Commony Rx Drugs - Erythromycin

Question 1

What is Erythromycin?

Answer 1

Macrolide

Question 2

What are the common s/e of Erythromycin? (3)

Answer 2

Nausea
Vomiting
Diarrhoea

Question 3

Give e.g. of macrolides. (2)

Answer 3

Azithromycin
Clarithromycin

Question 4

What are the common interactions of Erythromycin? (8)

Answer 4

Carbamazepine: Macrolide can raise plasma carbamazepine levels.

Drugs that prolong QT interval (e.g. antiarrhythmics, antipsychotics and TCA): All Macrolide can prolong the QT interval and concomitant use of drugs that prolong the QR isn’t recommended.

Drugs that cause hypokalaemia (diuretics, CS, short-acting beta2-agonists): Hypokalaemia is a risk factor for QT interval prolongation.

Statins: High risk of myopathy due to CP450 enzyme CYP3A4 inhibition if Clarithromycin/Erythromycin is taken with Atorvastatin or Simvastatin:
- For Simvastatin: Don’t Rx Clarithromycin or Erythromycin to a person taking Simvastatin, as Simvastatin is extensively metabolised by CYP3A4. If tx with Clarithromycin/ erythromycin can’t be avoided, stop tx with Simvastatin during tx course.
- For Atorvastatin, avoid concurrent use with Clarithromycin or erythromycin, as Atorvastatin is moderately metabolised by CYP3A4.

Theophylline: Erythromycin increases plasma concentrations of theophylline and theophylline can reduce absorption of oral erythromycin.

Warfarin: effect of warfarin may increase by Macrolide.

CCB: High risk of hypotension and CCBs metabolised by CYP3A4 e.g. Verapamil, Amlodipine and Diltiazem.

Anti diabetic drugs/Insulin: Concurrent use of Clarithromycin and Antidiabetics drugs (Sulphonylureas +/or insulin) can lead to hypoglycaemia.