The quality evaluation of magnesium oxide tablet due to acid neutralization action

For the purpose of quality evaluation of magnesium oxide (MgO) tablets, we considered the dissolution test method with changes in the pH of the dissolution medium as an indicator and studied the elution behavior of MgO from commercial MgO tablets. We also studied the effects of particle size on the elution rate of MgO from MgO tablets. A dissolution test was carried out using the rotating basket method in 100 ml of the first fluid (pH 1.2). The stirring speed was set at 200 rpm. The elution behaviors of MgO from two products were markedly different. The medium pH for the sample MM (Magmit) tablet after 15 min reached 9.5 but that for ML (Maglax) tablet was 2.7 even after 60 min. The apparent solubility of MgO in 100 ml of the first fluid were, respectively, 175 mg and 100 mg when medium pH as 9.5 and 1.5. The low dissolution of ML tablets is thought to be due to the large particle size (average particle size r = 226 microm) or due to the effects of additives on elution. These results suggest that neutralizing activity after ingestion of MgO tablets and subsequent laxative effects may, when conditions after ingestion of MM tablets and after ingestion of ML tablets are compared, produce differences between them. We found that the dissolution test method with pH as an indicator is useful in assessing the dissolution behavior of MgO preparations.     

Evaluation of the USP dissolution test method A for enteric-coated articles by planar laser-induced fluorescence

The USP drug release standard for delayed-release articles method A was evaluated using planar laser-induced fluorescence (PLIF). Prior authors have suggested that high pH “hot spots” could develop during the buffer medium addition of the method A enteric test. Additionally, previous studies have shown heterogeneous flow patterns and low-shear regions in the USP Apparatus II dissolution vessel, which may result in poor mixing of the buffer and acid media during the pH neutralization step of the method A enteric test. In this study, PLIF was used to evaluate the mixing patterns and evolution of pH neutralization during the buffer medium addition with rhodamine-B dye and the pH-sensitive dye fluorescein, respectively. Additionally, a comparison of the methods A and B enteric tests was performed with enteric-coated tablets containing rhodamine-B in the film so as to image the dissolution rate of the coating polymer with PLIF in order to determine if rapid buffer addition for the method A procedure accelerates the rate of film coat dissolution. Rapid addition of the 250 mL of buffer medium over 5 s to the 750 mL of acidic medium shows efficient mixing and pH neutralization due to the generation of large-scale stirring and enhanced turbulence resulting from the descending buffer medium. Slow addition near the paddle shaft over 5 min showed segregation in the recirculating region around the paddle shaft. In contrast, slow addition near the vessel wall introduces the medium into fluid outside of the recirculation region and enables transport over the entire vessel. Enteric-coated tablets tested according to method A with rapid medium addition and method B enteric tests performed identically, indicating no difference in polymer dissolution rate between the two tests. From the results of the PLIF imaging studies with rhodamine-B, fluorescein, and enteric-coated tablets, it was seen that “hot spots” affecting the dissolution performance of enteric dosage forms are not generated during the neutralization step of the method A enteric test namely when the media is added rapidly or outside of the recirculating region that surrounds the paddle shaft.     

苯磺酸左旋氨氯地平片在不同介质中的溶出度

目的：考察苯磺酸左旋氨氯地平片在盐酸溶液（9→1000）、醋酸-醋酸钠缓冲液（pH4．5）、磷酸盐缓冲液（pH6．8）、水等介质中的溶出度。方法：采用《中国药典》2010年版二部附录XC第三法操作,转速为50r／min,以紫外分光光度法测定溶液的光密度并计算溶出度。结果：两厂家苯磺酸左旋氨氯地平片在不同溶出介质中的溶出曲线基本一致,在盐酸溶液（9→1000）中的累积溶出度最高。结论：苯磺酸左旋氨氯地平片为碱性物质,溶出速率受介质的pH影响较大。     

