“If this blog helped you out, don’t keep it to yourself—share the link on your socials!” 👍 “Like what you read? Spread the love and share this blog on your social media.” 👍 “Found this useful? Hit share and let your friends know too!” 👍 “If you enjoyed this post, please share the URL with your friends online.” 👍 “Sharing is caring—drop this link on your social media if it helped you.”

Sunday, July 27, 2025

Clarithromycin


Clarithromycin is a macrolide antibiotic used to treat a variety of bacterial infections, especially those affecting the respiratory tract, skin, and soft tissues. It also plays a key role in combination regimens for the eradication of Helicobacter pylori in peptic ulcer disease. As a bacteriostatic agent, it works by inhibiting bacterial protein synthesis. Clarithromycin is available in multiple oral formulations including tablets, modified-release tablets, and suspensions, and in some countries, as an intravenous preparation for hospital use.

Below is a comprehensive professional profile for clarithromycin covering its pharmacologic class, mechanisms, clinical indications, dosage regimens, contraindications, adverse reactions, precautions, and clinically significant drug interactions.

Pharmacological Classification

  • Therapeutic class: Antibiotic

  • Pharmacologic class: Macrolide

  • Chemical class: 14-membered lactone ring macrolide

  • ATC Code: J01FA09

Brand Names

  • Biaxin® (US and Canada)

  • Klaricid® (UK and international)

  • Klacid® (Europe, Asia)

  • Generic formulations: Clarithromycin 250 mg / 500 mg tablets, oral suspension, modified-release tablets

Mechanism of Action

Clarithromycin binds to the 50S subunit of bacterial ribosomes, blocking the translocation step of protein synthesis by inhibiting peptidyl transferase activity. This leads to:

  • Inhibition of bacterial growth (bacteriostatic action)

  • At higher concentrations or in highly susceptible strains, can exhibit bactericidal activity

The spectrum of action includes Gram-positive, Gram-negative, atypical, and intracellular pathogens.

Antibacterial Spectrum

Susceptible Organisms

  • Streptococcus pneumoniae, Streptococcus pyogenes

  • Haemophilus influenzae, Moraxella catarrhalis

  • Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella pneumophila

  • Helicobacter pylori (in combination therapy)

  • Mycobacterium avium complex (MAC)

  • Bordetella pertussis

  • Toxoplasma gondii (off-label)

  • Propionibacterium acnes (acne adjunctive treatment)

Resistant Strains

  • Macrolide-resistant Streptococcus

  • Some Enterobacteriaceae

  • Methicillin-resistant Staphylococcus aureus (MRSA)

Resistance mechanisms include efflux pumps, target modification (methylation), and enzyme degradation.

Indications and Clinical Uses

Approved Uses

  • Community-acquired pneumonia

  • Acute exacerbation of chronic bronchitis (AECB)

  • Pharyngitis or tonsillitis (as an alternative to penicillin)

  • Acute maxillary sinusitis

  • Skin and soft tissue infections (e.g., impetigo, cellulitis, folliculitis)

  • Otitis media (especially in children)

  • Helicobacter pylori eradication (part of triple or quadruple therapy)

  • Mycobacterium avium complex (MAC) prophylaxis and treatment in HIV-positive patients

Off-label and less common uses

  • Pertussis (whooping cough)

  • Toxoplasmosis (with pyrimethamine and folinic acid)

  • Acne vulgaris (short-term)

  • Traveler’s diarrhea

  • Cat scratch disease (Bartonella henselae)

Dosage and Administration

Adults – Immediate-Release

  • Usual dose: 250–500 mg twice daily for 7–14 days depending on infection

  • Helicobacter pylori:

    • 500 mg twice daily for 7–14 days

    • In combination with amoxicillin and PPI (e.g., omeprazole)

Modified-Release Tablets

  • 500–1000 mg once daily (after food)

Pediatric Dose (suspension)

  • 7.5 mg/kg twice daily (max: 500 mg twice daily)

Renal Impairment

  • Reduce dose by 50% if creatinine clearance <30 mL/min

IV Formulation (if available)

