Clinical pharmacokinetics of fluvastatin

Safety of fluvastatin in patients undergoing high-risk non-cardiac surgery

IMPORTANCE OF THE FIELD

In patients undergoing vascular surgery there is a high incidence of adverse cardiac events, due to sudden coronary plaque rupture. The non-lipid lowering or pleiotropic effects of statins can help reduce adverse cardiovascular events associated with vascular surgery.

AREAS COVERED IN THIS REVIEW

The evidence for perioperative use of fluvastatin, as well as other statins, in high-risk surgery patients is summarized in this review. Data on pharmacokinetics and metabolism is presented, together with considerations on possible drug interactions in the perioperative period.

WHAT THE READER WILL GAIN

The reader will gain a comprehensive understanding of the existing safety and efficacy data for fluvastatin and other statins in the perioperative period. The practical considerations of perioperative fluvastatin therapy will be presented, including potential side-effects and management of the early non-oral phase immediately post surgery. Finally, advice on when to initiate therapy and safety recommendations are offered.

TAKE HOME MESSAGE

In patients scheduled for high-risk vascular surgery, fluvastatin improves postoperative outcome, reducing the incidence of myocardial damage by approximately 50% in the first 30 days following vascular surgery. In comparison with placebo, fluvastatin was not associated with a rise in liver enzymes or creatine kinase levels. To bridge the non-oral phase, an extended-release formula is recommended.

A gene score of nine LDL and HDL regulating genes is associated with fluvastatin-induced cholesterol changes in women

While conventional pharmacogenetic studies have considered single gene effects, we tested if a genetic score of nine LDL- and HDL-associated single nucleotide polymorphisms, previously shown to predict cardiovascular disease, is related to fluvastatin-induced lipid change. In patients with asymptomatic plaque in the right carotid artery, thus candidates for statin therapy, we related score LDL [APOB(rs693), APOE(rs4420638), HMGCR(rs12654264), LDLR(rs1529729), and PCSK9(rs11591147)] and score HDL [ABCA1(rs3890182), CETP(rs1800775), LIPC(rs1800588), and LPL(rs328)] as well as the combined score LDL+HDL to fluvastatin-induced LDL reduction (+/- metoprolol) (n = 395) and HDL increase (n = 187) following 1 year of fluvastatin treatment. In women, an increasing number of unfavorable alleles (i.e., alleles conferring higher LDL and lower HDL) of score LDL+HDL (P = 0.037) and of score LDL (P = 0.023) was associated with less pronounced fluvastatin-induced LDL reduction. Furthermore, in women, both score LDL+HDL (P = 0.001) and score HDL (P = 0.022) were directly correlated with more pronounced fluvastatin-induced HDL increase, explaining 5.9-11.6% of the variance in treatment response in women. There were no such associations in men. This suggests that a gene score based on variation in nine different LDL- and HDL-associated genes is of importance for the magnitude of fluvastatin HDL increase in women with asymptomatic plaque in the carotid artery.

Cytochrome P450-mediated metabolism in the human gut wall

Objective

Although the human small intestine serves primarily as an absorptive organ for nutrients and water, it also has the ability to metabolise drugs. Interest in the small intestine as a drug-metabolising organ has been increasing since the realisation that it is probably the most important extrahepatic site of drug biotransformation.

Key findings

Among the metabolising enzymes present in the small intestinal mucosa, the cytochromes P450 (CYPs) are of particular importance, being responsible for the majority of phase I drug metabolism reactions. Many drug interactions involving induction or inhibition of CYP enzymes, in particular CYP3A, have been proposed to occur substantially at the level of the intestine rather than exclusively within the liver, as originally thought. CYP3A and CYP2C represent the major intestinal CYPs, accounting for approximately 80% and 18%, respectively, of total immunoquantified CYPs. CYP2J2 is also consistently expressed in the human gut wall. In the case of CYP1A1, large interindividual variation in the expression levels has been reported. Data for the intestinal expression of the polymorphic CYP2D6 are conflicting. Several other CYPs, including the common hepatic isoform CYP2E1, are expressed in the human small intestine to only a very low extent, if at all. The distribution of most CYP enzymes is not uniform along the human gastrointestinal tract, being generally higher in the proximal regions of the small intestine.

Summary

This article reviews the current state of knowledge of CYP enzyme expression in human small intestine, the role of the gut wall in CYP-mediated metabolism, and how this metabolism limits the bioavailability of orally administered drugs. Possible interactions between drugs and CYP activity in the small intestine are also discussed.

Cytochrome P450 2C8 pharmacogenetics: a review of clinical studies

Cytochrome P450 (CYP) 2C8 is responsible for the oxidative metabolism of many clinically available drugs from a diverse number of drug classes (e.g., thiazolidinediones, meglitinides, NSAIDs, antimalarials and chemotherapeutic taxanes). The CYP2C8 enzyme is encoded by the CYP2C8 gene, and several common nonsynonymous polymorphisms (e.g., CYP2C8*2 and CYP2C8*3) exist in this gene. The CYP2C8*2 and *3 alleles have been associated in vitro with decreased metabolism of paclitaxel and arachidonic acid. Recently, the influence of CYP2C8 polymorphisms on substrate disposition in humans has been investigated in a number of clinical pharmacogenetic studies. Contrary to in vitro data, clinical data suggest that the CYP2C8*3 allele is associated with increased metabolism of the CYP2C8 substrates, rosiglitazone, pioglitazone and repaglinide. However, the CYP2C8*3 allele has not been associated with paclitaxel pharmacokinetics in most clinical studies. Furthermore, clinical data regarding the impact of the CYP2C8*3 allele on the disposition of NSAIDs are conflicting and no definitive conclusions can be made at this time. The purpose of this review is to highlight these clinical studies that have investigated the association between CYP2C8 polymorphisms and CYP2C8 substrate pharmacokinetics and/or pharmacodynamics in humans. In this review, CYP2C8 clinical pharmacogenetic data are provided by drug class, followed by a discussion of the future of CYP2C8 clinical pharmacogenetic research.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