采用计算机模拟技术结合Caco-2细胞模型与溶出度试验考察国产盐酸曲美他嗪片的生物等效性

目的：采用计算机模拟技术结合Caco-2细胞模型和溶出度试验，对国产盐酸曲美他嗪生物等效性进行研究。方法：首先基于Caco-2单层细胞膜模型考察盐酸曲美他嗪的渗透性，获得其表观渗透系数P_app；第二步采用HPLC法测定溶出曲线来比较10家国产企业与原研生产的盐酸曲美他嗪片在5种不同pH条件下体外溶出行为的差异；最后采用Gastrol Plus^TM软件，导入本试验实测P_app，通过该软件转化为P_eff值，建立准确的体外溶出曲线与体内药动学曲线之间的相关性模型，基于该模型预测国产盐酸曲美他嗪片的药动学曲线，对其生物等效性进行体内外相关的研究。HPLC测定法：C₁₈柱，以0.287%无水庚烷磺酸钠-甲醇（55：45）为流动相，检测波长为231 nm，流速1.0 mL·min^-1；溶出度方法：分别以0.05 mol·L^-1盐酸溶液，pH 1.2、pH 4.0、pH 6.8缓冲盐溶液和水为溶出介质，桨法50 r·min^-1，溶出体积900 mL，分别考察片剂在上述5种溶出介质中5，10，5，20，30，45，60，90 min取样的溶出曲线。结果：盐酸曲美他嗪的表观渗透系数P_app值随着药物浓度的增加反而下降，属于中等渗透的药物；不同pH的溶出介质对盐酸曲美他嗪片的溶出行为无区分性；但在每种溶出介质中，国外原研片剂溶出较慢，与国产片剂的溶出行为存在明显差异，多数国产片剂快速溶出；采用Gastrol Plus^TM软件从药物在体内具有不同释放速率时的体内吸收情况与通过体外溶出曲线模拟体内吸收情况两个方面进行模拟研究，结果显示现有的国产盐酸曲美他嗪片与原研片剂在体内能够生物等效。结论：尽管国产盐酸曲美他嗪片的体外溶出曲线与原研片剂存在差别，但体内生物等效的可能性极大。Gastrol Plus^TM软件能够预测口服固体制剂与原研制剂的生物等效性，可在一致性评价工作中推广应用。     

A dissolution test for a pressure-controlled colon delivery capsule: rotating beads method.

The rotating beads method is a new in-vitro dissolution test proposed for drugs formulated as pressure-controlled colon delivery capsules (PCDCs). The apparatus consisted of a glass vessel (500 mL) containing 4-mm (i.d.) glass beads (5000, 10000 or 15000) and dissolution medium (0-067 M phosphate buffer, pH 7; 25, 50 or 100 mL) containing polyvinyl alcohol (PVA; 5, 10 or 20 w/v%) to simulate the viscosity of the colon. The vessel was rotated at 5, 10 or 25 rev min(-1) and the temperature was maintained at 37 degrees C. Fluorescein was used as a model drug to explore the optimized conditions under which differences in the drug dissolution rate are detected between colon delivery systems. Fluorescein was formulated in four types of colon delivery systems. One was a tablet coated with an enteric polymer, Eudragit S-100, and the other three were PCDCs prepared with different thicknesses of ethylcellulose coating membrane (type I, II, III). The dissolution behaviour of fluorescein from the PCDC formulation was significantly different from that of the Eudragit S-100-coated tablets, when the dissolution conditions were as follows: rotation speed, 10 rev min(-1); bead number, 10000; dissolution medium, 50mL with 10% PVA. This dissolution method was applied to acetaminophen sustained-release tablets and two other drugs having low solubility in the colon, tegafur and 5-aminosalicylic acid. Similarly, significant differences in the dissolution rates of drugs from the PCDC formulation and the enteric tablet were detected. There was good correlation between the in-vitro dissolution rates and in-vivo absorption rates using T50 (the time for half of the amount of drug to be released from the preparation) and Cmax/Tmax (enteric tablet) or Cmax/(Tmax-Ti) (PCDC), where Ti is the first appearance time in the systemic circulation. The rotating beads method is a valuable technique for evaluating the dissolution rate of drugs formulated in PCDC.     

Dissolution testing of acetylsalicylic acid by a channel flow method—correlation to USP basket and intrinsic dissolution methods

A new modification of the channel flow dissolution method is introduced together with the theoretical basis to extract the solubility and mass transfer parameters from the dissolution experiments. Correlation of drug dissolution profiles in the channel flow apparatus was evaluated with respect to USP basket and intrinsic dissolution methods at pH 1.2 or 6.8. Acetylsalicylic acid (ASA) was studied as a pure drug substance and as three simple tablet compositions with microcrystalline cellulose (MCC) and/or lactose as excipients. The channel flow measurements of 100% ASA tablets correlated well with the results of intrinsic dissolution tests. In the channel flow method as well as in the USP basket method the release of ASA was fastest from the tablet compositions containing lactose, while the slowest dissolution rate was observed with the composition containing MCC as the only excipient. As presumed, the dissolution rate of the weak acid was decreased as the pH of the medium was lowered, which was clearly confirmed also by the three dissolution methods. MCC forms matrix tablets and in the USP basket method the dissolution profiles followed square root of time kinetics indicating that diffusion was the rate-controlling step of ASA dissolution. Also the channel flow results indicated that the dissolution of ASA was controlled by mass transfer. The swelling behaviour of the tablets is different in the channel flow method as compared to the basket method: only one tablet surface is exposed to the dissolution medium in the channel flow system. The contact between the tablet surface and the dissolution medium is more similar between the channel flow and intrinsic dissolution methods.     

