Mood stabilisers-pharmacokinetics

Question 1

Lithium

Answer 1

Orally well absorbed
Not metabolised by the liver, renally excreted
-4 -5 days to reach steady state
-not protein bound
-plasma half life is 18 hours initially but after 1 year increases to 36 hours
-ACE inhibitors, Loop diuretics, fluoxetine, NSAIDs and thiaides increase lithium levels
-osmotic diuretics, caffeine, aminophylline, theobromine, theophylline and carbonic anhydrase inhibitors all decrease lithium levels
-causing toxicity: carbamazepine, atracurium, haloperidol and clozapine, calcium channel blockers, metronidazole

Question 2

Valproate

Answer 2

• t 1/2 of 9-16 hours and 90% protein bound

- bioavailability is nearly 100%

Question 3

Carbamazepine

Answer 3

• hepatic metabolism
• bioavailability of 80%, 75% bound to plasma proteins
• induces it’s own breakdown- CYP3A3/4
• BD
• verapamil and diltiazem increase levels
• valproate increases levels
• reduces warfarin efficacy
• erythromycin can produce carbamazepine toxicity

Question 4

Gabapentin

Answer 4

• no significant mood stabilising effects but helps with anxiety
• not bound, not metabolise and 100% excreted in urine
• half life 6hrs
• does not induce or inhiibit hepatic metabolism
• usually given TDS
• steady state reached in 1-2 days

Question 5

Lamotrigine

Answer 5

-achieves peak concentrations within 3 hours post dose-
oral bioavailability of 98%
half life 24-36 hours
-56%plasma bound
-enzyme inducers reduce the half-life
-valproate increases thehalf-life
-does not affect CYP450