1. Introduction
Pharmaceutical microcrystalline cellulose (MCC) is a widely used filler and binder in oral solid dosage forms, especially for tablet manufacturing. In direct compression, MCC process robustness can influence production efficiency, tablet hardness, friability, and overall product quality. Magnesium stearate is commonly used as a lubricant, but excessive dosage or prolonged mixing may reduce inter-particle bonding. Evaluating lubricant sensitivity is therefore important when selecting an MCC excipient for tablets and defining a robust compression process.
DESU® Microcrystalline cellulose PH-101 and DESU® Microcrystalline cellulose PH-102 are representative pharmaceutical MCC grades used in tablet formulations. DESU® MCC PH-101 has a finer particle size, while DESU® MCC PH-102 provides a balance of flowability and compactibility. This study compares these DESU® grades with equivalent products from Europe, Japan, and the United States to evaluate lubricant sensitivity and process robustness under direct compression and dry granulation conditions.
2. Experimental Methods
2.1 Lubricant Sensitivity Testing
Microcrystalline cellulose PH-101 and PH-102 samples from different sources were mixed with 1% magnesium stearate (MS) (20 rpm, 10 min) and directly compressed. Five pressure gradients (0.8, 1.5, 2.6, 7.5, and 9.6 kN) were evaluated. Tablet hardness, friability, and disintegration time were measured. The Lubricant Sensitivity Index (LSI) was defined as the ratio of hardness at low pressure (2 kN) to hardness at medium pressure (7.5 kN); a lower LSI indicates greater lubricant sensitivity.
2.2 Process Robustness Evaluation
Amlodipine besylate tablets prepared by direct compression and apixaban tablets prepared by dry granulation were selected as model formulations. These models represent two common processing scenarios for pharmaceutical MCC: MCC for direct compression tablets and MCC for dry granulation. Conventional lubricant levels (0.5–1.0%) were used, while main compression pressure and mixing time were varied to evaluate the coefficient of variation (RSD) of tablet quality indicators. RSD <5% was considered process robust, while RSD >10% was considered process sensitive.
2.3 Statistical Analysis
One-way ANOVA was used to compare hardness differences among MCC products from different sources, with P<0.05 considered statistically significant. Dissolution-curve similarity was evaluated using the f2 factor, with f2>50 considered similar.
3. Results and Discussion
3.1 Lubricant Sensitivity Comparison
Table 1 compares the direct compression performance of four PH-102 MCC products after the addition of 1% magnesium stearate. In the low-pressure range of 0.8–2.6 kN, DESU® MCC PH-102 and the European Brand showed hardness of 25–52 N and 22–48 N, respectively, while the Japanese Brand and American Brand showed 28–58 N and 26–55 N. Friability for DESU® MCC PH-102 and the European Brand was 0.3–0.5%, compared with <0.3% for the Japanese and American products, indicating stronger low-pressure robustness for the latter two products.
Table 1 Comparison of Direct Compression Performance of PH-102 with Lubricant from Different Sources
| Source | Low Pressure Hardness (N) | Medium Pressure Hardness (N) | High Pressure Hardness (N) | Friability (%) | LSI Index |
| DESU® | 25-52 | 85 | 95 | 0.3-0.5 | 0.61 |
| European Brand | 22-48 | 82 | 92 | 0.3-0.5 | 0.59 |
| Japanese Brand | 28-58 | 90 | 102 | <0.3 | 0.64 |
| American Brand | 26-55 | 88 | 98 | <0.3 | 0.63 |
Note: Low pressure range 0.8-2.6 kN, medium pressure 7.5 kN, high pressure 9.6 kN
Figure 1 Hardness-Pressure Curve of PH-102 with 1% Magnesium Stearate Direct Compression from Different Sources
Lubricant Sensitivity Index (LSI) results (Figure 3) showed that, among PH-102 products, the Japanese Brand had the highest LSI (0.64) and therefore the lowest lubricant sensitivity. DESU® MCC PH-102 and the European Brand had LSI values of 0.61 and 0.59, respectively, indicating relatively higher sensitivity. Under lubricant dosage fluctuation or uneven mixing, DESU® MCC PH-102 therefore requires tighter process control to maintain consistent tablet quality.
