Tox: Anticonvulsants

Question 1

Mxn of anticonvulsant toxicity

Answer 1

Na+ channel blockade: dilantin, carbamazepine, topiramate, valproate.
GABA agonism: gabapentin.
Calcium channel blockade: gabapentin, pregabalin, valproate.

Question 2

Toxicity with rapid infusion of IV phenytoin

Answer 2

Can cause myocardial depression and cardiac arrest secondary propylene glycol diluent (not present in phosphenytoin).

Question 3

Lab abnormalities seen in valproate toxicity

Answer 3

Can induce hyperammonemia from depletion of carnitine and interference with urea cycle.

Question 4

What drug toxicity can carbamazepine mimic at high doses?

Answer 4

Carbamazepine is structurally similar to TCAs and at high doses, can cause similar CNA toxicity (rarely cardiac toxicity)

Question 5

What additional lab parameter can affect the ability to accurately measure phenytoin?

Answer 5

Albumin

Question 6

Symptoms of carbamazepine overdose

Answer 6

Ataxia, nystagmus.
Severe toxicity (>40mg/L) -> seizures, resp/CNS depression, dysrhythmias (AV block, QRS/QTc prolongation)

Question 7

Symptoms of phenytoin overdose

Answer 7

Nystagmus, ataxia, dysarthria. 
Severe tox (>50mg/L): stupor, coma, resp arrest. 

Rapid IV injection–> hypoTN, bradycardia, cardiac arrest (2* propylene glycol).

Question 8

What is ‘purple glove syndrome’ in relation to phenytoin?

Answer 8

Serious soft tissue reaction caused by phenytoin that results in edema, pain, ischemia, tissue necrosis and compartment syndrome.

Question 9

Symptoms of valproate toxicity

Answer 9

N/v, CNS depression.

Severe (>850mg/L): coma, resp depression, seizures, metabolic disturbances, cardiac arrest.

Question 10

When can HD be considered in anticonvulsant OD?

Answer 10

NOT effective for most overdoses but can be considered in massive valproate ingestions.

Question 11

What specific medication can be considered for treatment of valproate induced hyperammonemia

Answer 11

L carnitine

Question 12

What are the indications for MDAC in anticonvulsant OD?

Answer 12

Increases the clearance of phenytoin, carbamazepine, and phenobarbital.

Question 13

What dermatologic syndrome can be triggered by phenytoin, lamotrigine, carbamazepine, phenobarb

Answer 13

DRESS: drug reaction with eosinophilia, systemic symptoms.

Hypersensitivity reaction associated with aromatic antiepileptics.
Initial symptoms include fever, malaise, pharyngitis. Can progress to drug rash, lymphadenopathy, multiorgan involvement with fatality rate as high as 10%

Question 14

Oral complication that may be seen with chronic phenytoin use

Answer 14

Gingival hyperplasia.