Pharmacogenetics is the study of how interindividual variations in the DNA sequence of specific genes affect drug response. This article highlights current pharmacogenetic knowledge on important human drug-metabolizing cytochrome P450s (CYPs) to understand the large interindividual variability in drug clearance and responses in clinical practice. The human CYP superfamily contains 57 functional genes and 58 pseudogenes, with members of the 1, 2, and 3 families playing an important role in the metabolism of therapeutic drugs, other xenobiotics, and some endogenous compounds. Polymorphisms in the CYP family may have had the most impact on the fate of therapeutic drugs. CYP2D6, 2C19, and 2C9 polymorphisms account for the most frequent variations in phase I metabolism of drugs, since almost 80% of drugs in use today are metabolized by these enzymes. Approximately 5-14% of Caucasians, 0-5% Africans, and 0-1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant enzyme that demonstrates multiple genetic variants with a potentially functional impact on the efficacy and adverse effects of drugs that are mainly eliminated by this enzyme. Studies into the CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and *3 alleles. Extensive polymorphism also occurs in other CYP genes, such as CYP1A1, 2A6, 2A13, 2C8, 3A4, and 3A5. Since several of these CYPs (e.g., CYP1A1 and 1A2) play a role in the bioactivation of many procarcinogens, polymorphisms of these enzymes may contribute to the variable susceptibility to carcinogenesis. The distribution of the common variant alleles of CYP genes varies among different ethnic populations. Pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and currently available drugs. Further studies are warranted to explore the gene-dose, gene-concentration, and gene-response relationships for these important drug-metabolizing CYPs.

Polymorphisms of human cytochrome P450 2C9 and the functional relevance

Human cytochrome P450 2C9 (CYP2C9) accounts for ∼20% of hepatic total CYP content and metabolizes ~15% clinical drugs such as phenytoin, S-warfarin, tolbutamide, losartan, and many nonsteroidal anti-inflammatory agents (NSAIDs). CYP2C9 is highly polymorphic, with at least 33 variants of CYP2C9 (*1B through *34) being identified so far. CYP2C9*2 is frequent among Caucasians with ~1% of the population being homozygous carriers and 22% are heterozygous. The corresponding figures for the CYP2C9*3 allele are 0.4% and 15%, respectively. There are a number of clinical studies addressing the impact of CYP2C9 polymorphisms on the clearance and/or therapeutic response of therapeutic drugs. These studies have highlighted the importance of the CYP2C9*2 and *3 alleles as a determining factor for drug clearance and drug response. The CYP2C9 polymorphisms are relevant for the efficacy and adverse effects of numerous NSAIDs, sulfonylurea antidiabetic drugs and, most critically, oral anticoagulants belonging to the class of vitamin K epoxide reductase inhibitors. Warfarin has served as a practical example of how pharmacogenetics can be utilized to achieve maximum efficacy and minimum toxicity. For many of these drugs, a clear gene-dose and gene-effect relationship has been observed in patients. In this regard, CYP2C9 alleles can be considered as a useful biomarker in monitoring drug response and adverse effects. Genetic testing of CYP2C9 is expected to play a role in predicting drug clearance and conducting individualized pharmacotherapy. However, prospective clinical studies with large samples are warranted to establish gene-dose and gene-effect relationships for CYP2C9 and its substrate drugs.

Roles of different CYP enzymes in the formation of specific fluvastatin metabolites by human liver microsomes

Fluvastatin has been considered to be metabolised to 5-hydroxy fluvastatin (M-2), 6-hydroxy fluvastatin (M-3) and N-desisopropyl fluvastatin (M-5) in human liver microsomes by primarily CYP2C9. To elucidate the contribution of different CYP enzymes on fluvastatin metabolism, we examined the effect of CYP inhibitors and CYP2C-specific monoclonal antibodies on the formation of fluvastatin metabolites in human liver microsomes. Human liver microsomes were incubated with fluvastatin with or without pre-treatment with CYP inhibitors or monoclonal antibodies. Selective inhibitors of CYP2C9 (sulfaphenazole), CYP3A (ketoconazole) and CYP2C8 (quercetin) were employed and monoclonal antibodies were against CYP2C8, CYP2C9, CYP2C19 and CYP2C8/9/18/19. According to the amount of fluvastatin metabolites produced, the formation of M-3 was found to be major pathway of fluvastatin metabolism (the relative contribution was calculated to be more than 80%). Sulfaphenazole inhibited the formation of M-2 largely, but had little effect on the formation of M-3. It also inhibited the formation of M-5. Ketoconazole markedly inhibited the formation of M-3, but did not inhibit the formation of M-2 and M-5. Quercetin had a moderate inhibitory effect on the formation of all three fluvastatin metabolites. Monoclonal antibodies against CYP2C9 and CYP2C8/9/18/19 markedly inhibited the formation of M-2 and M-5. None of monoclonal antibodies showed clear inhibition on the formation of M-3. In contrast to previous published work, our results suggest that M-2 and M-5 are formed preferentially by CYP2C9, and that M-3 is mainly formed by CYP3A. In summary, the results contribute to a better understanding of the drug-drug interaction potential for fluvastatin in vivo.

Fluvastatin as co-medication in heart transplant recipients with elevated creatine-kinase

BACKGROUND

Statins reduce the risk for transplant vasculopathy and mortality among heart transplant recipients. Interactions between commonly used statins (ie, simvastatin, atorvastatin) and immunosuppressant drugs lead to side effects or withdrawal of statin therapy. Fluvastatin shows fewer interactions with the immunosuppressant agents because it is not metabolized via the cytochrome P-450 3A4 pathway like most immunosuppressants, steroids, or other statins. This study investigated the impact of a switch from other statins to fluvastatin in heart transplant recipients who revealed elevated creatine-kinase levels.

METHODS

A total of 23 heart transplant patients with elevated creatine-kinase levels were included in this study. Statins were replaced with an equal dosage of fluvastatin. We measured on the day of replacement as well as there after at 3, 6, 9, and 12 months creatine-kinase, lipid status, ALT, AST, and creatinine levels.

RESULTS

After 6 months creatine-kinase showed a significant reduction of 25% (P < .05) and after 9 months of 38% (P < .05). The HDL-cholesterol levels were significantly reduced at 6 months (8%; P < .05) and 9 months (23%; P < .05). At 3 months, triglyceride levels were significantly elevated (18%; P < .05). No differences were observed in ALT, AST, creatinine, total, and LDL-cholesterol at any time.

