12.17: Pharmacokinetics: Drug–Food and Drug–Viral Interactions

A drug interaction occurs when the concurrent use of another drug, food, or an external substance alters the pharmacological activity of a drug. This interaction can modify the action of the original drug, affecting its effectiveness and safety.

Drug–food interactions are significant as they impact drug absorption, metabolism, and excretion. For example, grapefruit juice is a well-known disruptor of drug metabolism. It inhibits the cytochrome P450 3A4 enzyme, crucial for the metabolism of many medications. This interaction can lead to increased drug levels and potential toxicity. A notorious case involved a 29-year-old man whose consumption of grapefruit juice, alongside terfenadine (an antihistamine), resulted in fatal cardiac toxicity. Another notable interaction involves the drug theophylline, which is used to treat respiratory diseases. Due to increased metabolism, high-protein diets and diets rich in charcoal-broiled foods can decrease theophylline clearance from the body, necessitating adjustments in dosing to maintain therapeutic levels.

Interactions between drugs and viruses, though less frequently discussed, can also profoundly affect drug efficacy and patient safety. An example is the use of aspirin in children with influenza B or varicella zoster viral infections, which can lead to Reye’s syndrome, a rare but serious condition causing liver and brain inflammation. This interaction is concerning because the exact mechanism through which aspirin and viruses interact remains poorly understood, yet the consequences can be severe.

Understanding drug interactions, particularly those involving food and viruses, is crucial for maximizing therapeutic efficacy and minimizing potential risks. These interactions highlight the need for careful management of medication regimens, particularly in settings where dietary habits and exposure to viruses can fluctuate significantly.

Drug interactions occur when a substance alters a drug's pharmacokinetics or pharmacodynamics, impacting its safety and efficacy.

Drug–food interactions affect drug pharmacokinetics. For example, grapefruit juice inhibits CYP3A4, a key metabolic enzyme. This can slow drug breakdown, leading to increased drug concentrations and a higher risk of toxicity.

Another example is the altered clearance of theophylline —a bronchodilator— when consumed with high-protein or charcoal-broiled foods.

Drug–viral interactions can also seriously impact drug efficacy and patient safety. However, the exact mechanism of such interactions is poorly understood.

For instance, aspirin use in children exposed to influenza B or varicella zoster infections can trigger Reye’s syndrome, leading to severe liver dysfunction and brain swelling.

Recognizing drug–food and drug–viral interactions is crucial for optimizing treatment outcomes and minimizing risks. Proper medication management is essential, particularly given the variation in dietary habits and viral infections across different patient populations.