罗红霉素原研制剂与自研制剂有关物质及降解机制研究

目的 对比研究自研制剂与原研制剂的杂质谱和杂质水平,初步探索罗红霉素的降解机理。方法 采用HPLC考察原研和自研制剂的有关物质,通过LC-MS定位EP系统适用性对照品的11种杂质,进而利用LC-MS对2种制剂的有关物质进行辅助结构确证。进行原研和自研制剂的强制降解实验,通过HPLC对比研究两者的主要降解途径,并利用LC-MS初步鉴定降解杂质的结构。结果 原研制剂检出的主要杂质为杂质F、杂质G、杂质H、杂质I,其中最大单杂为杂质G,含量为0.439%,自研制剂检测到杂质C、杂质D、杂质H、杂质I、杂质J,其中最大单杂为杂质C,含量为0.196%。原研制剂在碱、高温、光照条件下较稳定,强酸条件下主要产生杂质B、杂质D,强氧化条件下生成的杂质未能归属到EP系统适用性对照品的11种杂质中,已通过质谱确定分子量,推测可能为罗红霉素N氧化物。自研制剂主要降解途径及产生的杂质与原研制剂一致。2种制剂加速实验有关物质均无明显变化。结论 由于国产原料药和进口原料药的差异,自研制剂与原研制剂杂质谱不完全一致,自研制剂的杂质水平低于原研制剂。罗红霉素主要降解途径为水解、异构化和N的氧化,分别产生杂质B、D以及N氧化杂质（m/z=853.531 8）。     

HPLC测定保泰松原料及糖衣片剂有关物质的改进研究

目的 建立保泰松原料及糖衣片剂中5个已知杂质及其他未知杂质检测方法。方法 分离条件：Agilent Eclipse XDB-C₁₈（4.6 mm×250 mm,5 μm）,柱温为30℃,流动相为醋酸铵缓冲液（取醋酸铵2.72 g,加水700 ml溶解,用冰醋酸调节pH值至4.1,加水至1 000 ml,摇匀）-乙腈（58：42）,流速为1.5 mL·min^-1,检测波长为254 nm,进样量为20 μl。结果 5个已知杂质在25 min内能够完全分离,其中杂质A、B、C、D均在5~30 μg·ml^-1,杂质E在0.03~0.15 μg·ml^-1具有良好的线性关系;最低检出限量分别为27.86,28.52,26.28,31.96,0.24 ng;原料、糖衣片剂中5个已知杂质的平均回收率分别为98.1%,99.3%,97.6%,97.4%,95.1%和96.9%,97.1%,96.6%,96.1%,94.7%。结论 改进的方法灵敏度更高、定量准确,重复性更好,可有效控制保泰松原料及糖衣片剂中杂质含量。     

罗红霉素分散片有关物质分析方法优化及一致性评价研究

目的 优化有关物质分析方法,有效分离罗红霉素分散片中13种杂质,建立加校正因子的主成分自身对照法测定有关物质,并与原研制剂进行有关物质一致性评价研究。方法 使用Waters XBridge^® C₁₈柱（150 mm×4.6 mm,3.5 μm） ,以0.52 mol·L^-1磷酸二氢铵水溶液（用5 mol·L^-1氢氧化钠调节pH值至4.3）为流动相A,以乙腈-水（70∶30）为流动相B,进行梯度洗脱;体积流量0.9 mL·min^-1,柱温20℃,检测波长205 nm,进样20 μL。对13种杂质成分进行线性回归,以线性斜率计算各杂质相对于罗红霉素的校正因子,用加校正因子的主成分自身对照法计算杂质含量并进行方法验证。罗红霉素分散片经碱破坏、酸破坏、氧化破坏、高温破坏、光照破坏后检测色谱图变化;取参比制剂及自研制剂,置于温度40℃、相对湿度75%条件下放置6个月,分别于第1、2、3、6个月取样测定其有关物质含量。结果 在已建立的色谱条件下,罗红霉素与相邻杂质、杂质与杂质之间均能有效分离,分离度均≥1.5。罗红霉素在0.968 9～100.090 0 μg·mL^-1相关系数为0.999 4,其他已知杂质在相应浓度范围内相关系数也均在0.999 0～1.000 0,线性关系均良好。各已知杂质平均回收率均在90.0%～108.0%,9份回收率的RSD≤5.0%。采用加校正因子的主成分自身对照法测定3批样品中杂质含量,结果与杂质对照品外标法一致。自研制剂杂质与原研制剂具有有关物质一致性。自研制剂在光照条件下稳定;在氧化、酸、碱、高温破坏条件下均有不同程度的降解,在酸条件下主峰降解最为明显,杂质B、D显著增加;氧化条件下降解产生氮氧化物;原研制剂与自研制剂在加速条件下均未检出杂质B、K及氮氧化物,在加速6个月过程中,二者杂质D均有增长趋势,其他杂质无明显变化。结论 建立的方法具有良好的专属性、准确性和重复性,可采用加校正因子的主成分自身对照法测定罗红霉素分散片中有关物质。     

