In the generic pharmaceutical industry, developing an oral suspension goes far beyond simply matching flavor or color. It is a scientifically intensive process that starts at the material characterization stage, long before full analytical profiling is complete.
One of the most influential factors in suspension design is the Particle Size Distribution (PSD) of the Active Pharmaceutical Ingredient (API).
Why PSD Is Critical in Oral Suspensions
1. Suspendability and Physical Stability
APIs in suspensions are typically insoluble in water. A narrow PSD ensures the particles stay suspended longer without rapid settling or forming hard sediment (caking), allowing patients to receive the correct dose every time.
2. Redispersibility
Even if sedimentation occurs, a well-optimized PSD enables quick redispersion with gentle shaking. Oversized particles or wide distribution ranges may result in irreversible settling.
3. Bioavailability Impact
For BCS Class II and IV APIs, dissolution is the rate-limiting step. Controlling PSD enhances the surface area, improving the dissolution rate and ultimately bioavailability.
4. Taste and Mouthfeel
Finer particles reduce grittiness and improve patient compliance, especially in pediatric and geriatric formulations. PSD plays a vital role in sensory experience.
5. Process Robustness and Scalability
A defined PSD helps maintain consistency during scale-up and manufacturing, reducing batch-to-batch variability.
PSD Characterization – What to Include Early
As per industry best practices, early-stage evaluation includes:
- Microscopic observation for particle shape and crystal morphology
- Bulk and tapped density analysis
- PSD method development using techniques like laser diffraction
- B.E.T. surface area analysis
- Microscopic imaging of both API and reconstituted suspension to identify insoluble particles or unexpected excipients
Market and Regulatory Insight
Even before laboratory formulation begins, marketing intelligence provides valuable data such as:
- Target flavor and color for each strength
- Packaging formats and closures
- Container type (e.g., HDPE, glass)
All these details, combined with a deep understanding of PSD, set the foundation for a first-time-right suspension development.
In oral suspensions, controlling the particle size distribution of the API is not optional — it is foundational. It influences everything from dose uniformity and stability to patient acceptability and regulatory success.
Whether you're optimizing an existing formulation or developing a new generic suspension, never underestimate the power of PSD.
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