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2D Structure
Also known as: Frisium, Urbanyl, Chlorepin, Clorepin, Urbadan, 22316-47-8
Molecular Formula
C16H13ClN2O2
Molecular Weight
300.74  g/mol
InChI Key
CXOXHMZGEKVPMT-UHFFFAOYSA-N
FDA UNII
2MRO291B4U

A benzodiazepine derivative that is a long-acting GABA-A RECEPTOR agonist. It is used as an antiepileptic in the treatment of SEIZURES, including seizures associated with LENNOX-GASTAUT SYNDROME. It is also used as an anxiolytic, for the short-term treatment of acute ANXIETY.
Clobazam is a Benzodiazepine. The mechanism of action of clobazam is as a Cytochrome P450 2D6 Inhibitor, and Cytochrome P450 3A4 Inducer.
1 2D Structure

2D Structure

2 Identification
2.1 Computed Descriptors
2.1.1 IUPAC Name
7-chloro-1-methyl-5-phenyl-1,5-benzodiazepine-2,4-dione
2.1.2 InChI
InChI=1S/C16H13ClN2O2/c1-18-13-8-7-11(17)9-14(13)19(16(21)10-15(18)20)12-5-3-2-4-6-12/h2-9H,10H2,1H3
2.1.3 InChI Key
CXOXHMZGEKVPMT-UHFFFAOYSA-N
2.1.4 Canonical SMILES
CN1C(=O)CC(=O)N(C2=C1C=CC(=C2)Cl)C3=CC=CC=C3
2.2 Other Identifiers
2.2.1 UNII
2MRO291B4U
2.3 Synonyms
2.3.1 MeSH Synonyms

1. 1-phenyl-5-methyl-8-chloro-1,2,4,5- Tetrahydro-2,4-diketo-3h-1,5-benzodiazepine

2. Frisium

3. Hr 376

4. Lm 2717

5. Lm-2717

6. Lm2717

7. Onfi

8. Urbanyl

2.3.2 Depositor-Supplied Synonyms

1. Frisium

2. Urbanyl

3. Chlorepin

4. Clorepin

5. Urbadan

6. 22316-47-8

7. Onfi

8. Lm-2717

9. Hr 376

10. Clobazamum

11. Mystan

12. Lm 2717

13. H-4723

14. Ru-4723

15. H 4723

16. 1h-1,5-benzodiazepine-2,4(3h,5h)-dione, 7-chloro-1-methyl-5-phenyl-

17. 7-chloro-1-methyl-5-phenyl-1h-1,5-benzodiazepine-2,4(3h,5h)-dione

18. Hr-376

19. 7-chloro-1-methyl-5-phenyl-1,5-benzodiazepine-2,4-dione

20. Nsc 336279

21. 1-phenyl-5-methyl-8-chloro-1,2,4,5-tetrahydro-2,4-dioxo-3h-1,5-benzodiazepine

22. Chebi:31413

23. 7-chloro-1-methyl-5-phenyl-1h-1,5-benzodiazepine-2,4-(3h,5h)-dione

24. Nsc-336279

25. 2mro291b4u

26. Nsc336279

27. Ncgc00168249-01

28. Caastilium

29. Noiafren

30. Urbanil

31. Odipam

32. Clobazamum [inn-latin]

33. Clobazepam

34. 7-chloro-1-methyl-5-phenyl-1,5-dihydro-benzo[b][1,4]diazepine-2,4-dione

35. 7-chloro-1-methyl-5-phenyl-2,3,4,5-tetrahydro-1h-1,5-benzodiazepine-2,4-dione

