Antibiotic pill. Pill of the broad-spectrum anti- biotic drug oxytetracycline on its blister pack. This is a tetracycline drug used to treat infections such as Lyme disease, chlamydia and acne. Tetracycline drugs are used as an alternative to penicillin in patients with a penicillin allergy. Many bacteria have become resistant to tetracyclines, however, and their use is declining.