Drug interaction refers to an altered drug response produced by the administration of a drug or coexposure of the drug with another substance, which modifies the patient’s response to the drug.
- Some drug interactions are intentional to improve therapeutic response. For example, probenecid increases the plasma drug concentration of penicillin by decreasing its renal excretion.
- Some drug interactions are intentionally used to decrease potential adverse drug reactions. For example, a combination of pentazocine and naloxone (Talwin NX) incorporates an opioid agonist to decrease pain and naloxone, an opioid antagonist to prevent drug abuse.
Drug interactions include the following:
- Drug–drug interactions
- Drug–herbal interactions
- Drug–food/alcohol interactions
- Drug–chemical interactions, such as the interaction of a drug with a compounding agent.
Drug interactions that occur in vivo are generally classified as pharmacokinetic or pharmacodynamic interactions.
- Pharmacokinetic or biopharmaceutical interactions occur when the absorption, distribution (protein and tissue binding), metabolism, or elimination of the drug is affected by another drug, chemical, or food element. Pharmacogenetic interactions occur when the pharmacokinetic disposition of the drug is altered by genetic polymorphisms in affecting processes. The changes in the concentration of the object drug changes the therapeutic effect of the drug.
- Pharmacodynamic interactions occur when the pharmacodynamic effect of the drug is altered by another drug, chemical, or food element, producing an antagonistic, synergistic, or additive effect.