Untitled Quiz

Module 1: Pharmacokinetic Principles

• Pharmacokinetics is the study of how the body absorbs, distributes, metabolizes, and excretes drugs.
• It focuses on what the body does to the drug.

Pharmacology

• Pharmacology is the study of drugs and their interactions with living organisms.
• It includes pharmacokinetics (what the body does to the drug) and pharmacodynamics (how the drug works on the body).

Drug Administration

• The route of administration (ROA) significantly impacts how quickly and efficiently a drug acts.
• Routes of drug entry are broadly categorized as enteral and parenteral.

Enteral Routes

• Enteral routes place drugs directly in the gastrointestinal (GI) tract.
• Common enteral routes include oral and rectal administration.

Oral Administration

• Advantages: Convenient, self-administration, drug absorption along the entire length of the GI tract, and cost-effective compared to most parenteral routes.

• Disadvantages: Gastric acid/juices may destroy drugs, potential GI damage, inconsistent absorption rates, too slow for emergencies, unpleasant taste/unsuitable for unconscious patients.

• Factors influencing oral absorption: blood flow, surface area, and contact time. High intestinal blood flow and large surface area leads to better absorption than from the stomach. Food and diarrhea can decrease absorption.

Rectal Administration

• Advantages: Useful for unconscious patients, nausea, and vomiting. Easy to terminate exposure, and convenient in some cases.
• Disadvantages: Variable absorption rates.

Parenteral Routes

• Parenteral routes involve injecting drugs into the body.
• Examples of parenteral routes:
  • Intravascular (IV, IA): Direct injection into blood vessels. Provides 100% bioavailability, rapid onset, and allows for large dosages. But carries a higher risk of adverse effects like infection or vessel damage.
  • Intramuscular (IM): Injection into muscles, often ideal for depot (sustained release) preparations. Provides rapid absorption of aqueous solutions, or slower effects for depot preparations. However, pain at injection sites are common.
  • Subcutaneous: Injection beneath the skin. Enables slow, consistent absorption suitable for depot preparations, but may need to be adjusted if circulatory problems are present.
  • Inhalation: Absorption of drugs through the lungs. High blood flow, large surface area, and thin membranes allow for rapid onset, but the drug delivery systems needs to be optimized.
  • Topical: Application to skin or mucous membranes for local or systemic effects. Can treat specific areas for topical medication or to increase absorption for systemic medication.
  • Sublingual: Administered under the tongue allowing for rapid absorption by capillaries. This avoids a possible first pass effect. But requires careful selection for the needs of the patient.
  • Intraosseous (IO): Injection into bone marrow providing direct, non-collapsible access into the systemic venous system. Useful when IV access is not available or is needed quickly.

First-Pass Effect

• Hepatic metabolism of drugs occurs as they pass through the liver.
• The liver often inactivates drugs, making less drug available to the body.
• The greater the first-pass effect, the less drug will reach systemic circulation.

Drug Distribution

• Drugs are distributed throughout the body. factors affecting distribution include:
  • Lipid solubility (capillary permeability): Lipophilic (fat soluble) drugs pass through membranes easily.
  • Organ blood flow: High blood flow organs like liver, heart, and kidneys receive higher concentrations of drug.
  • Plasma protein binding: Bound drugs are not biologically active; free drugs are available to interact with tissues.
  • Depot storage: some drugs accumulate in tissues (e.g., fat) and are slowly released.
  • Molecular size: Larger molecules are more likely to remain in blood vessels (e.g., heparin).
  • Body fluid compartments

Volume of Distribution (Vd)

• A calculation indicating the apparent volume in which a drug is dissolved in the body.
• Assumes even distribution of drug.
• Doesn't correspond to a real volume. -Formula: Vd = Dose (mg) / Plasma Concentration (mg/mL)

Bioavailability

• The fraction of administered drug reaching systemic circulation unchanged.
• Affected by factors like first-pass effect, solubility, chemical instability, formulation.

Bioequivalence

• Drugs considered bioequivalent exhibit similar bioavailability and peak blood concentration times.

Therapeutic Equivalence

• Drugs deemed therapeutically equivalent have similar efficacy and safety profiles.

Drug Metabolism/Elimination

• The liver and kidney are the major sites of drug metabolism and elimination.
• Lipid-soluble drugs converted to more polar, excretable metabolites.
• Phase I reactions (oxidation, reduction, hydrolysis): Converts lipophilic molecules to more polar forms.
• Phase II reactions (conjugation): Add polar functional groups to make drugs more polar (and quickly excreted by the kidneys).
• Elimination routes: Urine, feces, sweat, exhaled air, mother's milk.
• Renal elimination (urine): involves filtration, secretion, and reabsorption, and impacted by urine pH and other conditions.
• Enterohepatic circulation: recirculation of drugs in bile to the intestines.