Pharmaceutical Chemistry and Drug Analysis
Pharmaceutical Chemistry and Drug Analysis covers drug chemistry, pharmacopoeial quality control and instrumental methods. The exam tests structure–activity reasoning, assay calculation, validation parameters and instrument selection.
Core rules
- Physicochemical properties drive behaviour: pKa and pH control ionization and partition; logP affects absorption; chirality can change receptor fit and clearance.
- Prodrugs are designed to improve absorption, stability or targeting, then must convert to the active moiety.
- Analytical validation includes accuracy, precision, specificity, linearity, range, LOD/LOQ and robustness. System suitability is checked before sample runs.
- HPLC is used for separation and quantitation; UV-Vis for chromophore-based assay; titration for suitable acid/base or redox systems; IR for identity.
Worked example
A 25 mg tablet is extracted to 100 mL. A 1 mL aliquot is diluted to 10 mL. The sample absorbance is 0.450; a 20 µg/mL standard gives 0.300. Sample concentration = 20 × (0.450/0.300) = 30 µg/mL. Correct for the 1:10 dilution: 300 µg/mL in the stock. The stock contains 300 µg/mL × 100 mL = 30,000 µg = 30 mg. Percentage label claim = 30/25 × 100 = 120%.
Traps
- Forgetting the dilution factor, producing a false label claim.
- Mixing µg/mL with mg/mL.
- Using a standard in a different solvent matrix without checking recovery.
- Treating LOD as LOQ.
- Assuming a single wavelength proves peak purity.