二甲双胍亚硝胺杂质研究及亲水凝胶骨架材料的筛选

目的 探讨不同亲水凝胶骨架材料与盐酸二甲双胍(metformin hydrochloride,MET)降解生成N-二甲基亚硝胺(N-dimethylnitrosamine,NDMA)之间的相关性,筛选合适的骨架材料用于制备MET缓释片。方法 以高效液相色谱-三重四极杆串联质谱为NDMA监测手段,通过原辅料相容性考察确定产生NDMA风险较低的骨架材料,而后考察溶胀性能,确定溶胀作用与参比制剂相似的骨架材料,将筛选出的骨架材料制备缓释片后考察其体外溶出和剂量倾泻的行为。结果 原辅料相容性考察发现羟丙甲纤维素(hypromellose,HPMC)是引起MET降解产生NDMA的主要原因,并筛选出溶胀作用与HPMC相似的卡波姆,以其为骨架材料制备缓释片可获得与参比制剂相似的溶出曲线,且剂量倾泻风险较低,产品稳定性良好。结论 卡波姆可作为HPMC的替代材料,用于制备MET缓释片。     

不同溶氧量与残氧量对硫辛酸注射液质量的影响

目的 通过测定不同来源的硫辛酸注射液中的顶空残氧量和溶解氧量以及有关物质和主成分的含量,分析数据变化趋势,为硫辛酸注射液的质量控制提供技术参考。方法 以原研制剂、自研3批不同溶氧量与残氧量的样品以及市售不同厂家样品为试验对象,采用高效液相色谱法测定不同样品的有关物质[杂质A（6,8-上硫辛烷酸）、杂质B（氧化杂质）、杂质C（降解杂质）]、含量和聚合物,X-325i顶空残氧/溶氧分析仪测定溶氧量与残氧量,进行高温、光照、低温、冻融循环等影响因素试验,以及加速试验、长期试验考察稳定性。结果 较高溶氧残氧产品在高温条件下杂质B、C和杂质总量增长趋势明显;光照无外包装条件下,样品中溶氧量与残氧量均显著降低,杂质A和聚合物增长显著;光照带外包装条件下各样品均稳定;低温条件下各样品均稳定;冻融条件下低溶氧量样品不受影响,高溶氧量样品聚合物增加明显;加速条件下,所有自研制剂样品中杂质B和C增加趋势明显,所有样品中溶氧量呈下降趋势,残氧量基本无变化;长期条件下,高溶氧残氧样品杂质C和聚合物有增长趋势。结论 越低的氧含量越有利于质量控制,建议在中间产品中控制溶解氧<2 μg/mL,残氧量<2.0%,产品较稳定。     

醋酸奥曲肽制剂的质量一致性评价

目的：评价醋酸奥曲肽制剂的质量现状。方法：依据现行法定质量标准,对全国范围内的醋酸奥曲肽进行检验,分析国内醋酸奥曲肽制剂的总体质量水平;并进一步开展了杂质谱、稳定性、醋酸盐、辅料乳酸、渗透压及相容性等方面的探索性研究,更深入地综合评价其质量。结果：本次抽验涉及的91批醋酸奥曲肽制剂按法定标准检验,合格率为100.0%;探索性研究结果表明,国内企业的制剂有关物质总体低于对照的醋酸奥曲肽注射液,制剂的杂质主要为降解杂质,冷冻干燥生产工艺可大大降低注射用醋酸奥曲肽中的醋酸盐含量,对照醋酸奥曲肽注射液的辅料乳酸较好;制剂的渗透压与处方组成及处方中甘露醇的量相关,中硼硅玻璃的金属离子迁移量较硼硅玻璃低。结论：国产醋酸奥曲肽注射液质量状况较好,而注射用醋酸奥曲肽因醋酸盐含量甚低,提示应注意该剂型工艺的合理性。本文探索性研究为今后更严格地控制该产品的质量提供了参考。     

