Explain the types and levels of drug targeting

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Q. Explain the types and levels of drug targeting. (5marks)

Targeting drug to a specific area not only increases the therapeutic
efficacy of drugs also it aims to decrease the toxicity associated with drug to
allow lower doses of the drug to be used in therapy. For the fulfilment of such
conditions, two approaches are used:

1. Passive targeting
2. Active targeting


Passive targeting:

It refers to the accumulation of drug or drug carrier system at a specific site
such as anti-cancerous drug. Hence, in case of cancer treatment the size and
surface properties of drug delivery nano-particles must be controlled
specifically to avoid uptake by the reticulo-endothelial system (RES) to
maximize circulation times and targeting ability.


Active targeting

It involves the modification or functonalization of the drug carriers so that
the contents are delivered exclusively to the site corresponding to which the
carrier is architected.

This active targeting approach can be further classified into three different
levels of targeting which are:

1) First order targeting

2) Second order targeting

3) Third order targeting




1) First order targeting:
It refers to restricted distribution of the drug carrier systems to the
capillary bed of a predetermined target site, organ or tissue.
Example: Compartmental targeting in lymphatics, peritoneal cavity,
plural cavity, cerebral ventricles and eyes, joints.

2) Second order targeting:
It refers to selective delivery of drugs to specific cell types such as

tumour cells and not to the normal cells.
Example: Selective drug delivery to kupffer cells in the liver.

3) Third order targeting:
It refers to drug delivery specifically to the intracellular site of targeted

Example: Receptor based ligand mediated entry of a drug complex into
a cell by endocytosis.