The degradation of the antitumor agent gemcitabine hydrochloride in an acidic aqueous solution at pH 3.2 and identification of degradation products.

A study of the degradation kinetics of gemcitabine hydrochloride (2'-deoxy-2',2'-difluorocytidine) in aqueous solution at pH 3.2 was conducted. The degradation of gemcitabine followed pseudo first-order kinetics, and rate constants were determined at four different temperatures. These rates were used to construct an Arrhenius plot from which degradation rates at lower temperatures were extrapolated and activation energy calculated. Four major degradation products were identified. Only one of these degradation products, the uridine analogue of gemcitabine, was a known degradation product of gemcitabine and was identified by comparison with synthesized material. The other three degradation products were isolated and characterized by spectroscopic techniques. Two of these products were determined to be the diastereomeric 6-hydroxy-5, 6-dihydro-2'-deoxy-2',2'-difluorouridines, and the other product was determined to be O(6),5'-cyclo-5,6-dihydro-2'-deoxy-2', 2'-difluorouridine. The mechanisms of formation of these degradation products are discussed.

Acute and long-term stability studies of deoxy hemoglobin and characterization of ascorbate-induced modifications.

The reaction of ascorbate with recombinant hemoglobin (rHb1.1) in the presence of differing partial pressures of oxygen was studied. In the presence of 15 000 ppm (1.5%) residual oxygen, ascorbate/oxygen-mediated reactions resulted in an increased rate of autoxidation, modification of the beta-globin, increased oxygen affinity and decreased maximum Hill coefficient. One of the observed modifications to the beta-globin was a 72 Da addition to its N-terminus. Detailed characterization indicates the modification was an imidazolidinone type structure. Thorough deoxygenation of the hemoglobin solution to <150 ppm of oxygen prior to addition of ascorbate was required to prevent these modifications. Addition of ascorbate to the deoxy hemoglobin (deoxyHb) at pH 8 induced aggregation, eventually leading to precipitation. No such precipitation was observed at pH 7. Long-term storage of the hemoglobin was carried out by addition of ascorbate to deoxyHb at pH 7. The level of methemoglobin remained at <2% for up to 1 year at 4 degreesC, with no detectable precipitation of the protein. Modifications similar to those observed by the acute studies were observed over the 1-year period and correlated with disappearance of the added ascorbate.

The physical state of mannitol after freeze-drying: effects of mannitol concentration, freezing rate, and a noncrystallizing cosolute.

The objectives of this study were to (1) measure the effects of freezing rate and mannitol concentration on the physical state of freeze-dried mannitol when mannitol is present as a single component, (2) determine the relative concentration threshold above which crystalline mannitol can be observed by X-ray powder diffraction in the freeze-dried solid when a variety of noncrystallizing solutes are included in the formulation, and (3) measure the glass transition temperature of amorphous mannitol and to determine the degree to which the glass transition temperature of freeze-dried solids consisting of mannitol and a disaccharide is predicted by the Gordon-Taylor equation. Both freezing rate and mannitol concentration influence the crystal form of mannitol in the freeze-dried solid when mannitol is present as a single component. Slow freezing of 10% (w/v) mannitol produces a mixture of the alpha and beta polymorphs, whereas fast freezing of the same solution produces the delta form. Fast freezing of 5% (w/v) mannitol results primarily in the beta form. The threshold concentration above which crystalline mannitol is detected in the freeze-dried solid by X-ray diffraction is consistently about 30% (w/w) when a second, noncrystallizing solute is present, regardless of the nature of the second component. The glass transition temperature of amorphous mannitol measured from the quench-cooled melt is approximately 13 degreesC. Accordingly, mannitol is an effective plasticizer of freeze-dried solids when the mannitol remains amorphous. Glass transition temperatures of mixtures of mannitol and the disaccharides sucrose, maltose, trehalose, and lactose are well predicted by the Gordon-Taylor equation with values of k in the range of 3 to 4.

