THERAPEUTIC DRUG 
MONITORING,DETERMINATION OF 
RATE CONSTANT &PLOTS OF 
DRUG DISTRIBUTION 
PRESENTED BY 
B.SUMAN 
RegNo.256212886007 
PHARMACEUTICS
CONTENTS 
1.TDM 
INTRODUCTION 
CRITERIA 
REASONS 
PROCEDURE 
CLINICAL INTERPRETATION 
FACTORS AFFECTING 
EXAMPLES 
PROBLEMS 
2.DETERMINATON OF RATE CONSTANT 
3.DIFFERENT PLOTS OF DRUG DISTRIBUTION
DEFINITION 
Therapeutic drug monitoring is 
measurement of drug concentrations in the 
blood or plasma that facilitates adjustment 
of dosage to produce a desired response 
Therapeutic drug monitoring aims to 
promote optimum drug treatment by 
maintaining serum drug concentration 
within a ‘Therapeutic Range’
INTRODUCTION 
Clinicians routinely monitor drug pharmacodynamics by 
directly measuring physiological indices of therapeutic 
response (E.g.: blood glucose, BP, clotting test) 
For many drugs there is no readily available measure of 
effect or it is insufficiently sensitive 
Large interindividual variation between dose and response 
can make individualizing drug dosage difficult 
DOSE 
Absoption 
Distribution 
Metabolism 
Elimination 
Receptor interaction 
&response 
Clinical 
effect 
Pharmacokinetics 
variability 
Pharmacodynamic 
variability
In other cases it is difficult to distinguish between 
the progress of the disease and the pharmacological 
effect of the drug 
In these situations ‘Therapeutic Drug Monitoring’ 
becomes an essential part of clinical management 
Therapeutic drug monitoring, or TDM as it is 
commonly called, is about using drug serum 
concentrations, pharmacokinetics, and 
pharmacodynamics to individualize and optimize 
patient response to drug therapy
•Therapeutic drug monitoring is a practice applied to a 
small group of drugs in which there is a direct 
relationship between concentration and response 
•Serum concentrations are used as the most practical 
intermediate endpoint to gauge treatment when 
there is no clearly observable therapeutic or toxic 
endpoint 
•‘Therapeutic Range’ represents a range of drug 
concentrations within which the probability of a 
desired clinical response is relatively high and the 
probability of unacceptable toxicity is relatively low
• Therapeutic Index is defined as the ratio between the average 
effective dose and the average lethal dose. It is an extremely 
close margin between an effective concentration of a 
therapeutic drug in the blood and a fatal concentration.
TDM will be Useful If… 
 The drug in question has a narrow therapeutic range 
 A direct relationship exists between the drug or drug 
metabolite levels in plasma and the pharmacological or 
toxic effects 
 The therapeutic effect can not be readily assessed by the 
clinical observation 
 Large individual variability in steady state plasma 
concentration exists at any given dose 
 Appropriate analytic techniques are available to 
determine the drug and metabolite levels
TDM is Unnecessary If… 
1) Clinical outcome is unrelated either to dose or to 
plasma concentration 
2) Dosage need not be individualized 
3) The pharmacological effects can be clinically 
quantified 
4) When concentration effect relationship remains 
unestablished 
5) Drugs with wide therapeutic range such as beta 
blockers and calcium channel blockers
1. Reasons for Requesting TDM: 
 Low therapeutic index 
 Poorly defined clinical end point 
 Non compliance 
 Therapeutic failure – Sub therapeutic 
Concentration? 
 Wide variation in the metabolism of drugs
1. Reasons for Requesting TDM… 
 Major organ failure 
 Prevention of adverse drug effects 
 Toxicity suspected – Toxic Concentration? 
 Change in clinical state of the patient 
 Assess therapy following a change in dosage 
regimen 
 Potential drug interaction due to change in 
co-medication
TDM PROCESS 
2.The Biological Sample: 
• Once the decision to monitor the concentration of 
the therapeutic drug has been made, it is important 
that the biological sample is collected which will 
provide a clinically meaningful measurement. 
