Comparing single and cumulative dosing procedures in human triazolam discriminators.
This study evaluated a cumulative dosing procedure for drug discrimination with human participants. Four participants learned to discriminate triazolam (0.35 mg/70 kg) from placebo. A crossover design was used to compare the results under a single dosing procedure with results obtained under a cumulative dosing procedure. Under the single dosing procedure, a dose of triazolam (0, 0.05, 0.15, or 0.35 mg/70 kg) or secobarbital (0, 25, 75, or 175 mg/70 kg) was administered 45 min before assessment. Determining each dose-effect curve thus required four sessions. Under the cumulative dosing procedure, four doses of triazolam (0, 0.05, 0.10, and 0.20 mg/70 kg) or secobarbital (0, 25, 50, and 100 mg/70 kg) were administered approximately 55 min apart, producing a complete dose-effect curve in one four-trial session. Regardless of procedure, triazolam and secobarbital produced discriminative stimulus and self-reported effects similar to previous single dosing studies in humans. Shifts to the right in cumulative dose-effect curves compared to single dose-effect curves occurred on several self-report measures. When qualitative stimulus functions rather than quantitative functions are of interest, application of cumulative dosing may increase efficiency in human drug discrimination. (+info)
Comparison of radioimmunoassay with thin-layer chromatographic and gas-liquid chromatographic methods of barbiturate detection in human urine.
A radioimmunoassay (I) for barbiturates was compared with thin-layer chromatographic (II) and gas-liquid chromatographic (III) methods for barbiturate detection in human urine. Timed urine samples were obtained from volunteers who had ingested 100 mg of a barbiturate. I detected barbiturate in all urines tested up to 76 h after the dose, and III in all up to 52 h and in 90% up to 76 h. II detected barbiturates in 90% of all urine samples for only 30 h, after which is reliability declined. Glutethimide interfered with radioimmunoassay of barbiturate, producing false positives. I is sensitive, reliable, and fast, and lends itself to screening large numbers of urine samples for barbiturates. For routine urine surveillance, however, we found I to be less useful than II, which is still the method of choice. I has, however, proved to be an excellent method for confirming results of II. (+info)
Isotopic analogues as internal standards for quantitative analyses of drugs and metabolites by GC-MS--nonlinear calibration approaches.
In order to achieve accurate quantitation of drugs and metabolites (analytes) in complex matrices, 2H- (and less commonly 13C-) labeled analogues of the analytes are now routinely adapted as the internal standards (IS) using linear calibration models to fit data generated by selected ion monitoring gas chromatography-mass spectrometry (GC-MS) protocols. In this study, the effects of cross-contribution (contribution of the IS to the intensity of the ion designated for the analyte and vice versa) on the linearity of the calibration data are examined. Nonlinear approaches that may address this problem are also studied. Two ion pairs (one with least and one with significant cross-contribution) from each of the following analyte/IS pairs are used as the exemplar systems for this study: butalbital/13C4-butalbital, butalbital/2H5-butalbital, secobarbital/13C4-secobarbital, and secobarbital/2H5-secobarbital. Analyte/IS ion intensity ratios of a series of standard solutions are correlated with the analyte/IS concentration ratios using one-point, multiple-point (unweighted and weighted) linear, and hyperbolic functions. The one-point calibration approach produces excellent calibration results in treating data derived from ion pairs with no significant cross contribution. In cases where significant cross-contribution exists, results derived from the one-point approach show, as expected, significant deviations at both ends of the concentration range. With the cross-contribution phenomenon accounted for, the hyperbolic calibration model is clearly more effective in fitting calibration data at both the lower and higher analyte concentration ends, thus significantly lowering the detection limit and extending the calibration range to a higher level. However, the calibration range cannot be extended indefinitely. At the low concentration end, noise-to-signal ratio and the cross-contribution of the IS to the intensity of the ion designated for the analyte, however insignificant, will incrementally reduce the quality of the observed ion intensity and intensity ratio data. At the high concentration end, detection saturation and the cross-contribution of the analyte to the intensity of the ion designated for the IS, however insignificant, will incrementally decrease the "slope" of the calibration curve. Thus, acceptable sensitivity (increase in analyte/IS ion-pair intensity ratio per unit increase in analyte concentration) of the calibration curve will become the limiting factor. (+info)
Simultaneous detection of morphine and barbiturates in urine by radioimmunoassay.
This report describes a radioimmunoassay for the simultaneous detection of morphine and barbiturates. Morphine and barbiturate antibodies, obtained from goats, were mixed with 125l-labeled antigens. By adjusting concentrations of the morphine and barbiturate antibodies and radiolabeled antigens, closely superimposed standard curves for the two drugs would be obtained. As a consequence, similar response curves were obtained for urine specimens containing morphine or barbiturates. Although concentrations as low as 25 mug/liter could be measured, to ensure against false positive reactions the test should be performed at the 100 mug/liter concentration. Unknown samples positive by the dual assay were confirmed by separately testing the specimens with the individual radioimmunoassay specific for morphine or barbiturate. Equivalency tests of urines positive for morphine, positive for barbiturates, or negative for both demonstrated complete correlation between the single and dual assays. The mixed reagent retained its sensitivity and specificity for at least three months when stored at 4 or 25 degrees C. The dual radioimmunoassay is a rapid, simple procedure that can be adapted to automated processes and that is suitable for large- and small-scale screening. (+info)
Interaction between sedative premedicants and ketamine in man in isolated perfused rat livers.