36. Mystan (tn)

37. Ccris 7506

38. Einecs 244-908-7

39. Brn 0758410

40. Unii-2mro291b4u

41. Clobazam (jan/usan/inn)

42. Clobazam [usan:inn:ban]

43. Colbazam

44. Perizam

45. Tapclob

46. Urbanol

47. Dea No. 2751

48. Sympazan

49. Onfi (tn)

50. Clobazam [usan]

51. Clobazam [inn]

52. Clobazam [jan]

53. Clobazam [mi]

54. Clobazam [vandf]

55. Colbazam [vandf]

56. Clobazam [mart.]

57. Clobazam [who-dd]

58. 1-phenyl-5-methyl-8-chloro-1,2,4,5-tetrahydro-2,4-diketo-3h-1,5-benzodiazepine

59. Dsstox_cid_26759

60. Dsstox_rid_81883

61. Dsstox_gsid_46759

62. Schembl43038

63. 5-24-08-00034 (beilstein Handbook Reference)

64. Mls003899217

65. Chembl70418

66. Clobazam [orange Book]

67. Gtpl7149

68. Zinc1175

69. Clobazam [ep Monograph]

70. Dtxsid2046759

71. Hsdb 8343

72. Clobazam 0.1 Mg/ml In Methanol

73. Clobazam 1.0 Mg/ml In Methanol

74. Hy-a0041

75. Tox21_112608

76. Bdbm50247888

77. Akos025401921

78. Cs-6756

79. Db00349

80. Smr000058811

81. Wln: T67 Gnv Jvn Ihj Cg G1 Kr

82. Cas-22316-47-8

83. Db-045870

84. C-2991

85. D01253

86. Q412164

87. Sr-01000937603

88. Sr-01000937603-2

89. 7-chloro-1-methyl-5-phenyl-1h-1,4(3h,5h)-dione

90. 7-chloro-1-methyl-5-phenyl-1h-1,4-(3h,5h)-dione

91. 1h-1,4(3h,5h)-dione, 7-chloro-1-methyl-5-phenyl-

92. 7-chloro-1-methyl-5-phenyl-1,5-benzodiazepine-2,4(3h)-dione

93. 1-phenyl 5-methyl 8-chloro 1,2,4,5-tetrahydo 2,4-dioxo 3h-1,5-benzodiazepine

94. 1-phenyl 5-methyl 8-chloro 1,2,4,5-tetrahydro 2,4-dioxo 3h-1,5-benzodiazepine

95. 1-phenyl-5-methyl-8-chloro-1,2,4,5-tetrahydro-2,4-dioxo-3h-1, 5-benzodiazepine

96. 1-phenyl-5-methyl-8-chloro-1,4,5-tetrahydro-2,4-dioxo-3h-1,5-benzodiazepine

97. Clobazam Solution, 1.0 Mg/ml In Methanol, Ampule Of 1 Ml, Certified Reference Material

2.4 Create Date
2005-03-25
3 Chemical and Physical Properties
Molecular Weight 300.74 g/mol
Molecular Formula C16H13ClN2O2
XLogP32.1
Hydrogen Bond Donor Count0
Hydrogen Bond Acceptor Count2
Rotatable Bond Count1
Exact Mass300.0665554 g/mol
Monoisotopic Mass300.0665554 g/mol
Topological Polar Surface Area40.6 Ų
Heavy Atom Count21
Formal Charge0
Complexity423
Isotope Atom Count0
Defined Atom Stereocenter Count0
Undefined Atom Stereocenter Count0
Defined Bond Stereocenter Count0
Undefined Bond Stereocenter Count0
Covalently Bonded Unit Count1
4 Drug and Medication Information
4.1 Drug Information
1 of 2  
Drug NameOnfi
PubMed HealthClobazam (By mouth)
Drug ClassesAnticonvulsant, Sedative-Hypnotic
Drug LabelTable 4. Description Proprietary Name: ONFI Established Name: Clobazam Dosage Forms: Tablet and Oral Suspension Route of Administration: Oral Established Pharmacologic Class of Drug: Benzodiazepine Chemical Name:...
Active IngredientClobazam
Dosage FormTablet; Suspension
RouteOral
Strength2.5mg/ml; 10mg; 20mg
Market StatusPrescription
CompanyLundbeck

