Flunitrazepam

🧬 Receptor activity

Target	Action	Affinity	Source
GABAA receptor α1 subunit	Positive (Allosteric modulator)	—	GTOPDB
GABAA receptor α2 subunit	Full agonist (Allosteric modulator)	—	GTOPDB
GABAA receptor α3 subunit	Full agonist (Allosteric modulator)	—	GTOPDB
GABAA receptor α5 subunit	Full agonist (Allosteric modulator)	—	GTOPDB
GABA-A receptor; alpha-2/beta-3/gamma-2	—	Ki 1.1 nM	CHEMBL
Gamma-aminobutyric acid receptor subunit alpha-5/beta-2/gamma-2	—	Ki 2.1 nM	CHEMBL
GABA-A receptor; alpha-5/beta-3/gamma-2	—	Ki 2.1 nM	CHEMBL
GABA-A receptor; alpha-1/beta-2/gamma-2	—	Ki 2.2 nM	CHEMBL
GABA-A receptor; alpha-1/beta-3/gamma-2	—	Ki 2.2 nM	CHEMBL
GABA A receptor alpha-2/beta-2/gamma-2	—	Ki 2.5 nM	CHEMBL
GABA-A receptor; alpha-3/beta-3/gamma-2	—	Ki 4.5 nM	CHEMBL
GABA A receptor alpha-3/beta-2/gamma-2	—	Ki 4.5 nM	CHEMBL
Unchecked	—	Ki 5.11 nM	CHEMBL
GABA-A receptor; alpha-6/beta-3/gamma-2	—	Ki 2000 nM	CHEMBL

Mechanism of action

Benzodiazepines bind nonspecifically to benzodiazepine receptors BNZ1, which mediates sleep, and BNZ2, which affects affects muscle relaxation, anticonvulsant activity, motor coordination, and memory. As benzodiazepine receptors are thought to be coupled to gamma-aminobutyric acid-A (GABAA) receptors, this enhances the effects of GABA by increasing GABA affinity for the GABA receptor. Binding of the inhibitory neurotransmitter GABA to the site opens the chloride channel, resulting in a hyperpolarized cell membrane that prevents further excitation of the cell.

Pharmacodynamics

Flunitrazepam is a powerful hypnotic drug that is a benzodiazepine derivative. It has powerful hypnotic, sedative, anxiolytic, and skeletal muscle relaxant properties. The drug is sometimes used as a date rape drug. In the United States, the drug has not been approved by the Food and Drug Administration for medical use, and is considered to be an illegal drug. It has however been approved in the United Kingdom and other countries.

Pharmacokinetics

Half-life

18-26 hours
The elimination half-life of flunitrazepam is reported to be between 16 and 35 hrs.

Absorption

50% (suppository) and 64-77% (oral)
... Flunitrazepam crosses the placenta slowly. About 12 hr after a 1 mg oral dose cord:maternal blood ratios in early and late pregnancy were about 0.5 and 0.22, respectively. Amniotic fluid:maternal serum ratios were in the 0.02-0.07 range in both cases. accumulation in the fetus may occur after repeated doses.
Flunitrazepam is excreted into breast milk. Following a single 2 mg oral dose in five patients, mean milk:plasma ratios at 11, 15, 27, and 39 hr were 0.61, 0.68, 0.9, and 0.75, respectively.
... The objective of this paper was to study elimination of flunitrazepam and 7-aminoflunitrazepam in urine collected from 10 healthy volunteers who received a single 2 mg oral dose of Rohypnol, to determine how long after drug administration 7-aminoflunitrazepam can be detected. A highly sensitive NCI-GC-MS method for the simultaneous quantitation of flunitrazepam (LOQ 100 pg/mL) and 7-aminoflunitrazepam (LOQ 10 pg/mL) in urine was developed. All samples were screened for benzodiazepines using optimized micro-plate enzyme immunoassay. The highest concns of 7-aminoflunitrazepam (70-518 ng/mL) and flunitrazepam (0.7-2.8 ng/mL) in urine were observed 6 hr after drug administration in 9 subjects and after 24 hr in one subject. In 6 subjects 7-aminoflunitrazepam was detected up to 14 days after flunitrazepam admin, in one subject up to 21 days and in 3 subjects up to 28 days. In urine samples collected from 6 volunteers, flunitrazepam was detected 3 days after Rohypnol intake, in 3 subjects 24 hr, and in one subject 5 days later. Benzodiazepine micro-plate enzyme immunoassay kit allowed the detection of flunitrazepam and metabolities 5 to 21 days after drug administration.
To study the pharmacokinetics of flunitrazepam (used for sedation in neonates and infants), to determine the influence of both gestational and postnatal age on the pharmacokinetic parameters, and to analyze the relationship between the hemodynamic parameters and flunitrazepam plasma concentration. Flunitrazepam was infused for 20 minutes as a single dose (0.2 mg x kg(-1)) and as multiple doses (0.1 mg x kg(-1)). Six to eight 1-mL blood samples were collected per patient. Flunitrazepam plasma concentration was measured by gas chromatography-mass spectrometry. Thirty-one patients (25 neonates and six infants) were included in the study. Only three of them received multiple doses. After the single dose (n = 28), half-life was 22.6 +/- 7.3 hours, clearance was 0.15 +/- 0.14 L x kg x h(-1), and volume of distribution was 4.6 +/- 4.1 L x kg(-1) (mean +/- SD). Plasma clearance and volume of distribution significantly increased with postnatal age (P < .05), but no pharmacokinetic parameter varied significantly with gestational age. Diastolic blood pressure significantly decreased with increasing flunitrazepam plasma concentrations (P < .05). Postnatal age but not gestational age influenced flunitrazepam pharmacokinetic parameters in neonates and infants. Diastolic blood pressure was inversely correlated to flunitrazepam plasma concentration.

