Postantibiotic Effect of Amikacin and Rifapentine against Mycobacterium avium Complex

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Abstract
Postantibiotic effect (PAE) has received little attention in the therapy of chronic intracellular infections, such as those caused by mycobacteria. Amikacin is active therapeutically against Mycobacterium avium complex, even though serum levels exceed the MIC for only a few hours. To determine the PAE of amikacin and rifapentine for M. avium, bacteria were exposed to concentrations of 1×, 4×, and 10× the MIC of each drug for up to 120 min. Regrowth of M. avium was compared with similarly diluted untreated cultures. No PAE was observed on an inoculum of 104 bacteria when rifapentine was used at 5× MIC, although a slight inhibition of growth was obtained at 10× MIC for 2 h. For amikacin, PAE was observed up to 48 h at concentrations of 4× and 8× MIC and exposure times of 30–120 min. A PAE of 22 h was seen with 107 cfu of M. avium during incubation for 30 min with amikacin at 4× MIC. These results show that amikacin, unlike rifapentine, has a long PAE against M. avium.

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