Comprehensive Pharmacology and Contrast Administration for Radiologic Technologists

Overview and Scope of Pharmacology in Radiography

• Definition of Pharmacology: The study of drugs within living systems. This field encompasses the study of diagnostic effects, therapeutic effects, and adverse effects of drugs.
• Curriculum Alignment: The study of pharmacology for radiologic technologists directly aligns with the American Society of Radiologic Technologists (ASRT) curriculum and the American Registry of Radiologic Technologists (ARRT) content specifications for registry preparation.
• Relevance to Radiologic Technologists:     * Inherent Risks: Contrast agents, which are administered by radiographers, carry inherent risks that must be understood.     * Medication Exposure: Radiographers encounter various medications in clinical practice, including sedatives, emergency drugs, and intravenous (IV) medications.     * Legal Responsibility: The technologist bears a legal responsibility for the proper administration and rigorous documentation of all medications they handle.

The Three Categories of Drug Effects

• Diagnostic Effects:     * These effects are intended to enhance the physiological visualization of internal body structures.     * In the field of imaging, contrast agents serve as the primary examples of drugs used for diagnostic purposes.
• Therapeutic Effects: These effects are intended to treat, manage, or cure specific medical conditions.
• Adverse Effects:     * These are unintended and potentially harmful outcomes resulting from drug administration.     * Technologists must operate under the principle that every administered agent carries some level of risk.

Drug Nomenclature and Identification

• Chemical Name:     * This name describes the exact molecular and chemical structure of the drug.     * While essential in research and manufacturing settings, the chemical name is never found on clinical orders or medication charts.
• Generic Name:     * This is the official, non-proprietary name assigned by the FDA based on the active ingredient.     * It is not owned by any specific company or manufacturer.     * Example: Diazepam is the generic name for a common antianxiety medication.
• Trade Name (Brand Name):     * This is the name assigned to the drug by a specific manufacturer for marketing purposes.     * Example: Valium is the trade name for the generic drug diazepam.     * A single generic drug may have multiple trade names depending on the manufacturers involved.     * Common Examples: Tylenol is the trade name for acetaminophen; Advil and Motrin are trade names for ibuprofen.
• Clinical Practice Tip: Radiographers should always verify the generic name when encountering a trade name they do not recognize.

Drug Classification Methods

• Chemical Group Classification:     * Drugs are grouped based on their molecular or chemical structure.     * Examples: Benzodiazepines and iodinated compounds.     * Drugs with similar structures often share mechanisms and side-effect profiles.
• Mechanism or Site of Action Classification:     * Drugs are grouped based on how they act or where they act within the body.     * Examples: Central Nervous System (CNS) depressants and beta blockers.     * This classification helps predict intended effects and potential drug-drug interactions.
• Primary Effect Classification:     * This is the most common classification method encountered in the radiology department, grouping drugs by their main therapeutic outcome.     * Categories include: analgesics, anesthetics, antianxiety agents, antiarrhythmics, antibiotics, anticholinergics, anticoagulants, antiemetics, antihistamines, antihypertensives, bronchodilators, corticosteroids, diuretics, NSAIDs, opioid agonists, sedatives and hypnotics, thrombolytics, vasoconstrictors, vasodilators, and hormones.

Controlled Substance Schedules

• Schedule I ($C-I$):     * Characterized by the highest abuse potential.     * These substances are not accepted for medical use in the United States.     * Examples: Heroin, cocaine, and LSD.
• Schedule II ($C-II$):     * Highest abuse potential among drugs with an accepted medical use.     * Administration can lead to severe psychological and physical dependence.     * Examples: Morphine, fentanyl, and oxycodone.     * These are tightly controlled with very specific prescribing and storage protocols.
• Schedule III ($C-III$):     * Less abuse potential than drugs in schedules I and II.     * Associated with moderate to low physical or psychological dependence.     * Example: Acetaminophen with codeine.
• Schedule IV ($C-IV$):     * Lower abuse potential than schedule III.     * Associated with limited physical or psychological dependence.     * Relevant Imaging Examples: Benzodiazepines such as diazepam, midazolam, and lorazepam.
• Schedule V ($C-V$):     * The lowest abuse potential of all controlled categories.     * Very limited dependence risk.     * Example: Low-dose codeine cough syrups.