CONCLUSION

A conversion from commonly used statins to fluvastatin in heart transplant patients with elevated creatine-kinase was safe, leading to a significant reduction in creatine-kinase levels. Except for an initial raise in triglycerides and a lowering of HDL-cholesterol, no changes in lipid status were seen. This conversion might help to maintain lipid-lowering therapy in transplant recipients who show side effects using conventional statins.

Lipid-lowering effects of statins: a comparative review

The pharmacological regulation of lipid metabolism in patients with dyslipidaemia is unequivocally associated with significant reductions in risk for cardiovascular morbidity and mortality. There is strong clinical trial data to support of the use of statin therapies in the settings of both primary and secondary prevention. This paper addresses: i) the mechanisms of action of antilipidaemic medications; ii) dosing regimens and the pharmacokinetic differences among drugs of the same class; iii) risk for drug interactions; and iv) reviews the clinical trial evidence used to support the use of particular antilipidaemic medications in specific physiological settings.

[Clinical pharmacogenomics for CYP2C8 and CYP2C9: general concepts and application to the use of NSAIDs]

OBJECTIVE

To study the major mutations in genes CYP2C8 and CYP2C9, their frequency in populations of diverse ethnical descent, their analysis methods, and the major drugs with affected metabolism, with a special emphasis on NSAIDs.

METHOD

Repeated searches of Pubmed (January 1966-January 2006) and Scholar Google were performed. All searches were restricted to studies in humans, and papers not written in Spanish or English were excluded.

RESULTS

Ten allelic variants of CYP2C8 and 24 of CYP2C have been reported. Not all of them exert a relevant effect on drug metabolism. In Caucasians 22% of CYP2C8 genes and 31% of CYP2C9 genes have mutations. In Asians fewer than 1% and nearly 3% are mutated, respectively. Major identification methods include endonuclease digestion, PCR, pyrosequencing, and microarrays. Not all NSAIDs are exclusive substrates for CYP2C8/9. The usefulness of allelic variant analysis varies with each individual drug. The risk for digestive hemorrhage associated with the CYP2C9 genotype is particularly relevant when using aceclofenac, celecoxib, diclofenac, ibuprofen, indomethacin, lornoxicam, piroxicam, or naproxen.

CONCLUSIONS

Although CYP2C8/9 activity plays an essential role in the metabolism of and clinical response to many NSAIDs, the use of pharmacogenomic techniques is not equally useful for all these drugs.

Mechanistic Approaches to Volume of Distribution Predictions: Understanding the Processes

PURPOSE

To use recently developed mechanistic equations to predict tissue-to-plasma water partition coefficients (Kpus), apply these predictions to whole body unbound volume of distribution at steady state (Vu(ss)) determinations, and explain the differences in the extent of drug distribution both within and across the various compound classes.

MATERIALS AND METHODS

Vu(ss) values were predicted for 92 structurally diverse compounds in rats and 140 in humans by two approaches. The first approach incorporated Kpu values predicted for 13 tissues whereas the second was restricted to muscle.

RESULTS

The prediction accuracy was good for both approaches in rats and humans, with 64-78% and 82-92% of the predicted Vu(ss) values agreeing with in vivo data to within factors of +/-2 and 3, respectively.

CONCLUSIONS

Generic distribution processes were identified as lipid partitioning and dissolution where the former is higher for lipophilic unionised drugs. In addition, electrostatic interactions with acidic phospholipids can predominate for ionised bases when affinities (reflected by binding to constituents within blood) are high. For acidic drugs albumin binding dominates when plasma protein binding is high. This ability to explain drug distribution and link it to physicochemical properties can help guide the compound selection process.

Drug-induced changes in P450 enzyme expression at the gene expression level: a new dimension to the analysis of drug-drug interactions

Drug-drug interactions (DDIs) caused by direct chemical inhibition of key drug-metabolizing cytochrome P450 enzymes by a co-administered drug have been well documented and well understood. However, many other well-documented DDIs cannot be so readily explained. Recent investigations into drug and other xenobiotic-mediated expression changes of P450 genes have broadened our understanding of drug metabolism and DDI. In order to gain additional information on DDI, we have integrated existing information on drugs that are substrates, inhibitors, or inducers of important drug-metabolizing P450s with new data on drug-mediated expression changes of the same set of cytochrome P450s from a large-scale microarray gene expression database of drug-treated rat tissues. Existing information on substrates and inhibitors has been updated and reorganized into drug-cytochrome P450 matrices in order to facilitate comparative analysis of new information on inducers and suppressors. When examined at the gene expression level, a total of 119 currently marketed drugs from 265 examined were found to be cytochrome P450 inducers, and 83 were found to be suppressors. The value of this new information is illustrated with a more detailed examination of the DDI between PPARalpha agonists and HMG-CoA reductase inhibitors. This paper proposes that the well-documented, but poorly understood, increase in incidence of rhabdomyolysis when a PPARalpha agonist is co-administered with a HMG-CoA reductase inhibitor is at least in part the result of PPARalpha-induced general suppression of drug metabolism enzymes in liver. The authors believe this type of information will provide insights to other poorly understood DDI questions and stimulate further laboratory and clinical investigations on xenobiotic-mediated induction and suppression of drug metabolism.

Risk and predictability of drug interactions in the elderly

The issue of drug-drug interactions is particularly relevant for geriatric patients with epilepsy because they are often treated with multiple medications for concurrent diseases such as cardiovascular disease and psychiatric disorders (e.g., dementia and depression). The antidepressants with the least potential for altering antiepileptic drug (AED) metabolism are citalopram, escitalopram, venlafaxine, duloxetine, and mirtazapine. The use of established AEDs with enzyme-inducing properties, such as carbamazepine, phenytoin, and phenobarbital, may be associated with reductions in the levels of drugs such as donepezil, galantamine, and particularly warfarin. Carbamazepine, phenytoin, and phenobarbital have been reported to decrease prothrombin time in patients taking oral anticoagulants, although with phenytoin, an increase in prothrombin time has also been reported. Drugs associated with increased risk of bleeding in patients taking oral anticoagulants include selective serotonin reuptake inhibitors (especially fluoxetine), gemfibrozil, fluvastatin, and lovastatin. Other drugs affected by enzyme inducers include cytochrome P450 3A4 substrates, such as calcium channel blockers (e.g., nimodipine, nilvadipine, nisoldipine, and felodipine) and the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors atorvastatin, lovastatin, and simvastatin. Although there have been no reports of AEDs altering ticlopidine metabolism, ticlopidine coadministration can result in carbamazepine and phenytoin toxicity. Also, there is a significant risk of elevated levels of carbamazepine when diltiazem and verapamil are administered. In addition, there are case reports of phenytoin toxicity when administered with diltiazem. Drugs with a lower potential for metabolic drug interactions include (1) cholinesterase inhibitors (although the theoretical possibility of a reduction in donepezil and galantamine levels by enzyme-inducing AEDs should be considered) and the N-methyl-D-aspartate receptor antagonist memantine and (2) antihypertensives such as angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, hydrophilic beta-blockers, and thiazide diuretics. There is a moderate risk that enzyme-inducing AEDs will decrease levels of lipophilic beta-blockers. Newer AEDs have a lower potential for drug interactions. In particular, levetiracetam and gabapentin have not been reported to alter enzyme activity. In summary, there is a significant potential for drug interactions between AEDs and drugs commonly prescribed in geriatric patients with epilepsy.

