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, and other genetic determinants). Other drugs that the patient may be taking can also influence the physician's drug selection. Risks and benefits of the drug are also assessed; every drug poses some risk.
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 [see Pharmacokinetics in Older Adults], sex, race, genetic polymorphisms, or hepatic or renal insufficiency), coexistence of other disorders, and use of other drugs.
Drug errors (eg, prescribing an inappropriate drug, misreading a prescription, administering a drug incorrectly) can also affect response.
