Adverse effects and drug interactions

• Adverse effects are all unintended effects of drug therapy. All drugs have adverse effects. Adverse effects may be very mild and merely bothersome or serious and life threatening. • Adverse effects are usually predictable or dose related. Adverse effects that are not predictable or dose related are attributable to allergic responses or idiosyncratic responses. The most serious allergic response is called anaphylaxis, which can be fatal if not treated. • Adverse effects that carry the risk for permanent damage or death and form specifi c patterns or groups of symptoms related to drug therapy are called toxicities. The major drug toxicities are hepatotoxicity, nephrotoxicity, neurotoxicity, cardiotoxicity, ototoxicity, and immunotoxicity. • Drug interactions occur between two drugs or a drug and food or another substance, such as alcohol. Some drug interactions are benefi cial, whereas others are harmful. • Drug interactions may affect any aspect of pharmacokinetics: absorption, distribution, metabolism, or excretion. • An important and common drug interaction is one that alters the metabolism of a drug by either inducing or inhibiting the P-450 system. Drug-drug interactions usually alter the P-450 system in the liver, whereas interactions between drugs and grapefruit juice primarily alter the P-450 enzymes in the GI tract. • Drug interactions may also alter the pharmacodynamics of drug therapy. Two or more drugs may compete for the same receptor site, or they may work in different ways in the body with confl icting or cumulative results. Drugs that act in different ways, or at different receptors, may create an additive effect, a synergistic effect, a potentiated effect, or an antagonistic effect. • Nurses must understand the core drug knowledge of adverse effects and drug interactions because these phenomena interact with the core patient variables during drug therapy. Recognizing the potential for these interactions allows the nurse to plan care in a way that will maximize the therapeutic effects, minimize the adverse effects, and provide effective patient and family education.