M3

• Pharmacokinetics refers to the movement of drugs into, through and out of the body
• Response to a drug depends on the inherent pharmacological properties of the drug and its site of action
• Inherent pharmacological properties are drug properties created by the manufacturer
• Site of action is where the drug exerts its effect
• Solubility, permeability, metabolic stability, and transporter effects are important factors
• Absorption involves the drug being taken into the body
• Distribution involves the drug moving into various tissues and anatomic barriers
• Metabolism changes the drug into a form that can be excreted
• Excretion involves removing the drug from the body
• The speed of onset, intensity, and duration of response depend on factors like drug uptake, distribution, and elimination
• Onset of action is when the drug starts taking effect
• Speed of onset refers to how quickly the drug's effect occurs
• Intensity and duration of response are influenced by dose, dosage, and affinity
• Absorption is the entrance of a drug into the bloodstream from the site of administration
• The ultimate goal of absorption is for the drug to reach the site of action in a concentration that produces a pharmacologic effect
• Factors affecting drug absorption include the drug's physicochemical properties and dosage form
• The rate of absorption depends on the proper selection of the dosage form
• Various routes of administration impact drug absorption
• Drugs must be in solution to be absorbed regardless of the route of administration
• Cell membranes act as barriers that drugs must cross before reaching systemic circulation
• Drugs can cross cell membranes through passive diffusion, facilitated passive diffusion, active transport, and pinocytosis
• Passive diffusion involves the movement of drugs from an area of high concentration to low concentration
• Factors affecting passive diffusion include drug's lipid solubility, size, and degree of ionization
• Facilitated passive diffusion and active transport are other mechanisms for drug crossing cell membranes
• Pinocytosis involves cells engulfing fluid or particles
• Factors related to the body that affect absorption include the area of absorbative surface and vascularity
• Presence of other substances like food can also impact drug absorption
• GI mobility, disease, pain, and stress can affect the amount of drug absorbed
• Distribution of drugs involves their passage into various body fluid compartments
• Drug distribution is determined by factors like ionization, lipophilicity, size, and pH of the environment
• Perfusion plays a role in drug distribution to tissues, with poorly perfused tissues having slower distribution
• Degree of protein and tissue binding of drugs also govern drug distribution
• Plasma protein binding refers to the degree to which medications attach to protein within the blood
• A drug in blood exists in two forms: bound and unbound
• The efficiency of a drug may be affected by the degree to which it binds to plasma proteins
• The less bound a drug is, the more efficiently it can traverse cell membranes or diffuse
• The unbound fraction of a drug exhibits pharmacologic effect
• The bound portion of the drug acts as a reservoir or depot from which the drug is slowly released
• The bound fraction of the drug will be released to maintain equilibrium as the unbound form is being metabolized and excreted
• Half-life of a drug is the time it takes for the concentration of the drug in the plasma or the total amount in the body to be reduced by 50%