Influence of polymorphic form, morphology, and excipient interactions on the dissolution of carbamazepine compacts.

To gain a deeper understanding of the behavior of carbamazepine (CBZ) and CBZ dihydrate (DH) compacts during in vitro dissolution tests various factors were investigated: hydrate formation of CBZ, crystal morphology, surface area, and excipient influence. Dissolution tests were performed in three different dissolution media: distilled water, hydroxypropyl methylcellulose (HPMC), and polyethylene glycol (PEG) solutions. For the CBZ compacts, the dissolution rate of CBZ in water was fastest (0.338 mg L(-1) min(-1)). With increasing ability of the excipients to inhibit the hydration of CBZ (PEG < HPMC), surprisingly the dissolution rate of CBZ compacts decreased: PEG solution (0.314 mg L(-1) min(-1)) > HPMC solution (0.257 mg L(-1) min(-1)). This implies that DH formation resulted in an apparent increase in the dissolution rate rather than slowing it down. For the DH compacts, the dissolution rate in water (0.055 mg L(-1) min(-1)) was slower than that of PEG and HPMC solutions (0.174 and 0.178 mg L(-1) min(-1), respectively). The contact angle measurements showed a significantly higher value in water (61.0 degrees) than in PEG and HPMC solutions (44.8 degrees and 43.1 degrees, respectively). Although the dissolution of CBZ and DH compacts in various dissolution media are complex processes, the influence and relative importance of these factors were clearly detected providing better understanding of the dissolution behavior of the drug.

The influence of various excipients on the conversion kinetics of carbamazepine polymorphs in aqueous suspension.

The influence of various excipients on the conversion of carbamazepine polymorphs to the dihydrate in aqueous suspension has been investigated. Ten excipients having functional groups which were potentially able to form hydrogen bonds with carbamazepine (group 1: methylcellulose, hypromellose (hydroxypropyl methylcellulose), hydroxypropylcellulose (HPC), 2-hydroxyethylcellulose (HEC), carmellose sodium (sodium carboxymethylcellulose), cellobiose; group 2: povidone (polyvinylpyrrolidone), povidone-vinyl acetate copolymer (povidone/VA) and N-methyl-2-pyrrolidone; group 3: macrogol (polyethylene glycol) and polyethylene oxide-polypropylene oxide copolymer (PEO/PPO)) were selected. Carbamazepine polymorphic forms III and I were dispersed separately into each aqueous excipient solution (0.1%, w/v) for 30 min at room temperature. The inhibition effect of each excipient was quantified using Raman spectroscopy combined with multivariate analyses. The solubility parameter of each excipient was calculated and used for categorizing excipients. Excipients in groups 1 and 2, which had both low solubility parameters (< 27.0 MPa(1/2)) and strong hydrogen bonding groups, inhibited the conversion completely. With increasing solubility parameter, the inhibition effect decreased for group 1 excipients, especially for carbamazepine form I, which had a higher specific surface area. Also, the excipients of group 3, lacking strong hydrogen bonding groups, showed poor inhibition although they had low solubility parameters (< 21.0 MPa(1/2)). This study indicated the importance of both hydrogen bonding interaction and a suitable hydrophobicity (expressed by the solubility parameter) in the inhibition of the conversion of carbamazepine to the dihydrate.

Transfer of metformin into human milk.

