Diazepam

🧬 Receptor activity

Target	Action	Affinity	Source
Translocator protein	—	Ki 0.9 nM	CHEMBL
Unchecked	—	Ki 1.53 nM	CHEMBL
GABA A receptor alpha-6/beta-2/gamma-2	—	Ki 2.1 nM	CHEMBL
GABA-A receptor; anion channel	—	Ki 2.9 nM	CHEMBL
GABA-A receptor; alpha-2/beta-3/gamma-2	—	Ki 6.6 nM	CHEMBL
GABA-A receptor; alpha-1/beta-2/gamma-2	—	Ki 9.8 nM	CHEMBL
GABA A receptor alpha-5/beta-3/gamma-2	—	Ki 9.8 nM	CHEMBL
GABA A receptor alpha-3/beta-2/gamma-2	—	Ki 10 nM	CHEMBL
Gamma-aminobutyric acid receptor subunit alpha-5/beta-2/gamma-2	—	Ki 11 nM	CHEMBL
Gamma-aminobutyric acid receptor subunit alpha-5	—	Ki 11 nM	CHEMBL
GABA A receptor alpha-1/beta-1/gamma-2	—	Ki 12 nM	CHEMBL
GABA-A receptor; alpha-1/beta-3/gamma-2	—	Ki 13 nM	CHEMBL
Gamma-aminobutyric acid receptor subunit alpha-1	—	Ki 14 nM	CHEMBL
GABA-A receptor; alpha-3/beta-3/gamma-2	—	Ki 15 nM	CHEMBL
Gamma-aminobutyric acid receptor subunit alpha-2	—	Ki 15 nM	CHEMBL
Gamma-aminobutyric acid receptor subunit alpha-3	—	Ki 15 nM	CHEMBL
GABA A receptor alpha-2/beta-2/gamma-2	—	Ki 20 nM	CHEMBL
Cholinesterase	—	Ki 43 nM	CHEMBL
Fatty acid-binding protein, liver	—	Ki 531 nM	CHEMBL
GABA-A receptor; alpha-6/beta-3/gamma-2	—	Ki 3000 nM	CHEMBL
Acetylcholinesterase	—	Ki 13000 nM	CHEMBL

Mechanism of action

Diazepam is a benzodiazepine tranquilliser with anticonvulsant, sedative, muscle relaxant and amnesic properties. Benzodiazepines, such as diazepam, bind to receptors in various regions of the brain and spinal cord. This binding increases the inhibitory effects of gamma-aminobutyric acid (GABA). GABAs functions include CNS involvement in sleep induction. Also involved in the control of hypnosis, memory, anxiety, epilepsy and neuronal excitability.
Diazepam is a benzodiazepine that exerts anxiolytic, sedative, muscle-relaxant, anticonvulsant and amnestic effects. Most of these effects are thought to result from a facilitation of the action of gamma aminobutyric acid (GABA), an inhibitory neurotransmitter in the central nervous system.
Benzodiazepines are widely used in clinical anesthesia as premedication, but also to induce general anesthesia. Recent in vitro studies suggest that gamma-aminobutyric acid type A receptors, harboring a classical high-affinity benzodiazepine binding site, possess another "nonclassical" binding site for benzodiazepines. At present, it is unclear if, and to what extent, this novel nonclassical binding site is of relevance for the actions of benzodiazepines in the central nervous system. Because neocortex is involved in mediating the sedative and hypnotic properties of general anesthetics, ... the actions of diazepam /were quantified/ over a wide range of concentrations (from 10 nM up to 100 uM) in organotypic slice cultures using extracellular multiunit recordings of spontaneous action potential activity. Up to a concentration of 6.25 uM, diazepam reduced the activity of neocortical neurons, approaching a maximum of approximately 20%. This action was nullified by the benzodiazepine antagonist flumazenil. At concentrations >12.5 uM, diazepam evoked a second concentration-dependent dampening of network activity. Unlike the low concentration effect, this high concentration component was resistant to flumazenil. Diazepam induced a biphasic attenuation of spontaneous action potential firing of neocortical neurons. Low to moderate concentrations caused a monotonic, mild depression that is mediated via the classical binding site as it is antagonized by flumazenil. However, the effects of diazepam observed at high concentrations were not affected by flumazenil. Hence, these findings support the concept of at least 2 different binding sites for benzodiazepines on gamma-aminobutyric acid type A receptors. Furthermore, /these/ results are consistent with the hypothesis that the classical high-affinity binding site mediates low-dose diazepam actions, such as amnesia, anxiolysis, and sedation, while a second, nonclassical and independent site contributes to the anesthetic effects of diazepam, such as hypnosis and immobility.
Benzodiazepine site agonists or inverse agonists enhance or reduce gamma-aminobutyric acid(A) (GABA(A)) receptor-mediated inhibition of neurons, respectively. Recently, it was demonstrated that the point mutation gamma 2F77I causes a drastic change in the affinity of a variety of benzodiazepine agonists or inverse agonists in receptor binding studies. Here we investigated the potency and efficacy of 10 benzodiazepine site ligands from 6 structural classes in wild-type and gamma 2F77I point mutated recombinant GABA(A) receptors composed of alpha 1 beta 3 gamma 2, alpha 2 beta 3 gamma 2, alpha 3 beta 3 gamma 2, alpha 4 beta 3 gamma 2, alpha 5 beta 3 gamma 2, and alpha 6 beta 3 gamma 2 subunits. Results indicate that the effects of the benzodiazepine site ligands zolpidem, zopiclone, Cl218872, L-655,708 and DMCM were nearly completely eliminated in all mutated receptors up to a 1 microM concentration. The effects of bretazenil, Ro15-1788 or abecarnil were eliminated in some, but not all mutated receptors, suggesting that the gamma 2F77I mutation differentially influences the actions of these ligands in different receptor subtypes. In addition, this point mutation also influences the efficacy of diazepam for enhancing GABA-induced chloride flux, suggesting that the amino acid residue gamma 2F77 might also be involved in the transduction of the effect of benzodiazepines from binding to gating.
Although the precise mechanism by which diazepam exerts its antiseizure effects is unknown, animal and in vitro studies suggest that diazepam acts to suppress seizures through an interaction with gamma-aminobutyric acid (GABA) receptors of the A-type (GABAA). GABA, the major inhibitory neurotransmitter in the central nervous system, acts at this receptor to open the membrane channel allowing chloride ions to flow into neurons. Entry of chloride ions causes an inhibitory potential that reduces the ability of neurons to depolarize to the threshold potential necessary to produce action potentials. Excessive depolarization of neurons is implicated in the generation and spread of seizures. It is believed that diazepam enhances the actions of GABA by causing GABA to bind more tightly to the GABAA receptor
For more Mechanism of Action (Complete) data for DIAZEPAM (8 total), please visit the HSDB record page.

