Individual Variation in Drug Responses - Pharmacology I PDF

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Lecture notes on individual variation in drug responses from NURS280, pathophysiology and pharmacology I with Professor Nicholls. Received an A- in the class....

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Chapter 8: Individual Variation in Drug Responses - Individual Variation in Drug Responses ● Key factors that cause one patient to respond to drugs differently than another patient ● Important for nurses to know these factors to be better prepared to reduce individual variation in drug responses ● Body weight and composition ○ Body surface area vs. weight ● Age ○ Significant variability with age ○ Infants and older patients especially sensitive to drugs ■ Infants: Organ immaturity ■ Older patients: Organ degeneration ● Due to increased severity of illness, multiple pathologies, treatment with multiple drugs ● Pathophysiology ○ Kidney disease ■ Reduced excretion and increased toxicity ○ Liver disease ■ Reduced metabolism and increased toxicity ● Acid-base imbalance ■ pH changes that alter absorption, distribution, metabolism, and excretion of drugs ● Altered electrolyte status ■ Rare for electrolyte changes to have a significant impact on drug responses ● Decreased responsiveness to a drug as a result of repeated drug administration - Three Types of Drug Tolerance ● Pharmacodynamic tolerance ○ Associated with long-term administration of drugs such as morphine and heroin ● Metabolic tolerance ○ Results from accelerated drug metabolism ● Tachyphylaxis ○ Reduction in drug responsiveness brought on by repeated dosing over a short time ● Placebo Effect ○ Any response that a patient has to a placebo is based solely on his or her psychological reaction to the idea of taking a medication and not to any direct physiological or biochemical action of the placebo itself ○ Nurses need to present a positive but realistic assessment of the effects of therapy ○ Placebos are primarily used for the control groups in clinical trials

● Variability in Absorption ○ Bioavailability ■ Ability of the drug to reach the systemic circulation from its site of administration ■ Occurs primarily with oral preparations rather than with parenteral administration ■ Tablet disintegration time, enteric coatings, and sustained-release formulations affect this ○ Other causes of variable absorption ■ Changes in gastric pH, diarrhea, constipation, and food in the stomach ● Genetics and Pharmacogenomics ○ Pharmacogenomics: Study of how genes affect individual drug responses ○ Altered drug metabolism ■ May accelerate or delay the metabolism ■ Warfarin, succinylcholine, isoniazid, cytochrome P450 ● Variations ○ Gender ■ Alcohol is metabolized more slowly by women than by men ● Men can drink more beer than women and feel less effects ■ Certain opioid analgesics are much more effective in women than in men ■ Quinidine causes greater QT interval prolongation in women than in men ○ Race ■ Genetic variations ■ Psychosocial factors ○ Comorbidities ■ Increased likelihood of drug interactions ■ More illness you have causes more drugs taken which means increases drug reactions ○ Diet ■ Starvation can reduce protein binding of drugs ■ Monoamine oxidase inhibitors: Malignant hypertension triggered by foods that contain tyramine ○ Genetic variations ○ Psychosocial factors ■ Temperament ○ Failure to take medicine as prescribed ■ Drug adherence ■ Issues include manual dexterity, visual acuity, intellectual capacity, psychological state, attitude toward drugs, and ability to pay for medication ○ Drug interactions

■ One drug alters the effects of another...