I was told it depends on how long you've been on them.
In my case it's a couple months.
Posted by TF (Member # 14183) on :
To research how long any drug stays in your system, look up its half life. "Half life" is how long it takes half of the dose to leave your body.
So, the half life for doxy is considered long--it is 15 to 26 hours. So, in that time, half of your dose is gone. Then, half of that half (or 3/4 of the dose) is gone in the next 15-26 hours, etc.
The half life for ceftin is 1-2 hours. The way you take the ceftin can affect when the dosage peaks in your system. By mouth, it peaks in 2 hours. IV, it peaks in 30 minutes.