INTRODUCTION TO PHARMACOLOGY CONCEPTS

Module 1 1.1: An Introduction to Pharmacology Concepts Pharmacology is the study or science of drugs. What is a drug? A drug is any chemical that affects the physiologic processes of a living organism. Commonly, the term drug refers to any medication that is used for diagnosing, curing, or treating disease. Drug Effects Drugs have many different effects on the body including the following: (1) therapeutic effects, (2) side effects, (3) adverse effects, and (4) toxic effects. Therapeutic effect is the desired drug effect to alleviate some condition or symptom. Side effects are the drug effect other than the therapeutic effect that are usually undesirable but not harmful. Adverse effect is a general term for undesirable and potentially harmful drug effects. Toxic effects are undesirable drug effects that implies the drug is poisoning the body and can be harmful or even lifethreatening. Clinically, it is important to recognize the difference between these different ways drugs can affect the body. A simple side effect could be something as harmless as mild nausea after taking a medication that can be managed by taking it with food. The drug therapy can continue without a problem. However, adverse effects need to be assessed to determine whether there is any risk of harm. Drug therapy is often a risk vs. benefit assessment. The patient’s provider should weigh the risk of taking the medication vs. the benefit. It often comes down to the severity of the disease being treated to decide the number of adverse events that will be tolerated. A good example of this is chemotherapy treatments for cancer. There are often adverse events associated with these treatment regimens, yet the treatment is continued because the benefit of treating the cancer is greater than the adverse events the patient experiences. However, there are certainly times when a treatment becomes too toxic, and the patient is unable to tolerate the regimen. This is often a large part of managing a cancer patient’s treatment, to assess how they are handling the adverse effects associated with the treatment regimen and determine whether it is becoming too toxic and needs to be suspended. Basic Concepts There are some basic concepts that are important to understand and that can be applied to any drug. Most important is the drug’s mechanism of action—how a drug produces its effects. This course will cover the accepted mechanism of action of known drugs. When a drug enters the body, it has a targeted site of action—the location within the body where a drug exerts its therapeutic effect, often a specific drug receptor. Generally, these sites of action or receptors are on the surface or inside a cell. Receptors are specific cellular structures that a drug binds to in order to produce a physiologic effect. When a drug binds to a receptor, it can act either as an agonist, works to activate a physiologic response or drug effect, or an antagonist, works to interfere with other drugs or substances from producing a drug-effect. The dose-dependent relationship is a basic principle of pharmacology which states that the response to any drug depends on the amount of drug given. This is referred to as the dose dependent relationship. A dose is the exact amount of drug that is given. As shown in Figure 1.1, the onset of action is the time from the drug administration to the first observable effect. The duration of action is the length of time that the drug continues to produce its effect. All drugs have a therapeutic range defined as when the drug concentration is above the minimum effective concentration and below the maximum tolerate concentration. INTRODUCTION TO PHARMACOLOGY CONCEPTS Figure 1.1 The change in plasma drug concentration over time. The Therapeutic range represented by the area between the Minimum tolerated concentration (MTC) and Minimum effective concentration (MEC). Cmax is the maximum concentration, and tmax is the time it takes to reach the maximum concentration. The time the drug is above the MEC is the duration of action. If the drug concentration goes above the MTC, it is considered the toxic range. Similarly, if the drug concentration is below the MEC, it is in the ineffective range. Nomenclature All drugs are chemicals, and many have long chemical names that define the chemical composition of the drug. In addition, they are given a shorter non-proprietary name or generic name. The generic name, also known as a nonproprietary name, is the name that we will use for assessments throughout the course. Drugs are marketed under a trade name, also called a brand name, by pharmaceutical companies under a patented proprietary name specific to that manufacturer. These names may be somewhat confusing because more often than not, one manufacturer will market a medication that leads to multiple trade names for the same pharmaceutical compound. For example, the common blood pressure medication, lisinopril, is marketed under both Prinivil and Zestril. Beyond this basic nomenclature system, it is important to know that drugs also fall into categories called drug classes. Drug classes represent a group of drugs that all work by a common general mechanism of action. They may have slight differences in their effect on the body in terms of effectiveness or side effect profile; however, generally drugs within the same drug class have many of the same characteristics. Dosage Forms and Routes of Administration Drugs are prepared in various forms for administration. The physical and chemical properties of the drug determine which form will be most effective. All drugs have the active ingredient, the drug itself, and inactive ingredients that help facilitate the administration and absorption of the drug. Common dosage forms are described in Table 1.1 below. Routes of administration are how the drug is introduced to the body. The two most common routes of administration are oral and parenteral. Oral administration is the route of drug administration by way of the mouth through swallowing. Parenteral administration is the route of drug administration that does not involve the GI tract. Although most commonly administered by injection, parenteral administration also technically includes routes such as inhalation and topical administrations because they bypass the GI tract. Oral administration is the safest and most convenient. However, since it must go through the GI tract the onset of action is delayed about 30-60 minutes compared to parenteral administration, which is fairly immediate. Many of the most common routes of administration are listed below in Table 1.2.