Relationship between dissolution and bioavailability for nimodipine colloidal dispersions: the critical size in improving bioavailability

To compare the dissolution and bioavailability for nimodipine microcrystals and nanocrystals, and to determine the critical size range in improving the oral absorption of nimodipine. Nimodipine microcrystals and nanocrystals were prepared using a microprecipitation method. The particle size was determined with a laser diffraction method. X-ray powder diffraction was applied to inspect the potential crystal form transition. The aqueous solubility was determined by shaking flasks, and the dissolution behavior was evaluated using the paddle method. The pharmacokinetics was performed in beagle dogs in a crossover experimental design. Three nimodipine colloidal dispersions (16296.7, 4060.0 and 833.3 nm) were prepared, respectively. Nimodipine had undergone crystal form transition during microprecipitation process, but experienced no conversion under the high-pressure homogenization. The colloidal dispersions did not show any difference in aqueous equilibrium solubility. Additionally, the three formulations also displayed similar dissolution curves in purified water and 0.05% SDS. The AUC for dispersions of 4060.0 and 833.3 nm sizes was 1.69 and 2.59-fold higher than that for 16296.7 nm system in dogs. To sum up, the critical particle size was found to be within the range of 833.3-4060.0 nm (average volume-weighted particle size) in improving the bioavailability of nimodipine, and dissolution performance was not an effective index in evaluating the bioavailability for nimodipine colloidal dispersions.     

Comparative bioavailability of furosemide from solution and 40 mg tablets with different dissolution characteristics following oral administration in normal men

Furosemide tablets, with markedly different dissolution characteristics, and solution were orally administered to 21 healthy adult males to determine the effect of in vitro dissolution rate on in vivo bioavailability profiles. Furosemide 40 mg was given as Tablet A (fast dissolution characteristics), Tablet B (slow dissolution characteristics), and an aqueous solution. Both batches of tablets had identical formulae and were produced by a common process. The dissolution rate of the slower Tablet B was probably retarded by extension of the wet granulation time. Blood was collected for 12 h postdose and urine for 24 h. Peak plasma furosemide concentrations after the solution were significantly greater than after the tablets; there was no significant difference between the tablets. The time to peak occurred significantly earlier with the solution, with no significant difference between the tablets. Relative bioavailabilities of Tablet A and B were 89 per cent and 101 per cent, respectively, as determined by AUC, and 79 per cent and 84 per cent, respectively, as determined by urine recovery. These differences are not statistically significant. These results indicate that dissolution rate profiles of furosemide tablets may not be predictive of in vivo bioavailability.     

In vitro evaluation of food effect on the bioavailability of rifampicin from antituberculosis fixed dose combination formulations

Rifampicin is one of the major first line anti-tuberculosis drugs used in the therapy of tuberculosis. In literature, there are conflicting reports regarding effect of food on the bioavailability of rifampicin. In vitro, effect of food on the bioavailability can be studied by simulating in vivo conditions in dissolution fluid hence, to understand the variable effect of food on rifampicin release, dissolution studies were done by simulating in vivo conditions after meal intake. In this study, we assessed the effect of hydrodynamic stress in presence of food and meal composition on two rifampicin containing fixed dose combination formulations by carrying out dissolution at different agitation rates (simulation of fasted and fed state) as well as in the presence of different percentage of oil (fatty food). Agitation intensity as well as presence of oil did not had any influence on rifampicin release from formulation A. This formulation had shown excellent release characteristics at all the conditions studied. Whereas, formulation B showed agitation rate dependent release and also release was affected in presence of oil. Hence, it is concluded that food may not have any effect on the release of rifampicin from the formulation and subsequently on its bioavailability if the formulation has excellent release profile (>85% release in 10 min). Further, effect of food on the rifampicin release was a function of dosage form characteristics such as disintegration time and dissolution rate, which will subsequently affect the release behavior of a formulation in presence of food.     

奥美沙坦酯氢氯噻嗪片的制备及其溶出度研究

目的 制备奥美沙坦酯氢氯噻嗪片并对其溶出度进行考察.方法 采用分别制粒混合压片工艺制备奥美沙坦酯氢氯噻嗪片,采用高效液相色谱法测定其溶出度,并通过加速试验考察该产品的溶出度.结果 样品质量稳定,高效液相色谱法测定该片奥美沙坦酯和氢氯噻嗪溶出度分别为99.3％和99.8％.结论 该处方工艺合理,所得产品溶出度较好.     

