Chemistry Labs

Industrial and applied chemistry

Drug formulation and quality testing

How formulation design controls drug release and stability, and how analytical tests establish identity, strength, purity and performance.

1 Lower secondary2 Upper secondary3 Undergraduate4 Advanced5 Research

IntuitionA medicine is more than its active molecule

The active pharmaceutical ingredient (API) produces the intended pharmacological effect, but excipients help make a usable product: binders hold a tablet together, disintegrants help it break apart, and coatings can protect contents or alter release. The dosage form determines how the API meets the body and must remain consistent from batch to batch.

SchoolDissolution precedes absorption

For many oral solid medicines, the API must dissolve before it can be absorbed. A dissolution profile measures the fraction released into a defined medium over time. It is a controlled in-vitro test, not a direct measurement of clinical benefit, but it can reveal formulation or manufacturing differences.

Q(t)=100 mdissolved(t)mlabelled  %Q(t) = 100\,\frac{m_{\mathrm{dissolved}}(t)}{m_{\mathrm{labelled}}} \;\%

Example: Interpreting a dissolution result

A tablet is labelled to contain 100 mg API. At 30 minutes, the assay finds 75 mg dissolved in the specified vessel. Calculate Q and state what additional information is needed before judging compliance.

Solution

Q = 75%. Compliance cannot be concluded without the applicable monograph or specification, medium, apparatus, sampling conditions and acceptance rule (which may use staged criteria).

UndergraduateQuality is built into the formulation

Preformulation characterizes solubility, pKa, polymorphism, hygroscopicity and compatibility. These properties guide salt selection, particle engineering, excipient choice and packaging. For a weak base, for example, pH-dependent solubility can cause precipitation after a gastric-to-intestinal pH shift; a dissolution test should reflect the intended question and method conditions.

Noyes ⁣– ⁣Whitney:dCdt=DAh(Cs−C)\mathrm{Noyes\!\text{–}\!Whitney:}\quad \frac{dC}{dt}=\frac{DA}{h}(C_s-C)

The Noyes–Whitney form relates dissolution rate to diffusivity D, exposed surface area A, boundary-layer thickness h and the concentration driving force (Cs − C). Particle size, agitation and medium composition can therefore alter a measured profile; method robustness and sink conditions must be considered.

Observe how compounds with different interactions with the stationary and mobile phases migrate at different rates. This illustrates separation, not a validated assay or a real patient-specific result.

Identity tests establish what the material is; assay measures strength; impurity methods characterize related substances and degradation products. Chromatography can separate components, while calibrated detectors quantify them. System suitability, reference standards, specificity, accuracy, precision, range and robustness support fitness for purpose.

ResearchResearch frontier

References