drugs
Drug Actions and Doses Calculations
Introduction to Drug Actions
Definition: Drug actions refer to the modifications in cellular function that result from the interaction of a drug with body cells.
Effects on Cells: Once a drug interacts with cells, it alters their function, which depends on the drug's ability to cross the cell membrane.
Limits on Drug Actions
Nature of Actions: Drugs do not create new cell functions but either speed up or slow down normal cellular processes.
Other Effects: Some drugs destroy specific cells (e.g., chemotherapy), while others replace substances that are deficient in particular cells.
How Drugs Alter Cell Function
Speeding Up Cell Processes: Drugs can enhance normal cellular activity, leading to an increased rate of processes.
Replacing Missing Substances: Some drugs restore normal functions by replacing substances lacking in cells (e.g., insulin for diabetics).
Slowing Down Cell Activities: Certain drugs can reduce the usual rate of cell activities, effectively dampening cellular processes.
Examples of Drug Actions
Stimulants: Caffeine increases neuronal activity.
Chemotherapy: Targets and eliminates cancer cells.
Replacement Drugs: Insulin assists in maintaining balance in diabetic patients.
Destruction of Specific Cells: Certain drugs specifically target and destroy cellular parts to restore normal function.
Pharmacokinetics
Overview: Describes the journey of drugs through the body — including absorption, distribution, metabolism, and excretion — which affects drug efficacy and duration of action.
**Key Steps:
Absorption: Transition of drugs from administration site into the bloodstream. Most drugs (except topical) must enter bloodstream to be effective.
Distribution: Involves transporting drugs from bloodstream to target tissues, influenced by factors such as age and body composition.
Metabolism: A series of chemical reactions converting drugs into inactive compounds, primarily occurring in the liver, but also lungs and kidneys.
Excretion: Removal of drugs from the body via kidneys, intestines, lungs, sweat, and milk glands in nursing mothers.
Absorption Explained
Definition of Absorption: The passage of drugs from their administration site into the bloodstream.
Importance of Absorption: The speed of absorption determines how quickly a drug exerts its actions, impacting drug effectiveness.
Factors Influencing Absorption: Rate of administration, solubility of the drug, and the conditions at the absorption site.
Routes of Drug Administration
Sublingual: Absorption under the tongue (e.g., nitroglycerin).
Buccal: Absorption in the cheek (e.g., methisterone).
Oral: Absorption in the stomach/intestines (e.g., ibuprofen).
Intramuscular: Absorption occurs in muscles (e.g., proprison).
Subcutaneous: Absorption beneath the skin (e.g., epinephrine, insulin).
Intravenous: Immediate absorption into the bloodstream (e.g., antibiotics, antineoplastics).
Distribution of Drugs in the Body
Definition of Distribution: The movement of a drug from the bloodstream to body tissues and the intended site of action.
Factors Affecting Distribution: Age, body water content, fat content, body mass, and presence of drug reservoirs.
Metabolism of Drugs
Definition of Metabolism: Chemical reactions that inactivate drugs, mainly within the liver.
Role of Enzymes: Enzymes are utilized to convert drugs into less active forms for detoxification.
Influencing Factors: Age and liver function can significantly affect metabolism rates.
Drug Excretion Mechanisms
Main Routes of Excretion: Primarily through kidneys and large intestines, also via lungs, sweat, and mammary glands.
Factors Affecting Excretion: The chemical nature of the drug, metabolism rate, administration frequency, and organ health.
Pharmacokinetics Summary Table
Absorption: Moves drugs into bloodstream, affected by route and solubility.
Distribution: Transports drug to tissues, influenced by age and mass.
Metabolism: Biochemical breakdown, primarily in liver.
Excretion: Removal of drug products, determined by organ health and frequency of administration.
Validity and Drug Responses
Influencing Personal Factors: Age, sex, body size, genetics, health conditions, and psychological state all impact drug responses.
