Pharmacogenetic Variants and Plasma Concentrations of Antiseizure Drugs: A Systematic Review and Meta-Analysis.

Importance: Precise estimation of a patient's drug metabolism capacity is important for antiseizure dose personalization. Objective: To quantify the differences in plasma concentrations for antiseizure drugs associated with variants of genes encoding drug metabolizing enzymes. Data Sources: PubMed, Clinicaltrialsregister.eu, ClinicalTrials.gov, International Clinical Trials Registry Platform, and CENTRAL databases were screened for studies from January 1, 1990, to September 30, 2023, without language restrictions. Study Selection: Two reviewers performed independent study screening and assessed the following inclusion criteria: appropriate genotyping was performed, genotype-based categorization into subgroups was possible, and each subgroup contained at least 3 participants. Data Extraction and Synthesis: The Meta-analysis of Observational Studies in Epidemiology (MOOSE) guidelines were followed for data extraction and subsequent quality, validity, and risk-of-bias assessments. The results from the included studies were pooled with random-effect meta-analysis. Main Outcomes and Measures: Plasma concentrations of antiseizure drugs were quantified with the dose-normalized area under the concentration-time curve, the dose-normalized steady state concentration, or the concentrations after a single dose at standardized dose and sampling time. The ratio of the means was calculated by dividing the mean drug plasma concentrations of carriers and noncarriers of the pharmacogenetic variant. Results: Data from 98 studies involving 12 543 adult participants treated with phenytoin, valproate, lamotrigine, or carbamazepine were analyzed. Studies were mainly conducted within East Asian (69 studies) or White or European (15 studies) cohorts. Significant increases of plasma concentrations compared with the reference subgroup were observed for phenytoin, by 46% (95% CI, 33%-61%) in CYP2C9 intermediate metabolizers, 20% (95% CI, 17%-30%) in CYP2C19 intermediate metabolizers, and 39% (95% CI, 24%-56%) in CYP2C19 poor metabolizers; for valproate, by 12% (95% CI, 4%-20%) in CYP2C9 intermediate metabolizers, 12% (95% CI, 2%-24%) in CYP2C19 intermediate metabolizers, and 20% (95% CI, 2%-41%) in CYP2C19 poor metabolizers; and for carbamazepine, by 12% (95% CI, 3%-22%) in CYP3A5 poor metabolizers. Conclusions and Relevance: This systematic review and meta-analysis found that CYP2C9 and CYP2C19 genotypes encoding low enzymatic capacity were associated with a clinically relevant increase in phenytoin plasma concentrations, several pharmacogenetic variants were associated with statistically significant but only marginally clinically relevant changes in valproate and carbamazepine plasma concentrations, and numerous pharmacogenetic variants were not associated with statistically significant differences in plasma concentrations of antiseizure drugs.

Phenytoin's Pharmacological Interactions with Medicinal Herbs: A Review.

Physiologic changes due to aging, pregnancy, nutritional status, drug interactions, and can affect pharmacokinetics and pharmacodynamics of antiepileptic drugs. In this review article, the interactions between phenytoin and herbs recorded in the literature were summarized according to the Medline database (via PubMed). Our results revealed that, changes in phenytoin's bioavailability were reported for co-administration of herbs or herbal extracts. An increase in phenytoin blood levels was established with Piper nigrum, Mentat, and Lipidum sativum in in vitro and/or in vivo studies. In contrast, herbphenytoin interactions led to sub-therapeutic levels of phenytoin in other cases with herbs such as Cannabis, Ginkgo biloba, Morinda citrifolia, Nigella sativa, and Trigonella foenum graceum. In addition, the findings of other pharmcodynamic experiments showed that various herbs, including Zizyphus jujube, Terminalia chebula, Curcuma longa L, and Centella asiatica, improved the pharmacological impact of phenytoin. To reduce the patients' health risks, health professionals involved in their treatment are expected to be thoroughly educated about the interactions between phenytoin and medicinal plants.

The Impact of CYP2C9*11 Allelic Variant on the Pharmacokinetics of Phenytoin and (S)-Warfarin.

