Serum Phenytoin Research Articles

Development of an HPLC method using relative molar sensitivity for the measurement of blood concentrations of nine pharmaceutical compounds

We developed a reliable high-performance liquid chromatographic analysis method using a relative molar sensitivity (RMS) technique that does not require an authentic, identical reference analyte material to quantify blood serum carbamazepine, phenytoin, voriconazole, lamotrigine, meropenem, mycophenolic acid, linezolid, vancomycin, and caffeine levels for routine blood concentration measurements. Carbamazepine and caffeine were also used as non-analyte reference materials to calculate the RMS of each analyte. The RMS was calculated from the ratio of the slope of the calibration equation (analyte/non-analyte reference material), then used to quantify analytes in control serum samples spiked with carbamazepine, phenytoin, voriconazole, meropenem, mycophenolic acid, linezolid or vancomycin. In addition, the concentrations of these six drugs in control serum samples determined by the proposed RMS method agreed well with that obtained using a conventional method. The proposed RMS method is a promising tool for the clinical determination of nine drugs, given the accuracy, precision, and efficiency of quantifying these analytes.

The Phenytoin Ataxia Enigma Unveiled ''A Case Report''.

Background: Phenytoin (PHT) has been approved for the treatment of epilepsy. It belongs to the category of medications with a limited therapeutic window and requires therapeutic drug monitoring (TDM). PTH has been observed to induce a variety of Adverse drug reactions (ADRs) including ataxia, dystonia, nystagmus, dyskinesia, etc. Phenytoin-induced ataxia is an uncommonly observed ADR of Phenytoin whose reports are extremely limited. Case: Herein, we present a case report of a 16-year-old Asian patient with a past history of epilepsy that was admitted to a tertiary care hospital due to the development of ataxia, giddiness, and vomiting when taking Phenytoin in addition to Oxcarbazepine, Clobazam, and Levetiracetam to treat seizures. On admission, Magnetic resonance imaging (MRI) findings revealed bilateral variable cerebrospinal fluid (CSF) lesions in the parieto-occipital region of the periventricular area (periventricular leukomalacia). Additionally, serum Phenytoin levels were observed to be in the toxic range (40μg/mL) due to which physicians confirmed the ADR to be due to Phenytoin toxicity. Thus, the Phenytoin drug was discontinued in the patient gradually and he was continued on clobazam, oxcarbazepine, and brivaracetam which led to reversal of the ADR in the patient. Conclusion: In this case, ataxia resulted from Phenytoin overdose, as confirmed by MRI and serum tests suggesting that TDM of Phenytoin is essential to prevent ADRs. Given the scarcity of ataxia cases caused by Phenytoin, awareness is lacking within the scientific community. Our aim is to provide insights to promote better monitoring and patient-centered treatment outcomes for epileptic patients.

To Study Perioperative Changes in Plasma Phenytoin Levels in Patients with Brain Tumor Undergoing Craniotomy and Its Correlation with Postoperative Seizures

Abstract Introduction Phenytoin, although commonly used for postoperative seizure prophylaxis, exhibits variable results in mitigating seizure frequency following craniotomy. These discrepancies may be linked to a reduction in plasma phenytoin levels subsequent to the surgical intervention. Aims This prospective study aims to characterize changes in plasma phenytoin levels after craniotomy and their relationship with intraoperative blood loss. Methods Fifty consecutive patients were enrolled in this study after obtaining written informed consent. These patients had either been on oral phenytoin for at least 7 days or had received an intravenous loading dose before undergoing craniotomy. Serum phenytoin levels were measured 24 hours preoperatively, immediately before craniotomy (prior to skin incision), postcraniotomy (after skin closure), and 24 hours postcraniotomy. Additionally, intraoperative blood loss was calculated using a modified Gross formula. Results Immediately following craniotomy, there was a statistically significant mean decline of 28.16% in serum phenytoin levels. Furthermore, the analysis revealed a robust positive correlation between the decrease in phenytoin concentration level and several factors, including blood loss during surgery, the duration of the surgical procedure, intravenous fluids administered during surgery, and the occurrence of postoperative seizures. Conclusion This study underscores the potential utility of routinely measuring perioperative serum phenytoin levels in high-risk patients to prevent postcraniotomy seizures. Moreover, it suggests that patients with substantial intraoperative blood loss may benefit from an additional bolus dose of phenytoin toward the end of the surgical procedure.

