Electrophysiologic recordings in a patient with a discrete unilateral thalamic infarction

The electroencephalogram, and somatosensory and auditory evoked potentials were recorded from a patient, who, at necropsy, showed a restricted unilateral thalmic infarct involving predominantly the anterior and lateral thalamus. The electroencephalogram showed distinct monomorphic delta activity and a suppression of the alpha rhythm over the side of the lesion. Short latency somatosensory evoked potentials were present bilaterally; mid-latency somatosensory evoked potentials were absent ipsilateral to the lesion. Both mid-latency and long latency auditory evoked potentials were normal.

Pharmacokinetics of primidone elimination by uremic patients

The hemodialyzability of primidone was investigated in four patients on long-term hemodialysis. Primidone, 500 or 250 mg, was given orally 2 hours before hemodialysis. Blood and dialyzate samples were collected periodically during the 4-hour dialysis and measured by gas-liquid chromatography and high-performance liquid chromatography for primidone. Dialysis clearance calculated by the instantaneous dialyzate method averaged 97.7 ml/min, which is considerably greater than the metabolic clearance of 30 ml/min for the drug. The extraction efficiency of the hollow-fiber dialyzers averaged 40.2 pr cent for plasma samples. A mean of 31.7 per cent of the administered dose of primidone was removed during hemodialysis. The half-life was 5.1 hours in our patients during hemodialysis, a nearly two-thirds reduction of the 13.9-hour half-life calculated in uremic patients. Because of the reduction in elimination half-life, greater dialysis clearance than metabolic clearance, high extraction efficiency, and significant drug removal during dialysis, we conclude that primidone is dialyzable.

In vivo uptake of valproic acid into brain

The pharmacokinetics of valproic acid (VPA) penetration into the central nervous system of cats were studied. VPA levels in cortical gray matter and plasma were measured at timed intervals after rapid intravenous drug infusion. Brain uptake of the drug was maximal at 1 min postinfusion and decayed rapidly with a mean elimination half-life of 41 min. After a rapid distribution phase, plasma VPA levels remained stable for 90 min. The brain:plasma ratio was maximal at 1 min and also declined rapidly. The volume of distribution was 0.125 1/kg. The small volume of distribution, low brain:plasma ratios and rapid clearance from brain indicate that VPA is not significantly bound in cerebral cortex after a single dose.

Valproate tremors

We made accelerometric recordings of the tremor induced by valproic acid. The tremor was similar to essential tremor and appeared within a month of starting therapy. It was present at rest and exacerbated by action or antigravity positioning. There was no close correlation of tremor severity and plasma valproate level, but the tremor usually appeared at dosages greater than 750 mg per day. This tremor has appeared in 20 of 25 patients recently studied. In some patients the tremor is markedly active; however, others note only minimal tremor activity.

Hemodialysis clearance of ethosuximide in patients with chronic renal disease

Clearance of ethosuximide by hemodialysis was studied. Four patients with chronic renal disease supported by hemodialysis were given ethosuximide 500 mg four hours before dialysis. Samples of arterial and venous blood and dialysate were collected before and during the four-hour dialysis procedure. Ethosuximide concentration was measured by gas-liquid chromatography. The extraction efficiency for the dialysis systems used in this study ranged from 61.1 to 100%, and dialysis clearance was from 122.3 to 156.3 ml/min. Recovery of ethosuximide from the dialysate was 38.8 to 52.4% of the administered dose. Hemodialysis reduced the elimination half-life of ethosuximide from a presumable value of 55 hours to an average of 3.5 hours. The authors concluded that ethosuximide is dialyzable. Hemodialysis patients concurrently receiving ethosuximide may require a supplemental dose or an altered ethosuximide dosing schedule. Because hemodialysis quickly clears ethosuximide, it may be useful in treating ethosuximide overdosage.

Effects of ethyl ester derivatives of valproic acid metabolites on pentylenetetrazol seizures in mice

The anticonvulsant activity of the ethyl esters of the major valproic acid metabolites was assessed against minimal pentylenetetrazol seizures in adult male ICR mice. The ethyl ester 3-hydroxy-propylpentanoic acid was found to possess significant anticonvulsant activity.

