In-vitro bactericidal synergism of rifampicin and trimethoprim and implications for treatment of carriers of Haemophilus influenzae

Antibiotic resistance in Haemophilus influenzae: mechanisms, clinical importance and consequences for therapy

Invasive and non-invasive infections caused by Haemophilus influenzae are frequently diagnosed in children below the age of 5 years. The treatment of choice for these infections was ampicillin. However, since the early 1970s the increasing prevalence of resistance to ampicillin and other antibiotics has necessitated major changes in antibiotic therapy. This article summarizes some of the important clinical features of diseases caused by H. influenzae. The epidemiology, the problems with in vitro susceptibility testing and the mechanisms of resistance to major antibiotics are reviewed. The consequences of antibiotic resistance for the treatment of diseases caused by H. influenzae are discussed.

In vitro interactions between rifampin and ampicillin or chloramphenicol against Haemophilus influenzae

Twenty clinical isolates of Haemophilus influenzae type b were used to determine the in vitro interactions of rifampin with ampicillin or chloramphenicol. Potential interactions of the drugs were evaluated by calculating the fractional inhibitory concentration index and fractional bactericidal concentration index for each strain after treatments with the drugs alone and in combination. There was no evidence of synergy or antagonisms between ampicillin and rifampin or between chloramphenicol and rifampin. With ampicillin-susceptible H. influenzae type b strains, an additive effect was observed with seven strains, and an indifferent effect was observed with three strains. Similarly, with chloramphenicol-susceptible H. influenzae type b strains, an additive effect was observed with eight strains, and an indifferent effect was observed with two strains.

Trimethoprim and rifampin in combination for chemoprophylaxis of household contacts of patients with invasive infections due to Haemophilus influenzae type b

We compared the effectiveness of rifampin-trimethoprim in fixed combination (3.75:1) to rifampin alone in the eradication of Haemophilus influenzae type b carriage among contacts of patients with invasive infection caused by this organism. The study population was composed of 127 index patients and 620 contacts. Twenty-six percent of contacts were colonized. Rifampin-trimethoprim eradicated carriage in 77.6% of contacts (71.1% in contacts less than 5 years, 84.2% in contacts greater than or equal to 5 years) whereas rifampin eradicated carriage in 69.9% of contacts (56.4% in contacts less than 5 years, 81.8% in contacts greater than or equal to 5 years). A single isolate resistant to rifampin and rifampin-trimethoprim was encountered. The eradication rate achieved with this regimen of rifampin-trimethoprim was too low to recommend its routine use. However, a higher dose or longer course might merit clinical trial.