Factors Affecting Drug Activity Chapter 11

Human Variability Differences in age, weight, genetics and gender as well as pregnancy are among the significant factors that influence the differences in responses to medication among different people. Drug distribution, metabolism, and excretion are quite different in the neonate and infant than in the adult because their organ systems are not fully developed.

Human Variability Children metabolize certain drugs more rapidly than adults. The elderly typically consume more drugs than other age groups. The elderly also experience more physiological change that significantly affects drug action. Genetic differences can cause different types & amounts of proteins to be produced in the body, causing a difference in drug action.

Adverse Drug Reactions Drugs generally produce a mixture of therapeutic (desired) and adverse (undesired) effects. Adverse drug reaction can be any symptom in any disease process & involve any organ. Almost any drug in any dose can produce an allergic or hypersensitive reaction in a patient. Anaphylactic shock (example: bee sting) is a potentially fatal hypersensitive reaction.

Adverse Drug Reactions Common GI tract adverse reactions include: Nausea Vomiting Constipation Diarrhea Teratogenicity is the ability of a substance to cause abnormal fetal development when given to pregnant women.

Adverse Drug Reactions Nephrotoxicity: the ability of a substance to cause harm to the kidneys. Carcinogenicity: the ability of a substance to cause cancer.

Drug-Drug Interactions The administration of more than one drug at a time to a patient can cause drug-drug interactions. Drug-drug interactions can affect the disposition of one or more drugs and result in the increase or decrease of therapeutic effects or adverse effects.

Drug-Drug Interactions (Terms) Additive effects: occur when two drugs with similar pharmacological actions result in an effect equal to the sum of the individual effects. Synergism: two drugs with similar pharmacological actions produce greater effects than the sum of the individual effects. Potentiation: when one drug with no inherent activity of its own increases the activity of another drug that produces an effect.

Drug-Drug Interactions (Terms) Antidote : blocks or reduces toxic effects of a drug. Displacement: a drug bound to a plasma protein is removed when another drug of greater binding potential binds to the same protein. Inhibition: a drug blocks the activity of metabolic enzymes in the liver. Induction: a drug that causes more metabolic enzymes to be produced, thus increasing metabolic activity.

Time Course of Drug Interactions The time it takes for drug-drug interactions to occur can vary substantially. Some interactions occur immediately, others may take weeks. Knowing the time-course of an interaction allows quick identification & treatment of potential interactions.

Drug-Diet Interactions Dietary intakes and pattern vary widely among individuals and can contribute to variability in the disposition of drugs. Some foods contain substances that react with certain drugs. Example: foods containing tyramine can react with MAO ( monoamine oxidase) inhibitors.

Disease States The disposition and effect of some drugs can be inhibited by the presence of diseases other than the one for which a drug is used. Hepatic, cardiovascular, renal and endocrine disease all increase the variability in drug response. Example: renal disease has been correlated with decreased renal excretion of many drugs.

Disease States Acute Viral Hepatitis: an inflammatory condition of the liver caused by viruses. The effects are less than cirrhosis, but long term exposure progresses into a chronic disease state. The chronic disease has the same characteristics as cirrhosis; which eventually causes fatal liver damage.

Disease States Hypothyroidism: a condition in which thyroid hormone secretions are below normal (under active thyroid). Hyperthyroidism: a condition in which thyroid hormone secretions are above normal (over active thyroid).