Methsuximide for refractory complex partial seizures

The efficacy and safety of methsuximide were evaluated for 12 weeks in 21 patients with complex partial (psychomotor) seizures refractory to conventional anticonvulsants. After addition of methsuximide to the previous anticonvulsant regimens, the number of complex partial seizures per patient decreased from a weekly average of 5.8 to 0.9 seizures. A 90 to 100% control of complex partial seizures was achieved in 15 (71%) of the patients. Dose reduction or discontinuation of one or more previous medications was possible in 42%. Seizure control was optimal at methsuximide doses of 9.5 to 11.0 mg per kilogram per day and plasma levels of 20 to 24 micrograms per milliliter. Adverse experiences, particularly somnolence and lethargy, were reported by 12 patients. Methsuximide appeared to be an effective and generally well tolerated adjunct medication in the management of complex partial seizures.

Homocysteine induced convulsions: enhancement by vitamin B6 and inhibition by hydrazine

The effects of pyridoxal phosphate, pyridoxine and hydrazine were studied on homocysteine-induced seizures in mice. Both of the B6 vitamers significantly decreased the latency and increased the severity, lethality and duration of seizures induced by homocysteine. The B6 inhibitor hydrazine sulfate, which is normally a convulsant, prevented the tonic component of the convulsions and increased the latency to the clonic component. This experiment indicates that a vitamin B6 dependent step is critically involved in the metabolic changes which precede homocysteine seizures.

Rapid infusion of phenytoin sodium loading doses

The use of rapid intravenous infusions of phenytoin sodium to achieve prompt plasma therapeutic concentrations of phenytoin was studied in adult epileptic patients. Six adult patients who experienced recent tonic-clonic seizures were selected for study. Four of them had not been treated with phenytoin before the study; two were on chronic phenytoin therapy but had subtherapeutic serum levels. A leading dose of phenytoin sodium (15 mg/kg in 100 ml of 0.9% sodium chloride injection) was infused at 30-50 mg/min. Blood samples were drawn before phenytoin administration, every five minutes during the infusion, and at 1, 2, 4, 8, 12, 18, and 24 hours after completion of the infusion. Adverse effects were monitored during the infusion. Pharmacokinetic variables were calculated. Patients received from 750 to 1500 mg phenytoin sodium (mean +/- S.D. = 1040.8 +/- 297.3 mg). From 5 to 30 minutes were required to reach therapeutic (10-20 micrograms/ml) serum phenytoin concentrations; concentrations peaked at 31.1 +/- 10.0 micrograms/ml. Four of the six patients had therapeutic serum concentrations at 18 hours after completion of the infusion. Adverse effects were minimal and not severe; no cardiotoxicities were noted. Phenytoin half-life was 31.2 +/- 8.4 hours, total plasma clearance was 47.2 +/- 10.7 ml/kg/hr, and volume of distribution was 1.96 +/- 0.46 liters/kg. It is concluded that rapid intravenous infusion of phenytoin appears to be a reasonably safe and effective method of rapidly reaching therapeutic phenytoin concentrations.

Interactions of valproic acid with phenytoin

The interaction of phenytoin and valproic acid was studied in four adults. We studied serial changes in total phenytoin concentrations, protein binding, urinary hydroxyphenylphenylhydantoin (HPPH) excretion, and half-life. In all four patients valproic acid caused an increase in the free fraction of phenytoin. Total phenytoin plasma concentrations decreased transiently in three patients and remained low throughout the study period in one patient. HPPH excretion increased transiently and then decreased, corresponding to changes in total phenytoin plasma concentrations. Biologic half-life transiently decreased in three patients (not statistically significant) and subsequently increased significantly in all four patients. The data suggest that valproic acid displaced phenytoin from protein-binding sites in all four patients and subsequently inhibited phenytoin metabolism in three patients.

Albumin-binding interactions of sodium valproate

In vitro equilibrium dialysis experiments show that salicylate and phenylbutazone displace valproate from its binding sites on human serum albumin at therapeutic concentrations, whereas warfarin and carbamazepin do not.

