Practically speaking, this means that if taken orally, a drug that is a weak acid will be absorbed primarily in the acidic environment; whereas, a drug that is a weak base will be absorbed in the alkaline environment small intestines.
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In the stomach, there is an acidic environment or low pH due to the presence of hydrochloric acid. When weakly acidic drugs like barbiturates, they are in unionized form in the stomach because of the acidic environment. So, there is a better absorption of drug in the stomach. In the intestine, there is alkaline environment.
Ionized (or charged) drugs are not absorbed as efficiently as un-ionized drugs are. Practically speaking, this means that if taken orally, a drug that is a weak acid will be absorbed primarily in the acidic environment; whereas, a drug that is a weak base will be absorbed in the alkaline environment small intestines.
Aug 29, 2021 · Weakly acidic drugs are easily absorbed in a low pH medium such as in the stomach. Whereas weakly basic drugs are not absorbed until they reach the higher pH medium in the small intestine. ... Lin L, Wong H. Predicting Oral Drug Absorption: Mini Review on Physiologically-Based Pharmacokinetic Models. Pharmaceutics. 2017 Sep 26; 9 (4) [PMC free ...
However, whether a drug is acidic or basic, most absorption occurs in the small intestine because the surface area is larger and membranes are more permeable (see Oral Administration Oral Administration Drug absorption is determined by the drug’s physicochemical properties, formulation, and route of administration. Dosage forms (eg, tablets, capsules, solutions), …
Other factors that also impact drug absorption include the following: Physiologically, a drug’s absorption is enhanced if there is a large surface area available for absorption (e.g. villi/microvilli of intestinal tract) and if there is a large blood supply for the drug to move down its concentration gradient.
Note, that if a drug is administered intravenously (placed directly into the blood stream), the need for absorption is bypassed entirely. For drug absorption to occur, a drug must cross biologic barriers (e.g. epithelial/endothelial cells, etc.).
The presence of food/other medications in the stomach may impact drug absorption – sometimes enhancing absorption and other times forming insoluble complexes that are not absorbed (it depends on the specific drug). Some drugs are inactivated before they can be absorbed by enzymes, acidity, bacteria, etc.
Absorption can be accomplished by administering the drug in a variety of different ways (e.g. orally, rectally, intra-muscularly, subcutaneously, inhalation, topically, etc.). Note, that if a drug is administered intravenously (placed directly into the blood stream), the need for absorption is bypassed entirely.
Before drugs can be clinically effective, they must be absorbed. Absorption is the process of a drug moving from its site of delivery into the bloodstream. The chemical composition of a drug, as well as the environment into which a drug is placed, work together to determine the rate and extent of drug absorption .
This simulation allows learners to apply the Henderson-Hasselbach equation to calculate percent ionization of a drug based upon its chemical properties (e.g. pK a) and the surrounding environment.
Drug-specific factors that affect drug absorption include the physicochemical and the pharmaceutical variables of drugs. One example of the physicochemical variables is the drug solubility and the effect of pH and pKa in which most drugs act as weak acids or bases in solutions in both ionized and non-ionized forms.
The study of drug absorption, distribution, metabolism, excretion, and how the body affects the drug is known as pharmacokinetics. The application of pharmacokinetic methods to ensure patients are treated safely and effectively is known as clinical pharmacokinetics. The introduction of pharmacokinetics as a discipline has facilitated ...
The application of pharmacokinetic methods to ensure patients are treated safely and effectively is known as clinical pharmacokinetics. The introduction of pharmacokinetics as a discipline has facilitated the development of rational drug therapy, the understanding of drug action and metabolism, understand of concentration-effect relationship, ...
The bioavailability of a drug product is known as the rate and extent of its absorption. A better understanding of the drug absorption process and affecting factors play an important role in achieving better bioavailability and thus better therapeutic effect.[3] .
Active diffusion is an energy-consuming system that is essential for GI absorption; and renal and biliary excretion of many drugs. This process facilitates the absorption of some lipid insoluble drugs, which mimics natural physiological metabolites such as 5-fluorouracil from the GI tract.
P-gp (also known as MDR1) is an energy-dependent efflux transporter that facilitates the secretion of molecules back into the intestinal lumen, thereby restricting overall absorption . Facilitated diffusion is another transporter system that appears to play a minor role in terms of drug absorption.
The rate of dissolution is the amount of the solid substance that turns into a solution per time at standard conditions of pH, solvent composition, and temperature and, at a constant surface area. For example, cisapride, a gastroprokinetic agent, has a low aqueous solubility.
Food, especially fatty food, slows gastric emptying (and rate of drug absorption), explaining why taking some drugs on an empty stomach speeds absorption. Drugs that affect gastric emptying (eg, parasympatholytic drugs) affect the absorption rate of other drugs. Food may enhance the extent of absorption for poorly soluble drugs (eg, griseofulvin ), ...
Controlled-release forms are designed to reduce dosing frequency for drugs with a short elimination half-life and duration of effect. These forms also limit fluctuation in plasma drug concentration, providing a more uniform therapeutic effect while minimizing adverse effects. Absorption rate is slowed by coating drug particles with wax or other water-insoluble material, by embedding the drug in a matrix that releases it slowly during transit through the gastrointestinal tract, or by complexing the drug with ion-exchange resins. Most absorption of these forms occurs in the large intestine. Crushing or otherwise disturbing a controlled-release tablet or capsule can often be dangerous.
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