Cytochrome P450 2C9 (CYP2C9) is responsible for the oxidative metabolism of about 15% of commonly used drugs, some of which are characterized by a narrow therapeutic window. CYP2C9 is highly polymorphic, and over 60 alleles have been described. CYP2C9*2 and CYP2C9*3 are the most common polymorphisms among White patients and both are associated with decreased activity. The evidence concerning the functional importance of less frequent variant alleles is scarce. The objective of the current study was to characterize the in vivo activity of CYP2C9 among carriers of CYP2C9*11, one of the "African" alleles and the fourth most common CYP2C9 variant allele among White patients by using two prototype substrates, phenytoin and (S)-warfarin. Single 300-mg phenytoin and 20-mg warfarin doses were given to 150 healthy Ethiopian Jewish participants who were nonsmokers, at least one week apart. (S)-warfarin oral clearance and phenytoin metabolic ratio (PMR) derived from the ratio of 5-(4-hydroxyphenyl)-5-phenylhydantoin in 24-hour urine collection to plasma phenytoin 12 hours (PMR 24/12) or 24 hours (PMR 24/24) post dosing, were used as markers of CYP2C9 activity. PMR 24/12 and PMR 24/24 were reduced by 50% and 62.2%, respectively, among carriers of CYP2C9*1/*11 (n = 13) as compared with carriers of CYP2C9*1/*1 (n = 127) (false discovery rate (FDR) q < 0.001). The respective decrease in (S)-warfarin oral clearance was 52.6% (FDR q < 0.001). In conclusion, the enzyme encoded by CYP2C9*11 is characterized by a more than 50% decrease in the enzymatic activity, resembling the extent of decrease associated with CYP2C9*3 ("no-function allele"). Among patients of African ancestry, CYP2C9*11 genetic analysis should be considered prior to prescribing of narrow therapeutic window drugs such as phenytoin, warfarin, nonsteroidal anti-inflammatory drugs, or siponimod.

Doxorubicin alters the disposition of phenytoin by reducing its metabolic elimination and binding affinity to serum albumin in rats.

OBJECTIVES: We investigated the pharmacokinetic interaction of doxorubicin (DOX) with phenytoin (PHT) and the underlying mechanism in rats to clarify why the serum PHT concentration decreases despite the impaired PHT metabolic capacity in patients receiving DOX. METHODS: Rats were administered 15 mg/kg of DOX or saline alone. The pharmacokinetic disposition of intravenously administered PHT was examined 4 days after DOX exposure. Enzyme kinetics of CYP2C-dependent PHT p-hydroxylation were analysed using hepatic microsomes. The unbound PHT concentration in serum was measured by the ultrafiltration method, and the relationship between the unbound fraction (fu) and serum albumin level was assessed. KEY FINDINGS: The total clearance (CLtot) of PHT was significantly increased by DOX, but the activity of PHT p-hydroxylation conversely decreased. The unbound serum PHT concentration and its fu were significantly higher in the DOX group than in the control group, and the CLtot/fu, a measure of intrinsic clearance, significantly decreased. An increase in the fu was observed even when using a serum sample with an albumin concentration equal to that in the control group. CONCLUSIONS: DOX treatment increases the unbound serum PHT concentration by depressing the metabolic capacity and alters the total PHT by reducing serum albumin and its affinity to PHT.

A meta-analysis of effects of CYP2C9 and CYP2C19 polymorphisms on phenytoin pharmacokinetic parameters.

