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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.

 

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