(W1230-03-14) Impact of Lubricant on Functional Tablet Coatings Containing Pectin

Purpose: Tablets are the most common dosage form for pharmaceutical and nutraceutical products. Most tablets utilize a coating to improve aesthetics, mask bitter taste from actives, and make the tablets easier to swallow. In the pursuit of clean-label alternatives for typical HPMC or PVA coatings, pectin has emerged as a promising tablet coating material. Depending on the type of pectin utilized in the coating, either immediate or delayed release functionality is possible. This work demonstrates the impact of tablet ingredients, specifically lubricants, on the stability of pectin coatings.

Methods: Pectin coating solutions were prepared at 5 wt % solids with the addition of 0.3% glycerin used as a plasticizer. Theophylline tablet cores, made with either Mg stearate or Na stearyl fumarate as the lubricant, were coated with the polymer solutions using a Freund-Vector LDCS Hi-coater equipped with a 0.7 mm nozzle positioned approximately 7 inches from the bed. The solution was sprayed at ~3 g/min while the pan was rotating at 20 rpm with a bed temperature of 50 °C. The resulting tablets were evenly coated to a weight gain of 5-8% and were then allowed to cure for 10 minutes in the coater. All dissolution testing was conducted at least one day after coating to allow for equilibration of the coating. Dissolution testing was conducted on freshly coated and aged tablets. Enteric dissolution testing was carried out in a standard USP II setup with 750 mL of pH 1.2 HCl buffer for the first two hours, followed by addition of 250 mL sodium phosphate tribasic to achieve a final pH of 6.8. The media was stirred with paddles at 50 rpm, and the concentration of theophylline was monitored by UV/vis at 272 nm over the course of 4 hours. Tablet aging was done by placing tablets in HDPE bottles sealed with foil into stability chambers set to ambient or accelerated conditions. Ambient conditions correspond to 25 °C and 60% RH, while accelerated conditions correspond to 40 °C and 75% RH.

Results: Pectin is broadly classified into two types: High Ester pectin (HE) and Low Ester pectin (LE). High Ester pectins are types with >50% degree of esterification (DE) and Low Ester pectins have < 50% DE. The amount of reactive -COOH groups changes the functionality of the pectin to achieve different properties. HE pectin tablet coatings create a smooth, shiny surface while maintaining an immediate release profile, while LE pectin can be utilized to create an enteric coating for active ingredients that need to be protected past the stomach. Figure 1 shows a comparison of the dissolution performance of an HE and LE pectin coating on a theophylline tablet. The HE pectin begins to release immediately even in the acidic pH, while the LE pectin shows only ~3.6% release at the end of the acid phase with release picking up immediately after the pH change to 6.8. With the high density of -COOH functionality on the pectin, it can be sensitive to divalent cations which can form crosslinks between polymer chains. While pectin is most reactive to Ca²⁺, other cations, especially over time, can still form those crosslinks. Many tablets utilize Mg stearate as a lubricant to help eject tablets from the rotary press, but alternatives such as Na stearyl fumarate are also available. In the case of pectin coatings, Na stearyl fumarate would be preferred to minimize any potential interaction of a divalent cation with the pectin-based coating. Figure 2 shows the dissolution profile of LE pectin coatings on theophylline tablets containing Mg stearate or Na stearyl fumarate as the lubricant. Freshly coated tablets show acid protection for the first two hours regardless of lubricant used in the tablet. After the acid phase however, tablets with Mg stearate show release, but have a slower onset and lower peak release than tablets where Na stearyl fumarate was used as the lubricant. Similarly, after 1 month of aging in ambient and accelerated conditions, the Na stearyl fumarate tablets show more consistent release performance than the Mg stearate tablets. This is likely due to a continued interaction of the coating with the Mg ions present on the surface of the tablet.

Conclusion: Pectin is a versatile ingredient that can be used to achieve different coating functionalities based on the type of pectin selected. HE pectin can be used to create an aesthetically pleasing, clean-label immediate release coating, while LE pectin can be used to create a highly functional enteric coating. When using gelling hydrocolloids, it is important to consider all formulation components to minimize the chance for polymer interactions that may impact performance. We found that using a lubricant such as Na stearyl fumarate avoids the potential for pectin crosslinking with divalent cations, providing a more robust enteric coating over time.


Figure 1: Dissolution profile showing immediate release (IR) of HE pectin coated tablets, and enteric release of LE pectin coated tablets


Figure 2: Dissolution of LE pectin coated tablets with Mg stearate or Na stearyl fumarate used as lubricant after storage under ambient (left) or accelerated conditions (right).