Tacrolimus and clarithromycin: why the BNF says to avoid the pair

Tacrolimus is an immunosuppressant. The NHS azathioprine page lists ciclosporin or tacrolimus as immunosuppressant medicines, and the NHS eplerenone page describes them as used to treat skin conditions such as psoriasis or eczema. The BNF entries read for this guide are about interactions rather than indications, so this page does not go further into why tacrolimus is prescribed to an individual.

The BNF describes the effect of clarithromycin in terms of the concentration of tacrolimus. A medicine that raises the concentration can move the level away from the one intended without any change to the dose taken, which is why the combination appears so prominently in prescribing references.

Antibiotics are a common short-term addition to a regular medicine list. A person with a chest or ear infection may be seen by a doctor who is not part of the specialist team that looks after their tacrolimus, so knowing about this pair is genuinely useful.

The BNF interaction list for tacrolimus states that clarithromycin is predicted to increase the concentration of tacrolimus. It advises that the manufacturer says avoid, adds that if concurrent use is unavoidable the product literature should be consulted, and rates the severity as severe with study as the evidence type.

The wording matters. Avoid is not a statement that the pair can never be used, since the entry itself says what to do if use is unavoidable. It means the prescriber should look for another option first and, if there is none, follow detailed specialist guidance, which typically includes closer monitoring.

The same BNF list says erythromycin increases the concentration of tacrolimus, with manufacturer advice to avoid and to consult product literature if use is unavoidable. Fluconazole is listed as increasing tacrolimus concentration with advice to monitor and adjust the dose.

The practical lesson is that choosing a different macrolide does not by itself solve the problem. Any new antibiotic or antifungal should be checked against the tacrolimus entry.

If you take tacrolimus and are offered an antibiotic, say so, and ask the prescriber or pharmacist whether it is on the BNF list for tacrolimus. Do not take leftover antibiotics from earlier illness, and do not stop tacrolimus yourself. The specialist team that prescribes it is usually the right first call if you are unsure.

• Tell every prescriber and pharmacist that you take tacrolimus.

• Carry a current medicine list, including herbal products.

• Keep any monitoring appointments you are given, and tell the team about any new medicines or infections.

• Report new symptoms such as fever, tremor, unusual headaches or reduced urine to your team promptly.

The sources read for this guide do not list a symptom set for this interaction. Contact the specialist team that looks after your tacrolimus the same day if you are unwell after an antibiotic is added, call NHS 111 if you cannot reach them, and call 999 for collapse, a seizure or severe breathlessness.

This site has a separate overview of tacrolimus neurotoxicity for readers who want background on the nervous system effects of high levels.