In the pharmaceutical industry, oral solid dosage forms (OSDs) such as tablets and capsules remain one of the most preferred and widely used drug delivery systems. The quality, stability, and patient acceptability of these products depend not only on their active ingredients but also on the coating process that protects and enhances them.
Among the various solvents used in coating formulations, acetone stands out as a critical enabler of coating uniformity. Its excellent solubility, rapid evaporation, and consistent performance make it a trusted choice for pharmaceutical coating operations across the globe.
Understanding Coating in Oral Solid Dosage Forms
The coating on a tablet is more than just an outer layer, it serves multiple vital purposes:
1. Protects the drug from environmental factors like moisture, light, and air.
2. Masks unpleasant tastes or odours, improving patient compliance.
3. Controls drug release, enabling sustained or delayed delivery.
4. Enhances appearance and identification, ensuring consistency in branding and safety.
To achieve these outcomes, the coating must be uniform, defect-free, and consistent across every tablet in a batch. This is where the choice of solvent, particularly acetone, plays a decisive role.
Why Solvent Selection Matters in Coating Processes
Solvents form the medium in which coating polymers and other excipients are dissolved or dispersed. They influence the viscosity, spray pattern, film formation rate, and drying efficiency of the coating solution.
An inappropriate solvent can lead to uneven coating thickness, colour variation, or defects such as orange peel, cracking, or rough surfaces. Therefore, choosing the right solvent system one that ensures smooth application and consistent drying is essential for coating success.
The Role of Acetone in Achieving Coating Uniformity
Acetone is a volatile, low-boiling, and highly polar organic solvent that has long been used in the pharmaceutical coating process.
Its ability to dissolve a wide range of film-forming polymers, plasticisers, and colourants makes it an ideal solvent for film coating formulations.
Let’s explore how acetone supports uniform and reproducible coating in oral solid dosage forms.
1. Excellent Solvent Power
Acetone readily dissolves many commonly used coating materials such as cellulose derivatives, acrylic polymers, and polyvinyl compounds. This ensures a homogeneous coating solution, which prevents undissolved particles from creating surface irregularities or coating defects. A consistent solution leads directly to uniform film formation, improving the overall appearance and performance of the dosage form.
2. Rapid Evaporation and Efficient Drying
One of acetone’s most valuable characteristics is its fast evaporation rate. During the coating process, droplets of the coating solution are sprayed onto tablets in a rotating pan or fluidised bed. Acetone’s quick drying action allows for immediate film formation, reducing the risk of sticking or over wetting. This property also helps maintain uniform coating thickness, especially in high-speed automated coating equipment.
3. Enhanced Film Formation
The film formed from acetone-based coatings tends to be smooth, glossy, and uniform.
Because acetone promotes even polymer deposition, it minimises issues like colour variation or uneven surface texture. Moreover, its high volatility allows operators to control film thickness precisely, which is essential for modified-release or enteric-coated formulations.
4. Compatibility with a Wide Range of Coating Systems
Acetone is compatible with both aqueous and solvent-based coating systems. In some cases, it is used as part of a mixed solvent system (with ethanol or isopropanol) to optimise drying rates and coating behaviour. This flexibility allows formulators to tailor coating properties according to specific product needs from immediate-release tablets to controlled-release coatings.
5. Process Efficiency and Reproducibility
Because of its volatility and strong solvating ability, acetone-based coatings often reduce drying times, improving throughput in manufacturing. Faster drying also means lower risk of coating defects, resulting in better batch reproducibility, a key requirement in GMP-compliant production environments.
Quality and Safety Considerations
While acetone is highly effective, it is also classified as a Class 3 solvent under ICH Q3C guidelines, meaning it has low toxic potential when used within accepted limits. Pharmaceutical-grade acetone must therefore meet stringent purity specifications, ensuring that residual solvent levels remain well within regulatory limits.
Certified pharmacopeia-grade acetone (compliant with USP, EP, BP, JP, CP, and IP) guarantees minimal impurities and safe use in oral dosage formulations. Such quality assurance is essential not only for product safety but also for regulatory compliance during audits and submissions.
Sustainability and Environmental Aspects
With growing awareness of sustainability, manufacturers are optimising solvent recovery systems to reduce waste and emissions. Acetone’s high volatility and recyclability make it easier to recover and reuse, aligning with green manufacturing practices.
Modern coating facilities equipped with solvent recovery units (SRUs) can efficiently reclaim acetone vapours, reducing both environmental impact and operational costs.
Purosolv’s Commitment to Coating Excellence
At Purosolv, we understand that solvent purity and performance directly influence product quality in pharmaceutical coating. Our certified pharmacopeia-grade acetone is produced under strict quality control and meets global pharmacopeial standards.
Each batch is backed by a Certificate of Analysis (CoA), full traceability, and compliance with GMP manufacturing requirements. With Purosolv, formulators gain consistent performance, reliable supply, and regulatory confidence ensuring flawless coating uniformity, every time.
Conclusion
In oral solid dosage manufacturing, coating uniformity is essential for ensuring product quality, stability, and appearance. Acetone plays a vital role in achieving this uniformity by delivering superior solubility, fast drying, and smooth film formation.
By using certified pharmacopeia-grade acetone from Purosolv, pharmaceutical manufacturers can achieve coatings that are not only visually consistent but also scientifically precise and regulatory compliant. Acetone remains a cornerstone solvent in tablet coating bridging the gap between process efficiency and pharmaceutical excellence.
FAQs
1. Why is acetone used in pharmaceutical coating?
Because of its high solvency and fast evaporation, acetone ensures smooth, uniform coatings with consistent thickness and appearance.
2. Can acetone affect drug stability?
When used within pharmacopeial limits and properly removed, acetone does not impact drug stability or patient safety.
3. Is acetone safe for pharmaceutical use?
Yes. Pharmacopeia-grade acetone meets strict purity standards and complies with global pharmacopeial requirements (USP, EP, BP, JP, CP, IP).
4. How does acetone improve coating uniformity?
Its fast-drying rate prevents over wetting and sticking, while its excellent solubility ensures even distribution of polymers and pigments.
5. How does Purosolv ensure acetone quality?
Purosolv supplies certified pharmacopeia-grade acetone with full documentation, batch traceability, and adherence to GMP ensuring quality and consistency in every batch.