Usefulness of blood levels of antiepileptic drugs

Multiple anti-epileptic drug use in children with epilepsy in Mulago hospital, Uganda: a cross sectional study

BACKGROUND

Seizures in up to one third of children with epilepsy may not be controlled by the first anti-epileptic drug (AED). In this study, we describe multiple AED usage in children attending a referral clinic in Uganda, the factors associated with multiple AED use and seizure control in affected patients.

METHODS

One hundred thirty nine patients attending Mulago hospital paediatric neurology clinic with epilepsy and who had been on AEDs for ≥6 months were consecutively enrolled from July to December 2013 to reach the calculated sample size. With consent, the history and physical examination were repeated and the neurophysiologic and imaging features obtained from records. Venous blood was also drawn to determine AED drug levels. We determined the proportion of children on multiple AEDs and performed regression analyses to determine factors independently associated with multiple AED use.

RESULTS

Forty five out of 139 (32.4 %) children; 46.7 % female, median age 6 (IQR = 3-9) years were on multiple AEDs. The most common combination was sodium valproate and carbamazepine. We found that 59.7 % of children had sub-therapeutic drug levels including 42.2 % of those on multi-therapy. Sub-optimal seizure control (adjusted odds ratio [OR(a)] 3.93, 95 % CI 1.66-9.31, p = 0.002) and presence of focal neurological deficits (OR(a) 3.86, 95 % CI 1.31-11.48, p = 0.014) were independently associated with multiple AED use but not age of seizure onset, duration of epilepsy symptoms, seizure type or history of status epilepticus.

CONCLUSION

One third of children with epilepsy in Mulago receive multiple AEDs. Multiple AED use is most frequent in symptomatic focal epilepsies but doses are frequently sub-optimal. There is urgent need to improve clinical monitoring in our patients.

Modern methods for analysis of antiepileptic drugs in the biological fluids for pharmacokinetics, bioequivalence and therapeutic drug monitoring

Epilepsy is a chronic disease occurring in approximately 1.0% of the world's population. About 30% of the epileptic patients treated with availably antiepileptic drugs (AEDs) continue to have seizures and are considered therapy-resistant or refractory patients. The ultimate goal for the use of AEDs is complete cessation of seizures without side effects. Because of a narrow therapeutic index of AEDs, a complete understanding of its clinical pharmacokinetics is essential for understanding of the pharmacodynamics of these drugs. These drug concentrations in biological fluids serve as surrogate markers and can be used to guide or target drug dosing. Because early studies demonstrated clinical and/or electroencephalographic correlations with serum concentrations of several AEDs, It has been almost 50 years since clinicians started using plasma concentrations of AEDs to optimize pharmacotherapy in patients with epilepsy. Therefore, validated analytical method for concentrations of AEDs in biological fluids is a necessity in order to explore pharmacokinetics, bioequivalence and TDM in various clinical situations. There are hundreds of published articles on the analysis of specific AEDs by a wide variety of analytical methods in biological samples have appears over the past decade. This review intends to provide an updated, concise overview on the modern method development for monitoring AEDs for pharmacokinetic studies, bioequivalence and therapeutic drug monitoring.

Drug treatment of epilepsy in the century of the ILAE: the second 50 years, 1959-2009

The drug therapy of epilepsy evolved enormously in this 50 year period. Advances in therapeutics included the incorporation of pharmacokinetics into clinical practice, enormous advances in neurochemistry, a trend to antiepileptic drug monotherapy, better drug assessment, better understanding of therapeutic outcomes, and the recognition of the large epilepsy treatment gap in many countries. An unprecedented range of new drugs was introduced in this period. Before 1989, these included carbamazepine, valproate, ethosuximide, and the benzodiazepines. Since 1989, 13 more new drugs have been licensed and marketed and there are others in the pipeline. The International League Against Epilepsy and its leading figures have played an important role in these developments. In this period, too, there has been a rapid expansion in research and development within the pharmaceutical industry and a rise in the value of the antiepileptic drug market. In parallel, governmental regulation of pharmaceuticals has greatly increased. To what extent the overall prognosis of epilepsy has improved as a result of these activities is an interesting and perplexing question.

Value of therapeutic drug level monitoring and unbound (free) levels

Therapeutic drug monitoring (TDM) has declined with newer anti-epileptic drugs (AEDs) having no therapeutic window. Use of unbound (free) fraction has almost completely disappeared. The case reported highlights its importance and offers sound reason for its retention. A 66-year-old Caucasian man with known epilepsy was admitted with vomiting, ataxia and nystagmus presumably due to AED toxicity. Medications included valproate (VPA) 1g bd; phenytoin (PHT) 200mg tds; carbamazepine (CBZ) 400mg mane, 200mg midi, 400mg nocte; levetiracetam (LEV) 250mg bd. Initial AED-TDM revealed total serum levels of CBZ: 27micromol/L; PHT: 37micromol/L; VPA 499micromol/L, therapeutic or subtherapeutic. Free levels were subsequently measured demonstrating CBZ: 8.2micromol/L; PHT: 5micromol/L; VPA 93micromol/L. Consequently, VPA was initially omitted and dosage reduced with cessation of toxicity. AED regimen was greatly simplified and remained efficacious. This case highlights the value of TDM with polypharmacy and suggested AED toxicity. Total AED levels failed to identify the cause, which the unbound, free fraction identified. While total PHT was borderline subtherapeutic (37micromol/L; range: 40-80) the free level was therapeutic (5micromol/L; range: 4-8) and while VPA was therapeutic (VPA 499micromol/L; range: 300-750) the free level was supratherapeutic (93micromol/L; range: 30-75). Acknowledgement of discordance between total and free levels for highly protein-bound AED is highlighted.