• Blood sample should be collected once the drug 
concentration have attained steady state (at-least 5 
half lives at the current dosage regimen). 
• Levels approximating SS may be reached earlier if a 
loading dose has been administered (drugs with 
long half lives).
2. The Biological Sample… 
• However, drugs with long half-lives 
should be monitored before SS is 
achieved to ensure that individuals with 
impaired metabolism or renal excretion 
are not in the risk of developing toxicity 
at the initial dosage prescribed 
• If toxicity is suspected the concentration 
should be measured as soon as possible
2. The Biological Sample… 
• Absorption is variable after oral drug administration 
and blood samples should be collected in elimination 
phase rather than absorption phase 
• Usually blood samples are collected at the end of the 
dosage interval (Trough) 
• For antibiotics given intravenously, Peak 
concentrations (30 minutes after cessation of i.v. 
infusion) are also measured 
• Usually drug concentrations are monitored in venous 
blood, serum or plasma
2. The Biological Sample… 
 In general serum or plasma concentrations are 
comparable but the blood collecting tube used is 
important as few anticoagulants used are 
inappropriate to few drugs and analytical procedures 
 Whole blood must be sampled for few drugs like, 
Cyclosporine A, that distributes between plasma and 
erythrocytes 
 Patient demographics are critically important so that 
the contribution of age, disease state, etc to 
interindividual variation in PK and PD can be 
considered
3. The Request: 
These details must be effectively 
communicated to the members of TDM 
team with a drug assay request 
When a drug which is commonly measured 
for TDM is suspected of causing toxicity, it 
is very important for requesting clinicians 
to clearly communicate the expectation of 
a high concentration and need for a rapid 
feedback of results
4. Laboratory Measurement: 
The assay procedure should be a validated 
one (accuracy, precision, sensitivity, 
specificity,linearrange,reproducibility, 
repeatability, robustness) 
Wherever possible assay procedure should 
be evaluated with an external quality 
assurance program
4. Laboratory Measurement… 
 Ideally the results of the assay should be 
available to the clinician before the next dose is 
given 
The analytical methodology employed should 
ideally: 
1) Distinguish between compounds of similar 
structure – unchanged drug and metabolites 
2) Detect small amounts 
3) Be simple enough to use as a routine assay 
4)Be unaffected by other drugs administered
4. Laboratory Measurement 
TDM are Various analytical techniques available for 
•Spectrophotometry and Fluorimetry 
•Thin layer chromatography 
•HPLC and GLC 
•Radio Immuno assay 
•Enzyme Immuno assay 
•Fluorescence polarization Immunoassay 
Some times, the drug’s metabolite(s) and or some 
endogenous compounds or drugs with similar structures 
can cross react, resulting in either a falsely elevated or 
decreased assayed drug concentration reading and that 
should be avoided
5. Communication of the results by 
Laboratory: 
• The assay results should be communicated as quickly 
as possible once it is verified by the senior laboratory 
personnel 
•The drug concentrations measured are generally 
reported in mass or molar units 
•But, since most of the assays are done by biochemical 
methods, results may be in molar units and the 
laboratory should be able to readily convert mass and 
molar units from one another
5. Communication of the results by 
Laboratory… 
 The result should clearly state the therapeutic 
concentration range for the drug assayed 
It must be remembered that different indications for 
therapy, age or ethnic differences in PK or PD could 
result in different therapeutic ranges being appropriate 
for different population groups 
Hence, critical assessment of the original literatures 
and consensus recommendations for therapeutic 
ranges should be encouraged
6. Clinical Interpretation: 
The information required to interpret the drug 
concentration include: 
Time at which blood sample taken 
Time at which dose is given 
Dosage regimen (Dose, Duration, Dosage Form) 
Patient demographic (sex, age, concomitant 
disease, ethnicity, etc) 
Co medications 
Indications for monitoring 
PK and therapeutic range of the drug
Serum Concentrations Higher than 
Anticipated 
