Table of Contents
Definition of Drug Interaction
Drug Interaction is an effect or action that occurs in the body as a consequence of taking two or more drugs that does not occur when taking any one of the drugs alone.
Most DRUG interactions are inadvertent, occurring when a person takes an OTC medication with prescription medications, for example, or when a doctor prescribes a new medication without knowing all of the other medications a person is taking.
The latter circumstance becomes a particular challenge when a person must receive urgent care in a clinic, hospital emergency department, or other setting in which the provider is someone other than the person’s regular health-care provider.
Drug Interaction Effects
Some drug interactions are neutral or even beneficial, such as when one medication potentiates (increases or enhances) or mitigates the action of another in a known and predictable way for a therapeutic effect. Such effect occurs, for example, with the combination of codeine (a narcotic pain reliever) and promethazine (Phenergan), an antiemetic medication (reduces NAUSEA). Though an effective pain reliever, codeine tends to cause nausea, but promethazine offsets this effect.
And though promethazine alone has no analgesic (pain-relieving) effects it does potentiate, or intensify, the actions of codeine on the CENTRAL NERVOUS SYSTEM as well as mitigate its tendency to cause nausea. Other drug interactions can lessen or intensify the effects of one or more of the involved drugs in ways that are detrimental, either by causing adverse actions in the body or preventing the therapeutic effects of one or any of the drugs. Certain ANTIBIOTIC MEDICATIONS, for example, diminish the effectiveness of oral contraceptives (birth control pills).
It is important for every doctor, dentist, or other health-care provider who prescribes a drug for an individual to know all of the drugs, prescription and overthe counter products (including herbal remedies and natural products) that the person is taking.
Key Role of Cytochrome P450 Enzymes
Most drug interactions occur as the result of a family of enzymes responsible for drug metabolism. These enzymes, called CYTOCHROME P450 (CYP450) ENZYMES, are abundant in the SMALL INTESTINE and the LIVER. CYP450 enzymes in the small intestine initiate the process of metabolism to allow molecules of the drug’s active ingredient to pass into the blood circulation. The blood carries the molecules to the liver, where the CYP450 enzymes there complete metabolism.
There are numerous subtypes of CYP450 enzymes, each responsible for specific metabolic activity for certain drugs. Some drugs work by inducing and others by inhibiting particular CYP450 enzyme subtypes, which in turn affects the metabolism of other drugs.
Other drug interactions may occur when the chemicals the drugs contain interact in some fashion. Iron and calcium in foods, vitamin supplements, and ANTACIDS bind with some antibiotics in the STOMACH, for example, preventing the antibiotic from becoming absorbed and entering the blood circulation.
The potential for drug interaction is extensive. The more medications a person takes, the higher the risk for drug interaction.
A useful safeguard is to ask the pharmacist when picking up a prescription what other drugs and foods might interact with it. Even when foods do not directly interact with drugs, they may affect the drug’s absorption into the body.