Extravascular routes of drug administration

Upon completion of this chapter, you will hove the ability to  

The gastrointestinal membrane separates the absorption site from the blood. Therefore, passage of drug across the membrane is a prerequisite for absorption. For this reason, drug must be in a solution form and dissolution becomes very critical for the absorption of a drug. The passage of 

The present discussion will deal with general principles that determine the rate and extent of 

8 mols of drug carried by portal circulation to liver 

Please note that a similar approach may be applied to determine pharmacokinetic parameters of drugs when any other extravascular route is used. 

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Important features of extravascular routes of drug administration... 

Determination of the area under the plasma concentration-4ime curve from extravascular route of drug administration... 

At 0 and >, X = 0 and Cp = 0 and at t= tmax (i e. peak time), X = (A)max and Cp = (Cp)max (i.e. peak plasma concentration or highest plasma concentration). Please note the difference between intra- and extravascular routes of drug administration with regard to the time at which the highest, or peak, plasma concentration occurs. 

Let us now explore the applications of these methods to calculate the MRT for another important pharmacokinetic model, namely the one-compartment model with extravascular route of administration. In the following discussion, though the oral route is specified in the derivations, the results apply to any other extravascular route of drug administration. For a one-compartment drug administered orally, the equation for mass of drug in the body (excluding the gastrointestinal tract, which is treated by... 

The IM and SC routes are by far the most frequently used extravascular parenteral routes of drug administration in farm animals. The less frequently used parenteral routes have limited application, in that they aim at directly placing high concentrations of antimicrobial agent close to the site of infection. These routes of administration include intra-articular or subconjuctival injection and intra-mammary or intra-uterine infusion. These local routes differ from the major parenteral routes in that absorption into the systemic circulation is not a prerequisite for delivery of drug to the site of action. The combined use of systemic and local delivery of drug to the site of infection represents the optimum approach to... 

Regardless of the route of drug administration, the "average" plasma concentration at steady state is influenced by the dose administered, the fraction of the administered dose that reaches the general circulation (for extravascular routes), the systemic clearance of the drug and the chosen dosing interval. 

Several routes of drug administration, including extravascular (oral, intramuscular, subcutaneous, transdermal, inhalation, etc.) and intravascular routes (intravenous and intra-arterial), are used to deliver drugs into the body. Oral administration of drugs is the most common route because it is... 

Bredberg, U. and Karlsson, M.O. (1991) In vivo evaluation of the semisimultaneous method for bioavailability estimation using controlled intravenous infusion as an extravascular route of administration. Biopharmaceutics el Drug Disposition, 12, 583-597. 

For a drug administered by the oral, or any other extravascular, route of administration, the apparent volume of distribution cannot be calculated from plasma drug concentration data alone. The reason is that the value of F (the fraction of administered dose that reaches the general circulation) is not known. From Eqs 6.7 and 6.8 ... 

For all commonly used routes of administration except intravenous, the drug must dissolve in body fluids and diffuse through one or more membranes to enter the plasma. Thus, all routes except intravenous are classed as extravascular routes, and absorption is defined as appearance of the drug in plasma. 

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