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Clarithromycin is a macrolide antibiotic used for respiratory infections, skin and soft tissue infections, and it is a fixed building block of Helicobacter pylori eradication. At the same time it counts as the antibiotic with the greatest interaction potential, because it strongly inhibits the liver enzyme CYP3A4. That is why statins such as simvastatin are paused during treatment and the QT interval is kept in view.
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No other common antibiotic has an interaction list as long as clarithromycin's. Almost every entry follows the same pattern: clarithromycin blocks the breakdown or the removal of another drug, whose level rises — and with it the side effects. The most important combinations:
| Combination | Consequence | What to do |
|---|---|---|
| Statins: simvastatin, atorvastatin | The statin level rises sharply, risk of muscle breakdown (rhabdomyolysis) | Simvastatin: contraindicated — pause it; atorvastatin: pause it or use the lowest dose, after consultation |
| QT-prolonging medicines, e.g. citalopram, amiodarone, some antipsychotics | Added QT prolongation, risk of serious heart rhythm disturbances | Have the combination checked beforehand; report a racing heart, palpitations or dizziness immediately |
| Phenprocoumon (vitamin K antagonist) | Anticoagulation is strengthened, the INR rises, risk of bleeding | Close INR checks during and after the course |
| DOACs: rivaroxaban, apixaban | The level of the anticoagulant can rise through CYP3A4 and P-glycoprotein | Have the combination assessed by a doctor, watch for signs of bleeding |
| Colchicine (for gout) | The colchicine level rises — poisonings, some of them fatal, have been described | Avoid the combination; contraindicated where kidney or liver function is impaired |
| Carbamazepine, ciclosporin, tacrolimus, theophylline | Levels rise, signs of toxicity possible | Level checks, dose adjustment by the practice |
| Midazolam and related sedatives | Increased and prolonged sedation | Combine only under medical supervision |
| St John's wort, rifampicin (enzyme inducers) | The reverse effect: the clarithromycin level falls, the treatment can fail | Mention them beforehand — herbal preparations count too |
| Alcohol | No specific interaction, but an additional burden on the stomach and the circulation | Restraint during an infection makes sense anyway |
Anticoagulants are worth a second look: on phenprocoumon the INR often rises only after a few days — which is why it is checked during and shortly after the antibiotic course. With the direct anticoagulants such as rivaroxaban and apixaban there is no laboratory value that shows the rise; here what counts is the medical judgement made before the prescription. Watch out yourself for signs of bleeding such as unusual bruises, bleeding gums or nosebleeds.
The list is long, but the consequence is simple: check everything against everything once, before the first tablet. How to go about that systematically is shown in the guide drug interactions — or the interaction check in the brite app does it directly.
The QT interval is a section of the ECG: the span of time the heart needs in order to recover electrically after each beat. Clarithromycin can lengthen this recovery phase — as all macrolides can. For most people that has no consequences. It becomes critical when several risk factors come together, because a markedly prolonged QT interval favours a rare but dangerous heart rhythm disturbance (torsade de pointes).¹
Risk constellations that the practice should know about before prescribing:
Important for perspective: in absolute terms these events are rare. The risk almost always arises out of the combination — an antibiotic that is well tolerated in itself meets a QT-prolonging long-term medicine and a low potassium level. That is exactly why the complete list of medicines belongs on the table before the prescription.
Clarithromycin is rarely the first choice "for everything" — it has a clearly defined role alongside the other standard antibiotics:
| Active ingredient | Class | Typical role | Practically relevant |
|---|---|---|---|
| Clarithromycin | Macrolide | Atypical pathogens, penicillin allergy, Helicobacter eradication | Greatest interaction potential; metallic taste; the QT issue |
| Amoxicillin | Aminopenicillin | Often the first choice for many respiratory and ENT infections | Hardly any CYP interactions; a rash as the typical side effect |
| Doxycycline | Tetracycline | Atypical pathogens, Lyme disease, acne | A gap around milk and minerals is needed; sensitivity to sunlight |
| Azithromycin | Macrolide | Short regimens over 3 to 5 days | Very long half-life; a weaker CYP3A4 inhibitor than clarithromycin, the QT issue remains |
Against the stomach bacterium Helicobacter pylori, clarithromycin is never used on its own but always as part of a combination regimen — classically together with a proton pump inhibitor and amoxicillin or metronidazole over 7 to 14 days. The guideline now makes the choice of regimen depend on how likely clarithromycin resistance is — which is one of the reasons why resistance testing before treatment is increasingly recommended.²
Macrolide resistance is a real problem. A relevant proportion of the pneumococci in Germany is insensitive to macrolides, and with Helicobacter pylori clarithromycin resistance has risen markedly over the past decades — above all in people who have had a macrolide before. That is exactly why the rule is: use clarithromycin in a targeted way, see the course through consistently and mention earlier macrolide treatments at your practice. The background is provided by the guide antibiotic resistance.³
Pregnancy and breastfeeding: clarithromycin is not the first choice in pregnancy. The advisory centre Embryotox puts better-tried alternatives — above all penicillins and cephalosporins — ahead of it; if a macrolide is needed, other members of the class are regarded as preferable. Having already taken it, though, is no reason to panic, but a reason for a medical conversation. While breastfeeding the drug passes into breast milk in small amounts; the decision is made by the practice case by case. Orientation is offered by the guide medications during pregnancy.⁴
In older age the risk of QT problems and interactions rises — simply because more long-term medicines come together. Anyone taking five or more preparations should have the prescription matched up particularly carefully; the guides polypharmacy and medications in old age are helpful here.
Kidney and liver: where kidney function is severely impaired, the dose is reduced according to the SmPC. Where there is severe liver dysfunction in combination with kidney problems, clarithromycin is not suitable. The combination with colchicine is contraindicated in kidney or liver failure. What applies generally is set out under medications for kidney and liver disease.
Yes and yes. The bitter to metallic taste is by far the most typical clarithromycin complaint. The drug is excreted through the saliva and irritates the taste buds there. That is harmless, but it can spoil your appetite. After the last tablet the taste disappears on its own within a few days. Until then, chewing gum, sour drops and drinking something straight afterwards help. It is not a reason to break off the course.
Both. Pausing the statin during a course of clarithromycin is exactly the textbook approach, not a contradiction. The short pause does practically no harm to the lowering of your cholesterol. The critical moment is a different one: the restart after the course, which is easily forgotten in everyday life. Make a note of the date or set it as a reminder — and if you are unsure, check briefly with your practice when the statin starts again.
As a rule, yes. Clarithromycin strengthens the effect of phenprocoumon, the INR can rise markedly, often with a delay of a few days. That is why practices check more closely — during the course and usually in the week afterwards as well. If you measure it yourself, agree the plan in advance. Additional safety comes from watching for signs of bleeding: unusual bruises, bleeding gums, blood in the urine. You will find more everyday tips in the guide living with blood thinners.
No, not on your own initiative. The complaints improve as soon as the number of pathogens falls — that does not mean the infection is over. With Helicobacter eradication in particular, consistency decides the outcome: take only half the regimen and you risk the bacterium surviving and becoming resistant. The prescribed duration applies; questions about it are settled by the practice, not by gut feeling.
In the digital medication plan you see pauses, restarts and every interaction at a glance.
