Basics of Pharmacology: Medication Cycle, Side Effects, and Resources

Introduction to Pharmacology and Fundamentals

  • Pharmacology Definition: The exploration of substances used to heal and comfort the sick, and in other ways help humans live longer and healthier lives.

  • The Medication Cycle: This is defined as the process of how medication reaches the target site and what happens to the medicine during its journey through the body.

Key Pharmacological Terminology

  • Absorption: The process of medication moving from the site of administration into the bloodstream (Part of pharmacokinetics).

  • Adverse Reaction: A severe or dangerous side effect, such as hallucinations, hypotension, or anaphylactic shock.

  • Agonist: A medication taken with another medicine so that the two can be more effective than either would be alone; often associated with synergism.

  • Antagonist: A medication that makes another medicine less effective.

  • Bioavailability: The proportion of a drug or other substance which enters the circulation when introduced into the body and so is able to have an active effect.

  • Biotransformation (Metabolism): The process by which medication is gradually transformed to a less active or inactive form, known as a metabolite.

  • Distribution: The delivery of a medication to the site in need after it has been absorbed into the bloodstream.

  • Excretion: The process by which waste products of medication are removed from the body.

  • Half-life: The time required for the concentration of a drug in the body to reduce by one-half.

  • Idiosyncratic Reaction: A unique, rare, and unpredictable reaction to a medication.

  • Pharmacokinetics: The study of drug movement throughout the body, including absorption, distribution, metabolism, and excretion.

  • Receptors: Specific sites where medication can "unlock" a cell to activate an effect or prevent one.

  • Side Effects: Usually mild effects that allow a patient to continue taking medication, such as nausea or constipation.

  • Synergism: The interaction of drugs such that their combined effect is greater than the sum of their individual effects (often involving an agonist).

  • Teratogenic: Refers to substances that can cause birth defects or malformations in a developing fetus.

  • Toxic: Refers to poisonous or harmful effects, often resulting from high levels of medication in the blood.

The Four Steps of the Medication Cycle

1. Absorption (Pharmacokinetics)

  • Process: Medication moves from the administration site to the bloodstream.

  • Factors Affecting Speed and Effectiveness:

    • Route of Administration:

      • Topical: Influenced by the condition of the skin (e.g., presence of scars, tattoos, etc.).

      • Systemic: Includes oral, intravenous, and injection routes.

    • Solubility: The more soluble a medication is in fat or lipids, the easier it is absorbed through the stomach into the bloodstream.

    • pH and Concentration: The acidity/alkalinity and the strength of the dose affect absorption rates.

    • Length of Contact: How long the medication stays at the site of absorption.

    • Age: Physical development and organ function changes with age influence absorption.

    • Food: Presence of food in the stomach can speed up or slow down absorption.

    • Depth of Breathing: Affects the absorption of inhaled medications.

2. Distribution

  • Process: Delivery of medication to the specific site in need after it enters the bloodstream.

  • Barriers to Distribution:

    • Blood–brain barrier: Protects the central nervous system.

    • Blood–testicular barrier: Protects reproductive organs.

    • Blood–placental barrier: Regulates what substances reach a developing fetus.

3. Metabolism (Biotransformation)

  • Process: Medications are transformed into a less active or inactive form called a metabolite.

  • Primary Organs: The liver is the primary site for most medication metabolism. Other sites include the kidneys and intestines.

  • Prodrugs: These are medications administered in an inactive form; the resulting metabolite produced during metabolism is the desired treatment.

  • Specific Example (Insulin): Insulin is virtually useless if given by mouth because stomach acid breaks it down to an inactive form before it can be absorbed into the bloodstream.

4. Excretion

  • Process: Removal of waste products from the body to limit exposure to medication.

  • Primary Organs: The kidneys are the main organs of excretion.

  • Secondary Routes: Small amounts of medication are excreted through the lungs, bile, saliva, sweat glands, and breasts.

  • Cumulation: The build-up of medication in the body, which can lead to illness if not excreted properly.

Therapeutic Levels and Potency

  • Therapeutic Level: The point at which the medication has its maximum desired effect.

    • Too Low: The medication does not work effectively.

    • Too High: Results in toxic effects, such as:

      • Ototoxic: Toxic to the ears/hearing.

      • Nephrotoxic: Toxic to the kidneys.

  • Medication Potency: Refers to the strength of the medication.

