Intravenous phenytoin: clinical and pharmacokinetic aspects

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.

Phenytoin Pharmacokinetics During Venoarterial Extracorporeal Membrane Oxygenation and Plasma Exchange

Currently, there is minimal guidance to antiepileptic dose adjustment for a patient requiring either venoarterial (VA) extracorporeal membrane oxygenation (ECMO) or plasma exchange (PLEX) therapy, and to our knowledge, there are rare guidances for a patient requiring both. Given the dangers with non-therapeutic concentrations of phenytoin, it is critical for the intensive care unit (ICU) practitioner to understand how the pharmacokinetic parameters of phenytoin change in critically ill patients requiring extracorporeal support. This case study presents a 41-year-old female transferred to the cardiovascular ICU requiring VA ECMO and PLEX for the treatment of systemic lupus erythematosus (SLE)-induced catastrophic antiphospholipid syndrome (CAPS). Free phenytoin concentrations were measured to assess the removal of phenytoin. There was no significant decrease in the free phenytoin concentrations post-PLEX and while on ECMO. Free phenytoin concentrations are not influenced in the setting of PLEX and while on ECMO.

Antiepileptic Drug Therapy for Status Epilepticus

Status epilepticus (SE) is one of the most serious neurologic emergencies. SE is a condition that encompasses a broad range of semiologic subtypes and heterogeneous etiologies. The treatment of SE primarily involves the management of the underlying etiology and the use of antiepileptic drug therapy to rapidly terminate seizure activities. The Drug Committee of the Korean Epilepsy Society performed a review of existing guidelines and literature with the aim of providing practical recommendations for antiepileptic drug therapy. This article is one of a series of review articles by the Drug Committee and it summarizes staged antiepileptic drug therapy for SE. While evidence of good quality supports the use of benzodiazepines as the first-line treatment of SE, such evidence informing the administration of second- or third-line treatments is lacking; hence, the recommendations presented herein concerning the treatment of established and refractory SE are based on case series and expert opinions. The choice of antiepileptic drugs in each stage should consider the characteristics and circumstances of each patient, as well as their estimated benefit and risk to them. In tandem with the antiepileptic drug therapy, careful searching for and treatment of the underlying etiology are required.

A systematic review of rescue analgesic strategies in acute exacerbations of primary trigeminal neuralgia

BACKGROUND

Trigeminal neuralgia (TN) can have a significant impact on wellbeing and quality of life. Limited data exist for treatments that improve TN pain acutely, within 24 h of administration. This systematic review aims to identify effective treatments that acutely relieve TN exacerbations.

METHODS

We searched Medline and Cochrane Central Register of Controlled Trials (CENTRAL) for relevant English language publications. The reference list for all articles was searched for other relevant publications. All studies that satisfied the following PICO criteria were included: (i) Population-adults with acute exacerbation of primary TN symptoms; (ii) Intervention-any medication or intervention with the primary goal of pain relief within 24 h; (iii) Comparator-usual medical care, placebo, sham or active treatment; (iv) Outcome-more than 50% reduction in pain intensity within 24 h of administration.

RESULTS

Of 431 studies, 17 studies were identified that reported immediate results of acute treatment in TN. The evidence suggests that the following interventions may be beneficial: local anaesthetic, mainly lidocaine (ophthalmic, nasal or oral mucosa, trigger point injection, i.v. infusion, nerve block); anticonvulsant, phenytoin or fosphenytoin (i.v. infusion); serotonin agonist, sumatriptan (s.c. injection, nasal). Other referenced interventions with very limited evidence include N-methyl-d-aspartate receptor antagonist (magnesium sulphate infusion) and botulinum toxin (trigger point injection).

CONCLUSIONS

Several treatment options exist that may provide fast and safe relief of TN. Future studies should report on outcomes within 24 h to improve knowledge of the acute analgesic TN treatments.

Status epilepticus in the elderly

Children and the elderly (≥60 years of age) have the highest incidence of status epilepticus (SE). Because of their general health, elderly individuals are much more likely than younger (<60 years of age) persons to have more severe consequences from seizures. The incidence of SE is 15.5/100 000 in the 60-69 age group, 21.5/100 000 in the 70-79 age group and 25.9/100 000 in persons 80 and older. The most common cause in the elderly is acute symptomatic, with stroke and hypoxia the most frequent. The overall mortality of SE is quite high and occurs early, often within the first few days, and is related to the cause, with mortality of more than 80% in persons with anoxia. Although the cause of SE is an important factor in mortality, the aging body and brain may contribute to an unfavorable outcome. Treatment in the elderly is essentially the same as in younger adults with benzodiazepines (lorazepam, diazepam, clonazepam) and longer acting antiseizure drugs (phenytoin, fosphenytoin, valproate, levetiracetam, and lacosamide. At this time there are no evidence-based studies regarding Axis 2 (etiology) and Axis 4 (age). All current interventions for SE involve antiseizure drugs that were developed for treatment of chronic epilepsy. Treatments should be developed that are more specific for the various etiologies and involve drugs that work on the underlying cause of the SE.

Evaluation of phenytoin serum levels following a loading dose in the acute hospital setting

PURPOSE

Due to the complex pharmacokinetic profiles of phenytoin (PHT) and fosphenytoin (FOS), achieving sustained, targeted serum PHT levels in the first day of use is challenging.

METHODS

A population based approach was used to analyze total serum PHT (tPHT) level within 2-24h of PHT/FOS loading with or without supplementary maintenance or additional loading doses among PHT-naïve patients in the acute hospital setting. Adequate tPHT serum level was defined as ≥20μg/mL.

RESULTS

Among 494 patients with 545 tPHT serum levels obtained in the first 2-24h after the loading dose (LD), tPHT serum levels of either

CONCLUSION

Close laboratory surveillance and PHT/FOS dose adjustments are recommended to ensure adequate and sustained tPHT serum levels early in treatment. Free serum PHT level is the preferred method of drug monitoring.

