Crystal structure and solid-state studies of aged samples of tienoxolol, an API designed against hypertension

Aging of drug molecules is generally studied following regulatory procedures, i.e. under forced conditions and for relatively limited storage time; therefore naturally aged samples are rare and provide scientific reference data beyond regulatory considerations. Tienoxolol was studied after 25 years of storage in the dark under ambient conditions. About 86% of the samples still consisted of tienoxolol and the main impurity (13%) was caused by the hydrolysis of the ester moiety. Protection from humidity is therefore important. Other sensitive groups containing nitrogen and sulfur appear to be quite stable with less than 0.8% conversion over 25 years. In addition, the crystal structure has been solved. Tienoxolol orange needles were found to crystallize in the orthorhombic non-centrosymmetric space group Iba2, indicating that the crystal is a racemic compound. The unit cell parameters at room temperature are a=10.069(5)?, b=45.831(10)?, and c=9.822(5)? and the unit cell volume is 4533(3)?(3) with Z=8.     

Rimonabant Dimorphism and Its Pressure–Temperature Phase Diagram: A Delicate Case of Overall Monotropic Behavior

Crystalline polymorphism occurs frequently in the solid state of active pharmaceutical ingredients, and this is problematic for the development of a suitable dose form. Rimonabant, an active pharmaceutical ingredient developed by Sanofi and discontinued because of side effects, exhibits dimorphism; both solid forms have nearly the same melting temperatures, melting enthalpies, and specific volumes. Although the problem may well be academic from an industrial point of view, the present case demonstrates the usefulness of constructing pressure–temperature phase diagrams by direct measurement as well as by topological approach. The system is overall monotropic and form II is the more stable solid form. Interestingly, the more stable form does not possess any hydrogen bonds, whereas the less stable one does. © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 102:2311–2321, 2013     

Dimorphism of the prodrug L-tyrosine ethyl ester: pressure-temperature state diagram and crystal structure of phase II

Polymorphism is important in the field of solid‐state behavior of drug molecules because of the continuous drive for complete control over drug properties. By comparing different structures of a series of l‐tyrosine alkyl esters, it became apparent that the ethyl ester possesses dimorphism. Its structure was determined by powder diffraction and verified by density functional theory calculations; it is orthorhombic, P2₁2₁2₁ with a = 12.8679(8) Å, b = 14.7345(7) Å, c = 5.8333 (4) Å, V = 1106.01(11) Å, and Z = 4. The density of phase II is in line with other tyrosine alkyl esters and its conformation is similar to that of l‐tyrosine methyl ester. The hydrogen bonds exhibit similar geometries for phase I and phase II, but the H‐bonds in phase I are stronger. The solid II–solid I transition temperature is heating‐rate dependent; it levels off at heating rates below 0.5 K min^–1, leading to a transition temperature of 306 ± 4 K. Application of the Clapeyron equation in combination with calorimetric and X‐ray data has led to a topological diagram providing the relative stabilities of the two solid phases as a function of pressure and temperature; phase II is stable under ambient conditions. © 2011 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 100:4774–4782, 2011     

Transfusion intensity, not the cumulative red blood cell transfusion burden, determines the prognosis of patients with myelodysplastic syndrome on chronic transfusion support

Transfusion-dependency is associated with poor prognosis in patients with MDS although the causal link for such association is disputed. This study tests thee hypotheses on the association between transfusion burden and prognosis in the MDS: (1) the cumulative transfusion burden is a confounder merely reflecting the time elapsed from diagnosis; (2) it is a surrogate for higher transfusion intensity, which would reflect a more severe disease; and (3) it is the total amount of transfused RBC units that influences on prognosis. We studied 191 transfusion-dependent patients with MDS or chronic myelomonocytic leukemia. Transfusion intensity was calculated at the time of each transfusion as the yearly-equivalent number of RBC units. The main outcome was acute leukemia-free survival from first transfusion. Median transfusion burden was 30 (range: 4-330) RBC units and 112 patients received ≥ 25 units after a median of 9 months from first transfusion. In nested Cox models, having received ≥ 25 RBC units had a significant effect on survival (P < 0.001) that was not abrogated by including follow-up ≥ 9 months as a time-dependent covariate. Including transfusion intensity in the model had a significant effect on leukemia-free survival (P < 0.001) and cancelled the prognostic value of having received ≥ 25 RBC units. In conclusion, transfusion intensity, instead of the cumulative transfusion burden, is the transfusion-related variable really influencing on the prognosis of patients with transfusion-dependent MDS.     

Solid-state studies of the triclinic (Z' = 2) antiprotozoal drug ternidazole

The solid-state properties of antiprotozoal ternidazole (3-(2-methyl-5-nitroimidazol-1-yl)-propan-1-ol) have been studied. Crystals are triclinic in the temperature interval between 100 and 333 K (melting point) with two different molecular conformations present in the asymmetric unit (Z' = 2) and two of each conformer make up a tetramer held together by hydrogen bonding. Its melting enthalpy at 333 K is 25.65 (± 1.29) kJ · mol(-1). Linear plots were obtained for the melting temperature versus pressure (dP/dT = 5.67 (± 0.08) MPa · K(-1)] and the glass transition versus pressure [dP/dT = 7.73 (±1.76) MPa · K(-1)]. No crystalline polymorphism could be detected; thus, the single-crystal structure that has been found is most likely the stable one.     

Assessing individual bioequivalence using the structural equation model

The structural equation model (SEM) is introduced as a useful approach for assessing individual bio-equivalence. SEM parameters are estimated using a partial likelihood analysis and the hypotheses of individual bioequivalence is evaluated in a disaggregate way, testing separately the hypothesis concerning SEM parameters, and assessing the overall hypothesis of individual bioequivalence using the intersection-union principle. Limits of bioequivalence for SEM parameters are proposed and a power analysis is carried out.