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8 Cards in this Set
- Front
- Back
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How do we get a solution into a solvent ?
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Based on the solubility, after placing a solute (drug) is in a solvent in which the drug is soluble, the drug’s/ solute’s intermolecular forces of attraction overcomes by forces of attraction between the drug/solute and solvent molecules. This attraction force helps break the solute- solute interaction forces and the solvent-solvent forces to achieve the solute-solvent attraction, which leads to form a solution.
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What are the Factors affecting the rate of dissolution ?
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The surface area (A) of the particle (size of particle
solubility temperature Dissolution rate constant PH, |
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What are the Factors that influence in Solubility ?
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Chemical properties
Temperature Molecular structure of solute Particle size |
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What happen for week acidic drugs when decrease the PH of the solution ?
think of absorption , ionisation , precipitation |
• For a solution of weakly acidic drug/salt: reduction in pH causes to increase the unionised part and precipitation occurs
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What happen for week basic drugs when increase PH of the solution ?
think of absorption , ionisation , precipitation |
For a solution of weakly basic drug/salt: increase in pH (by the addition of alkali) causes to increase unionisation part and precipitation occurs.
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How to determine the solubility
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A specific amount of solute (drug) is dissolved in a particular type of solvent (provided that the solute is soluble in the solvent) in a controlled temperature
• A saturated solution must be obtained • Remove the undissolved solutes form the solution by filtration. • Analyse the solution by HPLC, UV etc to determine the amount of drug dissolved in the solvent. |
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How can we increase the solubility of solute ?
4points |
1. Salt form of a drug:
2. •Addition of co-solvents: 2nd or 3rd solvent 3. •Addition of surfactants: reduce interfacial tension and forms micelles in solution above critical micelles conc (CMC) • 4. Structure modification –Add more polar groups for hydrogen bonding –Add ionizable group –Construct a pro-drug: a drug that is inactive when administered; however, becomes activated in the body by chemical/enzymatic processing |
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what is the relation between Pka and PH in terms of ionisation and unionisation for week acid ?
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for week acid , the particles are unionised when the PH is lower the PKa up to two degrees . the particles are completely ionised when the PH is grater than two degrees of PKa
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