Pharmacokinetics of gamma-hydroxybutyric acid in 6-week-old swine (Sus scrofa domesticus) after intravenous and oral administration

Sedative as well as protective effects during hypoxia have been described for gamma-hydroxybutyric acid (GHB). Six swine (Sus scrofa domesticus) of 6 weeks old were administered NaGHB at a dose of 500 mg/kg intravenously (IV) and 500 and 750 mg/kg orally (PO) in a triple cross-over design. Repeated blood sampling was performed to allow pharmacokinetic analysis of GHB. Whole blood concentration at time point 0 after IV administration was 1727.21 ± 280.73 μg/mL, with a volume of distribution of 339.45 ± 51.41 mL/kg and clearance of 164.94 ± 47.05 mL/(kg h). The mean peak plasma concentrations after PO administration were 326.57 ± 36.70 and 488.01 ± 154.62 μg/mL for 500 mg/kg and 750 mg/kg, respectively. These were recorded at 1.42 ± 0.72 and 1.58 ± 0.58 h after PO dose for GHB 500 mg/kg and 750 mg/kg, respectively. The elimination half-life for IV and PO 500 mg/kg and PO 750 mg/kg dose was respectively 1.33 ± 0.30, 1.16 ± 0.31 and 1.11 ± 0.33 h. The bioavailability (F) for PO administration was 45%. No clinical adverse effects were observed after PO administration. Deep sleep was seen in one animal after IV administration, other animals showed head pressing and ataxia.

GHB toxicokinetics and renal monocarboxylate transporter expression are influenced by the estrus cycle in rats

BACKGROUND

The illicit use and abuse of gamma-hydroxybutyric acid (GHB) occurs due to its sedative/hypnotic and euphoric effects. Currently, there are no clinically available therapies to treat GHB overdose, and care focuses on symptom treatment until the drug is eliminated from the body. Proton- and sodium-dependent monocarboxylate transporters (MCTs (SLC16A) and SMCTs (SLC5A)) transport and mediate the renal clearance and distribution of GHB. Previously, it has been shown that MCT expression is regulated by sex hormones in the liver, skeletal muscle and Sertoli cells. The focus of the current study is to evaluate GHB toxicokinetics and renal monocarboxylate transporter expression over the estrus cycle in females, and in the absence of male and female sex hormones.

METHODS

GHB toxicokinetics and renal transporter expression of MCT1, SMCT1 and CD147 were evaluated in females over the estrus cycle, and in ovariectomized (OVX) female, male and castrated (CST) male rats. GHB was administered iv bolus (600 and 1000 mg/kg) and plasma and urine samples were collected for six hours post-dose. GHB concentrations were quantified using a validated LC/MS/MS assay. Transporter mRNA and protein expression was quantified by qPCR and Western Blot.

RESULTS

GHB renal clearance and AUC varied between sexes and over the estrus cycle in females with higher renal clearance and a lower AUC in proestrus females as compared to males (intact and CST), and OVX females. We demonstrated that renal MCT1 membrane expression varies over the estrus cycle, with the lowest expression observed in proestrus females, which is consistent with the observed changes in GHB renal clearance.

CONCLUSIONS

Our results suggest that females may be less susceptible to GHB-induced toxicity due to decreased exposure resulting from increased renal clearance, as a result of decreased renal MCT1 expression.

Acute Sodium Oxybate Intoxication: A Case Report and Review of the Literature

PURPOSE

Despite a better safety profile than illicit γ-hydroxybutyric acid (GHB) and other GHB analogs, sodium oxybate continues to raise serious concerns regarding clinical safety. In this study, the authors report the case of near-fatal intoxication involving sodium oxybate-alcohol combination in a 40-year-old woman. In addition, a review of the literature on published cases of intoxication involving this pharmaceutical form of GHB was conducted. A 40-year-old woman was admitted to the intensive care unit in a coma after voluntary ingestion of 18 g of sodium oxybate and alcohol.

METHODS

The GHB plasma concentration was quantified to be 146 mg/L using liquid chromatography coupled with tandem mass spectrometry. An English literature search was performed using PubMed without any limiting period to identify all available scientific publications involving cases of sodium oxybate intoxication.

RESULTS

Six cases were identified. Five involved fatal intoxication cases, with GHB postmortem blood concentrations ranging from 11.5 to 3500 mg/L. One involved a nonfatal intoxication case with a GHB serum concentration of 569 mg/L 7 hours postingestion.

CONCLUSIONS

In the present case, the estimated elimination half-life was 154 minutes. The risk of acute poisoning seems to be high considering the pharmacokinetic properties of sodium oxybate. Physicians and toxicologists must take such properties into account.

γ-Hydroxybutyric Acid: Pharmacokinetics, Pharmacodynamics, and Toxicology

Gamma-hydroxybutyrate (GHB) is a short-chain fatty acid present endogenously in the brain and used therapeutically for the treatment of narcolepsy, as sodium oxybate, and for alcohol abuse/withdrawal. GHB is better known however as a drug of abuse and is commonly referred to as the "date-rape drug"; current use in popular culture includes recreational "chemsex," due to its properties of euphoria, loss of inhibition, amnesia, and drowsiness. Due to the steep concentration-effect curve for GHB, overdoses occur commonly and symptoms include sedation, respiratory depression, coma, and death. GHB binds to both GHB and GABAB receptors in the brain, with pharmacological/toxicological effects mainly due to GABAB agonist effects. The pharmacokinetics of GHB are complex and include nonlinear absorption, metabolism, tissue uptake, and renal elimination processes. GHB is a substrate for monocarboxylate transporters, including both sodium-dependent transporters (SMCT1, 2; SLC5A8; SLC5A12) and proton-dependent transporters (MCT1-4; SLC16A1, 7, 8, and 3), which represent significant determinants of absorption, renal reabsorption, and brain and tissue uptake. This review will provide current information of the pharmacology, therapeutic effects, and pharmacokinetics/pharmacodynamics of GHB, as well as therapeutic strategies for the treatment of overdoses. Graphical abstract.

Gamma-hydroxybutyrate abuse: pharmacology and poisoning and withdrawal management

Gamma-hydroxybutyrate (GHB) is a central nervous system depressant primarily used as a recreational drug of abuse, but also for the treatment of narcolepsy with cataplexy in adult patients and as an adjuvant for control of alcohol withdrawal syndrome. The main aim of this review is to summarise updated knowledge about GHB pharmacokinetics and pharmacodynamics, acute poisoning, and clinical features of GHB withdrawal syndrome, its diagnosis and medical treatment. The most common clinical signs and symptoms of acute poisoning include sleepiness to deep coma, bradycardia, hypotension, and respiratory failure. Therapy is essentially supportive and based on continuous monitoring of vital signs. GHB withdrawal syndrome shares patterns with other withdrawal syndromes such as alcohol withdrawal and is sometimes difficult to distinguish, especially if toxicological tests are GHB-negative or cannot be performed. There are no official detoxification protocols for GHB withdrawal syndrome, but its therapy is based on benzodiazepine. When benzodiazepine alone is not effective, it can be combined with barbiturates or antipsychotics. Information about abuse and distribution of GHB and its precursors/analogues among the general population is still limited. Their prompt identification is therefore crucial in conventional and non-conventional biological matrices, the latter in particular, to clarify all the issues around this complex molecule.