Aim: Phenytoin is metabolized through CYP2C9 and CYP2C19. Polymorphisms of CYP2C9 and CYP2C19 may increase plasma concentration and side effects. Materials & methods: Systematic review and meta-analysis were performed to evaluate the effects of CYP2C9 and CYP2C19 polymorphism on pharmacokinetic parameters. PubMed, Science Direct, Cochrane library, and Thai databases were systematically searched. Results: Eight observational studies, comprising a total of 633 patients were included. Michaelis-Menten constant was significantly higher in the polymorphism of CYP2C9IM/CYP2C19EM and CYP2C9IM/CYP2C19IM groups as compared with the control groups (CYP2C9EM/CYP2C19EM) at 2.16 and 1.55 mg/l (p < 0.00001, p < 0.0001). The maximum rate of action was significantly lower in the control groups as compared with the polymorphism of CYP2C9IM/CYP2C19EM and CYP2C9IM/CYP2C19IM groups at 3.10 and 3.53 mg/kg/day (p = 0.00001, <0.0001). Conclusion: The dosage regimen for patients in the CYP2C9IM group to achieve phenytoin therapeutic levels was 2.1-3.4 mg/kg/day.

A pharmacokinetic simulation study to assess the performance of a sparse blood sampling approach to quantify early drug exposure.

Estimating early exposure of drugs used for the treatment of emergent conditions is challenging because blood sampling to measure concentrations is difficult. The objective of this work was to evaluate predictive performance of two early concentrations and prior pharmacokinetic (PK) information for estimating early exposure. The performance of a modeling approach was compared with a noncompartmental analysis (NCA). A simulation study was performed using literature-based models for phenytoin (PHT), levetiracetam (LEV), and valproic acid (VPA). These models were used to simulate rich concentration-time profiles from 0 to 2 h. Profiles without residual unexplained variability (RUV) were used to obtain the true partial area under the curve (pAUC) until 2 h after the start of drug infusion. From the profiles with the RUV, two concentrations per patient were randomly selected. These concentrations were analyzed under a population model to obtain individual population PK (PopPK) pAUCs. The NCA pAUCs were calculated using a linear trapezoidal rule. Percent prediction errors (PPEs) for the PopPK pAUCs and NCA pAUCs were calculated. A PPE within ±20% of the true value was considered a success and the number of successes was obtained for 100 simulated datasets. For PHT, LEV, and VPA, respectively, the median value of the success statistics obtained using the PopPK approach of 81%, 92%, and 88% were significantly higher than the 72%, 80%, and 67% using the NCA approach (p < 0.05; Mann-Whitney U test). This study provides a means by which early exposure can be estimated with good precision from two concentrations and a PopPK approach. It can be applied to other settings in which early exposures are of interest.

Participation of Monocarboxylate Transporter 8, But Not P-Glycoprotein, in Carrier-Mediated Cerebral Elimination of Phenytoin across the Blood-Brain Barrier.

PURPOSE: In this study, we investigated in detail the transport of phenytoin across the blood-brain barrier (BBB) to identify the transporter(s) involved in BBB-mediated phenytoin efflux from the brain. METHODS: We evaluated the brain-to-blood efflux transport of phenytoin in vivo by determining the brain efflux index (BEI) and uptake in brain slices. We additionally conducted brain perfusion experiments and BEI studies in P-glycoprotein (P-gp)-deficient mice. In addition, we determined the mRNA expression of monocarboxylate transporter (MCT) in isolated brain capillaries and performed phenytoin uptake studies in MCT-expressing Xenopus oocytes. RESULTS: [14C]Phenytoin brain efflux was time-dependent with a half-life of 17 min in rats and 31 min in mice. Intracerebral pre-administration of unlabeled phenytoin attenuated BBB-mediated phenytoin efflux transport, suggesting carrier-mediated phenytoin efflux transport across the BBB. Pre-administration of P-gp substrates in rats and genetic P-gp deficiency in mice did not affect BBB-mediated phenytoin efflux transport. In contrast, pre-administration of MCT8 inhibitors attenuated phenytoin efflux. Moreover, rat MCT8-expressing Xenopus oocytes exhibited [14C]phenytoin uptake, which was inhibited by unlabeled phenytoin. CONCLUSION: Our data suggest that MCT8 at the BBB participates in phenytoin efflux transport from the brain to the blood.

Pharmacodynamic and pharmacokinetic interactions of hydroalcoholic leaf extract of Centella asiatica with valproate and phenytoin in experimental models of epilepsy in rats.

