Ondansetron

Chemical

Synthetic carbazole, structurally related to Serotonin

Use

Prevent & treat emesis

Presentation

Clear aqueous solution 2mg/mL

Tablets 4/8mg

Route / Dose

IV/SL 4 – 8mg TDS

MoA

  • Highly selective 5HT3 antagonist – CENTRALLY + PERIPHERALLY
  • Emetogenic stimuli cause 5HT release in SI
  • Acts on Vagal Afferents via 5HT3 receptor
  • Activates vomiting reflex

↓

  • Blocks this initiation
  • Activating vagal efferents can also cause 5HT release in Area Postrema (CTZ) promoting emesis centrally

↓

∴also blocked by Ondansetron

PD

(systems)s

PK

A

OBA 60%

D

70% PPB

VD 2L/kg

M

Extensively by hydroxylation or N-demethylation, then conjugated with glucuronic acid or sulphate

E

t ½ 3hrs

<5% unchanged in urine

Adverse Effects

  • May ↓ analgesic effects of tramadol