Collapse

Key Words

• Fosphenytoin
• Serum phenytoin level
• Status epilepticus

Collapse

MESH Headings

• Adolescent
• Adult
• Aged
• Aged, 80 and over
• Anticonvulsants/blood
• Anticonvulsants/therapeutic use
• Child
• Community Health Planning
• Epilepsy/blood
• Epilepsy/drug therapy
• Female
• Humans
• Male
• Middle Aged
• Phenytoin/blood
• Phenytoin/therapeutic use
• Retrospective Studies
• Statistics as Topic
• Young Adult

Collapse

Grants

• T32 ES007271 NIEHS NIH HHS
• TL1 TR002000 NCATS NIH HHS
• UL1 TR000042 NCATS NIH HHS
• UL1 TR002001 NCATS NIH HHS

Collapse

Affiliation(s)

Olga Selioutski Department of Neurology, Strong Epilepsy Center, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA.
Katherine Grzesik Department of Biostatistics, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA
Olga N Vasilyeva Department of Pharmacy, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA
Ágúst Hilmarsson Landspitali University Hospital, Slettuvegi, Reykjavik, Iceland
A James Fessler Department of Neurology, Strong Epilepsy Center, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA
Lynn Liu Department of Neurology, Strong Epilepsy Center, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA
Robert A Gross Department of Neurology, Strong Epilepsy Center, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA

Collapse

Predictors of Outcome in Children with Status Epilepticus during Resuscitation in Pediatric Emergency Department: A Retrospective Observational Study

Objectives:

To study the clinical profile and predictors of outcome in children with status epilepticus (SE) during resuscitation in pediatric emergency department.

Materials and Methods:

This retrospective study was carried out in a tertiary care teaching hospital. Admission and resuscitation data of children, aged between 1 month and 12 years, treated for SE, between September 2013 and August 2014, were extracted using a standard data collection form. Our SE management protocol had employed a modified pediatric assessment triangle to recognize and treat acute respiratory failure, cardiovascular dysfunction (CD), and subtle SE until all parameters resolved. Continuous positive airway pressure, fluid boluses based on shock etiology, inotropes, and cardiac safe anticonvulsants were the other modifications. Risk factors predicting mortality during resuscitation were analyzed using univariate and penalized logistic regression.

Results:

Among 610 who were enrolled, 582 (95.4%) survived and 28 (4.6%) succumbed. Grunt odds ratio (OR): 3.747 (95% confidence interval [CI]: 1.035−13.560), retractions OR: 2.429 (95% CI: 1.036−5.698), rales OR: 10.145 (95% CI: 4.027−25.560), prolonged capillary refill time OR: 3.352 (95% CI: 1.339−8.388), and shock requiring >60 mL/kg fluids OR: 2.439 (95% CI 1.040−5.721) were associated with 2−3 times rise in mortality. Inappropriate prehospital treatment and CD were the significant predictors of mortality OR: 7.82 (95% CI 2.10−29.06) and 738.71 (95% CI: 97.11−999), respectively. Resolution of CD was associated with improved survival OR: 0.02 (95% CI: 0.003−0.17).

Conclusion:

Appropriate prehospital management and treatment protocol targeting resolution of CD during resuscitation could reduce mortality in children with SE.

Seizures in the critically ill

Critically ill patients with seizures are either admitted to the intensive care unit because of uncontrolled seizures requiring aggressive treatment or are admitted for other reasons and develop seizures secondarily. These patients may have multiorgan failure and severe metabolic and electrolyte disarrangements, and may require complex medication regimens and interventions. Seizures can be seen as a result of an acute systemic illness, a primary neurologic pathology, or a medication side-effect and can present in a wide array of symptoms from convulsive activity, subtle twitching, to lethargy. In this population, untreated isolated seizures can quickly escalate to generalized convulsive status epilepticus or, more frequently, nonconvulsive status epileptics, which is associated with a high morbidity and mortality. Status epilepticus (SE) arises from a failure of inhibitory mechanisms and an enhancement of excitatory pathways causing permanent neuronal injury and other systemic sequelae. Carrying a high 30-day mortality rate, SE can be very difficult to treat in this complex setting, and a portion of these patients will become refractory, requiring narcotics and anesthetic medications. The most significant factor in successfully treating status epilepticus is initiating antiepileptic drugs as soon as possible, thus attentiveness and recognition of this disease are critical.

Investigation of the Crystallization of Phenytoin in Normal Saline

A study was designed to determine if the admixture of phenytoin in normal saline would remain physically stable for a suitable period of time to allow for intravenous infusion. Five phenytoin concentrations (1.0 mg/ml, 2.5 mg/ml, 5.0 mg/ml, 7.5 mg/ml, and 10.0 mg/ml) were prepared in triplicate by adding a sufficient volume of normal saline to the appropriate volume of phenytoin sodium injection to produce a total volume of 100 ml. Aliquots of all solutions were withdrawn at zero, 1, 8, 16, and 24 hours. Solutions were filtered through a 0.22 micron millipore filter and the concentration of phenytoin and pH of each solution was determined. A significant concentration difference was not seen between zero time and 24 hours. The pH of the samples ranged from 9.75 to 11.00. While phenytoin sodium appears to be stable in the concentrations tested when sodium chloride 0.9% is the vehicle, several important factors must be considered and caution must be used if the admixture is administered intravenously.

Pharmacotherapy Overview of Seizure Management in the Adult Emergency Department

Seizures are a common cause of emergency department visits, and approximately 28% of epilepsy patients present to an emergency department annually for treatment. This article will provide an overview of the pharmacotherapeutic management of seizures and anticonvulsant therapy for patients who present to the adult emergency department, including practical information for pharmacists covering or cross-covering this practice area. The benzodiazepines are reviewed as a class, including dosing strategies, pharmacodynamic considerations, and advantages and disadvantages of lorazepam, diazepam, and midazolam. Indications for the use of phenytoin and fosphenytoin will be reviewed, as well as dosing, adverse effects, and cost-effectiveness data. In addition, dosing, administration, pharmacokinetics, and adverse effects of phenobarbital, carbamazepine, and valproate will be discussed. Clinical indications for serum anticonvulsant concentration monitoring and subsequent calculation of loading doses from serum concentrations are reviewed. Since status epilepticus is a life-threatening emergency, its therapeutic management is reviewed, including the use of continuous infusion midazolam, pentobarbital, and propofol. There are many opportunities for clinical pharmacists to collaborate with other members of the health care team to optimize efficacy and minimize adverse effects of anticonvulsant agents in the emergency department setting.

Cardiovascular adverse effects of phenytoin

Phenytoin is an established drug in the treatment of acute repetitive seizures and status epilepticus. One of its main advantages over benzodiazepines is the less sedative effect. However, the possibility of cardiovascular adverse effects with the intravenous use of phenytoin cause a reluctance to its usage, and this has lead to a search for safer anticonvulsant drugs. In this study, we aimed to review the studies which evaluated the safety of phenytoin with respect to cardiovascular adverse effects. The original clinical trials and case reports listed in PUBMED in English language between the years of 1946-2014 were evaluated. As the key words, "phenytoin, diphenylhydantoin, epilepsy, seizure, cardiac toxicity, asystole, arrhythmia, respiratory arrest, hypotension, death" were used. Thirty-two clinical trials and ten case reports were identified. In the case reports, a rapid infusion rate (>50 mg/min) of phenytoin appeared as the major cause of increased mortality. In contrast, no serious cardiovascular adverse effects leading to death were met in the clinical trials which applied the recommended infusion rate and dosages. An infusion rate of 50 mg/min was reported to be safe for young patients. For old patients and patients with a cardiovascular co-morbidity, a slower infusion rate was recommended with a careful follow-up of heart rhythm and blood pressure. No cardiovascular adverse effect was reported in oral phenytoin overdoses except one case with a very high serum phenytoin level and hypoalbuminemia. Phenytoin is an effective and well tolerated drug in the treatment of epilepsy. Intravenous phenytoin is safe when given at recommended infusion rates and doses.

