What is pharmacokinetics?

When drugs are used to treat or prevent the disease, doses must be given that achieve the necessary concentrations for the required effects, but remain on blood levels that do not cause excessive toxicity. The processes that determine this are commonly called pharmacokinetics. This includes the study of drug absorption into the body, distribution throughout the body and metabolism and excretion to eliminate the drug from the body. To the variability of pharmacokinetics of the drug, including age, gender, body weight and health conditions. Pharmacokinetics are sometimes referred to as clinical pharmacokinetics. This most often concerns oral drugs absorbed from the gastrointestinal (GI) tract. The percentage of the dose that reaches blood after absorption is called biological availability.

The most common reason for low oral biological availability is the metabolism of the first pass. All drugs absorbed from the GI tract first pass through the liver. Here, medicines can be significantly divided or metabolized before the blood is achieved. BetweenOther reasons for decreased biological availability of oral availability include the destruction of drugs using gastric acid and inhibition of food absorption. Some medicines have saturable absorption, which means that only a certain amount can be absorbed at a time.

Once the medicine is in the blood, it can stay there or go to different tissues throughout the body. The volume of distribution (VD) is a sign of the extent to which the drug is distributed outside blood. It is a mathematical relationship between the amount of drug in the body and the blood concentration. It is more virtual than physiological volume and expresses the volume that would be needed to occupy all drugs in the body.

practically, VD is used to calculate the dose of the load for the drug. This is the amount of drug that quickly achieves effective blood concentrations. It is a dose that fills the tank completely if you want. Loading of the dose will be greater for medicines with a large VD compared to Dnem with little VD.

The half -life of the drug is the time required to decrease the blood concentration by half. It is usually expressed in hours, but for some drugs it may be a matter of minutes or for several days. In determining how often it gives the medicine. Longer half -life means that the drug can be administered less often.

Several organs in the body have the ability to decompose drugs. This is called drug metabolism. Organs with metabolic abilities include liver, kidneys, GI tract and lungs. Even blood contains enzymes that can metabolize drugs.

enzymes in Liver that the metabolization of drugs had evolved long before people were deliberately taking drugs. These enzymes inactivate toxins that are unintentionally consumed and thus prevent damage to the body. Because many drugs are derivatives of naturally occurring substances, they are also susceptible to the disintegration of liver enzymes. Liver disease, such as cirrhosis or hepatitis, can reduce the body's ability to metabolize drugs.

two separate processes characterizeMetabolism by liver: Phase I and Phase II reaction. Phase and usually inactivate or detoxify drugs. After inactivating the reaction of phase II, they add molecules to make the drug soluble. This increases the elimination of drugs with kidneys.

The most common phase enzymes in the liver are called P450 cytochrome enzymes. Some drugs may increase the production of these liver enzymes, leading to reduced concentration of metabolized blood drug. This is called the induction of the enzyme. Other drugs can inhibit the P450 cytochrome enzymes. These drugs are called enzyme inhibitors and may cause increased concentration of metabolized drug.

The last step in pharmacokinetics is to remove the drug from the body, also called excretion or clearance. For most drugs, clearance is a constant factor no matter how much drugs remain in the body. This is called linear pharmacokinetics. However, some drugs are saturable, usually because the metabolizing enzymes may break down a firm amount of drugs.gout. Drugs with saturable metabolism and/or clearance show non -linear pharmacokinetics.

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clearation of drugs is mainly carried out by the kidneys. Inactivated drugs are excreted into the urine and discarded from the body. Reducing kidney function, whether as a result of age or disease such as diabetes or high blood pressure, can reduce the body's ability to eliminate drugs. The liver also excludes medicines, usually to a white with elimination through feces.