Peter M. Lauven

The effects of a benzodiazepine antagonist Ro 15-1788 in the presence of stable concentrations of midazolam.

The benzodiazepine antagonist Ro 15–1788 was administered in a 10-mg intravenous bolus dose to seven healthy young adult volunteers to evaluate the drugs efficacy and duration of action against midazolam. A steady state serum concentration of midazolam was obtained by an initial fast infusion rate of 6.0 mg/min (duration: 10 min) and a maintenance infusion rate of 0.275 mg/min. After administering the antagonist, all subjects opened their eyes without any command in a median time of 36 s (range: 28–48 s). Their personal, temporal and local orientation was reestablished within 54–120 s (median time: 65 s). The subjects fell deeply asleep, again in a median time of 145 min (range: 115–150 min), which was interpreted as an indication of the returning action of midazolam, which was infused for a total period of 210 min. Ro 15–1788 deserves further study as an antagonist, since it could prove useful in the management of benzodiazepine overdosage and in the reversal of benzodizepine action following surgical anesthesia and in the intensive care.

Automated Gas Chromatography for Studies of Midazolam Pharmacokinetics

Plasma midazolam concentrations following single therapeutic doses can be quantitated using electron-capture gas-liquid chromatography. After addition of a benzodiazepine analogue as an internal standard, samples are extracted with benzeneisoamyl alcohol (98.5:1.5). The organic extract is evaporated to dryness, reconstituted, and chromatographed on an SP-2250 liquid phase. The automatic sampler allows up to 100 chromatographic analyses per 24-h period. The sensitivity limits are 2-3 ng of midazolam per ml of plasma, and the variation of identical samples is 7 per cent or less. The method was used in a study of six females who received single intravenous doses of midazolam for purposes of anesthetic induction prior to minor gynecologic procedures. Mean (+/- SE) kinetic variables for midazolam were: volume of central compartment, 0.37 (+/ 0.06 l/kg; total volume of distribution, 1.72 (+/- 0.05) l/kg: initial distribution half-life, 7.2 (+/- 1.6) min; elimination half-life, 2.5 (+/- 0.2) h; total clearance, 8.1 (+/- 0.52) ml.min-1.kg-1.

Automated Electron-Capture Gas Chromatographic Analysis of Flunitrazepam in Plasma

Nanogram quantities of flunitrazepam and its major metabolite, desmethylflunitrazepam, can be reliably quantitated in human plasma using electron-capture gas-liquid chromatography. After addition of methylnitrazepam as the internal standard, plasma samples are extracted with an organic solvent (benzene:isoamyl alcohol). The organic extract is separated, evaporated to dryness, reconstituted, and injected onto the chromatograph using an automatic sampling system which allows up to 100 analyses/24 h. The sensitivity limits are 0.5 ng/ml for flunitrazepam and 1-2 ng/ml for desmethylflunitrazepam. Use of the method is illustrated in a study of the pharmacokinetic properties of flunitrazepam following a single 1.0-mg intravenous dose.

Threshold hypnotic concentration of methohexitone.

SummaryMethohexitone was administered to 8 healthy adult volunteers as a microprocessor controlled infusion that generated 3 cycles of linearly increasing plasma levels with an anticipated slope of 0.2 µg·ml−1·min−1. When a deep unconscious state was obtained, as indicated by burst suppression in the EEG, the infusion was stopped and then restarted when the volunteer was fully orientated. Frequent venous blood samples were obtained during and after the infusions to evaluate the threshold concentration at induced sleep and the return of orientation, at the loss and return of the eye lid reflex and corneal reflex, and the appearance and disappearance of EEG burst suppression patterns.From the first to the third infusion cycle only a slight and insignificant increase in the mean threshold concentrations was observed so the plasma levels were averaged over all three infusion cycles. The concentrations (µg/ml) found were: asleep 3.39 and orientated 3.35, loss 4.42 and recurrence 4.32 of eye lid reflex, loss 6.51 and recurrence 5.18 of corneal reflex, and appearance 10.7 and disappearance 9.3 of burst suppression. Acute tolerance that would have led to a significant increase in threshold concentration from the first to the last infusion cycle was not demonstrated.If induced sleep and the appearance of EEG burst suppression are considered as clinical endpoints of anaesthesia, the therapeutic window of methohexitone covers a mean venous serum concentration range of 3.4 to 10.7 µg/ml.

Determination of Ro 15-1788, a benzodiazepine antagonist, in human plasma by gas-liquid chromatography with nitrogen-phosphorus detection. Application to single-dose pharmacokinetic studies.

A sensitive (to 3 ng/ml) and specific method for analysis of the benzodiazepine antagonist Ro 15-1788 is described. The method utilizes gas-liquid chromatography with nitrogen-phosphorus detection. A neutral pH ethyl acetate extraction of 0.1-3.0 ml plasma is used for sample preparation. Standard curves using methylclonazepam as the internal standard are linear for plasma concentrations up to 200 ng/ml. Applicability of the method is demonstrated by a pharmacokinetic study in a normal volunteer who received 10 mg Ro 15-1788 intravenously.