Premedication with diazepam, hydroxyzine or secobarbital significantly increased ketamine-induced sleep time (137 +/- 3.5 min, 135 +/- 9.2 min, 128 +/- 4.7 min) over that of unpremedicated controls (98.5 +/- 4.4 min) in man. The corresponding mean plasma half-lives (t1/2) of ketamine were longer in patients premedicated with diazepam or seconbarbital (57.8 +/- 4.9 min, 46 +/- 3.2 min) than in controls (36 +/- 1.8 min). Ketamine t1/2 in the perfusate of isolated, perfused rat livers was prolonged 30 to 50 per cent by addition of diazepam, secobarbital, or hydroxyzine. The data suggest that these commonly used premedicants decrease the rate of ketamine metabolism. (+info)
Alterations in ventricular fluid pressure during ketamine anesthesia in hydrocephalic children.
We studies ventricular fluid pressure changes in 26 hydrocephalic children following administration of ketamine. The increase in VFP previously found with intravenously administered ketamine was compared with changes after ketamine given intramuscularly, and the possible alteration of this increase with sedative premedicants was studies. Changing the route of administration did not change the time to peak VFP changes or the duration of pressure elevation. There was no demonstrable alteration of the increase in VFP by premedication with secobarbital, dorperidol, or diazepam in clinical dosage. We feel that acute rises of VFP may affect areas of marginal cerebral blood flow and may increase the risk of herniation of brain tissue. (+info)
Barbiturates and aortic and venous smooth-muscle function.
Using isolated rat aortic strips (AS) and portal veins (PV), it was found that all of the barbiturates studied (thiopental, secobarbital, pentobarbital, amobarbital, phenobarbital, and barbital): a) inhibit development of spontaneous mechanical activity (vasomotion) in AS and PV in concentrations used to induce surgical anesthesia or concentrations used for anticonvulsive therapy; b) dose-dependent attenuate contractions induced by epinephrine and potassium (K+); c) cause non-competitive displacement of the dose-response curves of these vasoactive compounds; d) attenuate calcium (Ca++)-induced contractions of K+-depolarized AS and PV; e) rapidly relax drug-induced, as well as Ca++-induced, contractions of AS and PV. In addition, the data indicate that: a) rat portal venous smooth muscle is more sensitive to the inhibitory actions of barbiturates than is rat aortic smooth muscle, and b) thiopental, but none of the other barbiturates, can elicit dose-dependent contractions of AS. Concentrations of barbiturates known to be present during induction of surgical anesthesia can exert depressant effects on at least two types of vascular smooth muscle that may be related to actions on movement and/or translocation of Ca++. (+info)
Barbiturates induce mitochondrial depolarization and potentiate excitotoxic neuronal death.
Barbiturates are widely used as anesthetics, anticonvulsants, and neuroprotective agents. However, barbiturates may also inhibit mitochondrial respiration, and mitochondrial inhibitors are known to potentiate NMDA receptor-mediated neurotoxicity. Here we used rat cortical cultures to examine the effect of barbiturates on neuronal mitochondria and responses to NMDA receptor stimulation. The barbiturates tested, secobarbital, amobarbital, and thiamylal, each potentiated NMDA-induced neuron death at barbiturate concentrations relevant to clinical and experimental use (100-300 microm). By using rhodamine-123 under quenching conditions, barbiturates in this concentration range were shown to depolarize neuronal mitochondria and greatly amplify NMDA-induced mitochondrial depolarization. Barbiturate-induced mitochondrial depolarization was increased by the ATP synthase inhibitor oligomycin, indicating that barbiturates act by inhibiting electron transport sufficiently to cause ATP synthase reversal. Barbiturates similarly amplified the effects of NMDA on cytoplasmic free calcium concentrations. The cell-impermeant barbiturate N-glucoside amobarbital did not influence mitochondrial potential or potentiate NMDA neurotoxicity or calcium responses. However, all of the barbiturates attenuated NMDA-induced calcium elevations and cell death when present at millimolar concentrations. Whole-cell patch-clamp studies showed that these effects may be attributable to actions at the cell membrane, resulting in a block of NMDA-induced current flux at millimolar barbiturate concentrations. Together, these findings reconcile previous reports of opposing effects on barbiturates on NMDA neurotoxicity and show that barbiturate effects on neuronal mitochondria can be functionally significant. Effects of barbiturates on neuronal mitochondria should be considered in experimental and clinical application of these drugs. (+info)