Carbamazepine

Question 1

What is carbamazepine?

Answer 1

Anticonvulsant used to congrol grand mal and psychomotor or focal seizures
-some actions resmeble that of phenytoin despire little chemical resemblance

3D structure is similar to phenytoin

Question 2

What class of compounds does carbamazepine belong to?

Answer 2

Anticonvulsants

Question 3

What are other drugs in the same class as carbamazepine?

Answer 3

primidone
gabapentin
topiramate
phenytoin
acetazolamide
clobazam
lamotrigine

Question 4

What is carbamazepine indicated for?

Answer 4

focal and secondary -generalised tonic-clonic seizures

• primary generalised tonic-clonic seizures
• trigeminal or glossopharyngeal neuralgia
• diabetic neuropathy
• acute mania and maintenace treatment of bipolar affective disroders
• diabetes insipidus

Question 5

What is the mechanism of carbamazepine?

Answer 5

inhibits sustained repetitive firing by blocking use-dependent sodium channels.

Pain relief assoc. with blockade of synpatic transmission in trigeminal nucleus

seizure control assoc with reduction of post-tetanic potentiation of synpatic transmission in the spinal cord.

Question 6

What is the role of carbamazepine in the role of therapy of epilepsy?

Answer 6

Drug of choice for simple and complex focal seizures
First line treatment for generalised tonic clonic seizures

Also used adjuctive treatment for focal seizures when monotherapy inefective

Question 7

Which seizures should carbamazepine not be used in?

Answer 7

tonic, atonic, myoclonic and absence seizures as it may exacerbate these forms of seizures

Question 8

What is the dose of carbamazepine given ?

Answer 8

ESSENTIAL to start at low dose, increasing 100-200mg/2weeks

Adult: initially 00-200mg daily in 1-2 divided doses (reduce in elderly) increased slowly to 0.8-1.2g daily in divided doses

In some cases 1.6-2g daily in divided doses may be needed

Question 9

What are relevant PD/PK parameters assoc with carbamazepine use?

Answer 9

76% bound to plasma proteins
metabolised by CYP3A4
72% is excreted in urine
half life ranges from 25-65 hours which reduces to 12-17 hours on repeated doses

variation of elimination half life due to carbamazepine being an auto inducer of the hepatic mono-oxygenase system

Question 10

What are the precautions associated with carbamazepine use?

Answer 10

• cardiac disease
• skin reactions
• HLA-B* 15:02 allele in individuals of Han Chinese or Thai origin
• history of haematological reactions to other drugs
• patients immobilised for long periods of time should consider vitamin D supplementation
• susceptibility to angle closure,
• cross sensitivity reported with oxcarbazepine and phenytoin
• renal impairment
• hepatic impairment

Question 11

What are the contraindications with carbamazepine use?

Answer 11

AV conduction abnormalities (unless paced)
history of bone marrow depression
acute porphyria
use of MAOI within 14 days
Do not use in pregnancy (class D), compatible with breastfeeding

Question 12

What are the adverse effects with carbamazepine use?

Answer 12

headache, ataxia, drowsiness, nausea, vomiting, blurring of vision, dizziness, unsteadiness, allergic skin reactions (dose related, may be dose limiting) common at start of treatment and in elderly. Can be reduced by altering the timing of medication or by using modified release formulations

Dry mouth, vomiting, oedema, ataxia, hyponatraemia, blood disorders, dermatitis, urticaria,

Question 13

What are the drug interactions with carbamazepine use?

Answer 13

Isoniazid increases carbamazepine levels markedly, to the point of toxicity

Decreases triazolam exposure, warfarin, itraconazole, oral midazolam, tramadol, fentayl, etonogestrel, ECP, doxycycline (but not tetracycline), clopidogrel,

Question 14

What are the alarm bells with carbamazepine use?

Answer 14

May be taken with or without food

initiate and withdraw slowly