Combined organ failure with combination antihyperlipidemic treatment: a case of hepatic injury and acute renal failure

OBJECTIVE

To report a case of acute hepatic injury and acute renal failure secondary to rhabdomyolysis associated with fluvastatin-gemfibrozil combination therapy for hyperlipidemia.

CASE SUMMARY

A 56-year-old woman with a history of hyperlipidemia presented with fatigue, weakness in her lower extremities, and red-colored urine. One month prior, she had started combination therapy of fluvastatin 80 mg/day and gemfibrozil 1200 mg/day. On physical examination, she had a serious loss of motor function in the upper and lower extremities. Her laboratory tests revealed severe liver enzyme elevation and abnormal renal function. Abdominal ultrasound did not show hepatic cholestasis, renal parenchymal abnormality, or obstruction.

DISCUSSION

Statins and fibric acid derivatives have complementary effects on mixed hyperlipidemia. However, such combination therapy increases the risk of myopathy, which may result in life-threatening rhabdomyolysis. Several reports have suggested that combination fluvastatin-gemfibrozil therapy is both effective and safe in mixed lipid disorders. In our patient, severe rhabdomyolysis with serious hepatocellular injury was observed one month after the combination antihyperlipidemic therapy was started. Assessment with the Naranjo probability scale determined that an adverse drug reaction was probable. The mechanism of this combined toxicity is difficult to clarify, although in vivo and in vitro studies to date have reported considerable data concerning antihyperlipidemic drug interactions.

CONCLUSIONS

Clinicians should carefully consider the risks and benefits of treating dyslipidemia with fluvastatin-gemfibrozil combination therapy.

Fluvastatin enhancement of trastuzumab and classical cytotoxic agents in defined breast cancer cell lines in vitro

The combination of anticancer drugs used in the clinic has been based upon empiricism, and the potential permutations of currently available drugs overwhelm the clinical trials system. Recently, investigators have suggested that the combination of a blockade of vital signal transduction pathways in combination with more standard therapy might enhance anticancer effect. Using a panel of breast cancer cell lines and isobologram median effect analysis, a method of determining synergism or antagonism of drugs, we have investigated in vitro potentially clinically useful combinations of agents with the human cell lines MCF7/wt, MCF7/adr, BT474, and SK-BR-3 grown in log phase. Results were confirmed by curve shift analysis. Cells were exposed to the agent(s) for 72 h and then analyzed for cytotoxicity using a MTT (3-(4,5-dimethylthiazolyl-2)-2,5-diphenyl-tetrazolium bromide) assay. Fluvastatin, an inhibitor of prenylation with excellent tolerability in man, was chosen to disrupt signal transduction pathways and thus potentially enhance the effect of more traditional anticancer agents. Anticancer agents tested were cytotoxics used in the treatment of breast cancer, trastuzumab, and rapamycin as an inhibitor of the AKT pathway. Fluvastatin combined with trastuzumab demonstrates global synergy of cytotoxic effect that is confirmed by apoptosis assay. These effects could only be partially reversed by adding farnesol or geranylgeraniol to restore prenylation. Epirubicin is also synergistic with fluvastatin in three of the four cell lines. Rapamycin, an inhibitor of MTOR, was synergistic with fluvastatin in two of the four cell lines and antagonistic in two other cell lines. The combination of fluvastatin or another inhibitor of prenylation and trastuzumab may be attractive for clinical development as the effect of trastuzumab in Her2/neu positive breast tumors is incomplete as a single agent.

The human intestinal cytochrome P450 "pie"

Cytochromes P450 (P450s) 3A, 2C, and 1A2 constitute the major "pieces" of the human liver P450 "pie" and account, on average, for 40, 25, and 18%, respectively, of total immunoquantified P450s (J Pharmacol Exp Ther 270:414-423, 1994). The P450 profile in the human small intestine has not been fully characterized. Therefore, microsomes prepared from mucosal scrapings from the duodenal/jejunal portion of 31 human donor small intestines were analyzed by Western blot using selective P450 antibodies. P450s 3A4, 2C9, 2C19, and 2J2 were detected in all individuals and ranged from 8.8 to 150, 2.9 to 27, <0.6 to 3.9, and <0.2 to 3.1 pmol/mg, respectively. CYP2D6 was detected in 29 individuals and ranged from <0.2 to 1.4 pmol/mg. CYP3A5 was detected readily in 11 individuals, with a range (average) of 4.9 to 25 (16) pmol/mg that represented from 3 to 50% of total CYP3A (CYP3A4 + CYP3A5) content. CYP1A1 was detected readily in three individuals, with a range (average) of 3.6 to 7.7 (5.6) pmol/mg. P450s 1A2, 2A6, 2B6, 2C8, and 2E1 were not or only faintly detected. As anticipated, average CYP3A content (50 pmol/mg) was the highest. Excluding CYP1A1, the remaining enzymes had the following rank order: 2C9 > 2C19 > 2J2 > 2D6 (8.4, 1.1, 0.9, and 0.5 pmol/mg, respectively). Analysis of a pooled preparation of the 31 donor specimens substantiated these results. In summary, as in the liver, large interindividual variation exists in the expression levels of individual P450s. On average, CYP3A and CYP2C9 represents the major pieces of the intestinal P450 pie, accounting for 80 and 15%, respectively, of total immunoquantified P450s.