Seizure Prophylaxis in Young Patients Following Traumatic Brain Injury.

Phenytoin is one of the commonly used anti.seizure medications in nontraumatic seizures. However, its utility and safety in young patients with traumatic brain injury (TBI) for the prevention of early-onset seizures (EOS) are debatable. We sought to explore the use of phenytoin as a seizure prophylaxis following TBI. We hypothesized that administering phenytoin is not effective in preventing EOS after TBI. This was a retrospective observational study conducted on adult TBI patients. EOS was defined as a witnessed seizure within a week postinjury. Data were compared as phenytoin versus no-phenytoin use, EOS versus no-EOS, and among TBI severity groups. During 1 year, 639 TBI patients were included with a mean age of 32 years; of them, 183 received phenytoin as seizure prophylaxis, and 453 received no prophylaxis medication. EOS was documented in 13 (2.0%) patients who received phenytoin, and none had EOS among the nonphenytoin group. The phenytoin group was more likely to have a higher Marshall Score (P = 0.001), lower Glasgow Coma Scale (GCS) (P = 0.001), EOS (P = 0.001), and higher mortality (P = 0.001). Phenytoin was administrated for 15.2%, 43.2%, and 64.5% of mild, moderate, and severe TBI patients, respectively. EOS and no-EOS groups were comparable for age, gender, mechanism of injury, GCS, Marshall Score, serum phenytoin levels, liver function levels, hospital stay, and mortality. Multivariable logistic regression analysis showed that low serum albumin (odds ratio [OR] 0.81; 95% confidence interval [CI] 0.676.0.962) and toxic phenytoin level (OR 43; 95% CI 2.420.780.7) were independent predictors of EOS. In this study, the prophylactic use of phenytoin in TBI was ineffective in preventing EOS. Large-scale matched studies and well-defined hospital protocols are needed for the proper utility of phenytoin post-TBI.

Measurement uncertainty estimation of free drug concentrations in clinical laboratories using equilibrium dialysis.

Developing procedures based on equilibrium dialysis (ED) that allow measuring the free drug concentration in plasma improves therapeutic drug monitoring (TDM) in those cases where its measurement is justified. However, this procedure requires specific sample preparation and presents different pitfalls, which are not error-free. As withany result provided by a clinical laboratory, this one should be as accurate as possible to allow a correct clinical interpretation. The measurement uncertainty (MU) is a parameter that enables the accuracy of results to be known, and that is mandated by ISO 15189. Herein, this study suggests how the MU for the results of the free drug concentrations in serum could be estimated when an ED isused. A combination of the top-down and bottom-up approaches was used to estimate the MU based on the ISO/TS 20914:2019 and JCGM 100:2008 guidelines, including the concentration of free phenytoin in serum, as an example. Different scenarios were incorporated considering or not asignificant bias related to the primary drawbacks of ED: thenon-specific binding, the volume shift effect and the Gibbs-Donnan effect. The expanded uncertainties estimated ranged between 13.0 and 30.9 %. The highest MU corresponded to the free drug concentrations in serum results when significant biases related to the volume shift and Gibbs-Donnan effects exist. A detailed estimation of MU for free drug concentrations is presented using ED, considering different scenarios. This study could stimulate clinical laboratories to perform MU studies and its application in TDM.

