Drug Latentation,

                                  Drug latentation

It is chemically transforming an active drug to an in active form which is converted by virtue of chemical or enzymatic attack or both to pattern drug with in body prior to exhibiting its pharmacological action

The latent drug and analogs are structurally similar to prototype drug but biological properties of those compounds are different form parent drug in regards to potency, drug action, therapeutic index and bioavailability.

Latent drugs can be divided into prodrugs and targeted drugs.

1.  Prodrug:-

Any compound which under goes biotransformation into active compound prior to exhibiting its pharmacological effect is prodrug.

It chemically modified form of drug which has superior delivery properties. It may be considered non protective group utilized in a non protective group utilized or eliminate undesirable properties in pattern drug.

Prodrug can be of 2 type

       a)  Carrier linked pro drug:-

It is compound that contains active drug linked to a carrier active drug linked to a carrier group that can be removed enzymatically such as an ester which is hydrolyzed to an active carboxylic acid containing drug.

The carrier group must be non toxic and biologically inactive when detached from drug. It should be removed easily to allow active drug to be released efficiently.

E.g. in Mannich bases of carbamazepine prepared has more than 104 fold greater solubility tan parent drug.

Mutual Prodrugs: In this case carrier may also have some activity. E.G, Anti neoplastic agent, Estramustrin is linked to normustard through a carbamate linkage.

2. Bio precursors:-

Bio-precursor results from molecular modification of active principle itself.

It does not contain temporary linkage between active moiety and carrier.

Bio-precursor  prodrug relay on metabolism to introduce functionality.

This type of activation involves, oxidative activation, reductive activation and in some rases chemical activation.

E.g. Sulindac, a non steroidal anti inflammatory bio-precursor gets converted to the sulphide metabolite (active drug )via sulphon

E.g. Biotransformation of benzodiazepines bio precursor to active alprazolam (anti depressant)

Advantages:-

• Alteration of drug pharmacokinetics bring about increased drug availability
• Improvement of solubility and stability
• Decreased toxicity and adverse reaction
• Increased site specifity
• Increased duration of action
• Increased absorption
• Increased in pain at site of injection if agent is given parent rally

   
Disadvantages:-

• Pro drug may generate toxic metabolites which are not generated by parent drug
• Inert carrier moiety could not remain inert and leads to formation of toxic metabolites.
• Te pro drug or /and carrier moiety generate suc metabolite which alter pharmacokinetic feature of parent drug by either introducing with active drug for binding with plasma protein

3.  Target drug delivery System :- (TDDS):-

These are latent forms of bioactive substance prepared by associating them with carries, capable of transporting those drugs from site of application selectively to their target cells.

Advantages:-

• Ensure specific interaction of drugs with their ,there by decreasing adverse reaction which may result from association with non targeted cells,
• Helps to lower down therapeutic dose of drug. target drug delivery system has been used for chemotherapy of cancer and certain prozoal diseases