ETHNOPHARMACOLOGICAL RELEVANCE: Centella asiatica (CA) is commonly used herbal medicine for treatment of epilepsy. CA has CYP2C9, CYP2D6 and CYP3A4 enzymes inhibition property and used as an adjuvant therapy with conventional antiepileptic drugs (AEDs). That may be responsible for herb-drug interaction. AIM OF THE STUDY: The present study was planned to evaluate interactions profile of hydroalcoholic extract Centella asiatica (HECA) with antiepileptic drugs in experimental models of epilepsy in rats. MATERIALS AND METHODS: Wistar rats (175-200 g) were used. In the pharmacodynamic interaction study, seizures were induced using pentylenetetrazole (PTZ) (60 mg/kg, i.p.) and maximal electroshock seizure (MES) (70 mA for 0.2 s). The therapeutic and sub-therapeutic doses of valproate (VPA) and phenytoin (PHT) were co-administrated with HECA in PTZ and MES model of seizures respectively. Behavioural parameters were assessed using elevated plus maze test and passive avoidance paradigm. Rat brain oxidative stress parameters were also assessed. In the pharmacokinetic interaction study, the serum levels of the VPA and PHT were estimated at different time intervals by HPLC and pharmacokinetic parameters were analyzed by WinNonlin software. RESULTS: The VPA and PHT produced complete protection against seizures in their therapeutic doses but not with sub-therapeutic doses. However, co-administration of HECA with a sub-therapeutic dose of VPA and PHT enhanced the protection of seizures and significantly (p < 0.001) attenuated the seizure induced oxidative stress and cognitive impairment. It also significantly increased (p < 0.001) serum levels of VPA and PHT. The alterations in pharmacokinetic parameters (maximum serum concentration, area under the curve, clearance) of AEDs were also found with co-administration of HECA. CONCLUSION: The results suggested that co-administration of HECA could improve the therapeutic efficacy of VPA and PHT. But, alteration in pharmacokinetic parameters revel that needs critical medical supervision to avoid any toxic reactions.

Silymarin as a flavonoid-type P-glycoprotein inhibitor with impact on the pharmacokinetics of carbamazepine, oxcarbazepine and phenytoin in rats.

P-glycoprotein (P-gp) is an efflux transporter involved in drug-resistant epilepsy and some flavonoids have been targeted as effective P-gp inhibitors. Herein, we assessed the impact of silymarin on the pharmacokinetics of three antiepileptic drugs (AEDs) in rats. Animals were pretreated with silymarin, verapamil (positive control) or vehicle (negative control) 1 h before AEDs administration (carbamazepine (25 mg/kg), oxcarbazepine (OXC) (50 mg/kg), or phenytoin (100 mg/kg)). Multiple blood samples were collected after AED dosing, and a non-compartmental analysis was performed. An independent study was also conducted to investigate the effects of silymarin on the OXC plasma-to-brain distribution. Silymarin altered the pharmacokinetics of OXC, increasing its peak plasma concentration by 50% and its extent of systemic exposure by 41%, which had also impact on brain drug concentrations. These findings support that the co-administration of silymarin and OXC should continue to be explored as a strategy to reverse the pharmacoresistance in epilepsy.

Early Exposure of Fosphenytoin, Levetiracetam, and Valproic Acid After High-Dose Intravenous Administration in Young Children With Benzodiazepine-Refractory Status Epilepticus.