2 of 2  
Drug NameOnfi
PubMed HealthClobazam (By mouth)
Drug ClassesAnticonvulsant, Sedative-Hypnotic
Drug LabelTable 4. Description Proprietary Name: ONFI Established Name: Clobazam Dosage Forms: Tablet and Oral Suspension Route of Administration: Oral Established Pharmacologic Class of Drug: Benzodiazepine Chemical Name:...
Active IngredientClobazam
Dosage FormTablet; Suspension
RouteOral
Strength2.5mg/ml; 10mg; 20mg
Market StatusPrescription
CompanyLundbeck

4.2 Therapeutic Uses

Anticonvulsants

National Library of Medicine's Medical Subject Headings. Clobazam. Online file (MeSH, 2016). Available from, as of June 24, 2016: https://www.nlm.nih.gov/mesh/2016/mesh_browser/MBrowser.html


/CLINICAL TRIALS/ ClinicalTrials.gov is a registry and results database of publicly and privately supported clinical studies of human participants conducted around the world. The Web site is maintained by the National Library of Medicine (NLM) and the National Institutes of Health (NIH). Each ClinicalTrials.gov record presents summary information about a study protocol and includes the following: Disease or condition; Intervention (for example, the medical product, behavior, or procedure being studied); Title, description, and design of the study; Requirements for participation (eligibility criteria); Locations where the study is being conducted; Contact information for the study locations; and Links to relevant information on other health Web sites, such as NLM's MedlinePlus for patient health information and PubMed for citations and abstracts for scholarly articles in the field of medicine. Clobazam is included in the database.

NIH/NLM; ClinicalTrials.Gov. Available from, as of July 6, 2016: https://clinicaltrials.gov/search/intervention=CLOBAZAM


Onfi (clobazam) is indicated for the adjunctive treatment of seizures associated with Lennox-Gastaut syndrome (LGS) in patients 2 years of age or older. /Included in US product label/

NIH; DailyMed. Current Medication Information for Onfi (Clobazam) Tablet; Onfi (Clobazam) Suspension (Updated: December 2014). Available from, as of July 1, 2016: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=de03bd69-2dca-459c-93b4-541fd3e9571c


Clobazam currently is FDA-labeled only for the adjunctive treatment of seizures associated with Lennox-Gastaut syndrome. However, the drug has demonstrated broad anticonvulsant activity and has been used extensively in adults and pediatric patients with a wide range of other seizure disorders, which have sometimes been refractory, including partial, generalized, and myoclonic seizures. /NOT included in US product label/

American Society of Health-System Pharmacists 2016; Drug Information 2016. Bethesda, MD. 2016, p. 2294


Clobazam has been used in the treatment of anxiety disorders and has been labeled for the short-term (2-4 weeks) treatment of anxiety in some countries outside the US. However, the drug currently is not FDA-labeled for the treatment of anxiety disorders in the US. /NOT included in US product label/

American Society of Health-System Pharmacists 2016; Drug Information 2016. Bethesda, MD. 2016, p. 2294


4.3 Drug Warning

Since clobazam has a CNS depressant effect, patients or their caregivers should be cautioned against concomitant use of other CNS depressant drugs or alcohol, and cautioned that the effects of other CNS depressants or alcohol may be potentiated.

American Society of Health-System Pharmacists 2016; Drug Information 2016. Bethesda, MD. 2016, p. 2295


Somnolence and sedation are among the most common adverse effects associated with clobazam therapy. These effects generally begin within the first month of treatment and may diminish with continued therapy. In a placebo-controlled study of patients with Lennox-Gastaut syndrome, somnolence or sedation was reported in 26% of patients who received clobazam compared with 15% of those who received placebo. Somnolence and sedation were observed at all effective dosages in clinical trials and were dose related. The sedative effect of clobazam is reportedly less pronounced than that of other commercially available benzodiazepines

American Society of Health-System Pharmacists 2016; Drug Information 2016. Bethesda, MD. 2016, p. 2295