•Patient compliance 
•Error in dosage regimen 
•Wrong drug product (immediate release instead 
of controlled release) 
•Rapid bioavailability 
•Smaller than anticipated apparent volume of 
distribution 
•Slow elimination (poor metabolizer) 
•Increased plasma protein binding 
•Deteriorating renal/hepatic function 
•Drug interaction due to inhibition of elimination
FACTORS AFFECTING SDC 
1. Disease states: renal, liver, cardiac 
2. Habits: diet, smoking, drinking 
3. Pregnancy, age, weight 
4. Non-compliance 
5. Electrolyte balance : Digoxin vs K+ & Ca++ 
6. Drug interactions 
7. Plasma protein binding 
8. Bioavailability 
9. Sampling time
COMMONLY MONITORED DRUGS 
 Bronchodilators: Theophylline 
 Antibiotics : Aminoglycosides - Gentamicin, 
Amikacin 
 Others - Vancomycin 
 Immunosuppressants: Cyclosporine 
 Anticancers: Methotrexate
COMMONLY MONITORED DRUGS 
Antiepileptics: Phenobarbital, 
Phenytoin,Carbamazepine, Valproate 
 Cardiac Drugs : Digoxin*, 
Procainamide, Lidocaine 
 Psychoactive Drugs: Lithium, 
TCA 
 Analgesics: Aspirin, Paracetamol
PROBLEMS OF TDM SERVICE 
Hospital personnel do not know the 
existence of TDM service 
Physicians do not understand the principles, 
benefits, and the limitations of TDM service 
Inappropriate sampling times 
Insufficient patient’s history and other 
necessary data 
No consultation when problems arise
DETERMINATION OF RATE CONSTANT 
:
Ppt tdm new
Ppt tdm new
PLOTS OF DRUG DISTRIBUTION 
d 
r
Ppt tdm new
Scatchard plot
N
Klotz plot
Ppt tdm new
Hitchcock plot
References:- 
Biopharmaceutics and pharmacokinetics, 
D.M.BRAHMANKAR pg no 134-136. 
Best practice in therapeutic drug monitoring 
Annette S. Gross Department of Clinical Pharmacology, 
Royal North Shore Hospital, St Leonards NSW 2065, 
Australia. 
THE THERAPEUTIC DRUG MONITORING AS A BASIS 
FOR INDIVIDUALIZING PATIENT DOSAGE REGIMEN, 
Journal of Health Sciences Management and Public 
Health, Jozef Novotný, Tomáš Èech1
Ppt tdm new

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Ppt tdm new

  • 1. THERAPEUTIC DRUG MONITORING,DETERMINATION OF RATE CONSTANT &PLOTS OF DRUG DISTRIBUTION PRESENTED BY B.SUMAN RegNo.256212886007 PHARMACEUTICS
  • 2. CONTENTS 1.TDM INTRODUCTION CRITERIA REASONS PROCEDURE CLINICAL INTERPRETATION FACTORS AFFECTING EXAMPLES PROBLEMS 2.DETERMINATON OF RATE CONSTANT 3.DIFFERENT PLOTS OF DRUG DISTRIBUTION
  • 3. DEFINITION Therapeutic drug monitoring is measurement of drug concentrations in the blood or plasma that facilitates adjustment of dosage to produce a desired response Therapeutic drug monitoring aims to promote optimum drug treatment by maintaining serum drug concentration within a ‘Therapeutic Range’
  • 4. INTRODUCTION Clinicians routinely monitor drug pharmacodynamics by directly measuring physiological indices of therapeutic response (E.g.: blood glucose, BP, clotting test) For many drugs there is no readily available measure of effect or it is insufficiently sensitive Large interindividual variation between dose and response can make individualizing drug dosage difficult DOSE Absoption Distribution Metabolism Elimination Receptor interaction &response Clinical effect Pharmacokinetics variability Pharmacodynamic variability
  • 5. In other cases it is difficult to distinguish between the progress of the disease and the pharmacological effect of the drug In these situations ‘Therapeutic Drug Monitoring’ becomes an essential part of clinical management Therapeutic drug monitoring, or TDM as it is commonly called, is about using drug serum concentrations, pharmacokinetics, and pharmacodynamics to individualize and optimize patient response to drug therapy
  • 6. •Therapeutic drug monitoring is a practice applied to a small group of drugs in which there is a direct relationship between concentration and response •Serum concentrations are used as the most practical intermediate endpoint to gauge treatment when there is no clearly observable therapeutic or toxic endpoint •‘Therapeutic Range’ represents a range of drug concentrations within which the probability of a desired clinical response is relatively high and the probability of unacceptable toxicity is relatively low
  • 7. • Therapeutic Index is defined as the ratio between the average effective dose and the average lethal dose. It is an extremely close margin between an effective concentration of a therapeutic drug in the blood and a fatal concentration.