Phenytoin-induced dyskinesia: a case report

BackgroundDyskinesia is a movement disorder categorized by involuntary movement of muscle. Although dyskinesia can be brought on by taking medications, it can also be a symptom of a variety of diseases. Antiepileptic drug-induced involuntary movements have been well researched. Rare reports have been made for dyskinesia, a type of dystonia caused by phenytoin. The mechanism of its occurrence must be succinctly studied.Case presentationA 53-year-old Asian patient taking phenytoin (100 mg twice daily) experienced symptoms of perioral muscle involuntary movement, impaired speech, and generalized tremors and was admitted to the hospital. Brain magnetic resonance imaging showed significant development of encephalomalacia and porencephaly. The serum phenytoin levels were in the toxic range (33 g/ml). These were suggestive of phenytoin-induced dyskinesia. Levetiracetam and clonazepam were initiated, and the patient showed significant improvement in the symptoms.ConclusionThis case presented a substantial reference value for the differential diagnosis and treatment prognosis of phenytoin-induced dyskinesia. The phenytoin-induced dyskinesia in this patient was successfully reversed with prompt identification and treatment. According to the case study’s findings, such people may benefit from periodic therapeutic drug monitoring.

Phenytoin concentration in people with epilepsy: a comparative study in serum and saliva

In clinical practice, therapeutic drug monitoring (TDM) makes it possible to measure the concentration of drugs in serum or saliva, the purpose of which is to reduce adverse effects and optimize pharmacological therapy. The objective was to determine the concentrations of Phenytoin in saliva and serum of people with epilepsy. Cross-sectional, descriptive study with dynamic recruitment of 30 people with epilepsy (n = 30; 17 men, 56.7% and 13 women, 43.3%; mean age 33.9 ± 11.83 years). Serum and saliva samples were collected at trough levels from patients, who were under phenytoin treatment for at least three months. Drug levels were assessed by the Cloned Donor Enzyme Immunoassay method. Phenytoin levels were found in saliva between 0.01 to 3.56 mg/L and in serum between 0.09 to 36.60 mg/L. Pearson’s analysis showed an association between the estimated serum and saliva phenytoin concentrations (R2 0.7026; 95% CI 0.685-0.921), with a significant statistical correlation (p < 0.05). The Bland-Altman test broke concordance, the difference between the two saliva/serum methods is within 95% confidence. It is concluded that there is an association and concordance between the concentrations of phenytoin in serum and saliva, therefore, this technique can be useful in the clinical monitoring of phenytoin.

Fosphenytoin dosing regimen including optimal timing for the measurement of serum phenytoin concentration in pediatric patients

IntroductionWe aimed to evaluate the pediatric fosphenytoin dosing regimen, including optimal timing for the measurement of total serum phenytoin concentration (CPHT). MethodsWe retrospectively investigated pediatric patients with status epilepticus or seizure clusters treated with fosphenytoin between April 2013 and March 2018. Two CPHT measurements were analyzed, one 2–4 h after the loading dose and another before the second dose. Individual pharmacokinetic parameters were estimated using the Bayesian method and were used to simulate CPHT. ResultsThe present study involved 12 pediatric patients; the loading dose of fosphenytoin was 22.1 (17.2–27.2) mg/kg. The CPHT was 13.4 (8.6–18.9) μg/mL 2–4 h after the loading dose. The CPHT estimated from individual pharmacokinetic parameters 12 and 24 h after the loading dose was 9.5 (6.7–14.2) and 5.8 (3.7–10.0) μg/mL, respectively. If fosphenytoin was administered at a loading dose of 22.5 mg/kg and a maintenance dose of 5 or 7.5 mg/kg (administered every 12 h, starting 12 h after the loading dose), then the CPHT on day 8 was estimated to be 5.74 (2.6–15.4) μg/mL at 5 mg/kg and 13.9 (5.7–31.0) μg/mL at 7.5 mg/kg. ConclusionsIn pediatric patients, a maintenance dose of fosphenytoin should be started 12 h after the loading dose, and a maintenance dose of 5–7.5 mg/kg/dose every 12 h may be better than every 24 h. We recommend measuring CPHT at 2 and 12 h after the loading dose to simplify and safely adjust the dosage in clinical practice.

Simultaneous Quantification of 11 Antiseizure Medications and Metabolites in Serum for Therapeutic Drug Monitoring Using High-Performance Liquid Chromatography with Ultraviolet Detection: A Short Communication.

