Introduction
Everyone responds to drugs differently. The way a person responds to a drug is affected by many factors, including genetic makeup, age, body size, the use of other drugs and dietary supplements (such as medicinal herbs (see Section 2, Chapter 19)), the consumption of food (including beverages), the presence of diseases (such as kidney or liver disease), and the development of tolerance and resistance. For example, a large person generally needs more of a drug than a smaller person needs for the same effect. Whether people take a drug as instructed (see Section 2, Chapter 16) also affects their response to it. These factors may affect what the body does to the drug (pharmacokinetics (see Section 2, Chapter 11)), what the drug does to the body (pharmacodynamics (see Section 2, Chapter 12)), or both.
 See the figure Many Factors Affect Drug Response.
Because so many factors affect drug response, doctors must choose a drug appropriate for an individual patient and must adjust the dose carefully. This process is more complex if the patient takes other drugs and has other diseases, because drug-drug and drug-disease interactions are possible.
A standard or average dose is determined for every new drug. But the concept of an average dose can be like "one size fits all" in clothing: It may fit a range of people well enough, but it may fit almost no one perfectly. For some drugs, the dose does not have to be adjusted, because the same dose works well in virtually everyone.
|