Influence of in vitro test conditions on release of aspirin from commercial tablets.

The influence of in vitro test conditions on the release of aspirin from commercial tablets was assessed with a USP rotating-basket dissolution apparatus. Three types of aspirin tablets were evaluated: plain, buffered, and microencapsulated. The variables investigated were stirring speed, pH, and volume and temperature of the dissolution medium. Plain tablets gave the best dissolution profiles under all experimental conditions, except at pH 3. Microencapsulated tablets showed sustained release. For all three types of tablets, faster dissolution was observed at pH 4.5 compared with that in artificial gastric juices. Increasing the stirring rate increased the dissolution rate, an effect most pronounced for plain tablets. Very similar dissolution curves were obtained when the dissolution test was conducted in 500 and 900 mL of dissolution media regardless of the pH of the media. No significant difference in dissolution profiles was observed when the effect of temperature was investigated. The dissolution data were evaluated on the basis of theoretical dissolution equations and by linear transformation of dissolution curves. Highly significant linear correlation coefficients revealed that the cube root equation could be used to describe drug release in artificial gastric juices, regardless of tablet type. When pH 4.5 buffer solution was used as the dissolution medium, different kinetic models were applicable.     

Roles of MgO release from polyethylene glycol 6000-based solid dispersions on microenvironmental pH,enhanced dissolution and reduced gastrointestinal damage of telmisartan

The roles of magnesium oxide (MgO) release from solid dispersions (SDs) in simulated gastric fluid (SGF), simulated intestinal fluid (SIF) and water were investigated to elucidate the enhanced dissolution and reduced intestinal damages of telmisartan as a model drug. The polyethylene glycol 6000 (PEG 6000) was used to prepare the SDs. Three SDs were prepared: SD1 (PEG, MgO, TEL), SD2 (PEG 6000, TEL), SD3 (MgO, TEL). The physical mixture (PM) consisting of SD2 and MgO was also prepared. A binary SD without MgO (SD2) was also prepared for comparison in microenvironmental pH (pH_M) modulation. The faster MgO released, the less control of pH_M and the less enhanced dissolution of TEL were in consequences. SD3 increased dissolution in SIF and water (about 67%). Interestingly, ternary SD1 showed almost complete dissolution in all three media but dissolution of PM was the lowest due to the fast release of MgO and poor modulation of pH_M. MgO did not change the drug crystallinity but did have a strong molecular interaction with the drug. Additionally, the SD3-bearing tablet quickly increased pH_M but then gradually decreased due to faster release of MgO while the SD1-bearing tablet gradually increased pH_M at all fractional dimensions of the tablet by the MgO slowly released. The pH_M of PM-bearing tablets was not varied as a function of time. Thus, the MgO-bearing SD1 also minimized gastrointestinal tissue damage caused by the model drug.     

国产盐酸二甲双胍片与国际公认参比制剂溶出度比较

目的建立盐酸二甲双胍片溶出度测定方法,并分别比较250 mg及500 mg 2种规格国产盐酸二甲双胍片与国际公认参比制剂的溶出曲线。方法分别以水、0.1 mol·L-1盐酸、pH 4.0及pH 6.8磷酸盐缓冲溶液为溶出介质,采用桨法进行体外溶出度试验。用高效液相-紫外分光光度法(HPLC-UV)测定溶出介质中药物含量,并采用溶出度相似因子(f2值)分别评价国产片(每片250 mg)与日本橙皮书Glycoran(每片250 mg)、国产片(每片500 mg)与欧盟上市Merck SantéS.A.S(每片500 mg)在各pH介质中的相似性。结果每片250 mg的2种制剂在各溶出介质中,15 min内的溶出百分率均>85%。在0.1 mol·L-1盐酸的溶出介质中,国产盐酸二甲双胍片(每片500 mg)与欧盟上市Merck SantéS.A.S(每片500 mg)的溶出曲线f2值为78.5(>50);在水、pH 4.0及pH 6.8磷酸盐缓冲溶液的溶出介质中,2种制剂的溶出曲线f2值均<50。结论 2种规格为每片250 mg的盐酸二甲双胍片溶出行为相似。除0.1 mol·L-1的盐酸介质外,2种规格为每片500 mg的盐酸二甲双胍片在各种溶出介质中的溶出行为不相似。     

