Tuesday, August 17, 2010


Cats giving a "THERAPEUTIC" massage.. sooo cute...

According to the book of Clinical Chemistry by Michael bishop:Therapeutic drug monitoring involves the analysis, assessment, and evaluation of circulating concentrations of drugs in whole blood plasma or serum. The main purpose of this is to make sure that a dosage of drug produce a maximum therapeutic effect and less side effects. Most of the time, the safe and effective dosage of a certain drug is fully established so therefor TDM is not needed. however some drugs the dosage and it's therapeutic effects/side effects is weak and you don't know the dose that should be used.
The standard dosage is derived from observations in a healthy population. Again TDM provides a basis for establishing a rational dosage regimen to fit individual situations.

Indications of TDM

- Drugs with narrow therapeutic index (NTP) should be monitored.
example : Lithium serum concentrations of 0.8-1.2 mmol/L are effective, but 1.2-2 mmol/L may cause apathy, lethargy, muscle weakness. greater than 2 mmol/ may lead to coma, seizures. Determination of serum lithium is commonly done by ion-selective electrode. Flame emission photometry and atomic absorption methods are also used.

-Patients who have impaired clearance of a drug with a narrow therapeutic index are candidates of drug monitoring.
example: patient's with renal failure.

- Drugs whose toxicity is difficult to distinguish from a patients underlying disease may require monitoring.
example: Theopylline

- Drugs whose efficacy is difficult to establish clinically may require monitoring.
example: Phenytoin

Routes of Administration

For a drug to express a therapeutic effect, it should be at it's correct concentration. Drug can be administered by several routes. IV (intravenous),IM (intramuscular) SQ (subcutaneous). they can be inhaled or absorb through the skin (transcutaneous). Rectal delivery (suppository) is commonly used in infants and in some situations wherein oral delivery is unavailable.


For orally administered drugs, gastro intestinal tract is the one at work, however changes in intestinal motility,pH,inflammation as well as food and other drugs may greatly change the normal absorption.

First-Pass metabolism - Certain drugs are subjected to significant hepatic uptake and metabolism during passage to the liver.

reference : Clinical Chemistry principles,procedures,correlations 5th edition by
Michael L. Bishop
Edward P. Fody
Larry E. Schoeff

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