FARMACOCINÉTICA VÍAS DE ADMINISTRACIÓN | GuiaMed

Introduction to Pharmacokinetics

Overview of the Session

• The speaker, Christian Poos Arico Halcón, introduces the topic of pharmacokinetics and outlines the agenda for the class.

• Key topics include defining pharmacokinetics, summarizing its importance, discussing routes of drug administration, and detailing the steps involved in pharmacokinetics.

Definition of Pharmacokinetics

• The term "pharmacokinetics" is derived from Greek: "pharmakon" meaning drug or medication and "kinetics" meaning movement.

• It is defined as the study of how drugs move through the body, encompassing all processes a drug undergoes after administration.

Steps in Pharmacokinetics

Key Steps Explained

• The first step is Liberation, where the drug is released from its pharmaceutical form (e.g., capsule).

• Next is Absorption, which involves transferring the drug from its site of administration into the bloodstream through various membranes.

Distribution and Metabolism

• After absorption, drugs are Distributed throughout the body to tissues where they exert their effects.

• The fourth step is Metabolism (or biotransformation), primarily occurring in the liver, where drugs are converted into metabolites that can be more easily eliminated.

Elimination Process

• Finally, drugs undergo Elimination, mainly via renal pathways but also through feces, sweat, tears, or breast milk.

Mnemonic for Remembering Steps

Mnemonic Device

• A mnemonic device to remember these steps is "ADME": Liberation (A), Absorption (D), Distribution (M), Metabolism (E), and Elimination. This aids in recalling each phase effectively.

Variability in Pharmacokinetic Processes

Important Considerations

Understanding Pharmacokinetics: Absorption, Distribution, Metabolism, and Elimination

Overview of Pharmacokinetic Processes

• In pharmacokinetics, there are instances where the processes of drug release may be overlooked, focusing instead on absorption, distribution, metabolism, and elimination.

• The extent to which all five pharmacokinetic steps occur depends primarily on the routes of administration used for the drug.

Routes of Drug Administration

• There are three main categories of pharmacological administration routes: enteral, parenteral, and other methods.

Key Concepts: Bioavailability and First-Pass Effect

• Understanding bioavailability and the first-pass effect is crucial for comprehending the significance of different administration routes.

Bioavailability

• Bioavailability is defined as the percentage of a drug that reaches systemic circulation intact.

• For example, when a drug is administered orally, it must travel through various digestive organs before reaching its target tissue.

• This journey can lead to a significant reduction in the amount of active ingredient that ultimately reaches its destination due to metabolic processes along the way.

First-Pass Effect

• The first-pass effect refers to hepatic metabolism that occurs before a drug enters systemic circulation.

• When taken orally, drugs may either directly enter systemic circulation or pass through the liver via the portal vein first.

• This process can result in inactivation or reduced potency of the drug before it has a chance to exert its intended effects.

Enteral Administration Routes

Oral Route

• The oral route is commonly used due to its convenience and safety; patients can self-administer medications easily.

Advantages

• It is practical and economical for most patients.

Disadvantages

• However, this route has drawbacks such as potential hepatic inactivation due to first-pass metabolism.

• Additionally, bioavailability may be low because gastric juices can degrade some drugs before they reach systemic circulation.

What is the Sublingual Route of Administration?

Overview of Sublingual Administration

• The sublingual route allows for drug absorption directly into the systemic circulation without passing through the liver or digestive system.

• This method enhances bioavailability since it avoids first-pass metabolism, leading to a more effective therapeutic effect.

Disadvantages of Sublingual Administration

• Limited availability of drugs suitable for sublingual administration restricts its use.

• Potential irritation at the application site can occur, which may deter patients from using this route.

Understanding Rectal Administration

Characteristics of Rectal Route

• The rectal route is often used when oral administration is not feasible, such as in cases of vomiting.

• It provides relatively rapid absorption but may still experience some first-pass metabolism effects.

Advantages and Disadvantages

• While it can be effective, many patients find rectal administration uncomfortable and it cannot be used during diarrhea due to rapid expulsion.

Exploring Parenteral Routes

Definition and Types

• Parenteral routes bypass the gastrointestinal tract entirely, including intraarterial, intravenous, subcutaneous, intramuscular, and intradermal methods.

Intraarterial Administration

• Involves injecting medication directly into an artery; commonly used for localized treatment of tumors.

• Direct action on affected organs is a key advantage but risks toxic effects if leakage occurs.

Intravenous Administration

• This method delivers drugs directly into the bloodstream with 100% bioavailability and avoids first-pass metabolism.

• However, it poses challenges like difficulty in finding veins and potential adverse reactions that cannot be reversed once administered.

Subcutaneous Administration

• Involves injecting drugs beneath the skin; it's efficient with high bioavailability but unsuitable for irritating substances.

Intramuscular Administration

• Administers medication deep into muscle tissue; allows for slightly irritating substances but carries risks like nerve damage if improperly injected.

Intradermal Administration

Overview of Parenteral Administration Techniques

Injection Techniques and Rapid Action

• The injection of solutions in small quantities at the dermis level is typically performed in specific regions, allowing for rapid action where it is needed.

Challenges in Medical Technique

• The technique for parenteral administration can be quite challenging for the physician performing it, highlighting the need for skill and precision.

Bioavailability in Parenteral Administration

• A key advantage of parenteral administration is its high bioavailability compared to enteral routes, which is crucial for effective drug delivery.

First-Pass Effect Considerations

• Parenteral routes avoid the first-pass hepatic effect, significantly increasing bioavailability and ensuring that more of the active drug reaches systemic circulation.

Types of Administration Routes

Overview of Various Routes

• Other administration routes include topical, intraperitoneal, inhalatory, intracardiac, intrapleural, intralymphatic, and intraosseous. Each route has specific applications based on context.

Importance of Bioavailability and First-Pass Effect

• Understanding bioavailability and first-pass effects is essential when considering pharmacological administration methods.

Enteral vs. Parenteral Routes

Classification of Routes

• The discussion categorizes routes into enteral (oral and rectal only) and parenteral (including sublingual), emphasizing their differences in absorption mechanisms.

Impact on Bioavailability

• In enteral administration, bioavailability decreases due to gastric juices and travel time through the digestive system; however, parenterally administered drugs can achieve up to 100% bioavailability intravenously.

Effects of First-Pass Metabolism

Absorption Locations

• Enterally administered drugs are primarily absorbed in the duodenum or stomach where first-pass metabolism often occurs.

Absence of First-Pass Effect

• In contrast, parenterally administered drugs bypass this effect entirely as they directly enter systemic circulation without undergoing initial metabolic processing.

Conclusion and Future Topics

Wrap-Up Remarks

• The video concludes with a promise to delve deeper into pharmacokinetics topics such as absorption, release, metabolism, expression elimination in future discussions.

Engagement Encouragement