Clinical application of the monitoring of anticonvulsant drug levels

The drug treatment of epilepsy poses considerable problems, including the high prevalence and early age of onset of seizures, the relatively poor prognosis in many patients, prolonged polypharmacy, chronic toxicity, and uncertainty of the relative efficacy of individual drugs. The application of recent knowledge of the clinical pharmacology of the major anticonvulsants offers a partial solution to several of these problems. Although there is no therapeutic range for any drug applicable to all patients, a more simple rational and effective approach to treatment is possible with the guidance of serum level monitoring. In new referrals, there is considerable potential for monotherapy, and the avoidance of polypharmacy and chronic toxicity. Reduction in polypharmacy in chronic patients is more difficult, but in many can be achieved with reduction in toxicity, and sometimes improved seizure control. Further studies will provide a clearer picture of the limits to modern anticonvulsant therapy, the relative efficacy of individual drugs, and the potential for improved long-term prognosis.

The logistics of drug monitoring

Although opinions differ to some extent there is increasing belief in the value of monitoring plasma levels for effective therapy with neuropsychiatric drugs, especially with anticonvulsants. Monitoring should not be on a comprehensive and routine basis, but should be selective and discriminating. In these circumstances the expenditure incurred on the laboratory operations involved might work out for Britain at about pounds 5 million per year. This figure should be compared to a total annual expenditure from the prescribing of neuropsychiatric medication amounting to an estimated pounds 40 million per year. The benefits thus achieved in patient care, together with the possible economies in prescribing, could well merit this monitoring exercise. In terms of personnel and administration, the laboratory facilities could be organized on a regional, or on a district general hospital, basis.

The use of oral fluid for therapeutic drug management: clinical and forensic toxicology

One of the underlying tenets of clinical pharmacology is that only free drugs are pharmacologically active. It is thought that only free drugs can cross biological membranes to interact with a given receptor to alter its function, and that drug responses, both efficacious and toxic, are a function of unbound concentrations. The rationale for measuring drugs in oral fluid is that the free fraction of a drug in plasma reaches equilibrium with the drug in saliva. Although reports concerning the appearance of organic solutes in saliva have been in the literature for over 70 years, it has only been in the past 30 years that there has been emphasis on the appearance of drugs. Although many assumptions for drug level monitoring in saliva are made, the primary requisite for salivary monitoring to be useful is a constant or predictable relationship between the drug concentration in saliva and the drug concentration in plasma. Measurement of oral fluid drug levels for the purpose of managing patients and making dosage adjustments may be useful for select drugs or drug classes. However, it does not appear to be useful for the majority of drugs therapeutically monitored. Some work with antipsychotic medications has indicated that although the measurement of drug concentrations themselves may not be useful for dosage adjustment, the ratio of parent drug to metabolite may reflect altered metabolic status due to either pharmacogenetic variation or other clinical conditions. Furthermore, analysis of saliva may provide a cost-effective approach for the screening of large populations.

Therapeutic monitoring of antiepileptic drugs for epilepsy

BACKGROUND

The aim of drug treatment for epilepsy is to prevent seizures without causing adverse effects. To achieve this, drug dosages need to be individualised. Measuring antiepileptic drug levels in body fluids (therapeutic drug monitoring) is frequently used to optimise drug dosage for individual patients.

OBJECTIVES

To review the evidence regarding the effects of therapeutic drug monitoring upon outcomes in epilepsy.

SEARCH STRATEGY

We searched the Cochrane Epilepsy Group Specialised Register (September 2006), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2005, Issue 4), MEDLINE (January 1966 to April 2005) and EMBASE (1974 to May 2005). No language restrictions were imposed. We checked the reference lists of retrieved articles for additional reports of relevant studies.

SELECTION CRITERIA

Randomised controlled trials comparing the outcomes of antiepileptic drug monotherapy guided by therapeutic drug monitoring with drug treatment without the aid of therapeutic drug monitoring.

DATA COLLECTION AND ANALYSIS

We based this review on published aggregate data. The main outcomes measured were the proportions of patients achieving a 12-month remission from seizures, reporting adverse effects, and being withdrawn from the treatment they had been randomised to receive.

MAIN RESULTS

Only one study met the inclusion criteria for the review. In this open study, 180 patients with newly-diagnosed, untreated epilepsy were randomised to treatment with the antiepileptic drug selected by their physician either with or without therapeutic drug serum level monitoring as an aid to dosage adjustments. The antiepileptic drugs used were carbamazepine, valproate, phenytoin, phenobarbital and primidone. A 12-month remission from seizures was achieved by 60% of the patients randomised to therapeutic drug monitoring (intervention group) and by 61% in the control group. A total of 56% in the intervention group and 58% in the control group were seizure free during the last 12 months of follow up. Adverse effects were reported by 48% in the intervention group and 47% of the control group patients. Of those randomised to therapeutic drug monitoring, 62% completed the two-year follow up compared with 67% of the control group.

AUTHORS' CONCLUSIONS

We found no clear evidence to support routine antiepileptic drug serum concentration measurement with the aim of reaching predefined target ranges for the optimisation of treatment of patients with newly-diagnosed epilepsy with antiepileptic drug monotherapy. However, this does not exclude the possible usefulness of therapeutic drug monitoring of specific antiepileptic drugs during polytherapy, in special situations or in selected patients, although evidence is lacking.

