TDM Flashcards by MAE AMOR D. CHIOCO

What is the primary goal of TDM?

Ensures that a given drug dosage produces maximal therapeutic effect and minimal toxic adverse effects.

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What does TDM involve in terms of analysis?

Involves analysis, assessment, and evaluation of circulating concentrations of drugs in serum, plasma, or whole blood.

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For what type of drugs is TDM a quantitative procedure?

TDM is a quantitative procedure performed for drugs with a narrow therapeutic index.

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Which fraction of the drug can interact with the site of action?

Only the free fraction of the drugs can interact with the site of action and result in a biologic response.

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T OR F

IS TDM is lifesaving in serious situations?

TRUE

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Which biological samples are analyzed in TDM?

Serum, plasma, or whole blood

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Causes of Drug Toxicity

Elevated concentration of free drug.
Abnormal response to the drug after administration.
The presence of active drug metabolites.

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can travel to the site where it is indicated.

Free drug

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Factors of TDM

 Route of administration
 Rate of absorption
 Protein binding
 Drug administration
 Drug distribution
 Drug elimination

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Therapeutic Failure

Non-compliance
 Sub therapeutic dose
 Bioavailability
 Malabsorption
 Drug interactions

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Types of Assay Required

Total drug
Free drug
Metabolites

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What are the two main types of drug assays focused on in TDM?

Total drug and free drug.

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Why are metabolites seldom checked in TDM?

TDM primarily focuses on total drug and free drug concentrations, not metabolites.

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In which field are metabolites primarily checked, and what is the usual specimen of choice for metabolite analysis?

Metabolites are primarily checked in toxicology, with urine being the usual specimen of choice.

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Routes of Administration

Injections
Inhaled
Absorbed in skin
Rectal (suppository)
Oral (most common)

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Injections

 Intravenous
 Intramuscular
 Subcutaneous
 Epidermal

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What is the bioavailable fraction of an intravenous injection?

The bioavailable fraction of an intravenous injection is 1.0 (100% bioavailability).

should achieved 0.7
bioavailability fraction

Oral (most common)

How are drugs usually distributed in the body?

Drugs are usually distributed by blood flow and via capillary permeability.

Where are drugs generally effective in the body?

Drugs are generally effective in the body tissues, not in the blood.

Distribution

-Usually by blood flow and via capillary
permeability
-Binding to proteins or free fractions
 Lipid solubility of the drug
 pH gradient

What happens to drugs during metabolism?

Drugs are broken down into metabolites.

What are the characteristics of metabolites?

Characteristics of metabolites:
Water-soluble
Pharmacologically active or inactive
Easily excreted

Where does the first-pass metabolism occur, and what is its effect on drug bioavailability?

The first-pass metabolism occurs in the liver, where the drug loses a fraction of its bioavailability before reaching the target.

The process by which a drug leaves the site of administration and reaches the target site.

absorption

What are the mechanisms of absorption?

Passive diffusion Active transport

Absorption Depends on

Formulation of drug: Pill (requires dissolution) Liquid (rapidly absorbed) Intestine motility pH levels Presence of inflammation Food intake Age Pregnancy Concurrent pathologic conditions

What are the primary routes of drug elimination?

Hepatic metabolism Renal filtration Other routes: Skin, Lungs, Breast, Saliva

What factors influence the rate of drug elimination?

Type of drug Patient’s capacity to metabolize and excrete the drug

How do functional changes of organs affect drug elimination?

Functional changes in organs, such as liver or kidney impairment, can affect the body's ability to eliminate drugs efficiently.

– time required to reduce blood level drug concentration to half after equilibrium is obtained

Steady state

What is the most important factor to consider in specimen collection?

Timing

What are the different timings for specimen collection?

Trough: 30 minutes before the next dose Peak: 1 hour after administration Random

What type of blood sample is preferred for analysis?

Whole blood --Avoid using EDTA, Citrate, or Oxalate as they add ions that can interfere with analysis Serum (avoid using gel) --Measurement of serum concentrations should be done after steady state has been achieved Plasma (Heparinized samples)

Why is urine rarely used in Therapeutic Drug Monitoring (TDM)?

Urine is primarily used in toxicology, not in TDM.

What is the principle behind the Enzyme Multiplied Immunoassay Technique (EMIT)?

The amount of enzyme activity is directly proportional to the amount of drugs present in the sample.

What are the characteristics of the Enzyme Link Immunosorbent Assay (ELISA)?

Moderate sensitivity Few assays available Automated Rapid turn-around time

What is characteristics of the Radio Immunoassay (RIA)?

High sensitivity Long turn-around time

What is characteristics of the High Performance Liquid Chromatography (HPLC)?

Highest sensitivity, least expensive Long turn-around time Measurement depends on the type of column used, the solvent, and detector systems used

What is characteristics of the Fluorescence Polarization Immunoassay (FPIA)?

Automated Rapid turn-around time Moderate sensitivity