Solubility principles and practices for parenteral drug dosage form development.

Solubilization of poorly water soluble or water insoluble drugs for use in intravenously administered dosage forms is a very formidable task for the parenteral formulation scientist. We have briefly reviewed pertinent literature for parenteral drug solubilization and provided tabular information to assist parenteral formulation scientists in tackling and solving their solubility problems. However, until we can better understand and predict solubility behavior in interactive solvent systems, the why's and how's for parenteral drug solubilization using acceptable (safe and regulatory compliant) approaches will largely remain an empirical effort, leaving great opportunities for scientists to get more involved in this field.

Glycine crystallization during freezing: the effects of salt form, pH, and ionic strength.

PURPOSE: The purpose of the study is to characterize glycine crystallization during freezing of aqueous solutions as a function of the glycine salt form (i.e., neutral glycine, glycine hydrochloride, and sodium glycinate), pH, and ionic strength. METHODS: Crystallization was studied by thermal analysis, microscopy, x-ray diffraction, and pulsed Fourier transform nmr spectroscopy. RESULTS: A solution of neutral glycine with no additives undergoes rapid secondary crystallization during freezing, forming the beta polymorph, with a eutectic melting temperature of -3.4 degrees C. Glycine hydrochloride solutions undergo secondary crystallization relatively slowly, and the eutectic melting temperature is -28 degrees C. Sodium glycinate crystallizes from frozen solution at an intermediate rate, forming a eutectic mixture with a melting temperature of -17.8 degrees C. Where secondary crystallization does not occur rapidly, a complex glass transition is observed in the -70 degrees to -85 degrees C temperature range in the DSC thermograms of all systems studied. Rates of secondary crystallization and the type of crystal formed are influenced by solution pH relative the the pKs of glycine, and also by the change in ionic strength caused by adjustment of pH. Increased ionic strength significantly slows the crystallization of neutral glycine and promotes formation of the gamma polymorph. Thermal treatment or extended holding times during the freezing process may be necessary in order to promote secondary crystallization and prevent collapse during freeze drying. CONCLUSIONS: The results underscore the importance of recognizing that seemingly minor changes in formulation conditions can have profound effects on the physical chemistry of freezing and freeze drying.

Sterility testing of antimicrobial-containing injectable solutions prepared in the pharmacy.

The need for sterility testing of antimicrobial-containing injectable solutions is discussed and specific testing methods are described. Despite their antimicrobial activity, antimicrobial-containing injectable drug products are not necessarily self-sterilizing and can become contaminated. In addition to practicing aseptic technique, pharmacists must perform end-product sterility testing on intravenous solutions to ensure their sterility. The United States Pharmacopeia provides guidelines for the performance and validation of two sterility test methods: membrane filtration and direct transfer to culture media. Membrane filtration is the method of choice for sterility testing of many antimicrobial-containing injectable solutions. After the test article is filtered, the membrane is rinsed with sterile fluid to remove residual antimicrobial agent, cut into two portions, and immersed in two types of culture medium. Visible turbidity of a sample within the appropriate incubation period indicates the presence of a contaminating microorganism. Closed filtration systems minimize false-positive results. In the direct transfer method, samples of the test article are directly inoculated into vessels of culture media, and antimicrobial activity is eliminated by dilution or by deactivation with chemical or enzymatic agents. Sterility testing as well as aseptic technique is needed to ensure the sterility of antimicrobial-containing injectable solutions.

Preformulation method for parenteral preservative efficacy evaluation.