Butanediol Conversion to Gamma-Hydroxybutyrate Markedly Reduced by the Alcohol Dehydrogenase Blocker Fomepizole

1,4-Butanediol (BDO)-used as solvent and abused for its euphoric effects-is converted to gamma-hydroxybutyrate (GHB) by the enzyme alcohol dehydrogenase. This double-blind, placebo-controlled crossover study with six healthy volunteers is the first to date investigating the role of the ADH inhibitor fomepizole (4-methylpyrazole (4MP)) in moderating this conversion in humans. Participants received on two different days either intravenous placebo or 15 mg/kg 4MP followed by oral administration of 25 mg/kg BDO. Pretreatment with 4MP resulted in significantly higher BDO maximal plasma concentration (P = 0.001) and area under the concentration-time curve (AUC; P = 0.028), confirming that ADH is the primary pathway for the conversion of BDO to GHB in humans. With 4MP, the mean arterial pressure was significantly lower at 105 minutes compared to baseline (P = 0.003), indicating that blood pressure lowering, observed not with a temporal relationship to 4MP administration but after the maximum BDO concentration was reached, may be an intrinsic effect of BDO.

Formulary Forum: Sodium Oxybate for Cataplexy

Objective:

To review the pharmacology, pharmacokinetics, clinical efficacy, adverse effects, drug interactions, precautions, dosing recommendations, and patient counseling of sodium oxybate for the treatment of cataplexy in patients with narcolepsy.

Data Sources:

OVID and PubMed databases were searched (1966–January 2006) using the key words sodium oxybate, gamma-hydroxybutyrate, narcolepsy, and cataplexy. Only English-language articles were selected.

Study Selection and Data Extraction:

All information on sodium oxybate related to narcolepsy and cataplexy was considered. Study selection included human trials evaluating safety and efficacy of sodium oxybate for the treatment of cataplexy.

Data Synthesis:

Sodium oxybate is approved by the Food and Drug Administration for the treatment of excessive daytime sleepiness and cataplexy in patients with narcolepsy. In placebo-controlled trials, sodium oxybate demonstrated efficacy in reducing the number of cataplexy attacks. The dosing regimen includes a split dose given at bedtime and 2.5–4 hours later due to its short elimination half-life. The drug is generally well tolerated, with headache, nausea, dizziness, pain, and somnolence being the most common adverse events.

Conclusions:

Sodium oxybate is safe and effective for the treatment of cataplexy. Potential disadvantages include a multiple dosing regimen, abuse potential, cost, and a closed distribution system. Potential advantages demonstrated in clinical trials include significant decreases in the number of weekly cataplexy attacks, improvement in daytime sleepiness, and improvement in the Clinical Global Impression of Change score and nighttime awakenings. Overall, sodium oxybate provides a new option for the treatment of cataplexy.

γ-Hydroxybutyric acid (GHB) is not an agonist of extrasynaptic GABAA receptors

γ-Hydroxybutyric acid (GHB) is an endogenous compound and a drug used clinically to treat the symptoms of narcolepsy. GHB is known to be an agonist of GABAB receptors with millimolar affinity, but also binds with much higher affinity to another site, known as the GHB receptor. While a body of evidence has shown that GHB does not bind to GABAA receptors widely, recent evidence has suggested that the GHB receptor is in fact on extrasynaptic α4β1δ GABAA receptors, where GHB acts as an agonist with an EC50 of 140 nM. We investigated three neuronal cell types that express a tonic GABAA receptor current mediated by extrasynaptic receptors: ventrobasal (VB) thalamic neurons, dentate gyrus granule cells and striatal medium spiny neurons. Using whole-cell voltage clamp in brain slices, we found no evidence that GHB (10 µM) induced any GABAA receptor mediated current in these cell types, nor that it modulated inhibitory synaptic currents. Furthermore, a high concentration of GHB (3 mM) was able to produce a GABAB receptor mediated current, but did not induce any other currents. These results suggest either that GHB is not a high affinity agonist at native α4β1δ receptors, or that these receptors do not exist in classical areas associated with extrasynaptic currents.

The Pharmacokinetics of Sodium Oxybate Oral Solution following Acute and Chronic Administration to Narcoleptic Patients

This trial was conducted to evaluate the pharmacokinetics and safety of a sodium oxybate (gamma-hydroxybutyrate [GHB]) oral solution in narcoleptic patients after acute and chronic treatment. An open-label, two-period, two-treatment study design was used. Trial subjects included 13 patients with polysomnographically confirmed narcolepsy. The patients were administered a bedtime dose of 4.5 g of sodium oxybate while in a sleep research center. They were subsequently treated with sodium oxybate at the nightly dose of 4.5 g for 8 weeks. The patients then returned to the sleep center and were again treated with the 4.5-g sodium oxybate dose at bedtime. Blood samples (5 mL) were collected at 18 time points before and up to 7 hours after both the first dose of sodium oxybate and following 8 weeks of dosing. Plasma samples were analyzed for oxybate content by a validated liquid chromatography/tandem mass spectrometry (LC/MS/MS) method. Noncompartmental methods were applied in the determination of pharmacokinetic parameters from each patient's plasma oxybate concentration versus time curve. No serious adverse events were recorded, and all patients completed the study. Headache, enuresis, and leg cramps were reported as adverse experiences. With both acute and chronic dosing, sodium oxybate was rapidly absorbed and eliminated with an apparent half-life of about 40 minutes. The only changes observed in the kinetics of oxybate after 8 weeks of treatment were a 13% and 16% increase in peak concentration (C(max)) and systemic exposure (AUC), respectively. The pharmacokinetics of sodium oxybate in narcoleptic patients were not changed in any clinically significant manner when the drug was chronically administered. The drug was well tolerated.