Therapeutic drug monitoring (TDM) of antiseizure medications (ASMs) is widely used to guide therapy, avoid toxicity, and assess patient compliance. Commercial immunologic quantification methods are common practice; however, as they are only applicable to one specific drug and prone to cross-reacting metabolites, their practical applicability is limited. In this article, the authors proposed a high-performance liquid chromatography method using ultraviolet detection (HPLC-UV) for simultaneous quantification of 11 ASMs and active metabolites (carbamazepine, felbamate, lacosamide, lamotrigine, levetiracetam, phenobarbital, phenytoin, primidone, zonisamide, carbamazepine-10,11-epoxide, and licarbazepine) in serum. Chromatographic separation was performed on a Phenomenex Luna PFP(2) (3-µm particle size; 150 × 4.6 mm i.d.) analytical column. The mobile phase comprised phosphate buffer (20 mM; pH 3), acetonitrile (ACN), and methanol using gradient elution. Analyses were conducted at 35°C and a 1.3-mL/min flow rate. The detection wavelength for all analytes was 210 nm. The samples were prepared by protein precipitation using ACN. The HPLC-UV method was validated according to the FDA guidelines and applied to measure patient samples in TDM. Calibration curves showed excellent linearity (r2 > 0.99) and covered the entire reference range for each analyte. Intraday and interday imprecisions and inaccuracies were <10% for all samples. Extensive stability testing showed no significant degradation (<15%), and interference measurements additionally ensured clinical applicability. Furthermore, the sensitivity was comparable with that of previously published HPLC methods using mass spectrometry. The authors developed an HPLC-UV method for the simultaneous quantification of 11 ASMs in the human serum and demonstrated its practical applicability in TDM. The method requires only standard laboratory equipment and simple sample preparation, making TDM available in less specialized laboratories.

Phenytoin-associated movement disorder: A literature review.

Phenytoin (PHT) was first synthesized as a barbiturate derivative and was approved in 1953 by the Food and Drug Administration. This work aimed to review the pathophysiology, epidemiology, clinical presentation, and treatment of PHT-associated movement disorders (MDs). Studies were searched in relevant databases (ScienceDirect, Google Scholar, Excerpta Medica, Latin American and Caribbean Health Sciences Literature, Medline, and Scientific Electronic Library Online) and were selected by two reviewers irrespective of language between 1963 and 2021. Papers of PHT-induced ataxia alone or tremor were excluded. In total, 127 reports with 219 individuals who developed MDs associated with PHT were encountered. MDs found: 126 dyskinesias, 49 myoclonus, 19 dystonia, 14 parkinsonism, 6 tics, 3 stuttering, and 2 restless legs syndrome. The mean age was 35 years (standard deviation [SD]: 23.5) and the predominant sex was male (53.4%). The mean PHT dose when the MD took place was 370.4 mg (SD: 117.5). A serum PHT concentration was reported in 103 cases, ranging from 4 to 110 μg/mL (median: 27.7 μg/mL). No significant relationship was found between PHT dose and age or PHT level. The mean onset time of PHT-associated MD was 23.4 months (SD: 4.4). The mean recovery time after MD management was 3.7 weeks (SD: 1.1). Regarding management, the most common form was PHT withdrawal in 90.4%. 86.3% of the individuals recovered fully. PHT-induced MD was extensively reported in the literature. Only general terms were used in the majority of the reports. The mechanisms underlying the adverse events caused by PHT probably depend on the presence of predisposing factors.

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

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. 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. 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. 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.

Use of Saliva as an Alternative Matrix to Serum/Plasma for Therapeutic Drug Monitoring Using Reverse-Phase HPLC

