clinical biochemistry

1. Jordan university of science
and Technology –Department
of medical laboratory sciences
Therapeutic Drug Monitoring
TDM
Sarah Jaradat

2. Drug definition
• In Pharmacology , a drug is "a chemical substance used in the
treatment, cure, prevention, or diagnosis of disease or used to
otherwise enhance physical or mental well-being. Drugs may be
prescribed for a limited duration, or on a regular basis for chronic
disorders.

3. Forms Of Drugs In The Blood
• A drug in blood exists in two forms  bound and unbound.
• Protein binding can influence the drug's biological half-life in the body.
• The bound portion may act as a reservoir from which the drug is slowly released
as the unbound form.

4. Binding of drug to globulin
4 KLECOP, Nipani 02-12-2010

5. Basic And Acidic Drugs
• Weak acids efficiency absorbed in the stomach.
• Weak basics preferentially absorbed in the intestine.
• Since albumin is alkalotic, acidic and neutral drugs will primarily bind
to albumin.
• If albumin becomes saturated, then these drugs will bind to lipoprotein.
Basic drugs will bind to the acidic α1 acid glycoprotein.

6. Therapeutic drug monitoring
• Involves the analysis, assessment and evaluation of circulating concentrations of
drugs in serum, plasma, or whole blood.
• The purpose of TDM is to ensure that the medication dose is at therapeutic range
and not toxic.
• Medications dosage differ between each patient based on metabolic process.
• Therapeutic range is narrow for some drugs
• below range: drug not effective
• above rang: drug toxic
• TDM can be used to :
• To ensure maximal therapeutic benefit.
• To ensure minimal toxic adverse effects.
• For patient not responding to drug therapy.

7. Indications of TDM
• The consequences of overdosing and under dosing are serious.
• There is a small difference between a therapeutic and toxic dose.
• There is a change in the patient's physiologic state that may
unpredictably affect circulating drug concentrations.
• A drug interaction may be occurring.
• TDM helps in monitoring patient compliance.

8. Routes Of Administration

9. Routes Of Administration
• For a drug to express a therapeutic benefit, it must be at the appropriate
concentration at its site of action.
• Measuring drug concentration at the site of action would be ideal.
• Unfortunately, for most drugs, this cannot be done.
• The circulatory system offers a convenient route that can effectively deliver most
drugs to its site of action
• The goal of most therapeutic regimens is to acquire a blood, plasma, or serum
concentration that has been correlated with an effective concentration at the site
of action

10. Factors That Influence The Circulating Concentration Of An
Orally Drug :
• Formulation of the drug : tablets and capsules require dissolution.
• Most of the drugs absorbed by passive diffusion (So the drug must be in
hydrophobic state).
• Weak acids efficiency absorbed in the stomach.
• Weak bases preferentially absorbed in the intestine.
• Changes in Intestinal motility , Stomach pH, Food or other drugs affect absorption.
• Absorption affected also by ; age , pregnancy , and pathological conditions.

11. Biological effect
• A drug is effective when it binds to a specific receptor in the target
tissue.
• TDM assumes that serum levels are proportional to the intercellular
tissue bind capacity of the drug.
• Drug utilization in the body is influenced by:
• Absorption
• Distribution
• Metabolism
• Excretion

12. Pharmacokinetics (PK) Vs pharmacodynamics (PD)

13. Pharmacokinetic
PK - What the body does to the
drug?
Absorption; distribution,
metabolism, excretion (ADME)
Include measurement of drug
concentrations in the blood or
plasma (serum)
Pharmacodynamic
PD - What the drug does to the
body?
Drug concentration at the site of
action or in the plasma is related to
a magnitude of effect
Include clinical or laboratory
measurements such arterial
blood pressure in patients with
hypertension, or INR in patients
treated with oral anticoagulants

14. Absorption
• The efficiency of drug absorption from GIT is dependent on many
factors:
 Tablets and capsules require dissolution before being absorbed.
 Liquid solutions are more rapidly absorbed.
 Weak acids are efficiently absorbed in the stomach.
 Weak bases are absorbed in the intestine.
 Changes in intestinal motility, pH, inflammation, as well as food or other drugs may
dramatically change absorption characteristics.

15. 15
Absorption
• All substances, including drugs, absorbed
from the intestine enter the hepatic portal
system.
• certain drugs are subjected to significant
hepatic uptake and metabolism (first-pass
metabolism).
 Absorption ma y be changed with age, pregnancy
and pathologic conditions.
first-pass effect (also known
as first-pass metabolism or
presystemic metabolism) is a
phenomenon of drug
metabolism whereby the
concentration of a drug is
greatly reduced before it
reaches the systemic
circulation

17. Distribution
• The free fraction of circulating drugs is subjected to diffusion out of the vasculature to the interstitial.
• The ability of the drug to leave the circulation is dependent on lipid solubility:
 Hydrophobic drugs easily traverse cellular membrane i.e. adipose and nerve cells.
 Polar but not ionized cross cell membrane but do not sequester.
 Ionized drugs diffuse out of the vasculature at a slow rate.
• Volume of distribution index Vd used to describe the distribution characteristic of a drug :
Vd = D/Ct
Vd  volume of distribution index ( liters).
D  intravenous injected dose ( grams or mg)
Ct  concentration in plasma (g/L or mg/L )
Hydrophobic drugs have high Vd , ionized have small Vd.