Modafinil and γ-hydroxybutyrate have sleep state-specific pharmacological actions on hypocretin-1 physiology in a primate model of human sleep

Hypocretin-1 is a hypothalamic neuropeptide that is important in the regulation of wake and the lack of which results in the sleep disorder narcolepsy. Using a monkey that has consolidated wake akin to humans, we examined pharmacological manipulation of sleep and wake and its effects on hypocretin physiology. Monkeys were given the sleep-inducing γ-hydroxybutyrate (GHB) and the wake-inducing modafinil both in the morning and in the evening. Cerebrospinal fluid hypocretin-1 concentrations changed significantly in response to the drugs only when accompanied by a behavioral change (GHB-induced sleep in the morning or modafinil-induced wake in the evening). We also found that there was a large (180-fold) interindividual variation in GHB pharmacokinetics that explains variability in sleep induction in response to the drug. Our data indicate that the neurochemical concomitants of sleep and wake are capable of changing the physiological output of hypocretin neurons. Sleep independent of circadian timing is capable of decreasing cerebrospinal fluid hypocretin-1 concentrations. Furthermore, hypocretin neurons do not seem to respond to an 'effort' to remain awake, but rather keep track of time spent awake as a wake-promoting counterbalance to extended wakefulness.

[Integrated treatment of the symptoms of narcolepsy-cataplexy syndrome with sodium oxybate]

INTRODUCTION

Treatment of narcolepsy-cataplexy is based on the use of different drugs that either stimulate or modify REM sleep, which makes it possible to improve the symptoms that characterise the disease.

AIM

To present the characteristics of sodium oxybate, a new drug that has been approved in the United States and in the European Union for use in treating narcolepsy-cataplexy; the main contribution made by this new agent is the possibility of acting on all the symptoms of the disease at the same time.

DEVELOPMENT

In four randomised, double-blind, placebo-controlled studies and with a class A level of evidence, sodium oxybate has proved to be effective in improving the cardinal symptoms of narcolepsy-cataplexy, that is to say, hypersomnia, cataplexy and fragmentation of nocturnal sleep. Treatment was well tolerated and the side effects, consisting mainly of nausea or symptoms related with the nervous system, such as anxiety, depression, confusion or drowsiness, were mild or moderate in most cases and rarely led to the patient's giving up the treatment. The drug has a favourable pharmacokinetic profile, with little potential to interact with other pharmaceuticals. It seems to have a synergic effect with modafinil, boosting its effects in the treatment of excessive sleepiness. Although it is a substance that has been used as a recreational drug, no cases of addiction or drug abuse have been observed in narcoleptic patients treated in a controlled manner.

CONCLUSIONS

Sodium oxybate can be considered to be a first-choice drug in the treatment of narcolepsy-cataplexy.

Use, function, and subjective experiences of gamma-hydroxybutyrate (GHB)

Self-reported use of gamma-hydroxybutyrate (GHB) among clubbers has increased over the last decade, and is often reported in the scientific literature in association with negative events such as amnesia, overdose, and use in drug facilitated sexual assault. However, there has been relatively little work investigating the phenomenology of GHB intoxication, and the reasons underlying use. In this study, 189 individuals reporting at least one lifetime use of GHB completed an online questionnaire recording GHB use behaviours, GHB use function, and subjective GHB effects. The most frequently reported primary GHB use functions were for recreation (but not in nightclubs) (18.3%); to enhance sex (18.3%); to be sociable (13.1%); and to explore altered states of consciousness (13.1%). GHB was more commonly used within the home (67%) compared to nightlife environments (26.1%) such as clubs, although this differed on the basis of respondent's sexuality. Principle components analysis of GHB user responses to the subjective questionnaire revealed six components: general intoxication effects, positive intoxication effects, negative intoxication effects, negative physiological effects, positive sexual effects and negative sexual effects. Component scores predicted function of use.

GHB urine concentrations after single-dose administration in humans

Gamma-hydroxybutyric acid (GHB) is used as an illicit drug and is implicated in drug-facilitated sexual assault, but it also has some therapeutic uses. Detection of GHB in urine is important for forensic testing and could be of clinical benefit in overdose management. Urine GHB concentration-time profiles have not been well-characterized or correlated with doses used therapeutically. GHB levels were measured by gas chromatography-mass spectrometry in urine collected over 24 h from 16 adults administered single doses of 50 mg/kg GHB (Xyrem) alone and combined with 0.6 g/kg ethanol. Peak GHB urine concentrations averaged 150-200 mg/L and occurred in the 0-3 h urine collection. Significant variability in GHB urine levels between individuals was observed. Caucasians had lower urine concentrations than other races/ethnicities (p = 0.03). Men had lower GHB levels than women in the first 3 h after dosing (p = 0.038). Coingestion of ethanol did not significantly affect renal clearance of GHB, but urine GHB concentrations were lower in the first 3 h when ethanol and GHB were coingested (p = 0.039). At a proposed cut-off of 10 mg/L to distinguish endogenous versus exogenous GHB levels, 12.5% of the samples collected from 3 to 6 h, 81.3% of samples collected from 6 to 12 h, and 100% of urine specimens collected from 12 to 24 h were below this level. We conclude that the detection time for GHB in urine may be shorter than the previously reported 12-h window in some people taking therapeutic doses of GHB.

Sodium oxybate: new drug. Fewer attacks of cataplexy in some patients

(1) Narcolepsy is characterised by sudden, overwhelming daytime drowsiness, sometimes associated with cataplexy (more or less complete loss of muscle tone during an emotional reaction). (2) Modafinil moderately reduces daytime drowsiness but has no effect on cataplexy. Methylphenidate, an amphetamine psychostimulant, seems to act on both drowsiness and cataplexy, although its clinical evaluation is limited to observational series. (3) Oxybic acid, long used in general anaesthesia, but also misused for recreational and criminal purposes (chemical or drug-induced submission), has been approved to treat adults with both narcolepsy and cataplexy, in the form of an oral solution of sodium oxybate. (4) The rationale behind the use of sodium oxybate is to re-establish a near-normal pattern of the different phases of sleep. Because of its short-lasting action, sodium oxybate has to be taken once at bedtime and then again 2.5 to 4 hours later. (5) Clinical evaluation mainly consists of 4 double-blind placebo-controlled trials of sodium oxybate. Three short-term trials, involving 136 patients treated for 4 weeks and 228 and 270 patients treated for 8 weeks, showed that sodium oxybate at a dose of 4.5 g to 9 g a day reduced the number of cataplexy attacks but that a dose of at least 6 g was needed to reduce daytime drowsiness. A trial involving 56 patients who had been taking sodium oxybate for nearly 2 years, assessed the effects of stopping versus continuing treatment. The results suggest that sodium oxybate is effective in the long term. (6) During clinical trials, 61% of patients had adverse effects attributed to sodium oxybate. These included gastrointestinal disorders (nausea (18%)), neurological disorders (dizziness (15%), headache (6%)), confusion (3%), and enuresis (7%). (7) Altered consciousness and respiratory depression occurred after a single intake of a dose two or three times higher than the recommended dose. (8) Misuse, especially to obtain chemical or drug-induced submission (i.e. as a 'date rape' drug), is facilitated by the odourless and colourless nature of the oral solution. (9) In practice, for some patients who are seriously affected by persistent episodes of cataplexy or drowsiness, despite treatment of narcolepsy, sodium oxybate is preferable to methylphenidate, which has been less thoroughly evaluated. However, the risks of misuse and overdose mean that this drug should only be proposed to patients in whom the benefits are likely to outweigh the risks.

