Blending: Using Low-Content Active Ingredients as an Indicator of Overall Blend and Tablet Uniformities

Blending uniformity studies are becoming more important during product development within the dietary supplement industry¹. A multivitamin and mineral (MVM) dietary supplement product usually contains more than 15 active ingredients. How do you know if each ingredient in the final blend of the MVM product is uniform? So far, data are scarce, if not absent, to answer this question. 

In the pharmaceutical industry, if an active ingredient of a drug product is greater than or equal to 50 milligrams (mg) per dosage form unit or the active ingredient is greater than or equal to 50 percent of the dosage form unit by weight, a blending uniformity study is not required². Among the FDA’s acceptance criteria for blending uniformity of generic drug products are that an active ingredient should be in the range of 90.0 percent to 110.0 percent of the amount specified, and relative standard deviation (RSD) must be no more than 5.0 percent (usually based on testing six to 10 samples)². 

Most drug products contain one active ingredient, and some incorporate two or three active ingredients. Whatever the case, the amount of the active ingredient(s) in a pharmaceutical dosage form (tablet or capsule) by weight is usually 2 percent or more³. In the dietary supplement industry, however, an MVM tablet may contain more than 15 active ingredients, some of which may account for less than 0.2 percent of the dosage form’s weight. Indeed, some supplement ingredients are present in amounts of less than 0.05 percent. At the other end of the spectrum, the active ingredients used in the highest amounts rarely exceed 50 percent of the dosage form. 

If we follow the pharmaceutical industry’s standards, our blending uniformity studies must test for nearly all the active ingredients. In this study, the MVM tablet contains 18 active ingredients, in which only calcium carbonate—since its use level exceeds 50 percent by weight—need not be tested. The other 17 active ingredients must be tested. But doing so would take a long time and cost a lot of money, an expense that would eventually be borne by consumers. 

But we can simplify blending uniformity studies of MVM tablets by making a reasonable assumption: If the active ingredients present in lower amounts are uniform in the final blend, then each active ingredient in the MVM tablet can also be considered to be uniform. Therefore, we only need to test several lower-content vitamin and mineral active ingredients in the final blend. In the present study, three vitamins (vitamin B12 at 0.035 percent, folic acid at 0.117 percent, and vitamin D3 at 0.189 percent) and two minerals (chromium chloride at 0.144 percent and zinc oxide at 0.692 percent) were chosen for testing. 

Methods 

Equipment

Blending uniformity studies of the MVM tablet formulation were conducted in a 5-cubic-foot Patterson-Kelly V-type blender (Hebeler, Tonawanda, NY). The final blend was compressed using a 36-station tablet press (Libra from Kikusui, Lakewood, NJ) operating at 30 rpm and equipped with oval tooling of 0.625 by 0.356 inch. 

Batches and batch size

Three pilot batches of the same formula were made. The formula contained calcium carbonate (55.556 percent), ascorbic acid (4.630 percent), selenium yeast (3.472 percent), vitamin E (2.249 percent), ferrous fumarate (1.744 percent), thiamine mononitrate (0.848 percent), zinc oxide (0.692 percent), calcium pantothenate (0.619 percent), riboflavin (0.585 percent), niacinamide (0.397 percent), vitamin A acetate (0.343 percent), biotin (0.320 percent), pyridoxine hydrochloride (0.294 percent), vitamin K1 (0.292 percent), vitamin D3 (0.189 percent), chromium chloride (0.144 percent), folic acid (0.117 percent), vitamin B12 (0.035 percent), microcrystalline cellulose (26.696 percent), and magnesium stearate (0.778 percent). Each batch weighed 50.000 kilograms. 

Blending, sampling, and analysis

As a pre-blending step, we added vitamin B12, riboflavin, folic acid, chromium chloride, vitamin K1, pyridoxine hydrochloride, thiamine mononitrate, biotin, niacinamide, calcium pantothenate, vitamin D3, and vitamin A acetate into a clean polyethylene bag. We blended the ingredients by tumbling the bag for 3 minutes by hand. We then passed the pre-blend and the remaining ingredients—except the magnesium stearate—through a 12-mesh screen, into the blender and blended for 15 minutes. Next, we passed the magnesium stearate through the 12-mesh screen into the blender and blended for 3 minutes. 

We collected two samples each from the bottom, middle, and top of the blender’s discharge stream. Each sample weighed approximately 300 grams. For each sample, vitamin B 12, folic acid, and vitamin D3 were analyzed using a high-performance liquid chromatography instrument (Alliance HPLC from Waters, Milford, MA). Chromium and zinc were analyzed by using an inductively coupled plasma instrument (Optima 5300DV from Perkin Elmer, Waltham, MA) according to Pharmavite’s standard methods.

