Activity of minocycline and tetracycline against respiratory pathogens related to blood levels

Abstract

A study was made of minocycline as a potential agent for use in respiratory tract infections. Pharmacological studies in 6 volunteers confirmed that serum levels of minocycline in the range 2 to 4 i.μ/ml can be obtained using a standard loading dose of 200 μg. In a cross-over study with tetracycline, minocycline showed more uniform absorption. At clinically achievable levels minocycline was more active than tetracycline against both tetracycline-sensitive and -resistant strains of Haemophilus species and Streptococcus pneumoniae. Minocycline at 2 μ/ml inhibited 96% of the 90 strains of both species. With β-haemolytic streptococci, however, the MICs of minocycline for tetracycline-resistant strains always remained above attainable blood levels.