Influence of tablet dissolution on furosemide bioavailability: a bioequivalence study

The developability classification system: application of biopharmaceutics concepts to formulation development

A revised classification system for oral drugs was developed using the biopharmaceutics classification system (BCS) as a starting point. The revised system is designed to have a greater focus on drug developability. Intestinal solubility, the compensatory nature of solubility and permeability in the small intestine and an estimate of the particle size needed to overcome dissolution rate limited absorption were all considered in the revised system. The system was then validated by comparison with literature on the in vivo performance of a number of test compounds. Observations on the test compounds were consistent with the revised classification, termed the developability classification system (DCS), showing it to be of greater value in predicting what factors are critical to in vivo performance than the widely used BCS.

Characterization of the complexes of furosemide with 2-hydroxypropyl-beta-cyclodextrin and sulfobutyl ether-7-beta-cyclodextrin

The purpose of this study was to prepare and characterize complexes of furosemide with 2-hydroxypropyl-beta-cyclodextrin (2-HP-beta-CD) and sulfobutyl ether-7-beta-cyclodextrin (SBE-7-beta-CD). Solid complexes of furosemide with 2-HP-beta-CD and SBE-7-beta-CD were prepared by using both a freeze-drying and kneading method. Physical mixtures were prepared for comparison. The inclusion complexes were characterized by differential scanning calorimetry, X-ray diffractometry (XRD) and 1H nuclear magnetic resonance spectroscopy (1H-NMR). 1H-NMR, and especially the use of the two-dimensional ROESY spectrum, was used to determine the position of the furosemide molecule inside the cyclodextrin cavity. 1H-NMR studies showed that furosemide fit into the cyclodextrin torus cavity with its furane ring nearest to the primary hydroxyl side.

Structure-solubility relationship and thermal decomposition of furosemide

Furosemide, a high ceiling diuretic, decomposes on heating and is very sparingly soluble in water. The aim of this study was to identify the thermal decomposition product(s) of furosemide and to calculate the activation energy needed for this reaction. This was done to gain a better understanding of the unusually low water solubility of this drug. The main thermal decomposition product was identified by nuclear magnetic resonance (NMR), mass spectrometry (MS), and infrared (IR) analysis as 4-chloro-5-sulfamoylanthranilic acid (saluamine), and the activation energy, calculated from thermogravimetric analysis (TGA) measurements, for this reaction was 47.7 (+/- 1.93) kcal/mol. The experimentally measured activation energy was well below the normal 59 +/- 4 kcal/mol needed for the cleavage of the C-N bond to form saluamine. This could possibly be explained by the weakening of the C-N bond through the I-effect of the furane ring and the delocalization of the electrons of the aniline nitrogen in the chlorosulfamoyl benzoic acid entity of furosemide. This decomposition of furosemide indicates the breaking of intramolecular bonds before those of intermolecular bonds (separation of individual furosemide molecules). Strong inter- and intramolecular bonds are a probable cause for the poor water solubility of furosemide because, when some of the inter- and intramolecular bonds that form part of the hydrogen bond network disappeared, as in the structurally related decomposition product saluamine, the aqueous solubility increased.

The influence of frusemide formulation on diuretic effect and efficiency

AIMS

Changes in drug delivery rate may result in clinically important changes in drug effects. For the loop diuretic frusemide, it would be desirable to develop controlled release preparations, that could maintain an effective urinary excretion rate over a prolonged period of time. The aim of this study was to investigate the influence of frusemide formulation on frusemide recovery, diuretic effect and efficiency.

METHODS

Twelve subjects were given 60 mg of four different frusemide controlled release formulations in a single-dose, double-blind, randomized 4-way cross-over design. The formulations were three study drugs with different extended dissolution rates (ER1Tab, ER2Tab and ER3Caps ) and one reference drug (LR). Urinary volume and contents of frusemide in urine were measured in samples collected over 24 h.

RESULTS

Substantial differences in frusemide recovery and diuretic efficiency were observed between LR and all other formulations. At 24 h, mean total frusemide recoveries of ER1Tab, ER2Tab and ER3Caps were 52%, 36% and 57% lower, respectively, compared with LR (P<0.01). Also at 24 h, mean total diuretic efficiency for ER1Tab, ER2Tab and ER3Caps was 83%, 31% and 135% higher, respectively, compared to LR. The rapid dissolution and absorption of LR resulted in a high diuretic response from 0 to 3 h after dosing. However, from 0 to 24 h, there were no differences in diuretic response between the formulations.

CONCLUSIONS

Controlled release formulations of frusemide with a low and extended rate of dissolution lead to a more prolonged absorption and subsequent diuresis, but still maintain a similar cumulative response, due to their higher diuretic efficiency.

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.

Effects of Various Modalities of Oral Furosemide Administration in Mild or Severe Congestive Heart Failure

BACKGROUND: This study evaluated the optimal formulation (tablet vs solution) and frequency (once vs twice daily) of maintenance oral furosemide in compensated congestive heart failure (CHF). METHODS AND RESULTS: Eighteen patients with mild (group 1) and 18 with severe (group 2) CHF were studied. On 2 consecutive days each patient's individual fixed oral furosemide daily dosage was administered in tablet or solution in a crossover design. In an additional study, 14 patients with severe CHF received the daily dosage in tablet or solution form in two divided doses. Pharmacokinetic data were obtained in six randomly allocated patients of each group, during the once daily administration periods of either formulation. Twenty-four-hour urinary sodium and 12-hour volume were significantly greater in group 1 following furosemide solution versus tablets. In group 2, all parameters were comparable in response to single identical doses in tablets or solution, as well as to once versus twice daily administration of either formulation. These results coincided with a higher C(max) and a shorter t(max) following solution. CONCLUSIONS: A once-daily oral furosemide solution is more effective than the same dosage in tablet form in patients with mild, but not those with severe, CHF. In patients with severe CHF, the natriuretic and diuretic effects are similar whether oral furosemide in tablet or solution is administered in a once or twice daily schedule.

