UV absorption method should not be applied for determining amoxycillin in acidic dissolution test medium.

In order to clarify the suitability of assay method, the stability of amoxycillin (AMX) in the acidic solution at pH 1.2 was determined by two different methods, ultraviolet absorption (UV) and HPLC methods. The determination was simultaneously performed for the same sample solutions. The data from HPLC method indicated that AMX degraded and the concentration of AMX in the acidic solution was decreased. The apparent first-order rate constant (k(obs)) for the degradation was 9.83x10(-2) h(-1), and the half-life was calculated to be 7.04 h. On the other hand, the data obtained from UV method apparently represented that the concentration of AMX increased with time-course. This phenomena was brought about by the increase of UV absorption at 272 nm, which accompanied with the degradation of AMX. These results clearly indicate that UV method can not be used for determining the samples accompanying the degradation of AMX. In general, the dissolution test (drug release test) has been used for the evaluation of a sustained-release dosage form of AMX. It is impossible to avoid the degradation of AMX in the test under acidic conditions. The results indicated that the UV method should not be used for the determination of AMX in the test.

Kinetics of nikkomycin Z degradation in aqueous solution and in plasma.

The stability of nikkomycin Z in aqueous solution at various pH values and in the plasma of several kinds of experimental animals was studied. The degradation of nikkomycin Z in aqueous solution at pH 4 to 11.5 and in plasma was an apparent first-order reaction. The degradation rate at 37 degrees C increased with increasing pH, from 4.0 to 7.5, and decreased with increasing pH from 7.5 to 10.2. Above pH 10.2, the degradation rate was constant. The maximal rate of nikkomycin Z degradation was observed in pH 7.5 buffer solution, in which the apparent first-order rate constant (k(obs)) was 8.08 x 10(-2) h(-1) (t1/2 = 8.6 h). The degradation rate of nikkomycin Z in dog plasma at 37 degrees C was the almost same as that in pH 7.5 buffer. The rates in rat, mouse, and rabbit plasma were much greater than that in pH 7.5 buffer; the k(obs) values for rat, mouse, rabbit, and dog plasma at 37 degrees C were 1.74 x 10(-1) min(-1), 3.64 x 10(-2) min(-1), 5.10 x 10(-1) h(-1), and 6.14 x 10(-2) h(-1), respectively. The degradation rate of nikkomycin Z in rat plasma was markedly decreased when NaF, an esterase inhibitor, was added to the plasma. The findings of faster degradation rates in rat, mouse, and rabbit plasma compared with that in pH 7.5 buffer were considered to be due to an esterase in the plasma. This notion was supported by results showing the degradation rate of nikkomycin Z in porcine liver esterase solution.

Evaluation of a pharmaceutical preparation of 2-[4-(p-fluorobenzoyl)-piperidin-1-yl]-2'-acetonaphthone hydrochloride with enhanced dissolution rate.

A granule of 2-[4-(p-fluorobenzoyl)-piperidin-1-yl]-2'-acetonaphthone hydrochloride (E2001) with an enhanced dissolution rate (preparation A) prepared by a method previously reported (T. Tokumura, T. Tanaka, Yakuzaigaku, accepted) was evaluated by the dissolution test and its bioavailability in beagle dogs was determined. The dissolution rate of E2001 from preparation A at pH 6.0-6.8 was increased significantly in comparison with that from preparation B (a physical mixture of the same formula). There was no significant difference in Cmax, area under the concentration-time curve (AUC0-6 h), or Tmax between preparations A and B when a dose equivalent to 20 mg of E2001 was administered to the beagle dogs. However, a significant difference was observed between the AUC0-6 h values after oral administration of the two preparations with NaHCO3. These findings suggest that the bioavailability of E2001 from the oral administration preparation A will be higher than that of preparation B.

Determination of a novel and potent cyclic GMP phosphodiesterase inhibitor, 4-([3,4-(methylenedioxy)-benzyl]amino)-6,7,8-trimethoxyquinazoline, in dog plasma by high-performance liquid chromatography.

A simple and accurate method for determining levels of 4-([3,4-(methylenedioxy)benzyl]amino)-6,7,8-trimethoxyquinazoline, a novel cyclic GMP phosphodiesterase inhibitor, in dog plasma was developed. This method involves extraction with diethyl ether and reversed-phase high-performance liquid chromatography with ultraviolet detection. Regression analysis showed that the method was linear over the range 1.0-1000 ng/ml. The method was employed for the analysis of plasma samples in a preliminary pharmacokinetic study in beagle dogs.

Determination of a novel beta-lactam antibiotic (E-1100) in rat plasma by high-performance liquid chromatography.

A fast, simple and accurate method to determine the concentration of E-1100, a novel beta-lactam antibiotic, in rat plasma has been developed. This method involves deproteinization by methanol with 0.2% perchloric acid and reversed-phase high-performance liquid chromatography with ultraviolet detection. Regression analysis showed that the method was linear over the standard-curve range from 0.191 to 191.0 micrograms/ml. This newly developed method has been applied for the analysis of plasma samples in a preliminary pharmacokinetic study in rats.

