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A Beginner’s Guide to Pharmaceutical Coating

Fabtech's Auto Coater

Medications have transformed from "only" medicinal ingredients during ancient Egpyt to acquiring various shapes, sizes, i.e. tablets, capsules and syrups in modern times. Also, it was not until the mid-twentieth century that colours became an essential addition to the coating in the pharma industry.

Senior Citizens and children find it difficult to swallow or gulp some oral dosage forms. The cause of this difficulty may be due to tablet size and possibly bitter taste of the drug.

This is a predictable scenario in many households where kids dislike taking medicines due to its awful taste. In essence, this blog on Pharmaceutical Coating discusses the need and the process carried out for coating.

Why Tablets/Granules/Pellets are coated?

The pharmaceutical coating can be applied to a wide range of Solid Oral Dosage forms including tablets, granules, crystals, powdersor pellets. Although this pharmaceutical process has been around for almost a century yet, it continues to be a crucial aspect of the modern medicine making process with advanced machinery and technologies. Coating systems for OSD units serve many purposes

  • Different Active Pharmaceutical Ingredients and (excipients) have different tastes or odour, some may be mildly bitter, yet some of them may be very bitter.
    • This unpleasant taste or odour can be taken care off by adding film-forming agents, taste-masking agents, flavouring agents, along with the coating ingredients.
  • Many of the drugs can be sensitive to light, moisture and atmospheric oxidation.
    • The use of stabilizers added to the coating ingredients help to protect drugs from light sensitivity, moisture and drugs that degrade due to atmospheric oxidation.
  • The core is pharmaceutically inelegant.
    • The use of pharma grade pigments or shining materials to the coating ingredients can increase the elegance or aesthetic value of the drug.
  • The coloured API migrates easily to stain the patient's clothes and hands.
    • These granules or core tablets are coated using soluble cellulose materials.
  • The drug release profile can be modified and or controlled.
    • The modification is effective with osmotic release oral delivery systems, enteric (delayed-release) or sustained-release coating.
  • Risk of interaction between two incompatible substances.
    • This risk can be mitigated by coating to contain one of the two or by coating a pellet previously compressed into a core.

Different types of coating:

Oral Solid Dosages constitute a significant portion of medicine manufacturing due to patient's adherence to recommended treatments, efficiencies in drug manufacturing and high-precision dosage.

Coating is a process by which the outer covering of a tablet is layered or coated with a substance that offers competent benefits over the uncoated variety. Tablets require different coating solutions based on their composition and the end consumer. They include

  • Sugar coating
  • Film coating
  • Particulate/pellet coating
  • Compression coating.

1. Sugar Coating

Do you recollect having a medication prescribed by your doctor that tastes sweet at first and later on leaves a bitter taste in the mouth or a lump in the throat for a couple of minutes after gulping it down? The tablet is masked with one of the coating methods - sugar coating.

Sugar Coating is largely borrowed from the confectionery industry which had developed this technique and is still widely used today. The sugar-coating process involves a skilled manipulative operation and could last for 3 – 5 days.

However, this coating technique is not as popular in the pharmaceutical industry as it was once, due to the laborious procedure and long process time, a requirement of skilled and trained personnel, and the inability to emboss, print or label the tablet and increases the size and weight of the tablet.

The coating process involves an iterative application of sucrose based solution to the tablet within the coating pan. The process of sugar-coating involves

  • Seal coating
  • Sub coating
  • Smoothing
  • Colour coating
  • Polishing and
  • Printing

2. Film coating:

A process where a thin polymer-based layer having a thickness between 20 and 100 µm is applied to the OSD which may be a tablet, granules or pellets is called film coating.

It is a single-stage process that is faster and increases the tablet weight marginally by only 2-3% in comparison with the sugar coating process, which results in an addition of 60 to 80% additional weight. It also allows embossing or printing on the tablet. However, it is very capital intensive and requires a massive facility for production.

Film-coating formulations usually contain the following components:

Components Examples Function
Polymer Hydroxy Propyl Methyl Cellulose (HPMC) Film forming agents
Plasticizer Poly Ethylene Glycol (PEG) Provides Elasticity
Pigment/opacifier Sunset yellow/Quinoline yellow/Brilliant blue/Titanium di oxide/Ponceau 4 R/Iron oxide yellow/ red etc Colouring agents
Vehicle Purified water, Isopropyl alcohol, Methylene Chloride Solvent to dissolve

3. Granules/Particles/Pellet coating:

Particle/ Granule or pellet coating is a thin layer of a substance that is placed around a core particle, granules or pellets. The coating application is through a physical deposition process, i.e. film coating resulting from the spraying and subsequent drying of solutions or dispersions.

This method

  •  leads to an improvement in the overall flowability,
  • offers protection from unstable or reactive substances, affecting through the air, humidity light and oxidation etc.
  • enhances mechanical properties (abrasion & compressibility),
  • improves aesthetic appeal (Texture, appearance, odour and taste), and
  • produces controlled and sustained release, thereby improving the drug dissolution.

The technologies include Microencapsulation, top spray and bottom spray (tangential or Wurster coating).

4. Compression coating:

Compression coating is similar to the tablet technology, where the core or coated tablets are surrounded by compressible excipients, which prevents the drug incompatibilities and protects the drug from environmental factors like light, humidity and oxidation.

  • Coating process parameters: 

The selection of instruments to measure the appropriate parameters; how the coating process may be optimized and the process scaled-up to control the coating of production size batches successfully.

The following are the process parameters to be monitored, validated and set for a product to get quality products with maximum yield.

Inlet airflow Outlet airflow
Inlet air temperature Outlet air temperature
Inlet air humidity Outlet air humidity
Spray concentration Bed temperature
Spray temperature Speed of the drum
Spray flow rate Air velocity
Pressure drop, inlet-outlet airstream Atomizing air pressure
  • Automation of coating processes:

The coating of OSD in pharmaceuticals has been practised since time immemorial. Current Good Manufacturing Practice (cGMP) and the demands of the regulatory authorities worldwide require utmost care not only in the equipment used in the preparation of tablets to be coated and the coating operation but also in the design of manufacturing facilities, the selection of materials used in their construction, their layout.

Management of Coating Processes is affected through an ascending range of Automation and Controls.
The automated controlled process parameters

  • indicate essential equipment functions
  • Batch parameter data logging
  •  Listing of Alarms, warnings & safety interlocks expected with specific and immediate action such as cycle stop, operator alert etc.

The "RECIPE" can be automated based on operations with different user levels such as operators, Supervisor and Manager.

We are all for the automated coating systems with 21 CFR part 11 compliance. Our equipment includes Auto Coater, Fluid Bed Processor and Fluid Bed Coater that is designed to meet all the critical process parameters and achieve the end product quality parameters. Our experts are on hand to offer you advice on the different pharmaceutical coating processes and deliver the best solution for your specific coating application.

Please use the form below to get in touch.

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