3.2 Process Robustness Comparison: PH-101 vs. PH-102
Comparing DESU® MCC PH-101 and DESU® MCC PH-102 with corresponding European grades (Figure 2), PH-101 showed higher low-pressure hardness (58 N and 55 N) than PH-102 (48 N and 45 N). The corresponding LSI values were 0.61 and 0.60 for PH-101 versus 0.56 and 0.55 for PH-102. These results indicate that PH-101 is less sensitive to lubricant under the tested conditions and provides a wider process window at low compression pressure.
Table 2 Comparison of Process Robustness between PH-101 and PH-102
| Grade | Source | Low Pressure Hardness (N) | Medium Pressure Hardness (N) | LSI Index | Process Robustness Evaluation |
| MCC PH-101 | DESU | 58 | 95 | 0.61 | Robust |
| MCC PH-101 | European Brand | 55 | 92 | 0.60 | Robust |
| MCC PH-102 | DESU | 48 | 85 | 0.56 | More Sensitive |
| MCC PH-102 | European Brand | 45 | 82 | 0.55 | More Sensitive |
Figure 2 Hardness Comparison of PH-101 and PH-102 under Same Formulation Conditions
The difference is associated with particle-size distribution. DESU® MCC PH-101 has a finer particle size (D50 approximately 50 μm), a larger specific surface area, and more complete contact with lubricant, which supports more uniform lubricant distribution and inter-particle bonding at low pressure. DESU® MCC PH-102 has a larger particle size (D50 approximately 100 μm); uneven lubricant distribution may therefore increase the risk of local over-lubrication and reduced compactibility.
3.3 Model Formulation Application Evaluation
In amlodipine besylate tablets produced by direct compression, the four PH-102 MCC products showed hardness of 72–78 N at 10 kN, with no significant difference. At 5 kN, however, DESU® MCC PH-102 and the European Brand showed lower hardness (52 N and 50 N) than the Japanese and American products (58 N and 56 N), consistent with the lubricant-sensitivity results obtained with pure MCC.
In apixaban tablets produced by dry granulation, increased granule density reduced the differences in lubricant sensitivity among the four PH-102 MCC products. Tablet hardness RSD remained <5% under three pressure conditions, and content-uniformity A+2.2S values were <5, meeting the stated quality requirements. Under the tested conditions, dry granulation reduced MCC sensitivity to lubricant and improved process robustness.
Figure 3 Comparison of Lubricant Sensitivity Index of Different MCC Products
4. Conclusion
This study used hardness-pressure curves and the Lubricant Sensitivity Index (LSI) to evaluate process robustness of DESU® MCC PH grades against comparator products. The results highlight how MCC grade selection and lubricant control can affect tablet compression performance.
(1) Lubricant sensitivity differences: Among PH-102 products, the Japanese and American brands showed the lowest lubricant sensitivity (LSI 0.63–0.64), while DESU® MCC PH-102 and the European Brand showed relatively higher sensitivity (LSI 0.59–0.61). When lubricant dosage fluctuated ±20%, the Japanese Brand hardness change was <8%, while DESU® MCC PH-102 hardness change was approximately 12%.
(2) Grade differences: PH-101 showed better process robustness than PH-102 under the tested conditions. At the same lubricant level, PH-101 low-pressure hardness was 15–20% higher than PH-102, supporting its use where stronger low-pressure compactibility is required.
(3) Process strategies: For DESU® MCC PH-102, the study recommends controlling lubricant dosage at 0.5–0.8%, limiting mixing time to within 5 minutes, maintaining main compression pressure above 7 kN, or using a dry-granulation process to reduce lubricant sensitivity.
In summary, DESU® MCC PH-101 showed process robustness comparable to the comparator products under the tested conditions, while DESU® MCC PH-102 required tighter lubricant and compression control. For formulators selecting pharmaceutical microcrystalline cellulose for tablet manufacturing, matching MCC grade characteristics with the intended direct-compression or dry-granulation process can help improve manufacturing consistency.