Potential surrogate markers for gamma-hydroxybutyrate administration may extend the detection window from 12 to 48 hours

The exogenous administration of gamma-hydroxybutyrate (GHB) as a drug of abuse, and especially in date rape sexual assaults, has recently increased. Chromatographic techniques are used to detect GHB in blood or urine, with a window of detection limited to 12 h. This brief window makes the proof of administration problematic in most rape cases. This study is aimed to extend the window of detection through surrogate markers of GHB administration. Microarray technology is used in a DBA/2J mouse model to detect gene expression changes in peripheral blood after GHB exposure at times as long as 96 h post exposure. This study focuses on two of the most significantly altered transcripts, epiregulin and phosphoprotein enriched in astrocytes 15 (Pea-15). Both genes have increased the ribonucleic acid expression (8.5- and 4.6-fold upregulation at 96 h, respectively) in GHB-dosed mice (1 g/kg) as compared with the control. To confirm these results at the protein level, an intracellular flow cytometric assay is developed to detect protein level changes in the peripheral blood of both these potential biomarkers after GHB exposure. These results suggest that after further development, epiregulin and Pea-15 may prove to be significant surrogate markers in the indirect detection of GHB administration.

Detection of gamma-hydroxybutyrate in striatal microdialysates following peripheral 1,4-butanediol administration in rats

The illicit use and abuse of 1,4-butanediol (1,4-BD) results from its presumed conversion to gamma-hydroxybutyrate (GHB) and subsequent pharmacological effects via action on GABA-B and GHB-specific receptors. Using in vivo microdialysis we measured the appearance of GHB in the striata of rats after peripheral 1,4-BD administration. We developed and utilized an HPLC-UV (215 nm) detection of GHB that yielded a limit of quantification (S/N=10) of 2.0 micro g/mL (40 ng/injection) and a limit of detection (S/N=3) of 0.75 micro g/mL (15 ng/injection). GHB appeared in the striatal microdialysates within 20 min after intraperitoneal (i.p.) administration of varying doses of 1,4-BD. GHB concentrations reached dose-dependent maxima 80-100 min post-1,4-BD administration, with peak values of 10.6+/-2.9, 25.3+/-3.4 and 48.1+/-7.1 micro g/mL (mean+/-S.E.M.), corresponding to 1,4-BD doses of 250, 500 and 750 mg/kg, respectively. The conversion of 1,4-BD to GHB was completely prevented by the alcohol dehydrogenase inhibitor 4-methylpyrazole (4MP), administered prior to 1,4-BD, as evidenced by the failure of GHB to appear in the striatal microdialysates. Sleep times in animals were similarly correlated with GHB concentrations in the microdialysates.

Gamma-hydroxybutyrate and ethanol effects and interactions in humans

BACKGROUND

Gamma-hydroxybutyrate (GHB) is a common drug of abuse that can produce serious toxicity, particularly when used with other sedatives. We examined the individual and combined effects of GHB and ethanol in human volunteers.

METHODS

Sixteen healthy adults (7 men) were given 50 mg/kg GHB (Xyrem), 0.6 g/kg ethanol in 2 doses, alone and combined in a double-blind, placebo-controlled, crossover study. Plasma concentrations, heart rate (HR), blood pressure (BP), and oxygen saturation (O2sat) were serially monitored for 24 hours.

RESULTS

Adverse events included 2 instances of hypotension and 6 episodes of vomiting with GHB-plus-ethanol ingestion. Oxygen saturation was decreased by GHB and ethanol individually, and maximally decreased by the drugs combined (max -2.1% +/- 0.3%, P < 0.0001 vs placebo). Compared with baseline, systolic and diastolic BP were significantly decreased, and HR was increased by ethanol but not affected by GHB alone (maximum systolic BP change -15.7 +/- 3.0 mm Hg, P = 0.0006; maximum HR change 13.5 +/- 2.3 beats per minute, P = 0.006). Ethanol coingestion resulted in 16% higher GHB maximal plasma concentration and 29% longer elimination half-life, indicating possible enhanced bioavailability or reduced clearance of GHB caused by ethanol, however, these effects were not statistically significant.

CONCLUSIONS

Modest doses of GHB do not affect hemodynamic function, but O2sat was decreased. Gamma-hydroxybutyrate-plus-ethanol resulted in more adverse effects, including gastrointestinal disturbances, hypotension, and decreased O2sat, but only minimal pharmacokinetic interactions were observed.

Alterations in neuronal transport but not blood-brain barrier transport are observed during gamma-hydroxybutyrate (GHB) sedative/hypnotic tolerance

PURPOSE

To investigate if gamma-Hydroxybutyrate (GHB) tolerance is mediated by alterations in GHB systemic pharmacokinetics, transport (blood brain barrier (BBB) and neuronal) or membrane fluidity.

MATERIALS AND METHODS

GHB tolerance in rats was attained by repeated GHB administration (5.31 mmol/kg, s.c., QD for 5 days). GHB sedative/hypnotic effects were measured daily. GHB pharmacokinetics were determined on day 5. In separate groups, on day 6, in situ brain perfusion was performed to assess BBB transport alterations; or in vitro studies were performed (fluorescence polarization measurements of neuronal membrane fluidity or [3H]GABA neuronal accumulation).

RESULTS

GHB sedative/hypnotic tolerance was observed by day 5. No significant GHB pharmacokinetic or BBB transport differences were observed between treated and control rats. Neuronal membrane preparations from GHB tolerant rats showed a significant decrease in fluorescence polarization (treated-0.320 +/- 0.009, n = 5; control-0.299 +/- 0.009, n = 5; p < 0.05). [3H]GABA neuronal transport Vmax was significantly increased in tolerant rats (2,110.66 +/- 91.06 pmol/mg protein/min vs control (1,612.68 +/- 176.03 pmol/mg protein/min; n = 7 p < 0.05).

CONCLUSIONS

Short term GHB administration at moderate doses results in the development of tolerance which is not due to altered systemic pharmacokinetics or altered BBB transport, but might be due to enhanced membrane rigidity and increased GABA reuptake.

