Pharmacokinetics is the branch of pharmacology that describes how the body affects a specific drug after administration. A number of phases occur once the drug enters into contact with the gastro intestinal wall, these are described using the acronym ADME, starting with the mechanisms of absorption, which is the process by which a substance enters the blood circulation.
Distribution, where the dispersion or dissemination of substances throughout the fluids and tissues of the body. ADME also include the process of metabolism, which is also known as biotransformation, it is inactivation of the xenobiotic substance.Additionally, excretion, defined as the removal of the substances from the body. Linear models assumed that the pharmacokinetic …show more content…
Following intravenous administration, there is no absorption process since the drug is directly introduced into the blood stream. However, for oral routes, there will be an absorption process that occurs. Following ingestion of a drug it begins to dissolve in the GI fluids and is absorbed into the blood. While the transportation of the drug in the gut wall, if any process becomes saturated, then increases in the administered dose will not correspond to increases in amount of drug absorbed into the body. This is called saturable drug absorption, such as Penicillin G and Saquinavir. Additionally, Dissolution can be the cause of dose dependency in the bioavailability for drugs with low aqueous solubility, when given orally in relatively large doses. With a fixed transit time through the gastrointestinal tract, the amount of drug dissolved and hence absorbed is unlikely to increase in proportion to the dose administered. An example are griseofulvin and Chlorotiazide. For a few drugs, absorption from the gastrointestinal tract occurs by a capacity-limited transport mechanism. An example of this mechanism is amoxicillin. This drug is absorbed by a peptide transport mechanism in the small intestine. This conclusion is supported by the observation that bioavailability decreases with increased oral dose, but the peak time changes. little. First-pass metabolism is …show more content…
The dependence of the rate of an enzyme reaction on substrate concentration is given by the Michaelis-Menten equation. During the metabolism the Nonlinearity is achieved due to many mechanisms, including capacity limited metabolism, which is explored with two examples, alcohol and phenytoin. Both compounds rapidly permeate the hepatocyte and achieve distribution equilibrium, with unbound drug in the circulating plasma virtually equal to that in the hepatocyte, in which small changes in dose administration leads to large variations in plasma concentration at steady state. Drugs with saturable metabolism show non-linear pharmacokinetics. For some drugs, clearance is saturable, usually because the metabolizing enzymes can only break down a fixed amount of drug at one time. Other mechanisms that lead to nonlinearity metabolism are enzyme inducer, such as carbamazepinem, which is a type of drug that increases the metabolic activity of an enzyme either by binding to the enzyme and activating it, or by increasing the expression of the gene coding for the enzyme. On the other hand, an enzyme inhibitor, such as PCT or alcohol, is a molecule that binds to an enzyme and decreases its activity also cause nonlinearity
Distribution, where the dispersion or dissemination of substances throughout the fluids and tissues of the body. ADME also include the process of metabolism, which is also known as biotransformation, it is inactivation of the xenobiotic substance.Additionally, excretion, defined as the removal of the substances from the body. Linear models assumed that the pharmacokinetic …show more content…
Following intravenous administration, there is no absorption process since the drug is directly introduced into the blood stream. However, for oral routes, there will be an absorption process that occurs. Following ingestion of a drug it begins to dissolve in the GI fluids and is absorbed into the blood. While the transportation of the drug in the gut wall, if any process becomes saturated, then increases in the administered dose will not correspond to increases in amount of drug absorbed into the body. This is called saturable drug absorption, such as Penicillin G and Saquinavir. Additionally, Dissolution can be the cause of dose dependency in the bioavailability for drugs with low aqueous solubility, when given orally in relatively large doses. With a fixed transit time through the gastrointestinal tract, the amount of drug dissolved and hence absorbed is unlikely to increase in proportion to the dose administered. An example are griseofulvin and Chlorotiazide. For a few drugs, absorption from the gastrointestinal tract occurs by a capacity-limited transport mechanism. An example of this mechanism is amoxicillin. This drug is absorbed by a peptide transport mechanism in the small intestine. This conclusion is supported by the observation that bioavailability decreases with increased oral dose, but the peak time changes. little. First-pass metabolism is …show more content…
The dependence of the rate of an enzyme reaction on substrate concentration is given by the Michaelis-Menten equation. During the metabolism the Nonlinearity is achieved due to many mechanisms, including capacity limited metabolism, which is explored with two examples, alcohol and phenytoin. Both compounds rapidly permeate the hepatocyte and achieve distribution equilibrium, with unbound drug in the circulating plasma virtually equal to that in the hepatocyte, in which small changes in dose administration leads to large variations in plasma concentration at steady state. Drugs with saturable metabolism show non-linear pharmacokinetics. For some drugs, clearance is saturable, usually because the metabolizing enzymes can only break down a fixed amount of drug at one time. Other mechanisms that lead to nonlinearity metabolism are enzyme inducer, such as carbamazepinem, which is a type of drug that increases the metabolic activity of an enzyme either by binding to the enzyme and activating it, or by increasing the expression of the gene coding for the enzyme. On the other hand, an enzyme inhibitor, such as PCT or alcohol, is a molecule that binds to an enzyme and decreases its activity also cause nonlinearity