Determination of intact oxazepam by electron capture gas chromatography after an extractive alkylation reaction

Hexapropymate self-poisoning causes severe and long-lasting clinical symptoms

Cases of hexapropymate poisoning requiring intensive care in an urban region of Sweden (420,000 inhabitants) were collected over 2.5 years (1985 to 1987). Only patients with serum hexapropymate concentrations above 5.5 mg/L (30 mumol/L) and with a negative history for intake of tricyclic antidepressants, phenothiazines, barbiturates, antihistaminic drugs and opiates were included. Clinical data about 8 intoxication events in 6 patients were evaluated retrospectively. Initial symptoms included coma, hypotension, hypothermia, and hypoventilation. Maximum coma depth (Glasgow coma score) was 3 to 5 in 5 out of 8 events. On 7 occasions assisted ventilation was required (for 12 hours or more in 5 events). There was no relationship between serum concentrations of hexapropymate and severity of clinical symptoms. All patients survived. Detailed analysis of the drug elimination in one patient showed a terminal elimination half-life of 21 hours, which is longer than previously reported (5 hours). The indications for use of this hypnotic drug may vary between doctors since an 8-fold variation was seen in drug prescription between Swedish counties in 1987. Poisoning with hexapropymate is a serious condition which may require symptomatic treatment in the intensive care unit. The clinical picture is similar to that seen in patients with burbiturate intoxication. There is no role for active forced elimination of the drug. It is questionable whether the clinical value of the drug is outweighted by its toxicity.

The effects of phenytoin dosage on the induction of alpha 1-acid glycoprotein and antipyrine clearance in the dog

Doses of phenytoin from 90 to 800 mg/d were used to study induction of hepatic cytochrome P-450 and plasma alpha 1-acid glycoprotein in dogs. The antipyrine clearance was increased by 80%, which is equivalent to an increase in cytochrome P-450 of 140%, and the plasma glycoprotein concentration rose 200% at the highest dose of phenytoin used. Plasma concentrations of phenytoin were measured at each dose level to provide a definitive value for the amount of inducer present. These data were used to assess the concentration-response relationship for phenytoin inducing either cytochrome P-450 or the glycoprotein. A simple relationship between concentration and effect was not observed, suggesting a complex mechanism of induction.

Derivatization reactions in the gas—liquid chromatographic analysis of drugs in biological fluids

Alkylation, acylation, silylation and other derivatization reactions applied to the gas chromatographic analysis of drugs in biological matrices are reviewed. Reaction conditions are discussed in relation to reaction mechanisms. Detector-oriented labelling of drugs, and derivatization with chiral reagents for the separation of enantiomers are surveyed. Data on the sample clean-up, derivatization and GLC analysis of more than 300 drugs and related compounds are listed.

Pharmacokinetics and bioavailability of intravenous and intramuscular lorazepam with an adjunct test of the inattention effect in humans

Single dose pharmacokinetics and bioavailability of intravenous and intramuscular lorazepam were investigated in 6 younger healthy human volunteers of either sex. The plasma concentration profile after intravenously administered lorazepam could in all cases be fitted by NONLIN to a biexponential function of time with a mean terminal (biological) half-life of 14.10 hrs +/- 2.94 S.D. (range 9.68 - 18.42 hrs). The mean half-life of the initial alpha-phase of distribution was 0.31 hrs +/- 0.11 S.D. The mean apparent volume of distribution derived from AUC, Vd-area (=Vd beta), was 1.24 1 kg-1 +/- 0.17 S.D. Mean plasma clearance of the drug was 62.17 ml kg-1 hr-1 +/- 8.85 S.D. The apparent central volume of distribution characterizing the open two-compartment pharmacokinetic model was 0.59 1 kg-1 +/- 0.19 S.D. After intramuscular administration to the same subjects the plasma concentration time lapse could be described by either tri- or bi-exponential kinetics, which are representative of open two- and one-compartment models with absorption phases, respectively. Mean biological half-life was 14.01 hrs +/- 2.31 S.D. and Vd-area 1.24 l kg-1 +/- 0.14 S.D., both values in full agreement with the findings based on intravenous administration. Half-life of the absorption phase varied from 0.08 to 1.76 hrs. Mean systemic availability of the drug was 88.8% +/- 8.3 S.D. The inattention effect of lorazepam was assessed by exposing the subjects during the intravenous pharmacokinetic experiments to a binaural stimulation test, which revealed various degrees of acute reduced attention in only three of the subjects.

