Comparison of cyclodextrin-barbiturate noncovalent complexes using electrospray ionization mass spectrometry and capillary electrophoresis.

Srinivasan K, Bartlett MG.

The Department of Pharmaceutical and Biomedical Sciences, College of Pharmacy, The University of Georgia, Athens 30602-2352, USA.

Various noncovalent complexes between native and derivatized cyclodextrins (CDs) and barbiturates were studied using capillary electrophoresis (CE) and electrospray ionization mass spectrometry (ESI-MS). This paper involves the study of four aspects of CD-barbiturate noncovalent inclusion complexes. The first study focused on determining the formation of CD-barbiturate inclusion complexes in ESI-MS. This determination was accomplished by the comparison of migration data from CE with ESI-MS inclusion complex peak abundances, which were found to be complementary. The second study found the possibility of predicting native beta-CD mediated CE elution orders for barbiturates using data from ESI-MS. A third study focused on the formation of barbiturate inclusion complexes with derivatized beta-CD and gamma-CD. As part of this study, the effect of the extent of side chain substitution on native CD complexation behavior was investigated. The results indicated that the number of side chains on the CD does not affect the formation of barbiturate complexes with the hydrophobic CD cavity. Finally, a comparison of the hydroxypropyl-beta-CD-barbiturate and hydroxypropyl-gamma-CD-barbiturate complexes in CE and ESI-MS was made to study the relationship between strength of drug-CD binding and enantioresolution. The results from the above studies indicated that the gas phase and the solution state complexes showed comparable behavior indicating that similar interactions played a role in stabilizing these complexes. While it was possible to use the ESI-MS data to determine drug binding to the CDs, it was not possible to predict whether a separation of the enantiomers of a chiral barbiturate would occur. However, the ESI-MS data could be used to eliminate certain CDs from consideration as chiral selectors.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10786897&dopt=Abstract barbiturate Butalbital Fioricet





Barbiturates for acute traumatic brain injury.

Roberts I.

Department of Epidemiology, Institute of Child Health, 30 Guilford Street, London, UK, WC1N 1EH. Ian.roberts ich.ucl.ac.uk

BACKGROUND: Raised intracranial pressure (ICP) is an important complication of severe brain injury, and is associated with a high mortality rate. Barbiturates are believed to reduce intracranial pressure by suppressing cerebral metabolism, thus reducing cerebral metabolic demands and cerebral blood volume. However, barbiturates also reduce blood pressure and therefore may adversely effect cerebral perfusion pressure. OBJECTIVES: To assess the effects of barbiturates in reducing raised intracranial pressure, mortality and morbidity in people with acute traumatic brain injury. To quantify any side effects resulting from the use of barbiturates. SEARCH STRATEGY: The review draws largely on the search strategy developed for the Cochrane Injuries Group as a whole. However, in addition the Cochrane Library was searched in December 1996 using the text terms "barbiturate*," "pentobarb*," "phenobarb*," "head," and "brain." An updated search was done in April 1999. SELECTION CRITERIA: Randomised or quasi randomised trials of any one or more of the barbiturate class of drugs (amobarbital, barbital, hexobarbital, mephobarbital, methohexital, murexide, pentobarbital, phenobarbital, secobarbital, thiobarbiturate) where study participants had a clinically diagnosed acute traumatic brain injury of any severity. DATA COLLECTION AND ANALYSIS: The reviewer extracted the data and assessed the quality of allocation concealment in the trials. MAIN RESULTS: The pooled relative risk for death (barbiturate vs no barbiturate) was 1.09 (95%CI 0.81 to 1.47). The pooled effect of barbiturates on adverse neurological outcome, measured using the Glasgow Outcome Scale (death, persistent vegetative state or severe disability) was 1.15 (95% 0.81 to 1.64). Two studies examined the effect of barbiturate therapy on intracranial pressure. In the study by Eisenberger et al, a smaller proportion of patients in the barbiturate group had uncontrolled ICP (68% vs 83%). The relative risk for uncontrolled ICP was 0.81 (95%CI 0.62 to 1.06). Similarly, in the study by Ward et al, mean ICP was lower in the barbiturate treated group. Barbiturate therapy results in an increase in the occurrence of hypotension (RR=1.80 95%CI 1.19 to 2.70). For every four patients treated one will develop clinically significant hypotension. Mean body temperature was significantly lower in the barbiturate treated group. Schwartz et al compared pentobarbital with mannitol in the control of intracranial pressure. Pentobarbital was less effective than mannitol for control of raised ICP. 68% of patients in the pentobarbital treated group required a second drug for the treatment of raised intracranial pressure compared to 39% in the mannitol treated group (RR=1.75 95%CI 1.05 to 2.92). There was no substantial difference in mortality between the two study groups (RR=1.18 95%CI 0.73 to 1.92). REVIEWER'S CONCLUSIONS: There is no evidence that barbiturate therapy in patients with acute severe head injury improves outcome. Barbiturate therapy results in a fall in blood pressure in 1 in 4 treated patients. The hypotensive effect of barbiturate therapy will offset any ICP lowering effect on cerebral perfusion pressure.

