Course 22 Pathology and Pharmacology

L098-001 Pharmacology

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.

L098-002 Anatomy

provides an understanding of the structures within the body.

L098-003 Pathology

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

L098-004 Chemistry

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

L098-005 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.

L098-006 The study of pharmacology includes several major subdivisions:

• 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.

L098-007 Drugs and Their Sources

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.

L098-008 Today, drugs are made from five sources:

plants, minerals, animals, synthetic sources, and modern engineering (recombinant DNA technology).

L098-009 Plants

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.

L098-010 Minerals

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.

many drugs contain minerals Phillips' Milk of Magnesia contains magnesium, Tums contains calcium, and Clearasil contains sulfur.

Animals

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.

Synthetic Sources

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.

Recombinant DNA Technology

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 host cell to change the way the cell reproduces.

The newer forms of insulin have been produced by this technique.

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.

Absorption

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:

Mucosa of the mouth

Lungs

Stomach

Small intestines and rectum

Subcutaneous tissue

Blood vessels in muscle tissue

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

• 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.

• 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 in the stomach will slow the rate of absorption but will also usually help to decrease stomach irritation from medications.

• Medications that are easily absorbed in fats and lipids are more readily absorbed in the gastrointestinal tract. 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.

• 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.

• 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.

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

Distribution

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.

-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.

-The placental membrane barrier isn't as restrictive as the blood-brain barrier.

Metabolism

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 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.

Excretion or Elimination

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.

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

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.

-A desired effect happens when the expected response occurs from the drug administration.

-. A side effect occurs when a predictable but undesired response occurs.

-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.

-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/illness often has signs/symptoms that then become the reason, or indication, for ordering a medication.

Toxicology

toxicology is the study of poisons.

All drugs and chemicals have a level at which they become toxic.

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.

some terms related to toxicology:

• Antidote. A drug used to counteract the effect of an excessive drug toxicity level.

• Adverse effects. 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. Reactions that may occur after only one dose of a drug has been taken.

-Itching

-Rash

-Hives

-Difficulty breathing

-Wheezing

Swelling of eyes, lips, or tongue

• Contraindication. A condition in which the use of a specific medication should be avoided.

• Anaphylaxis. A severe life-threatening allergic reaction that occurs a short time after drug administration.

-Hives and reddened skin

-Rapid swelling of the mouth and throat

-Difficulty breathing

S-welling of the eyelids, lips, mouth, throat, hands, and feet due to an accumulation of fluid in the subcutaneous tissue (angioedema)

-Eventually, cyanosis, low blood pressure, shortness of breath, vascular collapse, arrhythmias, and cardiac arrest

Indications for and Uses of Medications

Indications are reasons to use a particular drug to meet a certain need. When a patient presents with specific signs and symptoms, these may become indications for treatment.

The following are traditional reasons for prescribing or using medications:

-To relieve symptoms (therapeutic medications)

-To pinpoint disease through diagnostic testing (diagnostic medications)

-To replace missing chemicals in the patient (replacement medications)

-To avoid deficiencies or reinforce body chemicals (supplemental medications)

-To prevent or lessen the severity of a disease (preventive or prophylactic medications)

-To reduce symptoms (palliative medications)

-To kill or remove the causative agent of a disease (curative or healing medications)

-To maintain health (maintenance medications)