Diazepam

For medical students2 min readUpdated 2026-10-10

Diazepam (Diazepamum) is a central nervous system-acting drug and a classic anxiolytic. It is widely used in clinical practice, though its pharmacokinetics require thorough understanding: from its atypical muscle absorption profile to the formation of active metabolites.

Pharmacological groupCentral nervous system agents; Anxiolytics

PropertiesVery weak base (pKa 3.0)

MetabolismCYP2C19, CYP3A4/5; deamination and glucuronidation

Key featureForms active metabolites (prolonged duration of action)

FormulationsTablets 5 mg; 0.5% solution in 2 mL ampoules

Absorption and Distribution

Physicochemically, diazepam (Diazepamum) is a very weak base with a pKa of 3.0.

Intramuscular administration warrants special attention. As a general rule, absorption rate is directly proportional to the blood flow at the injection site. Because muscle tissue has a rich vascular network, peak concentration (Cmax) is typically reached within 10–30 minutes. However, diazepam is an exception. It binds specifically to muscle tissue proteins, which significantly delays its absorption from the depot into the systemic circulation.

Metabolism (Biotransformation)

The biotransformation of the drug occurs via hepatic endoplasmic reticulum enzymes.

Microsomal oxidation: Diazepam is metabolized by the cytochrome P-450 system via deamination.
Conjugation: The drug undergoes biosynthetic reactions with endogenous substrates, specifically glucuronidation (forming conjugates with glucuronic acid).

Diazepam acts as a substrate for several isoenzymes:

CYP2C19 (alongside omeprazole, clopidogrel, and propranolol).
CYP3A4 / CYP3A5 — the largest isoenzyme family metabolizing the majority of drugs.

Clinically significant fact: Diazepam biotransformation does not lead to immediate inactivation. The metabolic process generates active metabolites that retain pharmacological activity. This bioactivation phenomenon prolongs the drug's duration of action.

Elimination (Excretion)

The primary organ of diazepam excretion is the kidneys. Excretion kinetics depend on the ionization degree of this weak base relative to urine pH.

In an acidic environment (low pH), weakly alkaline substances such as diazepam become ionized. Ionized molecules lose their ability to be reabsorbed in the renal tubules and are eliminated from the body more rapidly. Consequently, urine acidification weakens and shortens the duration of diazepam action. This principle of urine pH modification underlies forced diuresis protocols in overdose management.

Indications and Restrictions

According to clinical guidelines, diazepam is used in the following settings:

Obstetrics: Threatened preterm labor with a risk of miscarriage. Strict restriction: the drug is prescribed exclusively after the first trimester of pregnancy.
Toxicology and Critical Care: Intravenous diazepam is standard symptomatic therapy for cocaine toxicity to control severe psychomotor agitation.

Prescribing and Dosing

Standard formulations and dosing regimens include:

Tablets: 5 mg. Administered orally at 5 mg 2–3 times daily.
Ampoules: 0.5% solution, 2 mL. For intravenous or intramuscular administration, the total daily dose ranges from 5 mg to 60 mg.

Mnemonic

Diazepam is a tricky base: it gets 'stuck' in muscles (protein binding), 'comes alive' in the liver (active metabolites), and 'runs away' in acidic urine (ionized and rapidly excreted).

Frequently asked questions

What conditions are indications for diazepam use?

Diazepam is indicated for the following conditions and clinical scenarios:

Epileptology and Emergency Care — management of status epilepticus and seizures; first-line drug of choice for acute seizure termination.
Obstetrics — threatened preterm labor with a risk of miscarriage; prescribed only after the first trimester.
Psychiatry and Toxicology — medical sedation for psychomotor agitation, cocaine toxicity, and psychomotor agitation secondary to psychotropic substance poisoning; used as an alternative when neuroleptics are contraindicated.
Anesthesiology, Surgery, and Dentistry — preoperative premedication, component of ataralgesia, and management of psychomotor agitation, hallucinations, and nightmares following ketamine administration.
Gynecology — symptomatic therapy when hormone replacement therapy is contraindicated.

Which specific active metabolites are formed during hepatic biotransformation of diazepam?

Hepatic biotransformation of diazepam yields active metabolites that ensure prolonged clinical effects. The sequential metabolic products include:

N-desmethyldiazepam (nordazepam) — an active metabolite with a long half-life (ranging from 40 to 200 hours).
Oxazepam — the terminal active metabolite, which is also used independently as a pharmaceutical drug.

Metabolism occurs in the liver via oxidation (deamination) followed by glucuronidation.

What is the synaptic mechanism of action of diazepam?

Diazepam's mechanism of action involves the potentiation of GABA-ergic inhibition within the central nervous system.

Key anatomical sites include the limbic system and the reticular formation. Diazepam exerts an inhibitory effect on emotional and autonomic brain centers, resulting in reduced emotional tension, anxiety, and fear, alongside anticonvulsant activity.

What dosage forms are available for diazepam?

Diazepam is available in multiple formulations for oral and parenteral administration depending on the clinical context:

Tablets — for oral use, containing 5 mg of the active substance.
Ampoules — for injection, supplied as 2 mL of a 0.5% solution.

What are the absolute contraindications for prescribing diazepam?

Based on the referenced sources, contraindications and restrictions for diazepam include:

Acute intoxication with CNS depressants — diazepam and other anxiolytics are contraindicated in this state.
Obstetric restriction: in threatened preterm labor, diazepam is indicated only after the first trimester.

What are the main adverse effects of diazepam?

Key adverse effects and risks associated with diazepam include:

During status epilepticus management: high risk of respiratory depression and arterial hypotension.
For long-acting agents such as diazepam: prolonged somnolence, lethargy, dizziness, ataxia, and memory impairment.
Hangover/after-effect syndrome: drowsiness, sluggishness, and delayed psychomotor reactions.
With repeated benzodiazepine use: potential for drug accumulation, tolerance development, substance dependence, and withdrawal syndrome.
In obstetrics: bolus doses of diazepam exert negative effects on the fetus.

Why is absorption delayed following intramuscular diazepam injection?

The drug binds specifically to muscle tissue proteins. This delays its entry into the systemic circulation despite good muscle vascularization.

What mechanism prolongs diazepam's effect in the body?

Microsomal oxidation in the liver produces active metabolites. These are not immediately inactivated and continue to exert pharmacological effects.

How does urine acidity affect drug elimination?

Diazepam is a very weak base (pKa 3.0). In acidic urine, it ionizes, undergoes poorer tubular reabsorption, and is eliminated faster, shortening its duration of action.

What is the role of diazepam in cocaine poisoning?

It is administered intravenously as part of symptomatic therapy to control severe psychomotor agitation.

Go deeper

Mechanism of action of anxiolytics at the GABA-benzodiazepine receptor complex.
Inducers and inhibitors of CYP2C19 and CYP3A4/5 isoenzymes: risks of drug-drug interactions.
Principles of urine pH manipulation (forced diuresis) in weak acid and weak base poisonings.
Pharmacokinetics of prodrugs compared to drugs that form active metabolites.
Decontamination and emergency management algorithms for psychostimulant overdose.