-Hydroxybutyrate (GHB) in Humans: Pharmacodynamics and Pharmacokinetics

Despite gamma-hydroxybutyrate (GHB) therapeutic uses and the increasing concern about its toxicity, few studies have addressed GHB dose-related effects under controlled administration and their relationship with its pharmacokinetics. The study design was double-blind, randomized, crossover, and controlled. As a pilot pharmacology phase I study, increasing doses of GHB were given. Single oral sodium GHB doses (40, 50, 60, and 72 mg/kg) were administered to eight volunteers. Plasma and urine were analyzed for GHB by gas chromatography-mass spectrometry. Physiological effects, psychomotor performance, and subjective effects were examined simultaneously. GHB produced dose-related changes in subjective effects as measured by questionnaires and VAS. GHB showed a mixed stimulant-sedative pattern, with initially increased scores in subjective feeling of euphoria, high, and liking followed by mild-moderate symptoms of sedation with impairment of performance and balance. Mean peak GHB plasma concentrations were 79.1, 83.1, 113.5, and 130.1 mug/L for 40, 50, 60, and 72 mg/kg, respectively. GHB-mediated physiological and subjective effects were dose dependent and related to GHB plasma concentrations. GHB urinary excretion was mainly related to administered doses. GHB-mediated subjective and physiological effects seem dose dependent and related to GHB plasma concentrations. Results suggest a high abuse liability of GHB in the range of dose usually consumed.

Sodium oxybate for the treatment of narcolepsy

Narcolepsy, a lifelong disease with diverse symptoms, poses a therapeutic challenge to physicians. Psychomotor stimulants are used to provide some relief from excessive sleepiness, whereas a variety of other medications have traditionally been used to treat the other symptoms of this disorder. Cataplexy, consisting of sudden episodes of bilateral skeletal muscle weakness, has long been treated with tricyclic antidepressants or selective serotonin re-uptake inhibitors. Although these drugs have brought relief to some patients, they cause intolerable adverse effects in others, whereas still others become tolerant to their beneficial effects. In July of 2002, sodium oxybate was approved by the US FDA for the treatment of cataplexy, representing a significant advance in the treatment of this unusual disease. The following drug evaluation summarises the role of this novel medication in the practice of sleep medicine.

Gamma hydroxy butyrate abuse and dependency

The recreational use of gamma hydroxy butyrate (GHB) has gained popularity over the last decade. GHB was initially sold as a safe body building and fat burning compound. It is now also widely abused by body builders and young ravers. GHB attracts young people due the euphoria that it initially produces, and the claimed increase in sociability and sexual function (it is also known as liquid Ecstasy). Over the last few years, there has been an increase in the number of cases of GHB intoxication, dependence and severe withdrawal, as reported in medical literature. The situation is complicated by the use of GHB analogues, other toxic chemicals that are easily converted into GHB. GHB has recently been classified as a class 'C' drug in the UK, but no provisions were made in relation to GHB analogues. GHB has been increasingly used in rape cases due to its capacity to produce intoxication and amnesia. The management of patients dependent on GHB is rather complicated due to the high doses of medication that they require to control withdrawal symptoms.

Pharmacokinetics and excretion of gamma-hydroxybutyrate (GHB) in healthy subjects

In Europe and the United States, the recreational use of gamma-hydroxy butyric acid (GHB) at dance clubs and "rave" parties has increased substantially. In addition, GHB is used to assist in the commission of sexual assaults. The aim of this controlled clinical study was to acquire pharmacokinetic profiles, detection times, and excretion rates in human subjects. Eight GHB-naïve volunteers were administered a single 25-mg/kg body weight oral dose of GHB, and plasma, urine, and oral fluid specimens were analyzed by using gas chromatography-mass spectrometry (GC-MS). Liquid-liquid extraction was performed after acid conversion of GHB to gamma-butyrolactone. Limits of quantitation of 0.1 (oral fluid), 0.2 (urine), and 0.5 microg/mL (plasma) could be achieved in the selected ion monitoring mode. GHB plasma peaks of 39.4 +/- 25.2 microg/mL (mean +/- SEM) occurred 20-45 min after administration. The terminal plasma elimination half-life was 30.4 +/- 2.45 min, the distribution volume 52.7 +/- 15.0 L, and the total clearance 1228 +/- 233 microL/min. In oral fluid, GHB could be detected up to 360 min, with peak concentrations of 203 +/- 92.4 microg/mL in the 10-min samples. In urine, 200 +/- 71.8 and 230 +/- 86.3 microg/mL, were the highest GHB levels measured at 30 and 60 min, respectively. Only 1.2 +/- 0.2% of the dose was excreted, resulting in a detection window of 720 min. Common side-effects were confusion, sleepiness, and dizziness; euphoria and change of vital functions were not observed. GHB is extensively metabolized and rapidly eliminated in urine and oral fluid. Consequently, samples should be collected as soon as possible after ingestion.

[Gamma-hydroxybutyrate (GHB) misuse or abuse and interpretation of toxicological findings]

Gamma-hydroxybutyrate (GHB) Misuse or Abuse and Interpretation of Toxicological Findings The paper presented is a review of important information on gamma-hydroxybutyrate abuse or misuse, its toxicological findings under various circumstances, endogenous concentrations and potentional neoformation, with stressing the difficulties of interpretation which shall be done very carefully.

Neuroleptic-like effects of gamma-hydroxybutyrate: interactions with haloperidol and dizocilpine

gamma-Hydroxybutyrate (GHB) is a drug of abuse with multiple mechanisms of action. Consistent with its ability to modulate dopaminergic systems, GHB reportedly shares behavioral effects with neuroleptics and interacts with them in a synergistic manner. Here, we examined the ability of GHB and haloperidol to induce catalepsy and to affect operant responding. When given alone, both compounds induced catalepsy and decreased response rate. When given together, however, they produced these effects in an additive manner. This is further evidence that GHB has neuroleptic-like effects, but suggests that GHB interacts additively, not synergistically, with neuroleptics. The mechanisms involved in GHB- and haloperidol-induced catalepsy are different because the N-methyl-D-aspartate (NMDA) receptor antagonist, dizocilpine (MK-801), attenuated the cataleptic effects of haloperidol, but enhanced those of GHB. The latter finding suggests that other NMDA receptor antagonists (e.g., the drugs of abuse--phencyclidine and ketamine) may also interact synergistically with GHB.

