A single case report describes elevated lithium blood concentration and lithium toxicity with concomitant tetracycline administration. Another report and clinical research study did not support the interaction. Elevated concentration of digoxin can occur in such patients, leading to digitalis toxicity, as manifested by salivation, visual disturbances and arrhythmias. Tetracycline or other broad spectrum antibiotics with warfarin or anisindione 4 Broad spectrum antibiotics are hypothesized to reduce the gut flora that normally synthesize vitamin K, a necessary cofactor for clotting. Since warfarin's and anisindione's anticoagulant mechanism involves an antagonism of vitamin K-dependent clotting factors, an increased risk of bleeding may occur.
Interaction appears significant only in patients with poor vitamin K intake.
These antibiotics decrease the metabolism of warfarin and anisindione and can significantly increase prothrombin times and increase the risk of serious bleeding in anticoagulated patients. Signs of this adverse interaction include hematuria, bruising and hematoma formation. Interactions involving antibiotics, JADA, vol. 130,236-251, Feb 1999, Copyright 1999 American Dental Association. These antimicrobial agents block the metabolism and thus increase blood levels of a number of drugs.