Global and regional cerebral metabolic rate of 2-[18F]fluoro-2-deoxy-D-glucose in the presence of ofloxacin, a gamma-aminobutyric acid a receptor antagonist

Effects of GABAA receptors activation on brain glucose metabolism in normal subjects and temporal lobe epilepsy (TLE) patients. A positron emission tomography (PET) study. Part I: Brain glucose metabolism is increased after GABAA receptors activation

Though gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the human central nervous system, the metabolic response to GABA system activation remains imperfectly known. We studied in vivo with positron emission tomography (PET) the variations of glucose metabolism in the human brain after stimulation of the GABAA receptors by systemic administration of the specific GABAA agonist, 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP). These investigations were performed in three normal volunteers and as part of presurgical evaluation for temporal lobe epilepsy in six patients. While clinical and electroencephalographic (EEG) monitoring showed a sedative effect and sleepiness after THIP administration, glucose metabolism was paradoxically increased in grey matter structures, which are known to have a high density of GABAA receptors. These findings suggest that the pharmacological activation of GABA pathways, although inhibitory and producing a decrease of vigilance, increases the energetic demand at least during a phase of GABA agonist action, probably at the synaptic or at the glial cell level.

Safety and tolerability of fluoroquinolones

Since their introduction in the mid-1980s, the fluoroquinolones have been administered to more than 100 million patients. Generally, adverse effects reported in association with the fluoroquinolones have been those that could have been predicted by previous experience with non-fluorinated derivatives and by animal toxicity studies. Examples of such adverse events are CNS-related toxicity, upper gastrointestinal tract reactions and phototoxicity. Some adverse experiences in animals, notably cartilage toxicity, have been of minimal clinical importance. This should lead to a re-evaluation of the possible paediatric indications for the fluoroquinolones. With temafloxacin, which was withdrawn from clinical use in June 1992, new and serious adverse events were reported at a frequency of about 1 per 3500 patients treated. This frequency of adverse events is too low to be detected even in very careful analyses of phase III registration studies. Anaphylaxis, haemolytic anaemia and renal failure were the most striking adverse events reported with temafloxacin, and, in addition, hypoglycaemia and hepatic failure were reported. These reactions may be attributable to an immunological reaction in some patients. Because of the rarity of these reactions, they can be detected only by studies encompassing thousands of patients, usually during postmarketing surveillance. Safety monitoring of each new fluoroquinolone during its early clinical use is therefore recommended.