GHB (gamma-hydroxybutyrate) carrier-mediated transport across the blood-brain barrier

gamma-Hydroxybutyrate (sodium oxybate, GHB) is an approved therapeutic agent for cataplexy with narcolepsy. GHB is widely abused as an anabolic agent, euphoriant, and date rape drug. Recreational abuse or overdose of GHB (or its precursors gamma-butyrolactone or 1,4-butanediol) results in dose-dependent central nervous system (CNS) effects (respiratory depression, unconsciousness, coma, and death) as well as tolerance and withdrawal. An understanding of the CNS transport mechanisms of GHB may provide insight into overdose treatment approaches. The hypothesis that GHB undergoes carrier-mediated transport across the BBB was tested using a rat in situ brain perfusion technique. Various pharmacological agents were used to probe the pharmacological characteristics of the transporter. GHB exhibited carrier-mediated transport across the BBB consistent with a high-capacity, low-affinity transporter; averaged brain region parameters were V(max) = 709 +/- 214 nmol/min/g, K(m) = 11.0 +/- 3.56 mM, and CL(ns) = 0.019 +/- 0.003 cm(3)/min/g. Short-chain monocarboxylic acids (pyruvic, lactic, and beta-hydroxybutyric), medium-chain fatty acids (hexanoic and valproic), and organic anions (probenecid, benzoic, salicylic, and alpha-cyano-4-hydroxycinnamic acid) significantly inhibited GHB influx by 35 to 90%. Dicarboxylic acids (succinic and glutaric) and gamma-aminobutyric acid did not inhibit GHB BBB transport. Mutual inhibition was observed between GHB and benzoic acid, a well known substrate of the monocarboxylate transporter MCT1. These results are suggestive of GHB crossing the BBB via an MCT isoform. These novel findings of GHB BBB transport suggest potential therapeutic approaches in the treatment of GHB overdoses. We are currently conducting "proof-of-concept" studies involving the use of GHB brain transport inhibitors during GHB toxicity.

Effects of sustained gamma-hydroxybutyrate treatments on spontaneous and evoked firing activity of locus coeruleus norepinephrine neurons

BACKGROUND

Gamma-hydroxybutyrate is currently used to promote nighttime sleep in the treatment of narcolepsy; however, it is also a drug of abuse ("Liquid Ecstasy") associated with a withdrawal syndrome with anxiety features. Of interest, the activity of locus coeruleus neurons is a reflective index of these above mentioned behavioral states.

METHODS

Using in vivo extracellular unitary recordings, sustained administration of gamma-hydroxybutyrate (40 mg/kg/day via minipump implanted subcutaneously) on the spontaneous and sensory-evoked burst firing of locus coeruleus norepinephrine neurons was assessed in rats.

RESULTS

A 2-day and 10-day gamma-hydroxybutyrate administration decreased the spontaneous firing activity of locus coeruleus neurons by 52% and 54%, respectively, when compared with controls. A similar degree of attenuation on evoked burst firing of norepinephrine neurons also occurred in these rats (2-day gamma-hydroxybutyrate: 47% and 10-day gamma-hydroxybutyrate: 58%), when compared with controls. In contrast, rats treated with gamma-hydroxybutyrate for 10 days followed by removal of the minipump for 36 hours resulted in a 33% augmentation in spontaneous locus coeruleus activity as compared with controls. Furthermore, a robust 79% increase in burst firing in response to paw-pinch was exhibited in theses rats.

CONCLUSIONS

Chronic gamma-hydroxybutyrate treatment inhibits the spontaneous and sensory-evoked burst firing of locus coeruleus norepinephrine neurons, whereas these indices are enhanced during drug withdrawal. The alteration in norepinephrine activity during chronic gamma-hydroxybutyrate administration may contribute to the ability of this agent to induce sleep and regulate narcoleptic episodes. Enhanced norepinephrine activity during withdrawal may be related to symptoms of anxiety on rapid termination of this drug in abusers.

The ??-Hydroxybutyrate Withdrawal Syndrome

gamma-Hydroxybutyrate (GHB) is endogenous inhibitory transmitter that, when administered in pharmacological doses, has sedative-hypnotic properties. It is used in anaesthesia for the treatment of narcolepsy/catalepsy and in alcohol/opioid detoxification treatment regimens. Based on its purported anabolic effects, GHB use became established among bodybuilders. As the euphorigenic effects of GHB became publicised, attendees at dance clubs and rave parties began to use it alone or in combination with other psychoactive drugs. Following the ban of GHB in 1990, several precursor products (e.g. gamma-butyrolactone, butanediol) became widely used as replacement drugs until their ultimate proscription from lawful use in 2000. GHB and its precursors, like most sedative-hypnotic agents, can induce tolerance and produce dependence. Although many GHB users will experience a mild withdrawal syndrome upon drug discontinuation, those with chronic heavy GHB use can experience severe withdrawal. This syndrome clinically resembles the withdrawal syndrome noted from alcohol and other sedative-hypnotic drugs (e.g. benzodiazepines). Distinct clinical features of GHB withdrawal are its relatively mild and brief autonomic instability with prolonged psychotic symptoms. Patients with fulminant GHB withdrawal require aggressive treatment with cross-tolerant sedative hypnotics, such as benzodiazepines.

Characterization of the pharmacokinetic and pharmacodynamic interaction between gamma-hydroxybutyrate and ethanol in the rat

It has been reported that ethanol enhances the hypnotic effect of gamma-hydroxybutyrate (GHB). In order to clarify the nature of this interaction we studied the pharmacokinetics and pharmacodynamics of combinations of GHB and ethanol in rats. Intraperitoneal injections of the GHB precursor gamma-butyrolactone (300 mg/kg) together with ethanol (3000 mg/kg) (n = 4) resulted in a longer "sleeping time" than the sum of the individual times (n = 8). Pharmacokinetic analysis of GHB concentrations with a two-compartment model with Michaelis-Menten (M-M) elimination in rats receiving a bolus of GHB (400 mg/kg, i.v.) in addition to steady-state ethanol concentrations (300-3000 microg/ml) (n = 12) or saline (n = 15) showed no marked differences in the area under the curve. The nature of the pharmacodynamic interaction was studied using isobolographs and an interaction model for the loss of the startle and righting reflex and a reaction to a painful tail clamp in rats receiving combinations of steady state concentrations of ethanol (1000-3000 microg/ml) and GHB (200-1400 microg/ml). For the righting reflex, synergy was observed at high ethanol concentrations (>2000 microg/ml) and additivity at lower concentrations. For the startle reflex, it was antagonistic at ethanol concentrations below 1000 microg/ml, and additivity was seen at higher concentrations. For the tail clamp reaction, a slight but significant antagonism was found at all combined concentrations. It is concluded that ethanol prolongs the sleeping time induced by GHB in the rat, which may not be due to a pharmacokinetic interaction. Pharmacodynamic interactions between GHB and ethanol in the rat occur, and the nature varies with the reflex studied and the concentration of ethanol used.