Fosphenytoin (FOS) and its active form, phenytoin (PHT), levetiracetam (LEV), and valproic acid (VPA) are commonly used second-line treatments of status epilepticus. However, limited information is available regarding LEV and VPA concentrations following high intravenous doses, particularly in young children. The Established Status Epilepticus Treatment Trial, a blinded, comparative effectiveness study of FOS, LEV, and VPA for benzodiazepine-refractory status epilepticus provided an opportunity to investigate early drug concentrations. Patients aged ≥2 years who continued to seizure despite receiving adequate doses of benzodiazepines were randomly assigned to FOS, LEV, or VPA infused over 10 minutes. A sparse blood-sampling approach was used, with up to 2 samples collected per patient within 2 hours following drug administration. The objective of this work was to report early drug exposure of PHT, LEV, and VPA and plasma protein binding of PHT and VPA. Twenty-seven children with median (interquartile range) age of 4 (2.5-6.5) years were enrolled. The total plasma concentrations ranged from 69 to 151.3 µg/mL for LEV, 11.3 to 26.7 µg/mL for PHT and 126 to 223 µg/mL for VPA. Free fraction ranged from 4% to 19% for PHT and 17% to 51% for VPA. This is the first report in young children of LEV concentrations with convulsive status epilepticus as well as VPA concentrations after a 40 mg/kg dose. Several challenges limited patient enrollment and blood sampling. Additional studies with a larger sample size are required to evaluate the exposure-response relationships in this emergent condition.

Effect of therapeutic plasma exchange on phenytoin plasma concentration in patients receiving intravenous fosphenytoin therapy.

We report for patients with encephalitis treated with plasma exchange (PE) and fosphenytoin. In patient 1, phenytoin levels decreased on the maintenance dose, and the phenytoin concentration was <10 µg/mL on day 12 of administration. In patient 2, the phenytoin levels was <10 µg/mL on day 4. Increasing the fosphenytoin dose pushed the phenytoin level into therapeutic range. There were no differences between the areas under the concentration-time curve of phenytoin with and without PE. We previously reported a decline in phenytoin levels after prolonged use of fosphenytoin. Therefore, dose adjustment of fosphenytoin in patients undergoing PE may be unnecessary.

Comparisons of Four Protein-Binding Models Characterizing the Pharmacokinetics of Unbound Phenytoin in Adult Patients Using Non-Linear Mixed-Effects Modeling.

BACKGROUND AND OBJECTIVE: Phenytoin is extensively protein bound with a narrow therapeutic range. The unbound phenytoin is pharmacologically active, but total concentrations are routinely measured in clinical practice. The relationship between free and total phenytoin has been described by various binding models with inconsistent findings. Systematic comparison of these binding models in a single experimental setting is warranted to determine the optimal binding behaviors. METHODS: Non-linear mixed-effects modeling was conducted on retrospectively collected data (n = 37 adults receiving oral or intravenous phenytoin) using a stochastic approximation expectation-maximization algorithm in MonolixSuite-2019R2. The optimal base structural model was initially developed and utilized to compare four binding models: Winter-Tozer, linear binding, non-linear single-binding site, and non-linear multiple-binding site. Each binding model was subjected to error and covariate modeling. The final model was evaluated using relative standard errors (RSEs), goodness-of-fit plots, visual predictive check, and bootstrapping. RESULTS: A one-compartment, first-order absorption, Michaelis-Menten elimination, and linear protein-binding model best described the population pharmacokinetics of free phenytoin at typical clinical concentrations. The non-linear single-binding-site model also adequately described phenytoin binding but generated larger RSEs. The non-linear multiple-binding-site model performed the worst, with no identified covariates. The optimal linear binding model suggested a relatively high binding capacity using a single albumin site. Covariate modeling indicated a positive relationship between albumin concentration and the binding proportionality constant. CONCLUSIONS: The linear binding model best described the population pharmacokinetics of unbound phenytoin in adult subjects and may be used to improve the prediction of free phenytoin concentrations.

Crown Ether Nanovesicles (Crownsomes) Repositioned Phenytoin for Healing of Corneal Ulcers.

