Pharmaceutics Flashcards
Hydrophobic Solutes
Cl, F, CH2, CH3, OCH2CH3
Hydrophilic Solutes
OH, COO-, NH3+
What is the flickering cluster model?
Involves clusters of H-bonded “ice-like” water within pools of unbound (i.e. no H-bonding) water.
What’s a Real solution?
Interactions occur between dissolved solutes which reduce the effective concentration
What’s an ideal solution?
There are no interactions between dissolved solutes.
Equation for activity coefficient
Activity/Concentration
Weakly Acidic Drugs Solubility Equation
pH=pKa + Log S-So/So
Weakly Basic Drugs Solubility Equation
pH=pKa + Log So/S-So
What’s the isoelectric point?
Isoelectric point is the pH at which the drug carries no net electric charge.
What’s Partitioning?
Partitioning is the distribution (or moving) of a substance between two miscible phases.
Partition coefficient equation
Co/Cw
Co=Conc. in organic phase
Cw=Conc. in aqueous phase
Partition of weak acid equation
Log (P/Papp -1) = pH-pKa
Partition of a weak base equation
Log (P/Papp -1)=pKa-pH
What does polydisperse mean?
Polymers exist within a range of different molecular weights
Methods of determining polymer molecular weight?
- Number average molecular weight (Mn)
- Weight average molecular weight (Mw)
A viscosity average molecular weight (Mv)
Mn>Mv>Mw
Techniques to characterise polymers
- Light scattering techniques
- Viscosity techniques
- Analytical ultracentrifugation
- Gel electrophoresis
- NMR
Water soluble polymers
Able to:
Increase solvent viscosity
Swell
Therefore good suspending agents
Velocity of penetration
S=kM-A
k and A constant
M-Polymer molecular weight
Viscosity and molecular weight
n=KMa
k and a are constants
M-Molecular weight
Gels
Type 1: Irreversible eg contact lenses
Type 2: Heat reversible eg agar
Serendipituous
A chance discovery eg alginate for heartburn, penicillin etc
Gavison Excipients
Carbomer: Suspending agent
Parahydroxybenzoate: Antimicrobial preservative
Sodium Saccharin: Sweetener
Sodium Hydroxide: pH adjuster (due to acidic parahydroxybenzoate)
Containers
Glass
High-density polyethylene
Polyethylene terephthalate
(Greater potential for parabens absorption as you go down)
Why coat tablets?
Protect from environement
Mask a taste
Easier to swallow
Identification
Film Coating
Polymer 10%
Solvent 90%
Drying process removes solvent and leaves behind film.
Cellulose and Cellulose ethers (Immediate release)
Enteric Coating
Cellulose acetate phthalate
Methacrylic acid copolymers
Omeprazole:
Gelatin capsule dissolves, enteric coat on granules doesnt
Granules can pass through pyloric sphincter
MUPS
Multiple Unit Pellet System
Enteric coated particles compressed into a tablet
Mathacrylic acid copolymers
