CLONAZEPAM
Clinical safety rating: avoid
CNS depressants including alcohol and opioids increase sedation risk Abrupt discontinuation can cause withdrawal seizures.
Enhances GABA-A receptor inhibitory neurotransmission by binding to benzodiazepine binding site, increasing frequency of chloride channel opening, leading to neuronal hyperpolarization.
| Metabolism | Hepatic metabolism via CYP3A4 to inactive metabolites; also undergoes nitroreduction and acetylation; at least 30 metabolites identified. |
| Excretion | Renal: 50-70% as metabolites (mostly glucuronide conjugates), <2% unchanged; fecal: 10-20%; biliary: minor. |
| Half-life | Terminal elimination half-life: 19-60 hours (mean 30-40 hours); clinical context: long-acting benzodiazepine, allows once or twice daily dosing; accumulation occurs with repeated use. |
| Protein binding | Approximately 85% bound to serum albumin. |
| Volume of Distribution | Vd: 1.5-4.4 L/kg (mean 3 L/kg); clinical meaning: extensive tissue distribution, high lipophilicity, crosses blood-brain barrier readily. |
| Bioavailability | Oral: 90% (tablet), ~100% (sublingual due to bypass of first-pass metabolism); rectal: 50-80% (inconsistent); intramuscular: bioavailability variable, not recommended due to erratic absorption. |
| Onset of Action | Oral: 30-60 minutes (peak effect 1-2 hours); sublingual: 20-30 minutes; intravenous: 1-5 minutes, rapid for status epilepticus. |
| Duration of Action | Duration: 6-12 hours for single dose (clinical effects); with chronic dosing, duration extends due to active metabolites and accumulation; anticonvulsant duration is longer than anxiolytic. |
| Molecular Weight | 315.71 |
0.5 mg orally three times daily; maximum 20 mg/day
| Dosage form | TABLET |
| Renal impairment | No specific adjustment recommended; use with caution in severe impairment (CrCl <10 mL/min) |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50%; Child-Pugh C: avoid use |
| Pediatric use | 0.01-0.03 mg/kg/day orally in 2-3 divided doses; maximum 0.05 mg/kg/day |
| Geriatric use | Initiate at 0.125-0.25 mg orally twice daily; titrate slowly due to increased sensitivity and fall risk |
| 1st trimester | Risk of major malformations (e.g., oral clefts) increased; use only if clearly needed. |
| 2nd trimester | Possible fetal growth restriction; use only if benefit outweighs risk. |
| 3rd trimester | Risk of neonatal withdrawal and floppy infant syndrome; avoid use near term. |
Clinical note
CNS depressants including alcohol and opioids increase sedation risk Abrupt discontinuation can cause withdrawal seizures.
| FDA category | Positive |
| Placental transfer | Clonazepam crosses the placenta; fetal levels approximate maternal levels. |
| Breastfeeding | Clonazepam is excreted into breast milk; infant serum levels may reach 25% of maternal levels. Monitor for sedation, poor feeding, and weight gain. Avoid if breastfeeding a preterm or ill infant. |
■ FDA Black Box Warning
Concomitant use with opioids may result in profound sedation, respiratory depression, coma, and death; reserve for patients for whom alternative treatments are inadequate.
| Common Effects | panic disorder |
| Serious Effects |
Hypersensitivity to benzodiazepinesSevere liver diseaseAcute narrow-angle glaucoma
| Precautions | Risk of dependence and withdrawal reactions, Abrupt discontinuation may precipitate withdrawal seizures, CNS depression may impair cognitive and motor function, Use in pregnancy associated with floppy infant syndrome and withdrawal in neonates, Elderly patients more sensitive to effects; risk of falls, Respiratory depression especially with COPD or sleep apnea |
| Food/Dietary | Grapefruit and grapefruit juice may increase clonazepam levels; avoid concurrent consumption. Alcohol consumption is contraindicated due to additive CNS depression. No other significant food interactions are documented. |
Loading safety data…
| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | First trimester: Increased risk of oral clefts (odds ratio 2.0-2.5) based on case-control studies. Second/third trimester: Risk of fetal benzodiazepine syndrome including hypotonia, respiratory depression, and withdrawal symptoms. Late third trimester or delivery: Risk of floppy infant syndrome and neonatal withdrawal. |
| Fetal Monitoring | Maternal: Liver function tests, CBC, and serum drug levels periodically; monitor for sedation, ataxia, and respiratory depression. Fetal: Ultrasound for structural anomalies if exposed in first trimester; fetal growth monitoring in third trimester; neonatal assessment for withdrawal symptoms (hypertonia, irritability, tremors) and respiratory depression after delivery. |
| Fertility Effects | Clonazepam may cause menstrual irregularities (amenorrhea, anovulation) via hypothalamic-pituitary axis suppression. No clear evidence of reduced fertility; limited human data. In animal studies, reversible reproductive effects at high doses. |
| Clinical Pearls | Clonazepam is a long-acting benzodiazepine with high potency; use lowest effective dose to avoid tolerance and dependence. Abrupt discontinuation may precipitate withdrawal seizures. Monitor for paradoxical reactions in children, elderly, and patients with brain injury. Titrate slowly in hepatic impairment; avoid in severe hepatic disease. May increase seizure frequency when added to other anticonvulsants due to CNS depression. Onset of action for panic disorder is 1-2 weeks; for seizures, acute effect is seen within minutes to hours. |
| Patient Advice | Do not stop taking this medication suddenly; abrupt discontinuation can cause withdrawal symptoms, including seizures. · Avoid alcohol and other CNS depressants; they can increase drowsiness and respiratory depression. · Use caution when driving or operating machinery until you know how this medication affects you. · Take exactly as prescribed; do not increase dose or frequency without consulting your doctor. · Inform your doctor if you are pregnant, planning to become pregnant, or breastfeeding. · Store at room temperature away from moisture and heat. |