Drug repositioning is an important drug development strategy as it saves the time and efforts exerted in drug discovery. Since reepithelization of the cornea is a critical problem, we envisioned that the anticonvulsant phenytoin sodium can promote reepithelization of corneal ulcers as it was repurposed for skin wound healing. Herein, our aim is to develop novel crown ether-based nanovesicles "Crownsomes" of phenytoin sodium for ocular delivery with minimal drug-induced irritation and enhanced efficacy owing to "host-guest" properties of crown ethers. Crownsomes were successfully fabricated using span-60 and 18-crown-6 and their size, morphology, polydispersity index, ζ potential, drug loading efficiency, conductivity, and drug release were characterized. Crownsomes exhibited favorable properties such as formation of spherical nanovesicles of 280 ± 18 nm and -26.10 ± 1.21 mV surface charges. Crownsomes depicted a high entrapment efficiency (77 ± 5%) with enhanced and controlled-release pattern of phenytoin sodium. The optimum crownsomes formulation ameliorated ex vivo corneal drug permeability (1.78-fold than drug suspension) through the corneal calcium extraction ability of 18-crown-6. In vivo study was conducted utilizing an alkali-induced corneal injury rabbit model. Clinical and histopathological examination confirmed that crownsomes exhibited better biocompatibility and minimal irritation due to complex formation and drug shielding. Further, they enhanced corneal healing, indicating their effectiveness as a novel drug delivery system for ocular diseases.

Predicted values for human total clearance of a variety of typical compounds with differently humanized-liver mouse plasma data.

Prediction of human pharmacokinetics is important in the preclinical stage. Values for total clearance of compounds from plasma should be one of the most important pharmacokinetic parameters for predictions. Although several physiological and empirical methods including single-species allometry for prediction of values for human clearance of compounds using humanized-liver mice have been reported, further improvement of prediction accuracies would be still expected. To optimize these approaches, we proposed methods for unbound intrinsic clearance in virtually 100% humanized-liver mouse by incorporating unbound plasma fractions of compounds in differently humanized-liver mice. Comparisons of prediction accuracies of values for human clearance of 15 model compounds were performed among our current physiological and previously reported models and single-species allometry using humanized-liver mice. Incorporation of the actual unbound plasma fractions of compounds and correction of residual mice hepatocyte in humanized-liver mice showed comparable prediction accuracy to that by single-species allometry. After exclusion of 3 compounds with large species differences in values of clearance and unbound plasma fractions between mice and humans out of 15 compounds, prediction accuracies were improved in the methods investigated. The previously and present reported physiological methods could show the good prediction accuracy of values for clearance of drugs from plasma.

An update on CYP2C9 polymorphisms and phenytoin metabolism: implications for adverse effects.

Introduction Phenytoin is a frequently used drug treatment for epilepsy. Genetic polymorphisms in the metabolism of phenytoin, particularly CYP2C9, are strongly associated with increased plasma concentrations and can result in toxicity. Human leukocyte antigen (HLA) alleles are well-known genetic predictors of certain antiepileptic drug-associated severe cutaneous adverse reactions (SCAR), including Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). Recent pharmacogenomic studies show genetic polymorphisms in CYP2C9, as well as HLA alleles, are significantly associated with phenytoin-related SCAR. Areas covered Updated pharmacogenomic information of CYP2C9 variants and HLA alleles involved in phenytoin-associated cutaneous adverse drug reactions (cADRs) are discussed in this article. Expert opinion CYP2C9*3 has been identified as the most significant genetic variant associated with increased phenytoin concentrations and adverse events. Recent pharmacogenomic findings reveal that CYP2C9*3 and HLA alleles, i.e. HLA-B*15:02, HLA-B*13:01, and HLA-B*51:01, are important genetic variants in the occurrence of phenytoin-induced cADRs or SCAR. A phenotype- and population-specific multigene panel can be used before prescribing to predict phenytoin-induced cADRs and further guide optimal dose selection.

Localized Disruption of Blood Albumin-Phenytoin Binding Using Transcranial Focused Ultrasound.

Plasma protein binding (PPB) plays an important role in drug pharmacokinetics, particularly for central nervous system drugs, as PPB affects the blood concentration of unbound drug available to cross the blood-brain barrier (BBB). We report the non-invasive, spatially specific disruption of PPB to phenytoin, an anti-epileptic drug with high affinity to albumin, using 250-kHz focused ultrasound (FUS) delivered in a pulsed manner (55-ms tone burst duration, 4-Hz pulse repetitions). Equilibrium dialysis performed on sonicated phosphate-buffered saline solution containing phenytoin and bovine serum albumin revealed a 27.7% elevation in the unbound phenytoin concentration compared with an unsonicated control. Sonication of a unilateral brain hemisphere in rats (n = 10) after intraperitoneal phenytoin injection revealed increased parenchymal phenytoin uptake compared with the unsonicated hemisphere, without evidence of temperature change or BBB disruption. These findings illustrate the use of FUS as a novel technique for spatially selective disruption of PPB, which may be applied to a wide range of drug-plasma protein interactions.