Therapeutic drug monitoring of the newer antiepileptic drugs

The aim of the present review is to discuss the potential value of therapeutic drug monitoring (TDM) of the newer antiepileptic drugs (AEDs) felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine, topiramate, vigabatrin, and zonisamide. Studies of the relationship between serum concentrations and clinical efficacy of these drugs are reviewed, and the potential value of TDM of the drugs is discussed based on their pharmacokinetic properties and mode of action. Analytical methods for the determination of the serum concentrations of these drugs are also briefly described. There are only some prospective data on the serum concentration-effect relationships, and few studies have been designed primarily to study these relationships. As TDM is not widely practiced for the newer AEDs, there are no generally accepted target ranges for any of these drugs, and for most a wide range in serum concentration is associated with clinical efficacy. Furthermore, a considerable overlap in drug concentrations related to toxicity and nonresponse is reported. Nevertheless, the current tentative target ranges for felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine (10-hydroxy-carbazepine metabolite), tiagabine, topiramate, vigabatrin, and zonisamide are 125 to 250 micromol/L, 70 to 120 micromol/L, 10 to 60 micromol/L, 35 to 120 micromol/L, 50 to 140 micomol/L, 50 to 250 nmol/L, 15 to 60 micromol/L, 6 to 278 micromol/L, and 45 to 180 micromol/L, respectively. Further systematic studies designed specifically to evaluate concentration-effect relationships of the new AEDs are urgently needed. Although routine monitoring in general cannot be recommended at present, measurements of some of the drugs is undoubtedly of help with individualization of treatment in selected cases in a particular clinical setting.

Simulation of the effect of patient nonadherence on plasma concentrations of carbamazepine from twice-daily extended-release capsules

OBJECTIVE

Carbamazepine (CBZ) effectively treats simple, complex, and secondarily generalized partial seizures. Computer simulations were carried out to investigate the effect of missing or delaying doses of carbamazepine extended-release capsules (CBZ-ERC) on plasma CBZ levels and the optimal dosing strategy to return plasma concentrations to therapeutic levels.

PATIENTS AND METHODS

A one-compartment open model with first-order absorption and elimination was generated from the results of a previous study measuring plasma concentrations following one 400-mg fasting dose of CBZ-ERC. The model was used to simulate plasma CBZ concentrations following multiple doses given every 12 h to hypothetical long-term CBZ-treated patients, with the CBZ elimination half-life set to 13.7 h to account for enzymatic autoinduction. The model was then used to simulate plasma CBZ concentrations when a dose is taken 3, 6, or 9 h late, or when two doses are taken at one time.

RESULTS

Predicted plasma CBZ concentrations in this simulation fell from a trough of approximately 6.4 microg/ml only to 4 microg/ml after 24 h without medication, and only to 2.5 microg/ml after 36 h without medication. Predicted plasma CBZ concentrations in this simulation never rose above 9 microg/ml, indicating that taking missed doses of CBZ-ERC as soon as remembered, up to two missed doses 3 h before taking the next scheduled dose, will not lead to harmful spikes in plasma concentrations of CBZ.

CONCLUSIONS

The simulations suggest that taking a missed dose of CBZ-ERC as soon as remembered, up to two doses at one time, may be the best strategy to return plasma CBZ concentrations to steady-state levels. Since the model used in this study is a simplified model of a highly complex situation, caution should be used when relating these results to clinical practice until trials are conducted in patients.

Anticonvulsant blood levels: historical review with a pediatric focus

Epilepsy is heterogeneous and its treatment is often complicated by variable drug responses. Buchtal et al reported a close correlation between serum phenytoin levels, electroencephalographic findings, and clinical status in 1960. They suggested that physicians adjust dosage to attain a "therapeutic level." The concept was enthusiastically received. "Therapeutic serum levels" were proposed for most anticonvulsant drugs, and by 1975, most authorities believed that pharmacokinetic factors explained individual differences in drug response. However, Froscher found that measuring levels did not improve patient outcome. More recently, Schumacher's double-blind study found no correlation between phenytoin levels and seizure control or adverse effects. Pharmacodynamic variables (differences in drug responsiveness) are more important than pharmacokinetic factors for many drugs, especially receptor-active drugs. Pharmacokinetic variables were studied first, and led to a simplistic model. They are less significant than pharmacodynamic factors in the case of warfarin anticoagulation. Anticonvulsant levels can reveal noncompliance and pharmacokinetic differences. They say nothing about pharmacodynamics. Reports of "subtherapeutic levels" imply a need to increase dosage, but this is not supported by outcome data. We still lack evidence that specific drug levels are a valid intermediate target 40 years after Buchtal's paper. Responses to some anticonvulsants could depend primarily on pharmacokinetic factors, while pharmacodynamic factors could be supreme for others.

Side effects from increased doses of carbamazepine on neuropsychological and posturographic parameters of humans

Patients taking anticonvulsant drugs display a broad spectrum of side-effects. Particularly, in the beginning of treatment and with increasing doses of carbamazepine, side effects such as dizziness, ataxia, drowsiness and reduction of alertness occur, which improve some days after the dose has reached a stable level. Our aim was to find objective parameters for grading these side effects and to differentiate between neurophysiological and neuropsychological side effects of carbamazepine in a clinical situation. Twenty-two patients with trigeminal neuralgia were included for a follow-up study with increasing carbamazepine doses (0 mg to 600 mg). The effect of carbamazepine on postural stability was quantified by posturography. Different neuropsychological tests to study cognitive effects of carbamazepine were performed. The composite equilibrium score showed a significant reduction of postural stability with increasing doses of carbamazepine. In sensory analysis the somatosensory ratio was significantly influenced by increased doses of carbamazepine during the study. Mean reaction time of tonic alertness and physical alertness varied significantly with different doses of carbamazepine. There was a significant influence in patients attention during trail making tests and divided attention tests with increase in carbamazepine. In conclusion our observations show that the rate of change of carbamazepine doses is an important determinant of cognitive and motor functions in the phase of increasing doses.