Pharmacodynamics

Diazepam is a benzodiazepine that exerts anxiolytic, sedative, muscle- relaxant, anticonvulsant and amnestic effects. Most of these effects are thought to result from facilitation of the action of gamma aminobutyric acid (GABA), an inhibitory neurotransmitter in the central nervous system.

Pharmacokinetics

Half-life

Diazepam has a biphasic half-life with an initial rapid distribution phase followed by a prolonged terminal elimination phase of 1 or 2 days; its action is further prolonged by the even longer half-life of 2-5 days of its principal active metabolite, desmethyldiazepam (nordiazepam), the relative proportion of which increases in the body on long-term administration. The plasma half-life of diazepam is prolonged in neonates, in the elderly, and in patients with kidney or liver disease.
... The distributive (alpha) half-life of diazepam is about 1 hr, while the elimination (beta) half-life is about 1.5 days initially and even longer after prolonged treatment.
In full term infants, elimination half-lives around 30 hours have been reported, with a longer average half-life of 54 hours reported in premature infants of 28 - 34 weeks gestational age and 8 - 81 days post-partum. In both premature and full term infants the active metabolite desmethyldiazepam shows evidence of continued accumulation compared to children. Longer half-lives in infants may be due to incomplete maturation of metabolic pathways
Elimination half-life increases by approximately 1 hour for each year of age beginning with a half-life of 20 hours at 20 years of age.
In mild and moderate cirrhosis, average half-life is increased. The average increase has been variously reported from 2-fold to 5-fold, with individual half-lives over 500 hours reported. ... Mean half-life is also prolonged with hepatic fibrosis to 90 hours (range 66 - 104 hours), with chronic active hepatitis to 60 hours (range 26 - 76 hours), and with acute viral hepatitis to 74 hours (range 49 - 129).
For more Biological Half-Life (Complete) data for DIAZEPAM (7 total), please visit the HSDB record page.

Absorption

After oral administration, it is considered that diazepam is rapidly and completely absorbed from the gastrointestinal tract as >90% of diazepam is absorbed and the average time to achieve peak plasma concentrations is 1 – 1.5 hours with a range of 0.25 to 2.5 hours. Absorption is delayed and decreased when administered with a moderate fat meal. In the presence of food mean lag times are approximately 45 minutes as compared with 15 minutes when fasting. There is also an increase in the average time to achieve peak concentrations to about 2.5 hours in the presence of food as compared with 1.25 hours when fasting. This results in an average decrease in Cmax of 20% in addition to a 27% decrease in AUC (range 15% to 50%) when administered with food.
Diazepam and its metabolites are excreted mainly in the urine, predominantly as their glucuronide conjugates.
In young healthy males, the volume of distribution at steady-state is 0.8 to 1.0 L/kg.
The clearance of diazepam is 20 to 30 mL/min in young adults.
Diazepam rectal gel is well absorbed following rectal administration, reaching peak plasma concentrations in 1.5 hours. The absolute bioavailability of Diazepam rectal gel relative to Valium injectable is 90%. The volume of distribution of Diazepam rectal gel is calculated to be approximately 1 L/kg. ... Both diazepam and its major active metabolite desmethyldiazepam bind extensively to plasma proteins (95-98%).
The concentration of diazepam in plasma and saliva and its binding to plasma protein was determined in normal subjects receiving 10 mg single oral dose over an 8 hr period. A linear relationship was found between diazepam concentration in plasma and that in both mixed and parotid saliva, over plasma concentrations ranging from 196-74.8 ug/mL. Results indicate that there is no significant difference between parotid saliva and mixed saliva concentrations over a period of 8 hr after a single oral dose of diazepam and that appearance of diazepam in saliva may provide an alternate, noninvasive method of determining plasma diazepam levels.

