Concentrations of doxycycline in human seminal plasma.

Single oral doses of 200 mg doxycycline was given to 16 healthy test subjects. The concentrations of the drug were measured in blood plasma and seminal plasma and related to the zinc content. Measurable concentrations of doxycycline were obtained in seminal plasma one to two hours after drug intake. The maximum level was reached after 4 to 6 hours and measurable concentrations were recorded in both blood plasma and seminal plasma after 24 hours. This means that measurable concentrations were maintained during almost the entire dose interval. In split ejaculate experiments it was shown that doxycycline is excreted mainly through the prostate gland. The mean concentration ratio for "prostatic fluid" vs. blood plasma in healthy volunteers was about 0.6. Indirect evidence is presented that the concentrations in the fluids from the accessory genital glands are higher if patients with prostatitis are given daily doses of 100 mg doxycycline.