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Parentral controlled Release Drug Delivery Systems


History of development

I. The first attempts at parentral therapy in ancient times apparently were blood transfusions tried by Egyptians, but these efforts failed.
The first parentral blood transfusions to be performed without any doubt of its validity was in 1654 by Francesco Folli.

II. Major Routes of Parentral Administration

Biopharmaceutics of sustained / controlled release parentral drug products

Polymorphism can be modify drug solubility ,hence drug dissolution rate can be modify. Most of organic substances exist in more than one crystal form called as polymorphs
pH of formulation :-
PH may affect drug absorption . For strongly acidic drugs or basic drugs, the vehicle pH will have little effect on the degree of ionization and therefore solubility of the drug.
In contrast, the vehicle pH has a significant effect on the degree of ionization of a weakly acidic or basic drug.
pKa of drug :-
A weakly acidic or basic drug can exist in either the ionized or unionized form depending on the pKa of the drug and pH of the medium. For acidic drugs ,the degree of ionization increases at pH values above the pKa and drug will exist predominately in the ionized form.
In contrast , basic drugs will exist predominately in the ionized form at pH’s above their pKa .Thus the solubility and dissolution rate of such drugs can be altered by changing the PH of the formulation.
Viscosity of the medium :
Viscosity can alter drug dissolution rate by affecting the diffusion coefficient of a drug molecules in accordance with the Stokes- Einstein equation.

.Biological and synthetic macromolecules :-

A variety of biological macromolecules have been tried as carriers for drug delivery.
Serum albumin can be polymerised and cross-linked to form micro beads to entrap steroid hormone ,anticancer drugs ,dyes and peptides .
Similar beads containing insulin. When implanted subcutaneously were found to sustain the release of this hormone in diabetic animals for longer than 2 months.
Other examples of biological carriers are DNA, lipoproteins , antibodies and dextrans . They are directed to the lysosomes following entry into cells by endocytosis , pinocytosis or phagocytosis.