1. Absorption and excretion of doxycycline
The blood concentration was de termined with 3 healthy adults orally given 200 mg of the antibiotic. Blood samples were drawn 1, 2, 4, 6, 8 and 12 hours after the administration and their drug concentrations were measured by diffusion tests in tubes. The average values of 3 individuals were 0. 85, 1. 28, 1. 19, 0. 99, 0. 85, and 0. 70 mcg/m1 at 1, 2, 4, 6, 8, and 12 hours, respectively. Eight andhalf per cent (mean value) of the amount administered was excreted in the urine. Moreover, detectable amounts of the antibiotic were also found in umbilical cord sera, genital excretion, and milk.
2. Antibacterial activity
MICs against 25 clinical isolates of coagulase (±) Staphylococcus aureus, 12 strains of E. coil, 11 strains of Klebsiella, Proteus and other gram (-) rods were determined by 2 fold dilution tests on heart infusion agar plates. The value for staphylococci was 0. 32 mcg/ml or less and distributed over the range between 0. 39 and 25 mcg/ml. The antibiotic was also active to 10 to 13 strains that were 330 CHEMOTHERAPY MAR. 1969 highly resistant to TC (100 mcg/m1 of MOTC or DMCT).
3. Therapeutic effects
The antibiotic was given to 36 cases with various infections including intrapelvic infection, gonorrhoea, and urinary tract infection and was effective in 28 cases among them (77. 8%).