EFFECT OF SOLVENTS ON TABLET COATING

The film coating of Pharmaceutical dosage forms is done by dispersing the polymers, plasticizers, opacifier Iubricant & pigments or Ready to use film coating material like INSTACOAT in the solvent system. The solvent system could be Organic, Aqueous or a combination of Organic and Aqueous. The most commonly used organic solvents are IPA and Methylene chloride.

Film coating of the tablets is a multivariable process, with many different factors, such as coating equipments. Process conditions, composition of the core tablet and solvent system, affect the quality of the final product.

In this article, we have examined the implication of change in solvent system on tablet coating. We have carried out six experiments using placebo tablets by conducting film coating trials in conventional coating pan (Semi automated).

The coating lot size was taken 500 gms. core tablets, the coating materials was used in two different colours- White and Blue (Indigo carmine) and the solvent system used are Aqueous, Hydro-alcoholic and Organic solvent.

The aim of the experiments is to determine the effect of organic solvents on coated tablets in respect of :

1. Change in appearance
2. Coating cost
3. DT of the finish product.

The details of the experiments are in table 1 and 2 (Table 1 gives the trial details for White colour coating and whereas Table 2 gives the details for Blue colour coating)
Table 1
Aim of the study : To determine the effect of organic solvents on coated tablets in respect of :
1) Appearance
2) Coating cost
Solvent system Core Aqueous Hydroalcoholic Organic
Total weight of core tablets to be coated 500 gms
Core weight 342.3 mg
Friability 0.147 %
Diameter 9.62 mm
Thickness 4.64 mm
D.T 12 secs.
Wt. gain theoritical 4 % 4 % 4 %
Coating material used ISP - 001 ISP - 001 ISP - 001
Total qnty. of Instacoat used 20 gms 20 gms 20 gms
Cost of Instacoat Rs. 25.00 Rs. 25.00 Rs. 25.00
Reconstitution level (solid contents) 12 % 10 % 5 %
Solvent required
Isopropyl alcohol kgs
D.M. water kgs
MDC kgs ----
146 gms
----- 90 gms
90 gms
----- 133 gms
-----
247 gms
Cost of solvents ----- Rs. 4.32 Rs. 16.26
Spray rate / min 4 gms / min 6-7 gms / min 12-13 gms / min
Bed Temperature 38°C - 42°C 38°C - 40°C 35°C - 38°C
(Instrument used) Multi Thermometer Multi Thermometer Multi Thermometer
Inlet air temperature 75°C 70°C 65°C
Dozing pump Electrolab Electrolab Electrolab
Pan RPM 25 - 26 25 - 26 25 - 26
Pan used conventional - spray gun used.
Conventional Bullows
Conventional Bullows Conventional Bullows
After coating results
Total weight of tablets 515 gms 515 gms 515 gms
Friability NIL NIL NIL
Diameter 9.66 mm 9.64 mm 9.66 mm
Thickness 4.72 mm 4.72 mm 4.70 mm
D.T 1 min 17 secs 1 min 04 secs 48 secs
a) Total time taken
40 min 30 min 30 min
b) appearance color matching white Off - white White to off - white
Total cost of coating material & solvents Rs. 25.00 Rs. 29.32 Rs. 41.26
Solvent used D.M.Water IPA / D.M.Water IPA / MDC

Table 2
Aim of the study : To determine the effect of organic solvents on coated tablets in respect of :
1) Appearance
2) Coating cost
Solvent system Core Aqueous Hydroalcoholic Organic
Total weight of core tablets to be coated 500 gms
Core weight 342.3 mg
Friability 0.147 %
Diameter 9.62 mm
Thickness 4.64 mm
D.T 12 secs.
Wt. gain theoritical 4 % 4 % 4 %
Coating material used ISP - 005 ISP - 005 ISP - 005
Total qnty. of Instacoat used 20 gms 20 gms 20 gms
Cost of Instacoat Rs. 25.00 Rs. 25.00 Rs. 25.00
Reconstitution level (solid contents) 12 % 10 % 5 %
Solvent required
Isopropyl alcohol kgs
D.M. water kgs
MDC kgs ----
146 gms
----- 90 gms
90 gms
----- 133 gms
-----
247 gms
Cost of solvents ----- Rs. 4.32 Rs. 16.26
Spray rate / min 4 gms / min 6-7 gms / min 12-13 gms / min
Bed Temperature 38°C - 42°C 38°C - 40°C 35°C - 38°C
(Instrument used) Multi Thermometer Multi Thermometer Multi Thermometer
Inlet air temperature 75°C 70°C 65°C
Dozing pump Electrolab Electrolab Electrolab
Pan RPM 25 - 26 25 - 26 25 - 26
Pan used conventional - spray gun used.
Conventional Bullows
Conventional Bullows Conventional Bullows
After coating results
Total weight of tablets 515 gms 515 gms 515 gms
Friability NIL NIL NIL
Diameter 9.68 mm 9.66 mm 9.68 mm
Thickness 4.72 mm 4.70 mm 4.74 mm
D.T 1 min 17 secs 1 min 04 secs 48 secs
a) Total time taken
40 min 30 min 30 min
b) appearance color matching Light Medium Dark
Total cost of coating material & solvents Rs. 25.00 Rs. 29.32 Rs. 41.26
Solvent used D.M.Water IPA / D.M.Water IPA / MDC

Cost of instacoat has been taken as Rs.1250/- per kg. &
the cost of IPA @ Rs.49 per kg. &
Methylene chloride @ Rs.40 Rs.per kg

Results and discussion:
1. In all the experiments nearly 3% coating weight gain was achieved, giving uniform coating and colour shade.
2. It was observed in White colour coating that the whiteness of the coated tablets was better in aqueous medium. The organic solvent based coating produced slightly off-white tablets though the tablet bed temperature was maintained at slightly lower level as compared to aqueous coating.
3. In case of blue colour coating, it was observed that aqueous coating produced slightly lighter shade than organic solvent based coating. This is probably due to the basic property of Indigo carmine colour.
4. The overall coating material cost was 40% less in case of aqueous coating as compared to organic solvent based coating.
5. It was observed that the DT of the finish product was slightly lower in case of organic solvent based coating than aqueous coating, however, the effect was not significant.

Conclusion :
The Instacoat coating material used for conducting various coating trials proved to the effect in different type of solvent system. It proved to be very coat effective in case of aqueous coating. The final product finish was also much better in case of aqueous coating in White colour. In case of Indigo carmine, the colour shade of the finish product should be decided based on the solvent system to be used, which should not be changed as it, the change in solvent system can change the colour shade of the finish product.