaneously in a single run lasting less than 22 min. The HPLC method was formally validated and showed good performances in terms of linearity, sensitivity, precision and accuracy. Finally, the method was found suitable for the screening of these compounds in plasma samples.

Voriconazole-a new therapeutic agent with an extended spectrum of antifungal activity

Voriconazole is a new antifungal agent that can be given orally and intravenously. It has proven efficacy for treating candidosis and invasive aspergillosis as well as other mould infections, such as those caused by Fusarium and Scedosporium spp. The drug is generally well tolerated.

Induction of Testosterone Metabolism by Esomeprazole in aCYP2C19*2 Heterozygote

The authors describe a 42-year-old woman with previously normal sexual function who gradually developed loss of libido during treatment with esomeprazole. While taking esomeprazole, the patient's loss of libido improved with oral testosterone supplementation and deteriorated after testosterone withdrawal. There was steady improvement in both sexual function and serum free testosterone concentration after discontinuation of esomeprazole. Due to the temporal relationship between esomeprazole intake and sexual dysfunction, the authors postulate that esomeprazole causes induction of testosterone metabolism. The authors believe this to be the first case of female sexual dysfunction associated with esomeprazole described in the literature. They discuss a number of possible mechanisms for this effect.

Pharmacokinetics of citalopram in relation to genetic polymorphism of CYP2C19

The study was designed to define the contribution of cytochrome p450 2C19 (CYP2C19) and cytochrome p450 3A4 (CYP3A4) to citalopram N-demethylation and to evaluate the relationship between the disposition of citalopram and CYP2C19 genotype. A single oral 40-mg dose of citalopram was administered to eight extensive metabolizers and five poor metabolizers recruited from 77 healthy Chinese volunteers whose genotypes and phenotypes were predetermined. The plasma concentrations of citalopram and desmethylcitalopram were determined by high-performance liquid chromatography. It was found that the genotype of CYP2C19 had a significant effect on the N-demethylation of citalopram. Poor metabolizers with m1 mutation had higher area under the plasma concentration versus time curve (AUC0--> infinity ) values than did extensive metabolizers. Terminal elimination half-life (t1/2) values of citalopram in poor metabolizers were significantly higher than the values in extensive metabolizers who were either homozygous or heterozygous with CYP2C19*1. The oral clearance (CLoral) of citalopram in poor metabolizers was significantly lower than that of extensive metabolizers. The AUC0--> infinity and maximum plasma concentration (Cmax) of desmethylcitalopram in poor metabolizers were significantly lower than the values of extensive metabolizers. The results show that CYP3A4 is not the major enzyme in the N-demethylation of citalopram among extensive metabolizers. The polymorphism of CYP2C19 plays an important role in the N- demethylation of citalopram in vivo. The extensive metabolizers and poor metabolizers of CYP2C19 had significant difference in disposition of citalopram in vivo.

How useful is the "cocktail approach" for evaluating human hepatic drug metabolizing capacity using cytochrome P450 phenotyping probes in vivo?

Relatively selective in vivo substrate probes have been developed for several major CYP isoforms involved in oxidative drug metabolism. There are basically two in vivo methods for identifying the phenotype. One method, the selective (CYP-specific) phenotyping method, involves administering one single probe drug, whereas the other is a mixed phenotyping or "cocktail" method involving the simultaneous administration of multiple probe drugs, specific for the individual P450. At present, caffeine and chlorzoxazone are used most often as probe drugs for CYP1A2 and CYP2E1, respectively, but these are not necessarily the best probe drugs. Of the potential probe drugs for CYP2C9, CYP2C19, CYP2D6 and CYP3A4, none is really useful. Despite current limitations, the cocktail method for obtaining information about multiple CYP activities in a single experimental session is likely to be more widely used as a screening or phenotyping method for humans in the future.