水合氯醛有关物质分析方法优化与稳定性检测

目的 建立水合氯醛中有关物质检查方法,提高水合氯醛相关产品的质量标准与控制限度。方法 建立水合氯醛三氯甲烷与卤代羧酸的检测方法,并通过稳定性监控水合氯醛的杂质变化。结果 经对比研究,本文建立的有关物质方法可满足相关法规要求,同一方法可准确检测原料及其制剂中的4种杂质。结论 本文为水合氯醛及其制剂的质量标准提升提供技术支持,通过水合氯醛杂质检测以及本品在高温、光照的稳定性对比,对实施制剂研究与生产过程中的杂质监控非常必要,可更大程度保障人民群众用药安全。     

HPLC法测定注射用头孢孟多酯钠中有关物质

目的 建立HPLC对注射用头孢孟多酯钠中有关物质进行测定的方法。方法 菲罗门Luna C₁₈(2)色谱柱(250 mm×4.6 mm,5μm),流动相为1%三乙胺溶液(用磷酸调节pH值至2.5)-乙腈(76:24),体积流量为1.5 mL/min,检测波长为254 nm,柱温为40℃,进样量为20μL。采用杂质对照品法外标法计算杂质D,采用加校正因子的主成分自身对照法计算杂质A、E、C。结果 杂质D为主要降解产物,定量限为0.01%,在0.02~0.20μg与峰面积线性关系良好。杂质A、E、C的校正因子分别为1.14、1.25、1.14,检测限分别为0.004%、0.02%、0.04%。结论 杂质D、A、E、C作为特定杂质应订入质量标准,可以更好地控制注射用头孢孟多酯钠中有关物质。     

奥沙利铂注射剂质量分析及探索性研究

目的：评价国内不同企业生产的奥沙利铂注射剂的质量。为奥沙利铂注射剂的标准提高和质量控制提供合理化建议。方法：将法定检验与探索性研究相结合,对抽验样品进行检验和研究,对结果进行统计分析。结果：共抽取样品51批次,按法定检验合格率100%。但现行注射液法定标准无法完全检出奥沙利铂已知和未知杂质,本研究建立了专属性更高的杂质检查方法,并通过杂质谱的比较,发现注射液剂型杂质检出量明显高于注射用无菌粉末。进一步研究表明注射液剂型的终端灭菌方式、贮藏时间、贮藏温度、金属离子含量等影响了奥沙利铂稳定性。结论：目前国内注射用奥沙利铂总体质量较好,奥沙利铂注射液（小水针和大输液）总体质量一般。注射液剂型现行标准有待进一步提高。建议小水针和大输液企业加强药品生产全过程风险管控,对各影响因素进行有效控制。     

对乙酰氨基酚、氢溴酸右美沙芬在口服液中的原辅料相容性研究

目的 制备以对乙酰氨基酚（PA）和氢溴酸右美沙芬（DX）为主成分的复方对乙酰氨基酚口服液,考察PA、DX与辅料间的相容性。方法 建立适合口服液中PA、DX含量测定和有关物质检查的高效液相色谱（HPLC）法,将PA和DX分别与辅料（甘油、丙二醇、山梨醇、三氯蔗糖、苯甲酸钠、依地酸二钠、黄原胶、色素、香精）按一定比例混合、加水溶解并调节pH值,制备二元相容性样品,并取制剂、PA阴性制剂、DX阴性制剂,于高温（60℃）和光照（4 500 lx）条件下破坏0、5、10 d,记录溶液性状、pH值;采用HPLC法检测主成分和有关物质含量变化。结果 建立的HPLC法专属性好,线性关系良好（r＞0.999）,回收率、精密度和耐用性等均符合要求。在光照条件下,除棕色PET瓶包装复方对乙酰氨基酚口服液外,相容性样品从木槿紫色变为深蓝色。与0 d相比,样品pH值逐渐增大,高温条件下增加幅度整体高于光照条件;PA阴性制剂、DX阴性制剂和复方对乙酰氨基酚口服液,作为一个比较完整的制剂体系,pH值变化不明显。光照条件下PA和DX的相容性样品含量降低程度总体高于高温条件;PA与依地酸二钠、黄原胶和香精的相容性样品含量降低幅度高于PA溶液;DX与苯甲酸钠和依地酸二钠的辅料相容性样品含量降低幅度较高;辅料相容性样品含量降低幅度均在2.5%以下。PA总杂质最高达到1.3%,DX总杂质最高达到2.25%,DX在高温条件下稳定性较高,在光照条件下稳定性较差。结论 光照和pH值对主成分稳定性影响较大,将主成分制备成具有一定pH值缓冲区间的制剂,并采用避光性较好的包装材料能够有效提高PA和DX的稳定性。     

