Which process involves the passage of a substance from its site of administration into the bloodstream?
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1821 Accesses AbstractPharmacokinetics, derived from the Greek words “pharmakon” (drug) and “kinesis” (movement), is the study of the time course of drugs in a biological system. This chapter discusses the major aspects of pharmacokinetics as it applies to drugs in humans. Absorption is the process of drugs entering the bloodstream. This may occur by diffusion, facilitated diffusion, or active transport. There are multiple routes of drug administration including oral, inhaled, intravenous, intramuscular, rectal, oral mucosal, intrathecal, dermal, ocular, and intranasal. Once in the bloodstream, drugs are distributed throughout the body. Distribution is dependent on plasma protein binding, tissue perfusion, and pH characteristics. Elimination of drugs occurs either through metabolism or excretion. Metabolism is the process of changing the chemical structure of the drug to better enable removal from the body. Metabolism may be Phase I where changes in functional groups on the drug are made, or Phase II where a drug or Phase I metabolite is conjugated with an endogenous substance. Excretion is the final removal of the drugs and/or metabolic products from the body, either into the bile, urine, or other means. Mathematical models that describe the pharmacokinetics of drugs are also included. Keywords
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Rights and permissionsCopyright information© 2020 Springer Nature Switzerland AG About this chapterCite this chapterSpiehler, V., Levine, B.S. (2020). Pharmacokinetics. In: Levine, B.S., KERRIGAN, S. (eds) Principles of Forensic Toxicology. Springer, Cham. https://doi.org/10.1007/978-3-030-42917-1_7 Download citation
ADME is the abbreviation for Absorption, Distribution, Metabolism and Excretion. ADME studies are designed to investigate how a chemical (e.g. a drug compound) is processed by a living organism. Toxicology tests are often a part of this process, yielding the acronym ADMET. What are the four steps of pharmacokinetics?Pharmacokinetics is a specific branch of pharmacology that studies what the body does to a drug. Pharmacokinetic studies evaluate:
ADME are the four steps of pharmacokinetics. Let us break down what each of these steps involves. AbsorptionAbsorption describes how a chemical enters the body. Absorption relates to the movement of a chemical from the administration site to the bloodstream. There are four main routes of administration:
Only injected compounds enter directly into the systemic circulation. For drugs administered through ingestion, inhalation or dermal contact, the chemicals must cross a membrane before entering the
bloodstream.
The route of administration influences bioavailability, which is a measure of how much of a drug is absorbed in an unchanged form. You can find the bioavailability by measuring the plasma drug concentration over time. Only intravenous administration results in 100% bioavailability. Drugs administered in other ways will have reduced bioavailability. Not all of the compound will make it into the bloodstream. For instance, a drug that is ingested first undergoes metabolism during which some of the drug is excreted before entering the bloodstream. DistributionOnce a drug has been absorbed, it moves from the absorption site to tissues around the body. This
distribution from one part of the body to another is typically accomplished via the bloodstream, but it can also occur from cell-to-cell. Researchers examine where the chemical travels to, the rate at which it arrives to certain sites, and the extent of the distribution to help determine efficacy. Some compounds move easily, while others do not. Factors such as blood flow, lipophilicity, tissue binding, and molecular size influence distribution. MetabolismDrug metabolism is the
biotransformation of a drug by organs or tissues (primarily the liver, kidney, skin or digestive tract) so that the drug can be excreted. To facilitate removal via feces or urine, the drug compound is altered to become more water-soluble. Chemical metabolism can result in toxicity, for instance by creating damaging biproducts or a toxic metabolite. Scientists map out the specific metabolic pathways of a drug candidate, something called adverse outcome pathways (AOPs). AOPs provide data needed to determine the potential safety or toxicity of a drug. Drug metabolism and interaction data provide researchers with the information they need to determine the likelihood of drug–drug interactions (DDIs). Anticipating drug interactions is essential for safe pharmaceutical development. ExcretionExcretion is the process by which the metabolized drug compound is eliminated from the body. Researchers want to know how rapidly the drug is excreted and what pathway it takes to exit the body. Most
drug excretion occurs as feces or urine. Other excretion methods include through the lungs or in sweat through the skin. Molecular size and charge influence the excretion pathway. Not every drug compound is fully excreted. When the chemical or metabolic by-products bioaccumulate, adverse effects can occur. Lipid-soluble compounds are more prone to bioaccumulate compared to water-soluble compounds. Why is ADME important?In drug discovery and development, researchers must examine the activity of a drug in the body to assess safety and toxicity. Drug metabolism and pharmacokinetics studies, such as ADME and toxicology studies, are a critical step in this process. The data collected tells researchers if a drug is viable and provides specific targets for future research and development. Advances in the field have precipitated the rise of personalized ADME approaches, where factors such as a patient's genome or even the time of day during which drugs are administered are considered. Computational techniques are often used to assist these more precise studies.  Which process the drug is transferred from its site of entry into the bloodstream?Absorption is the process by which a drug enters the bloodstream. There are many possible routes of administration, but the two most common are intravenous and oral. If a drug is administered intravenously, the absorption phase is skipped as the drug immediately enters circulation.
What term is used to describe medications that are absorbed into the bloodstream?Drug absorption is the movement of a drug into the bloodstream after administration.
Which route directly goes into the bloodstream?Parenteral Route of Medication
An intravenous route directly administers the medications to the systemic circulation. It is indicated when a rapid drug effect is desired, a precise serum drug level is needed, or when drugs are unstable or poorly absorbed in the gastrointestinal tract.
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