Preparation of enteric coated timed-release press-coated tablets and evaluation of their function by in vitro and in vivo tests for colon targeting

As a new oral drug delivery system for colon targeting, enteric coated timed-release press-coated tablets (ETP tablets) were developed by coating enteric polymer on timed-release press-coated tablets composed of an outer shell of hydroxypropylcellulose and core tablet containing diltiazem hydrochloride (DIL) as a model drug. The results of the in vitro dissolution tests in JP 1st fluid (pH 1.2) and JP 2nd fluid (pH 6.8) indicated that these tablets showed both acid resistance and timed-release. To clarify whether ETP tablets could have been of use in the gastrointestinal tract, ETP tablets with a layer of phenylpropanolamine hydrochloride (PPA) (a marker of gastric emptying) between the enteric coating layer and outer shell were prepared, and were administered to beagle dogs. The gastric emptying time and lag time after gastric emptying were evaluated by determining the times at which PPA and DIL first appeared in the plasma (TFA(PPA) and TFA(DIL), respectively). TFA(PPA) and TFA(DIL) were about 4 and 7 h, respectively. This value of TFA(PPA) indicated that ETP tablets displayed acid resistance in the stomach as well as in JP Ist fluid. Subtraction of TFA(PPA) from TFA(DIL) gave a value of about 3 h which agreed well with the lag time determined by in vitro dissolution test in JP 2nd fluid. Also, the results seemed to be in accordance with the time at which the tablets reached the colon after gastric emptying. Therefore, ETP tablets seemed to be an effective tool for oral site-specific delivery including targeting of the colon.     

无时滞非达霉素肠溶片的制备及溶出评价

目的: 制备无时滞非达霉素肠溶片,考察其溶出特性。方法: 采用湿法制粒工艺,通过正交实验进行片芯优化,以甲基丙烯酸与丙烯酸乙酯共聚物为肠溶包衣材料,制备非达霉素肠溶片,以体外释放度为指标,考察其溶出行为。结果: 片芯中羟丙甲纤维素和交联羧甲基纤维素钠的用量分别为1.2%和4.5%,微晶纤维素和淀粉的比例为3:1,肠溶层共聚物的比例为50%时,制备的非达霉素肠溶片在pH1.0盐酸中2h释放度小于10%,在pH4.5醋酸盐缓冲液中可以崩解释放,在pH6.8磷酸盐缓冲液中快速释放,10min释放度大于60%。结论: 制备的非达霉素肠溶片与普通肠溶片相比无时滞效应,有望进行工业化生产。     

盐酸曲美他嗪片溶出度测定方法的建立

目的:建立测定盐酸曲美他嗪片溶出度的方法。方法:溶出度测定采用桨法,分别以900mL水、pH1.0盐酸溶液和pH6.8磷酸盐缓冲液为溶出介质,转速为50、75、100r·min-1进行溶出条件的筛选。含量测定采用紫外分光光度法,检测波长为232nm。考察样品在30min时的体外溶出情况。结果:确立了以900mL水为溶出介质、桨法转速为50r·min-1的溶出方法;在30min内,样品溶出达到80%以上。结论:所建方法简便、准确、结果可靠,可用于盐酸曲美他嗪片溶出度测定。     

盐酸鲁拉西酮片的溶出度研究

目的:考察并比较自制盐酸鲁拉西酮片与原研片的溶出度。方法:溶出度测定采用桨法,以pH 3.8 McIlvaine缓冲溶液900 ml为溶出介质,转速为50 r/min,温度为(37±0.5)℃;采用反相高效液相色谱法测定盐酸鲁拉西酮的含量,色谱柱为C8,流动相为0.05 mol/L磷酸盐缓冲液(pH 3.0)-乙腈(60∶40),检测波长为230 nm,流速为1.2 ml/min,柱温为40℃。对5批自制片与1批原研片的溶出行为采用相似因子法和威布尔法进行评价。结果:盐酸鲁拉西酮检测质量浓度线性范围为10¹00μg/ml(r=0.999 9),平均回收率为99.88%(RSD=0.55%,n=3)。5批自制片与原研片的相似因子均大于85,威布尔法中各溶出参数比较差异无统计学意义(P>0.05)。结论:建立的溶出度测定方法简便、快速、准确、可靠;自制片与原研片体外溶出度一致。     