The influence of gender and food on the pharmacokinetics of sodium oxybate oral solution in healthy subjects

Sodium oxybate (Xyrem; gamma-hydroxybutyrate) oral solution was recently approved in the United States for the treatment of cataplexy in patients with narcolepsy. Two single-center, randomized, open-label studies in healthy volunteers receiving single oral 4.5-g doses of sodium oxybate evaluated effects of (1) gender on oxybate pharmacokinetics and (2) food on its oral bioavailability. In the latter study, one dose was administered after an overnight fast, another after a high-fat meal; 1 week separated treatments. Sodium oxybate pharmacokinetics was not significantly different between sexes. However, food significantly altered the bioavailability of oxybate by decreasing mean peak plasma concentration, increasing median time-to-peak concentration, and decreasing the area under the plasma concentration-time curve. Food did not affect elimination and urinary excretion of unchanged drug. No dose adjustment of sodium oxybate based on sex is indicated. Although significant food effects were observed, these are minimized in patients by the nocturnal dosing of sodium oxybate hours after the evening meal at a consistent time interval following food ingestion.

Influence of hypovolemia on the pharmacokinetics and electroencephalographic effect of gamma-hydroxybutyrate in the rat

BACKGROUND

Hypovolemia alters the effect of propofol in the rat by influencing the pharmacokinetics and the end organ sensitivity. We now studied the effect of hypovolemia on the anesthetic gamma-hydroxybutyrate (GHB) because in contrast with propofol it increases blood pressure.

METHODS

Thirty-two rats were randomly assigned to undergo moderate hypovolemia or a control procedure. Each rat received either an infusion of sodium-GHB (390 mg x kg(-1) x 5 min(-1)) or the same volume of an equimolar solution of sodium chloride (6.9%). Plasma samples were taken for GHB assay (high-performance liquid chromatography) and the electroencephalography and blood pressure values were recorded. A two-compartment model with Michaelis-Menten elimination was fitted to the concentration-time data and a sigmoid E(max) model to the electroencephalographic effect effect site concentration curve allowing the study of the end organ sensitivity.

RESULTS

Plasma concentration-time curves and the total volume of distribution in hypovolemic and normovolemic rats were comparable with only small but significant differences in central volume of distribution and the intercompartmental clearance. There was no significant difference either in the distribution from the plasma to the brain (k(e0)) or in the end organ sensitivity (EC50 = 335 +/- 76 microg/ml in control vs. 341 +/- 89 microg/ml in hypovolemic rats). GHB temporarily increased mean arterial pressure in both groups, which cannot be explained by the sodium salt alone.

CONCLUSIONS

Hypovolemia does not influence the overall concentration-time curve of GHB and induces no changes in the electroencephalographic effect of GHB in the rat. This difference with propofol may be due to the fact that it increases blood pressure but also due to its different pharmacokinetic properties.

Evidence for a gamma-hydroxybutyrate (GHB) uptake by rat brain synaptic vesicles

gamma-Hydroxybutyrate (GHB) is an endogenous metabolite of mammalian brain which is derived from GABA. Much evidence favours its role as an endogenous neuromodulator, synthesized, stored and released at particular synapses expressing specific receptors. One key step for GHB involvement in neurotransmission is its uptake by a specific population of synaptic vesicles. We demonstrate that this specific uptake exists in a crude synaptic vesicle pool obtained from rat brain. The kinetic parameters and the pharmacology of this transport are in favour of an active vesicular uptake system for GHB via the vesicular inhibitory amino acid transporter. This result supports the idea that GABA and GHB accumulate together and are coliberated in some GABAergic synapses of the rat brain, where GHB acts as a modulatory factor for the activity of these synapses following stimulation of specific receptors.

Gamma-Hydroxybutyrate (orphan medical)

Orphan Medical is developing gamma-hydroxybutyrate (Xyrem) for the potential treatment of narcolepsy [183352]. In October 2000, an NDA was filed with the FDA [384422], [405504] and Xyrem received an FDA approvable letter in July 2001. Orphan Medical stated that it believed it could meet the requirements in the letter, including a trial in respiratory-compromised patients, by the end of 2001 [414461]. The FDA also requested follow-up safety data from patients in previous Xyrem trials. At that time, the drug was not expected to be launched until mid-2002 [415301], [416305]. In October 1999, the US House of Representatives passed the HR 2130 bill, allowing the medical use of gamma-hydroxybutyrate, which is classified as a Schedule I controlled substance in the US [343562]; the Senate approved this legislation in November 1999 [348206]. In February 2000, a congressional bill supporting the continued development of medically formulated gamma-hydroxybutyrate was passed, making medically formulated gamma-hydroxybutyrate products Schedule III substances [354108], [356597]. GHB occurs naturally in many human tissues. It has previously been used in the treatment of narcolepsy and is not patentable for that indication.

[Gamma-hydroxybutyrate--an endogenous substance and a new central nervous system stimulant. Clinical aspects of acute poisoning]

During the last six months, the Poison Control Centre at Bispebjerg Hospital, Copenhagen, Denmark, has observed an increasing number of patients intoxicated with GHB, a drug of abuse. The patients are often admitted to the emergency ward shortly after having taken the drug, unconscious or comatose. If younger patients present with these symptoms, intoxication with GHB should be seriously considered. The effects are seen within 15 to 30 minutes after oral ingestion of the drug. Spontaneous recovery usually occurs within three to five hours. The most common effects are mild euphoria, sedation, vomiting, somnolence, bradycardia, aggressive behaviour, apnoea, respiratory depression, and coma. Normally the patient breathes adequately, but insufficient respiration may occur and deaths have been described. The drug is often consumed together with alcohol and other drugs of abuse, which strengthens the effect of GHB. Treatment is symptomatic. A review of the literature with special emphasis on clinical effects included toxicology and treatment is given.

Pharmacokinetics of gammahydroxybutyrate (GHB) in narcoleptic patients

Sodium gammahydroxybutyrate (GHB) is an endogenous compound that has been under investigation in the management of narcolepsy for about two decades. The data confirm that GHB treatment decreases daytime sleepiness and episodes of cataplexy, sleep paralysis, and hypnagogic hallucinations. The current study evaluated the pharmacokinetics of GHB, given twice in one night to six narcoleptic patients who had been chronically taking GHB nightly on a similar basis. Results confirmed earlier reports and showed nonlinear pharmacokinetics. Maximum concentrations were reached in 40 +/- 6.2 and 35.7 +/- 7 minutes after the first and second dose respectively. Mean AUCinf was 17731.6 +/- 4867 mg/mL/m. Mean GHB T1/2 was 53 +/- 19 minutes. GHB elimination appears to be capacity-limited in some patients when administered at a fixed dose of 3 g twice nightly at a 4-hour interval.