In vitro dissolution and oral bioavailability study of fenofibrate nanomatrix system prepared by hot-melt extrusion

Solvent evaporation method for preparation of nanomatrix has the disadvantages, such as residual organic solvent, environmental pollution, explosion-proofing and so on. To overcome these shortcomings, a series of fenofibrate nanomatrix drug delivery system (NDDS) consisting of nano-porous silica Sylysia^®350 (S350) and pH sensitive material Eudragit^® L100-55 (EL100-55) were prepared using hot-melt extrusion (HME), and their in vitro dissolution and in vivo bioavailability were compared. Finally, the formulation with the highest in vivo bioavailability was selected as the optimized formulation for DSC and PXRD characterization. The results showed that the optimized NDDS showed a higher bioavailability than the reference formulation, although there was crystalline form drug remaining in NDDS. The relative bioavailability of the optimized formulation was 157.1% compared with the commercial product Lipanthyl^®. In addition, the relative bioavailability of the optimized formulation was 124.8% in comparison with the formulation prepared by solvent evaporation method, showing that the NDDS prepared by the HME method was effective in improving the bioavailability of fenofibrate. In conclusion, HME was a promising method to prepare NDDS.     

氢氯噻嗪缓释片的制备及体外释放考察

目的:制备氢氯噻嗪亲水凝胶缓释片,并评价其体外释放特性. 方法:以羟丙基甲基纤维素和卡波姆为骨架材料,运用正交设计法,粉末直接压片制备氢氯噻嗪缓释片, 并测定其释放度.结果:正交设计获最优处方为A1B3(R3),药物体外释放行为符合Higuchi方程.结论:该方法制得的缓释片具有明显的缓释效果,影响药物释放的主要因素是卡波姆的用量.     

Effect of solubilizing and microemulsifying excipients in polyethylene glycol 6000 solid dispersion on enhanced dissolution and bioavailability of ketoconazole

Polyethylene glycol (PEG) 6000-based solid dispersions (SDs), by incorporating various pharmaceutical excipients or microemulsion systems, were prepared using a fusion method, to compare the dissolution rates and bioavailabilities in rats. The amorphous structure of the drug in SDs was also characterized by powder X-ray diffractometry (XRD) and differential scanning calorimetry (DSC). The ketoconazole (KT), as an antifungal agent, was selected as a model drug. The dissolution rate of KT increased when solubilizing excipients were incorporated into the PEG-based SDs. When hydrophilic and lipophilic excipients were combined and incorporated into PEG-based SDs, a remarkable enhancement of the dissolution rate was observed. The PEG-based SDs, incorporating a self microemulsifying drug delivery system (SMEDDS) or microemulsion (ME), were also useful at improving the dissolution rate by forming a microemulsion or dispersible particles within the aqueous medium. However, due to the limited solubilization capacity, these PEG-based SDs showed dissolution rates, below 50% in this study, under sink conditions. The PEG-based SD, with no pharmaceutical excipients incorporated, increased the maximum plasma concentration (Cmax) and area under the plasma concentration curve (AUC(0-6h)) two-fold compared to the drug only. The bioavailability was more pronounced in the cases of solubilizing and microemulsifying PEG-based SDs. The thermograms of the PEG-based SDs showed the characteristic peak of the carrier matrix around 60 degrees C, without a drug peak, indicating that the drug had changed into an amorphous structure. The diffraction pattern of the pure drug showed the drug to be highly crystalline in nature, as indicated by numerous distinctive peaks. The lack of the numerous distinctive peaks of the drug in the PEG-based SDs demonstrated that a high concentration of the drug molecules was dissolved in the solid-state carrier matrix of the amorphous structure. The utilization of oils, fatty acid and surfactant, or their mixtures, in PEG-based SD could be a useful tool to enhance the dissolution and bioavailability of poorly water-soluble drugs by forming solubilizing and microemulsifying systems when exposed to gastrointestinal fluid.     