Antiepileptic drug therapy: clinical laboratory significance

When evaluating a patient who is taking an antiepileptic medication, it is important for the emergency physician to correlate the clinical presentation with the antiepileptic drug level. Therapeutic ranges have been suggested for most antiepileptic medications, but these must be interpreted in light of clinical efficacy and patient tolerance. When considering the efficacy of anti-epileptic medications, it is necessary to consider the patient's unique metabolism, side-effect tolerance, and overall response to therapy. Suggested therapeutic ranges should be the first reference for the emergency physician. The purpose of this report is to discuss the laboratory values of commonly prescribed antiepileptic medications. Therapeutic ranges, side-effects, and common medication interactions are discussed concerning phenytoin, phenobarbital, carbamezapine, and valproic acid.

Pathogenesis of drug-induced gingival overgrowth. A review of studies in the rat model

Drug-induced gingival overgrowth is a side effect associated principally with 3 types of drugs: anticonvulsant (phenytoin), immunosuppressant (cyclosporine A), and various calcium channel blockers (nifedipine, verapamil, diltiazem). In this review, we describe the features of phenytoin-, cyclosporine A- and nifedipine-induced gingival overgrowth in rats and discuss factors influencing the onset and severity of these disorders. There are several features common to the gingival overgrowth induced by these drugs: 1) gingival overgrowth is more conspicuous in the buccal than in the lingual gingiva and less severe in the maxilla than in the mandible; 2) once the blood concentration of the drug reaches a certain level as a result of increasing the dose, the incidence of gingival overgrowth is 100% and its severity is dependent on the blood level, the most severe overgrowth being induced by cyclosporine A; 3) the duration of drug administration for maximal gingival overgrowth to develop is about 40 days; 4) the gingival overgrowth regresses spontaneously after discontinuing the drug; 5) accumulation of dental plaque is not essential for the onset of overgrowth, but plays a role in its severity; and 6) more severe overgrowth is induced in young than in old rats. Furthermore, male rats are more susceptible than females to nifedipine-induced gingival overgrowth. These results suggest that drug-induced gingival overgrowth in rats is dependent on the oral drug dose, blood drug level, age, and sex and that preexisting gingival inflammation is a factor relevant to its severity. Since these factors have also been suggested to be important determinants for human drug-induced gingival overgrowth, the rat model may prove valuable in the future for elucidating the molecular pathogenesis of the disorder.

High doses of carbamazepine for refractory partial epilepsy

Forty-eight patients with partial seizures were analysed during treatment with 1200 mg/d or more of carbamazepine (CBZ). Thirty-three were on monotherapy and fifteen on polytherapy. The other drugs were kept unchanged in the patients on polytherapy. The dose of CBZ was increased if no control was observed and the patient had no side effects. The doses used ranged between 1200 and 1900 mg/day (1200 mg/day, n = 18; 1300 mg/day, n = 1; 1400 mg/day, n = 7; 1600 mg/day, n = 9; 1700 mg/day, n = 4; 1800 mg/day, n = 8; 1900 mg/day, n = 1). Anticonvulsant plasma levels were taken to confirm patient compliance. The average plasma level was 9.6 ug/mL. The period of follow up varied from 3 to 96 months (M = 25.6). Seizure's control was observed in 7 (14.48%) patients taking 1200 mg/day and in 2 (4.16%) patients taking 1400 mg/day of CBZ. Thirty-nine patients did not show any control (81.21%). Ten patients (20.81%) had signs of intoxication. When patients have no improvement with 1400 mg/day, it is difficult to obtain any control despite the use of higher doses of CBZ, which frequently expose the patient to significant side effects.

Circadian carbamazepine toxicity

Owing to marked fluctuations in plasma concentrations, circadian CNS toxicity (maximum in the early afternoon) occurred in a 69-year-old female patient being treated with an instant-release formulation of carbamazepine (CBZ). The neurologic syndrome was reversible after administration of the same daily dose as sustained-release formulation. This case illustrates the importance of correct timing of blood sampling to detect drug-induced toxicity and of use of sustained-release formulations in antiepileptic therapy with CBZ.

[Repetitive serum determinations of anticonvulsants in epileptic patients]

To evaluate complacence in chronic epileptic women we collected weekly 144 blood samples from 38 patients for antiepileptic drugs determination. All the patients were supposed to have uncontrolled seizures using phenobarbital, phenytoin or carbamazepine monotherapeutically. We found that 34% of the blood levels were below the standard normal range. Blood level with great weekly variations were interpreted as inadequate intake by the patient. We conclude that repetitive antiepileptic blood levels determination may elucidate if the patient has drug-resistant seizures or if the patient is not complacent to the drug therapy.

Impairment of psychomotor function at modest plasma concentrations of carbamazepine after administration of the liquid suspension to naive subjects

1. The influence of pharmaceutical formulation on the plasma drug concentration-time curve and the psychomotor responses to 400 mg carbamazepine has been assessed in 12 healthy male volunteers; three formulations and placebo were compared in a randomised, blind, crossover study. 2. The plasma concentration of carbamazepine rose to a maximum of 3-7 mg l-1 by 2-3 h after administration of the liquid suspension. Conventional and controlled release tablet formulations gave lower peaks at about 8 and 32 h, respectively. From 32 h onwards the plasma concentrations from the three formulations were indistinguishable. 3. Significant impairment of psychomotor function was observed after the liquid suspension only; subjective sedation was significant at 1 and 2 h and the critical flicker fusion frequency threshold was lowered at 1-8 h. Digit-symbol substitution, choice reaction time and body sway gave less conclusive evidence of impairment. 4. The results do not support the hypothesis that a psychomotor effect from carbamazepine is a threshold phenomenon with a critical plasma drug concentration at about 8 mg l-1. 5. A second hypothesis that rate of rise of plasma carbamazepine concentration has an important influence on psychomotor effect fits the observations. This interpretation is tentative since the use of a fixed dose of carbamazepine meant that differences due to rate of rise of drug concentration were confounded with differences due to peak height.