Pharmacokinetics of (Me)Arg-Lys-Pro-Trp-tert-Leu-Leu-OEt and (Me)Arg-Lys-Pro-Trp-tert-Leu-Leu administered intravenously to beagle dogs.

The pharmacokinetics of two analogues (NT-1 and NT-2) of the smallest active fragment of neurotensin were investigated in beagle dogs after intravenous (iv) administration at the doses of 0.1 and 0.5 mg/kg for NT-1 and of 0.25 and 0.5 mg/kg for NT-2. After iv administration of these two drugs, the plasma levels decreased with time with a biexponential pattern, and linear kinetic behavior was observed. The pharmacokinetic parameters (mean +/- standard error of mean) after iv administration of NT-1 at 0.1 mg/kg were as follows: the half-life of the distribution phase (t1/2 alpha) was 0.29 +/- 0.11 h, the half-life of the terminal phase (t1/2 beta) was 1.99 +/- 0.41 h, total plasma clearance (CL) was 33.2 +/- 6.3 mL/h/kg, steady-state volume of distribution (Vdss) was 57.1 +/- 2.8 mL/kg, and mean residence time (MRT) was 2.20 +/- 0.55 h. The t1/2 alpha, t1/2 beta, CL, Vdss, and MRT values after iv administration of NT-2 at 0.25 mg/kg were 0.11 +/- 0.02 h, 0.58 +/- 0.04 h, 257.3 +/- 17.2 mL/h/kg, 180.3 +/- 4.6 mL/kg, and 0.71 +/- 0.04 h, respectively. After iv administration of NT-1, NT-2 was detected in the plasma. It was confirmed from this result that NT-1 was metabolically hydrolyzed to NT-2 in the body of beagle dog.

Evaluation of bioavailability upon oral administration of phytonadione preparations in beagle dogs.

Bioavailability of phytonadione was investigated after oral administration to beagle dogs. The administrations of phytonadione in a surfactant solution (preparation a) and in an oleic acid solution (preparations b) greatly increased the bioavailability of phytonadione. The AUCs of preparations a and b were about 2.5 times larger than those of commercially available tablets A and C. This result well corresponded to the results of the dissolution test previously reported. The absorption of phytonadione from the gastro-intestinal tract was affected by food and the bioavailability was largely increased under non-fasted conditions. However, a large scatter was observed in the data, and it was found that the evaluation of the bioavailability of phytonadione preparations could not be done in non-fasted animals.

Pharmacokinetics of novel hexapeptides with neurotensin activity in rats.

A high-performance liquid chromatographic method to determine (Me)Arg-Lys-Pro-Trp-tert-Leu-Leu (NT-2) with neurotensin (NT) activity in rat plasma was developed and a pharmacokinetic study was performed in rats. Quantitative analysis with high reproducibility was achieved for NT-2 over the concentration range of 1.14-500 ng/ml. (Me)Arg-Lys-Pro-Trp-tert-Leu-Leu-OEt (NT-1) was rapidly hydrolyzed to NT-2 in rat plasma at 37 degrees C. This degradation of NT-1 was observed as a pseudo first-order reaction, and the pseudo first-order rate constant was calculated to be 7.26 min-1 (t1/2 = 0.095 min). The pharmacokinetic profiles of NT-2 after intravenous administration of NT-1 at doses of 0.1 and 0.3 mg/kg were compatible with that of NT-2 after intravenous administration of NT-2 at 0.5 mg/kg. Range of the half-life of the terminal phase (t1/2 beta) of NT-2 was 0.36-0.53 h. The absolute bioavailabilities after oral administrations of NT-1 and NT-2 at a dose of 20 mg/kg were 0.61 +/- 0.17 (mean +/- S.E.) and 0.19 +/- 0.08%, respectively. It was found that NT-1 was more suitable for oral administration than NT-2.

Stability of a novel hexapeptide, (Me)Arg-Lys-Pro-Trp-tert-Leu-Leu-OEt, with neurotensin activity, in aqueous solution and in the solid state.

The stability and some physicochemical properties of a novel hexapeptide, (Me)Arg-Lys-Pro-Trp-tert-Leu-Leu-OEt (I), with neurotensin activity, were investigated. The degradation of I in aqueous solution was observed as a pseudo-first order reaction. By determining the degradation rate of I at various pH values, it was found that I was most stable at around pH 4. The activation energies of the degradation in aqueous solutions at pH 2.2, 6.1, 7.0 and 8.0 were 16.3, 22.2, 23.9 and 24.2 kcal/mol, respectively. The enzymatic hydrolysis of I was studied in vitro with a porcine liver esterase at 37 degrees C. The degradation of I in this system was observed as a pseudo-first order reaction. The degradation rate of I in the presence of the esterase was about 10000 times larger than the rate in a buffer solution. I in the solid state was stable under 65 degrees C and labilized by strong light and/or high humidity. The pKa1, pKa2 and pKa3 of I were 7.1, 10.0 and 11.3, respectively. The partition coefficients between n-octanol and the buffer solution at pH values ranging from 2 to 11 were measured. The partition coefficient increased with the increase of the pH value. But the value at pH 7.0 was 2.10 x 10(-2), which was very low. The solubility of I in aqueous solution was more than 10 mg/ml. From the results of the powder X-ray diffraction pattern, I in the solid state was found to be amorphous. The dissolution rates in the 1st and 2nd fluid of JPXI at 37 degrees C and 100 rpm were 19.4 and 9.0 mg/cm2.min, respectively.