地塞米松片的溶出度

目的：研究并建立地塞米松片溶出度的介质及测定方法。方法：采用转篮法分别以1%盐酸，5%乙醇溶液，10%乙醇溶液，15%乙醇溶液及磷酸盐缓冲液（pH=6.6)5种溶出介质进行地塞米松片的溶出试验。以HPLC法测定溶出介质中地塞米松的浓度。结果：研制片与市售地塞米松片在5%乙醇溶液中45min时的溶出度均大于标示量的79%。结论 所建立的HPLC方法准确。可靠；地塞米松片在5%乙醇溶液中的溶出度符合药典要求。     

羟丙基甲基纤维素的凝胶特性及其对曲尼司特缓释片释放行为的影响

目的：研究羟丙基甲基纤维素(HPMC)的凝胶特性及其对曲尼司特缓释片释放行为的影响。方法：采用称重法、图像法和体积测量法,研究HPMC辅料片和曲尼司特缓释片在不同pH环境中的水合度和溶胀度。结果：辅料片在SGF和SIF中的水合速率常数分别为0.897 h-1和0.681 h-1;溶胀速率常数分别为1.005 h^-1和0.713 h^-1。曲尼司特缓释片在SGF中,在0.5 h内迅速水合和溶胀,其后呈负增长;而在SIF中,重量和体积都缓慢增加,5 h后重量稍有下降,体积保持不变。结论：HPMC水凝胶的形成速度和形态与介质的pH有关,凝胶层的溶蚀速度控制药物的释放。     

In vitro release of valerenic and hydroxyvalerenic acids from valerian tablets

Although most commercial valerian formulations are coated tablets not any comparison study of their drug release profiles has been published so far. The main objective of this work is to establish a drug release test suitable for studying and comparing different valerian tablets. Thus, hydroxyvalerenic and valerenic acid concentrations were assayed by HPLC using a C18 Kromasil (200 x 4.6 mm, 5 microm) column and a mobile phase containing methanol and an orthophosphoric acid solution 0.5% v/v in water at a ratio of 75:25 at a constant flow rate of 1 ml/min. Saturation solubilities for hydroxyvalerenic and valerenic acid at pH 6.8 were 26 +/- 5.1 and 1 +/- 0.6 microg/ml, respectively. Usually for drugs with such low solubility values, their oral absorption and hence bioavailability are limited by their dissolution characteristics. A dissolution test was conducted according to the general method 2 (paddles) of USP 24 using 500 ml buffer medium (pH 6.8) at 50 rpm. Five different formulations were studied and compared: one uncoated tablet formulation and four marketed coated tablets. The uncoated tablet formulation had the fastest release profile, whereas the coated tablets manifested very different release patterns, depending on the type of formulation. Because of these differences in drug release pattern not every tablet formulation may be appropriate for the same clinical indications. Clinical data are required to confirm the correlation between drug release pattern and the therapeutically value of each formulation.     

Design and evaluation of a rotating filter-magnetic basket apparatus: tablet and basket position

The authors have designed a dissolution device which combines the properties of a rotating filter device developed by Shah and a magnetic basket designed by Shepard et al. The effects of stirring, tablet and basket placement were investigated. Visualization of flow and dissolution patterns was possible by testing non-disintegrating salicylic acid tablets containing 3% phenolphthalein in 0.1 N sodium hydroxide solution. Dissolution experiments were conducted on non-disintegrating salicylic acid in pH 7.4 U.S.P. phosphate buffer at 37°C. For the tablet placement experiments one tablet face and the tablet land was coated so that only a single tablet face was available for dissolution. The data for the same size tablets placed at the side of the bottom and at the center of the bottom of the dissolution fluid container indicated the importance of exact placement of a tablet in a dissolution fluid container. The differences in face position of the tablet either with or without a magnetic basket present indicates the importance of face position which must be accounted for especially in the testing of double-layer sustained release products. Through the dissolution data and the visualization studies the authors have characterized the hydrodynamics of this device.     