  • 8. TDM will be Useful If…  The drug in question has a narrow therapeutic range  A direct relationship exists between the drug or drug metabolite levels in plasma and the pharmacological or toxic effects  The therapeutic effect can not be readily assessed by the clinical observation  Large individual variability in steady state plasma concentration exists at any given dose  Appropriate analytic techniques are available to determine the drug and metabolite levels
  • 9. TDM is Unnecessary If… 1) Clinical outcome is unrelated either to dose or to plasma concentration 2) Dosage need not be individualized 3) The pharmacological effects can be clinically quantified 4) When concentration effect relationship remains unestablished 5) Drugs with wide therapeutic range such as beta blockers and calcium channel blockers
  • 10. 1. Reasons for Requesting TDM:  Low therapeutic index  Poorly defined clinical end point  Non compliance  Therapeutic failure – Sub therapeutic Concentration?  Wide variation in the metabolism of drugs
  • 11. 1. Reasons for Requesting TDM…  Major organ failure  Prevention of adverse drug effects  Toxicity suspected – Toxic Concentration?  Change in clinical state of the patient  Assess therapy following a change in dosage regimen  Potential drug interaction due to change in co-medication
  • 12. TDM PROCESS 2.The Biological Sample: • Once the decision to monitor the concentration of the therapeutic drug has been made, it is important that the biological sample is collected which will provide a clinically meaningful measurement. • Blood sample should be collected once the drug concentration have attained steady state (at-least 5 half lives at the current dosage regimen). • Levels approximating SS may be reached earlier if a loading dose has been administered (drugs with long half lives).
  • 13. 2. The Biological Sample… • However, drugs with long half-lives should be monitored before SS is achieved to ensure that individuals with impaired metabolism or renal excretion are not in the risk of developing toxicity at the initial dosage prescribed • If toxicity is suspected the concentration should be measured as soon as possible
  • 14. 2. The Biological Sample… • Absorption is variable after oral drug administration and blood samples should be collected in elimination phase rather than absorption phase • Usually blood samples are collected at the end of the dosage interval (Trough) • For antibiotics given intravenously, Peak concentrations (30 minutes after cessation of i.v. infusion) are also measured • Usually drug concentrations are monitored in venous blood, serum or plasma
  • 15. 2. The Biological Sample…  In general serum or plasma concentrations are comparable but the blood collecting tube used is important as few anticoagulants used are inappropriate to few drugs and analytical procedures  Whole blood must be sampled for few drugs like, Cyclosporine A, that distributes between plasma and erythrocytes  Patient demographics are critically important so that the contribution of age, disease state, etc to interindividual variation in PK and PD can be considered
  • 16. 3. The Request: These details must be effectively communicated to the members of TDM team with a drug assay request When a drug which is commonly measured for TDM is suspected of causing toxicity, it is very important for requesting clinicians to clearly communicate the expectation of a high concentration and need for a rapid feedback of results
  • 17. 4. Laboratory Measurement: The assay procedure should be a validated one (accuracy, precision, sensitivity, specificity,linearrange,reproducibility, repeatability, robustness) Wherever possible assay procedure should be evaluated with an external quality assurance program