Pharmacogenomics of cholesterol-lowering therapy

The prevention of cardiovascular disease is critically dependent on lipid-lowering therapy, including 3-hydroxymethyl-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins), cholesterol absorption inhibitors, bile acid resins, fibrates, and nicotinic acid. Although these drugs are generally well tolerated, severe adverse effects can occur in a minority of patients. Furthermore, a subset of patients does not respond to cholesterol-lowering therapy with a reduction in coronary heart disease progression. Significant progress has been made in the identification of common DNA sequence variations in genes influencing the pharmacokinetics and pharmacodynamics of statins and in disease-modifying genes relevant for coronary heart disease (CHD). Among the most promising candidate genes for pharmacogenomic analysis of statin therapy are HMG-CoA reductase as a direct target gene and other genes modulating lipid and lipoprotein homeostasis. Based on data from pharmacogenetic trials, a combined analysis of multiple genetic variants in several genes is more likely to give significant results than single gene studies in small cohorts. In the future, pharmacogenomic testing may allow risk stratification of patients to avoid serious side effects and enable clinicians to select lipid-lowering drugs with the highest efficacy resulting in the best response to therapy.

Pharmacokinetic interaction between fluvastatin and diltiazem in rats

The present study aimed to investigate the effect of fluvastatin on the pharmacokinetics of diltiazem in rats. Pharmacokinetic parameters of diltiazem were determined in rats following an oral administration of diltiazem (15 mg/kg) in the presence and absence of fluvastatin (0.6 and 2.0 mg/kg). Compared with the control given diltiazem alone, the C(max) and AUC of diltiazem increased by 30-70% in rats with the concurrent use of fluvastatin, while there was no significant change in T(max) and the plasma half-life (T(1/2)) of diltiazem. Consequently, absolute and relative bioavailability values of diltiazem in the presence of fluvastatin were significantly higher (p<0.05) than those from the control group, implying that fluvastatin could reduce the presystemic extraction of diltiazem. In conclusion, the concurrent use of fluvastatin significantly enhanced the oral exposure of diltiazem in rats.

Liquid chromatography/negative ion electrospray tandem mass spectrometry method for the quantification of fluvastatin in human plasma: validation and its application to pharmacokinetic studies

A simple, sensitive and rapid high-performance liquid chromatography/negative ion electrospray tandem mass spectrometry method was developed and validated for the assay of fluvastatin in human plasma. Following solid-phase extraction, the analytes were separated using an isocratic mobile phase on a reversed-phase column and analyzed by mass spectrometry in the multiple reaction monitoring mode using the respective [M-H]- ions, m/z 410/348 for fluvastatin and m/z 480/418 for the internal standard. The assay exhibited a linear dynamic range of 2-500 ng/mL for fluvastatin in human plasma. The lower limit of quantification was 2 ng/mL with a relative standard deviation of less than 5%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. A run time of 1.5 min for each sample made it possible to analyze more than 400 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies.

Effects of fluvastatin treatment on lipid profile, C-reactive protein trend, and renal function in dyslipidemic patients with chronic renal failure

The purpose of this trial was to evaluate the effects of fluvastatin on the lipid pro-file and on renal function, as measured by creatinine clearance, in dyslipidemic patients with chronic renal failure. In this 8-month prospective, open-label, randomized, parallel-group trial, 130 patients (70 men and 60 women), after a 2-month washout period following previous lipid-lowering treatments, were randomly assigned to fluvastatin XL 80 mg given once daily (80 patients) or to standard treatment (50 patients). Mean total cholesterol, low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, and triglyceride values after 3 and 6 months of treatment with fluvastatin showed statistically significant improvement compared with standard treatment. Improved renal function, as measured by creatinine clearance, was observed at the end of the 6-month treatment period in approximately 65% of patients treated with fluvastatin. The increase in creatinine clearance consistently reached 10% to 15% of baseline values. A statistically significant reduction in C-reactive protein (CRP) over baseline values was observed in approximately 75% of patients treated with fluvastatin. Furthermore, mean values of CRP for the fluvastatin standard treatment groups, respectively, were 6.78 and 10.19 at 3 months and 4.47 and 11 at 6 months. Both treatments were well tolerated. No major adverse events were noted. Results of this study suggest that fluvastatin treatment in patients with chronic renal failure is effective in improving the lipid profile, and it demonstrates good safety and tolerability. Furthermore, fluvastatin may contribute to improved nephroprotection in this patient population.

3-hydroxy-3-methylglutaryl-coenzyme a reductase inhibitor, fluvastatin, as a novel agent for prophylaxis of renal cancer metastasis

PURPOSE

Inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, also called statins, are currently used widely as a safe, effective therapeutic in the treatment of hypercholesterolemia. Recently, statins have been recognized for their activity against cancer. In the present study, we examined the effect of a synthetic statin, fluvastatin, on the development of renal cancer.

EXPERIMENTAL DESIGN

The effects of fluvastatin on cell viability, cell cycle, in vitro angiogenesis, and invasive properties were examined in murine renal cancer cell Renca. The changes in cell cycle-associated proteins, p21(Waf1/Cip1) and p53, and rac1 phosphorylation were analyzed by Western blotting. The prophylactic efficacy of fluvastatin to murine pulmonary metastasis of Renca was examined.

RESULTS

Fluvastatin inhibited in vitro growth of Renca cells in a time- and dose-dependent manner, with up to 70% inhibition at a concentration of 10 mumol/L. This inhibitory effect was due to cell cycle arrest at the G(1) phase and induction of apoptosis accompanied by up-regulation of p21(Waf1/Cip1) and p53. The invasive properties of Renca cells through Matrigel were inhibited by fluvastatin, with decreased phosphorylation of rac1. In vitro angiogenesis was also inhibited by fluvastatin. Furthermore, oral administration at doses of 1 to 10 mg/kg/d, for 12 days after inoculation of Renca cells via the tail vein, significantly decreased the amount of pulmonary metastasis.

CONCLUSIONS

Because our results suggest that fluvastatin may effectively inhibit in vitro tumor growth, invasion, angiogenesis, and metastasis of Renca cells, oral administration of fluvastatin could be a novel, safe, and effective agent for preventing metastasis of renal cancer.