Relation of plasma and brain concentrations of the anticonvulsant ameltolide to its pharmacologic effects

Ameltolide, a newly described anticonvulsant, was studied to determine the relation between dose administered, plasma and brain concentrations, and pharmacologic effects. The relation of the N-acetyl metabolite and the OH-N-acetyl metabolite to the dose administered and to the pharmacologic effects was also determined. Ameltolide plasma concentrations in both mice and rats were linearly related to dose administered over the entire dose range from low doses, at which the anticonvulsant effects were noted, to high doses, at which neurologic impairment occurred. The plasma concentrations of the metabolites were not as consistently linearly dose-related in the two species. In rats, the brain concentrations of ameltolide were highly correlated with plasma concentrations and the doses administered. Ameltolide was shown to have a phenytoin (PHT)-like anticonvulsant profile in vitro in the cortical slice preparation. These data confirm the potent anticonvulsant profile of ameltolide and the lack of significant activity of the metabolites.

The effects of the falling therapeutic and subtherapeutic barbiturate blood levels on electrocerebral silence in clinically brain-dead children

In a retrospective study at a large children's hospital, we identified 92 children who had received barbiturates that were simultaneously discontinued at the time they were being evaluated for brain death in the presence of electrocerebral silence and clinical brain death by physical exam. Of these 92 children, 67 had barbiturate levels that were monitored from initial therapeutic or subtherapeutic levels. Repeat EEGs were obtained in 76 patients, and in all electrocerebral silence and clinical brain death (by exam) persisted despite the lower barbiturate levels. The study suggests that therapeutic and subtherapeutic barbiturate levels have no effect on the outcome of children who fulfill the criteria for brain death.

Feeling-of-knowing in temporal lobe epilepsy: monitoring knowledge inaccessible to conscious recall

Feeling-of-Knowing was compared in left temporal, right temporal, and control subjects. Seizure patients, like controls, demonstrate knowledge of information that is not accessible to conscious recall, but they are less accurate in FOK judgements. Furthermore, there are significant differences between seizure patients and controls in the relationship between Feeling-of-Knowing and object level memory scores: (1) Controls spend more time searching memory for inaccessible information that is correctly identified on a later recognition test than they do for information that is incorrectly recognized. (2) Latency of correct recognition decreases as strength of FOK increases among controls, suggesting that controls correctly anticipate the outcome of memory search. These patterns of performance, which are consistent with an efficient memory search termination device, were not observed among seizure patients. The findings suggest that inaccurate Feeling-of-Knowing may play a role in inefficient memory search mechanisms in temporal lobe epilepsy.

Rapid anti-epileptic drug assay

The usefulness of rapid anti-epileptic drug assay in a paediatric neurology clinic was assessed. Compared with a method in which results were not available for seven to 10 days, there was an increased likelihood that levels would be within the target range, particularly for carbamazepine. Increased parental discussion, and therefore involvement with dosage, was possible. Management of children receiving phenytoin was more efficient and non-compliance could be dealt with immediately. When anti-epileptic drug levels are measured, rapid assay, with results available while the patient is still in the clinic, should be a standard facility.

Factors that preclude the successful use of monopharmacy in the medical treatment of patients with epilepsy

A neurologist conducted research efforts for more than 12 years as a step toward the establishment of monotherapy for epilepsy. Of 406 patients with epilepsy, seizures could be controlled for more than one year in 72% and for more than 3 years in 54%. Monotherapy was given to 57% of all the patients with a success rate of 54%. Factors that were found likely to interfere with a reduction in antiepileptic drug therapy to one drug modality included: symptomatic etiology, prolonged duration of illness, low age at onset and secondary generalized epilepsy with a large number of seizures in combination, for generalized epilepsies; symptomatic etiology, prolonged duration of illness, low age at onset, other than occipital lobe origin, complex partial seizure with secondary generalization, temporal lobe epilepsy with associated automatisms, elementary sensorimotor seizure and high frequency of seizures, for partial epilepsies. In addition to these factors relevant to the nature of epilepsies, other factors apparently unrelated to the disease process, e.g., liability of polypharmacy to produce side effects precluding dosage elevation, patient's rejection to reduce drug and the inability of a physician to treat the patient properly for want of information, were also recognized to exist.

The effect of concurrent administration of sodium valproate on serum levels of primidone and its metabolite phenobarbital

The effect of associated therapy on serum primidone (PRM) and derived phenobarbital (PB) concentrations, and on serum concentrations to PRM dose ratios (L/D ratio) were evaluated retrospectively from 100 consecutive PRM and derived PB determinations in 100 chronically treated epileptic patients. PRM administered was significantly (P less than 0.01) correlated with both serum PRM (r = 0.799 approximately 0.933) and derived PB levels (r = 0.545 approximately 0.870) in patients taking PRM. Derived PB L/D ratios and PB/PRM concentration ratios were higher in patients taking PRM in combination with phenytoin (PHT) and/or sodium valproate (VPA). Therefore, serum levels of PRM and derived PB should be monitored closely in patients taking PRM with PHT and/or VPA.

