Antianxiety and Antiepileptic

Question 1

Mechanism of action of benzodiazepines

Answer 1

Potentiates GABA actions via specific BDZ sites in CNS to increase frequency of Cl- channel opening

Question 2

AE of BDZ

Answer 2

Drowsiness, diminished motor skills, anterograde amnesia, decreased BP, talkative, easily irritable, hallucinations, tolerance

Question 3

Mechanism of action of phenytoins

Answer 3

Increases brain GABA, decreases membrane excitability by

• altering Na+ and Ca2+ conductance during AP
• increasing refractory period via K+ current

Question 4

Pharmacokinetics of phenytoin

Answer 4

Absorption is via oral, slow, Tmax 2-12h.
It follows first order kinetics at low concentrations, but zero order at higher concentrations, saturating liver enzymes and causing the plasma concentrations to keep increasing until toxic.
Phenytoin also is a hepatic enzyme inducer, so if the patient is on oral contraceptives, we should be careful at it might decrease its plasma drug concentration, causing its effectiveness to be lost.

Question 5

AE of phenytoin

Answer 5

Decreased vitamin D, low vitamin B12 and folate levels, gum hypertrophy, rashes, liver necrosis, teratogenic

Question 6

Carbamezepine mechanism of action

Answer 6

Increases brain GABA, decreases membrane excitability by

• altering Na+ and Ca2+ conductance during AP
• increasing refractory period via K+ current

Question 7

What else does carbamezepine treat besides epilepsy

Answer 7

Trigeminal neuralgia and mood disorders

Question 8

AE of carbamezepine

Answer 8

GI upset, diplopia, nystagmus, drowsiness, folate vitamin D deficiency, rashes, SLE, hepatits, teratogenic

Question 9

Phenobarbitone mechanism of action

Answer 9

Binds to GABA-receptor channel complex to potentiate GABA action
Low conc: increases frequency of channel opening induced by GABA
High conc: independent of GABA, prolonged duration and frequency

Question 10

AE of phenobarbitone

Answer 10

Sedation, drowsiness, ataxia, diplopia, loss of concentration, depression

Question 11

Valproate mechanism of action

Answer 11

Increases GABA by preventing its breakdown via inhibition of GABA-transaminase, hyperpolarising membrane potential by increased K+ conductance

Question 12

Which antiepileptic increases the levels of other antiepileptics when used in conjunction?

Answer 12

Valproate

Question 13

AE of valproate

Answer 13

GI upset, sedation, weight gain, hair loss, hepatotoxicity, thrombocytopenia, spina bifida, CVS