IV injections are given by infusion to avoid cardiovascular collapse. IV dose forms exist for minocycline, doxycycline, and the two that also have IM dose forms, oxytetracycline and tetracycline. The tetracyclines vary widely in their bioavailability and the effect that food has on it. Calcium, aluminum, and magnesium form insoluble chelates with tetracyclines to decrease bioavailability. Milk is high in calcium and all of these ions are high in antacids so these should be avoided.
Some laxatives have magnesium.
Because tetracyclines are irritants that produce stomach upset, patients should be cautioned not to use milk or antacids to counteract the distress. Owners of animals should be similarly cautioned. Distribution Doxycycline reaches therapeutic concentrations in the eye. Minocycline is also widely distributed, reaching high concentrations in saliva and tears. Both are used in treatment of genitourinary tract infections because they produce therapeutic concentrations in these tissues, including the prostate.