Therapeutic Drug Monitoring (TDM) is a branch of clinical chemistry and clinical pharmacology that specializes in the measurement of medication concentrations in blood. Its main focus is on drugs with a: “Narrow Therapeutic Range” i.e. drugs that can easily be under- or overdosed

TDM aimed at improving patient care by individually adjusting the dose of drugs for which clinical experience or clinical trials have shown it improved outcome in the general or special populations.

There are numerous variables that influence the interpretation of drug concentration data: 1-Route and dose of drug given. 2-Time of blood sampling. 3-Handling and storage conditions. 4-Precision and accuracy of the analytical method.

Many different professionals: 1-Physicians. 2-Clinical pharmacologists. 3-Clinical pharmacists. 4-Medical laboratory scientists. are involved with the various elements of drug concentration monitoring.

Characteristics of drugs subject to therapeutic drug monitoring: In pharmacotherapy, many medications are used without monitoring of blood levels. In a small group of drugs insufficient levels will lead to undertreatment or resistance, and excessive levels can lead to toxicity and tissue damage.

Examples of drugs analyzed by therapeutic drug monitoring: 1-Aminoglycoside antibiotics (gentamicin) 2-Antiepileptics: (such as Carbamazepine, phenytoin and valproic acid) 3-Mood stabilizers, especially lithium citrate 4-Antipsychotics. Therapeutic drug monitoring can also detect poisoning with above drugs, should the suspicion arise.

High-performance liquid chromatography (sometimes referred to as high-pressure liquid chromatography), HPLC: Chromatographic technique used to separate a mixture of compounds in analytical chemistry and biochemistry with the purpose of identifying, quantifying or purifying the individual components of the mixture.

(Mikhail Tsvet) ( )

(Basic Principle of Chromatography)

Chromatography System HPLC

Chromatography can be described as a mass transfer process involving adsorption. HPLC relies on Pumps to pass a pressurized liquid and a sample mixture through a column filled with a sorbent, leading to the separation of the sample components.

The active component of the column, the sorbent, is typically a granular material made of solid particles (e.g. silica, polymers, etc.) 2-50 micrometers in size The components of the sample mixture are separated from each other due to their different degrees of interaction with the sorbent particles.

The Pressurized Liquid is typically a mixture of solvents (e.g. water, acetonitrile and/or methanol) and is referred to as "mobile phase". Its composition and temperature plays a major role in the separation process by influencing the interactions taking place between sample components and sorbent. These interactions are physical in nature, such as hydrophobic (dispersive), dipole-dipole and ionic.

(Basic Principle of Chromatography)

(Chromatogram)

(Chromatography System) (HPLC)

Grave of Michail Semyenovich Tsvet with the inscription: "He invented chromatography, separating molecules but uniting people."