Carbamazepine, Lamotrigine, Phenytoin, Topiramate

Question 1

What are the indications for Carbamazepine?

Answer 1

Focal & generalised tonic clonic seziures, prevention of bipolar, diabetic neuropathy and acute alcohol withdrawal

Question 2

Which seizures should Carbamazepine and Oxcarbazepine NOT be used for and why?

Answer 2

• Absence
• Tonic
• Atonic
• Myoclonic

As it may worsen the symptoms

Question 3

Can different brands be used for Carbamazepine?

Answer 3

No, stick to the same brand because different preparations for oral have different bioavailability

Question 4

What patient and carer advice is given with Carbamazepine?

Answer 4

Advice that it can cause blood, hepatic and skin disorders.

Therefore seek medical attention if fever, rash, sore throat, mouth ulcers, bruising or bleedings occurs.

Question 5

What is the plasma concentration range for optimum response for Carbamazepine?

Answer 5

Optimum response is:
4 - 12mg/L
(20-50micromol/L)

Measured 1-2 weeks after starting the medication.

Question 6

What are the signs of carbamazepine toxicity?

Answer 6

HAND BAG

H - Hyponatraemia
A - Ataxia
N - Nystagmus
D - Drowsiness
B - Blurred vision
A - Arrhythmias
G - Gastro-intestinal

Most of these are common at the start of the treatment, are dose related and can be reduced by using MR preps.

Question 7

Explain Carbamazepine Pre-treatment screening?

Answer 7

People who are Han Chinese or Thai origin have an increased risk of getting stevens-Johnson syndrome (SJS).

Therefore test for HLA-B*1502 allele in these people.

Avoid use of carbamazepine unless there’s no alternative.

Question 8

What are the indications for Lamotrigine?

Answer 8

Focal seizures, secondary generalised tonic clinic seizures, bipolar disorder

Question 9

What is a caution associated with Lamotrigine?

Answer 9

Can cause serious skin reactions like Stevens-Johnsons syndrome (especially in children).

Most rashes occur in the first 8 weeks.

Withdraw if rash occurs or if hypersensitivity develops, and see GP.

Question 10

What other side effects can Lamotrigine cause?

Answer 10

Blood disorders.
Monitor liver.

Withdraw if signs occurs and see GP.

Question 11

Which antiepileptic drug interacts with Lamotrigine?

Answer 11

Valproate. It increases the plasma lamotrigine concentration.

Inducers reduce it.

Question 12

What is the indication for Phenytoin?

Answer 12

Tonic-clonic seizures & focal seizures.

Question 13

Are all formulations of Phenytoin the same?

Answer 13

NO!

Phenytoin sodium and Phenytoin base are different.

Phenytoin base is a suspension. And Phenytoin sodium is capsules and injections.
They have different bioavailability

Monitor plasma-phenytoin concentration is you need to switch formulations.

Question 14

What’s the MHRA warning for Phenytoin?

Answer 14

Risk of suicidal thoughts & behaviour.

Risk of death and severe harm from error with injectable phenytoin.

Therefore maintain patients on the same brand.

Question 15

What are some cautions given with Phenytoin?

Answer 15

Intramuscular route should NOT be used as absorption is slow and erratic.
Use IV route instead.

Consider using Vitamin D for patients immobilised for long periods or those that have inadequate sun exposure or dietary calcium intake.

Question 16

What is the target range for Phenytoin?

Answer 16

10 - 20mg/L
(40-80 micromol/L)

Question 17

Signs of Phenytoin toxicity?

Answer 17

Nystagmus (involuntary eye movements), slurred speech, ataxia, confusion, hyperglycaemia

Blood / skin disorders.
Seek medical attention if sigs of blood disorders like fever, rash, malaise, bruising, infection.

Question 18

When should Phenytoin be discontinued?

Answer 18

If rash develops.

Question 19

What are some side effects of Phyenytoin?

Answer 19

P - P45 inducer
H - Hirsutism
E - Enlarged gums (gingival hyperplasia)

NY - Nystagmus and other signs (ataxia, vertigo, diplopia)

T - Teratogenicity
O - Osteopenia
I - Interfers with folic acid
N - Neuropathy

Question 20

Is Phenytoin an enzyme induction or inhibitor?

Answer 20

Enzyme inducer.

Question 21

What drugs will interact with Phenytoin?

Answer 21

Amiodarone: This increases concentration of Phenytoin

Apixaban, Dabigatran, Edoxaban, Rivaroxaban: Phenytoin decreases exposure to apixaban.
[use with caution or avoid]

Bupropion & Buspirone: Phenytoin decreases exposure

Carbamazepine: Phenytoin decreases its concentration

Ciclosporin: Phenytoin decreases concentration of cyclosporin

Combined pill & Desogestrel, Levonorgestrel, Ulipristal: Phenytoin decreases their efficacy, so they may need a higher dose of the pill.

Miconazole: Increases risk of phenytoin toxicity.

Valproate: Valproate effects concentration of phenytoin and phenytoin decreases concentration of valproate.

Question 22

What do Enzyme inducers and inhibitors do?

Answer 22

Induces the breakdown of a medication. So reduce the concentration of a drug.

Inhibitors inhibit the breakdown of a drug. So increase the concentration of a drug.

Question 23

What is the indication for Topiramate?

Answer 23

Generalised tonic clonic seizures or focal seizures.

Myopla with secondary angle-closure glaucoma

Question 24

What are some side effects of Topiramate?

Answer 24

• Visual issues
• Increase in intra-ocular pressure

Question 25

What cautionary labels are on Topiramate?

Answer 25

Label 8 - Do not stop unless your doctor tells you to stop.

Label 3 - May make you drowsy, if that happens do not drive or use tools or machines.

Question 26

What are the indications and side effects for Ethosuximide?

Answer 26

First line treatment for absence seizures.
Also licensed for myoclonic seizures.

Report signs of bone marrow depression.

Question 27

What must all Clobazam prescriptions for epilepsy have?

Answer 27

Must be endorsed with SLS

Question 28

What is the MHRA warning for Gabapentin?

Answer 28

Risk of severe respiratory depression even without concomitant opioid medicines [adjust doses in patients with respiratory problems].

Observe patients for signs of abuse and dependence.

Patients must be informed of risk of interactions with alcohol, and medications which cause CNS depression especially with opioids.