Improvement of enalapril maleate chemical stability by high shear melting granulation

Abstract

Enalapril maleate is a widely used drug, which is chemically unstable when mixed with excipients resulting in enalaprilat and diketopiperazine as the main degradation products. The preparation of enalapril sodium salt has been used to improve drug stability in solid dosage forms; however, product rejection is observed when the chemical reaction for obtaining the sodium salt is not completely finished before packaging. In this study, granules were prepared by melting granulation using stearic acid or glyceryl monostearate, with a view to developing more stable enalapril maleate solid dosage forms. The granules were prepared in a laboratory-scale high shear mixer and compressed in a rotary machine. Size distribution, flow properties, in vitro drug release and enalapril maleate chemical stability were evaluated and compared with data obtained from tablets prepared without hydrophobic binders. All formulations showed good physical properties and immediate drug release. The greatest improvement in the enalapril maleate stability was observed in formulations containing stearic acid. This study showed that hot melting granulation could be successfully used to prepare enalapril maleate granules which could substitute the in situ formation of enalapril sodium salt, since they provided better enalapril stability in solid dosage forms.     

Effect of the drug-matrix on the stability of enalapril maleate in tablet formulations

The chemical stability of enalapril maleate in tablet dosage forms consisting of different formulation excipients has been studied in this work. The influence of various parameters such as heat, moisture, light and the drug-matrix was investigated. The degradation of enalapril maleate has been followed by using an HPLC method, which was demonstrated to be specific, stability indicating, accurate and precise. The degradation kinetics of enalalpril maleate in phosphate buffer solutions of pH values in the range of 2.2–10.5 were observed to be psuedo first order throughout the whole pH range studied. Enalapril maleate alone showed high stability for temperature under dry and humid conditions, however it became unstable when mixed with the drug-matrix in its tablet formulations and exposed to the same conditions. The pathway of degradation of enalapril maleate was found to be pH dependent. The extent of degradation of two different enalapril maleate tablet formulations (product A of a basic drug-matrix and product B of an acidic drug-matrix) has been investigated. The degree of degradation of the product with acidic matrix was significantly less than that of the basic matrix under same temperature and humidity conditions. Infact, diketopiperazine and enalaprilat degradants were mainly associated with the degradation of the product with the acidic matrix and that with the basic matrix, respectively. Dry enalapril maleate powder showed some photolysis, which was more significant with daylight (3.3%) compared with that under UV light (0.2%). Although the product with the acidic matrix showed some photolysis but the effect was not pronounced and the % recovery of enalapril was almost complete and within the acceptable experimental errors. However, the product with the basic matrix showed almost no response for photolysis.     

枸橼酸西地那非及关键中间体合成工艺的改进

目的 对枸橼酸西地那非及关键中间体西地那非合成工艺进行优化改进.方法 以邻乙氧基苯甲酰氯与4-氨基-1-甲基-3-正丙基-1H-吡唑-5-甲酰胺为起始物料,经缩合、环合、氯磺化、磺酰胺化、成盐等一系列反应,制备枸橼酸西地那非.结果 关键中间体西地那非纯度在99.5%以上,杂质D(《欧洲药典》)控制在0.3%以下,其他单杂控制在0.15%以下.结论 用精制后西地那非制备出枸橼酸西地那非,纯度在99.8%以上,总收率在45%以上.此工艺成本低,容易操作,且适合工业化生产.     

