Phenytoin dosage requirements and pharmacokinetic variables.

The relationships between phenytoin dose, pharmacokinetic variables, patient data, and serum phenytoin concentrations were studied. One hundred sixty-eight adult epileptic patients who were receiving phenytoin were randomly selected and studied retrospectively. The method of Ludden et al. or a Bayesian forecasting technique was employed to estimate the patients' pharmacokinetic values for maximum rate of drug metabolism (Vmax) and the Michaelis-Menten constant (Km). Resulting steady-state serum concentrations were estimated. The daily doses of phenytoin necessary to produce steady-state serum phenytoin concentrations of 10 and 20 micrograms/ml were also determined in patients whose values were definable. Analysis of variance was used to test possible correlations between patient demographic data, pharmacokinetic values, and doses. The majority of patients (85.6%) failed to achieve concentrations between 10 and 20 micrograms/ml when receiving phenytoin sodium 300 mg daily. Patients receiving more than one phenytoin dosage regimen had significant but weak correlations between Vmax and Km. The data suggest that low Km and Vmax values occur concurrently. Initial phenytoin dose based on patients' weights or body surface areas may be useful in determining initial dosage requirements, but estimated pharmacokinetic values for Vmax and Km provide the best guide for dosage adjustment.

Subacute arsenic neuropathy: clinical and electrophysiological observations.

Two patients with subacute arsenic neuropathy are described and the results of serial conduction velocity determinations from the very early stages of the illness to partial recovery are reported. Sensory and motor deficits were maximal within four weeks of the estimated time of exposure. Recovery was slow, with only partial improvement of the neurological deficits two years after onset of the illness. Progressive slowing of motor conduction velocity was observed in the first three months followed by a gradual increase in velocity thereafter. The possible mechanisms underlying the temporal profile of the electrophysiological changes are considered. The need for initiating chelation therapy before the development of the neuropathy is emphasised.

Mathematical analysis of a phenytoin--disulfiram interaction.

A case of phenytoin-disulfiram drug interaction is analyzed with a mathematical technique used in enzyme kinetics. Serum anticonvulsant levels, obtained before, during, and after disulfiram administration, were collected from hospital records retrospectively. Phenytoin kinetic constants--maximal velocity of metabolism (Vmax) and Michaelis-Menten constant (km)--before, during, and after disulfiram administration, were compared. The slopes (km) of the regression lines analyzed by a small sample t test for parallelism were not significantly different (p greater than 0.05). Y-intercept (Vmax) values obtained before (433 mg/day) and after (463 mg/day) disulfiram are both significantly different when compared with the y-intercept during (264 mg/day) disulfiram administration, by a small-sample t test for common intercept (p less than 0.05). Changes in the elimination rate of phenytoin or changes in y-intercept result from noncompetitive drug effects. It is concluded that disulfiram affects phenytoin's elimination rate by noncompetitive mechanisms.

Normal pressure hydrocephalus due to membranous obstruction of the sylvian aqueduct.

In a patient presenting with the clinical features of normal pressure hydrocephalus, a membranous obstruction of the aqueduct of Sylvius was demonstrated by combined air encephalography and contrast ventriculography. Ventriculoatrial shunting resulted in clinical improvement without significant change in ventricular size.

Orbicularis oculi reflex in coma: clinical, electrophysiological, and pathological correlations.

The orbicularis oculi reflex was studied in 48 comatose patients and the results were correlated with clinical and pathological findings. The late component of the reflex was absent or of minimal amplitude in all cases regardless of the site of lesions, reflecting a diffuse suppression of the reticular system rather than a specific or local block in the brain-stem. Alteration of the early component of the reflex, on the other hand, generally indicated primary or secondary structural changes in the pons, although reversible functional or pharmacological block of pontine conduction was also documented.

Orbicularis oculi reflex in the Wallenberg syndrome: alteration of the late reflex by lesions of the spinal tract and nucleus of the trigeminal nerve.

The orbicularis oculi reflex was studied in nine cases with lateral medullary lesions. Diagnosis of the Wallenberg syndrome was made clinically in seven cases and at necropsy in another. The clinical features of one other case were closely allied to but not typical of this syndrome. An afferent delay of the late reflex on the side of the lesion in the presence of a normal early reflex was seen in all but two cases. In one of the latter, the late reflex was normal and in the other, a comatose patient, the late reflex was totally absent. It was concluded that the neurones of the first order responsible for the bilateral late reflex on unilateral stimulation terminate in the ipsilateral spinal nucleus of the trigeminal nerve without significant crossing over to the same structure on the other side. An afferent delay of the late reflex in the presence of a normal or nearly normal early reflex is consistent with a lateral medullary lesion implicating the spinal tract and nucleus. The Wallenberg syndrome is a common clinical entity showing this abnormality of the orbicularis oculi reflex.

Transfemoral vertebral angiography as a cause of an anterior spinal artery syndrome. Case report.

A case with signs of a lower cervical anterior spinal artery syndrome incident to vertebral angiography by the transfemoral approach is described. The literature is reviewed and a probable pathogenesis of angiography-related spinal cord injury is discussed.