Therapeutic drug monitoring (TDM) is a vital procedure involving the measurement of a chemical parameter which, when medically interpreted, significantly impacts drug prescribing practices. Alternatively, TDM maintains plasma or blood drug concentrations within a defined therapeutic range or window. The therapeutic range denotes the concentration range of drug in plasma where the drug demonstrates efficacy without inducing toxic effects.
Therapeutic drug monitoring is employed to tailor individual doses, ensuring drug concentrations remain within optimal ranges, thus facilitating personalized dosage adjustments for patients. Therapeutic Drug Monitoring (TDM) depends on the inferred association between drug dosage, blood drug levels, and pharmacological efficacy. It is pivotal to collect the blood samples at the appropriate timing post dosing for accurate measurement of drug concentration.
Timing of sampling is crucial due to fluctuations in drug concentration throughout the dosing period and its correlation with the duration of administration in attaining a stable state. Trough concentrations, representing the lowest variability in drug levels, are utilized for defining therapeutic thresholds. Substances with brief half-lives necessitate monitoring at trough levels, while those with prolonged half-lives can be assessed at any juncture within the dosing interval.
Utilizing insights from pharmaceutics, pharmacokinetics, and pharmacodynamics, Therapeutic Drug Monitoring (TDM) facilitates the assessment of a drug's effectiveness and safety in diverse clinical contexts. Therapeutic drug monitoring encompasses the assessment of critical pharmacokinetic parameters, including I. Bioavailability. II. Volume of distribution and distribution phases. III. Clearance IV. Half-life V. Protein binding of drugs.
Therapeutic Drug Monitoring (TDM) is warranted in various scenarios, such as modifying dosages, validating suspected toxicity, detecting non-adherence, addressing drug interactions, and managing specific clinical conditions. These conditions encompass uremic patients, individuals with liver disease, pediatric and geriatric populations, critically ill patients, and pregnant women. Pharmacogenetics represents a forthcoming avenue in therapeutic drug monitoring aimed at the advancement of both effective and safe medication regimens.
Two primary origins of interindividual variability in drug response exist: pharmacokinetic variability, pharmacodynamic variability.
Therapeutic drug monitoring is used in two major situations: a) For drugs used prophylactically to maintain the absence of a condition, b) To avoid serious toxicity of drugs with a narrow therapeutic range.
TECHNIQUES FOR MEASUREMENT OF TDM
HPLC: High Pressure Liquid Chromatography HPLC separates substances based on their distribution between a mobile phase (transporting the mixture) and a stationary phase.
LC-MS: Liquid Chromatography Mass Spectrometry (LC-MS) works on the principle of differential absorption of substances in solution. It involves two phases: a mobile phase transporting the sample, and a stationary phase separating its components.
GC-MS: Gas chromatography vaporizes samples at elevated temperatures, while mass spectrophotometry separates vaporized fractions based on molecular weight to establish a unique "fingerprint" for drug identification, making GC/MS the gold standard for identifying drugs of abuse.
EIA: Enzyme immunoassay (EIA) employs a non-radioactive enzyme label and is used in modern drug testing. It utilizes homogeneous techniques, conducting assays in a single step with the use of only one antibody, thereby reducing testing turnaround time.
RIA: Radioimmunoassay (RIA) uses radioactivity to detect the analyte. The sample is incubated with an antibody and a radio-labeled drug. Quantitative results are obtained by comparing measured radioactivity with known standards in each run.
PETINIA: The Particle Enhanced Turbidimetric Inhibition Immunoassay, an immuno turbidimetric method, employs light scattering particles to quantify drug levels.
EMIT: The Enzyme Multiplied Immunoassay Technique operates on the principle of competition for binding sites on the target analyte antibody.
FPIA: Fluorescence Polarization Immunoassay employs a fluorescent molecule as a label instead of an enzyme, enhancing its sensitivity.
ACMIA: Affinity Chrome-Mediated Immunoassay (ACMIA) is a method for measuring drug concentrations. It involves the separation of free and drug-bound antibody enzyme conjugates using magnetic particles.
CEDIA: Cloned Enzyme Donor Immunoassay (CEDIA) uses recombinant DNA technology.
REFERENCES:
1. Arshad, A., Zulfiqar, M. I., Kiani, Z. H., Kiani, M. H., & Hassan, M. R. ul. (2020). Evaluation of the knowledge of Health Care Professionals regarding Therapeutic Drug Monitoring in Public Hospitals of Lahore, Pakistan. Global Pharmaceutical Sciences Review, V (I), 9–16. https://doi.org/10.31703/gpsr.2020(v-i).02
2. Baktır, G. (n.d.). THERAPEUTIC DRUG MONITORING (TDM).
3. Deori, C., Kalita, B., & Sonowal, T. (2024). THERAPEUTIC DRUG MONITORING (TDM) IN CLINICAL PRACTICES: OVERVIEW. In European Journal of Biomedical and Pharmaceutical Sciences www.ejbps.com │ (Vol. 11). www.ejbps.com
4. .Sphurthy Mitra, M., & Prasanth Kumar, G. (n.d.). INTERNATIONAL JOURNAL OF PROGRESSIVE RESEARCH IN ENGINEERING MANAGEMENT AND SCIENCE (IJPREMS) A REVIEW ARTICLE ON THERAPEUTIC DRUG MONITORING. In www.ijprems.com editor@ijprems.com @International Journal Of Progressive Research In Engineering Management And Science. www.ijprems.com
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