Intravenous and Intramuscular Formulations of Antiseizure Drugs in the Treatment of Epilepsy

Intravenous and intramuscular antiseizure drugs (ASDs) are essential in the treatment of clinical seizure emergencies as well as in replacement therapy when oral administration is not possible. The parenteral formulations provide rapid delivery and complete (intravenous) or nearly complete (intramuscular) bioavailability. Controlled administration of the ASD is feasible with intravenous but not intramuscular formulations. This article reviews the literature and discusses the chemistry, pharmacology, pharmacokinetics, and clinical use of currently available intravenous and intramuscular ASD formulations as well as the development of new formulations and agents. Intravenous or intramuscular formulations of lorazepam, diazepam, midazolam, and clonazepam are typically used as the initial treatment agents in seizure emergencies. Recent studies also support the use of intramuscular midazolam as easier than the intravenous delivery of lorazepam in the pre-hospital setting. However, benzodiazepines may be associated with hypotension and respiratory depression. Although loading with intravenous phenytoin was an early approach to treatment, it is associated with cardiac arrhythmias, hypotension, and tissue injury at the injection site. This has made it less favored than fosphenytoin, a water-soluble, phosphorylated phenytoin molecule. Other drugs being used for acute seizure emergencies are intravenous formulations of valproic acid, levetiracetam, and lacosamide. However, the comparative effectiveness of these for status epilepticus (SE) has not been evaluated adequately. Consequently, guidelines for the medical management of SE continue to recommend lorazepam followed by fosphenytoin, or phenytoin if fosphenytoin is not available. Intravenous solutions for carbamazepine, lamotrigine, and topiramate have been developed but remain investigational. The current ASDs were not developed for use in emergency situations, but were adapted from ASDs approved for chronic oral use. New approaches for bringing drugs from experimental models to treatment of human SE are needed.

Canine status epilepticus treated with fosphenytoin: A proof of principle study

OBJECTIVES

There are a limited number of marketed intravenous antiepileptic drugs (AEDs) available to treat status epilepticus (SE). All were first developed for chronic therapy of epilepsy, not specifically for SE. Epilepsy and canine SE (CSE) occur naturally in dogs, with prevalence, presentation, and percentage of refractory cases similar to human epilepsy. The objective of this study was to determine if CSE treated with fosphenytoin (FOS) results in a similar responder rate as for people.

METHODS

A randomized clinical trial was performed for dogs with CSE. Dogs who presented during a seizure or who had additional seizures after enrolling received intravenous (i.v.) benzodiazepine (BZD) followed immediately by intravenous infusion of 15 mg/kg phenytoin equivalent (PE) of fosphenytoin (FOS) or saline placebo (PBO). If seizures continued, additional AEDs were administered per the standard of care for veterinary patients. Total and unbound plasma phenytoin (PHT) concentrations were measured.

RESULTS

Consent was obtained for 50 dogs with CSE. Thirty-one had additional motor seizures and were randomized to the study intervention (22 FOS and 9 PBO). There was a statistically significant difference in the 12 h responder rate, with 63% in the FOS group versus 22% in the placebo group (p = 0.043) having no further seizures. The unbound PHT concentrations at 30 and 60 min were within the therapeutic concentrations for people (1-2 μg/ml) with the exception of one dog. There was mild vomiting in 36% of the FOS group (7/22) within 20 min of FOS administration and none of the placebo group (0/9) (p = 0.064).

SIGNIFICANCE

This proof of concept study provides the first evidence that FOS is tolerated and effective in canine SE at PHT concentrations clinically relevant for human SE. Furthermore, naturally occurring CSE can be utilized as a translational platform for future studies of novel SE compounds.

Use of IV fosphenytoin pharmacokinetics to determine the loading dose for a clinical trial of canine status epilepticus

OBJECTIVE

Canine status epilepticus (CSE) has potential as a translational platform to evaluate the safety and efficacy of novel compounds and inform human status epilepticus trials. The aim of this study was to determine the intravenous dose of fosphenytoin (FOS) needed for dogs in a CSE clinical trial to attain phenytoin (PHT) concentrations similar to those used for human status epilepticus and monitor PHT concentrations.

METHODS

Four healthy dogs were used to characterize PHT pharmacokinetics. Each received either 15 mg/kg or 25 mg/kg of PHT equivalent intravenously. Blood samples were collected and FOS (total) and derived PHT (total and unbound) plasma concentrations were measured using high-performance liquid chromatography-mass spectrometry (HPLC-MS). Noncompartmental pharmacokinetics (PK) parameter values were determined and compartmental PK modeling and simulations were used to select the dose for the clinical trial with a target goal of 1-2 μg/ml unbound PHT at 30-60 min postinfusion. Predicted total and unbound PHT concentrations were compared with concentrations in blood collected from dogs treated for CSE in the clinical trial.

RESULTS

Initial estimates suggested that a loading dose of 25 mg/kg would attain unbound concentrations of 1-2 μg/ml; however, this dose produced concentrations above 3-6 μg/ml, which resulted in clinically significant toxicity. A two-compartment model best fit the PHT concentration data with alpha-phase half-life of 2-5 min and elimination half-life of ~5 h. Based on the simulations, a dose of 15 mg/kg was selected and used in the clinical trial and 15 of 16 dogs randomized to the treatment arm had PHT plasma concentrations within the goal range.

SIGNIFICANCE

This study demonstrates that characterization of pharmacokinetics in a small number of dogs is useful in determining dosage regimens designed to attain targeted concentrations in clinical trials. Using this approach, we were able to determine a safe and effective dose of FOS for a clinical trial of CSE.

The relative effectiveness of five antiepileptic drugs in treatment of benzodiazepine-resistant convulsive status epilepticus: a meta-analysis of published studies

PURPOSE

Systematic evaluation of published evidence-base of the efficacy of five antiepileptic drugs - lacosamide, levetiracetam, valproate, phenytoin and phenobarbital - in convulsive benzodiazepine-resistant status epilepticus.

