Clonazepam

Indications

• FDA-approved for panic disorder with or without agoraphobia in adults, with efficacy shown across 6-9 week placebo-controlled trials.
• FDA-approved as monotherapy or adjunct for Lennox-Gastaut syndrome, akinetic and myoclonic seizures, and absence seizures refractory to succinimides.
• Off-label first-line pharmacotherapy for REM sleep behavior disorder, where low bedtime doses reduce dream enactment and injury risk.
• Off-label for catatonia and as a short-term adjunct in acute mania or agitation, though lorazepam is preferred when a parenteral route may be needed.
• Off-label for periodic limb movement disorder, restless legs and for akathisia when beta-blockers are ineffective or contraindicated.
• Guidelines keep SSRIs and SNRIs first line in panic disorder, with clonazepam used as a bridge during antidepressant titration.

Mechanism of action

• Positive allosteric modulator at the GABA-A benzodiazepine site, increasing chloride channel opening frequency and inhibiting limbic and cortical firing.
• Non-selective subunit binding gives anxiolysis, sedation, anticonvulsant and muscle relaxant effects together rather than separably.
• Potent anticonvulsant action reflects suppression of spike-and-wave discharge in absence seizures and of cortical spread in myoclonic seizures.
• Long receptor occupancy from its extended half-life yields steady plasma levels, which blunts interdose rebound and reduces reinforcement.
• Chronic exposure causes GABA-A receptor downregulation and uncoupling, the substrate for tolerance, dependence and withdrawal hyperexcitability.

Pharmacokinetics

• Essentially complete oral absorption with peak concentrations at 1-4 hours; food has no clinically important effect on absorption.
• Elimination half-life is 30-40 hours, giving once or twice daily dosing and a gentler withdrawal profile than short-acting agents.
• Reduced by CYP3A4 to 7-aminoclonazepam, then acetylated and glucuronidated; metabolites are pharmacologically inactive.
• Because it depends on hepatic oxidation, clearance falls in cirrhosis and in older adults, whereas lorazepam and oxazepam are unaffected.
• Steady state takes 5-7 days, so titration should be no faster than every 3-4 days or accumulation and oversedation follow.

Dosing

• Panic disorder: start 0.25 mg PO twice daily, increase to 1 mg/day after 3 days, usual target 1-2 mg/day, labeled maximum 4 mg/day.
• Adult seizures: start 1.5 mg/day in three divided doses, raise by 0.5-1 mg every 3 days to seizure control, maximum 20 mg/day.
• Children and infants under 10 years or 30 kg: start 0.01-0.03 mg/kg/day divided, maintenance 0.1-0.2 mg/kg/day divided three times daily.
• Available as scored tablets and orally disintegrating tablets; there is no injectable form in the United States, unlike lorazepam or diazepam.
• Older adults and hepatic impairment start at 0.25 mg once or twice daily; avoid in significant liver disease where glucuronidated agents are safer.
• Taper by 0.125-0.25 mg every 1-2 weeks after long use, slowing to 5-10 percent reductions near the end; abrupt stop risks status epilepticus and death.

Adverse effects

• Somnolence in about 37 percent, dizziness 8 percent, coordination problems and ataxia 7 percent, plus fatigue and slowed reaction time.
• Cognitive dulling, anterograde amnesia and reduced working memory that accumulate with dose and often go unrecognized by the patient.
• Behavioral disinhibition, irritability and aggression, seen in up to a quarter of children treated for seizures and in some older adults.
• Hypersalivation and increased bronchial secretions in children, which can compromise airway clearance in neurologically impaired patients.
• Falls, hip fracture and delirium in older adults, plus additive respiratory depression and overdose death when combined with opioids or alcohol.
• Withdrawal after abrupt discontinuation includes rebound anxiety, insomnia, psychosis, status epilepticus and death, and may be delayed several days.

Monitoring

• Screen for substance use disorder and query the prescription drug monitoring program before starting and at intervals during ongoing therapy.
• Reassess sedation, gait, cognition and driving safety at every visit, and document that the original indication still justifies continuation.
• No routine labs are required; check CBC and LFTs periodically during long-term anticonvulsant use as the label suggests.
• Serum levels are not used clinically for panic disorder; in epilepsy, dose to seizure control and tolerability rather than to a concentration.
• Co-prescribe naloxone and document the discussion whenever concurrent opioid therapy cannot be avoided.

Interactions

• Strong CYP3A4 inhibitors such as ketoconazole, ritonavir and clarithromycin raise clonazepam exposure and can produce marked sedation.
• Carbamazepine, phenytoin, phenobarbital and rifampin induce CYP3A4 and can lower levels enough to cause breakthrough seizures or panic.
• Additive CNS and respiratory depression with opioids, alcohol, gabapentinoids, sedating antihistamines and other benzodiazepines or hypnotics.
• Contraindicated in significant hepatic disease, acute narrow-angle glaucoma and known benzodiazepine hypersensitivity.
• Combining clonazepam with valproate has been reported to precipitate absence status epilepticus in susceptible patients.

Special populations

• Pregnancy: first-trimester exposure carries a small possible oral cleft signal, and late exposure causes neonatal sedation, hypotonia and withdrawal.
• Lactation: passes into milk in low amounts; monitor the infant for sedation, apnea and poor feeding, especially in preterm neonates.
• Pediatrics: approved for seizure disorders at weight-based dosing, but paradoxical disinhibition and hypersecretion limit tolerability.
• Older adults: the AGS Beers Criteria advise avoiding benzodiazepines in this group given delirium, falls, fractures and crash risk.
• Hepatic impairment: contraindicated in significant liver disease; use lorazepam, oxazepam or temazepam, which are cleared by glucuronidation alone.

Clinical pearls

• The 30-40 hour half-life covers panic without the clock-watching rebound seen with alprazolam.
• Switching alprazolam to equivalent clonazepam first makes a long benzodiazepine taper far more tolerable.
• First-line drug therapy for REM sleep behavior disorder; melatonin is the safer alternative.