Enhancement of dissolution amount and in vivo bioavailability of itraconazole by complexation with beta-cyclodextrin using supercritical carbon dioxide

The main objective of this study was to improve the inclusion formation between itraconazole and beta-cyclodextrin and thus enhance dissolution amount and bioavailability characteristics of itraconazole. Inclusion complexes between itraconazole and beta-cyclodextrin were prepared using simple physical mixing, conventional coprecipitation method, and supercritical carbon dioxide (SC CO(2)). Effects of process variables (temperature, pressure) and drug:cyclodextrin ratio on inclusion yield and thermal behavior of the solid complexes prepared by SC CO(2) were studied and compared to those obtained by physical mixing and coprecipitation methods. In addition, dissolution amounts of the products obtained by different methods were measured in gastric fluid. Finally, pharmacokinetic studies of the inclusion complexes were conducted in male Wistar rats to assess the bioavailability of the prepared complexes. Results showed that temperature, pressure and itraconazole:beta-cyclodextrin ratio had significant effects on the inclusion yield of the complex prepared by SC CO(2) method. Higher inclusion yields were obtained in the SC CO(2) method as compared to physical mixing and coprecipitation methods. In vivo drug pharmacokinetic studies showed that the itraconazole-beta-cyclodextrin product prepared using SC CO(2) gave higher bioavailability of itraconazole (in blood, liver and kidney of male Wistar rats) as compared to the products obtained by physical mixing or coprecipitation methods.     

Comparative in vitro and in vivo bioavailability of naproxen from tablet and caplet formulations

A 500 mg dose of naproxen in a caplet formulation (product A) or a tablet (Naprosyn 500, product B) was administered to 14 fasting healthy subjects on two separate occasions, separated by a 1–2 week washout period in an open, randomized crossover. Blood samples were drawn periodically and plasma naproxen concentrations measured by HPLC. The median time T_max to reach peak concentration for product A was shorter than that for product B (1·025 h versus 1·5 h) but A and B were similar with respect to median peak plasma concentration C_max (77·9 mg 1^?1 versus 71·4 mg 1^?1), and average area AUC_0–∞ under the plasma concentration—time curve (1210·2 mg 1^?1 h versus 1211·0 mg 1^?1 h). In vitro parameters (A versus B) of mean dissolution time MDT (5·03 min versus 15·0 min), and time for 70% dissolution T₇₀ (6·67 min versus 20·2 min), differed significantly.     

Effects of solid carriers on the crystalline properties, dissolution and bioavailability of flurbiprofen in solid self-nanoemulsifying drug delivery system (solid SNEDDS)

In order to investigate the effects of solid carriers on the crystalline properties, dissolution and bioavailability of flurbiprofen in a solid self-nanoemulsifying drug delivery system (solid SNEDDS), different solid SNEDDS formulations were prepared by spray-drying the solutions containing liquid SNEDDS and various carriers. The liquid SNEDDS, composed of Labrafil M 1944 CS/Labrasol/Trasncutol HP (12.5/80/7.5%) with 2% w/v flurbiprofen, gave a z-average diameter of about 100 nm. Silicon dioxide, a hydrophobic solid carrier, produced an excellent conventional solid SNEDDS with a nanoemulsion droplet size of less than 100 nm, similar to the liquid SNEDDS and smaller than the other solid SNEDDS formulations. The drug was in an amorphous state in this solid SNEDDS. Furthermore, it greatly improved the dissolution rate and oral bioavailability of flurbiprofen in rats because it allowed the spontaneous formation of an interface between the oil droplets and the water. Magnesium stearate, a hydrophobic carrier, produced a solid SNEDDS with the largest diameter. However, it greatly enhanced the dissolution rate and oral bioavailability due to the formation of a simple eutectic mixture. The hydrophilic carriers such as polyvinyl alcohol (PVA), sodium carboxymethyl cellulose (Na-CMC) and hydroxypropyl-β-cyclodextrantrin (HP-β-CD) did not form a solid SNEDDS but rather a solid dispersion (or microcapsule). HP-β-CD improved the dissolution rate but did not improve the oral bioavailability as much as the hydrophobic polymers. PVA and Na-CMC hardly improved the dissolution rate but maintained constantly high plasma levels in rats for a long period. Thus, the selection of carrier is an important factor in the development of solid SNEDDS, since the carriers had significant effects on the crystalline properties, dissolution and oral bioavailability of flurbiprofen and on the formation of solid SNEDDS.     