Pharmacokinetics: The ADME Process

• Absorption:     * Defines how a drug enters the bloodstream from its original site of administration.     * The Intravenous (IV) route provides immediate absorption.     * Oral and rectal routes generally provide slower absorption rates.
• Distribution:     * Defines how the drug moves through the body to reach target tissues.     * Iodinated contrast agents distribute through the vascular system.     * The distribution pattern determines which internal structures will be successfully visualized on the image.
• Metabolism:     * The process of chemical breakdown of the drug, which occurs primarily in the liver.     * Hepatic disease can significantly slow this process, leading to prolonged drug effects.     * Technologists must take a thorough patient history regarding liver conditions.
• Excretion:     * The process of removing the drug and its metabolites from the body, occurring primarily through the kidneys.     * This is a critical factor in contrast administration.     * Renal Health & Contrast: Patients with impaired renal function are at high risk for contrast-induced nephropathy.     * Assessment Values: Before IV contrast administration, technologists must assess renal function using Blood Urea Nitrogen ($BUN$), creatinine, and estimated Glomerular Filtration Rate ($eGFR$).     * Physician consultation is required if values are elevated or the $eGFR$ is reduced.

Pharmacodynamics and Pharmacogenetics

• Pharmacodynamics: This is defined as what the drug does to the body. It includes the mechanism of action, receptor binding, and the resulting physiological responses. Understanding this allows for the prediction of side effects, interactions, and contraindications.
• Pharmacogenetics: This is the study of how genetics affect an individual's response to drugs. Genetic variations can alter enzyme activity and receptor sensitivity. Consequently, patients may experience unexpected reactions to standard doses, or medications may fail to work as expected. This underscores the necessity of a thorough patient history.

The Six Rights of Drug Safety

• Right Medication: Verify the drug name against the physician's order. Distinguish between generic and trade names and look up any drug that is unfamiliar.
• Right Dose: Confirm the dose and the units before drawing the medication. Technologists must calculate the dose precisely; a decimal point error can lead to a tenfold ($10\times$) mistake.
• Right Time: Administer the drug at the exact time ordered. In CT, timing boluses are calculated based on delays relative to the body area being examined. For Intravenous Urograms ($IVU$), images are taken at specific intervals based on contrast movement through the urinary system.
• Right Route: Ensure the preparation matches the ordered route.     * Iodinated contrast varies; some are oral-only, while others are IV-compatible.     * Oral contrast must never be given intravenously.     * Barium sulfate can only be administered orally or rectally; it must never be administered intravenously.
• Right Documentation: Document immediately after administration. Include the drug name, dose, route, time, and the patient's response. In legal terms, if it was not documented, it did not happen.

Types of Contrast Agents in Imaging

• Barium Sulfate: A metallic salt used primarily for diagnostic imaging of the gastrointestinal (GI) tract.
• Ionic Organic Iodines:     * Characterized by higher osmolality and a higher rate of adverse reactions.     * Rarely used for IV administration today due to the increased risks.
• Nonionic Contrast:     * Characterized by lower osmolality and a lower reaction rate.     * The standard choice for contemporary IV administration.     * This reduces physiological stress on blood vessels and red blood cells.
• Gaseous Agents:     * Typically air or carbon dioxide ($CO_2$).     * Used in GI imaging (e.g., barium enemas) to provide "negative contrast."     * Air is pumped into the colon or induced in the stomach using crystals, which may cause the patient to feel a need to burp.

Management of Contrast Reactions

• Mild Reactions:     * Signs/Symptoms: Nausea, vomiting, warmth, flushing, hives, and itching.     * Actions: Stop contrast administration temporarily, monitor the patient, provide reassurance, notify the radiologist, and document the event.
• Moderate Reactions:     * Signs/Symptoms: Severe hives, bronchospasm, laryngospasm, tachycardia ($HR > 100 \text{ bpm}$), and hypotension.     * Actions: Stop contrast immediately, notify the radiologist, retrieve the crash cart/emergency medications, monitor vital signs, and prepare to assist the physician.
• Severe Reactions:     * Signs/Symptoms: Anaphylaxis, laryngeal edema, pulmonary edema, and cardiovascular collapse.     * Actions: Activate the emergency response system (code), administer epinephrine as directed by the radiologist, and prepare for potential intubation and life-saving measures.

Common Routes of Drug Administration in Radiology

• Oral: Absorbed through the GI tract; used for oral contrast and premedications.
• Intravenous (Parenteral): Injected into a vein; the primary route for iodinated contrast.
• Intra-arterial: Injected directly into an artery; used in angiography and interventional procedures (Cardiac Cath Lab or Interventional Radiology).
• Intrathecal: Injected into the subarachnoid space. This is used for myelograms in CT or MRI and must be administered by a radiologist under fluoroscopic guidance.
• Rectal: Used specifically for barium enemas to visualize the colon.