[Comparative study of permeability of derivatives of gamma-aminobutyric and gamma-hydroxybutyric acids through hemato-encephalic barrier]

The authors studied the permeability of the blood-brain barrier (CEB) to two nootropics: calcium ketogomopantothenate (KRA-Ca), a GABA derivative, and and calcium salt of oxybutyrate (OB-Ca), a derivative of GOBA. It was established that both preparations penetrate the CEB easily and are found in the brain at different intervals after their administration. However, essential differences in the distribution constant of these drugs were disclosed: KPA-Ca permeated the CEB more intensively and was accumulated in larger amounts in the late-term intervals.

[Gamma-hydroxybutyric acid--significance for anesthesia and intensive care medicine?]

Gamma-hydroxybutyric acid (GHB) as a natural component of the mammalian brain was first introduced in clinical anaesthetic practice more than 30 years ago. Although GHB induced a reliable state of sedation and anaesthesia without depressing either respiratory or cardiocirculatory parameters or liver and kidney function, the drug was nearly displaced from clinical practice because of its prolonged duration of action. The results of recent clinical studies indicate a re-evaluation of GHB in emergency and critical care medicine. GHB is regarded as a natural neuronal transmitter with circuits which synthesise, accumulate and release GHB. Specific binding sites have also been demonstrated and identified. GHB is completely metabolized in the liver to the natural substrates carbon dioxide and water without accumulation in central or peripheral tissues. The reduction of energy metabolism and its possible properties as an "oxygen radical scavenger" may be of therapeutic benefit if tissues are exposed to hypoxia or reperfusion. Therefore, the application of GHB seems to be of advantage in states of traumatic brain injury with cerebral oedema or ischaemic lesions of brain or extraneural tissues. In hypovolaemic states or in patients with impaired cardiovascular function, the pressure effects of GHB may be beneficial for the prevention of tissue damage and may improve survival in the case of cardiocirculatory resuscitation. In the intensive care unit, GHB might be a favourable alternative to established sedative agents. Occurrence of side effects such as tolerance and withdrawal syndromes after the application of sedative drugs, an impaired metabolism with the accumulation of metabolites in the case of liver or kidney dysfunction as well as an insufficient regulation of natural sleep may be diminished by the application of GHB. The results of various clinical studies also suggest that GHB may be useful in the treatment of alcohol and opiate withdrawal syndrome. However, further studies are necessary to specify the proposed indications of GHB in anaesthesiology and critical care medicine.

Displacement of [3H] gamma-hydroxybutyrate binding by benzamide neuroleptics and prochlorperazine but not by other antipsychotics

Since gamma-hydroxybutyrate receptor agonists exhibit dopaminergic regulatory properties and neuroleptic-like effects in neuropharmacological tests, the common neuroleptics were tested for [3H] gamma-hydroxybutyrate binding activity on rat brain membranes. (-)-Sulpiride, sultopride, amisulpride and prochlorperazine possess affinity for the gamma-hydroxybutyrate site(s), consistent with their therapeutic dosage. This study has revealed that gamma-hydroxybutyrate receptors represent an additional target for antipsychotics.

Dose-dependent absorption and elimination of gamma-hydroxybutyric acid in healthy volunteers

Gamma-hydroxybutyric acid (GHB) is effective in treatment of the alcohol and opiate withdrawal syndromes. Its absorption and disposition kinetics have been studied in 8 healthy male volunteers following oral administration of single doses of 12.5, 25 and 50 mg kg-1. The AUC increased disproportionately with the dose and so the apparent oral clearance decreased significantly as the dose was increased, whereas the terminal half-life and mean residence time increased. The peak plasma concentrations normalised to the lowest dose fell significantly with increasing doses, whilst the corresponding peak times increased. These findings suggest that both the oral absorption and the elimination of GHB are capacity-limited processes. GHB did not bind to significant extent to plasma proteins over the therapeutic concentration range. The pharmacokinetic parameters in healthy volunteers were not significantly different from those previously observed in alcohol-dependent patients with compensated alcoholic liver disease.

Pharmacokinetics of gamma-hydroxybutyric acid in alcohol dependent patients after single and repeated oral doses

1. The pharmacokinetics of gamma-hydroxybutyric acid (GHB) were studied in 10 alcohol dependent subjects after single and repeated therapeutic oral doses (25 mg kg-1 every 12 h for 7 days). 2. GHB was readily absorbed and rapidly eliminated (tmax = 20-45 min; mean t1/2z 27 +/- 5 s.d. min). Urinary recovery of unchanged GHB was negligible (less than 1% of the dose). gamma-butyrolactone was not detected in either plasma or urine, indicating that lactonization of GHB does not occur in vivo. 3. The multiple-dose regimen resulted neither in accumulation of GHB nor in time-dependent modification of its pharmacokinetics. 4. In five subjects, the data were consistent with nonlinear elimination kinetics of GHB. Administration of a 50 mg kg-1 dose to these subjects resulted in significant increases in dose-normalized AUC, t1/2z and mean residence time. 5. Doubling of the dose also resulted in a significant increase in tmax with little change in Cmax. 6. At the administered doses, GHB did not accumulate in the plasma and caused no serious side effects.

gamma-Hydroxybutyrate: a health-food product producing coma and seizurelike activity

Sixteen cases of adverse effects due to a new health-food product, gamma-hydroxybutyrate (GHB), were reported to the San Francisco Bay Area Regional Poison Control Center in the 5-month period from June to October 1990. Cases have also been reported in eight other states. Adverse effects included coma (four patients) and tonic-clonic seizurelike activity (two patients). Doses ranged from 1/4 teaspoon to 4 tablespoons. Acute symptoms resolved within 7 hours. GHB was investigated as an anesthetic agent during the 1960s until seizures and lack of analgesia precluded its use. It was recently introduced in the health-food market as a food supplement for body builders with claims of anabolic effects by stimulating growth hormone release. GHB remains under investigational new drug status with the Food and Drug Administration and is illegal for over the counter sale. The Food and Drug Branch of the California Department of Health Services has prohibited further sale of this product in California as have health departments in Florida and South Carolina; however, new cases continue to be reported. Health professionals should be aware of the potential health hazards of GHB.

Effect of gamma-crotonolactone in experimental models of generalized absence seizures

The effect of the unsaturated lactone, gamma-crotonolactone (GCL), against spike wave discharges (SWD) in two pharmacological models of generalized absence seizures in rat was investigated. The models used were the gamma-hydroxybutyrate (GHB) model and the low dose pentylenetetrazole model. GCL pretreatment resulted in a significant decrease in duration of SWD in both models. In addition, this compound reduced the ability of the agonist, muscimol, to enhance SWD duration in the GHB model and was effective in developing animals as well as in adult animals with GHB-induced SWD. These data suggest that GCL may be a useful tool in the study of basic mechanisms of SWD generation in experimental absence seizures.