Fluvastatin synergistically enhances the antiproliferative effect of gemcitabine in human pancreatic cancer MIAPaCa-2 cells

The new combination between the nucleoside analogue gemcitabine and the cholesterol-lowering drug fluvastatin was investigated in vitro and in vivo on the human pancreatic tumour cell line MIAPaCa-2. The present study demonstrates that fluvastatin inhibits proliferation, induces apoptosis in pancreatic cancer cells harbouring a p21ras mutation at codon 12 and synergistically potentiates the cytotoxic effect of gemcitabine. The pharmacologic activities of fluvastatin are prevented by administration of mevalonic acid, suggesting that the shown inhibition of geranyl-geranylation and farnesylation of cellular proteins, including p21rhoA and p21ras, plays a major role in its anticancer effect. Fluvastatin treatment also indirectly inhibits the phosphorylation of p42ERK2/mitogen-activated protein kinase, the cellular effector of ras and other signal transduction peptides. Moreover, fluvastatin administration significantly increases the expression of the deoxycytidine kinase, the enzyme required for the activation of gemcitabine, and simultaneously reduces the 5′-nucleotidase, responsible for deactivation of gemcitabine, suggesting a possible additional role of these enzymes in the enhanced cytotoxic activity of gemcitabine. Finally, a significant in vivo antitumour effect on MIAPaCa-2 xenografts was observed with the simultaneous combination of fluvastatin and gemcitabine, resulting in an almost complete suppression and a marked delay in relapse of tumour growth. In conclusion, the combination of fluvastatin and gemcitabine is an effective cytotoxic, proapoptotic treatment in vitro and in vivo against MIAPaCa-2 cells by a mechanism of action mediated, at least in part, by the inhibition of p21ras and rhoA prenylation. The obtained experimental findings might constitute the basis for a novel translational research in humans.

Statins' dosage in patients with renal failure and cyclosporine drug-drug interactions in transplant recipient patients

Dyslipidemia is frequent in patients with renal failure and in transplant recipient patients. This lead to a wide use of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors (statins) in patients with impaired renal function or in patients treated with cyclosporine as post-transplantation immunosuppressive therapy. As a result, it is crucial for those patients' physicians to be aware of how to handle these drugs when renal function is impaired and/or when cyclosporine is co-administered. Most statins have an extensive hepatic elimination and the renal route is usually a minor elimination pathway. However, pharmacokinetic alterations have been described for some of these drugs in patients with renal insufficiency. Cyclosporine is a widely used immunosuppresive therapy in solid organ transplant patients and drug-drug interactions are likely to occur when statins and cyclosporine are administered together. Those interactions may theoretically result in increased statins and/or cyclosporine serum levels with potential muscle and/or renal toxicity. As a result, caution is warranted if concurrent administration is performed. In this review, we synthesized the data from the literature on (1) the pharmacokinetics and dosage adjustment of atorvastatin, fluvastatin, pravastatin, rosuvastatin, and simvastatin in patients with renal failure and (2) the potential drug-drug interactions between these drugs and cyclosporine in transplant recipient patients.

A literature search on pharmacokinetic drug interactions of statins and analysis of how such interactions are reflected in package inserts in Japan

BACKGROUND AND OBJECTIVES

Statins (HMG-CoA reductase inhibitors) are one of the most widely prescribed classes of drugs throughout the world, because of their excellent cholesterol-lowering effect and overall safety profile except for rare but fatal rhabdomyolysis arising either directly or indirectly by pharmacokinetic interactions with certain other drugs. As package inserts in pharmaceuticals are the primary source of information for health care providers, we carried out a literature search to examine how crucial information was provided in package inserts of five statins approved in Japan (simvastatin, atorvastatin, fluvastatin, pravastatin and pitavastatin).

METHODS

A MEDLINE search from 1996 to June 2004 was carried out to identify studies on clinical pharmacokinetic drug interactions for the five statins. We mainly collected information on area under plasma concentration (AUC) following co-administration of statins with other drugs. The current package inserts used in Japan were obtained from the website of the Pharmaceutical and Medical Device Agency whereas USA package inserts were obtained from the Food and Drug Administration website.

RESULTS

The majority of package inserts listed the drugs that interacted with statins with most describing the risk of rhabdomyolysis because of the possibility of increases in blood concentration. However, quantitative information such as change in AUC was provided in only a few cases. Instructions for dosage adjustment are seldom provided in the Japanese package inserts. USA package inserts list almost identical drug interactions as the Japanese package inserts, although they contain more quantitative data, especially for typical cytochrome P450 (CYP) inhibitors.

CONCLUSION

All pharmacokinetic drug interactions including relevant quantitative data for potential effectors and details on mechanisms of interaction need to be given in package inserts as soon as the information becomes available, to ensure safe and proper use of the drugs concerned. Including such information in the package insert will be an extremely valuable aid for health care providers.

Female-specific aspects in the pharmacotherapy of chronic cardiovascular diseases

Differences in pharmacokinetics, pharmacodynamics, and physiology contribute to the phenomenon that women and men frequently respond differently to cardiovascular drugs. Hormonal influences, in addition, can play an important role: for example, the menstrual cycle, menopause, and pregnancy--as a result of fluctuations in concentrations of sexual steroids, and of changes in total body water--can be associated with gender-specific differences in the plasma levels of cardiovascular drugs. Clinical relevance accordingly results, especially for substances with a narrow therapeutic margin. This review treats the most important pharmacodynamic gender-relevant differences in this context, and surveys available evidence on the benefits of therapy of chronic cardiovascular diseases in women. On the whole, the study situation for women is appreciably less favourable than for men: owing to the fact that women are under-represented in most studies, and that few gender-specific analyses have been conducted.

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

In order to find whether torasemide is metabolized via CYP isozymes in rats, torasemide at a dose of 2mg/kg was infused in rats pretreated with SKF 525-A, a non-specific CYP isozyme inhibitor in male Sprague-Dawley rats. The total area under the plasma concentration-time curve from time zero to time infinity (AUC) of torasemide was significantly greater in rats pretreated with SKF 525-A (a non-specific CYP isozyme inhibitor in rats) than that in control rats (3570 versus 1350 microg min/ml). This indicated that torasemide is metabolized via CYP isozymes in rats. Hence, torasemide was infused in rats pretreated with various enzyme inducers and inhibitors to find what types of CYP isozymes are involved in the metabolism of torasemide in rats. The AUC values were not significantly different in rats pretreated with 3-methylcholanthrene, phenobarbital, isoniazid, quinine and troleandomycin (main inducers of CYP1A1/2, CYP2B1/2, and CYP2E1, and main inhibitors of CYP2D1 and CYP3A1/2 in rats, respectively) compared with those in respective control rats. However, in rats pretreated with dexamethasone (a main inducer of CYP3A1/2 in rats), the AUC was significantly smaller than that in control rats (1290 versus 1590 microg min/ml). Dexamethasone probably also induces rat CYP2C11; this could be due to an increase in CYP2C11 in rats pretreated with dexamethasone. It has been reported from our laboratories that in rats pretreated with sulfaphenazole (a main inhibitor of CYP2C11 in rats) the AUC was significantly greater than that in control rats (2970 versus 1610 microg min/ml). The above data suggested that torasemide could be metabolized in male rats mainly via CYP2C11.

