Nursing Pharmacology Chapter 1

Sources of Drugs

• Plant Products: Examples include Digoxin from Foxglove, Opium from Poppy, Atropine from Belladonna, Caffeine from Coffee, and Nicotine from Tobacco.
• Animal Products: Includes hormones like Premarin (conjugated Oestrogen), Insulin from pigs and cows, and Heparin from pigs and cows.
• Inorganic Compounds: Examples are Sodium Chloride, Zinc Sulfate, and Aluminium Hydroxide.
• Synthetic Sources: Genetically engineered products like Human Insulin (recombinant).

Drug Names

• Chemical Name: Long and complex, e.g., N-acetyl-para-aminophenol.
• Generic Name: Single lower-case name, less simple than the trade name, e.g., Paracetamol.
• Trade Name: Marketing name in upper case confirmed by the FDA, e.g., Tylenol.

Nursing Role in Pharmacology

• Anticipate patient responses to medications.
• Administer the correct drug by the right route, at the right time and dosage.
• Manage adverse drug effects and toxicities.
• Collect baseline data and identify high-risk patients.

Properties of an Ideal Drug

• Effectiveness: Must elicit the intended response.
• Safety: Should have minimal side effects and not cause addiction.
• Selectivity: Targets specific receptors with no adverse effects.
• Ease of Administration: Should require fewer doses and be straightforward to use.
• Cost-Effectiveness: Affordable, particularly for chronic conditions.
• Chemical Stability: Should remain effective during storage.
• Simple Generic Name: Easily remembered and pronounced.

Individual Variation Factors

• Variation in drug response due to age, gender, weight, liver and kidney function, and genetic variables.

Key Pharmacological Concepts

• Pharmacokinetics (ADME): Involves the study of the absorption, distribution, metabolism, and excretion of drugs.
• Pharmacodynamics: Focuses on the drug's mechanism of action and its effects on the body.
• Toxicology: Examines the adverse effects and toxicity of drugs.

Drug Development Process

• Preclinical Trials: Initial testing in vitro or on animals to assess safety and efficacy.
• Phase I Trials: Small group of healthy subjects to evaluate safety.
• Phase II Trials: Testing for effectiveness on patients with the target condition.
• Phase III Trials: Large-scale studies to gather more data on safety and efficacy across diverse populations.

Pharmacokinetics (ADME) Details

• Absorption: The process allowing drugs to enter the bloodstream.
• Distribution: The transfer of the drug from blood to interstitial and cellular spaces.
• Metabolism: Transformation of the drug into metabolites, primarily in the liver.
• Elimination: Removal of the drug and its metabolites from the body, mainly via urine.

Routes of Drug Administration

• Oral: Convenient but can face first-pass metabolism and absorption issues.
• Sublingual: Rapid absorption avoiding first-pass metabolism.
• Intravenous (IV): Immediate drug effect but higher infection risk.
• Intramuscular (IM) & Subcutaneous (SC): Varying absorption rates based on formulation.
• Inhalation: Quick entry into circulation via mucous membranes.
• Topical & Transdermal: Local effects and sustained release.

Factors Influencing Absorption

• pH and pKa: Uncharged drugs permeate membranes more easily; absorption depends on the drug's chemical properties.
• Blood Flow: Increased blood flow enhances absorption efficiency.
• Surface Area and Contact Time: More extensive absorptive surfaces (like intestines) increase the likelihood of drug uptake.

Distribution of Drugs

• Depends on factors like cardiac output, tissue volume, and protein binding in plasma and tissues.
• Volume of Distribution (Vd): Reflects how widely a drug disperses in body fluids. Higher Vd indicates more distribution in tissues.

Drug Elimination Dynamics

• Half-Life (t1/2): Time taken for plasma drug concentration to reduce by half; influences frequency and dosing.
• Clearance (CL): The speed at which drugs are eliminated from the body, can differ based on Vd.

Enzymatic Drug Metabolism

• Metabolism often occurs in two phases: Phase I (modifications like oxidation) and Phase II (conjugation). Phase I can involve cytochrome P450 enzymes.
• Potential for first-order (dependence on concentration) or zero-order kinetics (fixed rate regardless of concentration).

Adverse Reactions

• Can be predictable (common) or unpredictable (rare), including iatrogenic, carcinogenic, or teratogenic effects.### Drug Biotransformation
• Drug metabolism varies genetically among individuals, affecting biotransformation pathways.
• Inducers increase metabolism, lowering plasma concentrations and therapeutic effects if the metabolite is inactive.
• Inhibitors, particularly P450 inhibitors (e.g., grapefruit juice with CYP 3A4), can elevate drug levels, leading to enhanced therapeutic or toxic effects.

Conjugation Reactions

• Lipophilic Phase I metabolites undergo conjugation with endogenous substrates for easier excretion.
• Common substrates for conjugation include glucuronic acid, sulfuric acid, acetic acid, and amino acids.

Drug Excretion

• Kidney plays a crucial role in drug elimination, requiring drugs to be sufficiently polar.
• Three key processes of urinary drug elimination: glomerular filtration, proximal tubular secretion, and distal tubular reabsorption.
• Glomerular filtration rate averages 125 mL/min; lipid solubility and pH do not impact this rate.

Renal Excretion Mechanisms

• Anionic and cationic transport systems in renal tubules actively secrete drugs.
• Drug concentrations in nephric lumen can lead to diffusion back into circulation unless modified to increase polarity through liver metabolism.

Ion Trapping

• Weak acid excretion is enhanced by urine alkalinization (e.g., bicarbonate for phenobarbital overdose).
• Weak base excretion increases with urine acidification (e.g., NH4Cl for amphetamine overdose).

Routes of Drug Loss

• Elimination occurs through various means: liver metabolism, feces, lungs, and breast milk.
• Liver contributes to drug loss via metabolism or excretion into bile; renal failure patients may benefit from liver-excreted drugs.

Differences in Drug Metabolism Across Age Groups

• Infant metabolism: Immature gastric cells lead to higher gastric pH, affecting absorption; limited first-pass elimination due to low liver enzyme levels; greater total body water but less fat and protein binding.
• Elderly metabolism: Reduced gastric pH, slower GI transit, decreased liver enzyme production affects drug clearance and necessitates dosage adjustments.

Pharmacology Concepts

• Pharmacodynamics focuses on drugs' biological effects and mechanisms of action.
• Drug actions: physical (adsorption) or chemical (neutralization); interactions with enzymes can be reversible or irreversible.
• Factors affecting drug action include age, body weight, gender, routes of administration, drug tolerance and hypersensitivity, and pharmacogenetics.

Drug Toxicity and Dosage

• Types of drug toxicity: predictable (type A) and unpredictable (type B) based on genetic predispositions.
• Terminology includes therapeutic dose, maximum tolerated dose, lethal dose, loading dose, and maintenance dose.
• Drug interactions can lead to augmented pharmacological effects or unexpected reactions, particularly in sensitive populations.

Summary of Key Pharmacokinetic Principles

• Ideal pharmacology encompasses understanding drug formulation, actions, and effects in biological systems.
• Bioavailability defines the proportion of the drug reaching systemic circulation intact.
• Sublingual administration avoids first-pass metabolism and can provide rapid effects.

Questions for Review

• What factors modify the pharmacokinetics of drugs in different age groups?
• How do routes of administration influence drug efficacy?
• What is the significance of drug receptors and mechanisms of action in pharmacodynamics?

Explore the fundamentals of nursing pharmacology in this introductory quiz. Focus on the sources of drugs, including plant products and their medical uses. Test your knowledge on essential pharmacological concepts and their applications in nursing.