Metabolism

Diazepam is N-demethylated by CYP3A4 and 2C19 to the active metabolite N-desmethyldiazepam, and is hydroxylated by CYP3A4 to the active metabolite temazepam. N-desmethyldiazepam and temazepam are both further metabolized to oxazepam. Temazepam and oxazepam are further largely eliminated by way of conjugation to glucuronic acid via glucuronidation. Furthermore, oxidation of diazepam is mediated by cytochrome P450 isozymes; formation of desmethyl-diazepam mainly by CYP2C19 and CYP3A and 3-hydroxy-diazepam (temazepam) and oxazepam by CYP3A. Because CYP2C19 is polymorphic, extensive metabolizers (EMs), and poor metabolizers (PMs) of diazepam can be distinguished. PMs of diazepam showed significantly lower clearance (12 vs 26 mL/min) and longer elimination half-life (88 vs 41 h) of diazepam than EMs after a single oral dose. Also, PMs had lower clearance, higher AUC and longer elimination half-life of desmethyl-diazepam.
Diazepam is N-demethylated by CYP3A4 and 2C19 to the active metabolite N-desmethyldiazepam, and is hydroxylated by CYP3A4 to the active metabolite temazepam. N-desmethyldiazepam and temazepam are both further metabolized to oxazepam. Temazepam and oxazepam are largely eliminated by glucuronidation.
/Investigators/ observed variations in the metabolism of diazepam in Wistar rats. /The authors/ studied these variations carefully, and found that the variations are dimorphic and about 17% of male Wistar rats examined showed two times higher diazepam metabolic activities in their liver microsomes than the rest of animals at the substrate concentrations less than 5 uM. /They were/ classified as extensive metabolizer and poor metabolizer of diazepam. No sex difference was observed in the frequency of appearance of extensive metabolizer. Activities of the primary metabolic pathways of diazepam were examined to elucidate the cause of this polymorphism in male Wistar rats. No significant differences were observed in activities of neither diazepam 3-hydroxylation or N-desmethylation between extensive metabolizer and poor metabolizer rats, while activity of diazepam p-hydroxylation was markedly (more than 200 times) higher in extensive metabolizer rats, indicating that this reaction is responsible for the polymorphism of diazepam metabolism in Wistar rats. We examined the expression levels of CYP2D1, which was reported to catalyze diazepam p-hydroxylation in Wistar rats to find no differences in the expression levels of CYP2D1 between extensive metabolizer and PM rats. The kinetic study on diazepam metabolism in male Wistar rats revealed that extensive metabolizer rats had markedly higher V(max) and smaller K(m) in diazepam p-hydroxylation than those of poor metabolizer rats, indicating the presence of high affinity high capacity p-hydroxylase enzyme in extensive metabolizer rats. As a consequence, at low concentrations of diazepam, major pathways of diazepam metabolism were p-hydroxylation and 3-hydroxylation in male extensive metabolizer rats, while in male poor metabolizer rats, 3-hydroxylation followed by N-desmethylation. Due to this kinetic nature of p-hydroxylase activity, extensive metabolizer rats had markedly higher total CL(int) of diazepam than that of poor metabolizer rats. Polymorphism in diazepam metabolism in humans is well documented, but this is the first report revealing the presence of the polymorphism in diazepam metabolism in rats. The current results infer polymorphic expression of new diazepam p-hydroxylating enzyme with lower K(m) than CYP2D1 in extensive metabolizer Wistar rats.
Diazepam has known human metabolites that include Temazepam and nordiazepam.
Hepatic via the Cytochrome P450 enzyme system. The main active metabolite is desmethyldiazepam, in addition to minor active metabolites including temazepam and oxazepam.
Route of Elimination: Diazepam and its metabolites are excreted mainly in the urine, predominantly as their glucuronide conjugates.
Half Life: Biphasic 1-2 days and 2-5 days, active metabolites with long half lives.

Protein binding

Despite high binding to plasma proteins (98-99%) - mainly albumin and to a lesser extent α1-acid glycoprotein - diazepam is widely distributed into tissues and crosses the blood-brain barrier and is highly lipid soluble, which causes the initial effects to decrease rapidly as it is redistributed into fat deposits and tissues.