Environmental Factors: Weather conditions and altitude can modify drug effects, impacting circulation and absorption.
Drug Administration Timing: The route of administration and dietary factors may necessitate dosage adjustments.
Key Factors Influencing Drug Response
Age: Vulnerability in infants and older adults requires adjusted doses due to varying metabolism rates.
Size: Body mass index impacts drug metabolism and action.
Sex: Women may exhibit heightened reactions to certain drugs due to body composition differences.
Genetics: Genetic variations affect individual metabolism and drug effects.
Pathological Conditions: Diseases, particularly of the liver and kidneys, can interfere with drug responses.
Psychological Factors: Mental state influences treatment outcomes, with positivity enhancing drug efficacy.
Pharmacodynamics: Drug Actions versus Effects
Drug Action
Definition: Refers to the chemical changes induced by drug-cell interactions, modifying existing cellular functions.
Examples: Speeding or slowing physiological processes in cells.
Drug Effect
Definition: The observable biological, physical, or psychological changes resulting from drug action.
Side Effects: Unintended reactions that span harmless to severe, which are considered when prescribing medications.
Local vs. Systemic Drug Effects
Local Effects: Limited to the area of entry (e.g., eye drops).
Systemic Effects: Affect the entire body via bloodstream and require comprehensive pharmacokinetic processes.
Adverse Drug Reactions
Definition: Unexpected or dangerous responses to a drug that can be mild to severe; regular monitoring is crucial.
Drug Allergies and Anaphylaxis
Drug Allergy Definition: Abnormal immune response triggered by antibodies against a drug.
Symptoms of Allergic Reactions: Range from mild (rash, itching) to severe (anaphylaxis). Emergency treatment is necessary for life-threatening reactions.
Drug Dependence and Abuse
Psychological Dependence: Characterized by cravings and behavioral changes due to psychological need.
Physical Dependence: The body’s physiological requirement for a substance, leading to withdrawal symptoms upon interruption.
Drug Misuse: Irresponsible use of drugs, including overuse, which can escalate to drug abuse if left unaddressed.
Drug Abuse: Involves chronic overconsumption resulting in psychological or physical dependence.
Dosage Calculations
Importance
Ensures patient safety and effectiveness of medications.
Basic Fractions
Express amounts as parts of a whole (numerator/denominator).
Can be simplified for ease of calculation.
Decimals and Calculations
Fractions frequently converted to decimals for dosage calculations, especially in metric system contexts.
Adding/Subtracting Fractions
Step: Ensure common denominators before proceeding with numerators.
Multiplying fractions: Multiply numerators and denominators.
Canceling: Reduce fractions when possible, particularly through common factors.
Decimal and Metric Relationships
Role of Decimals in Dosage: Metric units use decimal expressions for ease of calculation.
Metric System: Based on base units (meter, liter, gram) and prefixes indicating size or fraction (milli, kilo).
Overview of Measurement Systems
Apothecary System: Outdated, uses units like grains and minim; written in Roman numerals.
Metric System: Commonly used, based on the decimal system with Arabic numerals for clarity.
Household System: Familiar units for everyday use; includes common volumes and weights.
Temperature Conversions in Medicine
Fahrenheit to Celsius: Subtract 32 from Fahrenheit, then divide by 1.8.
Celsius to Fahrenheit: Multiply Celsius by 1.8, then add 32.
Guidelines for Calculations
Leading Zeros: Numbers less than one should have leading zero (e.g., 0.75 mg).
Clear Labeling: Answers must include appropriate units (e.g., 60 ml).
Rounding Rules: Weight rounded to tenths, medications to hundredths; specific rules apply based on numerical values.
Pediatric Dosage Calculations
Weight-Based Dosage: Calculate doses ordered in mg/kg or mg/lb based on child's weight.
Body Surface Area (BSA): Critical in oncology for precise dosing based on height and weight. Adjustments made for accuracy.