  • 18. 4. Laboratory Measurement…  Ideally the results of the assay should be available to the clinician before the next dose is given The analytical methodology employed should ideally: 1) Distinguish between compounds of similar structure – unchanged drug and metabolites 2) Detect small amounts 3) Be simple enough to use as a routine assay 4)Be unaffected by other drugs administered
  • 19. 4. Laboratory Measurement TDM are Various analytical techniques available for •Spectrophotometry and Fluorimetry •Thin layer chromatography •HPLC and GLC •Radio Immuno assay •Enzyme Immuno assay •Fluorescence polarization Immunoassay Some times, the drug’s metabolite(s) and or some endogenous compounds or drugs with similar structures can cross react, resulting in either a falsely elevated or decreased assayed drug concentration reading and that should be avoided
  • 20. 5. Communication of the results by Laboratory: • The assay results should be communicated as quickly as possible once it is verified by the senior laboratory personnel •The drug concentrations measured are generally reported in mass or molar units •But, since most of the assays are done by biochemical methods, results may be in molar units and the laboratory should be able to readily convert mass and molar units from one another
  • 21. 5. Communication of the results by Laboratory…  The result should clearly state the therapeutic concentration range for the drug assayed It must be remembered that different indications for therapy, age or ethnic differences in PK or PD could result in different therapeutic ranges being appropriate for different population groups Hence, critical assessment of the original literatures and consensus recommendations for therapeutic ranges should be encouraged
  • 22. 6. Clinical Interpretation: The information required to interpret the drug concentration include: Time at which blood sample taken Time at which dose is given Dosage regimen (Dose, Duration, Dosage Form) Patient demographic (sex, age, concomitant disease, ethnicity, etc) Co medications Indications for monitoring PK and therapeutic range of the drug
  • 23. Serum Concentrations Higher than Anticipated •Patient compliance •Error in dosage regimen •Wrong drug product (immediate release instead of controlled release) •Rapid bioavailability •Smaller than anticipated apparent volume of distribution •Slow elimination (poor metabolizer) •Increased plasma protein binding •Deteriorating renal/hepatic function •Drug interaction due to inhibition of elimination
  • 24. FACTORS AFFECTING SDC 1. Disease states: renal, liver, cardiac 2. Habits: diet, smoking, drinking 3. Pregnancy, age, weight 4. Non-compliance 5. Electrolyte balance : Digoxin vs K+ & Ca++ 6. Drug interactions 7. Plasma protein binding 8. Bioavailability 9. Sampling time
  • 25. COMMONLY MONITORED DRUGS  Bronchodilators: Theophylline  Antibiotics : Aminoglycosides - Gentamicin, Amikacin  Others - Vancomycin  Immunosuppressants: Cyclosporine  Anticancers: Methotrexate
  • 26. COMMONLY MONITORED DRUGS Antiepileptics: Phenobarbital, Phenytoin,Carbamazepine, Valproate  Cardiac Drugs : Digoxin*, Procainamide, Lidocaine  Psychoactive Drugs: Lithium, TCA  Analgesics: Aspirin, Paracetamol
  • 27. PROBLEMS OF TDM SERVICE Hospital personnel do not know the existence of TDM service Physicians do not understand the principles, benefits, and the limitations of TDM service Inappropriate sampling times Insufficient patient’s history and other necessary data No consultation when problems arise
  • 28. DETERMINATION OF RATE CONSTANT :
  • 31. PLOTS OF DRUG DISTRIBUTION d r
  • 34. N
  • 38. References:- Biopharmaceutics and pharmacokinetics, D.M.BRAHMANKAR pg no 134-136. Best practice in therapeutic drug monitoring Annette S. Gross Department of Clinical Pharmacology, Royal North Shore Hospital, St Leonards NSW 2065, Australia. THE THERAPEUTIC DRUG MONITORING AS A BASIS FOR INDIVIDUALIZING PATIENT DOSAGE REGIMEN, Journal of Health Sciences Management and Public Health, Jozef Novotný, Tomáš Èech1