Correlation of in vitro release rate and in vivo absorption characteristics of four chlorpheniramine maleate extended-release formulations

An in vitro/in vivo correlation was established for four formulations of chlorpheniramine maleate (histamine, H1-blocker) extended-release tablets exhibiting different in vitro release rate characteristics. In vitro release rate data were obtained for 12 individual tablets of each formulation using the USP Apparatus 2, paddle stirrer at 50 rpm in 1000 ml of distilled water at 37.0 +/- 0.5 degrees C. Inspection of the individual and mean release rate data indicated that the in vitro release rate of chlorpheniramine maleate was consistent with the intended design of the four extended-release formulations. The in vivo bioavailability and pharmacokinetics of these formulations were evaluated in 24 healthy subjects under fasting conditions. Wagner Nelson analyses of the in vivo data revealed extended release absorption profiles for all four formulations. Linear regression analyses of the mean percentage of dose absorbed versus the mean in vitro release resulted in a statistically significant correlation (r2 greater than 0.98, P less than 0.001) for each formulation. Qualitative rank-order correlations were observed among all combinations of in vitro and in vivo parameters. These data support a Level A correlation between the in vitro release rate profiles and the in vivo absorption for chlorpheniramine maleate determined under fasting conditions.

Release and absorption characteristics of novel theophylline sustained-release formulations: in vitro-in vivo correlation

Five new experimental sustained-release (SR) formulations of theophylline, T-1, T-1-A, T-2, T-2-A, and T-2-E, in a matrix tablet form with a protein were developed. The in vitro release of theophylline from these novel experimental formulations and two commercial (Theotrim and Theo-Dur) SR formulations, was studied for 2 hr immersed in simulated gastric fluid TS, followed by an additional 10 hr immersed in simulated intestinal fluid TS. Like Therotrim and Theo-Dur, theophylline release profiles from all the novel experimental formulations were smooth, controlled, and unaffected by changes in the pH and the proteolytic enzyme content of the incubation media. Pharmacokinetic evaluation of T-1, T-1-A, T-2-A. Theotrim, and Theo-Dur was carried out in five dogs and six healthy human volunteers under fasting conditions, using immediate-release aminophylline tablets as controls. Pharmacokinetic analysis by the Wagner-Nelson procedure revealed sustained-release absorption characteristics for all the formulations with the exception of the immediate release aminophylline tablet. For each of the formulations tested, the regression analysis results of the percentage of theophylline absorbed in dogs or humans against the mean percentage released in vitro, at the corresponding times, indicated a high correlation. These data imply that the in vivo release profiles under fasting conditions in the gastrointestinal tract of dogs and humans may be similar to those in the in vitro studies.

Review article: mechanisms of drug release from tablets and capsules. 2. Dissolution

Optimal drug dissolution is crucial to the success of oral drug therapy. Slow dissolution has frequently been correlated with poor or erratic performance of oral dosage forms in vivo, and drugs of low aqueous solubility provide a major challenge to the designer of modern oral dosage forms. In this second of two reviews, we briefly describe the physical process of dissolution, the principal factors controlling drug dissolution from tablets and capsules, and the strategies that are utilized by pharmaceutical scientists to enhance drug dissolution of orally administered drugs.

The in-vitro pH-dissolution dependence and in-vivo bioavailability of frusemide-PVP solid dispersions

The dependence of the dissolution rate on the pH of the buffered medium, using constant surface area discs, has been examined for crystalline frusemide, a semi-crystalline frusemide-polyvinylpyrrolidone (PVP) solid dispersion and an X-ray amorphous frusemide-PVP dispersion. The marked changes observed in the pH-dissolution profiles indicate that differing dissolution mechanisms operate in the amorphous regions. This conclusion was further supported by the comparison of pH-dissolution and pH-equilibrium solubility profiles that suggested a supersaturation effect to be the relevant term in describing the dissolution enhancing effects of amorphous regions. A marked dissolution enhancement, relative to crystalline frusemide, was shown by the X-ray amorphous solid dispersion in weakly acidic solutions. A similar effect was observed in the dissolution characteristics of gelatin capsule formulations in simulated gastric and intestinal media. In a human bioavailability study, the X-ray amorphous frusemide-PVP solid dispersion exhibited a significant reduction in the time for maximum effect in comparison to crystalline frusemide and a semi-crystalline solid dispersion. This effect, demonstrated by the primary end organ response in seven healthy subjects, concurred with the in-vitro prediction of dissolution enhancement in weakly acidic media.

Furosemide pharmacokinetics and pharmacodynamics in health and disease--an update

The literature on furosemide pharmacokinetics and pharmacodynamics is critically reviewed, concentrating on those papers published subsequent to the 1979 reviews of this topic. Intravenous and oral data are presented for healthy volunteers and for patients with various disease states. It is the latter populations about which the majority of the studies have been published since 1979. Inter- and intraindividual variations in bioavailability are discussed, as are data on the metabolism of furosemide to its glucuronide conjugate. Published studies examining the relationship between furosemide pharmacodynamics and pharmacokinetics are also evaluated. The literature is reviewed through June 1988.