Ultra-high-performance liquid chromatography tandem mass spectrometry determination of GHB, GHB-glucuronide in plasma and cerebrospinal fluid of narcoleptic patients under sodium oxybate treatment.

Sodium oxybate (Xyrem®), the sodium salt of γ- hydroxybutyric acid (GHB), is a first-line treatment of the symptoms induced by type 1 narcolepsy (NT1) and it is highly effective in improving sleep architecture, decreasing excessive daytime sleepiness and the frequency of cataplexy attacks. Using an ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) validated method, GHB was determined together with its glucuronide (GHB-gluc), in plasma and cerebrospinal fluid (CSF) samples of NT1 patients under sodium oxybate treatment. To characterize the plasma pharmacokinetics of GHB, three subjects with NT1 were administered at time 0 and 4h with 1.25, 1.5 and 3.55g Xyrem®, respectively and had their blood samples collected at 7 time points throughout an 8-h session. CSF specimens, collected for orexin A measurement from the same three subjects 6h after their second administration, were also tested. The results obtained suggested that GHB plasma values increased disproportionally with the rising doses, (Cmax0-4: 12.53, 32.95 and 69.62µg/mL; Cmax4-8: 44.93, 75.03 and 111.93µg/mL for total Xyrem® dose of 2.5, 3 and 7g respectively) indicating non-linear dose-response. GHB-Gluc was present only in traces in all plasma samples from treated patients, not changing with increasing Xyrem® doses. GHB values of 5.62, 6.10 and 17.74µg/mL for 2, 3 and 7g Xyrem® were found in CSF with a significant difference from control values. GHB-Gluc was found in negligible concentrations with no differences to those of control individuals. In conclusion this simple and fast UHPLC-MS/MS method proved useful for pharmacokinetic studies and therapeutic drug monitoring of GHB in narcoleptic patients treated with sodium oxybate.

Ethanol inhibits the sensory responses of cerebellar granule cells in anesthetized cats.

BACKGROUND: Granule cells occupy a strategic position in the transmission of afferent information to the cerebellar cortex. They are also the most abundant type of neurons in the cerebellum. The functions of the cerebellum are thought to be sensitive to acute alcohol intoxication. The effects of acute alcohol intoxication on the in vivo physiology of cerebellar granule cells are, however, not completely known. METHODS: We studied chloralose-anesthetized cats at ethanol doses relevant to human drinking (0.3-1.2 g/kg). We recorded the electrophysiological responses of granule cell clusters to auditory and visual stimulation, and simultaneously monitored the concentration of ethanol in the cerebrospinal fluid (CSF). RESULTS: At an intravenous ethanol dose of 0.3 g/kg, CSF ethanol concentration peaked in 10 minutes at 17 mM, equivalent to a blood alcohol concentration (BAC) of about 0.08 g/dL. Ethanol quickly and almost completely abolished both auditory and visual responses from granule cells. Complete or near-complete inhibition lasted 15 to 20 minutes; approximately 50% recovery required an additional 15 minutes, and a full recovery yet another 15 minutes. A higher ethanol dose at 1.2 g/kg resulted in a more severe inhibition and required longer time for recovery. The relationship between ethanol dose, CSF ethanol concentration, and granule cell responses was dynamic and nonlinear, critically depending upon the elapsed time. CONCLUSIONS: Cerebellar granule cell sensory responses are highly sensitive to ethanol inhibition. A rapid development of acute tolerance appears to be a major factor contributing to the dynamic and nonlinear relationship among ethanol dosage, CSF ethanol concentration, and granule cell responses. It is likely that a generalized de-afferentation of the cerebellum from its mossy fiber afferents, followed by the subsequent development of acute tolerance may play major roles by which alcohol intoxication affects cerebellar functions.

Clinical pharmacokinetics of cerebrospinal fluid.

The distribution of drugs into the cerebrospinal fluid has long been considered a challenging field of investigation in 2 major respects: (a) understanding how the physicochemical properties (molecular weight, pKa, plasma protein binding) of various molecules influence their movements across such a specific structure as the blood-brain barrier; and (b) defining the relationship between cerebrospinal fluid concentrations of various drugs and their central (side) effects. An attempt has been made to review the very dispersed information presently available to offer a clinically orientated picture of this area of pharmacokinetics. Drugs acting on the central nervous system (benzodiazepines, tricyclic antidepressants, anticonvulsants, opioids), antibacterial agents, cardiovascular drugs (beta-adrenoceptor blockers and digoxin), antineoplastic drugs (mainly methotrexate), and other miscellaneous agents (corticosteroids, cimetidine, methylxanthines) are reviewed. The available evidence seems to support the conclusion that only for methotrexate and antibacterial agents does knowledge of cerebrospinal fluid pharmacokinetics have direct therapeutic implications, while the mosaic of information available for other drugs does little more than provide a partially satisfactory picture.