Which two classes of drugs have their absorption decreased by cations?

Tetracyclines and fluoroquinolones have their absorption significantly affected by the presence of cations, such as calcium, magnesium, iron, and aluminum. This is primarily due to the formation of insoluble complexes. When these drugs are taken with cation-containing substances, such as dairy products, certain antacids, or supplements, the cations bind to the drug molecules, preventing adequate absorption in the gastrointestinal tract.

Both tetracyclines and fluoroquinolones are known to have this interaction, leading to reduced efficacy as the concentration of the active drug in the bloodstream can be significantly lowered. This can result in treatment failure for infections, thereby highlighting the importance of timing when administering these medications relative to cation-containing products.

In contrast, the other classes listed—beta-lactams, glycopeptides, aminoglycosides, penicillins, and cephalosporins—do not exhibit the same level of absorption interference from cations. Therefore, tetracyclines and fluoroquinolones are the correct answer as they are the most affected by cation presence during absorption.