国产与原研阿莫西林/克拉维酸钾片溶出度考察

目的：考察阿莫西林和克拉维酸钾在4种介质中的稳定性及自制阿莫西林/克拉维酸钾片、市售品和原研制剂在不同介质中的溶出曲线,分析体外释放行为.方法：采用已知含量的原料溶解于不同溶出介质中,在不同的时间段测定其色谱峰面积,考察其稳定性.参考日本橙皮书中阿莫西林/克拉维酸钾片溶出曲线的测定方法,以不同溶出介质对阿莫西林/克拉维酸钾片进行溶出曲线考察.采用f2因子进行比较分析.结果：克拉维酸在pH1.2、pH4.0溶出介质中1 h分别降解90%和3%,在水、pH6.8介质中8 h稳定;阿莫西林在pH1.2溶出介质中1 h降解3%,在水、pH4.0、pH6.8溶出介质中8 h稳定.C厂样品与B厂样品在不同溶出介质中溶出曲线均与A厂（原研）产品相似;C厂样品与B厂样品在pH1.2的盐酸溶液与pH4.0的醋酸缓冲溶液中前10 min的溶出速度较原研A药品快10%~20%.D厂样品、E厂样品在水介质下与原研样品不具有相似性.结论：克拉维酸溶液（pH1.2）稳定性极差;国内有些厂家产品在4种溶出介质中的溶出曲线与原研产品不一致,质量存在差异.     

Investigation of physicochemical factors affecting the stability of a pH-modulated solid dispersion and a tablet during storage

The stability of solid dispersions (SD) during storage is of concern. We prepared the pH-modulated SD (pSD) and compressed tablets consisting of polyethylene glycol (PEG) 6000 as a carrier, drug and MgO (alkalizer). Telmisartan (TEL), an ionizable poorly water-soluble drug, was chosen as a model drug. The changes in physicochemical factors such as the dissolution rate, drug crystallinity, microenvironmental pH (pH(M)) and intermolecular interactions of the pSD and the tablets were investigated over 3 months under different temperature and relative humidity (RH) conditions: refrigerator (5-8 °C), 25 °C/32% RH, 25 °C/55% RH, 25 °C/75% RH, 40°C/32% RH, 40 °C/55% RH, and 40 °C/75% RH. Differential scanning calorimetry (DSC) analysis of all samples revealed no distinct changes in the drug melting point. In contrast, powder X-ray diffraction (PXRD) diffractograms revealed that samples stored at 40 °C/75% RH for 1 month, 25 °C/75% RH for 3 months and 40 °C at all humidity conditions for 3 months showed gradual recrystallization of the drug. Fourier transform infrared (FTIR) spectra indicated a reduced intensity of intermolecular interactions between TEL and MgO in the pSD and tablet. The pH(M) also gradually decreased. These altered physicochemical factors under the stressed conditions resulted in decreased dissolution profiles in intestinal fluid (pH 6.8). In contrast, the dissolution rate in gastric fluid (pH 1.2) was almost unchanged because of the high intrinsic solubility of TEL at this pH.     

Effect of pH on disintegration and dissolution of ketoconazole tablets

The effect of pH on the in vitro disintegration, dissolution, and solubility of ketoconazole tablets was studied. One 200-mg ketoconazole tablet was added to each of five different buffer solutions having pH values of 2 to 6;900 ml of each solution containing the ketoconazole was placed in a stationary basket dissolution device and stirred at 500 rpm at 37 degrees C for 60 minutes. Single 1-ml samples of each solution were obtained at 1,3, and 5 minutes after addition of the drug, and then every 5 minutes for the duration of the sampling period. This same procedure was repeated using two 200-mg tablets in the buffer solution at pH 3. The effect of pH on ketoconazole solubility was studied by gradually increasing the pH of a ketoconazole solution at pH 3 to pH 10. Samples of this solution were analyzed periodically after allowing a short period for equilibration of pH. All samples were assayed spectrophotometrically against blanks, and concentrations were determined by comparison with a standard curve. Disintegration of ketoconazole tablets occurred within 5 minutes in each buffer solution and was unaffected by pH. At pH 2 and 3, dissolution of ketoconazole was greater than 85% complete after five minutes, and all ketoconazole had dissolved after 30 minutes. As pH increased, the rate and extent of dissolution slowed; only 10% of ketoconazole was dissolved after 60 minutes at pH 6. Ketoconazole precipitated rapidly from solution as the pH of the dissolution medium exceeded 5.5. There was no difference in the rate or extent of dissolution of ketoconazole for the two doses studied at pH 3. In the buffer solutions tested, dissolution but not disintegration of ketoconazole tablets is pH-dependent. Dissolution characteristics of 200- and 400-mg doses of ketoconazole are similar at pH 3.