Macrolides (Abx)

Question 1

What is the general action of macrolides?

Answer 1

Bacteriostatic

Bind to the 50S ribosomal subunit causing cessation of bacterial protein synthesis

Question 2

Give examples of macrolides

Answer 2

The “mycins”

Azithromycin
Clarithromycin
Erythromycin

Question 3

Are macrolides broad or narrow spectrum?

Answer 3

Broad

Question 4

What is the typical dosing of azithromycin?

Answer 4

500mg PO OD - for most infections

1g PO STAT - for uncomplicated genital chlamydial infections,
non-gonococcal urethritis or IUD related infections

2g PO STAT - for uncomplicated gonorrhoea [anogenital and pharyngeal infection]

Question 5

What is the typical dosing of clarithromycin?

Answer 5

500mg PO BD

Question 6

Sources

Answer 6

https://www.ncbi.nlm.nih.gov/books/NBK551495/#:~:text=Macrolides%20are%20a%20class%20of,otitis%20media%20in%20pediatric%20patients.

https://bnf.nice.org.uk/drugs/azithromycin/#indications-and-dose

https://bnf.nice.org.uk/drugs/clarithromycin/

Azithromycin = https://go.drugbank.com/drugs/DB00207

Question 7

What is the typical dosing of erythromycin?

Answer 7

250-500mg PO QDS - most common (or BD/TDS)

Question 8

Which class of drugs are macrolides often used to replace in the case of allergy?

Answer 8

Penicillins

Question 8

Name very common/common side effects of macrolides in general

Answer 8

Decreased appetite

Diarrhoea

GI symptoms - e.g., discomfort

N + V

Headache

Hearing impairment

Pancreatitis (esp. azithromycin)

Altered taste

Vasodilation

Paraesthesia

Question 9

Name uncommon side effects of macrolides in general

Answer 9

QT prolongation

Palpitations

Arrhythmias

Anxiety

Candida infection

Chest pain

Constipation

Tinnitus

Vertigo

Drowsiness

Hepatic disorders

Leukopenia, neutropenia

Eosinophilia

Question 10

Name rare/very rare side effects of macrolides in general

Answer 10

Abx related colitis

Myasthenia gravis

Nephritis tubulointerstitial

Question 11

What are the cautions for macrolides with IV/oral use?

Answer 11

Electrolyte disturbances (predisposition to QT interval prolongation)

May aggravate myasthenia gravis

Predisposition to QT interval prolongation

Question 12

Which of the common macrolide should be avoided in pregnancy and in breastfeeding?

Answer 12

Clarithromycin

Question 13

Describe the pharmacokinetics of clarithromycin

Answer 13

Oral bioavailability = well-absorbed and may be taken with food

Protein binding = 70%

Half-life = 3-4 hours

Metabolism = mainly CYP3A4 (liver) - also an inhibitor of this enzyme

Excretion = urine (kidneys)

Question 14

Describe the pharmacokinetics of azithromycin

Answer 14

Oral bioavailability = 37%

Protein binding = 7-51%

Half-life = 68 hours

Metabolism = Unknown

Excretion = Liver via bile (majority), kidneys via urine (6%)

Question 15

Describe the pharmacokinetics of erythromycin

Answer 15

Oral bioavailability = 18-45%

Protein binding = 93%

Half-life = 2.4-3.5 hours

Metabolism = Liver via CYP3A4 - inhibits this enzyme

Excretion = Liver via bile (majority), <5% kidneys via urine