The Effects of Genetic Polymorphisms of CYP2C9 and CYP2C 19 on Phenytoin Metabolism in Japanese Adult Patients with Epilepsy: Studies in Stereoselective Hydroxylation and Population Pharmacokinetics

Mamiya, Kohsuke; Ieiri, Ichiro; Shimamoto, Junta; Yukawa, Eiji; Imai, Jun; Ninomiya, Hideaki; Yamada, Hiroaki; Otsubo, Kenji; Higuchi, Shun; Tashiro, Nobutada

doi:10.1111/j.1528-1157.1998.tb01330.x

Cited by 158 publications

(90 citation statements)

References 30 publications

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“…Patients with inactive CYP2D6 are at risk of toxicity from agents that are usually metabolised by this isoenzyme. Polymorphism of CYP2C9 and CYP2C19 accounts for the variable metabolism of some AEDs, including PHT (37)(38)(39). The frequency of mutations of the CYP2C9 gene is much higher in whites than in Japanese or other Asians, whereas the frequency of mutations of the CYP2C19 gene is much higher in Japanese than in whites (37,40).…”

Section: Genetic Polymorphismmentioning

confidence: 91%

The Importance of Drug Interactions in Epilepsy Therapy

et al. 2002

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Summary: Long-term antiepileptic drug (AED) therapy is the reality for the majority of patients diagnosed with epilepsy. One AED will usually be sufficient to control seizures effectively, but a significant proportion of patients will need to receive a multiple AED regimen. Furthermore, polytherapy may be necessary for the treatment of concomitant disease. The fact that over-the-counter drugs and nutritional supplements are increasingly being self-administered by patients also must be considered. Therefore the probability of patients with epilepsy experiencing drug interactions is high, particularly with the traditional AEDs, which are highly prone to drug interactions. Physicians prescribing AEDs to patients with epilepsy must, therefore, be aware of the potential for drug interactions and the effects (pharmacokinetic and pharmacodynamic) that can occur both during combination therapy and on drug discontinuation. Although pharmacokinetic interactions are numerous and well described, pharmacodynamic interactions are few and usually concluded by default. Perhaps the most clinically significant pharmacodynamic interaction is that of lamotrigine (LTG) and valproic acid (VPA); these drugs exhibit synergistic efficacy when coadministered in patients with refractory partial and generalised seizures. Hepatic metabolism is often the target for pharmacokinetic drug interactions, and enzyme-inducing drugs such as phenytoin (PHT), phenobarbitone (PB), and carbamazepine (CBZ) will readily enhance the metabolism of other AEDs [e.g., LTG, topiramate (TPM), and tiagabine (TGB)].The enzyme-inducing AEDs also enhance the metabolism of many other drugs (e.g., oral contraceptives, antidepressants, and warfarin) so that therapeutic efficacy of coadministered drugs is lost unless the dosage is increased. VPA inhibits the metabolism of PB and LTG, resulting in an elevation in the plasma concentrations of the inhibited drugs and consequently an increased risk of toxicity. The inhibition of the metabolism of CBZ by VPA results in an elevation of the metabolite CBZepoxide, which also increases the risk of toxicity. Other examples include the inhibition of PHT and CBZ metabolism by cimetidine and CBZ metabolism by erythromycin. In recent years, a more rational approach has been taken with regard to metabolic drug interactions because of our enhanced understanding of the cytochrome P450 system that is responsible for the metabolism of many drugs, including AEDs. The review briefly discusses the mechanisms of drug interactions and then proceeds to highlight some of the more clinically relevant drug interactions between AEDs and between AEDs and non-AEDs. Understanding the fundamental principles that contribute to a drug interaction may help the physician to better anticipate a drug interaction and allow a graded and planned therapeutic response and, therefore, help to enhance the management of patients with epilepsy who may require treatment with polytherapy regimens.