This study was conducted to examine and verify the use of saliva as an alternative matrix for monitoring phenytoin drug levels in patients with epilepsy. Drug concentrations are measured to evaluate whether a suitable drug level has been achieved to minimize the risk for toxicity, inadequate efficacy, or therapy resistance and compliance issues. Quantitative analysis was performed by using reverse-phase HPLC after sample pretreatment with acetonitrile. Seventy-eight patients who met the inclusion/exclusion criteria were examined in this study. Trough concentrations of both saliva and serum were taken at steady state. Of the 78 patients enrolled, only 11 (14.1%) had normal levels. Twenty-eight patients (35.9%) had subtherapeutic levels, and 39 (50%) had toxic levels. Simultaneously, salivary phenytoin levels were analyzed; only 13 patients (17.3%) had therapeutic levels, 25 patients (33.3%) had subtherapeutic levels, and 37 (49.3%) had toxic levels. Among the study population, most of the patients were aged 31 to 40 years (25.6%) followed by the age group 21 to 30 years (19.2%). The lowest percentage of patients were in the age groups 71 to 80 years and >80 years (1.3%) each. This study found a statistically significant relationship between free serum and salivary phenytoin levels (P < 0.001). A very weak and insignificant correlation was observed between serum/salivary phenytoin levels and sex/age of the study population. The results of the present study support the use of saliva as an alternative to serum/plasma for monitoring phenytoin therapy. The free concentration of a drug represents the freely diffusible drug fraction, which is the therapeutically active form. Accordingly, the free drug concentration correlates to clinical efficacy and drug toxicity better than total concentration.

Intravenous fosphenytoin therapy for rescue of acute trigeminal neuralgia crisis in patients awaiting neurosurgical procedures: A cross-sectional study

Few treatments exist for acute attacks of trigeminal neuralgia. Therefore, this study aimed to investigate the efficacy and safety of an intravenous fosphenytoin therapy protocol in a trigeminal neuralgia crisis. We conducted a single-center, retrospective, observational study of the records of 20 patients with trigeminal neuralgia who received intravenous fosphenytoin therapy (15 mg/mL in normal saline at 50 mg/min for 15 min, total 750 mg) during hospitalization between September 2015 and August 2020. Serum phenytoin concentration was measured 30 min post-infusion. Pain severity was evaluated using a numerical rating scale and was analyzed for statistical significance. The mean age of the patients was 67.5 years (female, 50.0%). The median numerical rating scale score (interquartile range) of pain severity was 2.35 (0–10), 0.65 (0–5), 0.15 (0–1), 2.00 (0–8), and 4.30 (0–10) at 15, 30, and 60 min, and 12 and 24 h, respectively (p < .001); the numerical rating scale score was 10 before treatment. Reduction in pain 24 h following treatment was significant. The mean phenytoin concentration was 12.8 μg/mL 30 min post-treatment. While mild dizziness occurred in four patients, all could walk independently within 60 min. The mean age and weight of patients with mild dizziness were significantly higher and lower, respectively (p < .001), than those of other patients. These results may provide physicians with new insights into the innovative therapeutic option of intravenous fosphenytoin and contribute to advancements in treating acute trigeminal neuralgia crisis.

Utility of monitoring the serum levetiracetam concentration for intraoperative seizure control during awake craniotomy

Awake craniotomy is an established procedure for resecting brain tumors in eloquent lesions, and intraoperative seizure is one of the most important complications. Phenytoin is normally used to control intraoperative seizures. Recently, phenytoin was replaced with levetiracetam at our institution because the latter has fewer side effects. While the phenytoin dose is calibrated in accordance with the serum concentration, there is currently no consensus on a method of monitoring the serum concentration of levetiracetam or the effective concentration range needed to control intraoperative seizures during awake craniotomy. The present study therefore aimed to determine whether monitoring the serum levetiracetam concentration is useful for controlling intraoperative seizures during awake craniotomy. The intraoperative serum concentration of levetiracetam during awake craniotomy was measured in 34 patients and compared with that of phenytoin in 33 patients undergoing the same procedure. The levetiracetam concentration inversely correlated with body surface area (BSA) and estimated glomerular filtration rate (eGFR). Levetiracetam was superior to phenytoin in terms of the correlation between the serum concentration and the dose adjusted for BSA and eGFR (correlation coefficient, 0.49 vs 0.21). Furthermore, the serum levetiracetam concentration in patients with intraoperative seizures was below the 95% confidence interval (CI) of the regression line whereas the serum phenytoin concentration of two patients with seizures was within the 95% CI, indicating that evaluating the serum levetiracetam concentration against the BSA and eGFR-adjusted dosage may be useful in preventing intraoperative seizures during awake craniotomy by allowing prediction of the seizure risk and enabling more accurate dosage calibration.

