Other

Question 1

Sodium valproate

Answer 1

Anticonvulsant, salt of carboxylic acid

• Stabilises the inactive state of voltage gated Na+ channels
• Inhibits enzymes that deactivate GABA -> stimulation of GABAergic inhibitory activity

S/E
- GIT upset
- Hepatitis
- Pancreatitis
- Transient hair loss
- Thrombocytopenia
- Teratogenic

Question 2

Phenytoin

Answer 2

Anticonvulsant, hydantoins

Indications
- Epilepsy
- Trigeminal neuralgia
- TCA toxicity
- Digoxin-induced arrhythmias

MoA
- Stabilises the inactive state of voltage gates Na+ channels -> limits repetitive generation of Ads

PK
- A - Slow PO absorption, PO bioavailability 70-100%
- D - Protein binding 90%
- M - hepatic hydroxylation P450 - saturable process (1st order kinetics -> zero order kinetics). Hepatic enzyme induction -> incr metabolism of BDZ, warfarin. Genetic polymorphism (5-15% poor metabolisers)
- E - metabolites excreted in urine

Dose dependent effects
- Anticonvulsant
- Class Ib anti arrhythmic
- N+V
- Drowsiness
- Tremour
- Vertigo
- Slurred speech
- Ataxia
- Rapid infusion -> hypotension, heart block, asystole

Idiosyncratic effects
- Rash
- Gum hyperplasia
- Acne
- Blood dyscrasias
- SLE
- Hepatotoxicity
- Allergic reactions
- Peripheral neuropathy
- Trigger of porphyria

Other
- Teratogenic
- Hypoglycaemia
- Hypocalcaemia

Question 3

Carbamazepine

Answer 3

Mechanism
- Stabilises inactive state of voltage channels and limits generation of repetitive AP

S/E
- Sedation
- Anti-diuretic effect
- Hepatitis
- Teratogenic
- Hepatic enzyme induction