Doxycycline MONOHYDRATE (Monodox) is better tolerated than doxycycline HYCLATE (Vibramycin).

There are two doxycycline oral solid dosage formulations on the market...doxycycline monohydrate (Monodox) and doxycycline hyclate (Vibramycin, Vibra-Tabs). Pharmacists often get prescriptions written for doxycycline with no specification of which formulation to dispense.

Both doxycyclines are equally effective. But some clinicians prefer the monohydrate salt because it dissolves slower in the stomach...potentially reducing GI effects.

But there is no proof that the monohydrate version is better tolerated...and it's more expensive.