18. Drug Elimination
• Drugs can be cleared from the body by various mechanisms.
 Independent of the clearance mechanism, decreases in the serum
concentration of drugs most often occurs as first order process “ exponential
rate of loss”.
 this implies that the rate of change of drug concentrations over time varies
continuously in relation to the concentration of drug.
• Hepatic metabolism or renal filtration, or a combination of the two,
eliminates most drugs.
• Functional changes in these organs may result in changes in the rate of
elimination.
• Half-life represents the time needed for the serum concentration to
decrease by one half.

20. Metabolic Clearance
• Most drugs are xenobiotics
Substances not normally found within human system, yet capable of entering biochemical
pathways intended for endogenous substances.
• The biochemical pathway responsible for a large portion of drug metabolism is the
hepatic mixed function oxidase "MFO" system.
• There are many enzymes involved in MFO system divided into 2 phases:
1. Phase I  produce reactive intermediates.
2. Phase II  conjugations of functional groups to these reactive sites, the products are water
soluble.
** Functional groups such as glutathione, glycine, phosphate and sulfate.

21. Renal Clearance
• Kidneys are the primary excretory organ.
• In Renal disease
 Other excretory organs or pathway become involved such as: biliary tract, lungs and sweat glands.
• H2O soluble drugs excrete faster than insoluble.
• Decreases in glomerular filtration rate directly results in increased serum half-life and
concentration, aminoglycosides antibiotics and cyclosporine are examples of drugs with
this behavior.

22. • Most drugs are not administered as a single bolus but
are delivered on a scheduled basis (e.g., once every
8 hours). With this type of administration, serum a drug
oscillates between a maximum (peak drug level) and a
minimum (trough drug level).
• The goal of a multiple dosage regimen is to achieve a
trough that is in the therapeutic range and a peak that
is not in the toxic range. Evaluation of this oscillating
function cannot be done immediately after initiation of a
scheduled dosage regimen. About seven doses are
required before a steady state oscillation is acquired.

23. Sample Collection
• Timing of specimen collection is the single most important
factor in TDM.
Collaborate with nursing & phlebotomy staff for appropriate timing
Trough concentration : right before next dose
Peak concentration : one hour post administration of dose (Verify drug
protocol).
• Specimen Type
Serum: no gel
Plasma: Heparinized
 EDTA, Citrated, Oxalated not acceptable
Whole Blood
Saliva.

24. Factor Affecting Drug Protein Binding
1. factor relating to the drug :
a) Physicochemical characteristic of drug.
b) Concentration of drug in the body.
c) Affinity of drug for a particular component.
2. factor relating to the protein and other binding component :
a) Physicochemical characteristic of the protein or binding component.
b) Concentration of protein or binding component.
c) Number of binding site on the binding site.
3. drug interaction .
4. patient related factor.

25. Drugs commonly measured
A. Cardiac medications (digoxin)
B. Antibiotics (amikacin, gentamicin, vancomycin)
C. Antiepileptic drugs (phenobarbital)
D. Psychoactive Drugs (lithium)
E. Immunosuppressants (Cyclosporine)
F. Antineoplastics (Methotrexate)

26. Drug Groups: Cardio-active
• Digoxin
• Cardiac glycoside used in the treatment of Congestive heart failure.
• Serum concentrations greater than 2 ng/mL can cause adverse effects such as
nausea, vomiting, visual disturbances and cardiac effects such as premature
ventricular contraction.
• Serum levels peak between 2 and 3 hours after an oral dose.

27. Drug Groups: Cardio-active (2)
• Quinidine
• Used to treat cardiac arrhythmic problems
• Inhibits sodium and potassium channels
• Prevents arrhythmias, atrial flutter and fibrillation
• Procainamide
• Used to treat cardiac arrhythmic situations
• Blocks sodium channels
• Affects cardiac muscle contraction
• Often measured with NAPA(N-Acetyl procainamide)

28. Drug Groups: Antibiotics
• Aminoglycosides
• Used to treat infections with gram-negative bacteria that are resistant to
less toxic antibiotics
• Inhibits protein synthesis of the micro-organism
• Examples include: gentamycin, tobramycin, amikacin and kanamycin
• Vancomycin
• Used to treat infections with more-resistant gram-positive cocci and bacilli
• Inhibits cell wall synthesis