Focal and generalized experimental seizures induced by homocysteine

Electrocorticographic and behavioral effects of parenteral injections of homocysteine in rats are described. Homocysteine activates experimental foci and produces focal seizures in experimental animals with pre-existing lesions. It produces generalized ECoG seizures and generalized convulsions in unlesioned animals in higher doses.

Protein binding of valproic acid in uremic patients

Protein binding of valproic acid was studied in four uremic patients on long-term hemodialysis. Before dialysis, the free fraction was 0.31 +/- 0.11 (SD); this was larger than in nonuremic subjects. During hemodialysis, the free fraction increased significantly (p less than 0.01) in three patients (mean, 0.64 +/- 0.32 SD).

Effects of intracortical injection of blood and blood components on the electrocorticogram

Long term effects of the intracortical implantation of blood and blood products on the electrocorticogram were studied in cats and guinea pigs. Focal epileptiform paroxysmal discharges developed after implantation of whole blood, hemolyzed erythrocytes, methemoglobin, ferritin, ferrous chloride, ferric chloride, fibrinogen, hemin, and cottonoid. In each group recurrent paroxysmal discharges became more prominent and more frequent after several months, suggesting a physiological change caused by a breakdown product of blood. The lesions were characterized by varying degrees of cell loss, iron deposition and glial proliferation. It is thought that posttraumatic epilepsy, which is frequently accompanied by extravasation of blood into the brain, might share a similar physiopathogenesis.

Clinical efficacy and long-term effects of valproic acid therapy on spike-and-wave discharges

Twenty-two patients with absence seizures and other seizure types were treated with valproic acid and followed up for 1 year. Results were excellent with more than 75% improvement in 80% of patients with absence seizures, in 40% of those with tonic-clonic seizures, in all of those with myoclonic seizures, and in 43% of those with partial seizures. Fifty-seven percent of the patients had more than a 75% reduction in the total number of paroxysmal spike-wave discharges, and 62% had more than a 75% reduction in the number of spike-wave discharges lasting longer than 3 seconds. Photosensitivity and activation by hyperventilation decreased. More patients achieved good EEG control in 1 year than in 10 weeks.

Valproic acid and plasma levels of phenobarbital

During concurrent administration of phenobarbital and valproic acid, phenobarbital plasma concentrations often increase. This often requires a reduction of phenobarbital dosage. In normal cats and patients with epilepsy, we found no evidence of decreased renal excretion of phenobarbital. Metabolic studies in four patients revealed a decrease in the conversion of phenobarbital to hydroxyphenylphenobarbital and decreased urinary ratios of hydroxyphenylphenobarbital to phenobarbital. These data suggest that phenobarbital metabolism is inhibited by therapeutic plasma levels of valproic acid.

Effect of phenytoin on protein binding of valproic acid

In vitro experiments using the equilibrium dialysis technique were performed to determine the binding of valproic acid to plasma components in the absence and presence of therapeutic concentrations of phenytoin. The free fraction of valproic acid was found to be dependent on the total valproic acid concentration. Phenytoin did not influence valproic acid protein binding.

Distinction between normal and epileptic rhythms in rodent sensorimotor cortex

Characteristics of spontaneous spindling in electrocorticograms from awake rodents are described. Comparisons are made between this spontaneous activity and epileptic activity generated in the sensorimotor cortex.

Valproic acid. Review of a new antiepileptic drug

Valproic acid is a new antiepileptic drug. It has a marked effect on generalized spike-wave discharges. The exact mechanism of action is uncertain; however, some evidence suggests an effect on the metabolism of gamma-aminobutyric acid. It is rapidly absorbed from the gastrointestinal (GI) tract. Concurrent administration with phenobarbital may result in elevated phenobarbital plasma concentrations. Administration with phenytoin sodium may transiently result in lower total phenytoin plasma levels. Side effects are generally mild and include fatigue, GI disturbances, weight gain, a fine postural and resting tremor, mild thrombocytopenia, and an increase in hepatic enzymes. Platelet counts and liver function monitoring should be done during valproic acid therapy. Drowsiness may be seen in patients receiving other antiepileptic drugs concurrently.