Withdrawal symptoms (e.g., convulsions, psychosis, hallucinations, behavioral disorders, tremor, anxiety, irritability, dysphoria, insomnia, headache, palpitations, diarrhea) have been reported following abrupt discontinuance of benzodiazepines, including clobazam; the risk of withdrawal symptoms is greater with increasing dosage and duration of treatment. Such withdrawal reactions occur in patients who have developed physical dependence on these drugs. More severe withdrawal symptoms usually are limited to patients who abruptly discontinue therapy after receiving excessive dosages of benzodiazepines for an extended period of time. Milder withdrawal symptoms (e.g., dysphoria, anxiety, insomnia) generally have been reported following abrupt discontinuance of benzodiazepines in patients continuously receiving therapeutic dosages for several months.

American Society of Health-System Pharmacists 2016; Drug Information 2016. Bethesda, MD. 2016, p. 2295


Abrupt discontinuance and rapid dosage reduction of clobazam should be avoided to minimize the risk of precipitating or exacerbating seizures, status epilepticus, and withdrawal symptoms. When therapy is discontinued, dosage of the drug should be decreased gradually (i.e., by 5-10 mg daily at weekly intervals).

American Society of Health-System Pharmacists 2016; Drug Information 2016. Bethesda, MD. 2016, p. 2295


For more Drug Warnings (Complete) data for Clobazam (21 total), please visit the HSDB record page.


4.4 Drug Indication

For treatment and management of epilepsy and seizures associated with Lennox-Gastaut syndrome, a difficult-to-treat form of childhood epilepsy.


FDA Label


5 Pharmacology and Biochemistry
5.1 Pharmacology

Similar to other benzodiazepines, clobazam binds to the interface of the and 2-subunit of the GABA-A receptor. However, it is considered a partial agonist to GABA-A receptors which sets clobazam apart from 1,4-benzodiazepines which are full agonist. The significance of this difference is that one may experience less sedation with clobazam than with other benzodiazepines. Unlike the endogenous GABA ligand, clobazam binds allosterically to the GABA receptor to increase the frequency of the chloride channel opening and membrane permeability to chloride ions. Pharmacodynamic tolerance has been demonstrated in animal models.


5.2 MeSH Pharmacological Classification

Anticonvulsants

Drugs used to prevent SEIZURES or reduce their severity. (See all compounds classified as Anticonvulsants.)


Anti-Anxiety Agents

Agents that alleviate ANXIETY, tension, and ANXIETY DISORDERS, promote sedation, and have a calming effect without affecting clarity of consciousness or neurologic conditions. ADRENERGIC BETA-ANTAGONISTS are commonly used in the symptomatic treatment of anxiety but are not included here. (See all compounds classified as Anti-Anxiety Agents.)


GABA-A Receptor Agonists

Endogenous compounds and drugs that bind to and activate GABA-A RECEPTORS. (See all compounds classified as GABA-A Receptor Agonists.)


5.3 FDA Pharmacological Classification
5.3.1 Active Moiety
CLOBAZAM
5.3.2 FDA UNII
2MRO291B4U
5.3.3 Pharmacological Classes
Benzodiazepines [CS]; Cytochrome P450 2D6 Inhibitors [MoA]; Cytochrome P450 3A4 Inducers [MoA]; Benzodiazepine [EPC]
5.4 ATC Code

N05BA09

S76 | LUXPHARMA | Pharmaceuticals Marketed in Luxembourg | Pharmaceuticals marketed in Luxembourg, as published by d'Gesondheetskeess (CNS, la caisse nationale de sante, www.cns.lu), mapped by name to structures using CompTox by R. Singh et al. (in prep.). List downloaded from https://cns.public.lu/en/legislations/textes-coordonnes/liste-med-comm.html. Dataset DOI:10.5281/zenodo.4587355


N - Nervous system

N05 - Psycholeptics

N05B - Anxiolytics

N05BA - Benzodiazepine derivatives

N05BA09 - Clobazam


5.5 Absorption, Distribution and Excretion

Absorption

After oral administration of clobazam, it is almost completely absorbed (87% of dose). Bioavailability relative to solution was almost at 100%. Food does not affect absorption. Tmax = 1-3 hours.


