Pharmacology Basics

Introduction

Pharmacology is the study of drugs and their interactions on living systems. Different academic areas, such as chemistry, anatomy, pathology, and psychology comprise our understanding of pharmacology. Allied health professionals in a variety of career paths need to understand the basics of pharmacology, as they will inevitably encounter the use of drugs and medications in their work with patients.

 

Studying Drugs

Allied health professionals like medical coders, transcriptionists, and front-office employees need to have a basic understanding of pharmacology. So let's start by defining it. Pharmacology is the study of drugs and their interactions on living systems. Pharmacology draws on knowledge from many other areas of science, like anatomy and physiology, pathology, chemistry, and psychology, to name a few.

Anatomy provides an understanding of the structures within the body. 

Pathology contributes an understanding of what happens when body structures aren't functioning normally due to disease or injury.

Chemistry contributes significantly to understanding the chemical composition of medications and how they interact with the body.

Psychology is important because it's related to how patients perceive their health status and understand the health education being provided. Psychology also plays an important role in understanding and encouraging medication compliance.

 

In addition to these terms, you should be familiar with the difference between a pharmacist and a pharmacologist. A pharmacist is a person who dispenses drugs at a pharmacy. A pharmacologist is a scientist who studies all aspects of drugs including their origins, functions, chemistry, effects, and uses.

Major Subdivisions of Pharmacology  

• Medicinal chemistry is the study of new-drug synthesis.
• Pharmacodynamics is the study of drug action and effects on the body.
• Pharmacokinetics is the study of the movement of drugs in the body.
• Molecular pharmacology is the study of the interaction of drugs with molecules such as DNA, RNA, and enzymes.
• Pharmacotherapeutics is the treatment of disease with therapeutic medications.
• Toxicology is the study of poisons. 

 

Sources of Drugs

Drugs are substances that change physiological processes in the body. These changes can be therapeutic (helpful) or toxic (harmful). The substances that are used to make the drugs may be derived from plants, animals, or minerals, or they may be synthesized from chemicals in a laboratory. People have been creating and writing down recipes for medicinal treatments since as early as 2000 BCE. The medicinal qualities of opium, alcohol, and many other substances have been long known. Today, drugs are made from five sources: plants, minerals, animals, synthetic sources, and modern engineering (recombinant DNA technology).

Plants have always provided effective folk remedies. Berries, seeds, sap, stems, bark, leaves, oils, and roots were used in these remedies. Today, plants are still important sources of drugs. An example of medication derived from a plant source is digoxin, which is a medication used to treat certain heart conditions.

 

Minerals are naturally occurring substances. They usually come from the ground. Many minerals are also present in the human body and must, in fact, occur in sufficient amounts for the body to function properly. Salt, iron, and potassium are just a few examples. Also, many drugs contain minerals—for example, Philips' Milk of Magnesia contains magnesium, Tums contains calcium, and Clearasil contains sulfur.

Animals provide another natural source of drugs. Substances missing from a human body may be found in the body tissues of animals. Many drug substances are taken from animals that are slaughtered for food, particularly drugs used in hormone replacement therapy. The insulin used to treat diabetics may be derived from the pancreas of cows or hogs, depending on the formulation.

 

The advances of science since the nineteenth century made it possible to manufacture, or synthesize, drugs from chemicals in a laboratory. Synthetic drugs duplicate the desired properties of natural substances. However, they don't have the inconsistency or unpredictable side effects of other drugs, because chemists can control their purity and potency. One of the most common synthetic drugs is aspirin. 

Recombinant DNA technology is one of the fastest-growing areas in pharmacological studies. This technology uses artificially manipulated DNA segments from different organic sources by transferring a cell from a different species to a different host cell to change the way the cell reproduces. Basically, the cell becomes a protein factory that creates genetic instructions, leading the organism to produce chemical substances for use as drugs. The newer forms of insulin have been produced by this technique. Also, some skin grafts can be produced with this technology. Medications produced by recombinant DNA technology are often referred to as biologics.