光纤药物溶出度实时测定仪监测氢氯噻嗪片的溶出度

目的:建立考察氢氯噻嗪片溶出过程的方法,初步评价制剂质量。方法:用光纤溶出度测定仪实时监测氢氯噻嗪片的溶出过程。考察同一厂家10批产品的溶出曲线。结果:显示样品批间差异和批内差异均很大,说明该厂家生产工艺不稳定。结论:光纤溶出度实时测定仪能够有效监测固体药物的体外溶出过程,为改进制剂工艺、监控制剂工艺稳定性,提高药品分析能力提供有益的参考。     

Steady-state pharmacokinetics of diltiazem and hydrochlorothiazide administered alone and in combination

Diltiazem and hydrochlorothiazide are widely used to treat cardiovascular disease, often in combination. The purpose of this investigation was to determine whether a drug–drug pharmacokinetic interaction exists between diltiazem and hydrochlorothiazide. In a randomized, crossover, open study, multiple doses of diltiazem (60 mg four times daily for 21 doses) and hydrochlorothiazide (25 mg twice daily for 11 doses) were administered alone and in combination on three separate occasions to 20 healthy male volunteers. Trough and serial blood samples were collected and plasma was assayed for diltiazem, hydrochlorothiazide, and diltiazem metabolites (desacetyldiltiazem and N-desmethyldiltiazem) using HPLC. Total urine was also collected and quantified for hydrochlorothiazide. Coadministered hydrochlorothiazide did not significantly (p >0.05) alter diltiazem (alone versus combination) steady-state maximum plasma concentration (C; 145 versus 158 ng mL⁻¹, respectively), time to maximum plasma concentration (t_max; 3.0 versus 2.8 h, respectively); area under the plasma concentration–time curve (AUC_ss; 688 versus 771 ng·h mL⁻¹), oral clearance (Cl_oral; 96.2 versus 88.0 L h⁻¹), or elimination half-life (t_1/2; 5.2 versus 5.2 h). Similarly, administration of diltiazem did not significantly (p >0.05) influence hydrochlorothiazide (alone versus combination) C (221 versus 288 ng mL⁻¹), t_max (1.8 versus 2.0 h), AUC_ss (1194 versus 1247 ng·h mL⁻¹), Cl_oral (22.4 versus 21.2 L h⁻¹); t_1/2 (9.8 versus 9.6 h), or renal Cl (15.5 versus 15.2 L h⁻¹). In conclusion, a clinically significant pharmacokinetic interaction between diltiazem and hydrochlorothiazide does not exist. © 1998 John Wiley & Sons, Ltd.     

Analytical techniques in dissolution testing and bioavailability studies

The rate and extent of absorption of a drug into the bloodstream is an important quality characteristic of a dosage form. In vivo bioavailability and in vitro dissolution studies are important in the development and ultimately in the quality control of a dosage form. The integrity of these tests is dependent on the analytical methods used. The advent of very potent drugs used in low dosage and the development of novel drug delivery systems require that the most sophisticated methods are used.

This paper surveys recent trends in analytical advances that are useful in dissolution and bioavailability testing and suggests some future directions.     

苯那普利与小剂量氢氯噻嗪合用治疗高血压疗效观察

目的：研究苯那普利与小剂量氢氯噻嗪合用对高血压患者的疗效。方法：采用随机分组法将60例原发性高血压病人分为两组,A组30例单用苯那普利10mg,每日一次;B组30例用苯那普利10mg,每日一次,加服氢氯噻嗪12．5mg,每日一次。两组治疗时间均为4周。观察治疗前后的基础血压及24h动态血压,并测定治疗前后的空腹血糖、血脂、血尿酸、尿素氮、肌酐。结果：苯那普利加小剂量氢氯噻嗪组的总有效率及24h动态血压的结果明显优于单用苯那普利组,两组治疗前后的代谢指标均无明显改变。结果：苯那普利与小剂氢氯噻嗪合作治疗高血压较单用苯那普利更有效,而且对代谢无明显影响。     

Development and application of a validated HPLC method for the analysis of dissolution samples of levothyroxine sodium drug products

A rapid, selective, and sensitive gradient HPLC method was developed for the analysis of dissolution samples of levothyroxine sodium tablets. Current USP methodology for levothyroxine (L-T(4)) was not adequate to resolve co-elutants from a variety of levothyroxine drug product formulations. The USP method for analyzing dissolution samples of the drug product has shown significant intra- and inter-day variability. The sources of method variability include chromatographic interferences introduced by the dissolution media and the formulation excipients. In the present work, chromatographic separation of levothyroxine was achieved on an Agilent 1100 Series HPLC with a Waters Nova-pak column (250 mm × 3.9 mm) using a 0.01 M phosphate buffer (pH 3.0)-methanol (55:45, v/v) in a gradient elution mobile phase at a flow rate of 1.0 mL/min and detection UV wavelength of 225 nm. The injection volume was 800 μL and the column temperature was maintained at 28°C. The method was validated according to USP Category I requirements. The validation characteristics included accuracy, precision, specificity, linearity, and analytical range. The standard curve was found to have a linear relationship (r(2)>0.99) over the analytical range of 0.08-0.8 μg/mL. Accuracy ranged from 90 to 110% for low quality control (QC) standards and 95 to 105% for medium and high QC standards. Precision was <2% at all QC levels. The method was found to be accurate, precise, selective, and linear for L-T(4) over the analytical range. The HPLC method was successfully applied to the analysis of dissolution samples of marketed levothyroxine sodium tablets.     