Estudio del índice nivel/dosis de la fenitoína en pacientes epilépticos voluntarios de Mérida / Study of the level/dose index of phenytoin in volunteer epileptic patients from Mérida

INTRODUCCIÓN La fenitoína es usada con mucha frecuencia en nuestro medio, por lo que se requiere hacer estudios de monitorización terapéutica, que contribuya a minimizar los efectos adversos y optimizar la terapia farmacológica. En ese contexto, nuestro objetivo ha sido determinar el índice nivel/dosis de la fenitoína en pacientes epilépticos voluntarios de Mérida. MÉTODOS Se realizó un estudio descriptivo, observacional y por reclutamiento consecutivo concurrente, conformado por 30 pacientes voluntarios con diagnóstico de epilepsia. Las muestras de suero se obtuvieron en niveles mínimos de pacientes que estaban en tratamiento con fenitoína durante 1 mes. Los niveles del fármaco se cuantificaron por el método de Inmunoensayo de enzima donante clonada en el equipo Indiko Thermo Scientific. RESULTADOS El índice nivel/dosis fue de 1,4 y 1,6, la concentración plasmática de 4,8mg/l y 8,0mg/l, la capacidad metabólica de 388,4 y 462,9mg/día, respectivamente en mujeres y hombres. Mientras que el nivel de la concentración plasmática en el estado estacionario fue de 6,5mg/l y 5,5mg/l, la dosis de carga máxima de 237,3mg y de 395,6mg, respectivamente en mujeres y hombres con epilepsia de la ciudad de Mérida. CONCLUSIONES Nuestros resultados sugieren que se debe individualizar la dosis en base al índice nivel/dosis de cada paciente, ya que no se puede extrapolar para todos los pacientes con epilepsia, debido a diversos factores como al fenotipo metabólico y al uso de fármacos inductores e inhibidores enzimáticos.

INTRODUCTION Phenytoin is used very frequently in our environment, so it is necessary to do studies of therapeutic monitoring, which helps to minimize adverse drug reaction and optimize pharmacological therapy. In this context, our objective was to determine the level/dose index of phenytoin in volunteer epileptic patients from Mérida. METHODS A descriptive, observational and consecutive concurrent recruitment study was carried out, consisting of 30 volunteer patients with a diagnosis of epilepsy. The serum samples were obtained in minimum levels from patients who were in treatment with phenytoin for 1 month. The levels of the drug were quantified by the method of donor enzyme immunoassay cloned in the Indiko Thermo Scientific equipment. RESULTS The level/dose index was 1,4 and 1,6, the plasma concentration of 4,8mg/l and 8,0mg/l, the metabolic capacity of 388,4 and 462,9mg/day, respectively in women and men. While the level of plasma concentration at steady state was 6,5mg/l and 5,5mg/l, the maximum loading dose of 237,3mg and 395,6mg, respectively in women and men with epilepsy of the city of Mérida. CONCLUSIONS Our results suggest that the dose should be individualized based on the level/dose index of each patient, since it can not be extrapolated for all patients with epilepsy, due to various factors such as the metabolic phenotype and the use of enzyme-inducing drugs and inhibitors.

Associations of CYP2C9 and CYP2C19 Pharmacogenetic Variation with Phenytoin-Induced Cutaneous Adverse Drug Reactions.