 

Pharmacokinetics

Pharmacokinetics refers to the movement of drugs through the body. There are four processes involved in pharmacokinetics:

1. Absorption refers to the movement of a drug from its site of administration into the blood.
2. Distribution is the movement of a drug from the blood into the tissues and cells.
3. Metabolism involves physical and chemical alteration of the drug in the body.
4. Excretion (elimination) refers to the removal of waste products of drug metabolism from the body.

 

The rate of absorption of a drug is related to the route of administration and the drug's ability to dissolve (solubility). Some medications dissolve rapidly and others dissolve slowly.

The primary sites of absorption are as follows:

1. Mucosa of the mouth
2. Lungs
3. Stomach
4. Small intestine and rectum
5. Subcutaneous tissue
6. Blood vessels in muscle tissue

 

There are several factors that can influence the rate of absorption.

Administration 

Incorrect administration of a drug influences the rate of absorption. The medication could be destroyed before it reaches the site of action. For correct absorption, medication must be administered according to the package insert instructions.

Drug PH

The pH of a drug also influences how it's absorbed. An acidic medication like aspirin is more readily absorbed in the stomach compared to an alkaline antacid, which is more readily absorbed in the small intestine. 

Food

Food in the stomach will slow the rate of absorption but will also usually help to decrease stomach irritation from medications. On the other hand, an empty stomach will increase the rate of absorption but increase the stomach irritation that can be caused by medications.

A high concentration of medication tends to be absorbed more rapidly.

Location

Medications that are easily absorbed in fats and lipids are more readily absorbed in the gastrointestinal tract. Medications that have an alcohol base are more easily absorbed in lipids. Medications with low lipid solubility are better absorbed when given in routes other than oral.

Topical

The absorption of topical drugs is influenced by the length of contact with the skin, the size of the area to which the medication is applied, skin thickness, and how well hydrated the skin tissue is at the application site.

Inhalation

When medication is administered through the inhalation route, the depth of respiration, patient's level of hydration, blood supply to the lungs, amount of medication administered, and surface area in the lungs will all influence the rate of absorption.

 

The fat solubility and the protein-binding ability of a drug influences its distribution. The amount of drug circulating in the bloodstream is the drug blood level. Fat-soluble drugs can be stored in the fatty tissues and provide a relatively stable reserve of the drug. Drugs like hormones in an oil base administered by injection tend to have a longer duration.

 

Some drugs can't pass through certain types of cell membranes. The blood-brain barrier protects the brain by restricting entry of water-soluble electrolytes. However, lipid-soluble drugs can pass into the brain and cerebrospinal fluid.

The placental membrane barrier isn't as restrictive as the blood-brain barrier. Water- and fat-soluble drugs can cross this barrier. Many medications given to a mother will also reach the fetus. Therefore, an expectant mother should take medications only as prescribed by the physician. 

 

Metabolism is a process of chemical reactions that change the drugs into water-soluble compounds for excretion. Without metabolism, the drug would continue to build up in a person's system, eventually causing toxic effects. The liver is the primary site for drug metabolism.

The rate of metabolism is an important issue when a physician is deciding drug dosages. The drug half-life is the time the body takes to metabolize half of the available drug. Patients who are elderly or have liver or renal impairment may not have adequate metabolism of the drug, and the physician may need to prescribe a lower dosage.

The rate at which a drug is excreted or eliminated depends on the chemical composition of the drug, the rate of metabolism, and the route of administration.

When people age, their metabolic and excretory functions naturally slow down. Because the elderly can't process and eliminate drugs at an ideal rate, they're at increased risk for overdose. Drugs tend to accumulate in the elderly; the cumulative effect is more likely to occur in debilitated patients or those with chronic medical conditions.

 

 

Pharmacodynamics and Pharmacotherapeutics

The term pharmacodynamics refers to the way in which a drug works, such as its mechanism of action in the body or the body's chemical reaction to the drug.