Absorption and disposition of a new low-dose combination formulation of hydrochlorothiazide and triamterene

Two studies are reported that assess the bioequivalence of a new half-strength drug combination containing 25 mg hydrochlorothiazide and 37.5 mg triamterene compared to a full-strength formulation containing 50 mg hydrochlorothiazide and 75 mg triamterene. The first study (I) compared the absorption and disposition of the two drugs after administration of two tablets of the half-strength product as a single dose compared to a single dose of the full-strength product. The second study (II) assessed the bioavailability of the new product given as a single tablet on two occasions separated by an interval of 12 h compared to the full-strength product given as a single dose. Urine parameters in the first study indicated bioequivalence of the half-strength to the full product for both rate and extent of absorption. When given in divided doses, the half-strength product demonstrated bioequivalence to the full-strength product for extent of absorption. Additional data from the second study suggest that absorption of triamterene is greater when given in smaller divided doses and when given at night.     

液相色谱串联质谱法测定人血浆中氯沙坦/氢氯噻嗪的浓度及其人体相对生物利用度研究

目的 建立一种快速、灵敏的测定人血浆中氯沙坦/氢氯噻嗪(抗高血压药)浓度的高效液相色谱串联质谱法,并评价2种氯沙坦钾氢氯噻嗪片在健康志愿者体内的生物等效性.方法 20例健康男性志愿者,用随机双交叉试验方法,单剂量口服受试或参比氯沙坦钾氢氯噻嗪片(50 mg/12.5 mg),用HPLC-MS/MS法测定血浆中氯沙坦/氢氯噻嗪浓度.结果 20名健康男性受试者口服含氯沙坦钾50 mg、氢氯噻嗪12.5 mg的受试制剂和参比制剂后,氯沙坦:tmax分别为(1.09±0.56)、(1.12±0.55)h,Cmax分别为(118.9 ±68.9)、(110.2±51.0)μg·mL-1,t1/2分别为(3.15±0.76)、(2.96±0.71)h,AUC0-t分别为(22.2±65.0)、(241.9±77.4)ng·h·mL-1,AUC0-t分别为(250.5±68.7)、(265.7±81.5)ng·h·mL-1;氢氯噻嗪:tmax分别为(1.93±0.54)、(2.25±0.60)h,Cmax分别为(73.2±11.0)、(74.5±17.4)ng·mL-1,t1/2分别为(9.45±3.57)、(8.33±2.58)h,AUC0-t分别为(401.8±138.3)、(390.6±149.3)ng·h·mL-1,AUC0-∞分别为(438.2±146.8)、(415.5±156.1)ng·h·mL-1.以氯沙坦AUC0-t计算,氯沙坦钾氢氯噻嗪片中氯沙坦与氢氯噻嗪相对生物利用度分别平均为(96.5±21.2)、(106.8±22.9)%.结论 受试制剂与参比制剂在人体内具有生物等效性.     

Bioavailability studies with ciglitazone in beagles. I. Effect of a meal on the bioavailability of three ciglitazone dosage forms

Three separate Latin square crossover studies were conducted in beagles to examine the effect of a meal on the bioavailability of a ciglitazone tablet, suspension, and solution. In these studies, drug was administered to fasted animals with either 50 ml water or with 180 g Purina Dog Chow and 20 g butter. The data indicated that the meal significantly increased the AUC by about 40 per cent for both the tablet and the suspension but had no significant effect on the solution treatment. Comparisons across studies indicated low bioavailability in fasted animals from either the tablet or suspension relative to the solution. When drug was co-administered with a meal, however, bioavailability appeared to be independent of dosage form.     

Long-term effects of an amiloride/hydrochlorothiazide combination ('Moduretic') on electrolyte balance

Summary

A study was carried out of plasma electrolyte estimations made before and after long-term use of a combination of amiloride and hydrochlorothiazide in 23 patients. The mean duration of use was 20.3 months. No significant differences were found in plasma potassium, sodium, bicarbonate or urea from baseline levels.