Because tetracyclines have been shown to depress plasma prothrombin activity, patients who are on anticoagulant
therapy may require downward adjustment of their anticoagulant dosage.
Since bacteriostatic drugs may interfere with the bactericidal action of penicillin, it is advisable to avoid
giving tetracyclines in conjunction with penicillin.
Absorption of tetracyclines is impaired by antacids containing aluminum, calcium, or magnesium, and
Absorption of tetracycline is impaired by bismuth subsalicylate.
Barbiturates, carbamazepine, and phenytoin decrease the half-life of doxycycline.
The concurrent use of tetracycline and Penthrane (methoxyflurane) has been reported to result in fatal renal
Concurrent use of tetracycline may render oral contraceptives less effective.
Drug/Laboratory Test Interactions
False elevations of urinary catecholamine levels may occur due to interference with the fluorescence test.