Clinical Monograph: Lorazepam 2.5 mg

1. Classification and Chemical Overview

Lorazepam is a short-acting benzodiazepine derivative possessing anxiolytic, sedative, hypnotic, anticonvulsant, and muscle-relaxant properties. Under the Anatomical Therapeutic Chemical (ATC) classification system, it is indexed under N05BA06.

Chemically designated as (RS)-7-chloro-5-(2-chlorophenyl)-1,3-dihydro-3-hydroxy-2H-1,4-benzodiazepin-2-one, lorazepam is a 3-hydroxy benzodiazepine. In United Kingdom clinical practice, lorazepam 2.5 mg is presented as oral tablets. In accordance with the Human Medicines Regulations 2012, lorazepam 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

Lorazepam acts as a positive allosteric modulator at central nervous system FRONTA​ receptor complexes. It binds with high affinity to the benzodiazepine site located at the interface between the $\alpha$ und γ2​ subunits of the ionotropic FRONTA​ receptor.

Binding increases the affinity of the receptor for gamma-aminobutyric acid (GABA), enhancing endogenous GABAergic neurotransmission. This increases the opening frequency of the integral chloride ion channel, causing neuronal membrane hyperpolarisation via increased chloride influx. The resulting elevation in threshold for action potential firing produces widespread inhibition across limbic, cortical, and subcortical structures, yielding anxiolytic, sedative, anticonvulsant, and amnesic effects.

3. Approved UK Clinical Indications and Therapeutic Scope

Licensing by the Medicines and Healthcare products Regulatory Agency (MHRA) for oral lorazepam includes:

• Anxiety States: Short-term management of severe, disabling anxiety states or anxiety associated with transient insomnia or organic disease (2 to 4 weeks maximum duration).

• Pre-medication: Pre-operative medication or premedication before brief diagnostic procedures.

Note on 2.5 mg Dosage Strength: The 2.5 mg tablet represents a higher single dose for oral lorazepam. Standard daily doses for severe anxiety range from 1 mg to 4 mg daily in divided doses. Single doses of 2.5 mg are typically reserved for acute, severe anxiety, refractory insomnia, or pre-medication in non-elderly patients.

NICE & BNF Guidance Context: National guidelines specify that treatment should be limited to the shortest duration possible (2 to 4 weeks maximum) at the lowest effective dose. Lorazepam is also used off-label in UK specialist pathways for status epilepticus (where intravenous/buccal routes are unavailable) and acute behavioural disturbance/agitation in acute psychiatric settings.

4. Pharmacokinetic Profile and Metabolic Fate

• Absorption: Lorazepam is rapidly and almost completely absorbed following oral administration. Peak plasma concentrations (Tmax​) are achieved approximately 2 hours post-dose. Absolute oral bioavailability is approximately 90%.

• Distribution: Lorazepam is widely distributed throughout body tissues, with an apparent volume of distribution (Vd​) of approximately $1.3\text{ L/kg}$. Plasma protein binding is approximately 85% to 90%. Lorazepam crosses the blood-brain barrier, the placental barrier, and is excreted into human breast milk.

• Biotransformation: Lorazepam undergoes direct Phase II hepatic conjugation via UDP-glucuronosyltransferases (predominantly UGT2B7 and UGT2B15) to form lorazepam glucuronide. It does not undergo Phase I oxidative metabolism via cytochrome P450 pathways and produces no active metabolites.

• Elimination: Lorazepam glucuronide is excreted predominantly via renal clearance in urine (accounting for over 80% of the dose). The mean terminal elimination half-life (t1/2​) of lorazepam is approximately 10 to 20 hours. Because clearance bypasses CYP-mediated metabolism, elimination is relatively uninfluenced by mild-to-moderate hepatic impairment or drug interactions involving CYP enzymes.

5. Physiological Effects and Adverse Event Spectrum

Lorazepam depresses central nervous system activity, resulting in sedation, reduced emotional reactivity, muscle relaxation, anterograde amnesia, and potential psychomotor impairment.

Adverse Drug Reaction Spectrum

• Very Common ($\ge 1/10$): Sedation, somnolence, fatigue, drowsiness, ataxia, muscle weakness.

• Common ($\ge 1/100$ to $<1/10$): Confusion, depression, unmasking of depression, dizziness, asthenia, ataxia, balance disorder, anterograde amnesia.

• Uncommon ($\ge 1/1,000$ to $<1/100$): Nausea, changes in libido, impotence, skin reactions (rashes, dermatitis), dysarthria, headache.

• Rare ($\ge 1/10,000$ to $<1/1,000$): Blood dyscrasias (thrombocytopenia, agranulocytosis, pancytopenia), hyponatremia, hypersensitivity reactions, syndrome of inappropriate antidiuretic hormone secretion (SIADH), jaundice, elevated hepatic enzymes, respiratory depression, paradoxical reactions (including anxiety, agitation, excitation, aggressiveness, rage, and hallucinations).

6. Contraindications, Drug Interactions, and Clinical Precautions

Kontraindikationen

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

• Severe respiratory insufficiency or acute respiratory depression.

• Myasthenia gravis.

• Sleep apnoea syndrome.

• Severe hepatic impairment (risk of precipitating hepatic encephalopathy).

Key Drug Interactions

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

• Opioids: Co-prescribing increases the risk of sedation, respiratory depression, coma, and death; reserve for cases where alternative treatment options are inadequate.

• Probenecid & Sodium Valproate: Inhibit the glucuronidation of lorazepam, increasing plasma concentrations and half-life; lorazepam dosage reduction by 50% is recommended during co-administration.

Clinical Precautions and Monitoring

• Dependence, Tolerance, and Withdrawal: Physical and psychological dependence can develop within weeks of continuous therapeutic use. Abrupt discontinuation risks severe withdrawal phenomena, including rebound anxiety, tremor, sweating, agitation, confusion, and convulsions. Gradual tapering is mandatory.

• Anterograde Amnesia: May occur following ingestion; patients should ensure an adequate period of uninterrupted rest following administration.

• Elderly & Debilitated Patients: Increased sensitivity to central nervous system depression elevates the risk of cognitive impairment, unsteady gait, and falls. Lower starting doses (e.g., 500 micrograms to 1 mg daily) are indicated.