[Antihypertensive drug-drug interactions]

A drug interaction is the quantitative or qualitative modification of the effect of a drug by the simultaneous or successive administration of a different one. Hypertensive patients, mainly the more elderly ones, frequently present concomitant diseases that require the administration of several medicines which facilitates the appearance of interactions. The lack of effectiveness of the antihypertensive treatment is a relatively frequent fact that sometimes is due to interactions of antihypertensive drugs with other treatments. It is difficult to determine the incidence of interactions, but it is related to the number of drugs administered simultaneously. Between 37 and 60% of hospital-admissions are treated with potentially dangerous drug associations and up to a 6% of fatal events are due to this circumstance. Among antihypertensive drugs, diuretics and angiotensin converting enzyme inhibitors are less affected by drug-interactions. Lipophilic beta-blockers agents may present some clinical relevant interactions, whereas calcium channel blockers, especially the non-dihydropiridinic ones, are implied in clinically relevant pharmacokinetic interactions. Among the angiotensin receptor blockers there are differences that would have to be considered when they are used in patients who receive other drugs. Although it is impossible for the doctor to remember all the clinical relevant interactions, it is important to bear in mind their existence and the possible mechanisms of production which can help to identify them and to contribute to their prevention. The most frequent interactions related with clinical problems are the pharmacokinetic ones, mainly those related to the metabolism through the cytochrome P450 system or the presystemic clearance by means of the P-glycoprotein. Enzymes of the cytochrome P450 system may present polymorphisms that can explain the individual differences in the response to drugs or the appearance of drug-interactions.

The effect of the cytochrome P450 CYP2C8 polymorphism on the disposition of (R)-ibuprofen enantiomer in healthy subjects

AIMS

To study the effect of CYP2C8*3, the most common CYP2C8 variant allele on the dis-position of (R)-ibuprofen and the association of CYP2C8*3 with variant CYP2C9 alleles.

METHODS

Three hundred and fifty-five randomly selected Spanish Caucasians were screened for the common CYP2C8 and CYP2C9 mutations. The pharmacokinetics of (R)-ibuprofen were studied in 25 individuals grouped into different CYP2C8 genotypes.

RESULTS

The allele frequency of CYP2C8*3 (0.17) was found to be higher than that reported for other Caucasian populations (P = 0.0001). The frequencies of CYP2C9*2 and CYP2C9*3 were 0.19 (0.16-0.21) and 0.10 (0.08-0.12), respectively. An association between CYP2C8*3 and CYP2C9*2 alleles was observed, occurring together at a frequency 2.4-fold higher than expected for a random association of alleles (P = 0.0001). The presence of the CYP2C8*3 allele was found to influence the pharmacokinetics of (R)-ibuprofen in a gene-dose effect manner. Thus, after administration of 400 mg ibuprofen, the plasma half-life (95% confidence intervals) for individuals with genotypes CYP2C8*1/*1, CYP2C8*1/*3 and CYP2C8*3/*3, was 2.0 h (1.8-2.2), 4.2 h (1.9-6.5; P < 0.05) and 9.0 h (7.8-10.2; P < 0.002), respectively. A statistically significant trend with respect to the number of variant CYP2C8*3 alleles was also observed for the area under the concentration-time curve (P < 0.025), and drug clearance (P < 0.03).

CONCLUSION

Polymorphism of the CYP2C8 gene was found to be common, with nearly 30% of the population studied carrying the variant CYP2C8*3 allele. The presence of the latter caused a significant effect on the disposition of (R)-ibuprofen. This suggests that a substantial proportion of Caucasian subjects may show alterations in the disposition of drugs that are CYP2C8 substrates.

Identification of biliary metabolites of ifosfamide using 31P magnetic resonance spectroscopy and mass spectrometry

Biliary excretion is a significant component in the metabolism of many drugs, but remains difficult to detect and characterise non-invasively. A previous publication recently described the detection of metabolites of ifosfamide in gall bladder in a guinea pig model using in vivo 1H-decoupled 31P 3-D magnetic resonance spectroscopic imaging and a clinical 1.5 T MR scanner.. Here high-resolution 31P magnetic resonance spectroscopy (MRS) of extracted bile identifies peaks as parent ifosfamide (1.19+/-1.47 mM; mean+/-sd), carboxyifosfamide (2.04+/-1.04 mM) and a major contribution from a previously unreported peak at 16.0 ppm (4.05+/-2.38 mM). The unknown resonance was identified using liquid chromatography-mass spectrometry (LCMS) as the glutathione conjugate of ifosfamide (MW=531). This was confirmed by analysing products from the reaction of glutathione with ifosfamide using LCMS and MRS. These results demonstrate how combined in vivo and analytical MRS, together with mass spectrometry, can help identify visceral routes of drug metabolism, thereby aiding understanding of +/-drug disposition and mechanisms of action and toxicity. In particular, the distribution of ifosfamide and its metabolites into bile may be related to oxazophosphorine-related cholecystitis reported in patients.

Drug interactions with angiotensin receptor blockers

Many patients with high blood pressure receive multiple medications for hypertension and other conditions, placing them at risk for adverse drug interactions. Additionally, as the prevalence of hypertension increases with age, factors like greater frailty, comorbidity of the elderly requiring polypharmacy, and reduced hepatic and renal clearance rates for the elimination of drugs increase the likelihood of drug interactions. Angiotensin receptor blockers (ARBs) are the most recent class of agents for the treatment of hypertension. Due to a favourable side effect profile, this class of drugs deserves increased attention. This article reviews drug interactions of ARBs and suggests measures for reducing the risk of adverse events when drugs are co-administered. MEDLINE, EMBASE, Cochrane library, and CINAHL were searched. Reported and likely clinical relevant interactions of ARBs with concomitantly given drugs are summarised in Table 2 and 3. Compared to other classes of antihypertensive agents, the ARBs appear to have a low potential for drug interactions; however, interactions with this class occur and variations within the class have been detected, mainly due to different affinities for cytochrome P450 isoenzymes.

