Chapter 2: Key points Flashcards
What is pharmacodynamics?
Pharmacodynamics is the process by which a drug works within or affects the body.
How do drugs work?
Drugs may work by replacing a missing body chemical, by stimulating or depressing cellular activity, or by interfering with the functioning of foreign cells.
How are drugs thought to work by? (2)
Drugs are thought to work by reacting with specific receptor sites or by interfering with enzyme systems in the body.
Box 2.1: Focus on Safe Medication Administration
The liver is very important in metabolizing drugs in the body, and the kidneys are responsible for a large part of the excretion of drugs from the body. One should get into the habit of always checking a patient’s liver and renal function before a patient starts a drug regimen. If the liver is not functioning properly, the drug may not be metabolized correctly and may reach toxic levels in the body. If the kidneys are not functioning properly, the drug may not be excreted properly and could accumulate in the body. Dose adjustment needs to be considered if a patient has problems with either the liver or the kidneys.
What is pharmacokinetics?
Pharmacokinetics is the study of how medication travels through the body.
How is the concentration of a drug in the body determined?
The concentration of a drug in the body is determined by the balance of absorption, distribution, metabolism (biotransformation), and excretion of the drug.
When should the pharmacokinetics of a drug be considered?
In determining the amount, route, and appropriate timing of a drug dose, the pharmacokinetics of that drug must be considered.
Box 2.3: Factors Affecting the Body’s Response to a drug
Weight
Age
Sex
Physiological factors—diurnal rhythm, electrolyte balance, acid–base balance, hydration
Pathological factors—disease, hepatic dysfunction, renal dysfunction, gastrointestinal dysfunction, malnutrition, vascular disorders, low blood pressure
Genetic factors
Immunological factors—allergy
Psychological factors—placebo effect, health beliefs, compliance
Environmental factors—temperature, light, noise
Drug tolerance
Accumulation effects
Interactions
Box 2.4 Focus on Calculations - Pediatric Doses
Children often require different doses of drugs than adults because children’s bodies often handle drugs very differently from adults’ bodies. The medications that are approved by the FDA will have both adult and pediatric doses or dose ranges listed. Some of the medications will be dosed by age, body weight, or body surface area.
Concept Mastery Alert: Adverse Effects of Medication
When taken in excess, drugs may have adverse effects that are extensions of the primary actions, such as an antihypertensive medication causing low blood pressure. Secondary actions of the drug are those adverse effects that are additional to, not in correlation with, the desired effects.
Box 2.5 Focus on Safe Medication Administration
Always check the monograph of any drug that is being given to monitor for clinically important drug–drug, drug–alternative therapy, or drug–food interactions.
Summary- Pharmacodynamics is the
Pharmacodynamics is the study of the way that drugs affect the body.
Summary- How do most drugs work by?
Most drugs work by replacing natural chemicals, by stimulating normal cell activity, or by depressing normal cell activity.
Summary- How do chemotherapeutic agents work by?
Chemotherapeutic agents work by interfering with normal cell functioning, causing cell death. The most desirable chemotherapeutic agents are those with selective toxicity to foreign cells and foreign cell activities.
Summary- Where do drugs frequently act at and why?
Drugs frequently act at specific receptor sites on cell membranes to stimulate enzyme systems within the cell and to alter the cell’s activities.
Summary- Pharmacokinetics-
the study of the way the body deals with drugs—includes absorption, distribution, biotransformation, and excretion of drugs.
Summary- What is the goal of establishing dosing schedules?
The goal of established dosing schedules is to achieve a critical concentration of the drug in the body. This critical concentration is the amount of the drug necessary to achieve the drug’s therapeutic effects.
Summary- What does arriving at a critical concentration involve?
Arriving at a critical concentration involves a dynamic equilibrium among the processes of drug absorption, distribution, metabolism or biotransformation, and excretion.
Summary- What does absorption involve?
Absorption involves moving a drug into the body for circulation. Oral drugs are absorbed from the small intestine, undergo many changes, and are affected by many things in the process. IV drugs are injected directly into the circulation and do not need additional absorption.
Summary- Where are drugs distributed to?
Drugs are distributed to various tissues throughout the body depending on their solubility and ionization. Most drugs are bound to plasma proteins for transport to reactive tissues.
Summary- Drug metabolism
Drugs are metabolized or biotransformed into less toxic chemicals by various enzyme systems in the body. The liver is the primary site of drug metabolism or biotransformation. The liver uses the cytochrome P-450 enzyme system to alter the drug and start its biotransformation.
Summary- What is the first-pass effect?
The first-pass effect is the breakdown of oral drugs in the liver immediately after absorption. Drugs given by other routes often reach reactive tissues before passing through the liver for biotransformation.
Summary- drug excretion
Drug excretion is removal of the drug from the body. This occurs mainly through the kidneys.
Summary: What is the half-life of a drug?
The half-life of a drug is the period of time it takes for an amount of drug in the body to decrease to one half of the peak level it previously achieved. The half-life is affected by all aspects of pharmacokinetics. Knowing the half-life of a drug helps in predicting dosing schedules and duration of effects.
