Calcidin Plus Ca: Other supplements or medicines containing Ca. Phenytoin or tetracyclines (eg, doxycycline, minocycline), fluoroquinolones, & levothyroxine. Do not take w/ high-fiber meal (eg, bran, whole grain, cereal or bread, fresh fruits). Do not smoke cigarettes or cigars & do not drink large amounts of alcohol or caffeine (>8 cups of coffee).