How long after starting antibiotic is pink eye contagious?

10-14 days. Use of antibiotics does not shorten the contagious stage, the drops shorten the time you have to deal with goopy eyes.
It Depends. If the pink eye is caused by bacteria and the drops have effective antibiotics, then it is thought 24-48 hrs eliminates the contagion. Since the drops are ineffective for viral pink eye, as long as the eye is red, the infection is probably contagious.