Fluvastatin and fluvastatin extended release: a clinical and safety profile

Cardiovascular diseases due to atherosclerosis are the leading causes of mortality in the Western world. Cholesterol-lowering therapy with 3-hydroxy-3-methylglutaryl coenzyme Areductase inhibitors (statins) has demonstrated a reduction in cardiovascular morbidity and mortality in diverse populations. Fluvastatin (Lescol, Novartis Pharmaceuticals) was the first totally synthetic 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor on the market and has recently become available in an extended-release formulation (Lescol XL, Novartis Pharmaceuticals). Data from several clinical outcome trials have shown substantial benefits from fluvastatin treatment in diverse populations. Fluvastatin exists primarily in its acid form and as inactive metabolites in vivo, while active metabolites as well as the lactone form are only present in small amounts. The demonstration of the safe use of fluvastatin in a wide range of patients may be associated with the predominant acid form of the drug in vivo, as well as its predominant metabolism via the cytochrome P450 2C9 pathway.

Treatment of the metabolic disturbances caused by antipsychotic drugs: focus on potential drug interactions

The risk of excessive bodyweight gain, glucose dysregulation and hyperlipidaemia is differentially increased by conventional and atypical antipsychotic drugs. Switching or combining agents may be sufficient in some cases, but in many instances additional drug treatment will be required. This includes oral antidiabetics, insulin and agents to treat hyperlipidaemia, hypertension and platelet dysfunction, among others. Numerous pharmacokinetic and pharmacodynamic interactions with the antipsychotics are possible, although few have been tested in formal studies. After reviewing the literature, the authors provide preliminary guidelines to assist clinicians in drug selection for this complex and fragile clinical population.

AN EVALUATION OF THE IN VITRO METABOLISM DATA FOR PREDICTING THE CLEARANCE AND DRUG-DRUG INTERACTION POTENTIAL OF CYP2C9 SUBSTRATES

In the early drug discovery process, metabolic stability and cytochrome P450 inhibition are often used as an early selection tool to identify useful compounds for further development. The reliability of the data in this process is therefore crucial. In the present study, in vitro enzyme kinetic data were used to predict the in vivo clearance and drug-drug interaction potential of four well known CYP2C9 substrates (tolbutamide, fluvastatin, ibuprofen and diclofenac) that are frequently used as benchmark substances in screening programs. Quantitative predictions of hepatic clearance using the well stirred prediction model and CL(int) calculated from enzyme kinetic measurements were not useful. Including and excluding protein binding resulted in under- and overestimation, respectively, of in vivo clearance. The only predicted in vivo clearance that fell into the range of reported measured values was for fluvastatin when protein binding was not included. In an open, randomized, seven-armed, crossover study in healthy volunteers, tolbutamide, ibuprofen, and fluvastatin were investigated as inhibitors of the metabolism of diclofenac, and vice versa. None of the combinations was found to interact with each other in vivo. The in vitro drug-drug interaction potential was investigated by K(i) determinations of the same combinations. In contrast to clearance predictions, the interaction potential in vivo was best predicted when plasma protein binding was included in the various models used. This study points to the uncertainty in calculating in vivo kinetics from in vitro enzyme kinetic data. The in vitro metabolic screening can thus be questioned as a compound selection tool without a proven in vitro-in vivo correlation.

Antihypertensive therapy: special focus on drug interactions

Today, the lifetime risk of patients aged 55-65 years to receive antihypertensive drugs approaches 60%. Yet, recent trials suggest that hypertension is not adequately controlled in the majority of patients. The prevalence of hypertension increases with advancing age, as does the prevalence of comorbid conditions and the total number of medications taken. Multi-drug therapy, advancing age and comorbid conditions are also key risk factors for adverse drug reactions and drug interactions. In this review, the authors evaluate the most frequently used antihypertensive drugs (diuretics, beta-adrenergic blockers, angiotensin-converting enzyme inhibitors, calcium channel blockers, angiotensin II receptor Type 1 blockers and alpha-adrenergic blockers) with special reference to pharmacodynamic and pharmacokinetic drug interactions. As the spectrum of drugs prescribed is constantly changing, safety yesterday does not imply safety today and safety today does not imply safety tomorrow. Furthermore, therapeutic efficacy should not be neglected over concerns regarding drug interactions. Many patients are at risk of clinically relevant drug interactions involving antihypertensive drugs but, presently, even more patients may be at risk of suffering from the consequences of their inadequately treated hypertension. In this respect, the authors discuss controversial viewpoints on the overall clinical relevance of drug interactions occurring at the level of cytochrome P450 metabolism.

Characterization of the CYP2C8 Active Site by Homology Modeling

To compare the features of the active sites of CYP2C8, CYP2C9, and CYP2C19, homology modeling was performed based on the crystallographic coordinates of mammalian CYP2C5. It was found that CYP2C8 has a much larger pocket than the other forms due to the existence of an additional pocket. The approach to the additional pocket is comprised of Ile102, Ser114, Leu208, Val366, and Ile476, and the side chains of Ser114, Val366, and Ile476, which are smaller than the corresponding residues in the other CYPs, enable access to the pocket. The general features of the active site in the CYP2C8 model are similar to those of the previously constructed CYP3A4 model, which may account for the 2 CYPs sharing some of their substrates. The CYP2C8 model was validated by examining the bound orientation of paclitaxel and showing that it is consistent with the formation of the 6-beta hydroxylated derivative during metabolism. Docked paclitaxel was found to form a hydrogen bond with the side chain of Asn 99, which is a characteristic residue of CYP2C8 and is located in the additional pocket. Descriptors for CYP2C8 and CYP2C9 substrates were also examined with the molecular operating environment (MOE). The descriptor by which CYP2C8 and CYP2C9 substrates were classified most distinctly was found to be molar refractivity, which might be related to the longer shape and more polar nature of the active site of CYP2C8 in the CYP2C subfamily.