A method is described for rapidly and reliably evaluating parenteral preservative efficacy. Solutions containing antimicrobial preservatives were challenged with microorganisms, sampled from 0.5 to 6 h following introduction of the challenge, cultured, and counted for surviving microbial cells. Data were analyzed by computer according to two models: linear and quadratic. Decimal reduction times (D values) were calculated for each microbial challenge in each preservative solution. A D value of less than or equal to 2 h for bacteria predicts that the preservative system will pass the British Pharmacopoeia (BP) preservative efficacy test, a more rigorous test than the USP test. Fourteen preservative systems were tested in both neutral isotonic saline solutions and neutral regular insulin solutions. D values and correlation coefficients for both models were calculated. The ranking of preservative effectiveness in neutral saline solutions closely correlated with the results found using neutral regular insulin solutions. The most effective preservative systems were found to be 0.3% m-cresol and various combinations of m-cresol and phenol. The advantages and limitations of this method are discussed.

Stability of extemporaneous suspensions of carbamazepine.

The stability of carbamazepine in four suspending vehicles is reported. Suspensions of carbamazepine 200 mg/5 ml in sorbitol 70%, simple syrup, modified Hospital of the University of Pennsylvania Suspending Vehicle (HUP), and diluted HUP (HUP-A) were prepared. The first three suspensions were stored in amber glass bottles and oral syringes at 4, 25, and 37 degrees C, and the HUP-A suspension was stored at 4 degrees C. Physical stability was assessed by visual inspection of sedimentation, ease of pouring, and foaming upon shaking. Carbamazepine concentrations were determined periodically over 90 days by an enzyme-multiplied immunoassay. The assay was validated by acid-heat degradation of the drug, separation of breakdown products by thin-layer chromatography, and confirmation of non-reactivity of the breakdown products with the assay. The concentration of carbamazepine in sorbitol 70%, simple syrup, and HUP-A was at least 90% of the prepared concentration at all sampling times. Although separation occurred, the simple syrup suspensions could be redispersed. The suspension in HUP-A remained homogeneous, was easy to pour, and produced less foam than the HUP suspension. Extemporaneously compounded suspensions of carbamazepine in HUP-A or in simple syrup can be used for patients who require a liquid dosage form. Even though sorbitol 70% produced a pharmaceutically acceptable product, its use is not recommended because it has been reported to cause intractable diarrhea.

Particulate evaluation of parenteral nutrition solutions by electronic particle counting and scanning electron microscopy.

The particulate matter contamination of four commercial parenteral nutrition solutions that contained high concentrations of amino acids and dextrose was evaluated. Electron particle counting and scanning electron microscopy (SEM) were used to evaluate the amount of particulate matter over a 24-hour-period. The effect of adding 10 meq calcium and 20 meq phosphate electrolytes on the particulate content of these four solutions was determined also. Both counting methods agreed in the rank order comparison of particulate contamination, in that the Abbott and Travenol solutions contained the fewest particles while the Cutter solutions contained the most. The addition of calcium and phosphate resulted in at least a 50% increase in the mean particle count of all solutions. The SEM analysis showed the mean presence of microscopically large, yet subvisible, particles in the solutions containing phosphate and calcium. All of the solutions followed a previously published relationship between particle number and size. Although all of the solutions contained particulate matter, even the solutions with calcium and phosphate contained fewer particles than allowable by the USP-NF standard.

Evaluation of emulsion stability by diffuse reflectance spectroscopy.

A new method is described for evaluating the stability of emulsion bases and active components contained within such emulsions. Diffuse reflectance spectroscopy (DRS) is a technique that has the capability of detecting changes in particle size, surface properties, or drug quality of emulsions as a function of time without disturbance of the system. Such physical or chemical changes are monitored by changes in the visible and UV wavelength spectral characteristics of the emulsified systems. Four basic emulsion systems were prepared and analyzed for physical stability for 6 months by three techniques: visible coalescence, particle counting measurement, and DRS. Two drugs, aspirin and ascorbic acid, were then incorporated within stable emulsion bases, and the chemical stability of these drugs was monitored by DRS for 6 months. Results were compared with concomitant quantitative drug assay procedures. Good agreement was observed when data from DRS and analytical measurements were compared. The DRS technique may be used as a supportive method, offering simplicity and expedience, with other methods of evaluating emulsion stability and drug stability within emulsified systems.