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Effects of thiopental on transport and metabolism of glutamate in cultured cerebellar granule neurons.

Qu H, Waagepetersen HS, van Hengel M, Wolt S, Dale O, Unsgard G, Sletvold O, Schousboe A, Sonnewald U.

Department of Pharmacology and Toxicology, Norwegian University of Science and Technology, Trondheim.

This study was performed to analyze the effects of the barbiturate thiopental on neuronal glutamate uptake, release and metabolism. Since barbiturates are known to bind to the GABA(A) receptor, some experiments were carried out in the presence of GABA. Cerebellar granule neurons were incubated for 2 h in medium containing 0.25 mM [U-(13)C]glutamate, 3 mM glucose, 50 microM GABA and 0.1 or 1 mM thiopental when indicated. When analyzing cell extracts, it was surprisingly found that in addition to glutamate, aspartate and glutathione, GABA was also labeled. In the medium, label was observed in glutamate, aspartate and lactate. Glutamate exhibited different labeling patterns, indicating metabolism in the tricarboxylic acid cycle, and subsequent release. A net uptake of [U-(13)C]glutamate and unlabeled glucose was seen under all conditions. The amounts of most metabolites synthesized from [U-(13)C]glutamate were unchanged in the presence of GABA with or without 0.1 mM thiopental. In the presence of 1 mM thiopental, regardless of the presence of GABA, decreased amounts of [1,2, 3-(13)C]glutamate and [U-(13)C]aspartate were found in the medium. In the cell extracts increased [U-(13)C]glutamate, [1,2, 3-(13)C]glutamate, labeled glutathione and [U-(13)C]aspartate were observed in the 1 mM thiopental groups. Glutamate efflux and uptake were studied using [(3)H]D-aspartate. While efflux was substantially reduced in the presence of 1 mM thiopental, this barbiturate only marginally inhibited uptake even at 3 mM. These results may suggest that the previously demonstrated neuroprotective action of thiopental could be related to its ability to reduce excessive glutamate outflow. Additionally, thiopental decreased the oxidative metabolism of [U-(13)C]glutamate but at the same time increased the detectable metabolites derived from the TCA cycle. These latter effects were also exerted by GABA.

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Latent overexpression of hepatic CYP2C7 in adult male and female rats neonatally exposed to phenobarbital: a developmental profile of gender-dependent P450s.

Agrawal AK, Shapiro BH.

University of Pennsylvania School of Veterinary Medicine, Philadelphia 19104-6048, USA.

For more than 20 years it has been known that neonatal exposure to phenobarbital results in a delayed, but permanent overexpression of drug-metabolizing enzymes in adult male and female rats. Accordingly, to identify the specific isoform(s) of P450 responsible for the imprinted overexpression of hepatic monooxygenases, we have monitored the developmental profile of some dozen hepatic P450 isoforms in 4- to 150-day-old male and female rats neonatally treated with the barbiturate. Some of the cytochrome P450s (CYP), i. e., CYP2A1, 2A2, 2C6, 3A1, and 3A2, exhibit the typical transient response in which isoform levels (mRNA, protein, and/or specific catalytic activity) rise precipitously at the time of phenobarbital administration and rapidly decline to preinduction levels after withdrawal of the barbiturate. Other isoforms, i.e., CYP1A1, 1A2, 2C7, 2C11, 2C12, and 2C13, were neither constitutively expressed nor phenobarbital inducible in the neonate. Only one of these isoforms, female predominant (M:F, approximately 1:2) CYP2C7, exhibited a barbiturate-induced delayed, but persistent approximately 30 to 50% overexpression from puberty through adulthood. We propose that at the time of exposure, neonatally administered phenobarbital produces a "silent" programming defect resulting in a delayed, but persistent overexpression of the isoform, contributing, at least in part, to a permanent elevation of hepatic drug-metabolizing enzyme activities.

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