Substances can get in the human body through miscellaneous means. Drugs have the right to be smoked, snorted, injected, swallowed (pills, capsules, liquids), or applied through transdermal way (applied come the skin).1,2 some substances deserve to be eaten, such together marijuana.3

The an approach by which a drug is administered, in addition to other factors, determines the rate of start of effects.4

Drugs undergo four stages within the body: absorption, distribution, metabolism, and also excretion. After a medicine is administered, that is took in into the bloodstream. The circulatory device then distributes the medicine throughout the body. Then it is metabolized by the body. The drug and its metabolites room then excreted.5,6

How a medicine travels through body


Step 1: Absorption

Absorption describes the movement of a medicine from its site of administration to the bloodstream.5 It occurs after a problem is administered, however there are several various methods in i m sorry someone deserve to use or abuse a substance that will affect how the drug is absorbed.

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The assorted routes of drug administration include:

Oral management – This has swallowing pills, drinking a liquid, or eating a substance. In this technique of administration, most of the absorption of the problem takes location in the tiny intestine.5 The drug will then relocate to the liver and also then back into the bloodstream to it is in transported to its destination.7 The liver and also intestinal walls metabolize plenty of drugs, lessening just how much gets to the bloodstream, a procedure called “the first-pass effect”, or “first happen metabolism”.5,7,8 because drugs ceded via various other routes such together injection don’t go through an initial pass metabolism, it might only take a lower dose than the dental dose to accomplish the intended effects (if that drug is significantly prone come the first-pass impact when provided orally). This is why a medical professional who is injecting a prescription may carry out a reduced dose 보다 if they were prescribing the same drug in pill form.5,7Subcutaneous Injection—A subcutaneous injection is an injection right into the fatty organization underneath the skin, which allows the problem to relocate to the capillaries or lymphatic vessels and into the bloodstream.7Inhalation (including smoking)—Vapor or smoke goes right into the lung to be soaked up into the bloodstream as rapidly as it would certainly if it to be injected. Smoking cigarettes produces really rapid high, and effects dissipate quickly. An instance of a rapid and short-lived high from smoking is crack cocaine. The effects are quick yet go far within 5 come 10 minutes.9 Transdermal administration—The misuse of medicine via this course is no as typical as oral management or injection. Building material that space administered this means may be done so with a patch applied to the skin, which allows the medicine to be took in into the bloodstream and also circulate transparent the body.11 an instance of a drug administered this means is the fentanyl patch.12
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Step 2: Distribution

Once the medicine is absorbed, it is carried through the body. It moves from the bloodstream to the tissues and also intracellular fluids and also binds come receptors. Distribution is reversible: molecules exit from the receptors have the right to travel ago to the bloodstream.5

It is this step, distribution, that can be partially responsible because that the unintended side effects of a drug. Together the drug is carried throughout the body, it can also negatively impact an organ, or organs, the is no the target body organ the drug is intended come reach.13

Before a medicine can get in the central worried system (CNS)–the mind and spinal cord–it need to pass with the blood-brain barrier. This is a network of tightly woven capillaries that stays clear of many international substances from reaching the brain. Countless substances room not may be to successfully penetrate the CNS.5,13

Drugs that do cross the blood-brain barrier (BBB) deserve to have miscellaneous effects, including the rush of euphoria or the “high” the is commonly connected with illegal drugs and also the nonmedical use of some medications. Repeated use of medicine that space able to overcome the BBB can also influence the brain in many other ways, such together making it hard to feeling pleasure from natural rewards (leading to continued, compulsive drug use) and causing problems with executive functioning (planning, making decisions, and also solving problems).14

Research has displayed that use of specific drugs, such as cocaine and methamphetamine, can even readjust the BBB’s role over time. Usage of this drugs can reason increased permeability that the BBB, making the a less effective barrier and making it much easier for toxins like viruses and bacteria to get in the brain. For example, in individuals who have actually HIV, the usage of stimulants might permit increased migration of HIV-infected leukocytes right into the brain, heightening the likelihood and severity that neuroAIDS.15

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Step 3: Metabolism

After the drug has actually been distrusted, the next phase is metabolism. This is where the drug is broken down. This take away place largely in the body largest interior organ, the liver. (Note: if the liver is the main site for drug metabolism, various other organs such together the kidneys, GI tract, and lungs may likewise perform metabolic functions.)13,16

During this phase, proteins called enzymes malfunction the medicine molecules, which creates metabolites. These metabolites room usually less energetic chemically than the original drug molecule yet may in some instances be same as powerful or even much more so.5,13

The process of enzymatic break down can do it simpler for the drug to it is in excreted, which is the final phase.13

Step 4: Excretion

The last phase the a drug within the human body is excretion. This is the procedure by i m sorry drugs and their metabolites leave the body, primarily via urine or feces.5,17 drugs may additionally be excreted in sweat, saliva, breast milk, or exhaled air. A substance might be excreted in that is altered, or metabolized, kind or excreted intact.17



Sakai, J. B.

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(2011). Practical pharmacology for the pharmacy technician, thing 3.