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+
  1. Smooth m. relaxation & bronchoconstriction
  2. Inhibits MC degranulation “stabilises MC”
  3. Inhibits microvascular leakage
  4. ↑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)