Neuropharmacology and drug interactions in clinical practice

Antiepileptic drug treatment: outcomes and adherence

The goal in treating patients with epilepsy is a cost-effective approach to the elimination of seizures or a reduction in their number and frequency while avoiding drug interactions and side effects, so as to achieve the best possible quality of life. Among the desirable outcomes are an enhanced understanding of epilepsy by patients, caregivers, and society, and a lessening of the psychosocial risks of this disease. Patients fail to achieve their goals and outcomes when they fail to adhere to the drug regimen or when a less-than-adequate drug regimen is prescribed. To help improve adherence, once- or twice-daily formulations should be used. New antiepileptic drugs (AEDs) increase the possibility of effective treatment for a patient who initially fails therapy. Working together, patients and clinicians can maximize the effectiveness of AED therapy and the potential for achieving desired goals and outcomes.

Comparison of topiramate concentrations in plasma and serum by fluorescence polarization immunoassay

Topiramate has been recently licensed as an antiepileptic drug. A fluorescence polarization immunoassay (FPIA), the Innofluor, has been developed to determine topiramate in heparinized plasma. Since therapeutic drug monitoring laboratories may not have control over collection of the samples submitted to them, it is important for analytical methods to be robust and able to cope with any specimen. The effect of different anticoagulants on the topiramate FPIA assay was investigated by collecting blood from 50 patients with epilepsy being maintained on a range of topiramate doses as part of their therapy. After venesection the blood was divided among four tubes: plain, heparinized, EDTA, and fluoride/oxalate. Erythrocytes were separated by centrifugation and supernatant fluid frozen to await duplicate assay by FPIA. Results were compared by means of Altman and Bland difference plots which indicated that there was no significant difference between values obtained with heparinized plasma and the other fluids. It was concluded that the Innofluor assay is robust and gives similar results when blood samples are collected into any of the specified anticoagulants.

Metabolism and excretion of mood stabilizers and new anticonvulsants

1. The mood stabilizers lithium, carbamazepine (CBZ), and valproate (VPA), have differing pharmacokinetics, structures, mechanisms of action, efficacy spectra, and adverse effects. Lithium has a low therapeutic index and is renally excreted and hence has renally-mediated but not hepatically-mediated drug-drug interactions. 2. CBZ has multiple problematic drug-drug interactions due to its low therapeutic index, metabolism primarily by a single isoform (CYP3A3/4), active epoxide metabolite, susceptibility to CYP3A3/4 or epoxide hydrolase inhibitors, and ability to induce drug metabolism (via both cytochrome P450 oxidation and conjugation). In contrast, VPA has less prominent neurotoxicity and three principal metabolic pathways, rendering it less susceptible to toxicity due to inhibition of its metabolism. However, VPA can increase plasma concentrations of some drugs by inhibiting metabolism and increase free fractions of certain medications by displacing them from plasma proteins. 3. Older anticonvulsants such as phenobarbital and phenytoin induce hepatic metabolism, may produce toxicity due to inhibition of their metabolism, and have not gained general acceptance in the treatment of primary psychiatric disorders. 4. The newer anticonvulsants felbamate, lamotrigine, topiramate, and tiagabine have different hepatically-mediated drug-drug interactions, while the renally excreted gabapentin lacks hepatic drug-drug interactions but may have reduced bioavailability at higher doses. 5. Investigational anticonvulsants such as oxcarbazepine, vigabatrin, and zonisamide appear to have improved pharmacokinetic profiles compared to older agents. 6. Thus, several of the newer anticonvulsants lack the problematic drug-drug interactions seen with older agents, and some may even (based on their mechanisms of action and preliminary preclinical and clinical data) ultimately prove to have novel psychotropic effects.

Monotherapy versus polytherapy in epilepsy: a framework for patient management

The long-standing debate between proponents of monotherapy and those of polytherapy for treatment of epilepsy has been rekindled by the recent development of several new antiepileptic drugs. The likelihood of improved seizure control on polytherapy must be weighed against the risk of increased side effects, complex drug interactions and cost. Providing maximal seizure control while avoiding overtreatment is a challenge which requires an ongoing critical evaluation of each patient's management. This review provides a framework for decision-making by considering issues affecting the choice between monotherapy and polytherapy in five clinical situations: 1) newly diagnosed epilepsy; 2) seizures on monotherapy; 3) seizures controlled on polytherapy; 4) not controlled on polytherapy; 5) change in medical condition.

Children with focal sharp waves: clinical and genetic aspects

PURPOSE

To investigate the spectrum of clinical manifestations in children with benign focal sharp waves in the EEG to gain further insight into the genetic background of clinical and EEG symptomatology in a family study.

METHODS

All 147 children (134 with seizures, 13 without) met the following inclusion criteria: (a) at least one EEG with focal sharp waves characteristic of benign partial epilepsies, and (b) at least 1 sibling investigated by EEG. The families were questioned orally or in writing regarding the occurrence of seizures. Patients' records were evaluated by a standardized scheme.

RESULTS

The following types of seizures occurred: febrile convulsions (FC), afebrile generalized tonic-clonic seizures (GTCS), simple and (rarely) complex partial seizures; and rolandic seizures in the strict sense. Neonatal seizures were overrepresented (6%); there were no indications of lesional causes. FC occurred in 38 children (26%). As compared with unselected cases of FC, complex symptoms were overrepresented. Family data suggested a maternal preponderance in the transmission of FC liability. Affected relatives of FC probands manifested FC more often than did relatives of probands without FC. Families of 32 patients with typical rolandic seizures (24% of the 134 probands with seizures) showed no aggregation of rolandic epilepsy, but did show variable seizure types. In the entire sample, EEG investigations showed focal sharp waves in 11% of siblings aged 2-10 years. No relation existed between clinical symptomatology and sharp wave findings in siblings. In 66% of probands, the EEG disclosed generalized genetic patterns. Siblings with generalized spike-waves (sw) and/or theta rhythm had focal sharp waves more often than those without sw and/or theta rhythm.

CONCLUSIONS

The phenotypic expression of the genetic anomaly underlying focal sharp waves shows considerable variability. The clinical and EEG findings are in agreement with a multifactorial pathogenesis of epilepsies with "benign" focal epileptiform sharp waves.

Pharmacokinetics and interaction profile of topiramate: review and comparison with other newer antiepileptic drugs

Standard antiepileptic drugs (AEDs) have a number of pharmacokinetic shortcomings, and AEDs with more favorable profiles would be preferred. The pharmacokinetics and interaction profile of the recently developed AED topiramate (TPM), is reviewed and compared with those of other newer AEDs including lamotrigine (LTG), gabapentin (GBP), vigabatrin (VGB), and oxcarbazepine (OCBZ). Although none of these agents meets all of the criteria of the "ideal" AED from the pharmacokinetic standpoint, a number of these drugs, including TPM, have desirable properties that distinguish them from the older AEDs and should contribute to their clinical utility.

Rational polypharmacy

The medical treatment of seizure disorders is a complex process, requiring extensive interaction and co-operation between physician and patient. The physician must have an accurate diagnosis of the patient's illness and a comprehensive understanding of seizures and seizure disorders. The physician must consider specific individual characteristics of the patient, especially those that will influence the choice of medical therapy, and the interrelationship between the patient's lifestyle and the seizure disorder must be appreciated to maintain an optimal quality of life. Finally, the physician must have a thorough understanding of the pharmacology of antiepileptic drugs (AEDs) and experience with their therapeutic applications. It is important for patients to be fully involved in the treatment of their illness. Each patient should be informed about their disorder, should be involved in all therapeutic plans and strategies, and should be a responsible and active participant in treatment.