METHODS

Data sources included electronic databases, personal communication, and back tracing of references in pertinent studies. These were prospective and retrospective human studies presenting original data for participants with convulsive benzodiazepine-resistant status epilepticus. Interventions were intravenous lacosamide, levetiracetam, phenobarbital, phenytoin and valproate. Outcome measured is clinically detectable cessation of seizure activity. Level-of-evidence was assessed according to Oxford Centre of Evidence-Based Medicine and The Cochrane Collaboration's Tool for Assessment of Risk. Twenty seven studies (798 cases of convulsive status epilepticus) were identified and 22 included in a meta-analysis. Random-effects analysis of dichotomous outcome of a single group estimate (proportion), with inverse variance weighting, was implemented. Several sources of clinical and methodological heterogeneity were identified.

RESULTS

Efficacy of levetiracetam was 68.5% (95% CI: 56.2-78.7%), phenobarbital 73.6% (95% CI: 58.3-84.8%), phenytoin 50.2% (95% CI: 34.2-66.1%) and valproate 75.7% (95% CI: 63.7-84.8%). Lacosamide studies were excluded from the meta-analysis due to insufficient data.

CONCLUSION

Valproate, levetiracetam and phenobarbital can all be used as first line therapy in benzodiazepine-resistant status epilepticus. The evidence does not support the first-line use of phenytoin. There is not enough evidence to support the routine use of lacosamide. Randomized controlled trials are urgently needed.

Phenytoin loading doses in adult critical care patients: does current practice achieve adequate drug levels?

Phenytoin is regularly employed in the critically ill for prophylaxis against or treatment of seizure disorders. No prior studies have examined current dosing practices in an Australasian intensive care unit (ICU) setting. The aims of this study were to: a) describe the adequacy of contemporary dosing in respect to free and total serum phenytoin concentrations; b) identify factors associated with therapeutic drug concentrations; and c) examine the accuracy of predictive equations that estimate free concentrations in this setting. All patients receiving a loading dose of phenytoin in a tertiary-level ICU were eligible for enrolment; 53 patients were enrolled in the study. Serum samples to determine free and total phenytoin concentrations (measured by high performance liquid chromatography) were then drawn prior to the following dose. Free concentrations below the recommended target (<1 mg/l) were considered as suboptimal. The most common indication for phenytoin loading was traumatic brain injury (49%) and the mean administered dose was 14.5 (3.66) mg/kg. Twenty-six patients (49%) had suboptimal trough free concentrations, although this subgroup was significantly heavier and therefore received a lower per kilogram dose (12.8 [3.1] vs 16.3 [3.4] mg/kg, P=0.001). In multivariate analysis, larger weight adjusted doses (P=0.018), higher albumin concentration (P=0.034) and receiving phenytoin for an indication other than seizure (P=0.035), were associated with a greater likelihood of adequate concentrations. In conclusion, phenytoin dosing remains complex in critically ill patients, although lower per kilogram loading doses are strongly associated with free concentrations below the desired target.

Requirement for cardiac telemetry during intravenous phenytoin infusion: guideline fact or guideline fiction?

Guidelines recommend the use of cardiac telemetry when phenytoin is administered intravenously. Clinical areas where telemetry is available may not always be the most suitable place to monitor and treat these sick patients. We sought to clarify the evidence regarding the need for cardiac telemetry during intravenous infusion of phenytoin.

Review article: phenytoin use and efficacy in the ED

This article reviews the evidence regarding the use of phenytoin in adult and paediatric patients experiencing seizures in the ED in Australasia, including relevant pharmacokinetics, dosage, therapeutic drug monitoring and methods of administration. It summarizes current evidence regarding the use of phenytoin in a number of seizure types commonly seen in ED. A search of Medline, Embase and Cochrane was performed using appropriate keyword and MeSH headings. A loading dose of phenytoin should be given to phenytoin naïve patients for the emergency treatment of seizures; parenteral administration results in therapeutic concentration sooner than oral administration but is associated with more frequent and significant adverse effects. Diluting phenytoin is safe but there is limited evidence regarding adverse effects of diluted phenytoin; a filter is probably not needed. Free phenytoin concentrations correlate best with antiseizure efficacy. Phenytoin is used in the treatment of status epilepticus although evidence here is limited; it may also be given to prevent early post-traumatic seizures. It should not be given to treat or prevent eclamptic or alcohol-related seizures. There is insufficient evidence regarding its use in preventing febrile convulsions, treating or preventing seizures due to space occupying lesions or intracerebral haemorrhage and thrombosis. In conclusion, phenytoin is appropriate for treatment of some seizures seen in the ED; it is associated with significant adverse effects; trials are ongoing regarding the use of other anticonvulsants in the treatment of status epilepticus.

Phenytoin, levetiracetam, and pregabalin in the acute management of refractory status epilepticus in patients with brain tumors

BACKGROUND

There were nearly 700,000 patients in the United States in 2010 living with brain tumor diagnoses. The incidence of seizures in this population is as high as 70% and is historically difficult to control. Approximately 30-40% of brain tumors patients who present with status epilepticus (SE) will not respond to typical therapy consisting of benzodiazepines and phenytoin (PHT), resulting in patients with refractory status epilepticus (RSE). RSE is usually treated with anesthetic doses of propofol or midazolam infusions. This therapy can have significant risk, particularly in patients with cancer.

METHODS

A retrospective chart review was performed on 23 patients with primary or metastatic brain tumors whose SE was treated with intravenous PHT, levetiracetam (LEV), and oral pregabalin (PGB).

RESULTS

In all the patients under study, PHT or LEV was used as first-line therapy. PGB was typically used as third-line treatment. The median daily dose of PGB was 375 mg (usually divided BID or TID), and the median daily dose of LEV 3000 mg (usually divided BID). Cessation of SE was seen in 16/23 (70%) after administration of PHT, LEV, and PGB. SE was aborted, on average, 24 h after addition of the third antiepileptic drug. Only one patient in the responder group required intubation. Mortality rate was zero in the responder group. No adverse reactions to this medication regimen were observed.

CONCLUSION

Our study suggests that the administration of PHT, LEV, and PGB in brain tumor patients with RSE is safe and highly effective.

Treatment of refractory trigeminal neuralgia with intravenous phenytoin

PURPOSE

The case of a patient who was successfully treated with i.v. phenytoin for an acute exacerbation of refractory trigeminal neuralgia (TN) is reported.

