Drugs administered intravenously have 100 percent bioavailability. Prostaglandins are an exception since they are inactivated or digested in the lungs, therefore their bioavailability after I/V injection may be nil. Drugs that are absorbed from the GI tract have variable degrees of absorption. The extent to which a drug is absorbed is called its oral availability. Oral drugs range in availability from 10 to 90 percent. Bioavailability depends on several factors such as solubility of the drug, rate and extent of intestinal wall permeability, and presence of any chemical changes (e.g., oxidation) that might affect activity or absorption.
Answer: B. Bioavailability refers to the amount of drug that reaches the systemic circulation following administration by any route. The bioavailability of a drug can be expressed statistically as the ratio of the area under the plasma concentration-time curve for the administered dose to the total area under the plasma concentration-time curve for a standard dose. For example, if the area under the plasma concentration-time curve for a 0.5 mg/kg IV dose of drug X is 1.0 micrograms/ml x min and the area under the plasma concentration-time curve for a 2 mg oral dose is 2.0 micrograms/ml x min, then the bioavailability of drug X is 50 percent.
The proportion of a medicine delivered that enters the systemic circulation and is therefore accessible for distribution to the target site of action is referred to as bioavailability. Drugs that are administered through direct IV injection are considered to have 100% bioavailability. If drugs are absorbed from the gastrointestinal tract, they will have a variable degree of absorption, depending on how they are formulated (e.g., tablets, capsules, liquids) and whether they are taken with or without food. The rate-limiting step in the absorption process is often the release of the drug from the formulation into the small intestine. However, if drugs are extensively metabolized before they reach the intestinal wall, then they will also have low bioavailability. In general, oral medications have higher bioavailability than injected ones because some of them are absorbed by the intestinal wall and enter the blood stream directly.
Bioavailability can be expressed as a percentage. For example, the bioavailability of orally administered acetaminophen is approximately 50%. This means that that drug will be available to provide pain relief and other effects when taken by an individual after it has been absorbed from the stomach. Acetaminophen is one of the most widely used medications in the world. It is found in many over-the-counter and prescription medications for pain, fever, inflammation, and nausea/vomiting. Oral contraceptives contain both estrogen and progesterone.
This is seen in the diagram to the right. The percentage of an oral medicine that enters the circulatory system is referred to as the drug's bioavailability. For oral drugs, bioavailability will be less than 100% for any of the following reasons: Oral medications absorb and distribute more slowly than IV drugs. This is called absorption/distribution phase limitations. Medications absorbed but not distributed by body tissues or stored in these tissues are eliminated primarily through urine. These medications can still have an effect on blood clotting time or other aspects of pharmacology, but they cannot be detected in plasma samples because they have been removed from the body. Oral medications also interact with food, beverages, or other medications in a way that reduces or eliminates their effectiveness. For example, caffeine increases the activity of cytochrome P-450 enzymes in the liver, which can lead to increased metabolism of certain medications. The presence of alcohol in the bloodstream may cause similar effects.
IV medications do not enter the circulation bound to proteins like hormones do when taken by mouth. Thus, they go directly into the blood stream where they can reach all parts of the body without being restricted by tissue barriers. Because only the soluble portion of a medication is available for absorption, it is important that it is dissolved completely before it is injected. If it isn't, the undissolved fraction will remain in suspension and be delivered to another injection site or stomach cavity. This can have an adverse effect on its therapeutic effect or possible side effects.
Bioavailability refers to the extent to which a chemical or medicine becomes totally accessible to its designated biological destination(s). In other words, it describes how much of the drug is available for absorption into the body after oral administration.
The bioavailability of drugs can be affected by many factors. These include the type of drug, dose, how it is administered, food interactions, etc.
Generally, an orally administered drug will have greater bioavailability than one given by injection. This is because the digestive system reduces the concentration of any substance that cannot pass through the intestinal wall. Thus, increasing the distance between the site of action and the site of absorption (by using intravenous injections, for example) decreases the amount of drug that reaches the bloodstream and tissues. Drugs with very low bioavailability include colloidal particles such as gold and silver. Their small size makes them difficult for the digestive system to break down and absorb into the blood stream.
The bioavailability of a drug can also be increased by forming stable suspensions or solutions of it. For example, the use of certain surfactants can help dissolve drugs that would not otherwise be soluble in water. The resulting solution is then dispersed into some kind of vehicle, such as oil or emulsion-based products.
Bioavailability is a measure of the pace and proportion of a drug's initial dosage that effectively reaches the site of action or the physiological fluid domain from which the drug's intended targets have unrestricted access. Formalized paraphrase The majority of the time, bioavailability is defined as the proportion of.../span >
The bioavailability of a drug can be affected by many factors, such as its solubility in water, how it is absorbed into the bloodstream, how quickly it is cleared from the body, and any potential interactions with other drugs or substances of abuse. Approximately 80% of orally administered drugs reach the systemic circulation in the form of their free (unconjugated) forms.
For therapeutic agents, the goal is to maximize exposure to the target tissue while minimizing exposure to extraneous tissues. This can be achieved through modifications to the formulation or delivery route of the drug. For example, oral formulations should be designed to increase absorption efficiency by using lipid-based formulations or mucoadhesive polymers. Drugs that are injected intramuscularly or intravenously should not contain particles smaller than 10 microns due to the risk of pulmonary embolism. Drugs that are inhaled should have an aerosol particle size less than 5 microns.
For diagnostic agents, the goal is to enhance uptake into specific cells or tissues. This can be achieved through modifications to the probe itself (e.g., modification with antibodies that recognize cell surface receptors).
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