You are on page 1of 3 Search inside document Oral dosage forms are widely used due to the convenience of drug administration. This can be explained by the LADMER system which includes liberation of a drug from the dosage form, absorption of the drug, distribution of the drug, metabolism of the drug, excretion of the drug and finally the response. Biopharmaceutics deals with the study of physiochemical and physiological factors that influence the liberation and absorption of drugs from different dosage forms. Pharmacokinetics deals with the absorption, distribution, metabolismn and excretion of a drug; the study of drug response is known as pharmacodynamics.
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You are on page 1of 3 Search inside document Oral dosage forms are widely used due to the convenience of drug administration. This can be explained by the LADMER system which includes liberation of a drug from the dosage form, absorption of the drug, distribution of the drug, metabolism of the drug, excretion of the drug and finally the response.
Biopharmaceutics deals with the study of physiochemical and physiological factors that influence the liberation and absorption of drugs from different dosage forms.
Pharmacokinetics deals with the absorption, distribution, metabolismn and excretion of a drug; the study of drug response is known as pharmacodynamics. In simple terms, biopharmaceutics is what the pharmceutical scientist does to the drug, pharmacokinetics is what the body does to the drug, and pharmadynamics is what the drug does to the body.
Optimisation of biopharmaceutics and pharmacokinetic properties plays a significant role in the development of new drugs. Drug solubility and permeability are the two most important biopharmaceutical properties that influence drug absorption and oral bioavailability.
This led to the biopharmaceutics classification system BCS , which classifies drugs into four classes based on their aqueous solubility and permability. Drugs with good aqueous solubility and membrane permeability generally show good oral absorption and bioavailability provided the drug is stable in the gastrointestinal tract and does not undergo first-pass metabolism in the liver.
Several technologies have emerged to address the poor solubility and permeability of drugs. The important pharmacokinetic parameters that influence the biological performance of dosage forms are volume of distribution, half-life, clearance and fraction absorbed.
Clearance and fraction absorbed influence the bioavailability, which in turn determines the dose of a drug. Depending on how the drug is distributed into the body, different mathematical models can be used to characterise the drug disposition and estimate the pharmacokinetic parameters.
In oral modified-release systems when or where the drug is released in the gastrointestinal tract is modified. These systems can be broadly divided into delayed-release systems aned extended release systems.
In the case of delayed-release systems, the drug release is delayed but not sustained. In the case of extended-release systems, the drug release is sustained or controlled with respect to time, thus reducing the frequency of administration.
Liberation is the first step in the process by which medication enters the body and liberates the active ingredient that has been administered. The pharmaceutical drug must separate from the vehicle or the excipient that it was mixed with during manufacture.
Factors such as poor compound solubility, gastric emptying time, intestinal transit time, chemical instability in the stomach, and inability to permeate the intestinal wall can all reduce the extent to which a drug is absorbed after oral administration. Drugs that absorb poorly when taken orally must be administered in some less desirable way, like intravenously or by inhalation e.
Routes of administration is an important consideration Distribution The compound needs to be carried to its effector site, most often via the bloodstream. From there, the compound may distribute into muscle and organs, usually to differing extents. After entry into the systemic circulation, either by intravascular injection or by absorption from any of the various extracellular sites, the drug is subjected to numerous distribution processes that tend to lower its plasma concentration.
Distribution is defined as the reversible transfer of a drug between one compartment to another. Some factors affecting drug distribution include regional blood flow rates, molecular size, polarity and binding to serum proteins, forming a complex. Distribution can be a serious problem at some natural barriers like the bloodbrain barrier.
Metabolism Compounds begin to break down as soon as they enter the body. The majority of small-molecule drug metabolism is carried out in the liver by redox enzymes, termedcytochrome P enzymes. As metabolism occurs, the initial parent compound is converted to new compounds called metabolites. When metabolites are pharmacologically inert, metabolism deactivates the administered dose of parent drug and this usually reduces the effects on the body.
Metabolites may also be pharmacologically active, sometimes more so than the parent drug. Excretion Compounds and their metabolites need to be removed from the body via excretion, usually through the kidneys urine or in the feces.
Unless excretion is complete, accumulation of foreign substances can adversely affect normal metabolism. There are three main sites where drug excretion occurs. The kidney is the most important site and it is where products are excreted through urine. Biliary excretion or fecal excretion is the process that initiates in the liver and passes through to the gut until the products are finally excreted along with waste products or feces.
The last main method of excretion is through the lungs e. Excretion of drugs by the kidney involves 3 main mechanisms: Glomerular filtration of unbound drug. Filtrate fold concentrated in tubules for a favorable concentration gradient so that it may be secreted by passive diffusion and passed out through the urine. The route of administration critically influences ADME. The LADMER System In the relationship between dose and effectiveness, or doseresponse, not only the amount of drug administered and the pharmacologic effect of the drug are of importance; many other factors are responsible for the entrance of a drug into the body.
These factors are based on the physical and chemical properties of the drug substance and of the drug product. What happens to the active ingredient in the body after administration of a drug product in its various dosage forms? This entire cycle of processes is Related Interests.
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