Bacterial Infection
"I have had Doxycycline 100mg for 7 days in two occasions, first for a gynecological infection and recently for sinusitis. In both cases, the drug had a very slow unset of action. The symptoms mostly disappeared on day 5 but the short treatment couldn&#039;t clear the infection. In the first occasion, I couldn&#039;t get it continued and got a bad recurring infection. This time I try a prolonged treatment.

I believe the reason is that doxycycline is a bacteriostatic agent and merely prevents bacteria from reproducing. The immune system itself should kill the bacteria. So, if your immune system is somehow weak it can&#039;t do the work in time. 

Anyway, doxycycline had a positive effect, even if it was prescribed empirically."