Skip to main content

Renin Angiotensin Mechanism.

Controlled Drug Delivery System: Introduction.

Introduction:

  • Oral route of drug administration is the most common, convenient, and  popular route of drug administration.  

  • There are various reasons for such popularity.  

  • The most important and common reasons for their popularity are the  convenience of administration, the ease of carrying, and the  ease of  preparation on an industrial scale. 

  • About 80% of the dosage forms sold in the market are tablet dosage forms. 

Limitations of conventional tablet formulations:

  1. The frequency of dose administration in a day is high.

  2. It is difficult to monitor the daily-dose.

  3. Chances of missing a dose are very high. 

  4. The careful calculation is required to prevent overdosing, as it is difficult to calculate the exact dose for a child or elderly patient who should not receive the normal adult dose.

  5. The drug goes to non-target cells and can cause damage; orally administered drugs must reach the circulatory bloodstream every time and pass through the liver.

  6. Thus, the drug is available at the sites that do not need it.  

  7. Low concentrations are not useful.  

  8. After oral administration, some of the dose may not be absorbed, some may be metabolized; hence, the amount of drug must be sufficient to produce its therapeutic action. 

  9. More of the drug is consumed, which is not at all necessary.

  10. Higher blood concentrations of the drug may cause adverse effects on the organs.

Bioavailability profile of drug after oral administration.

  • After oral administration of a  drug, the concentration of the  drug  increases gradually with time (absorption phase).

  • During this phase, absorption  >> elimination.

  • Therapeutic action starts when the concentration of the drug reaches the          minimum effective concentration (MEC).

  • Once the concentration reaches its peak level, the descending phase  starts (elimination phase); the metabolism and elimination is more than absorption in this phase. 

  • During this phase, elimination >> absorption.

  • The therapeutic effect is available as long as the concentration remains above the MEC.

  • The period during which the drug concentration remains above the MEC is referred to as the duration of action.

  • After the concentration falls below the MEC, a second dose is required to achieve continuous therapeutic action of the drug.

  • Maximum safe concentration (MSC) is the concentration of the drug above which the drug shows its adverse effects.

  • The area between MSC and MEC is called the therapeutic window, the drugs with a wider therapeutic window are safer than those with a smaller therapeutic window.

  • C max is the maximum concentration of a drug that can be achieved.

  • T max is the time taken by the drug to reach C max.

Commonly Asked Questions

  1. Write the limitations of conventional oral dosage forms.

  2. Explain the following terms with the help of a graph.

    1. MEC

    2. MSC

    3. C max

    4. T max

    5. AUC.

 

Labels:

Popular posts from this blog

Rate of Drying Curve.

  Definition Drying is defined as the removal of liquid from a product usually with application of heat. Rate of Drying Curve. Drying process can be divided into three periods Initial Adjustment Period. Constant drying rate period. First falling drying rate period. Second falling rate period. Initial Adjustment Period (A-B): Also called the “ Heating up” period . In this period the substance gets heat and increases in temperature. Drying has not yet started. Constant drying rate period (B-C): During this period the temperature of the solid and the rate of drying remain constant. The moisture evaporating from the surface is replaced by water diffusing from the interior of the solid at a rate equal t o the rate of evaporation.  The moisture content at the end of constant rate (point C) is referred to as the critical moisture content (CMC).  At CMC, dry spots start appearing and drying rate starts falling . First falling drying rate period (C-D): This period is also called ...
Read more

Heat Exchangers and Heat Interchangers.

  In pharmaceutical industries many types of equipments are used for transfer of heat, they can be classified as follows, Heat Exchangers. Heat Interchangers. Heat Exchangers: These devices are used for transferring heat from a fluid (Hot Gas or Steam) to another fluid (Liquid) through a metal wall. Heat Interchangers: These devices are used for transferring heat from a One liquid to another liquid or one gas to another gas through a metal wall. HEAT EXCHANGERS; The equipment used for heat transferring are known as heat exchangers. Some of the processes that involves heat transfer in pharmaceutical industries are: Preparation of starch paste (in steam jacketed kettle). Crystallization. Evaporation. Distillation.  Classification of heat exchangers On the basis of transfer of heat, heat exchangers are classified as: Direct transfer type:  The hot and cold fluids are separated by a metal wall through which the heat is transferred from hot fluid to cold fluid. E.g. shell and ...
Read more

Flash Distillation.

  Principle: When a hot mixture is allowed to enter from a high-pressure zone into a low pressure zone, the entire liquid mixture is suddenly vaporized. This process is known as flash vaporization .  During this process, the chamber is cooled.  The less volatile fraction is condensed and the more volatile component remains in the vapor phase .  This process requires time, hence liquid and vapor are kept in intimate contact until equilibrium is achieved. Flash distillation is also called equilibrium distillation because separation of two liquids takes place when liquid and vapor phases are at equilibrium. Equipment used for Flash Distillation: Construction: It consists of a pump, which is connected to a feed reservoir.  Pumps help in pumping the feed into the heating chamber.  The heating chamber is heat supplied by steam.  The other end of the pipe is directly introduced into the vapor-liquid separator through a reducing valve.  The vapor outlet...
Read more