Drugs can change and modify the way the body acts, but drugs don't give body organs and tissues new functions. Drugs normally slow down or speed up ordinary cell functions. No drug has one single action. When a drug enters the body, a fairly predictable chemical reaction is expected. However, all individuals can react differently to the same drug, and many unpredictable drug reactions can occur. 

A desired effect happens when the expected response occurs from the drug administration. A side effect occurs when a predictable but undesired response occurs. For example, the desired effect of a narcotic analgesic is pain relief. A side effect is drowsiness.

The site of the drug action may be either local or systemic. A local action is limited to the site of administration and the area immediately surrounding the application site. Topical lotions and creams applied to an area are examples of local action. When the drug effect occurs throughout the body, not just at the site of administration, the result is considered systemic action.

*Pharmacotherapeutics refers to the effect of a drug in the treatment of disease. It's the combination of biologic, physical, and psychological changes that occur in the body. 

A physician may order medications as part of a treatment plan for a medical condition. This disease or illness often has signs or symptoms that then become the reason, or indication, for ordering a medication. 

 

Uses of Medication and Toxicology

As mentioned earlier, toxicology is the study of poisons. More specifically, it's the study of the adverse effects that chemicals (and drugs) can have on living organisms. All drugs and chemicals have a level at which they become toxic. When taken in excess, these drugs act as poisons.

The goal of pharmacology is to select medication in a dose that produces the desired effect with minimal side effects. This dosage is called the therapeutic dose. A toxic dose, on the other hand, is the smallest amount of a drug that would produce an adverse effect in a person.

 

The difference between the therapeutic dose and the toxic dose is referred to as the margin of safety.

Here are some terms related to toxicology:

Antidote is a drug used to counteract the effect of an excessive drug toxicity level.

Adverse effects are unintended and undesirable effects that result from a drug. Adverse effects are more severe than side effects. An allergic reaction is a type of adverse effect.

Allergic reactions may occur after only one dose of a drug that has been taken. These reactions occur either because the drug was taken many years before or because the person is allergic to a similar substance.

Anaphylaxis is a medical emergency that can occur with drug administration, insect stings, and some foods. It is a severe life-threatening allergic reaction that occurs a short time after drug administration. It has been noted most often after administration of antibiotics, especially from the penicillin family.

Signs and symptoms of an allergic reaction are: itching, rash, hives, difficulty breathing, wheezing, and swelling of eyes, lips, or tongue.

Signs and symptoms of anaphylaxis are: hives and reddened skin, rapid swelling of the mouth and throat, and difficulty breathing. Swelling of the eyelids, lips, mouth, throat, hands, and feet due to an accumulation of fluid in the subcutaneous tissue (angioedema). Eventually, a person will experience cyanosis, low blood pressure, shortness of breath, vascular collapse, arrhythmias, and cardiac arrest.

Contraindication is a condition in which the use of a specific medication should be avoided. For example, a previous allergic reaction to a drug is a contraindication for future use.

 

Key Points

• Pharmacology is the study of drugs and their interactions with living systems.
• A pharmacist is a person who dispenses drugs at a pharmacy. A pharmacologist is a scientist who studies all aspects of drugs.
• Drugs are substances that change physiological processes in the body, either therapeutic (helpful) or toxic (harmful).
• Drugs are made from five sources: plants, minerals, animals, synthetic sources, and modern engineering, such recombinant DNA technology.
• Pharmacokinetics refers to the movement of drugs through the body. There are four processes: absorption, distribution, metabolism, and excretion.
• The rate of absorption of a drug is related to the route of administration and the drug's solubility. The fat solubility and the protein-binding ability of a drug influences its distribution.
• The rate at which a drug is excreted depends on the chemical composition of the drug, the rate of metabolism, and the route of administration.
• Pharmacodynamics refers to the way in which a drug works, such as its mechanism of action in the body or the body's chemical reaction to the drug. Pharmacotherapeutics refers to the effect of a drug in the treatment of disease.
• Toxicology is the study of adverse effects that chemicals and drugs can have on living organisms.