Experimental studies and controlled clinical testing of valproate and vigabatrin

Gamma-aminobutyric acid (GABA) is the most important inhibitory transmitter, quantitatively, in the CNS. Evidence exists that decreased GABAergic neurotransmission may play a role in some forms of epilepsy. Consequently, manipulating the GABA system may be a therapeutic possibility in the treatment of this disease. Inhibition of the major GABA degrading enzyme, GABA-transaminase (GABA-T), seems to be the most promising approach. Currently, 2 antiepileptic drugs, valproate (VPA) and vigabatrin, gamma-vinyl GABA (GVG), are available, which are supposed to inhibit the degradation of GABA. Both drugs cause an increase in the total concentration of GABA in the brain, but to a different extent. VPA produces a moderate elevation, which seems to be the result of a marked increase in the transmitter-related GABA pool, while the pronounced elevation in GABA concentration observed during treatment with GVG seems to be caused mainly by an increase in the non-transmitter-related (glial) GABA pool. In order to investigate this apparently differential influence of VPA and GVG on the GABA system, a number of studies were undertaken in selectively cultured astrocytes and neurons from mice. For both drugs neuronal GABA-T proved far more sensitive with regard to inhibition than glial GABA-T. In order to obtain a more direct measure of a potential GABAergic mechanism of action of VPA and GVG, synaptic release of endogenous GABA was determined after culturing neurons in the presence of clinically relevant concentrations of the drugs. GVG caused a significant increase in GABA release, even at concentrations as low as 25 microM. For VPA only the highest of the investigated concentrations (300 microM) augmented GABA release. It is concluded that the antiepileptic effect of GVG seems to be caused by a direct GABAergic mechanism of action. For VPA an influence on the GABA system may play a role in the antiepileptic effect of the drug. However, the lack of definite data on human brain levels of VPA after chronic treatment, combined with evidence that VPA exhibits a number of other effects that may be relevant for its antiepileptic properties, makes the interpretation of a GABAergic mechanism of action difficult. Controlled clinical trials have been increasingly applied within all areas of medicine. In 1982 a survey of the literature identified 29 studies of antiepileptic drugs, where the design involved randomization, the double-blind principle and a statistical analysis of the results.(ABSTRACT TRUNCATED AT 400 WORDS)

Metamemory in temporal lobe epilepsy: self-monitoring of memory functions

Temporal lobe seizure patients and control subjects participated in an investigation of metamemory. The two-part study explored the individual's perception of memory abilities for both encoding and retrieval. Experiment I addressed self-monitoring of encoding through a study of prediction of memory span. Experiment II explored self-monitoring of retrieval through a study of "Feeling of Knowing." The results indicate that left and right temporal lobe seizure patients tend to overestimate their memory capacities, in comparison with normal controls, and that self-monitoring tends to be less accurate for material (verbal or nonverbal) mediated by side of lesion. The potential impact of inaccurate memory monitoring on the memory dysfunction observed in seizure patients is discussed.

Gist recall in temporal lobe seizure patients (a study of adaptive memory skills)

This study investigates the capacity of lateralized temporal lobe seizure patients to process and retain complex narrative information, to recall the most important elements of verbal material, and to make effective use of mnemonic strategies during a brief study period to improve performance. Compared to normal controls, both left and right temporal lobe samples recall significantly less information on both immediate and post-study trials. In addition seizure patients, particularly left temporal subjects, engaged in fewer active learning strategies and produced more instances of major distortion. However, despite their reduced efficiency in total recall, seizure patients, like control subjects, do tend to remember a higher proportion of important idea units and a smaller proportion of details. The findings are discussed in relation to previous research which documented memory monitoring failures in temporal lobe seizure patients, and in terms of the development of adaptive memory skills to circumvent memory deficits.

If a well-stabilized epileptic patient has a subtherapeutic antiepileptic drug level, should the dose be increased? A randomized prospective study

In an attempt to determine whether the dose of an antiepileptic drug should be increased in epileptic patients who were seizure-free and had subtherapeutic serum levels, 79 patients with idiopathic generalized tonic-clonic seizures treated with monotherapy [phenytoin (PHT) or phenobarbital (PB)] and with a subtherapeutic serum level were prospectively studied. Their last seizure was at least 3 months prior to entry, and no patient had any clinical evidence of toxicity. They were randomized to study arm A (keeping the level in the subtherapeutic range) or study arm B (increasing the dose until the level reached and stayed at the therapeutic range). Over a mean follow-up period of 24 months, there was no significant difference between the two study arms in the occurrence of seizures, but arm B patients had an increased incidence of neurotoxic side effects from the dose increment. These results confirm the clinical impression that it is unnecessary to increase the dose of the antiepileptic drug despite a subtherapeutic serum concentration in a relatively well-stabilized patient, thus minimizing the frequency of dose adjustment and the need for expensive therapeutic drug monitoring.

Valproate monotherapy in 30 patients with partial seizures

This retrospective pilot study describes 30 patients diagnosed and treated for complex partial seizures (CPS) and simple partial seizures (SPS) with and without generalization who received valproate (VPA) monotherapy after lack of response or allergic reaction for carbamazepine (CBZ), phenytoin (PHT), or phenobarbital (PB). Seizures were tabulated daily on seizure calendars by the patients. Three time periods were examined for seizure frequency, 90 days before VPA treatment and 90 and 180 days after VPA treatment. Twenty-two were "controlled" or "improved" (reduction of seizure activity by greater than or equal to 51%) 6 months following the initiation of VPA. VPA was particularly effective in 17 patients who had secondarily generalized tonic-clonic seizures (GTCS) as a subtype of partial seizures. Failure of response to VPA in eight patients appears to be related to their type of partial seizure (SPS or CPS alone, without GTCS) and duration of uncontrolled recurrent seizures. Etiology and compliance were not related to treatment failure. This study supports the need for a double-blind controlled trial with VPA in patients with partial seizures.

