Lawson L D, Wang Z J, Papadimitriou D
Research Department, Murdock Madaus Schwabe, Inc., Springville, Utah, USA.
Planta Med. 2001 Feb;67(1):13-8. doi: 10.1055/s-2001-10624.
The failure of five recent clinical trials to show significant reduction in elevated serum cholesterol by a single brand of allicin-standardized garlic powder tablets is in contrast to many prior positive studies with the same brand. The hypocholesterolemic activity of garlic is mainly due to allicin, a compound that is produced by the acid-sensitive garlic enzyme, alliinase, only after tablet consumption. Therefore, the allicin-releasing ability of ten lots of these tablets--manufactured over the same years that the positive and negative clinical trials were conducted (1989-1997)--was determined under simulated gastrointestinal dissolution conditions, as defined by U.S. Pharmacopeia Method 724A. It was found that the older lots were more resistant to acid-disintegration (2.5 h vs. 1.3 h, P < 0.001) and that they released three times as much allicin (44% vs. 15 % of their potential, P < 0.001) as the newer lots. A second brand of tablets employed in a recent negative trial released no detectable amount of allicin, while a third set of tablets with high allicin release was used in a trial that gave positive effects. Hence, the persons involved in the recent negative clinical trials probably received considerably less allicin than did those in the older positive studies, possibly accounting for much of the discrepancy in the outcomes. In conclusion, clinical trials using garlic powder tablets to assess any effect of garlic that might be related to allicin, as most are, cannot be considered valid for garlic when the trial shows no effect, unless the expected allicin release from the tablets has at least been determined under standardized drug release conditions (USP 724A).
最近五项临床试验未能证明某一品牌的蒜素标准化大蒜粉片剂能显著降低血清胆固醇水平，这与之前许多针对该品牌的阳性研究形成了对比。大蒜的降胆固醇活性主要归因于蒜素，蒜素是一种仅在片剂服用后由对酸敏感的大蒜酶——蒜氨酸酶产生的化合物。因此，在由美国药典方法724A定义的模拟胃肠道溶解条件下，测定了在进行阳性和阴性临床试验的同一年（1989 - 1997年）生产的十批此类片剂的蒜素释放能力。结果发现，较老批次的片剂对酸崩解更具抗性（2.5小时对1.3小时，P < 0.001），并且它们释放的蒜素是较新批次的三倍（分别为其潜在蒜素含量的44%对15%，P < 0.001）。最近一项阴性试验中使用的第二个品牌的片剂未检测到蒜素释放，而在一项产生阳性效果的试验中使用了第三组蒜素释放量高的片剂。因此，参与最近阴性临床试验的人可能比参与早期阳性研究的人摄入的蒜素要少得多，这可能是导致结果差异的主要原因。总之，使用大蒜粉片剂评估大蒜可能与蒜素相关的任何作用的临床试验，如果试验显示无效果，除非已在标准化药物释放条件（USP 724A）下至少测定了片剂预期的蒜素释放量，否则不能认为对大蒜是有效的。
