PTCB - Chapter 11 - Factors Affecting Drug Activitiy - Key Concepts

Human Variability
- Differences in age, weight, genetics, and genders are among the significant factors that influence the differences in medication responses among people.
- Drug distribution, metabolism, and excretion are quite different in the neonate and infant than in adults because their organ systems are not fully developed
- Children metabolize certain drugs more rapidly than adults
- The elderly typically consume more drugs and have a higher incidence of drug interactions than other age groups. They also experience more physiological changes that significantly affect drug action.
- Genetics can cause differences in the types and amounts of proteins produced in the body, which can result in different responses to the same drug at the same dose.

Disease States
- The disposition and effect of some drugs may be altered in one patient but not another by the presence of disease. Such changes are well documented in cardiovascular, hepatic, renal, and thyroid disease.

Adverse Drug Reactions
- Almost any drug, in almost any dose, can produce an allergic or hypersensitive reaction in a patient. Anaphylactic shock is a potentially fatal hypersensitivity reaction.
- Anorexia, nausea, vomiting, constipation, and diarrhea are among the most common adverse reactions to drugs in the GI tract.

Drug-Drug Interactions
- Many drug-drug interactions affect the disposition of one drug and result in either an increased or decreased effect.
- Decreased intestinal absorption of oral drugs occurs when drugs complex to produce nonabsorbable compounds.
- Displacement of one drug from protein binding sites by a second drug increases the effects of the displaced drug.
- Drugs that induce liver metabolism may also increase metabolism of other drugs that use the same metabolizing enzymes.
- Some drugs increase excretion by altering urinary pH and lessening renal reabsorption.
- Some drug-drug interactions do not alter a drug's disposition but interact at the site of action.
- Additive effect occur when two drugs with similar pharmacological actions result in an effect equal to the sum of the individual effects.
- Synergism occurs when two drugs with similar pharmacological actions produce greater effects than the sum of the individual effects.
- Potentiation occurs when one drug with no inherent activity of its own increases the activity of another drug that produces an effect.

Drug-Diet Interactions
- Dietary intake can influence drug action by altering one or all of the ADME processes.
- Some foods contain substances that react with certain drugs, e.g., foods containing tyramine can react with monoamine oxidase (MAO) inhibitors.