Ephedrine

[PHW2:p201]

Found naturally in some plants

But is synthesized for medical use

 

Structure

[PHW2:p201]

4 isomers

Only L-isomer is active

 

 

Pharmacodynamics

Mechanism of action

[PHW2:p201]

Both direct and indirect sympathomimetic actions

Indirect actions
--> Prone to tachyphylaxis as NE stores in sympathetic nerves become depleted

Also inhibits MAO breakdown of NE

Effects

[PHW2:p203]

CVS

Increases CO, HR, BP, coronary perfusion, myocardial oxygen consumption (MVO2)

May precipitate arrhythmias

 

Respiratory

Respiratory stimulant

Bronchodilation

 

Renal

Decreased renal perfusion

Decreased GFR

 

Interaction

Used with extreme caution with MAO inhibitors

Pharmacokinetics

Well absorbed orally, IM, and S/C

 

NOT metabolised by MAO or COMT
* Unlike adrenaline
--> Longer duration of action

Elimination half-life = 4 hours

 

Some metabolism in liver

65% excreted unchanged in urine

 

Pharmaceutics

Clinical

[PHW2:p201]

Used to treat hypotension associated with regional anaesthesia, especially in obstetrics
* Due to lesser alpha1-mediated vasoconstriction in uterine blood vessels