Which of the following medications should be taken on an empty stomach?

Tetracycline should be taken on an empty stomach because food can significantly affect its absorption in the gastrointestinal tract. Specifically, the presence of food, especially dairy products, can interfere with the drug's ability to be absorbed effectively. Consuming tetracycline with food or dairy can lead to decreased serum concentrations, which might result in suboptimal therapeutic effects and potentially increase the risk of antibiotic resistance.

In contrast, doxycycline, cephalexin, and amoxicillin with clavulanate can generally be taken without regard to meals, as their absorption is not significantly impacted by food. Understanding the specific administration requirements for each antibiotic helps ensure maximum effectiveness when treating infections.