Specific radioimmunoassay for flunitrazepam

Simultaneous determination of flunitrazepam and its metabolites in plasma and urine by HPLC/DAD after solid phase extraction

A high performance liquid chromatography (HPLC) assay was developed for the determination of flunitrazepam (FNZ) and its metabolites in urine and plasma. The analytes and the internal standard (triazolam, TRZ) were extracted by Sep-Pak C18 SPE-cartridge and separated utilizing a 5 microm ChromSpher C8 glass column with a gradient mobile phase containing methanol and 0.125% (v/v) of isopropylamine in water. Diode array detection (DAD) was carried out at a monitoring wavelength of 240 nm and a reference wavelength of 550 nm. Standard curves were linear from their quantitation limits until 200 ng ml(-1) urine or 250 ng ml(-1) plasma for 7-amino-desmethyl-flunitrazepam (ADF), 7-amino-flunitrazepam (AF), 7-acetamino-flunitrazepam (ACF) and until 400 ng ml(-1) urine or 500 ng ml(-1) plasma for FNZ, 1-desmethyl-flunitrazepam (DF), and 3-hydroxyl-flunitrazepam (HF). The intraday and interday coefficients of variation ranged from 2.04 to 9.07% and from 2.64 to 14.10%, respectively in urine and from 5.13 to 8.60% and from 7.27 to 10.46%, respectively in plasma. The developed method is used in forensic toxicology and is also applicable to pharmacokinetic studies in man.

A specific immunoassay for the detection of flunitrazepam

The development of an immunochemical procedure for the determination of flunitrazepam in whole blood is described. Flunitrazepam was derivatized in position 3 of the benzodiazepine ring to a hapten which was coupled to a carrier protein. To obtain antibodies, rabbits were immunized with these immunogens and the collected antisera were tested in a heterogeneous, competitive RIA. The antibodies showed a very specific reaction with flunitrazepam and hardly any cross-reactivity with related 1,4-benzodiazepines. Because of its high specificity the antiserum has the advantage of a definite determination of low levels of flunitrazepam without the risk of false-negative results obtained by using the commercially available group-specific test systems. The drug was extracted from whole blood in a simple batch process with a polystyrene suspension and the extracts were measured by RIA. The advantages of an immunochemical system, such as short analysis time and simple sample preparation, and the exactness of a drug-specific method are combined in this procedure, which allowed the specific and very sensitive determination of flunitrazepam in the low therapeutic range.

Production of a high affinity antiserum to benzodiazepines

Antibodies specific for benzodiazepines were raised in rabbits by immunization with a conjugate of a benzodiazepine derivative, Ro 7-1986/1, with bovine serum albumin. The presence of anti-Ro 7-1986/1 antibodies in the sera was demonstrated by a radioimmunoassay using the radioligand [3H]flunitrazepam ([3h]FNZ). The antibodies displayed a high-affinity for [3H]FNZ (KD = 0.073 +/- 0.003 nM) and and cross-reacted with a broad spectrum of benzodiazepine derivatives. Benzodiazepine levels in samples of sera and urine of benzodiazepine-treated humans were determined. Due to the high sensitivity of the assay only minute volumes (microliter quantities) of body fluids are employed and, therefore, no extraction of the drugs is required. Nitrazepam and diazepam levels as low as 20 picograms can be easily observed. Intoxicating levels of benzodiazepines can be detected by a single measurement in less than 10 min. This radioimmunoassay is advantageous for pharmacokinetic studies, toxicological examinations and forensic medicine due to its high sensitivity, wide-range specificity and technical simplicity.