3D打印氨茶碱分剂量片的辅料相容性研究

目的 制备性质稳定的3D打印氨茶碱分剂量片，通过考察其理化性质，对药物与辅料的相容性进行研究。方法 制备不同处方和工艺的3D打印氨茶碱分剂量片，根据中国药典2020年版方法进行检测，初步确定影响药物稳定性的因素。采用差式扫描量热法(differential scanning calorimetry，DSC)、X射线粉末衍射(X-ray powder diffraction，XRPD)、傅里叶变换红外光谱(Fourier transform infrared spectroscopy，FTIR)、HPLC等方法对3D打印氨茶碱分剂量片进行分析，揭示药物与辅料的相容性以及影响药物稳定性的机制。根据研究结果，制备性质稳定的3D打印氨茶碱分剂量片，并考察其质量。结果 根据中国药典2020年版方法检测无水茶碱和乙二胺含量，初步确定影响药物稳定性的因素为填充剂的添加。添加MCC或乳糖的2种3D打印氨茶碱分剂量片在DSC、XRPD检测均有药物特征峰的消失；FTIR检测结果表明反应产物的官能团吸收峰与药物的有重叠，使特征谱带变宽；HPLC在检测无水茶碱时有小的杂质峰出现，说明MCC中存在少量的糖类降解产物，而乳糖不适合作氨茶碱的辅料，会影响药物的稳定性，因此3D打印氨茶碱分剂量片处方采用非糖类无水磷酸氢钙做填充剂，并根据临床需求规格设计药物处方并打印药片。所得片剂的药物含量及溶出度均符合中国药典2020年版规定，在DSC、FTIR、XRPD图谱中，药物特征峰均未受辅料影响，药物与辅料相容性良好。结论 3D打印药品分剂量片添加辅料时，需考察药物与辅料的相容性，MCC中微量杂质还原糖会与氨茶碱中乙二胺发生Maillard反应，在制备3D打印分剂量片时，需选择不影响药物稳定性的辅料。     

Eudragit E Accelerated the Diketopiperazine Formation of Enalapril Maleate Determined by Thermal FTIR Microspectroscopic Technique

PURPOSE: Enalapril may undergo the thermal-induced intramolecular interaction to cause an enalapril diketopiperazine (DKP) formation. It is interesting to study the influence of Eudragit E, as a coating polymer, on the stability of enalapril maleate. The reaction kinetics of the solid-state degradation process of pure enalapril maleate and Eudragit E/enalapril maleate mixture with different weight ratios were examined. The mechanism of solid-state interaction between Eudragit E and enalapril maleate was also discussed. METHODS: The cast samples of pure enalapril maleate or Eudragit E/enalapril maleate mixture after evaporating the solvent were prepared on an aluminum foil and also determined by reflectance Fourier transform infrared (FTIR) microspectroscopy equipped with thermal analyzer. RESULTS: The result indicates that the interaction might occur between enalapril maleate and Eudragit E in the solid state after evaporating the solvent. The thermal-dependent FTIR spectra show that not only the formation of DKP but also the six-membered cyclic anhydride occurred in the enalapril maleate/Eudragit E mixture in the heating process. Two pathways for solid-sate interaction were proposed. The stability of enalapril maleate was dependent on the weight ratio of enalapril maleate and Eudragit E. The activation energy (n = 3) of DKP formation for pure enalapril maleate was about 141.2+/-0.7 kJ/mol, but it was reduced significantly to 86.7+/-0.8 kJ/mol after interaction with Eudragit E (weight ratio: 1:1), suggesting Eudragit E might exacerbate the degradation of enalapril maleate. However, the degradation accelerated by Eudragit E was reduced in high content of Eudragit E. CONCLUSIONS: When the weight ratio of both components was 1:1, Eudragit E might interact with the carboxyl group of maleic acid to exacerbate the degradation of enalapril maleate. However, the excess amount of Eudragit E might somewhat reduce the degradation of enalapril, due to the interaction that occurred between Eudragit E and carboxyl group of enalapril.     

阿替洛尔片原料与辅料相容性问题的探讨

目的：观察阿替洛尔片原料药与辅料的相容性,为更好地控制和提高质量提供依据和信息.方法：通过加速稳定性试验,应用《中国药典》2010年版二部阿替洛尔片有关物质检查方法,考察阿替洛尔片的有关物质变化,作为阿替洛尔片原辅料相容性的观察指标.结果：有新杂质产生,表明阿替洛尔原辅料发生了相容性反应.结论：阿替洛尔片的原辅料存在相容性问题,初步分析可能是由于阿替洛尔原料和辅料羧甲基淀粉钠中残留的一氯乙酸的相互作用有关,进而提示药品生产企业应关注上市后药品的原辅料相容性问题.     

The application of VIS spectrophotometric determination of enalapril maleate in substance, in tablets and estimation of ester group stability

A new spectrophotometric VIS method is proposed for the determination of enalapril maleate in pure substance and in tablets. Attempts have been made to estimate stability of the ester group in the molecule of enalapril maleate in the solid phase at 70 degrees C.     

