Table 5.

Treatment Regimens for Mycobacterium abscessus by Macrolide Susceptibility (mutational and inducible resistance)

Macrolide Susceptibility Pattern
Mutationala	Inducibleb	No. of Drugsc	Preferred Drugs	Frequency of dosing
Susceptible	Susceptible	Initial phase ≥3	Parenteral (choose 1–2) Amikacin Imipenem (or Cefoxitin) Tigecycline Oral (choose 2) Azithromycin (clarithromycin)d Clofazimine Linezolid	Daily (three times weekly may be used for aminoglycosides)
		Continuation phase ≥2	Oral/inhaled (choose 2–3) Azithromycin (clarithromycin)d Clofazimine Linezolid Inhaled amikacin
Susceptible	Resistant	Initial phase ≥ 3	Parenteral (choose 2) Amikacin Imipenem (or Cefoxitin) Tigecycline Oral (choose 2–3) Azithromycin (clarithromycin)e Clofazimine Linezolid	Daily (three times weekly may be used for aminoglycosides)
		Continuation phase ≥2	Oral/inhaled (choose 2–3) Azithromycin (clarithromycin)e Clofazimine Linezolid Inhaled amikacin
Resistant	Resistant	Initial phase ≥3	Parenteral (choose 2–3) Amikacin Imipenem (or Cefoxitin) Tigecycline Oral (choose 2–3) Azithromycin (clarithromycin)e Clofazimine Linezolid	Daily (three times weekly may be used for aminoglycosides)
		Continuation Phase ≥2	Oral/inhaled (choose 2–3) Azithromycin (clarithromycin)e Clofazimine Linezolid Inhaled amikacin

^aMutational resistance: None present - Isolate determined to be phenotypically susceptible at 3–5 days of incubation in culture. Present – Isolate determined to be phenotypically resistant at 3–5 days of incubation or sequencing identifies rrl mutation know to confer resistance.

^bInducible resistance: Functional erm(41) gene - Isolate determined to be resistant after 14 days of incubation or sequencing identifies functional gene sequence. Nonfunctional erm(41) gene - Isolate determined to be susceptible after 14 days of incubation or sequencing identifies truncated sequence or C28 mutation (in subspecies abscessus).

^cInitial phase refers to the time that the parenteral agents are being given. Continuation phase refers to the subsequent phase of therapy that typically includes oral antimicrobial agents sometimes paired with inhaled agents.

^dAzithromycin (clarithromycin) is active in this setting and should be used whenever possible.

^eAzithromycin (clarithromycin) activity is unlikely but can be added for its immunomodulatory effects but should not be counted as active against M. abscessus with a functional erm(41) gene. In this setting, frequent sputum cultures should be obtained to detect potentially new organisms like M. avium complex.