Metabolism

Hepatic.
/The authors/ have identified CYP2C19 & CYP3A4 as the principal cytochrome P450s involved in the metab of flunitrazepam to its major metabolites desmethylflunitrazepam & 3-hydroxyflunitrazepam. Human CYP2C19 & CYP3A4 mediated the formation of desmethylflunitrazepam with Km values of 11.1 & 108 microM, respectively, & 3-hydroxyflunitrazepam with Km values of 642 & 34.0 microM, respectively. In human liver microsomes (n=4) formation of both metabolites followed biphasic kinetics. Desmethylflunitrazepam formation was inhibited 31% by S-mephenytoin & 78% by ketoconazole, suggesting involvement of both CYP2C19 & CYP3A4. Formation of 3-hydroxyflunitrazepam was also significantly inhibited by ketoconazole (94%) & S-mephenytoin (18%). In support of these chemical inhibition data, antibodies directed against CYP2C19 & CYP3A4 selectively inhibited formation of desmethylflunitrazepam by 26 & 45%, respectively, while anti-CYP3A4 antibodies reduced 3-hydroxyflunitrazepam formation by 80%. Our data also suggest that CYP1A2, -2B6, -2C8, -2C9, -2D6, & -2E1 are not involved in either of these metabolic pathways. /The authors/ estimate that the relative contributions of CYP2C19 & CYP3A4 to the formation of desmethylflunitrazepam in vivo are 63 & 37%, respectively, at therapeutic flunitrazepam concns (0.03 microM). /The authors/ conclude that the polymorphic enzyme CYP2C19 importantly mediates flunitrazepam demethylation, which may alter the efficacy & safety of the drug, while CYP3A4 catalyzes the formation of 3-hydroxyflunitrazepam.
The aims were to examine the kinetics of the oxidative metabolism of flunitrazepam in vitro when flunitrazepam was dissolved in dimethylformamide and acetonitrile, and to determine which cytochrome P450 isoform(s) are involved. The kinetics of the formations of 3'-hydroxyflunitrazepam and desmethyl-flunitrazepam were non-linear and best estimated using the Hill equation. Inhibition of their formation was studied using specific chemical inhibitors, expressed enzyme systems and specific antibodies. Ks, Vmax, Clmax and n (slope factor) for the formation of 3'-hydroxyflunitrazepam and desmethylflunitrazepam had ranges of 165-338 and 179-391 microM, 22-81 and 3-10 nmol x mg protein(-1) x h(-1), 6-17 and 0.9-1.9 microl x mg protein(-1) x h(-1), and 2.3-3.6 and 1.6-2.6 respectively when dimethylformamide was the organic solvent. When acetonitrile was the solvent, Ks, Vmax, Clmax and n (slope factor) for the formation of 3'-hydroxyflunitrazepam and desmethylflunitrazepam had ranges of 173-231 and 74-597 microM, 35-198 and 2.7-48 nmol.mg protein(-1) x h(-1), 1347 and 0.7-6.3 microl.mg protein(-1) x h(-1), and 1.5-3.6 and 1.1-2.7 respectively. CYP2C19, CYP3A4 and CYP1A2 mediated the formation of both 3'-hydroxyflunitrazepam and desmethylflunitrazepam. Investigators need carefully to consider the choice of organic solvent to avoid false CYP identification.
In recent years, there has been a notable increase in the number of reports on drug-facilitated sexual assault. Benzodiazepines are the most common so-called "date-rape" drugs, with flunitrazepam (Rohypnol) being one of the most frequently mentioned. The aim of this study was to determine whether flunitrazepam & its major metabolite 7-aminoflunitrazepam could be detected in hair collected from 10 healthy volunteers after receiving a single 2 mg dose of Rohypnol using solid phase extraction & NCI-GC-MS. Such data would be of great importance to law enforcement agencies trying to determine the best time interval for hair collection from a victim of drug-facilitated sexual assault in order to reveal drug use. Ten healthy volunteers (8 women & 2 men, 21 to 49 yr old) participated in the study. The following hair samples were collected from each volunteer: one before flunitrazepam admin, & 1, 3, 5, 14, 21, & 28 days after. In 5 volunteers, 7-aminoflunitrazepam was detected 24 hr after flunitrazepam admin & remained in hair throughout the entire 28-day study period (0.6-8.0 pg/mg). In 2 cases, 7-aminoflunitrazepam appeared in hair 21 days after drug intake (0.5-2.7 pg/mg), & in two subjects 14 days later (0.5-5.4 pg/mg). In one volunteer, 7-aminoflunitrazepam was detected on day 14 & 21 but concns were below the quantitation limit. Flunitrazepam was detected in some samples but all concns were below the quantitation limit (0.5-2.3 pg/mg).
Flunitrazepam has known human metabolites that include 3-hydroxyflunitrazepam and desmethylflunitrazepam.
Hepatic.
Half Life: 18-26 hours