Correlation between glass-forming ability and fragility of pharmaceutical compounds.

Fragility is a measure of the departure from non-Arrhenius behavior for supercooled liquids and glasses, and various simple methods are available for its quantification. However, the obtained values usually do not agree with each other. One of the purposes of this study was to compare the fragility values obtained by different methodologies. Thermodynamic fragility (FT) is a simple concept that is evaluated from the heat capacity change at the glass transition temperature (Tg). Dynamic fragility is evaluated using three methodologies in this study: extrapolation of the configurational entropy (Sc) to the Kauzmann temperature (Tk) (FDC), ramp-rate dependence of Tg (FDTg), and that of the fictive temperature (Tf) (FDTf). FT and FDC of 19 pharmaceutical compounds were correlated, whereas FDTg and FDTf did not correlate with either of them. This result seems reasonable because both FT and FDC are calculated from thermodynamic parameters in the quasi-equilibrium state, but FDTg and FDTf are likely affected by kinetics as well. Another goal of this study was to find the correlation between the glass-forming ability (GFA) and fragility. FDTg was shown to correlate with GFA, presumably because both were determined on the balance of thermodynamic and kinetic factors. This correlation suggests that fragile glass has low GFA. Furthermore, the relevance of fragility to isothermal crystallization is discussed. Compounds with small FDTg and FDTf tended to exhibit pressure-controlled crystallization, for which better storage stability can be expected relative to temperature-controlled compounds. Fragility was shown to be a useful parameter practically as well as scientifically.

Relationship between crystallization tendencies during cooling from melt and isothermal storage: toward a general understanding of physical stability of pharmaceutical glasses.

The lack of protocols to predict the physical stability has been one of the most important issues in the use of amorphous solid dispersions. In this paper, the crystallization behaviors of pharmaceutical glasses, which have large variations in their crystallization tendencies, have been investigated. Although each compound appears to have a wide variation in their crystallization time, the initiation time for crystallization could be generalized as a function of only Tg/T, where Tg and T are the glass transition temperature and storage temperature, respectively. All compounds in which crystallization was mainly governed by temperature had similar activation energies for crystallization initiation, ca. 210-250 kJ/mol, indicating that physical stability at any temperature is predictable from only Tg. Increased stability is expected for other compounds, where crystallization is inhibited by an large energetic barrier, and stochastic nucleation plays an important role in initiating crystallization. The difference in the dominant factor, either temperature or pressure, appeared to correlate with the nucleation mechanism, and this could be determined by a cool-heat cycle after melting using thermal analysis. This conclusion should make prediction of physical stability of amorphous formulations easier, although the investigation was conducted under ideal conditions, which eliminated surface effects.

Practical approach for measuring heat capacity of pharmaceutical crystals/glasses by modulated-temperature differential scanning calorimetry.

A practical protocol to obtain accurate heat capacity values of pharmaceutical compounds using modulated-temperature differential scanning calorimetry was established. Three pharmaceutical compounds, acetaminophen, indomethacin, and tri-O-methyl-ß-cyclodextrin were used as model compounds. Powder samples did not produce reproducible results, presumably due to inclusion of gas in gap of powders that influenced the measured heat capacity and thermal homogeneity in the sample. Thus, the amorphous characteristics were evaluated using quench-cooled samples. Crystalline samples were obtained by partially melting the sample to allow recrystallization using the residual crystal as a template. Optimum sample mass was about 10 mg. Use of too small sample size resulted in poor reproducibility due to localization of the sample in the pan, while too large size resulted in low heat capacity values probably because of heterogeneity of the sample temperature. The optimum modulation period was in the range of 60 s and 90 s, to which the ramp rates of 2°C/min and 1°C/min, respectively, were applied. The ramp amplitude was less significant in the evaluation. This information should help in comprehending basic characteristics of pharmaceutical compounds.

Polycationic gramicidin S analogues with both high antibiotic activity and very low hemolytic activity.

The substitution of each constituent amino acid residue of gramicidin S (GS), cyclo(-Val(1,1')-Orn(2,2')-Leu(3,3')-D-Phe(4,4')-Pro(5,5')-)(2) with Lys residue indicated that each side chain structure of the constituent amino acid residues affect largely the antibiotic activity and hemolytic activity of GS. Further, the substitution of D-Phe(4,4') and Pro(5,5') residues with basic amino acid residues as a Lys residue results the high antibiotic activity and the very low hemolytic activity. Thus, we have found novel positions on the scaffold of GS at D-Phe(4,4') and Pro(5,5') residues whose modification will significantly increase the therapeutic index.

Synthesis of novel fatty-acyl gratisin derivatives.

