Macrolides

Question 1

list 3 Macrolides

Answer 1

clarithromycin, erythromycin, azithromycin

Question 2

outline the MoA of macrolides

Answer 2

1) similar activity to penicillin - alternative to allergic patients
2) Bacteriostatic: Binds to ribosomes and Inhibits cell wall protein synthesis
3) broad spectrum, Gram-positive and some Gram-negative also against Haemophilus influenzae.

Question 3

what are the indications for macrolides?

Answer 3

1) respiratory, skin and soft tissue infections - whooping cough
2) Lyme disease
3) severe pneumonia added to a penicillin
4) Chlamydia - azithromycin - OTC - over 16 + positive test

Question 4

Outline the side effects caused by macrolides

Answer 4

1) GI disturbances - erythromycin - safe to continue
2) Hepatotoxicity- cholestatic jaundice
3) Steven-Johnson syndrome
4) QT interval prolongation
5) Visual disturbances
6) Affect performance - driving, skilled tasks
7) antibiotic-associated colitis
8) ototoxicity with high doses

Question 5

who should macrolides be used in caution with?

Answer 5

1) elimination is mostly hepatic, so caution in severe hepatic impairment
2) Dose reduction in severe renal impairment
3) Predisposed to QT prolongation - drugs, electrolyte disturbances
4) Muscle weakness

Question 6

Erythromycin and clarithromycin (but not azithromycin) inhibit cytochrome P450 (CYP) enzymes. list some of the important interactions with regards to macrolides

Answer 6

1) warfarin there is an increased risk of bleeding and with statins an increased risk of myopathy (stop statin)
2) Drugs that prolong the QT interval or cause arrhythmias, such as amiodarone, antipsychotics, quinine, quinolone antibiotics and SSRIs

Question 7

Discuss the different half lives of each macrolide

Answer 7

1) Erythromycin has a short around 2 hours and is usually prescribed at a dosage of 250–500 mg 6-hrly
2) Clarithromycin is concentrated in tissues is prescribed at a dosage of 250–500 mg 12-hrly
3) Azithromycin highly concentrated in tissues and has a long half-life, dosage of 250–500 mg OD

Question 8

how can the GI side effects associated with macrolides be reduced?

Answer 8

food may improve GI tolerability

Question 9

what other indications can erythromycin be given for?

Answer 9

early syphilis and uncomplicated genital chlamydial infection