The role of cytochrome P450 (CYP)2C9 and CYP2C19 genetic variation in risk for phenytoin-induced cutaneous adverse drug events is not well understood independently of the human leukocyte antigen B (HLA-B)*15:02 risk allele. In the multi-ethnic resource for Genetic Epidemiology Research on Adult Health and Aging (GERA) cohort, we identified 382 participants who filled a phenytoin prescription between 2005 and 2017. These participants included 21 people (5%) who self-identified as Asian, 18 (5%) as black, 29 (8%) as white Hispanic, and 308 (81%) as white non-Hispanic. We identified 264 (69%) CYP2C9*1/*1, 77 (20%) CYP2C9*1/*2, and 29 (8%) CYP2C9*1/*3. We also determined CYP2C19 genotypes, including 112 with the increased activity CYP2C19*17 allele. Using electronic clinical notes, we identified 32 participants (8%) with phenytoin-induced cutaneous adverse events recorded within 100 days of first phenytoin dispensing. Adjusting for age, sex, daily dose, and race/ethnicity, participants with CYP2C9*1/*3 or CYP2C9*2/*2 genotypes were more likely to develop cutaneous adverse events compared with CYP2C9*1/*1 participants (odds ratio 4.47; 95% confidence interval 1.64-11.69; P < 0.01). Among participants with low-intermediate and poor CYP2C9 metabolizer genotypes, eight (22%) who also had extensive and rapid CYP2C19 metabolizer genotypes experienced cutaneous adverse events, compared with none of those who also had intermediate CYP2C19 metabolizer genotypes (P = 0.17). Genetic variation reducing CYP2C9 metabolic activity may increase risk for phenytoin-induced cutaneous adverse events in the absence of the HLA-B*15:02 risk allele.

Efficacy, Tolerability and Serum Phenytoin Levels after Intravenous Fosphenytoin Loading Dose in Children with Status Epilepticus.

OBJECTIVE: To evaluate the efficacy and tolerability of intravenous fosphenytoin in children with status epilepticus, and resulting serum total phenytoin levels. METHODS: In this prospective study, 51 children aged less than 18 years received intravenous loading dose of fosphenytoin (18-20 mg/kg). Serum total phenytoin levels were estimated at 90 -100 minutes. Outcomes studied were (i) seizure control and local and/or systemic adverse effects in next 24 hours and (ii) phenytoin levels and its correlation with dose received, seizure control and adverse effects. RESULTS: The actual dose of fosphenytoin received varied from 15.1 to 25 mg/kg. Seizures were controlled in 45 (88%) children and, two required additional dose of 10 mg/kg. None of the children showed any local or systemic adverse effects. Serum total phenytoin levels were in the therapeutic range (10-20 µg/mL) in 12 (23.5%), sub-therapeutic in 16 (31.3%) and supra-therapeutic in 25 (49%) children. There was weak correlation of the phenytoin levels with dose of fosphenytoin received, seizure control, or adverse effects. CONCLUSIONS: Intravenous fosphenytoin loading dose of 20 mg/kg is effective in controlling seizures in 88% of children with status epilepticus, with a good safety profile. Seizure control and adverse effects appear to be independent of serum total phenytoin levels achieved.

Three-ply biocompatible pH-responsive nanocarriers based on HNT sandwiched by chitosan/pectin layers for controlled release of phenytoin sodium.

Today, efficient straightforward biocompatible drug carriers have revoluted advanced drug delivery systems. The study aims to investigate the modification of halloysite nanotubes by chitosan (CTS) and pectin (PCN) for forming a new pH-sensitive bionanocomposites via Layer-by-Layer method. The main objective of this study is to improve loading efficiency and control release of phenytoin sodium (PHT) prepared in various pH. The formation of nanocomposite was confirmed through using FTIR, zeta-potential, TG, SEM, XRD, and UV spectroscopy analyses. Based on the obtained results, HNT/CTS/PCN nanocomposite prepared with the molar ratio of 2:1:2 had the best loading capacity (34.6 mg/g) compared with pure HNT (18.3 mg/g). In-vitro studies showed that prepared bionanocomposites had a low release of PHT in the simulated gastric fluid while having a more controlled release in the simulated intestinal fluid. Because of the loading efficiency and controlled release profile, the composites exhibited great potential for the controlled drug delivery of PHT.