Alkylation with alkylhalides as a derivatization method for the gas chromatographic determination of acidic pharmaceuticals

The various types of alkylation reactions with alkyl halides and their application in the gas chromatographic analysis of acidic compounds of pharmaceutical interest are reviewed. An extensive survey of the use of these methods for the analysis of various (classes of) compounds is given, with special reference to their determination in biological matrices.

Clinical pharmacokinetics of oxazepam and lorazepam

Oxazepam and lorazepam are 3-hydroxy benzodiazepine derivatives used as sedatives and anxiolytics. The major metabolic pathway for both compounds involves conjugation to glucuronic acid at the 3-position, followed by urinary excretion of the inactive glucuronide metabolite. Oxazepam has been administered to humans by the oral route only. Usual ranges for kinetic parameters are: elimination half-life, 5 to 15 hours; volume of distribution, 0.6 to 2.0 L/kg; clearance, 0.9 to 2.0 ml/min/kg. Age and liver disease have a minimal influence on oxazepam kinetics, but renal disease is associated with a prolonged half-life and increased volume of distribution. Typical kinetic values for lorazepam are: elimination half-life, 8 to 25 hours; volume of distribution, 1.0 to 1.3 L/kg; clearance, 0.7 to 1.2 ml/min/kg. Lorazepam clearance is somewhat reduced in old age, but liver disease has a minimal effect on clearance. Oral and intramuscular lorazepam are rapidly absorbed, with systemic availability averaging 90% or more. Both oxazepam and lorazepam are extensively bound to plasma protein, but the free fraction for lorazepam (8 to 12%) is greater than that for oxazepam (2 to 4%).

Disposition pharmacokinetics of lorazepam in the rabbit

The disposition pharmacokinetics of the sedative and anxiolytic drug lorazepam were investigated in 8 rabbits in relation to intravenous bolus injection of 0.3 or 0.6 mg of the compound. Lorazepam showed distinct linear two-compartment characteristics with a mean biological half-life (t 1/2 beta) of only 73.7 min. +/- 17.3 S.D. The mean half-life of the alpha phase of distribution was 18.4 min. +/- 4.7 S.D. The mean apparent steady state volume of distribution was 1.64 1 kg-1 +/- 0.27 S.D., Vc-mean was 1.11 1 kg-1 +/- 0.24 S.D. and Vdarea 2.26 1 kg-1 +/- 0.16 S.D. The calculated apparent volume of the peripheral compartment amounted to 0.53 1 kg-1 +/- 0.28 S.D. Compared to human data the distribution of lorazepam takes place somewhat slower in an about two-times as great apparent volume of distribution, while the disposition of the compound proceeds with an about 20 times as high rate.

Simplified determination of lorazepam and oxazepam in biological fluids by gas chromatography-mass spectrometry

Lorazepam and oxazepam in plasma and urine were measured by gas chromatography-mass spectrometry. Oxazepam was used as an internal standard in the assay of lorazepam and vice versa. After removal of interfering substances with n-hexane, the drugs were extracted with benzene and converted to N1,O3-bistrimethylsilyl derivatives. Glucuronide forms of the drugs were extracted after hydrolysis with beta-glucuronidase. A common fragment ion at m/e 429 was used to monitor the two drugs. The sensitivity was 2 ng/ml for both drugs, which was sufficient to determine plasma and urine concentrations after therapeutic doses to humans.