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