    • Agonist: Enhances effectiveness (Synergism).

    • Antagonist: Decreases effectiveness.

Side Effects and Adverse Reactions

  • Side Effects: Usually mild; patients frequently continue medication. Examples include nausea, vomiting, and constipation. These can often be minimized by dietary or activity changes.

  • Adverse Reaction: A severe side effect. Examples include hallucinations, hypotension, and anaphylactic shock.

  • Comparison: Topical medications generally have fewer side effects than systemic medications.

  • Idiosyncratic Reactions: Unique and rare reactions specific to an individual.

System-Specific Side Effects

Central Nervous System (CNS)

  • Agitation

  • Hallucinations

  • Confusion

  • Delirium

  • Disorientation

  • Depression

  • Drowsiness and Sedation

  • Decreased respiration and circulation

  • Dizziness and Coma

Liver

  • High liver enzyme levels in the blood

  • Jaundice (yellowing of the skin/eyes)

Gastrointestinal (GI) System

  • Anorexia

  • Nausea and Vomiting

  • Constipation and Diarrhea

  • Ulcers and Colitis

Urinary (Genitourinary) System

  • Fluid and electrolyte imbalance

  • Abnormally high potassium levels

  • Increased Blood Urea Nitrogen (BUN) levels

Hematology System

  • Decreased White Blood Cells (WBCs)

  • Decreased Red Blood Cells (RBCs)

  • Decreased Platelets

Drug Information Resources

Comprehensive Resources

These cover medications in depth and are typically printed materials.

  • The United States Pharmacopoeia/National Formulary (USP/NF): The official source of medication information for drugs approved by the FDA.

  • The United States Pharmacopoeia/Dispensing Information (USP/DI):

    • Volume 1: Written for the prescriber.

    • Volume 2: Written in layperson terms for the patient.

  • Prescriber’s Digital Reference (PDR): Features detailed summaries including drug classes, boxed warnings, common brand names, dosages, indications, storage, contraindications, precautions, adverse reactions, interactions, and pharmacokinetics. It contains six specific sections:

    1. Manufacturer’s index.

    2. Brand and generic name index.

    3. Classification index.

    4. Product identification guide.

    5. Product information section.

    6. Catch-all section.

Clinically Based Resources

More "user-friendly" and often include terms patients can understand.

  • Drug Handbooks: Smaller print, includes administration, dosing, indications/contraindications, and patient education. Often includes digital/smartphone downloads.

  • Package Inserts: Provided by the manufacturer with the medication.

  • Pharmacists: A direct professional resource for medication information.

Questions & Discussion

Clicker Questions

  • Q: Solubility of medication affects absorption in what way?

    • A: The more soluble a medication is in fat or lipids, the easier it is absorbed through the stomach into the bloodstream.

  • Q: Which medication will be inactivated through metabolism if given orally?

    • A: Insulin. Stomach acid breaks it down before absorption.

  • Q: Electrolyte imbalances are a side effect of which system?

    • A: Genitourinary (Urinary system).

  • Q: Which of the following is an example of a comprehensive resource? (Handbooks, Inserts, PDR, Textbook)

    • A: A PDR (Prescriber's Digital Reference).

Critical Thinking Scenarios

  • Scenario (Inhaled Meds): How to help a patient who takes shallow breaths and cannot follow deep breathing directions to increase absorption?

    • Analysis: Shallow breathing reduces the depth to which the medication travels in the lungs, decreasing the surface area for absorption and bioavailability.

  • Scenario (Pregnancy): Why should a woman trying to conceive consult a physician before OTC meds?

    • Analysis: Many medications cross the blood-placental barrier and can be teratogenic (causing birth defects).

  • Scenario (Blood-Brain Barrier): Why do medications crossing the blood-brain barrier have strong negative effects?

    • Analysis: These medications affect the Central Nervous System directly, leading to severe side effects like coma or respiratory depression.

  • Scenario (Chronic Alcoholism): How does alcohol damage affect metabolism?

    • Analysis: Since the liver is the primary site of biotransformation, liver damage from alcohol impairs the body's ability to process drugs, potentially leading to toxic buildup.

  • Scenario (PDR): What are the advantages and disadvantages of comprehensive books like the PDR?

    • Analysis: Advantages include official, detailed, and exhaustive information; disadvantages include being bulky, technical, and potentially quickly outdated compared to digital versions.