Route of Elimination

Clobazam is eliminated via the urine (~94%) as metabolites.


Volume of Distribution

Vdss = 100 L. This high volume of distribution suggests extensive distribution to body tissues.


Clearance

Median estimated clearance = 2.49 L/h


/MILK/ Onfi is excreted in human milk.

NIH; DailyMed. Current Medication Information for Onfi (Clobazam) Tablet; Onfi (Clobazam) Suspension (Updated: December 2014). Available from, as of July 1, 2016: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=de03bd69-2dca-459c-93b4-541fd3e9571c


/MILK/ After oral administration of (14)C-clobazam (NH-15,7- chloro-1-methyl-5-phenyl-1H-1,5-benzodiazepine-2,4-(3H,5H)-dione) (4 mg/kg) to pregnant and lactating rats, the placental transfer and the secretion of radioactivity into milk were studied. Whole body autoradiograms of pregnant rats showed that radioactivity was distributed to the whole body of the fetus. Concentrations of radioactivity in fetal brain and blood were lower than the maternal plasma and placental levels, and decreased rapidly. The extent of transfer of radioactivity into the fetus reached maximum at 30 min after administration, amounting to 0.10% of the radioactivity administered per fetus. The composition of clobazam and its metabolites in plasma of pregnant rats at 30 min after oral administration was similar to that of non-pregnant rats. Concentration of radioactivity in the milk was 1.4 times higher than that in the blood, reached maximum 30 min after administration, then declined rapidly. The radioactivity transferred to the suckling via milk reached a maximum of 0.023% of the dose up to 8 hr after administration. Excretion of radioactivity from the suckling was slow. The composition of clobazam and its metabolites in aggregated milk in the suckling stomach was similar to that of female rat plasma.

Yokoyama N et al; Iyakuhin Kenkyu 25 (8): 640-7 (1994)


Clobazam is lipophilic and distributes rapidly throughout the body. The apparent volume of distribution at steady state was approximately 100 L. The in vitro plasma protein binding of clobazam and N-desmethylclobazam is approximately 80-90% and 70%, respectively.

NIH; DailyMed. Current Medication Information for Onfi (Clobazam) Tablet; Onfi (Clobazam) Suspension (Updated: December 2014). Available from, as of July 1, 2016: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=de03bd69-2dca-459c-93b4-541fd3e9571c


Clobazam is rapidly and extensively absorbed following oral administration. The time to peak concentrations (Tmax) of clobazam tablets under fasted conditions ranged from 0.5 to 4 hours after single- or multiple-dose administrations. The relative bioavailability of clobazam tablets compared to an oral solution is approximately 100%. After single dose administration of the oral suspension under fasted conditions, the Tmax ranged from 0.5 to 2 hours. Based on exposure (Cmax and AUC) of clobazam, Onfi tablets and suspension were shown to have similar bioavailability under fasted conditions. The administration of Onfi tablets with food or when crushed in applesauce does not affect absorption. Although not studied, the oral bioavailability of the oral suspension is unlikely to be affected under fed conditions.

NIH; DailyMed. Current Medication Information for Onfi (Clobazam) Tablet; Onfi (Clobazam) Suspension (Updated: December 2014). Available from, as of July 1, 2016: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=de03bd69-2dca-459c-93b4-541fd3e9571c


5.6 Metabolism/Metabolites

Clobazam is extensively metabolized in the liver via N-demethylation and hydroxylation to form two major metabolites, N-desmethylclobazam (norclobazam) and 4'-hydroxyclobazam, respectively. N-desmethylclobazam (norclobazam) retains pharmacological activity. Norclobazam is one-fourth the potency of clobazam. The main enzyme that facilitates the process of N-demethylation is CYP3A4, and to a lesser extent by CYP2C19 and CYP2B6. Norclobazam itself is also metabolized via hydroxylation, primarily by CYP2C19. The formation of 4'-hydroxyclobazam is facilitated by CYP2C18 and CYP2C19. A factor in determining extent of metabolism is the genetic profile of the individual patient as CYP2C19 is a polymorphic enzyme.


