Pharmaceutics is the second big subject in Pakistani pharmacist papers. These notes cover the definitions, tests and excipient roles examiners return to.
How this book helps in the exam
- Definitions of physical pharmacy terms and the laws behind them.
- Excipients and what each one does in a formulation.
- Quality tests for tablets, capsules and sterile products.
- Stability, packaging and storage questions.
What the book covers
12 high-yield topics. Each has the points most often examined and links to practise them.
1Solubility and dissolution
- Noyes-Whitney: dissolution rate rises with surface area and solubility and falls with layer thickness.
- Reducing particle size increases dissolution of poorly soluble drugs.
- Salt forms, cosolvents and surfactants improve solubility.
- Polymorphs differ in solubility; the metastable form dissolves faster.
2Rheology
- Newtonian fluids (water, simple syrups) have constant viscosity.
- Pseudoplastic flow (shear thinning) is typical of polymer solutions.
- Dilatant flow (shear thickening) occurs in concentrated suspensions.
- Thixotropy is gel-to-sol change on shaking and recovery on standing, ideal for suspensions.
3Micromeritics and powder flow
- Angle of repose below about 30° means good flow.
- Carr's index and Hausner ratio use bulk and tapped density to predict flow.
- Glidants such as colloidal silica improve flow.
- Particle size is measured by sieving, microscopy or laser diffraction.
4Surface phenomena and emulsions
- HLB of 3–6 favours water-in-oil emulsions; 8–18 favours oil-in-water.
- Creaming is reversible; cracking (coalescence) is not.
- Critical micelle concentration is where surfactant molecules start forming micelles.
- The dilution test shows the external phase of an emulsion.
5Suspensions
- Stokes' law: settling rate rises with particle size and density difference, and falls with viscosity.
- Flocculated suspensions settle fast but redisperse easily.
- Deflocculated suspensions settle slowly but can form a hard cake.
- Suspending agents raise viscosity; wetting agents help hydrophobic powders disperse.
6Tablets
- Binders hold granules together; disintegrants (starch, croscarmellose) break tablets apart.
- Lubricants such as magnesium stearate reduce sticking but slow dissolution if overused.
- Capping and lamination often come from trapped air or too many fines.
- Wet granulation suits most drugs; direct compression needs good flow and compressibility.
7Tablet quality tests
- Friability should usually be no more than 1% weight loss.
- Disintegration: uncoated tablets typically within 15 minutes, film-coated within 30.
- Weight variation and content uniformity confirm dose consistency.
- Dissolution testing uses basket or paddle apparatus.
8Capsules and coatings
- Hard gelatin capsules hold powders; soft gelatin capsules hold liquids and oils.
- Enteric coatings dissolve at intestinal pH and protect acid-labile drugs.
- Film coating masks taste and protects from moisture.
- Sugar coating is bulky and slow compared with film coating.
9Sterile products
- Parenterals must be sterile, pyrogen-free and particle-free.
- Moist heat at 121 °C for 15 minutes is the standard autoclave cycle.
- Heat-sensitive solutions are filter-sterilised through 0.22 micron filters.
- Pyrogens are destroyed by dry heat (depyrogenation), not by autoclaving.
10Semisolids and suppositories
- Ointments are greasy and occlusive; creams are emulsions that rub in easily.
- Pastes contain a high proportion of powder.
- Cocoa butter melts at body temperature; PEG bases dissolve in fluids.
- Displacement values tell how much base a drug replaces in a suppository mould.
11Stability and kinetics
- Hydrolysis and oxidation are the main routes of chemical breakdown.
- Shelf life (t90) is the time for 10% of the drug to degrade.
- The Arrhenius equation predicts how heat speeds breakdown; it underpins accelerated stability tests.
- Antioxidants, chelating agents and amber packaging limit oxidation and light damage.
12Packaging
- Type I glass (borosilicate) is used for parenteral products.
- Light-resistant containers protect light-sensitive drugs.
- Plastics can leach additives or absorb drugs (such as GTN into PVC).
- Child-resistant closures are used for hazardous medicines.
These are PharmaPrep's own notes on the knowledge this book teaches. No text, tables or figures are reproduced from it. Read the book for full explanations, and check doses and laws against current official sources.
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