The relevance of polymorphism in rifampicin

Tuberculosisis is an infectious Neglected Tropical Disease (NTD) considered a public health problem in several countries. Rifampin (RIF) is one of the first choice drugs in the treatment of this disease since it has bactericidal action on susceptible strains of Mycobacterium tuberculosis, the etiological agent of tuberculosis affecting humans. According to the literature RIF can exist in two polymorphic forms, namely forms I and II, a penta-hydrate and an amorphous solid1. Each form has different solubility in aqueous medium affecting the bioavailability of the drug when it formulated in solid dosage forms for oral administration since they are expected to content form II2. The objective of this research is to characterize and understand in detail the pharmaceutically relevant forms of RIF. It is an important and challenging problem related to the development of formulations because the physical mixture of these forms is usually observed in raw materials from generic suppliers. Thus, the reference sample (USP standard) and two lots from different suppliers were investigated by electron microscopy, Raman and infrared spectroscopies, X-ray diffraction powder and thermal analysis. In addition, pure samples of these solid forms were produced by recrystallization under different conditions in order to establish the structural reference standards. The results of this study will be useful for the development of efficient quality control methods for a drug which is very important to the social health programs.

Reversible De-/Rehydration Process in Paroxetine Hydrobromide

Paroxetine (PRX) is an antidepressant widely used in depression treatment for decades. The anhydrous and hemidrate chloride forms have been used in pharmaceutical formulations. During their developing a discussion associated with its physical forms and the complex hydration/dehydration behavior involving these phases were established. To improve our understanding of this issue we investigate the crystal structure of paroxetine bromide hemidrate, (PRX+.Br-).H2O, as a model for understanding the stability anhydrous/hemihydrate paroxetine arrangements and the nature of the intermolecular interaction of water within the crystal lattice by single crystal X-ray diffraction experiments. A combination of complementary characterization techniques were also used including Differential Scanning Calorimetry (DSC), thermogravimetric analysis (TGA), Hot Stage microscopy and solubility measurements. As expected the paroxetine bromide hemidrate, (PRX+.Br-).H2O, is isostructural with the paroxetine chloride hemidrate, (PRX+.Cl-).H2O. As in that case, the crystal packing of (PRX+.Br-).H2O is stabilized by strong NH2+...O and NH2+...Br hydrogen bonds which forms infinite channels along the b axis. The water and bromide anions are located along these channels. The DSC/TGA analysis for (PRX+.Br-).H2O show an endothermic desolvation process with an onset temperature of 77.09 °C, that is not present in the paroxetine chloride hemidrate DSC curve. This process leaves to a paroxetine anhydrous bromide crystal structure that is isomorphic to the anhydrous chloride one. However, this structure is spontaneously rehydrated at ambient atmosphere. This rehydration phenomenon probe the stability of paroxetine hemihydrate arrangement, since (PRX+.Br-) is slightly more soluble that its hydrate form. As opposed to chloride hemidrate, the rehydration of paroxetine bromide only involves a rearrangement of the water molecule within the cavities.

Phase transitions in efavirenz induced by mechanical activation

Efavirenz,(S)-6-chloro-4(cyclopropylethynyl)-1,4-dihydro-4-(trifluoromethyl)-2H-3,1-benzoxazin-2-one, is a anti HIV agent belonging to the class of the non-nucleoside reverse transcriptase inhibitors, which is used in combination with other protease inhibitors or nucleoside reverse transcriptase inhibitors. Several polymorphs were reported in patents and scientific publications, being form I the thermodynamically most stable and the selected for commercial formulations. Mechanochemistry has emerged as an experimental methodology to efficiently and rapidly screen for new solid forms of a pharmaceutical active ingredient. These methods include neat and drop assisted grinding have been successfully applied to produce solvates, polymorphs, salts and cocrystals. In this contribution, we investigate the structural stability of efavirenz under mechanochemistry conditions. Room temperature and cryogenic neat and drop assisted grinding were applied to induce new crystalline forms, which were characterized by x-ray powder diffraction, vibrational spectroscopy and thermal analysis. The mechanism involved in these transformations were also investigated and discussed.