CHAPTER 1

Orientation to pharmacology

By now, you’ve been hitting the books for many years, and have probably asked yourself, “What’s the purpose of all this education?” In the past your question may have lacked a satisfying answer. Happily, now you have one: You’ve spent most of your life in school so you could study pharmacology!

There’s good reason why you haven’t approached pharmacology before now. Pharmacology is a science that draws on information from multiple disciplines, among them anatomy, physiology, chemistry, microbiology, and psychology. Consequently, before you could study pharmacology, you had to become familiar with these other sciences. Now that you’ve established the requisite knowledge base, you’re finally ready to learn about drugs.

Four basic terms

At this point, I’d like to define four basic terms: drug, pharmacology, clinical pharmacology, and therapeutics. As we consider these definitions, I will indicate the kinds of information that we will and will not discuss in this text.

Drug.

A drug is defined as any chemical that can affect living processes. By this definition, virtually all chemicals can be considered drugs, since, when exposure is sufficiently high, all chemicals will have some effect on life. Clearly, it is beyond the scope of this text to address all compounds that fit the definition of a drug. Accordingly, rather than discussing all drugs, we will focus primarily on drugs that have therapeutic applications.

Pharmacology.

Pharmacology can be defined as the study of drugs and their interactions with living systems. Given this definition, the science of pharmacology can claim a huge body of knowledge as its own. Under our definition, pharmacology encompasses the study of the physical and chemical properties of drugs as well as their biochemical and physiologic effects. In addition, pharmacology includes knowledge of the history, sources, and uses of drugs as well as knowledge of drug absorption, distribution, metabolism, and excretion. Because pharmacology encompasses such a broad spectrum of information, it would be inappropriate (not to mention impossible) to address the entire scope of pharmacology in this text. Consequently, we limit consideration to information that is clinically relevant.

Clinical pharmacology.

Clinical pharmacology is defined as the study of drugs in humans. This discipline includes the study of drugs in patients as well as in healthy volunteers (during new drug development). Because clinical pharmacology encompasses all aspects of the interaction between drugs and people, and since our primary interest is the use of drugs to treat patients, clinical pharmacology includes some information that is outside the scope of this text.

Therapeutics.

Therapeutics, also known as pharmacotherapeutics, is defined as the use of drugs to diagnose, prevent, or treat disease or to prevent pregnancy. Alternatively, therapeutics can be defined simply as the medical use of drugs.

In this text, therapeutics is our principal concern. Accordingly, much of our discussion focuses on the basic science that underlies the clinical use of drugs. This information is intended to help you understand how drugs produce their effects—both therapeutic and adverse; the reasons for giving a particular drug to a particular patient; and the rationale underlying selection of dosage, route, and schedule of administration. This information will also help you understand the strategies employed to promote beneficial drug effects and to minimize undesired effects. Armed with this knowledge, you will be well prepared to provide drug-related patient care and education. In addition, by making drugs less mysterious, this knowledge should make working with drugs more comfortable, and perhaps even more satisfying.

Properties of an ideal drug

If we were developing a new drug, we would want it to be the best drug possible. In order to approach perfection, our drug should have certain properties, such as effectiveness and safety. In the discussion below, we consider these two characteristics as well as others that an ideal drug might have. Please note, however, that the ideal medication exists in theory only: In reality, there’s no such thing as a perfect drug. The truth of this statement will become apparent as we consider the properties that an ideal drug should have.

The big three: effectiveness, safety, and selectivity

The three most important characteristics that any drug can have are effectiveness, safety, and selectivity.

Effectiveness.

An effective drug is one that elicits the responses for which it is given. Effectiveness is the most important property a drug can have. Regardless of its other virtues, if a drug is not effective—that is, if it doesn’t do anything useful—there is no justification for giving it. Current U.S. law requires that all new drugs be proved effective prior to release for marketing.

Safety.

A safe drug is defined as one that cannot produce harmful effects—even if administered in very high doses and for a very long time. There is no such thing as a safe drug. All drugs have the ability to cause injury, especially with high doses and prolonged use. The chances of producing adverse effects can be reduced by proper drug selection and proper dosing. However, the risk of adverse effects can never be eliminated. The following examples illustrate this point:

• Certain anticancer drugs (eg, cyclophosphamide, methotrexate), at usual therapeutic doses, always increase the risk of serious infection.

• Opioid analgesics (eg, morphine, meperidine), at high therapeutic doses, can cause potentially fatal respiratory depression.

• Aspirin and related drugs, when taken chronically in high therapeutic doses, can cause life-threatening gastric ulceration, perforation, and bleeding.

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