OBJECTIVES: Our objectives were to determine the milk-to-plasma ratio of metformin in lactating mothers and to estimate infant exposure. METHODS: Two studies were performed. In study 1, 3 nursing mothers taking metformin were studied throughout a dosing interval at steady state. Blood samples were obtained from 2 suckling infants. In study 2, 5 healthy lactating women who volunteered to express milk after weaning were given metformin, 500 mg, at weaning and were studied for up to 72 hours. In both studies, areas under the plasma and milk concentration-time curves were estimated, and the milk-to-plasma concentration ratio based on area under the concentration-time curve analysis was derived. The infant dose was calculated by standard methods. RESULTS: In study 1 the milk-to-plasma concentration ratios based on area under the concentration-time curve analysis were 0.37, 0.50, and 0.71. The estimated "doses" of metformin that would be ingested by the breast-fed infants were 0.18%, 0.20%, and 0.21% of the maternal doses, adjusted for weight. In the breast-fed infants, no metformin was detected (n = 2) or adverse effects noted (n = 3). In study 2, the milk-to-plasma concentration ratio based on area under the concentration-time curve analysis was unable to be calculated for 3 subjects because of the unexpected persistence of metformin in milk beyond the study period. For the 2 subjects studied for 72 hours, the milk-to-plasma concentration ratios based on area under the concentration-time curve analysis were 0.27 and 0.47 and the infant doses were 0.11% and 0.25%. The concentration-time profile for metformin in milk in all subjects was unexpectedly flat. CONCLUSIONS: Metformin appears to be "safe" during lactation because of low infant exposure. The unusual concentration-time profile for metformin in milk suggests that the transfer of metformin into milk is not solely dependent on passive diffusion.

Influence of particle size and preparation methods on the physical and chemical stability of amorphous simvastatin.

This study investigated the factors influencing the stability of amorphous simvastatin. Quench-cooled amorphous simvastatin in two particle size ranges, 150-180 microm (QC-big) and < or =10 microm (QC-small), and cryo-milled amorphous simvastatin (CM) were prepared, and their physical and chemical stability were investigated. Physical stability (crystallization) of amorphous simvastatin stored at two conditions was monitored by X-ray powder diffractometry (XRPD) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Assessment of enthalpy relaxation of amorphous forms was conducted using DSC in order to link the physical and chemical stability with molecular mobility. Chemical stability was studied with high-performance liquid chromatography (HPLC). Results obtained from the current study revealed that the solubility of amorphous forms prepared by both methods was enhanced compared to the crystalline form. The rank of solubility was found to be QC-big=QC-small>CM>crystalline. For the physical stability, the highest crystallization rate was observed for CM, and the slowest rate was detected for QC-big, with an intermediate rate occurring for QC-small. QC exhibited lower molecular mobility and higher chemical degradation than CM. Therefore, the current study demonstrated that QC and CM have obvious differences in both physical and chemical properties. It was concluded that care should be taken when choosing preparation methods for making amorphous materials. Furthermore, particle size, a factor that has often been overlooked when dealing with amorphous materials, was shown to have an influence on physical stability of amorphous simvastatin.

Hepatic cytochrome P450 activity and pollutant concentrations in paradise shelducks and southern black-backed gulls in the South Island of New Zealand.

Cytochrome P450 (CYP) enzymes catalyse the oxidative metabolism of various xenobiotics including environmental pollutants. We investigated liver microsomal CYP marker activities in 60 paradise shelducks (Tadorna variegata; herbivore) and 77 southern black-backed gulls (Larus dominicanus; omnivore) collected at three sites with putatively different levels of pollution in the South Island of New Zealand. Ethoxyresorufin O-deethylase (EROD) activity was high in birds at an urban landfill site compared to those at a relatively pristine and an agricultural site. Analysis of p-nitrophenol hydroxylase and erythromycin demethylase activities indicated the presence of two additional CYP isoforms in shelducks but no additional form in gulls. Total polychlorinated biphenyl (PCB) concentrations (ranges: shelducks, 0.073-6.2; gulls, 8.2-330 ng/g wet weight) were high in landfill samples suggesting a link to EROD induction and, in landfill shelducks, EROD was independently associated with Hg and Pb concentration. PCB congener-specific assessments indicated the metabolism of at least two congeners (#28 and #74) is induced in shelducks. DDE concentrations (ranges: shelducks, 0.85-320; gulls, 44-4800 ng/g) were high in birds at the landfill and agricultural sites. Body weight tended to be lower in landfill birds, but whether this reflects the greater energetic demands of pollutant detoxification remains to be investigated.