Clinical pharmacology includes pharmacokinetics (what the body does to a drug as it moves through the body) and pharmacodynamics (what a drug does to the body as the drug is being absorbed, metabolized, and excreted). An adverse drug reaction is a broad term that is generally used to refer to unwanted effects of a drug.
Clinical Pharmacology Chapters (A-Z)
Adverse Drug Reactions
Adverse drug reaction (ADR, or adverse drug effect) is a broad term referring to unwanted, uncomfortable, or dangerous effects that a drug may have. ADRs can be considered a form of toxicity; however, toxicity is most commonly applied to effects of overingestion (accidental or intentional—see Poisoning) or to elevated blood levels or enhanced drug effects that occur during appropriate use (eg, when drug metabolism is temporarily inhibited by a disorder or another drug). Side effect is an imprecise term often used to refer to a drug’s unintended effects that occur within the therapeutic range. Because all drugs have the potential for ADRs, risk-benefit analysis (analyzing the likelihood of benefit vs risk of ADRs) is necessary whenever a drug is prescribed.
Concepts in Pharmacotherapy
Drugs are selected based on characteristics of the drug (eg, efficacy, safety profile, route of administration, route of elimination, dosing frequency, cost) and of the patient (eg, age, sex, other medical problems, likelihood of pregnancy, ethnicity, other genetic determinants). Risks and benefits of the drug are also assessed; every drug poses some risk.
Factors Affecting Response to Drugs
Response to a drug depends partly on the patient’s characteristics and behaviors (eg, consumption of foods or supplements; adherence to a dosing regimen; differences in metabolism due to age, sex, race, genetic polymorphisms, or hepatic or renal insufficiency), coexistence of other disorders, and use of other drugs. Drug errors (see Drug Errors), including prescribing an inappropriate drug, misreading a prescription, or administering a drug incorrectly, also can affect response.
Pharmacodynamics, sometimes described as what a drug does to the body, involves receptor binding (including receptor sensitivity), postreceptor effects, and chemical interactions. Pharmacodynamics, with pharmacokinetics (what the body does to a drug—see Pharmacokinetics), helps explain the relationship between the dose and response, ie, the drug's effects. The pharmacologic response depends on the drug binding to its target. The concentration of the drug at the receptor site influences the drug’s effect.
Pharmacokinetics, sometimes described as what the body does to a drug, refers to the movement of drug into, through, and out of the body—the time course of its absorption (see Drug Absorption), bioavailability (see Drug Bioavailability), distribution (see Drug Distribution to Tissues), metabolism (see Drug Metabolism), and excretion (see Drug Excretion). Pharmacodynamics (see Pharmacodynamics), described as what a drug does to the body, involves receptor binding, postreceptor effects, and chemical interactions. Drug pharmacokinetics determines the onset, duration, and intensity of a drug’s effect. Formulas relating these processes summarize the pharmacokinetic behavior of most drugs (see Formulas Defining Basic Pharmacokinetic Parameters).