Protein Synthesis Inhibitors (Macrolides)

What bacterial ribosomal subunit do macrolides bind?

50S ribosomal subunit.

What is the mechanism of action of macrolides?

They bind the 50S ribosomal subunit and prevent movement (translocation) along the mRNA, inhibiting protein synthesis.

Are macrolides bacteriostatic or bactericidal?

Bacteriostatic (may be bactericidal at high concentrations).

What three macrolides should you know?

- Azithromycin

- Clarithromycin

- Erythromycin

Which macrolide is available as an oral, IV, and ophthalmic formulation?

Erythromycin.

Which macrolide is commonly used as an ophthalmic ointment for neonatal gonorrhea prophylaxis?

Erythromycin.

Which macrolide enhances gastrointestinal motility?

Erythromycin.

Why does erythromycin increase gastrointestinal motility?

It stimulates motilin receptors, increasing GI motility.

Which macrolide is most commonly associated with nausea, vomiting, diarrhea, and abdominal cramping?

Erythromycin.

Which macrolide has the greatest number of CYP450 drug interactions?

Erythromycin.

Which erythromycin formulation is associated with acute cholestatic hepatitis?

Erythromycin estolate.

Which macrolide is commonly used in H. pylori eradication therapy?

Clarithromycin.

Which macrolide is commonly associated with CYP450 drug interactions?

Clarithromycin.

Which macrolide is commonly used to treat Mycobacterium avium complex (MAC)?

Clarithromycin.

Which macrolide is commonly known as the Z-Pak?

Azithromycin.

Which macrolide has the fewest CYP450 drug interactions?

Azithromycin.

Which macrolide does NOT significantly inhibit CYP450?

Azithromycin.

Which macrolide is commonly used for respiratory tract infections?

Azithromycin.

Which macrolide is commonly used for community-acquired pneumonia?

Azithromycin.

Which macrolide is commonly used for atypical pneumonia?

Azithromycin.

What Gram-positive organisms are commonly covered by macrolides?

- Streptococcus

- Some MSSA

Which common respiratory pathogens are covered by macrolides?

- Streptococcus pneumoniae

- Haemophilus influenzae

- Moraxella catarrhalis (except erythromycin has poor coverage)

Which respiratory pathogen is NOT well covered by erythromycin?

Moraxella catarrhalis.

Which atypical organisms are covered by macrolides?

- Chlamydia

- Mycoplasma

- Legionella

- Listeria

Which sexually transmitted infection is commonly treated with macrolides?

Chlamydia (nongonococcal urethritis/cervicitis).

Which organism causes whooping cough that can be treated with macrolides?

Bordetella pertussis.

Which gastric organism is commonly treated with clarithromycin?

Helicobacter pylori.

Which mycobacterial infection is treated or prevented with azithromycin or clarithromycin?

Mycobacterium avium complex (MAC).

What upper respiratory tract infections are commonly treated with macrolides?

- Pharyngitis

- Sinusitis

What lower respiratory tract infections are commonly treated with macrolides?

- Bronchitis

- Pneumonia

Which ear infection is commonly treated with macrolides?

Acute otitis media.

Which skin infections are commonly treated with macrolides?

- Erysipelas

- Cellulitis

Which topical macrolide is commonly used for acne?

Topical erythromycin.

What are the common gastrointestinal side effects of macrolides?

- Nausea

- Vomiting

- Diarrhea

Which serious gastrointestinal infection can occur with macrolide use?

Clostridioides difficile (C. diff) infection.

Which important cardiac adverse effect is associated with macrolides?

QT interval prolongation.

Why is QT prolongation clinically important?

It increases the risk of torsades de pointes and other ventricular arrhythmias.

Which macrolides inhibit CYP450?

- Erythromycin

- Clarithromycin

Which macrolide has minimal CYP450 inhibition?

Azithromycin.

Which macrolide is primarily used to treat Clostridioides difficile infection?

Fidaxomicin.

What is unique about fidaxomicin's mechanism of action?

It inhibits RNA polymerase, unlike the other macrolides.

Which newer macrolides belong to the ketolide class?

- Telithromycin

- Solithromycin

Match each macrolide with its unique feature.

- Azithromycin → Z-Pak; respiratory infections; fewest CYP450 interactions

- Clarithromycin → H. pylori; CYP450 inhibitor; MAC

- Erythromycin → GI motility; ophthalmic ointment; cholestatic hepatitis (estolate); most GI side effects

Match the macrolides with their major distinguishing feature.

- Azithromycin → Minimal drug interactions

- Clarithromycin → H. pylori

- Erythromycin → Motilin receptor stimulation

What are the highest-yield facts to remember about macrolides?

- 50S ribosomal inhibitor

- Prevent translocation along mRNA

- Usually bacteriostatic

- Azithromycin = Z-Pak; respiratory infections; fewest CYP450 interactions

- Clarithromycin = H. pylori; MAC

- Erythromycin = GI motility; ophthalmic ointment; cholestatic hepatitis (estolate)

- Cover atypicals (Chlamydia, Mycoplasma, Legionella)

- QT prolongation

- Erythromycin and clarithromycin inhibit CYP450

- Fidaxomicin treats C. difficile and inhibits RNA polymerase

Which macrolides inhibit CYP450, and which does not?

- Erythromycin → CYP450 inhibitor

- Clarithromycin → CYP450 inhibitor

- Azithromycin → Does NOT significantly inhibit CYP450

Which macrolide is least likely to cause drug interactions?

Azithromycin.

Which macrolide is most associated with gastrointestinal side effects?

Erythromycin.

Which macrolide stimulates motilin receptors?

Erythromycin.

Which macrolide is commonly used in penicillin-allergic patients with respiratory infections?

Azithromycin.

Which macrolides are commonly used to treat atypical pneumonia?

- Azithromycin

- Clarithromycin

- Erythromycin

Match the organism with the appropriate macrolide association.

- H. pylori → Clarithromycin

- Mycobacterium avium complex (MAC) → Azithromycin or Clarithromycin

- Bordetella pertussis → Macrolides

- Chlamydia → Macrolides

Which macrolide is available as an ophthalmic ointment?

Erythromycin.

What types of organisms do macrolides primarily cover?

- Gram-positive organisms

- Atypical organisms

- Some Gram-negative respiratory pathogens

Match each macrolide with the one fact you should immediately think of.

- Azithromycin → Z-Pak; fewest drug interactions

- Clarithromycin → H. pylori

- Erythromycin → GI motility

Compare tetracyclines and macrolides.

- Tetracyclines: 30S; prevent aminoacyl-tRNA attachment; bacteriostatic; Lyme disease/Chlamydia; photosensitivity & tooth discoloration

- Macrolides: 50S; prevent translocation; bacteriostatic; respiratory infections/atypical pneumonia; QT prolongation & GI upset

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