Naloxone
Chemical
Thebaine derivative
Use
- Reverse opioid depression
- Diagnosis of opioid overdose
- Prevent opioid abuse
Presentation
400mcg/ml
Dose
100-200mcg at 2min intervals up to 2mg
5mcg/kg/hr infusion
Route
IV/IM/SC
Onset
Immediate
DoA
90min
MoA
Pure pioid antagonist (competitive)
μ>>>k>y opioid receptors in CNS
PD
Reversal of µ-opioid receptor effects
- Sedation, ↓BP, Resp depression, dysphoria
CVS – ↑SNS activity → ↑HR, ↑MAP, dysrhythmias
CNS – reverses opioid depression, ↓pain threshold
Gut – N&V
Pregnancy – crosses placenta (v lipid soluble) → acute withdrawal of neonate
Other – acute withdrawal symptoms
Alleviates pruritus, nausea + resp D assoc with CNB opioids
PK
A
90% oral absorption
High 1st PM → OBA 2%
D
Highly lipophilic, distributes rapidly to brain
VD 2L/kg PPB 30-45%
pKa 8
25% UNIONISED at pH 7.4
M
Liver by conjugation to glucuronic acid forming naloxone-3-glucuronide and excreted in urine
E
t1/2b 1-1.5hrs
Adverse Effects
Opioid withdrawal/Pain crisis
Seizures
Pulmonary oedema