Abstract: Pharmaceutical delivery systems containing 7-dimethyl-6-deoxy-6-demethyltetracycline or a non-toxic acid addition salt thereof comprising mixtures of a minor proportion of slow-release blended polymer coated spherical granules adapted to release part of the minocycline in a medium having a pH of below 3.9 and the rest in the range of from about 4.0 to about 7.5 and a major proportion of coated or uncoated quick-release granules adapted to release minocycline in a medium having a pH of less than about 3.9 and oral dosage unit form capsules containing the above are provided. These systems and formulations provide enhanced therapeutic blood levels of minocycline for at least about 24 hours when administered to a subject only once-a-day, regardless of whether the patient is fed or fasted. Methods for the preparation of the systems and formulations are provided as well.