Clarithromycin
Macrolide antibiotic with broad spectrum for bacterial infections
Clarithromycin is a semi-synthetic macrolide antibiotic that was developed by chemical modification of erythromycin and has been used in clinical practice since the 1990s. Compared to erythromycin, clarithromycin is distinguished by improved acid stability, a longer half-life, higher bioavailability, and an expanded spectrum against atypical pathogens. In Germany, clarithromycin is available under brand names such as Klacid and numerous generics.
Clarithromycin is primarily used for the treatment of bacterial infections of the respiratory tract, skin, and mucous membranes. A particularly important application is the eradication of Helicobacter pylori as part of triple therapy for stomach ulcers. Due to its favourable side effect profile and oral availability, it is a frequently prescribed antibiotic in outpatient medicine.
Mechanism of Action
Clarithromycin inhibits bacterial protein synthesis by reversible binding to the 50S subunit of the bacterial ribosome. The binding site is located at the 23S rRNA molecule of the 50S subunit; through this binding, the translocation of the growing peptide and the peptidyltransferase reaction are blocked. The result is premature termination of the polypeptide chain and thus a halt in protein biosynthesis of the bacterial cell.
Clarithromycin acts bacteriostatically (inhibiting growth) or bactericidally (killing) depending on pathogen density and concentration. With susceptible pathogens and sufficiently high tissue levels, the bactericidal effect predominates. The active ingredient accumulates markedly in tissues and intracellularly, which is particularly advantageous for intracellularly persisting pathogens such as mycobacteria, chlamydia, and legionella.
The active metabolite 14-hydroxy-clarithromycin, which is formed during liver passage, also contributes to antibacterial activity and can act synergistically with the parent compound, extending the overall spectrum of activity.
Indications
- Respiratory tract infections: Community-acquired pneumonia, acute exacerbation of chronic bronchitis, sinusitis, pharyngitis, and tonsillitis in penicillin allergy
- Helicobacter pylori eradication: Component of the French triple therapy (PPI + clarithromycin + amoxicillin or metronidazole) for gastric and duodenal ulcers
- Skin and soft tissue infections: Erysipelas, impetigo, infected wounds (in penicillin allergy or uncomplicated cases)
- Mycobacterioses: Mycobacterium avium complex (MAC) in immunosuppressed patients (e.g. HIV/AIDS) as prophylaxis and therapy
- Atypical pneumonias: Mycoplasma pneumonia, Legionella pneumonia, Chlamydophila infections
- Otitis media: In children, particularly when beta-lactam antibiotics cannot be used
- Helicobacter pylori eradication: Standard component of various eradication regimens according to the Maastricht VI consensus
Dosage and Administration
Standard dosage adults: 250 to 500 mg twice daily for 7 to 14 days, depending on the severity of the infection. For severe respiratory tract infections 500 mg twice daily. Helicobacter pylori eradication: 500 mg twice daily in combination with a PPI and a further antibiotic for 7 to 14 days. Mycobacterioses: 500 mg twice daily, often for months in combination with other antimycobacterials. Children: 7.5 mg/kg body weight twice daily (max. 500 mg/dose), as granules for suspension. Modified-release tablets (500 mg once daily) are available for patients with gastrointestinal intolerance.
Clarithromycin can be taken with or without food; modified-release tablets should, however, be taken with a meal to optimise bioavailability and reduce gastrointestinal side effects. Do not split or chew tablets. The duration of therapy is determined by the indication; premature interruption promotes resistance development.
Side Effects
Very common and common: Gastrointestinal complaints predominate: nausea, vomiting, diarrhoea, abdominal pain, dyspepsia. These are usually mild and rarely lead to treatment discontinuation. Changes in taste (metallic or bitter taste) are typical of macrolides and occur particularly frequently with clarithromycin.
Occasional: Headache, insomnia, anxiety disorders, dizziness, elevated liver values (transaminases), prolonged QTc interval on ECG (cardiac monitoring required in at-risk patients), skin rashes.
Rare to very rare: Severe liver damage (hepatitis, cholestasis, liver failure in individual cases), torsades de pointes (life-threatening cardiac arrhythmia), pseudomembranous colitis (caused by Clostridioides difficile overgrowth), Stevens-Johnson syndrome, toxic epidermal necrolysis, hearing loss (usually reversible at high doses or prolonged use).
Interactions
Clarithromycin is a potent inhibitor of the cytochrome P450 enzyme CYP3A4 and the transporter protein P-glycoprotein. This property leads to numerous clinically significant interactions:
- Statins (simvastatin, lovastatin): Markedly elevated statin levels; combination contraindicated (risk of rhabdomyolysis)
- Colchicine: Life-threatening intoxication possible; combination contraindicated in renal insufficiency
- Ergotamine: Risk of ergotism (vasoconstriction); combination contraindicated
- Anticoagulants (warfarin, phenprocoumon): Increased bleeding tendency due to enhanced anticoagulation; close INR monitoring
- Benzodiazepines (midazolam, triazolam): Markedly increased sedation due to delayed breakdown
- Antiarrhythmics (amiodarone, sotalol): Additive QTc-prolongation potential; combination critical
- Immunosuppressants (ciclosporin, tacrolimus, sirolimus): Markedly elevated levels; close level monitoring required
- Rifampicin: Markedly reduced clarithromycin levels due to enzyme induction; avoid combination
Special Notes
Pregnancy: Clarithromycin is contraindicated during pregnancy. Animal studies have shown embryotoxic and teratogenic effects. Alternative antibiotics (e.g. amoxicillin, cefuroxime) should be preferred in pregnant women.
QTc prolongation: Clarithromycin can prolong the QTc interval. In patients with known QTc prolongation, electrolyte disturbances (hypokalaemia, hypomagnesaemia), or concurrent use of other QTc-prolonging medications, special caution is required and an ECG before and during therapy may be appropriate.
Resistance development: In Germany and Europe, increasing clarithromycin resistance in Helicobacter pylori is observed (up to 25% in some regions). Resistance testing before use in H. pylori eradication is therefore recommended.
Hepatic insufficiency: In severe hepatic insufficiency, clarithromycin is contraindicated, as the active ingredient is hepatically metabolised and further damage cannot be excluded.
Frequently Asked Questions
How long does a clarithromycin course last?
The treatment duration is 5 to 14 days depending on the indication. For respiratory tract infections, 7 days is usual; for H. pylori eradication likewise 7 to 14 days in combination. Completing the full prescribed course is important to avoid resistance.
May clarithromycin be taken with grapefruit juice?
Grapefruit juice inhibits CYP3A4 and can theoretically increase clarithromycin levels; however, the effect is considerably weaker than with some other medications. As a precaution, consumption of grapefruit juice should be avoided during therapy.
Why does everything taste metallic during treatment?
Changes in the sense of taste are a typical and well-known effect of clarithromycin. The metallic or bitter intrinsic taste of the active ingredient can temporarily influence taste perception. This effect is completely reversible after the end of therapy.
References
- Product information Klacid (Abbvie), as of 2024
- European Society of Clinical Microbiology and Infectious Diseases (ESCMID): Guidelines on respiratory tract infections
- Malfertheiner P et al.: Management of Helicobacter pylori infection - the Maastricht VI/Florence consensus report. Gut, 2022
- Federal Institute for Drugs and Medical Devices (BfArM): Dear Doctor Letter Clarithromycin and cardiovascular risks, 2017
- European Medicines Agency (EMA): Clarithromycin EPAR