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Section: Genetic Polymorphismmentioning

confidence: 91%

The Importance of Drug Interactions in Epilepsy Therapy

et al. 2002

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“…Phenytoin is an anticonvulsant drug metabolized through the 2C9 and 2C19 isoforms of the cytochrome P450 enzyme system (24). Therefore, phenytoin metabolism may be affected by concomitant administration of drugs that induce or inhibit the cytochrome P450 system (19).…”

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confidence: 99%

Drug Interactions with Clinafloxacin

Randinitis¹,

Alvey²,

Koup³

et al. 2001

Antimicrob Agents Chemother

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Many fluoroquinolone antibiotics are inhibitors of cytochrome P450 enzyme systems and may produce potentially important drug interactions when administered with other drugs. Studies were conducted to determine the effect of clinafloxacin on the pharmacokinetics of theophylline, caffeine, warfarin, and phenytoin, as well as the effect of phenytoin on the pharmacokinetics of clinafloxacin. Concomitant administration of 200 or 400 mg of clinafloxacin reduces mean theophylline clearance by approximately 50 and 70%, respectively, and reduces mean caffeine clearance by 84%. (R)-Warfarin concentrations in plasma during clinafloxacin administration are 32% higher and (S)-warfarin concentrations do not change during clinafloxacin treatment. An observed late pharmacodynamic effect was most likely due to gut flora changes. Phenytoin has no effect on clinafloxacin pharmacokinetics, while phenytoin clearance is 15% lower during clinafloxacin administration.Clinafloxacin is a potent quinolone antibacterial with a broad range of activity that is of potential clinical importance in the management of serious infections, including those caused by many bacteria resistant to a wide variety of other antibiotics (5,6,7,11,16,27). It has been studied primarily in adults hospitalized for the treatment of serious and potentially life-threatening infections, including nosocomial pneumonia, community-acquired pneumonia, febrile neutropenia, complicated intra-abdominal infections, complicated skin and soft tissue infections, endocarditis, and acute gynecologic infections.Clinafloxacin pharmacokinetics in healthy subjects have been reported previously (31). Following administration of 200-and 400-mg twice-daily intravenous doses, the mean values for total body clearance and volume of distribution are approximately 320 ml/min and 156 liters, respectively, and the mean terminal elimination half-life (t 1/2 ) is approximately 5.8 h. Clinafloxacin is approximately 50% bound to plasma protein, independent of concentration. Approximately 50 to 70% of a clinafloxacin dose is excreted unchanged in urine, indicating that renal clearance is the primary route of elimination. Clinafloxacin clearance is correlated to degree of renal function as measured by creatinine clearance (CL CR ). Based on the relationship between clinafloxacin clearance and CL CR , patients with CL CR values of Ͻ40 ml/min should have their daily clinafloxacin dose halved (34).The ability of clinafloxacin to inhibit seven major cytochrome P450 enzymes, CYP1A2, CYP2A6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4, was investigated using isoform-selective marker substrates and human liver microsomal preparations (T. F. Woolf and W. F. Trager, personal communication). Clinafloxacin was most effective in inhibiting CYP1A2 with nearly 50% inhibition observed at the 5 M concentration. CYP2A6, CYP2E1, and CYP3A4 were not inhibited even at a clinafloxacin concentration of 125 M. CYP2C19 was 15 and 75% inhibited at 5 and 125 M clinafloxacin concentrations, respectively. A weaker interaction...

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“…Genetic variation in the CYP2C9 gene can affect metabolism, leading to altered phenotypes. Individuals with poor metaboliser alleles of CYP2C9 gene were shown to have a reduced metabolism of phenobarbital, phenytoin and valproate compared with those with wild-type (normal) alleles [2][3][4][5][6][7][8][9] . Several studies indicate that the most common allelic variants are Arg 144 Cys (CYP2C9*2) and Ile 358 Leu (CYP2C9*3) which encode enzymes with decreased substrate turnover 10,11 .…”

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confidence: 99%

CYP2C9 polymorphism in patients with epilepsy: genotypic frequency analyzes andphenytoin adverse reactions correlation

Twardowschy

Werneck

Scola

et al. 2011

Arq. Neuro-Psiquiatr.

