Controlled Drug Delivery System: Advantages, Disadvantages, Selection of Drug Candidates.

 

Introduction:

• Controlled drug delivery is one which delivers the drug at a predetermined rate, locally or systemically, for a specified period of time.

• The rationale of controlled release dosage form can be summarized as below:

• To provide a location-specific action within the GIT.

• To avoid an undesirable local action within the GIT.

• To provide a programmed drug delivery pattern.

• To increase the rate and extent of absorption/bioavailability.

• To extend the duration of action of the drug.

Advantages of Controlled Drug Delivery Systems:

1. Maintains the drug level within the desired range.

2. Useful for delivery of ‘difficult’ drugs: the slow release of water-soluble drugs, and/or fast release of poorly soluble drugs,

3. Reduces dosing frequency,

4. Avoids over or underdosing,

5. Prevention or reduction of side effects,

6. Reduction in total health care cost,

7. Improved efficacy in the treatment,

8. Reduction in adverse side effects and improvement in tolerability

9. Improved patient compliance,

10. Uses less amount of total drug,

11. Minimizes or removes local or systemic side effects.

12. Minimal drug accumulation on chronic usage

13. Cures or controls the condition more promptly

14. Reduces the fluctuation in drug level

15. Improves the bioavailability of some drugs.

Disadvantages of Controlled Drug Delivery Systems:

1. May be costly,

2. Unpredictable and often provide poor in-vitro – in-vivo correlations,

3. May cause dose dumping, if the release design is failed,

4. Provides less scope for dosage adjustment,

5. May increase the first pass clearance,

6. Poor systemic availability in some cases,

7. Effective drug release period is influenced and limited by the gastric residence time.

8. All drugs are not suitable for formulating into ER dosage form.

Selection of Drug Candidates for Controlled Drug Delivery Systems:

• All the drugs cannot be formulated as their controlled release dosage forms. 

• A drug must have the following characteristics for the formulation of controlled release dosage forms.

Parameter	Preferred Value.
Molecular weight/ size	< 1000
Solubility	> 0.1 μg/ml for pH 1 to pH 7.8
Pka Non ionized moiety	> 0.1% at pH 1 to pH 7.8
Apparent partition coefficient	High
Absorption mechanism	Diffusion
General absorbability	From all GI regions.
Release	Should not be influenced by pH and enzymes

• Characteristics that may make a drug unsuitable for Control release dosage form,

• Short elimination half-life

• Long elimination half-life

• Narrow therapeutic index

• Poor absorption

• Active absorption

• Low or slow absorption

• Extensive first pass effect

Commonly Asked Questions.

1. What is a Controlled Drug Delivery System? Give its advantages and disadvantages.

2. Give its advantages and disadvantages of Controlled Drug Delivery System. Discuss which drug candidates are suitable for the Controlled Drug Delivery System?