Drug toxicity: Drug–Drug Interaction

The use of multiple drugs, over-the-counter medications, and supplements can cause drug interactions, compromising treatment efficacy and potentially causing toxicity.

Drugs can affect each other’s GI absorption. Famotidine increases gut pH, which can reduce the absorption of certain drugs like ketoconazole.

Drugs like aspirin and warfarin undergo plasma protein binding. Their overdose saturates plasma proteins, increasing free drug levels and the risk of toxicity.

Drugs can also alter each other’s metabolism through the hepatic cytochrome P450 system. For example, chronic ethanol intake induces CYP2E1, increasing the conversion of acetaminophen to toxic NAPQI, leading to liver damage.

Coadministration of drugs with different therapeutic actions can enhance efficacy or cause adverse effects.

For example, the sulfonylurea glipizide acts by increasing insulin secretion from the pancreas, and the biguanide metformin reduces hepatic glucose production. Together, they effectively regulate blood sugar levels in diabetes.

On the other hand, combining aspirin, an antiplatelet agent, and heparin, an anticoagulant, increases bleeding risk.