Phenytoin induced Chorea: commonly used antiepileptic drug causing a rare movement disorder

Background: Phenytoin, a commonly prescribed antiepileptic drug, causes side effects like ataxia, tremor, hirsutism, gum hyperplasia, insomnia, confusion, headache and vertigo when used for longer duration. However, chorea is a rarely reported side effect of phenytoin and is completely reversible on stopping treatment. Case presentation: A twenty-one-year-old Indian male patient, who had generalized epilepsy and had been on sodium valproate for 2 years, presented with acute onset chorea four days after starting phenytoin sodium. He had normal serum phenytoin levels. A thorough evaluation was done, which suggested phenytoin as a possible cause of chorea. Phenytoin was withdrawn, resulting in a dramatic subsiding of chorea. A rechallenge with the drug resulted in reappearance of choreiform movements. These disappeared again after drug withdrawal, implicating phenytoin as the possible etiological agent for chorea. Conclusion: Phenytoin rarely induces involuntary movements as an adverse effect. During phenytoin therapy, if a patient develops involuntary movements, phenytoin toxicity should be suspected even with normal drug levels. This is important as drug withdrawal leads to complete symptomatic improvement thereby avoiding extensive workup for other secondary causes.

Influenza immunization does not predominantly alter levels of phenytoin, and cytochrome P-450 enzymes in epileptic patients receiving phenytoin monotherapy

ObjectiveThe study aims to test the effect of influenza vaccination on phenytoin, CYP2C9, and IFNγ levels in epileptic patients receiving phenytoin monotherapy MethodsThirty-one epileptic patients receiving stable-dose phenytoin monotherapy were enrolled onto the study. Serum concentrations of phenytoin, CYP2C9, and IFNγ were compared before and after influenza immunization. The participants were given 0.5 mL of quadrivalent influenza vaccine types A and B subvirion. Blood samples were drawn at baseline, and days 3, 7, 14 post-immunization. The outcomes were levels of phenytoin, CYP2C9, IFNγ, and the incidence of adverse events. ResultsNo significant changes in serum phenytoin, IFNγ, and CYP2C9 levels between baseline and days 3, 7, and 14 after immunization were found. The mean levels of phenytoin, IFNγ, and CYP2C9, respectively, were 11.94 ± 7.43, 1.14 ± 0.98, and 47.69 ± 37.53 pg/mL (baseline); 12.15 ± 6.57, 2.13 ± 3.41, and 49.44 ± 39.83 pg/mL (day 3); 12.19 ± 7.69, 1.15 ± 0.94, and 49.48 ± 33.83 pg/mL (day 7); 12.79 ± 7.94, 2.15 ± 3.11, and 53.65 ± 40.91 pg/mL (day 14). The incidence of vaccine-related adverse events, which were generally mild and resolved without clinical consequences, was 58.1 %. No seizure or changes in seizure frequency were observed during the study. One patient experienced dizziness and ataxia which were symptoms attributed to phenytoin toxicity (34.57 μg/mL) by day 14. ConclusionsInfluenza vaccine has no significant effect on the serum phenytoin and CYP2C9 levels in epileptic patients receiving chronic phenytoin monotherapy. The administration of influenza vaccine to epileptic patients receiving phenytoin monotherapy appears to be safe. Therefore, it is not necessary to routinely measure the serum phenytoin level after influenza immunization.

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

To evaluate the efficacy and tolerability of intravenous fosphenytoin in children with status epilepticus, and resulting serum total phenytoin levels. 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. 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. 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.