To find candidates with high antimicrobial and low hemolytic activities, many gratisin (GR) analogues have been designed and synthesized. In the present account, we synthesized novel derivatives of GR having both the polycationic and fatty acyl groups, cyclo{-Val(1)-Orn(2)-Leu(3)-D-Phe(4)-Pro(5)-D-Lys(6)(X)-Val(7)-Orn(8)-Leu(9)-D-Phe(10)-Pro(11)-D-Lys(12)-} {X=-CO(CH(2))(6)CH(3) (1), -Lys-CO(CH(2))(6)CH(3) (2), -(Lys)(2)-CO(CH(2))(6)CH(3) (3), and -(Lys)(3)-CO(CH(2))(6)CH(3) (4)}, and examined the biological activities. Among them, we found that 2-4 have differential ionic interaction against the prokaryotic membrane and eukaryotic membrane. In other words, the dissociation with high antimicrobial activity and low hemolytic activity is caused by the addition of D-Lys(6)-{(Lys)(n)-CO(CH(2))(6)CH(3)} residues at position 6 of [D-Lys(6,12)]-GR. Our findings should be helpful in finding drug candidates with high antimicrobial activity and low hemolytic activity that are capable of combating microbial resistance.

Fatty acyl-gramicidin S derivatives with both high antibiotic activity and low hemolytic activity.

In the present study, novel eight GS derivatives having the octanoyl-(Lys)(n)- moieties, cyclo{-Val-Orn-Leu-d-Phe-Pro(4ß-NH-X)-Val-Orn-Leu-d-Phe-Pro-} {X=-H (1), and -(Lys)(n)-CO(CH(2))(6)CH(3)n=0 (2), 1 (3), 2 (4), and 3 (5)} and cyclo{-Val-Orn-Leu-d-Phe-Pro(4α-NH-X)-Val-Orn-Leu-d-Phe-Pro-} {X=-H (6), and -(Lys)(n)-CO(CH(2))(6)CH(3)n=1 (7), and 2 (8)} were synthesized. Among them, 4, 5 and 8 result the high antibiotic activity against both Gram-positive and Gram-negative microorganisms tested. In addition, 4 and 5 showed very low hemolytic activity compared with that of GS. Thus, the introduction of the excess amino groups and the fatty acyl moiety to the γ-NH(2) group of Pro(5) residue in GS molecule lowered the unwanted hemolytic activity and enhanced the desired antibiotic activity.

Novel cycloundecapeptides related to gramicidin S with both high antibiotic activity and low hemolytic activity.

To find candidates with high antimicrobial and low hemolytic activities, many gramicidin S (GS) analogs of various ring sizes have been designed and synthesized. However, syntheses of antimicrobially active analogues of GS having a disordered symmetry structure from C(2) have almost never been reported, because the stable, amphiphilic ß-sheet structure of GS with C(2) symmetry is considered essential for its strong antibacterial activity. In the present studies, novel thirteen cycloundecapeptides 1-13 related to GS were synthesized and examined. Among them, cyclo(-Va1(1)-Orn(2)-Leu(3)-D-Phe(4)-X(5)-Pro(6)-Val(7)-Orn(8)-Leu(9)-D-Phe(10)-Pro(11)-) (X=Lys (10), Orn (11), Arg (12) and Lys(Lys) (13)) resulted in high antibiotic activity against both Gram-positive and Gram-negative microorganisms tested. In addition, 11 showed low toxicity against sheep blood cells compared with that of GS. Further, circular dichroism (CD) spectra of 10-13 had a curve similar to each other, suggesting that the conformations of these analogues in methanol are similar to each other. However, CD spectra of 10-13 were different from that of GS in the 190-210 nm region. These results suggest that the presences of one added amino acid residue at position 5 of 10-13 might be partially effective through a structural change in the biological activity of 10-13. In addition, the structural modifications at position 5 lower the undesirable hemolytic activity and enhance the desirable antibiotic activity.

[Two familial cases of psittacosis].

We report here 2 cases of psittacosis in a family. In the first case, a 51-year-old woman was admitted with fever, dry cough, and a chest radiograph showed increased opacity in the right upper lung field. On a diagnosis of atypical pneumonia, minocycline was given and her clinical symptoms and abnormal laboratory data were improved. The second case was her husband, a 58-year-old man who presented with fever 4 days after his wife's admission. His chest radiograph revealed increased opacity in the left lower lung field. The administration of azithromycin for 3 days attenuated his clinical symptoms and his abnormal laboratory data improved. The serum titer of complement fixation (CF) test and ELISA test against Chlamydophila psittaci were elevated in both cases on analysis of paired acute- and convalescent-phase serum speciments. The antigen of Chlamydophila was revealed from these parrots, which had been raised in their family. Therefore, we concluded that the psittacosis had originated from the parrots.

[A case of multiple lung abscesses successfully treated with computed tomography guided percutaneous thoracic drainage].

A 48-year-old woman who had abused alcohol admitted to our hospital because of fever and chest pain. Laboratory data presented inflammation and liver dysfunction. Chest X-ray films revealed multiple mass lesions with air fluid levels. We diagnosed multiple lung abscesses and started treatment with antibiotics. However, her fever did not improve and mass lesions increased. On day 6 of hospitalization, three drainage tubes were inserted percutaneously into the mass lesions under computed tomography (CT) guidance, and alpha-hemolytic streptococcus, peptostreptococcus sp. and neutrophils were isolated from the drainage fluid. Abcesses and inflammation were improved by administration of the antibiotics selected according to the result of fluid culture. Because all multiple abcesses were located near the pleura, we successfully treated them with simultaneous percutaneus thoracic drainage.