Evaluation of Pharmaceutical Quality of Phenytoin Sodium Capsules and Tablets from Multinational Markets

Dissolution and in vivo evidence of differences in reference products: impact on development of generic drugs

The WHO List of International Comparator Pharmaceutical Products (CPP) For Equivalence Assessment of Interchangeable Multi-Source (Generic) Products will address an important issue in developing new generic drugs because it will identify the 'correct' reference product. This list will reduce unnecessary clinical studies in jurisdictions requiring new generics to be compared with brand products sold locally. Eventually, by employing the CPP, there will be a world-wide standard for brand and generic drugs, assuring the same level of quality internationally. The strategy of a single global reference is meritorious, but there are several hurdles to overcome. Most important is that the same brand may differ in dissolution and/or bioavailability in various jurisdictions, including some drugs with a narrow therapeutic index like phenytoin. Several examples are provided in this manuscript. This issue of regional differences has relevance, not only to the WHO list, but also to the matter of how safety and efficacy was established for that product in the first place. Normally, phase III clinical studies are conducted on a product manufactured in a single site, set to one standard. If the product differs in bioavailability in different jurisdictions, one is left with the question: 'which product has remained true to the original formulation?' Alternatively, if safety and efficacy is maintained with all formulations, then one is faced with the question: 'are the criteria currently employed for bioequivalence unnecessarily restrictive?'

Assessment of pharmaceutical quality of furosemide tablets from multinational markets

This report describes results of a collaborative study in which samples of the 40-mg strength of furosemide tablets were evaluated following a common protocol based on British (BP), European (Ph. Eur.), and US Pharmacopoeial (USP) specifications. Several tests, including identification, uniformity of mass, and dissolution, were performed. In total, excluding Lasix lots, results for 162 lots obtained from 115 manufacturers or suppliers were submitted. Also, 23 laboratories identified and submitted data for 34 lots of Lasix products available in their countries. There were no reported abnormalities in the physical test requirements of the products analyzed. The summaries (n, mean, and 95% CI) of the assay results for the "standard sample" (a common sample), Lasix lots from participating countries, and for all other furosemide products, respectively, are as follows: 30, 99.8%, 96-104; 33, 100.0%, 94-106; and 162, 99.6, 94-105. About half (approximately 62%) of the reported uniformity of mass results based on tablet weights were in the range 150-175 mg/tablet. However, there appears to be notable variability in tablet weights that would result in significant differences in the ratios (0.14 to 0.40) of active ingredient to excipient. The reported disintegration times ranged from 0 (instantaneous) to 18 min, with most less than 1 min. The drug dissolution testing was conducted with phosphate buffer at pH 5.8 (USP recommended). Another test was conducted with acetate buffer at pH 4.6 (noncompendial). There appears to be remarkable similarity in overall percentage of drug release from the three types of products (standard sample, Lasix lots, and other products). Although apparently there is a very wide spread in dissolution characteristics of the products tested, the analyses of variance did not detect differences among the products tested and, to this extent, would not indicate differences in bioavailability characteristics for most of these products. It is observed that about 20-38% of the variability in dissolution testing is not product related (i.e., it is from the dissolution testing itself), while the remaining 62-80% variability is product related (manufacturing, formulation, etc). The results of this multinational collaborative study showed that most of the furosemide products available in different countries met the required pharmaceutical quality standards, including drug-release characteristics. Based on an extensive statistical analysis, the main concern from the study was that the high variability in drug dissolution testing would require wide tolerance standards (e.g., pharmacopoeial standards). This may result in lack of needed discriminating ability of the test in revealing the impacts of formulation and manufacturing changes on in vitro, and perhaps in vivo, drug-release characteristics.