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Tricuspid endocarditis due to Pseudomonas cepacia in a heroin addict persisted despite intensive antibiotic therapy as well as replacement of the infected valve on four occasions. The isolated organism and 10 other strains of Pseudomonas cepacia were resistant to all antibiotics except chloramphenicol and trimethoprim (TMP), to which moderate sensitivity was demonstrated. Addition of TMP or both TMP and sulfonamide to polymyxin B produced sensitivity to low concentrations of the latter drug in vitro. Treatment with polymyxin B and TMP (1,000 mg/day) yielded bactericidal activity in serum at a 1:4 dilution. The combination of polymyxin B, TMP, and sulfisoxazole is effective and bactericidal against Pseudomonas cepacia in vitro and deserves further clinical trial in the treatment of serious infection due to this organism.
Rahal et al. (1973) studied this question.