Failure of azithromycin therapy in gonorrhea and discorrelation with laboratory test parameters.
BACKGROUND
Azithromycin is efficacious in the treatment of chlamydial genital tract infection but less so in gonorrhea. However, MICs of azithromycin for gonococci from previously reported azithromycin treatment failures were consistently below the 'susceptible' MIC level of 2 mg/L.


OBJECTIVE
To examine gonococci not eliminated with 1 g azithromycin therapy to establish treatment outcome/MIC correlates in gonorrhea.


METHODS
The MICs and phenotypes of gonococci isolated from five cases of treatment failure after 1 g azithromycin therapy were determined and compared with the MICs of a systematic sample of routine isolates.


RESULTS
Azithromycin MICs of gonococci from five cases of failed 1 g azithromycin treatment were 0.125 or 0.25 mg/L, well within the current 'susceptible' MIC range. None of the isolates were of the mtr phenotype. The MIC90 of a systematic sample of 219 gonococcal isolates was 0.25 mg/L.


CONCLUSIONS
The antibiotic MIC/treatment outcome correlates that are usually found in gonorrhea do not apply for azithromycin. Current MIC criteria do not accurately define susceptibility or resistance of gonococci to azithromycin and by themselves do not predict the likely outcome of therapy. Pharmacokinetic factors may decrease the predictive value of MIC data.
Tapsall
J W
JW
Department of Microbiology, The Prince of Wales Hospital, Randwick, Sydney, Australia.
Shultz
T R
TR
Limnios
E A
EA
Donovan
B
B
Lum
G
G
Mulhall
B P
BP
D000328:Adult; D000900:Anti-Bacterial Agents / Q000494:pharmacology / Q000627:therapeutic use*; D017963:Azithromycin / Q000494:pharmacology / Q000627:therapeutic use*; D005260:Female; D006069:Gonorrhea / Q000188:drug therapy*; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests / Q000379:methods; D008875:Middle Aged; D009344:Neisseria gonorrhoeae / Q000145:classification / Q000187:drug effects* / Q000302:isolation & purification; D010641:Phenotype; D012680:Sensitivity and Specificity; D017211:Treatment Failure
D000900:Anti-Bacterial Agents; D017963:Azithromycin