Tabletting, sampling, and analysis

The final blend was compressed into 0.900-gram tablets, and we collected a composite sample from each lot and then randomly chose 10 tablets from the sample for testing. Vitamin B 12, folic acid, and vitamin D3 were analyzed using the same test equipment and methods we used on the blending samples. Chromium and zinc were analyzed using the same test equipment and methods we used on the blending samples. 

Physical testing

We measured each tablet’s weight, thickness, hardness, and disintegration time.

Results and Discussion 

Test results for the vitamin B 12, folic acid, vitamin D3, chromium, and zinc were all in the range of 90.0 to 110.0 percent of their respective specified amounts. Table 1 summarizes the RSDs of the uniformity data of the final blend samples. 

According to the FDA’s 1999 draft Guidance, an RSD of 5.0 percent or less indicates that an ingredient is uniformly distributed in the final blend². Folic acid, chromium, and zinc were homogenous in all three lots, while vitamin B 12 was uniform in one lot and non-uniform in two lots. 

Likewise, vitamin D3 was uniform in one lot and non-uniform in two lots. The higher RSDs for uniformity in vitamin B12 and vitamin D 3 may have been caused by sampling errors during the lab analysis. Specifically, the errors could have arisen because we used a stainless steel spatula in weighing powder samples of about 900 mg. That method could easily have produced different errors for some of the lower-content ingredients due to the effect of an electrostatic charge [1]. In fact, the effect of the charge on the uniformity of the vitamin B12 and vitamin D3 would likely have been greater than on the folic acid, chromium chloride, and zinc oxide because vitamin B 12 and vitamin D3 are covalent compounds, which would make the electrostatic charge have a greater effect on the motion of their particles. As a result, they would be more likely to adhere to the spatula’s surface¹. 

In order to verify the effects of the sampling error, we conducted content uniformity tests on the tablets. Table 2 shows the results of that testing. 

According to USP-38, if the calculated acceptance value of the active ingredient—based on 10 dosage units—is less than or equal to 15.0, then the product is considered to meet the USP’s quality standard⁴. The test results in Table 2 show that all the acceptance values are less than 15.0, indicating that the vitamin B12, folic acid, vitamin D3, chromium, and zinc in the MVM tablet product meet the USP’s quality standard. 

Based on the results for tablet content uniformity, we believe that each of the five ingredients (vitamin B12, folic acid, vitamin D3, chromium chloride, and zinc oxide) was uniform in the final blend. As explained above, the higher RSDs of the vitamin B 12 and vitamin D3 results in the final blend, as shown in Table 1, may reflect sampling errors during lab analysis.

Table 3 lists the weight, thickness, hardness, and disintegration time of the tablets taken from the three lots. Table 4 shows the assay test results of the finished products. 

All test results in tables 3 and 4 meet the product specifications, demonstrating that both the formulation and the manufacturing process are robust enough for commercial production. All results in Table 4 appear to support our assumption that if the lower-content active ingredients are uniform in the final blend of an MVM tablet, then each active ingredient in the MVM tablet is likewise homogenous. 

According to this study, for a low-content ingredient (less than 0.7 percent), RSD may be considered to relax to 7.2 percent from 5.0 percent (the pharmaceutical standard). However, further studies are needed to confirm this change and to demonstrate that uniformity of low content ingredients can be used as an indicator to verify the uniformity of the other active ingredients.

Acknowledgements 

The authors thank Victor Ramos for manufacturing the three pilot batches and conducting the weighing, blending, sampling, tabletting, and physical testing. We also thank Bill Shultz, Piya Vong, Alice Carbajal, and Johanna Maligaya in Pharmavite’s analytical group for conducting all the chemical tests. 

References 

1. Zeng W, Wang D, Roper, D (2016). Effect of sampling methods on vitamin D blending uniformity. Tablets & Capsules: 14(7): 17-20. 

2. Guidance for Industry (1999). ANDAs: Blend Uniformity Analysis, Draft Guidance. US Department of Health and Human Services, FDA, Center for Drug Evaluation and Research. 

3. Muselik I, Franc A, Dolezel P, Gonec R, Krondlova A, Lukasova I (2014). Influence of process parameters on content uniformity of a low dose active pharmaceutical ingredient in a tablet formulation according to GMP. Acta Pharm 64(3): 355-67. 

4. General Chapter <905> Uniformity of Dosage Units (2015). USP-38: 675-79.