Which of the following antibiotics obtains higher gingival crevicular fluid levels than serum?

a. erythromycin
b. azithromcyin
c. tetracycline
d. clindamycin

c. Another property of tetracyclines is their ability to concentrate in the gingival crevicular fluid (GCF) at two to four times blood levels following multiple doses. Doxycycline and minocycline also concentrate in higher levels in the GCF than in serum.