Preparation and evaluation of intragastric buoyant preparations.

The design and preparation of two drug formulations which float in gastric juice are described. One, a buoyant tablet, consisted of powdered soybean protein, drug and sodium bicarbonate. The other, a laminated film-type preparation, consisted of a drug film, an effervescing film containing sodium bicarbonate and outer drug release regulating films. Cinnarizine, an acid-soluble drug, was chosen as model drug, and carboxyvinyl polymer, ethyl cellulose and hydroxypropyl cellulose were used in the preparation of the films. Both formulations showed favorable buoyancy in an in vitro acidic dissolution test medium and also sustained release properties. In an absorption study using beagle dogs, cinnarizine was found in the blood even 24 hr after oral administration of the buoyant tablet or film-type preparation. Similar buoyant tablets containing barium sulfate were administered orally to a healthy volunteer, and it was confirmed by roentgenography that the tablets floated for almost three hours.

Enhancement of the oral bioavailability of cinnarizine in oleic acid in beagle dogs.

The present study was an attempt to develop a new dosage form of cinnarizine, which is slightly soluble in water, using lipid as a vehicle. The solubility of cinnarizine in several organic solvents was determined. It was found that cinnarizine dissolved well in oleic and linoleic acids. The bioavailability of cinnarizine from the oral administration of an oleic acid solution in a hard capsule was investigated and compared with that of a cinnarizine tablet, using beagle dogs. When cinnarizine was administered in a capsule, the bioavailability was greatly enhanced [i.e., the maximum concentration (Cmax) and AUC values were 2.9 and 4.0 times larger than those of a cinnarizine tablet, respectively]. Meanwhile, the tmax value (the time to reach Cmax) was unchanged. The absorption of cinnarizine from an oleic acid solution was considered to depend on the action of bile salts. This was supported by the results of a dissolution test using a bile salts solution as the dissolution test medium.

Use of soybean protein for controlled release of drugs administered orally.

The influence of soybean protein (SBP) on the release of drugs from per-oral formulations was investigated, using dl-propranolol as model drug. Directly compressed tablets of SBP/lactose containing more than 40% of SBP did not disintegrate and kept their shape for long periods. Then, dissolution tests (JPX) were carried out with similar tablets containing dl-propranolol hydrochloride as active ingredient. The dissolution profiles showed sustained release of the drug, the dissolution rate being prolonged with increasing amounts of added SBP. Dissolution was affected by the pH of the test medium and accelerated by addition of pancreatin to the test medium. Our results suggest that interaction between SBP, drug and lactose may influence the dissolution rate. Dissolution was unaffected by varying compressional pressure (100-300 kg/cm2) in the preparation of tablets.

Per-oral controlled release dosage form of theophylline using soybean protein.

The potential of powdered soybean protein (SBP) as a vehicle for controlled drug release was investigated, using theophylline as the model drug, an in vitro dissolution test and in vivo absorption studies in beagle dogs. The results of the dissolution test demonstrated that the addition of SBP to the tablet brought about retarded dissolution of theophylline. In the in vivo absorption study, Tmax values for theophylline-SBP tablets were larger than those for tablets containing only theophylline; there was no difference in AUC between the two tablets. In addition, there was no detectable difference in the results with theophylline-SBP and Theodur tablets. The practical usefulness of SBP as a vehicle for controlled release tablets was confirmed not only from our in vitro experiment, but also from our in vivo absorption test using beagle dogs.

Enhancement of bioavailability of cinnarizine from its beta-cyclodextrin complex on oral administration with DL-phenylalanine as a competing agent.

The present investigation is concerned with an improvement of the bioavailability of cinnarizine by administering its beta-cyclodextrin complex together with another compound which competes with the beta-cyclodextrin molecule in complex formation in aqueous solution (competing agent). The bioavailability of cinnarizine on oral administration of the cinnarizine-beta-cyclodextrin inclusion complex was enhanced by the simultaneous administration of DL-phenylalanine as a competing agent, e.g., the AUC was 1.9 and 2.7 times as large as those of the cinnarizine-beta-cyclodextrin complex alone and cinnarizine alone, respectively. The enhancement of AUC and Cmax completely depended on the dose of DL-phenylalanine. It was found from these results that DL-phenylalanine acted as a competing agent in the GI tract and the minimum effective dose required of DL-phenylalanine might be 1 g for 50 mg of cinnarizine in the cinnarizine-beta-cyclodextrin complex. Evaluating the competing effect of DL-phenylalanine in vitro using an absorption simulator, it was found that the decreased penetration rate of cinnarizine through the artificial lipid barrier with addition of beta-cyclodextrin was restored with the addition of DL-phenylalanine.