Core pharmacology

Class Group

ADRENERGIC

Legacy Cicm Level

Level 2

Introduction

Synthetic direct and indirect sympathomimetic with alpha and beta activity

Indications Uses

1. Hypotension during surgery
2.Nocturnal enureisis
3. Diabetic autonomic neuropathy
4.Hiccups
5. Nasal decongestant

Presentation

- Clear colourless solution for injection (3-9mg slow injection, dose repeated ever 3-4 min)
- Oral tablets
- Nasal spray

Main Action

alpha and beta activity

Mechanism of action

direct and indirect sympathomimetic with alpha and beta activity

Physiological effects

1. CVS
- Effects similar to adrenaline but longer duration as drug is not metabolized by MAO or COMT
- Positive inotrope, chronotrope. Increases CO MVO2
- Increases coronary blood flow
- Increased SVR and PVR

2. Resp
- Respiratory stimulant
- Bronchodilation

3. CNS
- Stimulatory effect similar to amphetamine
- Cerebral blood flow increases
- Mydriasis occurs
- Has local anesthetic effects

4. GIT
- Relaxes GI smooth muscle
- Splanchnic vasoconstriciton

5. GU
- Decreased RBF
- Contracts bladder sphincter and relaxes detrusor muscle- acute urinary retention
- Does not cause uterine constriction

6. Metabolic
- Increased hepatic glycogenolysis
- Increased BMR

Adverse Effects Toxicity

Insomnia, anxiety, tremor, headache, dysrhythmias, nausea and vomiting, and chest pain
irritant to mucous membranes
Acute hypertensive crisis with: MAOIs, doxapram, beta-blockers, oxytocin, and ergot alkaloids

Absorption

- Rapidly absorbed orally

Distribution

- Widely distributed and crosses BBB, placenta and breast milk

Metabolism

- Resistant to MAO and COMT. Hepatic metabolism with a major metabolite being active and may have central effects

Excretion

- 50-90% excreted unchanged in urine. Urinary elimination is pH dependent (enhanced by acidic urine)
- Tachyphylaxis rapidly occurs

Half-life

Elimination T1/2 is 6 hours

Route And Dose

IV 3-6mg bolus