Antimicrobials · Macrolides
The facts most likely to be tested
Press 1–5 to rate · ↑↓ to navigate
Clarithromycin functions by binding to the 50S ribosomal subunit, effectively inhibiting bacterial protein synthesis.
Clarithromycin is a potent CYP3A4 inhibitor, significantly increasing the risk of toxicity for drugs like statins, warfarin, and theophylline.
Clarithromycin is a first-line component of the triple therapy regimen for Helicobacter pylori eradication alongside amoxicillin and a proton pump inhibitor.
Clarithromycin is the drug of choice for the prophylaxis and treatment of Mycobacterium avium complex (MAC) in patients with advanced HIV/AIDS.
Clarithromycin carries a significant risk of QT interval prolongation, which can precipitate life-threatening torsades de pointes.
Clarithromycin is contraindicated in patients taking ergot alkaloids or pimozide due to the risk of severe vasospasm or arrhythmias.
Clarithromycin is associated with a metallic dysgeusia (altered taste) and significant gastrointestinal distress as common adverse effects.
Vignette unlocked
A 42-year-old male with a history of HIV and a CD4 count of 45 cells/mm³ presents for a routine follow-up. He is currently not on any prophylactic antibiotics. He complains of a persistent non-productive cough, fever, and night sweats. Physical examination reveals hepatosplenomegaly and lymphadenopathy. Laboratory studies show elevated alkaline phosphatase.
Which medication is the most appropriate choice for the primary prophylaxis of this patient's most likely opportunistic infection?
Clarithromycin
The patient's presentation is classic for disseminated Mycobacterium avium complex (MAC), and clarithromycin (or azithromycin) is a standard prophylactic agent for patients with CD4 counts <50 cells/mm³ once active disseminated MAC has been excluded.
Full handout
High yield triage
Classification
Macrolide antibiotic; protein synthesis inhibitor.
Indications
H. pylori eradication, community-acquired pneumonia, and MAC prophylaxis.
Mechanism of Action
Binds 50S ribosomal subunit to inhibit translocation of bacterial proteins.
Side Effects
GI distress (nausea/diarrhea), QT prolongation, ototoxicity.
Contraindications / Monitoring
CYP3A4 inhibitors; monitor QTc interval and hepatic function.
Full handout
Mechanism of Action
Clarithromycin binds reversibly to the 50S ribosomal subunit of susceptible organisms. This action inhibits peptidyl transferase and blocks the translocation of the growing peptide chain. It is primarily bacteriostatic, preventing bacterial growth by halting essential protein synthesis.
Unique Properties
Compared to erythromycin, it has improved acid stability and better oral bioavailability. It also possesses an active metabolite, 14-hydroxyclarithromycin, which provides synergistic activity against Haemophilus influenzae.
Indications
It is a core component of triple therapy for H. pylori eradication. It is also indicated for community-acquired pneumonia and as primary prophylaxis for Mycobacterium avium complex (MAC) in patients with advanced HIV.
Pharmacokinetics
Metabolized extensively by the hepatic CYP3A4 enzyme system. It is a potent CYP3A4 inhibitor, leading to significant drug-drug interactions with statins and warfarin. Excretion is primarily renal and biliary.
Side Effects & Adverse Events
Common effects include nausea, vomiting, and abdominal cramping. QT prolongation is a major risk, potentially leading to Torsades de pointes. Rare but serious ototoxicity and cholestatic jaundice may occur.
Contraindications
Concurrent use with HMG-CoA reductase inhibitors (statins) due to risk of rhabdomyolysis. History of QT prolongation or ventricular arrhythmia is a strict contraindication. Avoid in patients with severe hepatic impairment.
Monitoring
Obtain baseline ECG in patients with cardiac risk factors to assess QTc interval. Monitor liver function tests if therapy is prolonged. Assess for signs of myopathy if used with interacting medications.
Clinical Pearls
Always check the patient's medication list for CYP3A4 substrates like simvastatin or colchicine to prevent toxicity. Remember it as the 'C' in the triple therapy regimen for peptic ulcer disease.