The stability of insulin in biodegradable microparticles based on blends of lactide polymers and polyethylene glycol

Abstract

Non-pareil cores were spray-coated with a chlorpheniramine maleate (an alkylamine antihistamine) layer and a Eudragit^R N overcoat in a Wurster air-suspension apparatus. In vitro dissolution studies demonstrated that drug release was a function of polymer membrane thickness. Polyethylene glycol 6000, as a hydrophillic additive, increased the in vitro release of chlorphenir amine maleate from the pellets. Pellets coated with 8 0% Eudragit^R N, 0 0% talc and 0% polyethylene glycol 6000 were found to display desirable controlled release characteristics for chlorpheniramine maleate over the 8-h testing period, which were also comparable with that of Dykatuss^R capsules. The controlled release pellets exhibited first-order release characteristics for chlorpheniramine maleate. Reproducibility of the manufacturing conditions employed in the study were confirmed thus ensuring reproducibility of drug release characteristics between batches of chlorpheniramine maleate pellets. Drug release from the pellets was shown to be independent of the dissolution method and medium used. Pellets displayed no significant change in drug release characteristics relative to the initial drug release data when stored for 12 weeks at room temperature (20+2) and for 8 weeks at a low temperature (5 + 1 °C). However, pellets stored at 37 °C with 80% relative humidity and at 40 + 2 showed a slower in vitro drug release after 8-week storage and therefore failed to maintain their initial drug release profile.     

中国药典2015年版中诺氟沙星胶囊有关物质测定方法的改进研究

目的 考察中国药典2015年版中诺氟沙星胶囊有关物质测定方法的质量可控性,并对现行方法进行改进。方法 分别采用中国药典2015年版和EP9.3版的方法对浙江省各地区抽样的57批诺氟沙星胶囊的有关物质进行检查,对结果进行比较研究;并对中国药典2015年版方法的合理性进行探讨。结果 57批抽样样品按EP9.3版有关物质测定方法检查,结果有5批样品检出杂质E超出限度（0.15%）,1批杂质K为限度边缘（0.15%）,而根据中国药典2015年版方法检查结果,57批样品全部合格。现行的中国药典2015年版诺氟沙星胶囊有关物质测定方法专属性不强,杂质E被包含在主峰之中难于检出;现行标准有关物质测定方法中不同品牌的C₁₈色谱柱以及流动相条件对测定结果影响较大,选择Waters Sunfire C₁₈色谱柱,调整流动相的比例和梯度条件可以使杂质E与诺氟沙星主峰很好地分离,样品的测定结果也与EP9.3方法的测定结果一致,能达到控制杂质E、杂质K以及其他杂质的目的。结论 目前浙江省市场上的诺氟沙星胶囊中杂质E有超标的情况,但根据中国药典2015年版的现行有关物质测定方法难以检出,难以有效控制药品的质量,需修订提高。     

Bioequivalence study of two enalapril maleate tablet formulations in healthy male volunteers Pharmacokinetic versus pharmacodynamic approach

Objective: Two different conventional release enalapril maleate tablet formulations were evaluated for their relative bioavailability (Eupressin tablets 10 mg, Biosintética as the test formulation vs Renitec tablets 10 mg Merck Sharp & Dhome, as the reference formulation). A single 20 mg oral dose of each preparation was administered to 18 healthy male adult volunteers and their bioequivalence was assessed by comparing the serum enalaprilat and total enalapril (enalaprilat plus enalapril maleate) concentration-time curves. Angiotensin converting enzyme (ACE) activity was also quantified in each serum sample. Results: The pharmacokinetic parameters obtained for each formulation were the area under the time-concentration curve from 0 to 24 h (AUC_[0–24]), maximum concentration C_max and the time at which it occurred (t_max). When serum enalaprilat concentration-time curves were employed to assess bioequivalence, the formulations were bioequivalent in the extent but not in the rate of absorption. However, no difference in either the extent or the rate of absorption were observed when serum total enalapril vs time curves were analysed. ACE activity-time curves were similar for both formulations and showed that ACE was 90% inhibited 3–5 h after enalapril administration, and till approximately 50% after 24 h. At that time, circulating enalaprilat and total enalapril levels were less than the tenth of C_max. Conclusion: The results show that complete bioequivalence of the two formulations can be concluded from serum total enalapril concentration data, and that serum ACE activity is not a suitable pharmacodynamic variable for assessing bioequivalence. Received: 29 May 1995/Accepted in revised form: 30 October 1995