Clonidine
Dexmedetomidine
Route of Administration
  • Administered orally, transdermally, or intravenously
  • Administered via intravenous infusion only
Pharmacokinetics
  • Onset of action 10 minutes IV
  • Terminal half-life ~7 hours
  • 20% bound to plasma proteins
  • Volume distribution of 1.7–2.5 L/kg
  • 40% hepatically metabolised to inactive metabolites
  • 60% excreted renally unchanged
  • Accumulates in renal failure
  • Onset of action <5 minutes IV
  • Half-life 2 hours
  • 90% bound to plasma proteins
  • Volume distribution of 1.3–2.4 L/kg
  • Primarily hepatically metabolised to inactive metabolites
  • Does not accumulate in renal failure
Mechanism of Action
  • Lesser selectivity for α2-adrenoceptors (α2:α1 ratio 220:1)
  • Greater agonism at imidazoline receptors and therefore tends to cause more hypotension
  • Greater selectivity for α2-adrenoceptors (α2:α1 ratio 1,620:1) producing more potent sedation
  • Lesser action on imidazoline receptors
Price
  • Cheap - estimated cost £8/day
  • Expensive - estimated cost £100/day
Clinical Uses
  • Used as sedative, analgesic and anaesthetic adjunct
  • Availability of oral and transdermal formulations makes it easier to use in non-intensive care settings
  • Primarily used as a sedative for procedures or intensive care
  • Better suited for intensive care than clonidine due to:
    • Increased titratability
    • Rapid onset of sedative effect
    • Predictable haemodynamic response with less prominent hypotension and bradycardia
    • Better pharmacokinetic profile in renal failure