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Drugs and the Body
Pharmacodynamics
- Pharmacodynamics is the science of dealing with interactions between living organisms and foreign chemicals
- Chemical reactions occur continuously in the body of each living system
- When other chemicals (drugs) are added to the body, additional effects occur
Drug Actions
- To replace or act as substitutes for missing chemicals
- To increase or stimulate certain cellular activities
- To depress or slow certain cellular activities
- To interfere with the functioning of foreign cells
Receptor Cells
- Receptor site reacts to certain chemicals
- The better the fit between receptor site and chemical, the more pronounced the reaction
- Enzymes within the body are needed to break down the chemicals to open up the receptor site
Lock & Key
Drugs and The Body: Lock and Key
Enzymes
- Drugs can interfere with the enzymes that may be catalysts for chemical reactions
- Enzymes produce a cascade effect
Pharmacokinetics
- Onset of drug action
- Drug half-life
- Timing of the peak effect
- Duration of drug effects
- Metabolism or biotransformation of the drug
- Site of excretion
The Processes by Which Drugs Are Handled in the Body
The Processes by Which Drugs Are Handled in the Body
Pharmacokinetics
- Critical concentration
- The amount of a drug that is needed to cause a therapeutic effect
- Loading dose
- A higher dose than that usually used for treatment
- Dynamic equilibrium
- The actual concentration that a drug reaches in the body
Dynamic Equilibrium
- The actual amount of drug that reaches the body results in a dynamic equilibrium
- Dynamic equilibrium is affected by:
- Absorption
- Distribution
- Biotransformation
- Excretion
Absorption
- Administration
- Affected by route of administration
- Oral medications affected by presence of food in the stomach
- First-pass effect
- Medications are extensively metabolized by the liver
Factors Affecting Absorption
Factors That Affect Absorption of Drugs
Distribution
- Protein binding
- Blood–brain barrier
- Placenta/breast milk
Biotransformation
- The liver is the single most important site for biotransformation (metabolism)
- This process breaks down medications
- It helps to prevent medications from causing adverse effects on the body
Excretion
- Removal of drugs from the body
- Kidneys play the most important role in the excretion of medication
Half-Life
- Half-life is the time it takes for the amount of drug in the body to decrease to one-half the peak level
- Half-life is affected by the absorption, distribution, metabolism, and excretion
Pharmacokinetics
Pharmacokinetics
Half-life
Half-Life
Calculating Half-Life
Focus on Calculations
Factors Influencing Drug Effects
- Weight
- Age
- Gender
- Physiologic factors
- Pathologic factors
- Genetic factors
- Immunologic factors
- Psychological factors
- Environmental factors
- Drug tolerance
- Cumulative effect
Drug-to-Drug Interactions
- Can occur any time two or more drugs are taken together
- Can occur at:
- Site of absorption
- During distribution
- During biotransformation
- During excretion
- At the site of action
Drug–Food Interaction
- Certain foods interact with drugs
- Drugs are best taken on an empty stomach
Drug–Laboratory Test Interaction
- Drugs may alter the results of lab testing
- Laboratory tests may be used to monitor the effects of other medications
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Tags
absorption, biotransformation, cascade effect, catalysts, cellular activities, chemical reactions, critical concentration, drug actions, drug effects, drug half life, dynamic equilibrium, enzymes, excretion, half life, interactions between living organisms, loading dose, metabolism, peak effect, receptor cells, therapeutic effect