Formulation factors affecting drug dissolution

1. Excipients                                                                           

are added to a formulation to provide certain function properties to the drug & dosage form. Some of these functional properties of the excipients are used to improve the compressibility of the active drug. Stabilize the drug from degradation, decrease gastric irritation, control the rate of drug absorption from the absorption site, increase drug bioavailability……………etc.

·    Tablet lubricants such as magnesium stearate may repel water and reduce dissolution when used in large quantities.

·    Low conc. of surfactants decrease the surface tension  and increase the rate of drug dissolution, whereas higher surfactants conc. Tend to form micelles with the drug cause ↓the dissolution rate

·     Large drug particles have a smaller surface area and

dissolve more slowly than small particles.

Table 1. effect of excipients on the pharmacokinetic parameters of oral drug products

Excipients                          example                                             KA         Tmax        AUC

Disintegration               Avicel                                                 ↑              ↓                 ↑ Lubricants                       Talc                                                    ↓              ↑                 ↓ Coating agent                   hydroxylpropylmethyl cellulose     --             --                 -- Enteric coat                      cellulose acetate phthalate               ↓             ↑                 ↓ Sustained-release            methylcellulose                                  ↓              ↑                 ↓ Agents

↓=decrease     ↑ =increase   -- = no effect   KA =absorption rate constant   Tmax= time for peak drug conc. In plasma   AUC = area under plasma drug conc. Curve.