CYP2C9 polymorphisms are associated with phenytoin toxicity in South-Indian epileptic patients

Background and Aims: The contribution of CYP2C9 in phenytoin metabolism is generally modest, but it increases with increasing serum phenytoin concentration. In the current study, we sought to study the association of CYP2C9*2 and CYP2C9*3 polymorphism with clinical and biochemical phenytoin toxicity in epileptic patients presenting to a tertiary care hospital in South-India. Methods: In total, 50 patients on phenytoin therapy and clinically diagnosed with phenytoin toxicity in neurology outpatient department/casualty/intensive care unit and medicine wards were considered as cases. A total of 50 patients on phenytoin therapy without any evidence of toxicity were considered as controls. CYP2C9*2 (exon-3) and CYP2C9*3 (exon-7) gene polymorphisms were studied using the allele specific PCR method. Results: Out of 100 patients, CYP2C9*2 polymorphism was seen in 8 (8%) patients in which 6 (12%) were cases and 2 (4%) were controls. CYP2C9*3 polymorphism was seen in 23 (23%) patients out of which 17 (34%) were cases and 6 (12%) were controls. Mean serum phenytoin level in cases was 24.23 ± 1.3 μg/ml, whereas in controls, it was 17.10 ± 0.6 μg/ml and the difference was statistically significant with P value Conclusion: Our findings conclude that the presence of CYP2C9*2 and CYP2C9*3 polymorphisms are associated with increased serum phenytoin levels and increased risk of clinical toxicity with phenytoin.

Population Pharmacokinetic Analysis of Phenytoin After Intravenous Administration of Fosphenytoin in Adult and Elderly Epileptic Patients.

Fosphenytoin, the diphosphate ester salt of phenytoin, is widely used to treat status epilepticus. The aim of this study was to develop a population pharmacokinetic (PPK) model to describe serum phenytoin concentrations after the intravenous administration of fosphenytoin in adult and elderly epileptic patients. Patient backgrounds, laboratory tests, and prescribed drugs were retrospectively collected from electronic medical records. Patients who received fosphenytoin were enrolled. The PPK analysis was performed using NONMEM 7.3.0 with the first-order conditional estimation method with interaction. Age, sex, laboratory tests, and coadministered drugs were selected as candidates for covariates. Significance levels for forward inclusion and backward elimination were set at 0.05 and 0.01, respectively. The study protocol was approved by the Fukuoka Tokushukai Ethics Committee. A total of 340 serum phenytoin concentrations from 200 patients treated with fosphenytoin were available. The median age and body weight of the population were 71 years and 53.4 kg, respectively. A linear 1-compartment model with the conversion rate of fosphenytoin to phenytoin clearly described the pharmacokinetics of phenytoin after the intravenous administration of fosphenytoin. Age was detected as a covariate of clearance (CL): CL (L/h) = 1.99 × (body weight/53.4) × (age/71). Goodness-of-fit plots revealed the high-predictive performance of the final PPK model, and systematic deviations were not observed. The final model was validated by a prediction-corrected visual predictive check and bootstrap analysis. We herein developed a PPK model to describe phenytoin concentrations after the intravenous administration of fosphenytoin. Age was identified as a significant covariate for CL.

Prophylactic Use of Antiepileptic Drug (Phenytoin) in Preventing Early Postoperative Seizure in Patients with Chronic Subdural Hematoma: A Randomized Control Trial

Abstract Introduction Antiepileptic drug (AED) therapy has been used prophylactically in various centers in patients with chronic subdural hematoma (CSDH) after surgical evacuation, although the benefit is unclear. Materials and Methods In this randomized controlled trial, patients with CSDH undergoing burr hole drainage were enrolled into two groups—one which received prophylactic phenytoin and the other without the drug use. Their clinical presentation, imaging findings and postoperative complications were analyzed. Primary objective of the study was to assess the efficacy of phenytoin in the reduction of early postoperative seizure. Results A total of 54 patients were enrolled in the study and randomized into two groups. Twenty-seven patients were assigned into the phenytoin group while another 27 patients to the “no phenytoin” group. Analysis of all patients in the no phenytoin group and those in the phenytoin group with therapeutic serum phenytoin levels were done. The incidence of postoperative seizure was 5.7%; and all patients who had seizures were in the no phenytoin group. This, however, was not statistically significant (p = 0.262). Two out of 25 patients on phenytoin (8%) developed adverse drug reactions. Conclusion Incidence of postoperative seizure in patients undergoing burr hole drainage for CSDH was low. Routine prophylactic use of AED, did not reduce seizure in early postoperative period.