Valproate monotherapy in partial seizures

Results of a retrospective study in 30 patients indicate that, contrary to the findings of some earlier studies, valproate monotherapy is highly effective in the treatment of partial seizures, especially those that become secondarily generalized. In 22 of these 30 patients (73 percent), valproate monotherapy either abolished seizures (12 patients) or reduced their frequency by at least 51 percent (10 patients), whereas eight patients experienced minimal or no reduction in seizure frequency. All these patients had previously experienced treatment failure with carbamazepine, phenytoin, or phenobarbital--either alone or combined--because of lack of efficacy or unacceptable side effects. In these patients, failure to have a response to valproate therapy appeared to be related to the type of seizure (simple partial seizures alone/complex partial seizures alone, without secondarily generalized tonic-clonic seizures) and longer duration of uncontrolled seizures. Although these results cannot be generalized to all patients with partial seizures, they do indicate that a double-blind randomized trial of valproate in patients with all types of partial seizures is warranted.

Serum phenobarbital concentration predictions by a personal computer software system

The ability of a personal computer software system to predict actual serum phenobarbital concentrations (SPC) in outpatients taking phenobarbital chronically was assessed by comparing actual with predicted SPC for accuracy, bias, and precision. Data for a four-year period were collected on patients at an outpatient clinic's pharmacokinetic consultation service. The study group included 50 adults and children with at least one SPC taken at a known time after dose administration. Input variables were weight, sex, height, age, concomitant drugs and diseases, phenobarbital dosage regimen, and the time and reported value of all SPC. Initially, SIMKIN (SIMulated KINetics) simulated dosing regimens on the basis of literature estimates of pharmacokinetic parameters; SPC were then estimated for these regimens and compared with actual values. One or two additional SPC were added to the input data and analyzed, and the predicted SPC compared with actual values. Although SIMKIN's accuracy and bias as measured by regression analysis and mean prediction error, respectively, were within clinically acceptable limits, the precision was not. However, these results are limited by the population studied. Patient compliance, concomitant phenytoin therapy, changes in phenobarbital pharmacokinetic parameters with chronic dosing, and disease interactions may significantly affect predictive ability. The clinical effects of these factors need to be evaluated to further improve predictions.

Phenytoin and phenobarbital protein binding alterations in a uremic burn patient

A case is reported in which dramatic decreases in the protein binding of phenytoin and phenobarbital were noted. A 57-year-old burn patient with a history of a seizure disorder had increased free fractions of phenytoin and phenobarbital. The patient later developed renal failure and the free fractions of both drugs were further increased. Decreases in the protein binding of phenytoin in patients with hypoalbuminemia and/or uremia have been well documented, but the effects of these conditions on phenobarbital protein binding have not been well studied. In the case described here, the presence of both hypoalbuminemia and uremia were necessary before a doubling of the free fraction of phenobarbital was noted. Although it is not a highly protein-bound drug, in some circumstances protein binding alterations of phenobarbital may be of clinical significance.

New anticonvulsants in pediatrics: carbamazepine and valproate

The majority of patients with epilepsy have their first seizure during childhood and are first evaluated and diagnosed by their pediatrician. For many patients the medication selected by the pediatrician will be taken for an extended time period, perhaps even for a lifetime. The first job of the pediatrician is to be sure that the patient's recurrent attacks represent genuine epilepsy and not some other paroxysmal medical disorder such as migraine or cardiac arrhythmias. Epileptic seizures are then classified by a careful clinical description of the attacks in conjunction with the results of the physical and EEG examinations. Based on all of the information at hand, the clinician chooses the drug that is most likely to reduce or eliminate further seizures without exposing the child to unnecessary medical risk or behavioral-cognitive adverse effects. In properly selected patients, both carbamazepine and valproate are safe, physically well tolerated, and less likely to provoke chronic mental side effects than the pediatrician's "traditional" choices: phenobarbital or phenytoin. Although carbamazepine and valproate have been widely acclaimed by neurologists and epileptologists, practicing pediatricians have heretofore been less likely to initiate treatment with these drugs. Yet pediatricians have something of priceless value to offer the child with epilepsy: seizure control and a clear mind. The information in this monograph should assist the practicing pediatrician in the rational choice, initiation, and follow-up of treatment with these two excellent anticonvulsants.

Neurological manifestations and toxicities of the antituberculosis drugs. A review

The neurological manifestations and toxicities of 12 antituberculosis drugs [isoniazid, rifampicin (rifampin), ethambutol, p-aminosalicylic acid, pyrazinamide, streptomycin, kanamycin, ethionamide, cycloserine, capreomycin, viomycin and thiacetazone] are reviewed. Their effects upon the central nervous system, cranial nerves, peripheral nerves and the neuromuscular junction are examined, and drug interactions of neurological concern are briefly discussed. Isoniazid is well known to increase the concentrations of gamma-aminobutyric acid in neural tissues. Although conflicting data have been published, isoniazid may play a limited future role in reducing the degree of adventitious movements noted in certain neurological diseases such as multiple sclerosis, spasmodic torticollis, and other segmental dystonic syndromes. With rifampicin neurological complications have been observed infrequently. Rifampicin penetrates into the CSF and has been shown to have useful activity against various micro-organisms in the CSF, including certain viruses; however, contrary to earlier suggestions, it appears to have no role in the treatment of subacute sclerosing panencephalitis. A number of studies have indicated that isoniazid is associated with a large number of accidental and intentional poisonings. The highest incidence has been observed with Southwestern American Indians in which this agent was involved in 7% of all suicide attempts and 19% of the suicide deaths. Degeneration of the optic chiasma and nerve is a well-known adverse effect of ethambutol; toxicity is manifested by impairment of visual acuity, marked loss of colour discrimination, constricted visual fields, and central and peripheral scotoma. Ototoxicity is a well known problem caused by streptomycin, kanamycin, capreomycin and viomycin. The use of streptomycin in pregnant mothers is associated with congenital deafness in newborns in certain cases. The aminoglycoside antibiotics are also associated with flaccid paralysis following neuromuscular blockade. Adverse reactions to cycloserine are mainly dose-related with neurological and psychiatric syndromes noted in up to 50% of patients. Recent data indicate that isoniazid, rifampicin, ethambutol, pyrazinamide, streptomycin, kanamycin, ethionamide, and cycloserine appear in measurable quantities in the cerebrospinal fluid. Five of these compounds (isoniazid, rifampicin, ethambutol, kanamycin, cycloserine) pass to some degree through non-inflamed meninges. Other than discontinuation of the therapeutic regimen and general supportive measures, very few methods are described in the literature for treatment of acute intoxications with antituberculosis drugs.