29. Drug Groups: Antiepileptics “AEDs”
• Most first and second generation AEDs used to treat seizure disorders and
epilepsy
Second Generation
Felbamate
Gabapentin
Levetiracetam
Oxcarbazpine
Tigabine
Topiramate
Zonisamide
First Generation
Phenobarbital
•Barbiturate Primidone is a
proform
Phenytoin=Dilantin
Valproic Acid= Depakene
Carbamazepine=Tegretol

30. Drug Groups: Psychotherapeutic
• Used to treat manic depression (bipolar disorder)
• Lithium
• Tricyclic Antidepressants “TCAs”
• Clozapine

31. Drug Group: Antiasthmatic
• Used to treat neonatal breathing disorders or respiratory disoders of
adults or children, like asthma
• Examples include theophylline and theobromine

32. Drug Group: Immunosuppressive
• Monitoring of this group of drugs important to prevent organ
rejection (host-versus-graft)
• Used to treat autoimmune disease
• Examples
• Cyclosporine
• Whole blood is the specimen of choice, since it sequesters in the RBC
• Tacrolimus (Prograf)
• Prevents rejection of liver and kidney transplants

33. Drug Group: Antineoplastics
• Inhibit RNA or DNA synthesis of tumor cells, leading to cell death
• Methotrexate
• Inhibits DNA synthesis
Drug Group: Antihypertensive
• Used in treatment of high blood pressure
• Dilate blood vessels
• Sodium nitroprusside
• Used for short-term control of hypertension

34. TDM ASSAY METHODOLOGIES
• ELISA: highly automated, rapid
turnaround, moderate sensitivity but few
assays available, heterogenous.
• RIA: high sensitivity but long turnaround,many
interferences, heterogenous, radiation hazards

35. • FPIA” fluorescence polarization immunoassay “:
highly automated, rapid turnaround,
many assays available, stability of reagents
and calibration curves, moderate sensitivity,
homogenous
• HPLC: highest sensitivity, most assays
available, least expensive but long turnaround,
requires highly trained personnel

36. Drug Time to steady state Sampling time Therapeutic range
(mg/L)
Aminoglycosides
Amikacin Adults
(< 30 y): ~ 2.5-15 h Peak 0.5-1 h after IV infusion Peak 15-25, Trough< 5
Kanamycin (> 30 y): ~ 7.5-75 h (1 h after IM)
Gentamicin Children: ~ 2.5-12.5 h
Dibekacin Neonate: ~ 10-45 h
Netilmicin
Tobramicin
Streptomycin 10-15 h Peak 1-2 h after IM Peak 15-40
Trough < 5
Antineoplastics
Methotrexate 12-24 h Depend on dose & 24 h > 5 umol/L
duration of infusion 48 h > 0.5 umol/L
72 h > 0.05 umol/L
Immunosuppressants
Cyclosporine 1 d Day 3 or 4 of therapy, then 100-200 ug/L
twice weekly for few weeks
and reduce to every 1-2 mo

37. Drug Time to steady state Sampling time Therapeutic range
(mg/L)
Antiarrhythmics
Disopyramide 1-2 d Trough 2-5
Lidocaine 1 h after LD 2 h after LD 1.5-5
5-10 h (no LD) 6-12 h (no LD)
Procainamide/NAPA
Adult (no LD) Immediately after IV LD Procainamide 4-10
: normal renal 15-25 h 2 h after start of IV infusion, NAPA 6-20
: renal insuff 30-65 h once more during 24 h period
Oral: peak (1-4 h) and trough
Quinidine 2 d Trough 2-5
Cardiac Glycosides
Digitoxin 1 mo 8-24 h 13-25 ug/L
Digoxin 5-7 d 8-24 h 0.9-2.2 ug/L
May be longer in renal
insufficiency

38. Drug Time to steady state Sampling time Therapeutic range
(mg/L)
Antiepileptics
Carbamazepine 2-6 d Trough 4-10
Ethosuximide 1-2 wk Any time 40-100
Phenobarbital 3 wk Any time 15-40
Phenytoin 7 d 2-4 h 10-20
Valproate 2-3 d Trough 50-100
Bronchodilators
Theophylline Adult: 2 d IV: 30 min after IV LD 10-20
Children: 1-2 d : 4-6 h after beginning therapy
Infants: 1-5 d : 12-18 h after beginning therapy
Newborn: 120 h Oral: peak
Premy: 150 h 2 h after rapid release prep
4 h after sustained release prep

39. Drug Time to steady state Sampling time Therapeutic range
(mg/L)
Analgesics
Aspirin 1-5 d 1-3 h 150-300 (antiinflam.)
250-400 (rheumatic fev)
Paracetamol 4 h postingestion > 200
toxicity 12 h postingestion > 50
Psychoactive Drugs
Amitriptyline 3-8 d Trough 150-250 ug/L
Imipramine 2-5 d Trough 150-250 ug/L
Nortriptyline 4-20 d Trough 50-150 ug/L
Lithium 3-7 d Trough 0.6-1.2 mEq/L