The polymorphic CYP2C19 is the major contributor to the metabolism of the pharmacologically active N-desmethylclobazam. In CYP2C19 poor metabolizers, levels of N-desmethylclobazam were 5-fold higher in plasma and 2- to 3-fold higher in the urine than in CYP2C19 extensive metabolizers.

NIH; DailyMed. Current Medication Information for Onfi (Clobazam) Tablet; Onfi (Clobazam) Suspension (Updated: December 2014). Available from, as of July 1, 2016: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=de03bd69-2dca-459c-93b4-541fd3e9571c


Clobazam is extensively metabolized in the liver, with approximately 2% of the dose recovered in urine and 1% in feces as unchanged drug. The major metabolic pathway of clobazam involves N-demethylation, primarily by CYP3A4 and to a lesser extent by CYP2C19 and CYP2B6. N-desmethylclobazam, an active metabolite, is the major circulating metabolite in humans, and at therapeutic doses, plasma concentrations are 3-5 times higher than those of the parent compound. Based on animal and in vitro receptor binding data, estimates of the relative potency of N-desmethylclobazam compared to parent compound range from 1/5 to equal potency. N-desmethylclobazam is extensively metabolized, mainly by CYP2C19. N-desmethylclobazam and its metabolites comprise approximately 94% of the total drug-related components in urine. Following a single oral dose of radiolabeled drug, approximately 11% of the dose was excreted in the feces and approximately 82% was excreted in the urine.

NIH; DailyMed. Current Medication Information for Onfi (Clobazam) Tablet; Onfi (Clobazam) Suspension (Updated: December 2014). Available from, as of July 1, 2016: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=de03bd69-2dca-459c-93b4-541fd3e9571c


A four-year-old male with symptomatic generalized epilepsy presented with ataxia, eye rolling, and episodes of back arching which were of non-epileptic origin following the introduction of clobazam at 0.75 mg/kg/day. Concurrent antiepileptic medication was lamotrigine at 13 mg/kg/day. Clobazam plasma levels were within the normal range, while N-desmethylclobazam (DCLB) concentrations were between five and seven times above the upper limit of the normal range. The plasma elimination half-life for DCLB was prolonged, suggesting a genetic variability in DCLB metabolism leading to toxicity. Reduction in the dose of clobazam to 0.3 mg/kg/day was associated with resolution of the non-epileptic neurological symptoms, reduction in DCLB plasma levels, and maintenance of seizure control.

PMID:16780634 Aylett SE et al; Dev Med Child Neurol 48 (7): 612-5 (2006)


Clobazam has known human metabolites that include 4-Hydroxyclobazam and N-desmethylclobazam.

S73 | METXBIODB | Metabolite Reaction Database from BioTransformer | DOI:10.5281/zenodo.4056560


5.7 Biological Half-Life

The mean elimination half life of an oral dose of clobazam 40 mg is 32 hours. It's main metabolite, norclobazam, as a half life of 57 hours. The half life in adult patients with epilepsy are higher than those that are healthy.


The mean elimination half-life of clobazam is approximately 36-42 hours and the mean elimination half-life of N-desmethylclobazam is approximately 71-82 hours.

American Society of Health-System Pharmacists 2016; Drug Information 2016. Bethesda, MD. 2016, p. 2297


5.8 Mechanism of Action

Clobazam binds at distinct binding sites associated with the chloride ionopore at the post-synaptic GABA receptor. These GABA receptors are in various locations in the CNS (limbic, reticular formation) and clobazam increases the duration of time for which the chloride ionopore is open. As a result, hyper polarization and stabilization of the membrane occur as the post-synaptic inhibitory effect of GABA is enhanced.