Lormetazepam 1 mg

Clinical Monograph: Lormetazepam 1 mg

1. Classification and Chemical Overview

Lormetazepam is a short-acting benzodiazepine derivative possessing hypnotic, anxiolytic, sedative, muscle relaxant, and anticonvulsant properties. Under the Anatomical Therapeutic Chemical (ATC) classification system, it is indexed under N05CD06.

Chemically designated as 7-chloro-5-(2-chlorophenyl)-3-hydroxy-1-methyl-1,3-dihydro-2H-1,4-benzodiazepin-2-one, lormetazepam is an $N$-methylated derivative of lorazepam. In United Kingdom clinical practice, lormetazepam 1 mg is presented as oral tablets. Under the Human Medicines Regulations 2012, lormetazepam is classified as a Prescription Only Medicine (POM) and is controlled under Schedule 4 (Part I) of the Misuse of Drugs Regulations 2001 (as amended).

2. Mechanism of Action and Pharmacodynamics

Lormetazepam acts as a positive allosteric modulator at central nervous system FRENTEA​ receptor complexes. It binds with high affinity to the benzodiazepine binding site located at the interface between the $\alpha$ y γ2​ subunits of the chloride-channel receptor complex.

This binding increases the affinity of the receptor for gamma-aminobutyric acid (GABA), enhancing endogenous GABAergic neurotransmission. The resulting increase in the opening frequency of integral chloride ion channels leads to hyperpolarisation of neuronal membranes via increased chloride influx. This depresses neuronal activity within the ascending reticular activating system, shortening sleep onset latency, reducing nocturnal awakenings, and increasing total sleep time.

3. Approved UK Clinical Indications and Therapeutic Scope

Licensing by the Medicines and Healthcare products Regulatory Agency (MHRA) for lormetazepam tablets includes:

• Insomnia: Short-term treatment of severe insomnia that is disabling or subjecting the individual to extreme distress.

Note on 1 mg Dosage Strength: The 1 mg tablet represents the standard recommended daily dose for adults, taken immediately before retiring. In elderly or debilitated patients, a initial dose of 500 micrograms (0.5 mg) is recommended to minimise residual daytime sedation and ataxia.

NICE & BNF Guidance Context: In UK clinical practice, hypnotic treatment with lormetazepam is restricted to a maximum duration of 2 to 4 weeks. National Institute for Health and Care Excellence (NICE) guidelines advise that non-pharmacological interventions (such as Cognitive Behavioural Therapy for Insomnia, CBT-I) should precede or accompany hypnotic treatment. Benzodiazepines are not indicated for long-term management of chronic sleep disorders.

4. Pharmacokinetic Profile and Metabolic Fate

• Absorption: Lormetazepam is rapidly and almost completely absorbed following oral administration. Peak plasma concentrations (Tmax​) are reached between 1.5 and 2 hours post-dose. Absolute oral bioavailability is approximately 80%.

• Distribution: Lormetazepam is extensively bound to plasma proteins (approximately 85%). It crosses the blood-brain barrier, the placental barrier, and is excreted into human breast milk. The volume of distribution (Vd​) at steady state is approximately $1.2\text{ to }1.5\text{ L/kg}$.

• Biotransformation: Lormetazepam is cleared predominantly via Phase II hepatic pathways. It undergoes direct glucuronidation to yield lormetazepam glucuronide, an inactive metabolite. Unlike long-acting benzodiazepines, it does not undergo Phase I oxidative metabolism via cytochrome P450 pathways, nor does it produce active metabolites.

• Elimination: Elimination occurs primarily via renal clearance of the inactive glucuronide conjugate (accounting for over 80% of the dose in urine). The mean terminal elimination half-life (t1/2​) of lormetazepam is approximately 10 to 12 hours.

5. Physiological Effects and Adverse Event Spectrum

Lormetazepam depresses central nervous system function to facilitate sleep, accompanied by secondary decrements in psychomotor performace, alertness, and motor coordination.

Adverse Drug Reaction Spectrum

• Very Common ($\ge 1/10$): Headache.

• Common ($\ge 1/100$ to $<1/10$): Drowsiness, daytime sedation, lightheadedness, dizziness, ataxia, muscle weakness, dry mouth, confusion, anterograde amnesia, anxiety, visual disturbances.

• Uncommon ($\ge 1/1,000$ to $<1/100$): Nausea, vomiting, abdominal discomfort, changes in libido, skin reactions (rashes, urticaria), dysarthria, emotional blunting.

• Rare ($\ge 1/10,000$ to $<1/1,000$): Hypersensitivity reactions, angioedema, blood dyscrasias, elevated liver enzymes, respiratory depression, paradoxical reactions (such as agitation, aggression, hallucinations, nightmares, and inappropriate behaviour), urinary retention, hypotensive episodes.

6. Contraindications, Drug Interactions, and Clinical Precautions

Contraindicaciones

• Hypersensitivity to lormetazepam, other benzodiazepines, or formulation excipients.

• Severe respiratory insufficiency or acute respiratory depression.

• Myasthenia gravis.

• Severe sleep apnoea syndrome.

• Severe hepatic impairment (risk of precipitating encephalopathy).

Key Drug Interactions

• CNS Depressants & Alcohol: Concomitant administration with opioids, sedatives, hypnotics, antipsychotics, sedating antihistamines, or alcohol markedly potentiates central nervous system depression, sedating effects, and the risk of fatal respiratory depression.

• Opioids: Combined use increases the risk of sedation, respiratory depression, coma, and death. Prescribing should be restricted to patients for whom alternative options are inadequate, using the lowest effective dose for the shortest duration.

• Sodium Oxybate: Co-administration with sodium oxybate is contraindicated due to increased risk of severe central respiratory depression.

Clinical Precautions and Monitoring

• Tolerance, Dependence, and Withdrawal: Repeated use over several weeks may lead to physical and psychological dependence. Abrupt discontinuation can trigger withdrawal phenomena (including rebound insomnia, tremors, sweating, anxiety, confusion, and convulsions). Gradual dose reduction is mandatory.

• Anterograde Amnesia: May occur within several hours of ingestion; patients must ensure they are able to have an uninterrupted sleep period of 7 to 8 hours to reduce this risk.

• Elderly & Debilitated Patients: Heightened sensitivity to central nervous system effects increases the risk of falls, confusion, and impaired motor coordination. Lower initial dosing is required.