The Effect of Film Coating and Storage Conditions on the Performance of Metformin HCl 500 mg Extended Release Hypromellose Matrices ABSTRACT SUMMARY
This study investigates the influence of three film coating systems on the performance of metformin HCl
(500mg) extended release (ER) hypromellose matrices stored under different conditions up to 12 months.
Keywords: metformin, hypromellose, extended release, film coating, stability
INTRODUCTION
There is a growing interest for extended release oral drug delivery systems, especially in the design of
challenging formulations such as those with high dose, highly water soluble actives.
Metformin HCl is prescribed for the treatment of non-insulin dependent diabetes mellitus.1 The primary benefit
of ER preparations of this active compared to an immediate release (IR) formulation is that a more uniform
maintenance of drug blood plasma concentration is achieved, thus potentially avoiding undesirable peaks and
troughs associated with multiple IR preparations and the loss of disease control these fluctuations represent.
The development of an ER metformin HCl 500 mg formulation using hypromellose (hydroxypropyl
methylcellulose, HPMC) was previously investigated.2 Consistent and robust tablets were produced by direct
compression (DC), in which the inclusion of 30% w/w polymer resulted in a drug release profile statistically
A large proportion of the tablets produced globally are film coated, for a variety of reasons including
aesthetics, taste or odour masking, enhanced mechanical strength, improved swallowability; and/or protection
from environmental conditions (e.g. moisture, light, air). It is therefore surprising that there are few studies
reported in the literature on film coated hypromellose matrices and the enhanced characteristics obtained.3
However, in this study the influence of three aqueous film coating systems on the performance and stability of
metformin HCl ER HPMC tablets, stored under two different ICH conditions for up to 12 months, is
EXPERIMENTAL METHOD
Tablet formulation contained 50.0% w/w metformin HCl (Ferico Labs), 19.0% w/w microcrystalline cellulose
(MCC), 0.5% w/w fumed silica (Aerosil 200, Degussa) and 0.5% w/w magnesium stearate (Peter Greven).
Hypromellose (METHOCEL™, premium cellulose ethers, K100M CR, Dow Chemical Company) was included
as a matrix former at 30.0% w/w. MCC and fumed silica were passed through a 500 Ìm sieve prior to use. All
ingredients, with the exception of magnesium stearate, were blended in a Turbula mixer for 5 minutes.
Magnesium stearate was then added and the formulation was mixed for an additional 2 minutes.
METHOCEL™
Tablets with a target weight of 1000 mg and a target breaking force of 20 kp were manufactured using an
instrumented 10 station rotary press (Piccola, Riva), fitted with 7 x 18 mm caplet tooling. Manufactured
matrices were coated in a 38 cm side-vented pan (Labcoat II-X, O’Hara) using a Schlick spray gun with three
• Opadry® II, high performance film coating system, (standard) to 4% weight gain,
• Opadry II (85 series) to 4% weight gain, and
• Opadry® tm, taste mask film coating system, to 5% weight gain
Table 1 shows the coating parameters utilized.
Table 1. Coating Parameters Opadry II Opadry II Opadry tm (standard) (85 series)
Samples of uncoated and coated tablets were stored in Securitainer polypropylene jars (Jaycare) at
30ºC/65% RH and 40ºC/75% RH for up to 12 months. Tablet weight, mechanical strength and drug release
were determined after 1, 3, 6 and 12 months storage.
Dissolution tests were conducted using an USP compliant bath (Sotax), Apparatus II (paddle method) with
sinkers in 1000 mL of purified water (37 ± 1°C) at 100rpm. A dual beam spectrophotometer (Perkin Elmer),
fitted with 0.1 mm matched quartz cells, was used for the detection of metformin HCl at a wavelength of 233
RESULTS AND DISCUSSIONS
Metformin HCl 500mg ER HPMC matrices displayed low weight variation (less than 1%) and good
mechanical strength (19.9 ± 2.2kp). The application of all three film coatings resulted in an increase in tablet
breaking force values (Figure 1) and no significant changes to the drug release profile (Figure 2). The rate of
metformin HCl dissolution did not change after 1, 3, 6 and 12 months storage at both conditions (Figures 3-6).
METHOCEL™ Figure 1. Tablet Breaking Force Figure 2. Drug Dissolution from Uncoated and Coated Tablets – INITIAL Figure 3. Drug Dissolution from Uncoated Tablets on Storage METHOCEL™ Figure 4. Drug Dissolution from Coated with Opadry II (Standard) Tablets on Storage Figure 5. Drug Dissolution from Coated with Opadry II (85 Series) Tablets on Storage Figure 6. Drug Dissolution from Coated with Opadry tm Tablets on Storage METHOCEL™ CONCLUSION
Application of all three Colorcon immediate release film coating systems resulted in a significant increase in
mechanical strength of metformin HCl 500 mg hypromellose ER tablets and no change to the drug
dissolution. Uncoated and coated matrices exhibited consistent release rates at all storage conditions after 1,
Reprint of poster presented at CRS – July 2006. Authors: Hue Vuong, Marina Levina and Ali Rajabi-METHOCEL™ REFERENCES
1. Dunn C.J. and Peters D.H., Metformin. A review of its pharmacological properties and therapeutic use in non-insulin-dependent
diabetes mellitus in Drugs. (1995) 49, 5, 721-749, NEW ZEALAND.
2. Palmer F., Levina M., Rajabi-Siahboomi A.R., Investigation of a directly compressible metformin HCl 500mg extended release
formulation based on hypromellose, CRS Annual Meeting, 2005.
3. Levina M., Influence of fillers, compression force, film coatings and storage conditions on performance of hypromellose matrices,
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METHOCEL™ 
Tablets with a target weight of 1000 mg and a target breaking force of 20 kp were manufactured using an
instrumented 10 station rotary press (Piccola, Riva), fitted with 7 x 18 mm caplet tooling. Manufactured
matrices were coated in a 38 cm side-vented pan (Labcoat II-X, O’Hara) using a Schlick spray gun with three
• Opadry® II, high performance film coating system, (standard) to 4% weight gain,
• Opadry II (85 series) to 4% weight gain, and
• Opadry® tm, taste mask film coating system, to 5% weight gain
Table 1 shows the coating parameters utilized.
Table 1. Coating Parameters 
Figure 1. Tablet Breaking Force 
Figure 4. Drug Dissolution from Coated with Opadry II (Standard) Tablets on Storage 
CONCLUSION 
REFERENCES