Simple Pharmanotes

  Drug distribution: The reversible transfer of a drug between the blood and the extravascular fluids and tissues of the body.  Volume of Distribution: A hypothetical volume of body fluid into which a drug is distributed.  The Volume of distribution (VD), also known as the apparent volume of distribution, is used to quantify the distribution of a drug between plasma and the rest of the body after oral or parenteral dosing.  It is called the Apparent Volume because all parts of the body equilibrated with the drug do not have equal concentration. It is defined as the volume in which the amount of drug would be uniformly distributed to produce the observed blood concentration. The apparent volume of distribution is a proportionality constant relating the plasma concentration to the total amount of drug in the body. XαC X = VdC Vd = X/C Apparent volume of distribution = amount of drug in the body/ plasma drug concentration . It is expressed in liters or liters /kg body weight . Apparent v

  Drug distribution: The reversible transfer of a drug between the blood and the extravascular fluids and tissues of the body.  Drugs come into the circulation after absorption. From plasma, drugs have to cross the capillary membrane to come to interstitial space. And then need to cross the cell-membrane to enter into the intracellular fluid. Distribution is a passive process, for which, the driving force is concentration gradient between the blood and the extravascular tissues.  The process occurs by diffusion of free drugs only until equilibrium is achieved .  As the pharmacological action of a drug depends upon its concentration at the site of action, distribution plays a significant role in the onset, intensity and sometimes duration of drug action. FACTORS AFFECTING DISTRIBUTION OF DRUGS: Tissue Permeability of the Drug Physicochemical Properties of the drug like Molecular size, pKa and o/w Partition coefficient. Physiological Barriers to Diffusion of Drugs.  Organ / Tissue Siz

  Absorption of drugs by Non per Oral Route. Movement of the unchanged form of drug molecules from site of administration to systemic circulation is called absorption. Non-per oral absorption indicates drug administration routes other than the oral route, which bypasses the GIT & enters the systemic circulation. Some of the non-oral absorptions are discussed here: Buccal-Sublingual Administration: Buccal Route :  The medication is placed b/w cheek & the gum.  They are absorbed by passive diffusion. Sublingual Route:  The drug is placed under the tongue & allowed to dissolve.  They are absorbed by carrier-mediated transport. Advantages - Rapid absorption. No first-pass hepatic Metabolism. No degradation of drugs. Disadvantages limited mucosal surface area Concern for taste & discomfort of the medication. Factors to be Considered: Lipophilicity of drugs. Salivary secretion. pH of the saliva. Binding of the drug to the oral mucosa Thickness of oral mucosa epithelium. Examp