SUMMARY

A 77-year-old, 87-kg Caucasian man with a 12-year history of right-sided, classical TN was admitted for an acute exacerbation of TN refractory to pharmacologic treatment with carbamazepine, baclofen, hydrocodone-acetaminophen, tramadol, hydromorphone, and gabapentin. His medical history included atrial fibrillation, peripheral vascular disease, benign prostatic hyperplasia, and chronic ataxia secondary to antibiotic therapy in the 1970s. His outpatient medications included carbamazepine, warfarin, ergocalciferol, and saw palmetto. A 15-mg/kg dose of i.v. phenytoin sodium (1300 mg on the basis of total body weight) was recommended by neurology consultants. Because of potential adverse reactions related to high serum phenytoin concentrations and rapid infusion rates (e.g., hypotension, ataxia, nausea, vomiting, apnea, nystagmus), the patient's age, the baseline presence of atrial fibrillation and ataxia, and the fact that seizures were not being treated, the clinical pharmacist recommended dividing the 1300-mg dose into two 650-mg doses separated by four hours, with each infused at 25 mg/min; this suggestion was accepted. The patient's pain score dropped from a self-rated 12/10 to 2/10 after the first infusion and to 1/10 after completion of the second infusion. The patient's blood pressure and heart rate were monitored via telemetry every five minutes during both infusions. No adverse events were noted.

CONCLUSION

Phenytoin sodium 15 mg/kg i.v. divided into two doses separated by four hours was safe and effective in treating an acute exacerbation of refractory TN.

Canine status epilepticus: a translational platform for human therapeutic trials

Current treatment of human status epilepticus (SE) relies on drugs developed for chronic treatment of epilepsy. Many potent compounds have been discovered in animal models of SE. But they may never be useful for chronic treatment of epilepsy and thus not available for human use. Naturally occurring canine SE may become a translational platform for evaluating these compounds for eventual use in human trials. A pilot study of levetiracetam in canine SE demonstrated a 56% response rate compared to 10% for placebo. Based on these results we have obtained an NIH R-21 to further evaluate canine SE as a translational platform for developing new approaches for treating human SE.

Counseling for driving restrictions in epilepsy and other causes of temporary impairment of consciousness: how are we doing?

In Arizona, other states, and other countries, people who experience a seizure or other transient alteration of consciousness may be legally restricted from driving. Arizona law requires that people with these conditions submit themselves for a medical review, whereas health care providers are not required to report to the authorities. Therefore, counseling people with these medical conditions about driving generally falls to health care providers, who are often not neurologists. Three hundred thirty-five consecutive charts of patients discharged from our Emergency Department were retrospectively reviewed by diagnosis codes associated with altered consciousness. A total of 267 patients met our inclusion criteria, of whom 27 (10.1%) were counseled regarding driving--by the Emergency Department physician and/or consulting neurologist. Although the counseling rate for driving was 10/29 (34.5%) when a neurologist was involved, it was found to be only 17/238 (7.1%) when neurological services were not sought. Patients presenting with seizure were more likely to be counseled than those presenting with other episodes of loss of consciousness. Accurate knowledge of driving laws by health care workers and patients has the potential to minimize liability and improve public safety and quality of care.

Status epilepticus

Status epilepticus (SE) in adults is a state of continuous seizures lasting more than 5 minutes, or rapidly recurrent seizures without regaining consciousness. The overall US and European estimated crude incidence rate of SE ranges from 6.8 to 41/100,000/yr. The etiologies of SE include primary central nervous system pathologies and systemic disorders. The two basic mechanisms involved in the genesis of SE are an excess of excitatory activity and a loss of normal inhibitory neurotransmission. Mortality associated with SE can be as high as 26% for the average adult. Early recognition and treatment are important for improving the chances for a good outcome. The first line of treatment is an intravenous benzodiazepine, with lorazepam being the current preferred agent. All patients with SE who remain with altered awareness 20 to 30 minutes after cessation of clinical seizures should undergo electroencephalographic studies, because up to 20% of patients without clinical evidence of seizures after initial treatment can have nonconvulsive SE.

Epidemiology and outcomes of status epilepticus in the elderly

Status epilepticus (SE) is a serious condition of prolonged or repetitive seizures. The annual incidence (86/100,000) of SE in the elderly who are aged 60 and greater is almost twice that of the general population and is even higher in those who are 70 years and older. Either acute or remote symptomatic stroke causes approximately 60% of SE seen in the elderly. SE is associated with a high mortality in the elderly (38%), with a rate approaching 50% in patients older than 80 years of age. Etiology is a strong determinant of mortality in the elderly: mortality approaches 100% in patients with anoxia and 30% in patients with either metabolic disorders, hemorrhages, tumors, or systemic infections. Mortality is almost three times higher in SE associated with acute ischemic stroke than in stroke alone, indicating synergistic effects. Duration of SE is also a factor in mortality. Treatment should be initiated for any convulsive seizure that lasts at least 10 min or is repetitive. An electroencephalogram (EEG) should be promptly obtained so that a diagnosis can be made without delay. Because older patients have a greater likelihood of nondiagnostic findings on routine EEGs, prolonged EEG recordings and inpatient video-EEG monitoring significantly increase the rate of establishing a definitive diagnosis. Nonconvulsive status epilepticus in the elderly is especially difficult to diagnose and should be evaluated with an EEG. Treatment of SE is complicated by altered pharmacokinetics in the elderly. Initial treatments, usually the administration of an intravenous benzodiazepine, have overall success rates of 55% for overt convulsive SE and 14.9% for subtle SE. For refractory SE, little is gained by using additional standard drugs, and general anesthesia with continuous EEG monitoring is recommended.

[Refractory status epilepticus: diagnosis, therapy, course, and prognosis]

Status epilepticus (SE) is a frequent neurological emergency with an annual incidence of 10-20/100,000 individuals. The overall mortality is about 10-20%. Patients present with long-lasting fits or series of epileptic seizures or extended stupor and coma. Furthermore, patients with SE can suffer from a number of systemic complications possibly also due to side effects of the medical treatment. In the beginning, standardized treatment algorithms can successfully stop most SE. A minority of SE cases prove however to be refractory against the initial treatment and require intensified pharmacologic intervention with nonsedating anticonvulsive drugs or anesthetics. In some partial SE, nonpharmacological approaches (e.g., epilepsy surgery) have been used successfully. This paper reviews scientific evidence of the diagnostic approach, therapeutic options, and course of refractory SE, including nonpharmacological treatment.

