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Why different people respond differently to drugs?

Drug response can be affected by a wide range of factors, including genetics, age and certain environmental considerations. The differences in genetic makeup between individuals plays a big role on drug response. The effectiveness of drugs depends on our DNA, as DNA directly determines the level of activity of our enzymes. Therefore, in order to get the best possible treatment, we need pharmacogenomics tests to determine which drugs work best for us.

Everyone responds differently to drugs, what works for you may cause serious side effects on another. Once a drug has been administered inside the body, four main processes involved in drug disposition are absorption, distribution, metabolism and excretion; called ADME.

Absorption is the process which drugs molecules pass across tissue membranes to enter the bloodstream.

Distribution is the process which drugs move around the body. Drug molecules in the blood steam move across capillary walls to enter different body’s tissues.

Metabolism is the process which drugs are chemically altered to make them sufficiently water-soluble for excretion in urine or faeces. Liver is the primary site that process drug metabolism as the enzymes that facilitate the reactions are concentrated there. For drugs to excrete out of our body, drugs can be metabolized by oxidation, reduction, hydrolysis, hydration, conjugation, condensation, or isomerization. The level of specific enzymes controls the drug metabolism rate. However, this metabolise rate is limited by the enzyme and affect the duration and intensity of a drug's pharmacological action. When blood levels of a drug are high which may result in accumulation toxic substance in body.

Excretion is the process of removal of the waste substance from the body. Kidneys are the main organs of the body’s excretory system. Some drugs are excreted out as metabolites in urine or bile. Small amounts of the drug can be excreted naturally through tears, sweat, breath and saliva.

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