Therapeutic Drug Monitoring and Absorption

Study Notes

Therapeutic Drug Monitoring (TDM)

Definition: The clinical practice of measuring specific drug levels in a patient's bloodstream to ensure optimal dosing.
Purpose:
- Improve therapeutic outcomes.
- Minimize toxicity.
Indications:
- Narrow therapeutic index drugs (e.g., lithium, warfarin).
- Drugs with variable pharmacokinetics.
Process:
- Sample collection (blood).
- Laboratory analysis of drug concentration.
- Adjustment of dosage based on results.

Drug Absorption

Definition: The process by which a drug enters the bloodstream from the site of administration.
Factors Affecting Absorption:
- Route of administration (oral, intravenous, etc.).
- Drug formulation (e.g., tablets, injections).
- Physiochemical properties (solubility, pH).
- Gastrointestinal (GI) factors (motility, presence of food).
Key Concepts:
- Bioavailability: The fraction of the administered dose that reaches systemic circulation.
- First-pass metabolism: The metabolism of a drug before it reaches systemic circulation, significantly affecting bioavailability.

Mechanisms of Action

Definition: The specific biochemical interaction through which a drug produces its pharmacological effects.
Common Mechanisms:
- Receptor binding: Drugs interact with cellular receptors (e.g., agonists, antagonists).
- Enzyme inhibition: Drugs inhibit enzymes that catalyze biochemical reactions (e.g., ACE inhibitors).
- Ion channel modulation: Drugs affect the opening or closing of ion channels (e.g., calcium channel blockers).
- Transporter interactions: Drugs can inhibit or stimulate transport proteins (e.g., SSRIs).

Pharmacokinetics

Definition: The study of the absorption, distribution, metabolism, and excretion (ADME) of drugs.
Key Processes:
1. Absorption: How a drug enters the bloodstream.
2. Distribution: How a drug disperses throughout the body tissues and fluids.
3. Metabolism: The chemical modification of a drug, primarily in the liver.
4. Excretion: The elimination of the drug from the body, mainly via kidneys.
Concepts:
- Half-life: The time it takes for the concentration of a drug in the bloodstream to reduce by half.
- Clearance: The volume of plasma from which a substance is completely removed per unit time.

Adverse Drug Reactions (ADRs)

Definition: Unintended, harmful reactions to a drug that occur at normal therapeutic doses.
Types of ADRs:
- Type A (predictable): Dose-dependent, related to drug’s pharmacological action (e.g., sedation from benzodiazepines).
- Type B (unpredictable): Idiosyncratic reactions not related to the drug’s pharmacological action (e.g., allergic reactions).
Risk Factors:
- Patient-specific factors (age, genetics, comorbidities).
- Drug-specific factors (potency, interactions).
Management:
- Avoiding causative drugs.
- Monitoring and reporting ADRs.
- Symptomatic treatment.

Therapeutic Drug Monitoring (TDM)

Measures drug levels in the bloodstream for optimal dosing.
Aims to enhance therapeutic outcomes and reduce toxicity.
Essential for narrow therapeutic index drugs like lithium and warfarin.
Particularly useful for drugs with variable pharmacokinetics.
Involves blood sample collection, laboratory analysis, and dosage adjustments based on results.

Drug Absorption

Drug absorption refers to how a drug enters the bloodstream post-administration.
Influenced by route of administration (oral, intravenous, etc.).
Affected by drug formulation (tablet, injection) and physiochemical properties (solubility, pH).
Gastrointestinal factors like motility and food presence can alter absorption.
Bioavailability measures the fraction of the dose reaching systemic circulation.
First-pass metabolism occurs before drugs enter systemic circulation, impacting bioavailability significantly.

Mechanisms of Action

Describes biochemical interactions that yield pharmacological effects of drugs.
Involves receptor binding, where drugs act as agonists or antagonists at cellular receptors.
Enzyme inhibition occurs when drugs block enzymes that catalyze biochemical reactions (e.g., ACE inhibitors).
Ion channel modulation involves drugs influencing the opening or closing of channels (e.g., calcium channel blockers).
Transporter interactions result from drugs inhibiting or stimulating transport proteins (e.g., SSRIs).

Pharmacokinetics

Studies the absorption, distribution, metabolism, and excretion (ADME) of drugs.
Absorption pertains to how drugs enter the bloodstream; distribution includes how they spread through tissues.
Metabolism involves chemical changes mainly in the liver, impacting drug activity.
Excretion is the process of drugs being eliminated, primarily through the kidneys.
Half-life indicates the time required for drug concentration in the bloodstream to decrease by half.
Clearance measures the volume of plasma from which a substance is fully removed per unit of time.

Adverse Drug Reactions (ADRs)

ADRs are unintended reactions that occur at normal therapeutic doses.
Type A reactions are predictable and dose-dependent, linked to the pharmacological action (e.g., sedation from benzodiazepines).
Type B reactions are unpredictable, often idiosyncratic, and not related to drug actions (e.g., allergic reactions).
Risk factors for ADRs include patient age, genetics, and existing comorbidities.
Management involves avoidance of causative drugs, monitoring and reporting ADRs, and symptomatic treatment.

Description

This quiz explores two critical concepts in pharmacology: Therapeutic Drug Monitoring (TDM) and Drug Absorption. Understand the importance of TDM in ensuring optimal drug dosing and minimizing toxicity, alongside the factors influencing how drugs are absorbed into the bloodstream. Test your knowledge on these key aspects of medication management.