  • 500 mg every 12 hours; switch to oral ASAP when clinically indicated

Pharmacokinetics

  • Bioavailability: ~55% (oral), increased with food

  • Peak plasma concentration: 1–3 hours (IR); 6–8 hours (MR)

  • Half-life: ~3–4 hours; prolonged in renal impairment

  • Metabolism: Hepatic, via CYP3A4, forming active metabolite 14-hydroxyclarithromycin

  • Excretion: ~40% in urine (unchanged and metabolites); ~40% in feces

Contraindications

  • Known hypersensitivity to macrolides

  • Concurrent use with drugs metabolized by CYP3A4 that prolong QT interval:

    • Cisapride, pimozide, terfenadine, astemizole, ergot derivatives

  • Severe hepatic impairment with concurrent renal dysfunction

  • History of QT prolongation, torsades de pointes, or ventricular arrhythmias

  • Concomitant colchicine in patients with renal or hepatic impairment (↑ colchicine toxicity)

Warnings and Precautions

  • Risk of QT prolongation and arrhythmias, especially in:

    • Older adults

    • Patients with electrolyte abnormalities (e.g., hypokalemia)

    • Concomitant use of QT-prolonging drugs

  • May cause hepatotoxicity — monitor liver enzymes in long-term use

  • Risk of Clostridioides difficile–associated diarrhea (CDAD)

  • Renal impairment — reduce dose

  • Myasthenia gravis — may exacerbate weakness

  • Cross-resistance possible with erythromycin, azithromycin

  • Drug-resistant infections — use only when necessary based on susceptibility

Adverse Effects

Common

  • Gastrointestinal: Nausea, diarrhea, abdominal pain, dyspepsia

  • Taste disturbances (dysgeusia)

  • Headache

  • Skin rash or urticaria

Less Common

  • Elevated liver enzymes, hepatitis

  • Prolonged QT, palpitations, arrhythmia

  • Jaundice

  • Anxiety, insomnia, hallucinations (rare CNS effects)

  • Hearing loss (reversible)

Rare

  • Stevens-Johnson syndrome, toxic epidermal necrolysis

  • Anaphylaxis

  • Interstitial nephritis

  • Pancreatitis

Drug Interactions

Clarithromycin is a strong inhibitor of CYP3A4, resulting in numerous drug interactions.

Increased Risk of Toxicity (contraindicated or to be avoided)

  • Statins (simvastatin, lovastatin): Risk of rhabdomyolysis

  • Colchicine: Risk of fatal toxicity, especially in renal/hepatic disease

  • Warfarin: Enhanced anticoagulant effect → monitor INR

  • Carbamazepine, phenytoin, valproate: Serum levels may increase

  • Theophylline, digoxin, verapamil, cyclosporine, tacrolimus: Monitor for toxicity

QT-Prolonging Agents (additive risk)

  • Amiodarone, sotalol, quinidine, fluoroquinolones, antipsychotics

Antivirals

  • Ritonavir, lopinavir: Inhibit clarithromycin metabolism → increased clarithromycin exposure

Antifungals

  • Itraconazole, ketoconazole: Compete for CYP3A4 → possible toxicity

Pregnancy and Lactation

Pregnancy

  • Category C (U.S.) – Adverse effects observed in animal studies

  • Use only if benefits outweigh risks

  • Avoid in first trimester unless essential

Lactation

  • Excreted into breast milk

  • Generally considered safe for short durations

  • Monitor infant for gastrointestinal upset or rash

Clinical Monitoring

  • Symptom resolution (clinical cure)

  • Signs of QT prolongation if used with interacting agents

  • Hepatic enzymes in long-term therapy or liver disease

  • Renal function in elderly or renally impaired

  • Therapeutic drug levels for interacting drugs (e.g., digoxin, warfarin)

Patient Counseling

  • Take with or without food, but food may improve tolerance

  • Modified-release tablets should be swallowed whole, not crushed

  • Complete the full course even if feeling better

  • Report signs of allergic reactions (rash, breathing difficulty), jaundice, or irregular heartbeat

  • Avoid combining with antacids or other macrolides unless prescribed

  • Store suspension in refrigerator (some brands) and discard after 14 days




on
Labels:

No comments:

Post a Comment

Subscribe to: Post Comments (Atom)