doxycycline hu tetracycline semi sintetiku li jinkiseb minn oxytetracycline li jaġixxi fuq is sotto unità batterjali tar ribosom 30s f unjoni riversibbli billi jimblokka t twaħħil ta  aminoacyl trna (transference rna) mal kumpless mrna/ ribosom u jevita ż żieda ta  amino acids ġodda mal katina tal peptide li tkun qed tikber u għalhekk jinterferixxi fuq il proċess tas sintesi tal proteina