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Bronchiectasis with newly isolated Mycobacterium avium complex during long-term azithromycin — SCE Respiratory

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HardAzithromycinBronchiectasis with newly isolated Mycobacterium avium complex during long-term azithromycinSCE Respiratory

A 63-year-old woman with idiopathic bronchiectasis and chronic Pseudomonas aeruginosa infection is reviewed in a specialist clinic. Despite optimised airway-clearance therapy and regular nebulised colistin, she previously had five exacerbations in 12 months. Azithromycin 250 mg three times weekly was therefore added after a negative mycobacterial sputum culture, normal liver biochemistry and a QTc of 432 ms. Her exacerbation frequency has fallen substantially over the subsequent 9 months. At routine review she is clinically stable, with unchanged weight, spirometry and sputum volume. Surveillance sputum is smear-negative but grows Mycobacterium avium complex for the first time. The isolate is macrolide-susceptible. High-resolution CT shows her established cylindrical bronchiectasis without new nodules, tree-in-bud opacities or cavitation. Which is the most appropriate next management step?

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Correct answer: B — Stop azithromycin, continue nebulised colistin, and obtain further sputum samples for mycobacterial culture after a 2-week macrolide washout before deciding whether NTM pulmonary disease requires treatment

The new MAC isolate changes the risk–benefit balance despite clear benefit from azithromycin. Continuing macrolide monotherapy could select macrolide-resistant MAC, substantially compromising the key drug class used in any subsequent MAC regimen. Azithromycin should therefore be withheld while the finding is evaluated. Macrolides can also suppress mycobacterial growth, so respiratory samples should be collected after a 2-week washout. One positive expectorated sputum culture does not by itself establish NTM pulmonary disease. This patient lacks clinical or radiological progression and therefore needs repeat cultures and integrated clinical, radiological and microbiological assessment rather than immediate multidrug therapy. Nebulised colistin remains indicated for her chronic P. aeruginosa infection. B risks selecting resistance and may reduce the sensitivity of repeat cultures. C and D initiate burdensome multidrug MAC treatment before diagnostic criteria or evidence favouring treatment are established; D additionally continues azithromycin during incomplete diagnostic evaluation. E correctly stops azithromycin but abandons evaluation of a clinically consequential isolate, while long-term doxycycline is not a routine equivalent substitute for macrolide prophylaxis.

Reference: British Thoracic Society guideline for the use of long-term macrolides in adults with respiratory disease (2020) — https://www.brit-thoracic.org.uk/document-library/guidelines/long-term-macrolide-use/british-thoracic-society-guideline-for-the-use-of-long-term-macrolides-in-adults-with-respiratory-disease/ British Thoracic Society Guideline for the management of non-tuberculous mycobacterial pulmonary disease (2017) — https://www.brit-thoracic.org.uk/document-library/guidelines/ntm/bts-ntm-guideline-summary-of-recommendations/ British Thoracic Society guideline for bronchiectasis in adults (2019) — https://www.brit-thoracic.org.uk/document-library/guidelines/bronchiectasis/bts-guideline-for-bronchiectasis-in-adults/?uid=81026986520221111201429