How and Why Drugs Work PPT Series 5B

Pharmacokinetic Factors That Influence Drug Effects Pharmacokinetics is the study of the movement of drugs in the body, including the processes of administration, absorption, distribution, activation biotransformation, and excretion. Administration = how the drug enters the body Absorption = how drug moves from site of administration into body system(s)

Pharmacokinetic Factors That Influence Drug Effects Distribution – How the drug distributed to the various areas in the body Activation – How and where the drug produce its effects Biotransformation and elimination – How the drug inactivated, metabolized, and/or excreted from the body Video Overview of Pharmacokinetics

Forms and Methods of Taking Drugs There are multiple modes of drug administration. How a drug is administered will determine how quickly the drug will be distributed. Common Modes: Oral ingestion Inhalation Injection Topical application

Forms and Methods of Taking Drugs Oral ingestion: On of the most common and convenient modes of administration. Once administered, it is difficult to control the amount of drug that reaches the target site due to: Drug must be absorbed through stomach / intestines without being destroyed or inactivated or receive interference from other solids or liquids in the stomach Must diffuse through the blood stream with sufficient concentration to have the desired effect. Must pass through the liver (perhaps multiple passes) without being significantly denatured. © Oscar Knott/FogStock/Alamy Images

Forms and Methods of Taking Drugs Inhalation: Inhalation is the administration of a drug through the respiratory pathways of the mouth and nose. Then lungs have a high surface area and diffusion capacity. Thus drugs which have a high diffusion capacity can enter into the circulation as quickly as injectable drugs. Complications of this mode of delivery include: Irritation of the mucous membrane lining (pleura) of the lungs Depending on the drug concentration, continuous inhalation may be warranted

Forms and Methods of Taking Drugs Injection: Drugs administered by injection are typically transferred by needle and syringe. Typical methods of injection are by: A) intravenous (vein); B) intramuscular (muscle); and, C) subcutaneous (beneath skin) delivery. With intravenous injection the drug is delivered rapidly and directly into the blood stream. Complications of this mode of delivery include improper dosing, especially if the drug effects or potency are unknown Impurities in the injected drug may irritate the vein, and multiple injections can cause the vein to collapse Sharing injectables is a common medium of disease transmission.

Forms and Methods of Taking Drugs Injection: Intramuscular injection can directly damage directly via the damage to the motor nerve causing atrophy. A subcutaneous injection may damage the skin and cause bruising, and possible infections. Topical Application: Topical application is drug administration applying it to the exterior of the skin or mucous membrane. The drug is absorbed via the through the skin or membrane. Transdermal delivery tends to be long acting (nicotine patches), but some drugs can be absorbed via mucous membranes rapidly (cocaine). Some topical applications may cause local irritation and rashes.

Distribution of Drugs Following administration, most drugs are distributed throughout the body in the blood. It takes approximately one minute for a drug to circulate throughout the body after it enters the bloodstream. Factors Affecting Distribution Drugs have different patterns of distribution depending on their chemical properties: The ability of the drug to pass through membranes and tissues The molecular size of the drug The drug solubility properties (water vs. fat soluble) The drugs tendency to attach to proteins and tissues throughout the body. The properties above may present barriers to the action (activity) of the drug and limit therapeutic efficacy (ability to produce a desired amount of a desired effect).

Required Doses for Drug Effects Most drugs do become (therapeutically) effective until a threshold concentration has reached the target site(s). Threshold dose: The minimum amount of a drug necessary to have an effect Plateau (ceiling) effect: The maximum effect a drug can have regardless of the dose

Time-Response Factors Time-response is the amount of elapsed time between administration of the drug and the onset of the drug action (effect). The closer a drug is placed to the target area, the faster the onset of action. Acute drug response: Immediate or short-term effects after a single drug dose Chronic drug response: Long-term effects after a repeated doses of a drug Cumulative Effects – If there is an insufficient amount of time for drug metabolism and elimination between doses the drug may “accumulate” in the body producing unexpected effects or toxicity.

Drug Inactivation and Elimination Immediately following drug administration drug elimination mechanisms (ex. metabolism, excretion by perspiration, urination, exhalation), begin. Biotransformation: The process of changing the chemical or pharmacological properties of a drug by metabolism. The liver is the major organ that metabolizes drugs in the body. The kidney is the next most important organ for drug elimination. Some drugs, such as ethanol, small percentages (1%) can be eliminated via breathing End of PPT Series 5B