Levels of total gamma-aminobutyric acid (GABA), free GABA and homocarnosine in cerebrospinal fluid of epileptic patients before and during gamma-vinyl-GABA (vigabatrin) treatment

Monitoring vigabatrin in head injury patients by cerebral microdialysis: obtaining pharmacokinetic measurements in a neurocritical care setting

Aims

The aims were to determine blood–brain barrier penetration and brain extracellular pharmacokinetics for the anticonvulsant vigabatrin (VGB; γ-vinyl-γ-aminobutyric acid) in brain extracellular fluid and plasma from severe traumatic brain injury (TBI) patients, and to measure the response of γ-aminobutyric acid (GABA) concentration in brain extracellular fluid.

Methods

Severe TBI patients (n = 10) received VGB (0.5 g enterally, every 12 h). Each patient had a cerebral microdialysis catheter; two patients had a second catheter in a different region of the brain. Plasma samples were collected 0.5 h before and 2, 4 and 11.5 h after the first VGB dose. Cerebral microdialysis commenced before the first VGB dose and continued through at least three doses of VGB. Controls were seven severe TBI patients with microdialysis, without VGB.

Results

After the first VGB dose, the maximum concentration of VGB (C_max) was 31.7 (26.9–42.6) μmol l⁻¹ (median and interquartile range for eight patients) in plasma and 2.41 (2.03–5.94) μmol l⁻¹ in brain microdialysates (nine patients, 11 catheters), without significant plasma–brain correlation. After three doses, median C_max in microdialysates increased to 5.22 (4.24–7.14) μmol l⁻¹ (eight patients, 10 catheters). Microdialysate VGB concentrations were higher close to focal lesions than in distant sites. Microdialysate GABA concentrations increased modestly in some of the patients after VGB administration.

Conclusions

Vigabatrin, given enterally to severe TBI patients, crosses the blood–brain barrier into the brain extracellular fluid, where it accumulates with multiple dosing. Pharmacokinetics suggest delayed uptake from the blood.

Free-GABA levels in the cerebrospinal fluid of patients suffering from several neurological diseases Its potential use for the diagnosis of diseases which course with inflammation and tissular necrosis

Free GABA levels were measured in the cerebrospinal fluid (CSF) of 74 neurological patients suffering from cerebral cysticercosis (n = 9), Parkinson's disease (n = 5), multiple sclerosis (n = 6), epilepsy (n = 24), meningeal tuberculosis (n = 6), viral encephalitis (n = 3), cerebrovascular disease (n = 8) and several kinds of dystonia (n = 5). A statistical significant four-fold elevation in free GABA levels was found in patients with cerebral cysticercosis. A non statistical significant two-fold increase in free GABA levels was also encountered in the CSF of patients affected by cerebrovascular disease and viral encephalitis. No changes in CSF free GABA levels were found in patients suffering from any of the other disorders. It is suggested that free GABA levels may be elevated in the CSF of patients suffering from neurological diseases which course with inflammation and tissular necrosis such as cerebral cysticercosis. Much work is needed however to establishd whether CSF free GABA levels can be used as a diagnostic tool in at least some type of these patients.

A microdialysis study of oral vigabatrin administration in head injury patients: preliminary evaluation of multimodality monitoring

BACKGROUND

We assessed the feasibility of administering a neuroprotective drug, vigabatrin (VGB; gamma-vinyl-gamma-aminobutyric acid) with multimodality monitoring, including cerebral microdialysis, in severe head injury patients, to measure surrogate endpoints and blood-brain barrier (BBB) penetration.

METHODS

Patients (n = 20) were randomised to VGB (0.5 g twice-daily, enteric) or control. ICP, ABP, CPP and cerebrovascular pressure reactivity index (PRx) were monitored. Microdialysate glucose, lactate, pyruvate, glutamate, glycerol, amino acids, VGB and GABA were analysed.

RESULTS

Preliminary evaluation of results (five VGB-treated patients) showed that VGB levels rose in brain microdialysates, followed by a modest increase in GABA. VGB and GABA increased more in abnormal brain than in sites further from lesions, and were higher after multiple VGB doses. Highest VGB and GABA microdialysate levels were 75 and 4 μmol/L respectively. Microdialysate glucose and glycerol sometimes decreased, and glutamate and tyrosine sometimes increased, following VBG administration; causation unproven. VGB did not overtly affect ICP, ABP, CPP, PRx, or microdialysate lactate, pyruvate and lactate/pyruvate ratio.

CONCLUSION

Multimodality monitoring, including cerebral microdialysis, is feasible for studying surrogate endpoints following drug administration. VGB crosses the BBB, leading to modest increases in extracellular GABA. Further analyses are ongoing. Microdialysis may assist the development of neuroprotective agents by determining penetration into extracellular fluid of the brain.