Refractory generalised convulsive status epilepticus : a guide to treatment

The patient with status epilepticus has continuous or rapidly repeating seizures. Generalised convulsive status epilepticus (GCSE) is the most common form of the disorder and is a life-threatening condition that requires prompt medical management. Status epilepticus that does not respond to first-line benzodiazepines (lorazepam or diazepam) or to second-line antiepileptic drugs (phenytoin/fosphenytoin, phenobarbital or valproate) is usually considered refractory and requires more aggressive treatment. The optimal treatment of refractory GCSE has not been defined, but patients should be treated in an intensive care unit, as artificial ventilation and haemodynamic support are required. Invasive haemodynamic monitoring is often necessary and EEG monitoring is essential. The drug treatment of refractory GCSE involves general anaesthesia with continuous intravenous anaesthetics given in doses that abolish all clinical and electrographic epileptic activity, often requiring sedation to the point of burst suppression on the EEG. Barbiturate anaesthetics, pentobarbital in the US and thiopental sodium in Europe and Australia, are the most frequently used agents and are highly effective for refractory GCSE both in children and adults. Indeed, they remain the only way to stop seizure activity with certainty in severely refractory cases. Other options are midazolam for adults and children and propofol for adults only.Regardless of the drug selected, intravenous fluids and vasopressors are usually required to treat hypotension. Once seizures have been controlled for 12-24 hours, continuous intravenous therapy should be gradually tapered off if the drug being administered is midazolam or propofol. Gradual tapering is probably not necessary with pentobarbital or thiopental sodium. Continuous EEG monitoring is required during high-dose treatment and while therapy is gradually withdrawn. During withdrawal of anaesthetic therapy, intravenous phenytoin/fosphenytoin or valproate should be continued (these agents having been administered during earlier phases of GCSE) to ensure an adequate baseline of antiepileptic medication so as to prevent the recurrence of status epilepticus. If additional medication is needed, the most appropriate antiepileptic drugs are gabapentin for focal seizures and levetiracetam and topiramate for all seizure types, as these drugs can be started at high doses with a low risk of idiosyncratic reactions. Even with current best practice, mortality in patients who experience refractory GCSE is about 50% and only the minority return to their premorbid functional baseline. Therefore, new treatment options are urgently needed. The ideal new drug for refractory GCSE would be one that has the ability to stop seizures more effectively and safely than current drugs, and that has neuroprotective properties to prevent the brain damage and neurological morbidity caused by GCSE.

Successful Initiation of Combined Therapy with Valproate Sodium Injection and Divalproex Sodium Extended-release Tablets in the Epilepsy Monitoring Unit

PURPOSE

Patients in epilepsy monitoring units (EMUs) often require aggressive initiation or reinitiation of therapy before discharge. We developed a simple dosing scheme using valproate sodium injection (VPA-IV) and divalproex sodium extended-release (VPA-ER) tablets to minimize the time required for initiation of therapy, without increasing the likelihood of seizures and adverse effects.

METHODS

We identified 42 patients in the EMU, naïve to VPA-IV and VPA-ER, for whom one of the discharge AEDs included divalproex sodium. On the day of discharge, patients were loaded with 20 mg/kg VPA-IV at 6 mg/kg/min, followed by approximately 20 mg/kg VPA-ER within 1 h. The discharge daily dose of VPA-ER was identical to the dose given after the IV load. We assessed tolerability and seizure occurrence during infusion, at 1 h, 4 h, and 1 week after discharge.

RESULTS

All patients tolerated the VPA-IV dose followed by VPA-ER. Four patients reported mild nausea, and two patients reported mild dizziness within 4 h. No seizures or significant changes in heart rate or blood pressure occurred within 4 h, and all patients were discharged the same day. All patients denied systemic complaints at 1 week, and five had seizures during the week after discharge. All patients had improved seizure frequencies at the end of the first week.

CONCLUSIONS

VPA-IV is well tolerated and convenient for rapid loading in the EMU. When promptly followed by VPA-ER, seizure control remains excellent.

A comparison of phenytoin-loading techniques in the emergency department

OBJECTIVES

To compare the effectivenesses of three phenytoin-loading techniques.

METHODS

Patients with subtherapeutic phenytoin concentrations who presented within 48 hours of a seizure were randomized to receive either 20 mg/kg of oral phenytoin (PO), divided in maximum doses of 400 mg every two hours, 18 mg/kg of intravenous phenytoin (IVP) at an initial infusion rate of 50 mg/min, or 18 mg/kg (phenytoin equivalents) of intravenous fosphenytoin (IVF) at an initial infusion rate of 150 mg/min.

RESULTS

A total of 45 patients were enrolled: 16 in the PO group, 14 in the IVP group, and 15 in the IVF group. The times required to reach therapeutic drug concentrations were (mean +/- standard deviation [SD]) 5.62 +/- 0.28 hours, 0.24 +/- 0.3 hours, and 0.21 +/- 0.28 hours, respectively. A total of 17, 27, and 32 adverse drug events were observed in the PO, IVP, and IVF groups, respectively, with significantly fewer events in the PO group (p = 0.02, p = 0.01). No significant difference was found between the numbers of necessary adjustments to the infusions in the two IV groups. The average time to safe emergency department discharge was significantly shorter for the IV groups compared with the PO group (p < 0.001).

CONCLUSIONS

Oral loading has fewer adverse drug events than either IV loading method, but its use may be limited when therapeutic concentrations are required quickly. Although IVF loading is faster, from an adverse-drug event perspective, no advantage of IVF over IVP was apparent.

Pharmacokinetics and clinical effects of phenytoin and fosphenytoin in children with severe malaria and status epilepticus

AIMS

Status epilepticus is common in children with severe falciparum malaria and is associated with poor outcome. Phenytoin is often used to control status epilepticus, but its water-soluble prodrug, fosphenytoin, may be more useful as it is easier to administer. We studied the pharmacokinetics and clinical effects of phenytoin and fosphenytoin sodium in children with severe falciparum malaria and status epilepticus.

METHODS

Children received intravenous (i.v.) phenytoin as a 18 mg kg-1 loading dose infused over 20 min followed by a 2.5 mg x kg(-1) 12 hourly maintenance dose infused over 5 min (n = 11), or i.v. fosphenytoin, administered at a rate of 50 mg x min(-1) phenytoin sodium equivalents (PE; n = 16), or intramuscular (i.m.) fosphenytoin as a 18 mg x kg(-1) loading dose followed by 2.5 mg x kg(-1) 12 hourly of PE (n = 11). Concentrations of phenytoin in plasma and cerebrospinal fluid (CSF), frequency of seizures, cardiovascular effects (respiratory rate, blood pressure, trancutaneous oxygen tension and level of consciousness) and middle cerebral artery (MCA) blood flow velocity were monitored.