Antiepileptic drugs in adolescents

Adolescence is a critical developmental period in which major metabolic changes occur. The majority of adolescents with epilepsy can be fully controlled with medications and can lead productive lives. A knowledge of basic principles of pharmacotherapy with AEDs will enable the physician to treat effectively most adolescents with epilepsy.

Correlation between the saliva and free serum concentration of phenobarbital in epileptic children

Twenty epileptic children taking phenobarbital (PB) were evaluated for the concentration of PB in their saliva (Sa), total serum concentration (TS), free serum concentration (FS), and also the pH of the saliva samples. The Sa/TS ratio was 43.0 +/- 5.2% (mean +/- SD), and showed a close relationship between the two (r = 0.98). The free serum concentrations for PB were also observed to be closely correlated to the saliva concentration (r = 0.99), as well as to the total serum concentration, with the FS/TS ratio being 45.0 +/- 5.6%. However, no obvious relationship between the salivary pH and the Sa/TS ratio for PB was observed. This suggested the usefulness of monitoring the PB saliva concentrations in clinical management of epilepsy.

Behavioral toxicity associated with antiepileptic drugs: concepts and methods of assessment

The BTB designed for the VA Epilepsy Cooperative Study is a conceptually organized and practical set of test procedures that can be utilized to assess change in the areas of motor integration, visual perception, speech and language, and mood that might be attributable to AED therapy. If the data warrant, these categories can be compressed into motor, attention-concentration, and mood. The unique methodological advantages of the VA Epilepsy Cooperative Study provide an opportunity to determine empirically the occurrence of behavioral toxicity for specific AED. The advantage of the BTB is the capacity to measure change from an objective baseline over an extended period during chronic AED treatment. The disadvantages are the requirements for apparatus, trained technicians, and additional time for the patient, which now limit its use to research. If BTB data confirm its sensitivity to behavioral toxicity often unappreciated during a neurological exam, the BTB will become a useful clinical tool. Additionally, a common vocabulary for communicating behavioral toxicity may emerge. This optimistic picture is presented with the simultaneous acknowledgment that a clear solution to the problem lies in accumulation of data in future studies which will have had the opportunity to examine the forthcoming results of this multicenter study.

Drug compliance and seizure control in epileptic children

The drug taking habits and compliance of 16 epileptic children were studied by means of a questionnaire, "pill" count and serum antiepileptic drug levels (AEDL). The questionnaire method overestimated patients' compliance while, because of the pharmacokinetics of antiepileptic drugs in children, single outpatients' drug levels may be misleading thereby not always reflecting the true degree of compliance. Ten patients (62%) took more than 85% of their medication. Above this level of compliance there was a positive relationship to seizure control. It would appear that drug compliance in epileptic children is as unsatisfactory as it is in adults on whom they largely depend for the administration of their medication.

Effect of empiric dosing on blood levels of theophylline and phenytoin

To evaluate empiric dosing guidelines for aminophylline and phenytoin in the management of acute exacerbations of obstructive lung disease and seizure disorders, we utilized an emergency department (ED)-based EMIT system to measure stat plasma theophylline and phenytoin levels in patients intended to receive these drugs. Plasma drug level results were available prior to initiation of therapy. Of the patients evaluated, 45 of 163 (27.6%) aminophylline patients and 21 of 73 (28.7%) phenytoin patients were projected to have plasma concentrations below the recommended therapeutic range if empiric dosing schedules were employed. In addition, 39 of 163 (23.9%) aminophylline and 10 of 73 (13.7%) phenytoin patients, had they received these drugs empirically, would have had plasma theophylline and phenytoin levels in excess of the recommended therapeutic range using empiric dosing. We conclude that the use of empiric dosing guidelines for aminophylline and phenytoin in the ED do not reliably produce therapeutic plasma concentrations. The development of a stat drug analysis laboratory in the hospital or within the ED would improve the effectiveness and safety of these acutely used drugs with narrow therapeutic ranges.

[Plasma levels of antiepileptic agents in the treatment of epilepsy]

From a total of 560 different epileptics visited during 16 months, we have practiced 140 plasmatic dosifications of antiepileptic drugs according to EMIT technic. The antiepileptic drugs studied were: PB, DPH, PRM, VPA, CBZ and ESM. In this study only the 70 patients treated with PB in monotherapy or combined with DPH, CBZ, VPA and PRM are considered. From the 70 patients, 45 have been controlled; from them 21 (46,5%) did not reach efficient levels from anyone of the used antiepileptics. From the 70 patients 25 have been partially or bad controlled, 20 of them (80%) had PB in efficient levels, 13 (52%) had the other antiepileptic in efficient levels, 12 (47%) had both antiepileptics in efficient levels and 4 (16%) had no antiepileptic drug in efficient levels in spite of using the efficient dose in mg/Kg/day. The conclusions of this results are: we reached a good effect by using PB alone or combined under the considered efficient levels in a 46.5% of the patients; the bad controlled patients, kept on being bad controlled in spite of having 80% of them PB, the other antiepileptic or both in efficient levels.