Salbutamol
Chemical
Short acting β agonist (β2 > β1) synthetic sympathomimetic amine
Use
Tx bronchoconstriction
Presentation
Tablets, syrup, aerosol, dry powder for inhalation
Solution for neb & solution for injection
Salbutamol is a racemic of (R) & (S) isomers
- (R) isomer = x 150 more affinity for β2
- (S) isomer = assoc. with toxicity
Route/Dose
Neb: 2.5 – 5mg PRN
IV: 0.5mcg/kg/min
INH: 200 – 400mcg PRN
PO: 2 – 4mg TDS
MoA
Β2 receptor = GPCR
G5 (activation = ↑cAMP)
- Activates AC
- ↑cAMP
- ↑Protein kinase A
- Inhibits phosphorylation of myosin = ↓Intrac Ca2+
- Smooth m. relaxation & bronchoconstriction
- Inhibits MC degranulation “stabilises MC”
- Inhibits microvascular leakage
- ↑mucociliary clearance
PD
Resp – bronchodilation; interferes with HPVC
CVS
- Low dose → β2 predominates → ↓SVR → ↓VP
- High dose → β1 predominates → +ve inotropy + chronotropy
GU
- ↓uterine tone
- 10% dose crosses placenta → foetal tachycardia
Metabolic
- Hypokalaemia
- ↑FFAs
- ↑glucose
- Stimulates insulin release
PK
A
10% inhaled dose reaches site of action → rest is ingested
D
64% PPB
VD 156L
M
Significant 1st pass metabolism → salbutamol 4-O-sulphate
Hydrolysed by esterases in tissue & blood → active compound
E
30% unchanged in urine
Rest as metabolites in urine/faeces
Adverse Effects
- Anxiety, insomnia, tremor
- Seating, N&V, palpitations
- Potentiates muscle relaxants (non-depol)