RESULTS

After all routes of administration, a plasma unbound phenytoin concentration of more than 1 microg x ml(-1) was rapidly (within 5-20 min) attained. Mean (95% confidence interval) steady state free phenytoin concentrations were 2.1 (1.7, 2.4; i.v. phenytoin, n = 6), 1.5 (0.96, 2.1; i.v. fosphenytoin, n = 11) and 1.4 (0.5, 2.4; i.m. fosphenytoin, n = 6), and were not statistically different for the three routes of administration. Median times (range) to peak plasma phenytoin concentrations following the loading dose were 0.08 (0.08-0.17), 0.37 (0.33-0.67) and 0.38 (0.17-2.0) h for i.v. fosphenytoin, i.v. phenytoin and i.m. fosphenytoin, respectively. CSF: plasma phenytoin concentration ratio ranged from 0.12 to 0.53 (median = 0.28, n = 16). Status epilepticus was controlled in only 36% (4/11) following i.v. phenytoin, 44% (7/16), following i.v. fosphenytoin and 64% (7/11) following i.m. fosphenytoin administration, respectively. Cardiovascular parameters and MCA blood flow were not affected by phenytoin administration.

CONCLUSIONS

Phenytoin and fosphenytoin administration at the currently recommended doses achieve plasma unbound phenytoin concentrations within the therapeutic range with few cardiovascular effects. Administration of fosphenytoin i.v. or i.m. offers a practical and convenient alternative to i.v. phenytoin. However, the inadequate control of status epilepticus despite rapid achievement of therapeutic unbound phenytoin concentrations warrants further investigation.

Valproate unbound fraction and distribution volume following rapid infusions in patients with epilepsy

The availability of an intravenous formulation now makes possible rapid administration of valproate (VPA) loading doses, but estimates of key VPA pharmacokinetic parameters in patients have limited the use of this approach. VPA disposition was characterized in 112 epilepsy patients, with or without enzyme inducing comedications, randomized to either 3.0 or 1.5mg/kg/min infusions of valproate sodium injection. Maximum dose was </=15mg/kg per infusion. Total and unbound plasma VPA concentrations were determined from blood samples obtained prior to and for 6h following the infusion. Analyses of covariance assessed the effect of induction, weight, age, gender, albumin, creatinine, and infusion rate on pharmacokinetics. Maximum total and unbound VPA concentrations were 94 and 14mg/l, respectively. Total concentration fell below 50mg/l within 3h in induced and 6h in uninduced patients. VPA unbound fraction decreased from 15% at maximum concentration to 9% at 45mg/l. The mean (S.D.) distribution volume was 0.21 (0.044)l/kg. Induction status, albumin concentration, and infusion rate significantly affected pharmacokinetics. Measurement of unbound VPA may be useful when alterations in binding are suspected. Infusions up to 3mg/kg/min produce predictable total VPA concentrations when induction status and albumin levels are considered.

Progress in clinical neurosciences: Status epilepticus: a critical review of management options

Although generalized tonic-clonic status epilepticus (SE) is frequently seen, an evidence-based approach to management is limited by a lack of randomized clinical studies. Clinical practice, therefore, relies on a combination of expert recommendations, local hospital guidelines and dogma based on individual preference and past successes. This review explores selected and controversial aspects of SE in adults and provides a critical appraisal of currently recommended management strategies.

Pharmacokinetics of phenytoin following intravenous and intramuscular administration of fosphenytoin and phenytoin sodium in the rabbit

The purpose of this study was to evaluate and compare plasma phenytoin concentration versus time profiles following intravenous (i.v.) and intramuscular (i.m.) administration of fosphenytoin sodium with those obtained following administration of standard phenytoin sodium injection in the rabbit. Twenty-four adult New Zealand White rabbits (2.1 +/- 0.4 kg) were anaesthetized with sodium pentobarbitone (30 mg/kg) followed by i.v. or i.m. administration of a single 10 mg/kg phenytoin sodium or fosphenytoin sodium equivalents. Blood samples (1.5 ml) were obtained from a femoral artery cannula predose and at 1, 3, 5, 7, 10, 15, 20, 30, 45, 60, 90, 120, 180, 240 and 300 min after drug administration. Plasma was separated by centrifugation (1000 g; 5 min) and fosphenytoin, total and free plasma phenytoin concentrations were measured using high performance liquid chromatography (HPLC). Following i.v. administration of fosphenytoin sodium plasma phenytoin concentrations were similar to those obtained following i.v. administration of an equivalent dose of phenytoin sodium. Mean peak plasma phenytoin concentrations (Cmax) was 158% higher (P = 0.0277) following i.m. administration of fosphenytoin sodium compared to i.m. administration of phenytoin sodium. The mean area under the plasma total and free phenytoin concentration-time curve from time zero to 120 min (AUC(0-120)) following i.m. administration was also significantly higher (P = 0.0277) in fosphenytoin treated rabbits compared to the phenytoin group. However, there was no significant difference in AUC(0-180) between fosphenytoin and phenytoin-treated rabbits following i.v. administration. There was also no significant difference in the mean times to achieve peak plasma phenytoin concentrations (Tmax) between fosphenytoin and phenytoin-treated rabbits following i.m. administration. Mean plasma albumin concentrations were comparable in both groups of animals. Fosphenytoin was rapidly converted to phenytoin both after i.v. and i.m. administration, with plasma fosphenytoin concentrations declining rapidly to undetectable levels within 10 min following administration via either route. These results confirm the rapid and complete hydrolysis of fosphenytoin to phenytoin in vivo, and the potential of the i.m. route for administration of fosphenytoin delivering phenytoin in clinical settings where i.v. administration may not be feasible.

Add-on phenytoin fails to prevent early seizures after surgery for supratentorial brain tumors: a randomized controlled study

PURPOSE

To determine the potential effectiveness of phenytoin (PHT) in preventing early postoperative seizures in patients undergoing craniotomy for supratentorial brain tumors.

METHODS

Two hundred patients requiring elective craniotomy for supratentorial brain tumors were randomized to two groups of equal size, with a prospective, open-label, controlled design. One group received PHT (18 mg/kg as an intravenous intraoperative load, followed by additional daily doses aimed at maintaining serum PHT concentrations within the 10- to 20-aeg/ml range) for 7 consecutive days. In the other group, PHT was not administered. More than 90% of patients in both groups continued to take preexisting anticonvulsant medication (AEDs) with carbamazepine or phenobarbital throughout the study. The primary efficacy end point was the number of patients remaining free from seizures during the 7-day period after the operation.

RESULTS

Of 100 patients allocated to PHT, 13 experienced seizures during the 7-day observation period, compared with 11 of 100 patients in the placebo group (p > 0.05). Most seizures occurred in the first day after surgery in both groups. There were no differences between groups in the proportion of patients experiencing more than one seizure, but there was a trend for generalized seizures to be more common in PHT-treated patients than in controls (11 vs. five patients, respectively). Status epilepticus occurred in one patient in the PHT group and in two patients in the control group. Of the 13 PHT-treated seizure patients, 11 had serum PHT concentrations within the target range, and only two had concentrations below range on the days their seizures occurred.

