Core pharmacology

Class Group

ADRENERGIC

Legacy Cicm Level

Level 3

Introduction

synthetic catecholamine which used primarily for its beta agonist properties.

Indications Uses

In Australia-indicated in heart block, unstable bradycardia and as an adjunct in cardiogenic, septic or hypovolaemic shock.

Presentation

injectable form only, in concentrations of 200mcg/mL, in 1 and 5ml vials

Available as MDI though no longer used for reversible airway constriction due to increased mortality

Main Action

β1,2 agonist.

Mechanism of action

β1,2 agonist. ↑HR, inotropy (beta1), and tends to maintain SBP but ↓DBP due to ↓TPR (beta2). Potent bronchodilator
but worsen V/Q matching (withdrawn due to ↑mortality). CNS stimulant. ↑Splanchnic and renal perfusion due to vasodilation (beta2)

Physiological effects

CVS
- Power inotrope, chronotrope and dromotrope leading to increased cardiac output
- Beta-2 effects decrease SVR leading to a decrease in DBP
- Increased myocardial O2 consumption, and a decrease in diastolic time and aortic DBP may significantly decrease delivery. Increased coronary arterial vasodilation may offset this effect
- Increased automaticity

CNS
- CNS stimulant

Resp
- Potent bronchodilator
- Worsens dead space and may cause hypoxia

Renal
- Reduces renal blood flow in non-shocked states
- Uterine relaxation

GIT
- Decreased GIT tone and motility

Metabolic
- Lipolysis and hyperglycaemia
- Inhibits histamine release

Adverse Effects Toxicity

contraindicated in tachycardia, and may worsen ischaemia due to increased MVO2.
May cause hypoxia due to a worsening of V/Q matching. Tachyphlaxis may occur in prolonged use.

Absorption

IV. BA 100%
20mcg bolus or 0.5-10mcg/min
onset / dur IV imm / 10-15 mins

Distribution

65% protein bound

Protein binding

65% protein bound

Metabolism

Via conjugation in many tissues including hepatic and pulmonary

Excretion

Urine (1° as sulfate conjugates)

Half-life

2.5-5 minutes

Route And Dose

IV infusion. Dose 0.5-8mcg/min