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Objective: CYP2C9 is a major enzyme in human drug metabolism and the polymorphism observed in the corresponding gene may affect therapeutic outcome during treatment. The distribution of variant CYP2C9 alleles and prevalence of phenytoin adverse reactions were hereby investigated in a population of patients diagnosed with epilepsy. Method: Allele-specific PCR analysis was carried out in order to determine frequencies of the two most common variant alleles, CYP2C9*2 and CYP2C9*3 in genomic DNA isolated from 100 epileptic patients. We also analyzed the frequency of phenytoin adverse reactions among those different genotypes groups. The data was presented as mean±standard deviation. Results: The mean age at enrollment was 39.6±10.3 years (range, 17-72 years) and duration of epilepsy was 26.5±11.9 years (range 3-48 years). The mean age at epilepsy onset was 13.1±12.4 years (range, 1 month-62 years). Frequencies of CYP2C9*1 (84%), CYP2C9*2 (9%) and CYP2C9*3 (7%) were similar to other published reports. Phenytoin adverse reactions were usually mild and occurred in 15% patients, without correlation with the CYP2C9 polymorphism (p=0.34). Conclusion: Our findings indicate an overall similar distribution of the CYP2C9 alleles in a population of patients diagnosed with epilepsy in the South of Brazil, compared to other samples. This sample of phenytoin users showed no drug related adverse reactions and CYP2C9 allele type correlation. The role of CYP2C9 polymorphism influence on phenytoin adverse reaction remains to be determined since some literature evidence and our data found negative results. Key words: CYP2C9, polymorphism, Brazilian population, phenytoin, adverse reactions.Polimorfismo do CYP2C9 em pacientes com epilepsia: estudo da frequência genotípica e correlação com os efeitos colaterais da fenitoína RESUMO Objetivo: A CYP2C9 é uma das principais enzimas do metabolismo de drogas humano e o polimorfismo observado no respectivo gene pode afetar o resultado terapêutico durante o tratamento. Neste trabalho investigamos em uma população de pacientes portadores de epilepsia a distribuição dos alelos variantes do CYP2C9 e a frequência de efeitos adversos da fenitoína tentando estabelecer uma correlação. Método: Realizamos uma análise através de uma PCR alelo específica para determinar a frequência dos alelos variantes mais comuns, CYP2C9*2 e CYP2C9*3, isolados da amostra de 100 pacientes com epilepsia. Também levantamos a frequência de reações adversas da fenitoína nestes diferentes grupos genotípicos. Os dados são apresentados na forma de média e desviopadrão. Resultados: A idade média na inclusão foi 39,6±10,3 anos (variando de 17-72 anos) e a duração da epilepsia era 26,5±11,9 anos (variando de 3-48 anos). A idade média dos pacientes no início da epilepsia era 13,1±12,4 anos (variando de 1 mês-62 anos). As frequências do CYP2C9*1 (84%), CYP2C9*2 (9%) e CYP2C9*3 (7%) foram similares Correspondence Carlos Silvado Hospital de Clínicas / UFPR Rua General Carneiro 181 / 3° andar 80060-900 Curitiba PR -Brasil

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The Effects of Genetic Polymorphisms of CYP2C9 and CYP2C 19 on Phenytoin Metabolism in Japanese Adult Patients with Epilepsy: Studies in Stereoselective Hydroxylation and Population Pharmacokinetics

Cited by 158 publications

References 30 publications

The Importance of Drug Interactions in Epilepsy Therapy

The Importance of Drug Interactions in Epilepsy Therapy

Drug Interactions with Clinafloxacin

CYP2C9 polymorphism in patients with epilepsy: genotypic frequency analyzes andphenytoin adverse reactions correlation

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