CONCLUSIONS

PHT, given at dosages producing serum concentrations within the target range, failed to prevent early postoperative seizures in patients treated with concomitant AEDs. Prophylactic administration of PHT cannot be recommended in these patients.

Status epilepticus in older patients: epidemiology and treatment options

Status epilepticus (SE) is a medical and neurological emergency that has been associated with significant morbidity and mortality. The most widely accepted definition of SE is more than 30 minutes of either continuous seizure activity, or intermittent seizures without full recovery of consciousness between seizures. SE is a major clinical concern in the elderly population, both because it has increased incidence in the elderly compared with the general population, and because of concurrent medical conditions that are more likely to complicate therapy and worsen prognosis in elderly individuals. The incidence of SE in the elderly is almost twice that of the general population at 86 per 100,000 per year. With the anticipated growth of the elderly population, SE is likely to become an increasingly common problem facing clinicians, and an important public health issue. The elderly have the highest SE-associated mortality of any age group at 38%, and the very old elderly (>80 years of age) have a mortality of at least 50%. Acute or remote stroke is the most common aetiology of SE in the elderly. Nonconvulsive SE (NCSE) has a wide range of clinical presentations, ranging from confusion to obtundation. It occurs commonly in elderly patients who are critically ill and in the setting of coma. Electroencephalogram is the only reliable method of diagnosing NCSE. The goal of treatment for SE is rapid cessation of clinical and electrical seizure activity. Most treatment protocols call for the immediate administration of an intravenous benzodiazepine, followed by phenytoin or fosphenytoin. Recent studies suggest that when this initial treatment of SE fails, little is gained by using additional standard drugs. General anaesthetic agents (such as pentobarbital, midazolam, or propofol) should be expeditiously employed, although these treatments have their own potential complications. Intravenous valproic acid is a recent addition to the armamentarium of drugs for the treatment of SE, with a low risk of hypotension, respiratory depression and hypotension, making it a potentially useful drug for the treatment of SE in the elderly. However, further information is needed to establish its role in the overall treatment of SE.

Pharmacologic management of epilepsy in the elderly

OBJECTIVE

To review the epidemiology and pharmacologic management of epilepsy in elderly patients.

DATA SOURCES

Controlled trials, case studies, and review articles identified via MEDLINE using the search terms epilepsy, seizures, elderly, phenobarbital, primidone, phenytoin, carbamazepine, valproic acid, felbamate, gabapentin, lamotrigine, topiramate, tiagabine, levetiracetam, oxcarbazepine, and zonisamide. Recently published standard textbooks on epilepsy were also consulted.

DATA SYNTHESIS

Epilepsy is a common neurologic disorder in the elderly. Cerebrovascular and neurodegenerative diseases are the most common causes of new-onset seizures in these patients. Alterations in protein binding, distribution, elimination, and increased sensitivity to the pharmacodynamic effects of antiepileptic drugs (AEDs) are relatively frequent, and these factors should be assessed at the initiation, and during adjustment, of treatment. Drug-drug interactions are also an important issue in elderly patients, because multiple drug use is common and AEDs are susceptible to many interactions. In addition to understanding age-related changes in the pharmacokinetics and pharmacodynamics of AEDs, clinicians should know the common seizure types in the elderly and the spectrum of AED activity for these seizure types. AEDs with activity against both partial-onset and generalized seizures include felbamate, lamotrigine, levetiracetam, topiramate, valproic acid, and zonisamide. Other AEDs discussed in this review (carbamazepine, gabapentin, phenobarbital, phenytoin, primidone, and tiagabine) are most useful for partial-onset seizures.

CONCLUSION

The provision of safe and effective drug therapy to elderly patients requires an understanding of the unique age-related changes' in the pharmacokinetics and pharmacodynamics of AEDs as well as an appreciation of common seizure types and the drugs that are effective for the specific types seen in the elderly.

[Status epilepticus: pharmacokinetic basis of anticonvulsant treatment in adults]

In status epilepticus, the optimal efficacy of the antiepileptic drugs depends notably on effective, quickly reached and sufficiently lasting cerebral concentrations and the optimal tolerability notably on the lack of excessive storage in the brain and other tissues. So, the best efficacy-tolerability ratio of these drugs is largely determined by their pharmacokinetic properties. A linear kinetics, a not too short distribution half-life, a neither too brief nor too long elimination half-life, a fast and easy crossing of the blood-brain barrier and the lack of long-lasting accumulation in fat tissues are among the main ideal pharmacokinetic properties. Any of the antiepileptic drugs currently used in status epilepticus has all these properties together. An accurate knowledge of the pharmacokinetics is absolutely crucial to rationally decide the route of administration, the loading dose and the maintenance doses. However, pharmacokinetics must only complete, but cannot replace, the clinical experience and judgement, especially because some limitations: kinetic equations are mathematically exact but theoretical; individual kinetics in a given patient is exceptionally known in clinical practice; finally the pharmacokinetics may be significantly modified during a status epilepticus, especially of the generalized convulsive type, due to systemic consequences and complications of the seizures. In the emergency situation of status epilepticus, the correlation between the clinical efficacy and the so-called "therapeutic" plasma levels remains ill defined. The reported values are often very high and their range appears very large. Nevertheless plasma levels are useful, especially for the monitoring of the evolution; they are mandatory for nonlinear-kinetics drugs.

Status epilepticus: an overview of the clinical problem

Status epilepticus has been recognized since antiquity. The terms état de mal and "status epilepticus" are derived from the slang used by epilepsy patients housed in Salpêtrière and Bicêtre hospitals in Paris during the 1800s. The definition of status epilepticus has been evolving, and is still not precise. In 1903-04 it was described as a development of epilepsy in which seizures are so frequent that "coma and exhaustion are continuous between seizures." In 1964 the International League Against Epilepsy adopted the definition "a seizure [that] persists for a sufficient length of time or is repeated frequently enough to produce a fixed and enduring epileptic condition." 30 min has been the most common specified duration of seizures for the diagnosis of status epilepticus, although a duration of 10 or 20 min has been suggested as well. However, a new set of definitions for generalized, convulsive status epilepticus in adults has been proposed and includes an operational definition (specifying a seizure duration of a least 5 min) and a mechanistic definition. In the future, laboratory tests will provide the means for detecting and defining the critical factors that distinguish a single epileptic seizure from status epilepticus. Recent epidemiological studies suggest status epilepticus occurs in 100,000 to 150,000 people in the US each year, and is associated with substantial morbidity and mortality. Etiology, duration of the seizures, and the patient's age seem to be important determinants of the outcome in status epilepticus.