Search PubMedSearch

SEARCH · Search PubMed

Results for “Stability analysis”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6Linked to original sources

[Analysis and stability of atropine sulfate and scopolamine hydrobromide. 2. Quantitative determination of the alkaloid in its decomposition product; 79. contribution to problems concerning the use of plastic containers for liquid pharmaceuticals].

The authors describe a method which permits, after thin-layer chromatographic separation and elution by means of the Eluchrom apparatus, to determine the tropane alkaloids and apoatropine in the presence of their decomposition products using tropaeolin 00. The recommended method has proved to be superior to other elution variants with regard to accuracy and reproducibility. Detectable amounts (microgram/ml): atropine, 0.4-4.0; scopolamine, 1.2-7.2; apoatropine, 0.8-3,2.

Atropine

[Analysis and stability of atropine sulfate and scopolamine hydrobromide. 3: Studies on the stability of tropane alkaloids; 80: contribution to problems in the use of plastic containers for liquid pharmaceuticals].

On evaluating their investigations, the authors discuss the degradation mechanism of tropane alkaloids in aqueous solution. As evidenced by competitive and consecutive reactions (hydrolysis, dehydration, dimerization), the degradation mechanism is characterized by a complicated course. Apart from temperature, a series of other factors, above all the pH value, exerts a considerable effect on the stability of both the alkaloids. Unbuffered solutions are more stable than buffered ones. The isothermal short-time test is not suitable for stability prediction. In the long-time test it was found that unbuffered aqueous atropine sulphate solutions still contained 90% of their initial drug content after 18 months' storage in low-density polyethylene containers at 20 degrees C. Scopolamine hydrobromide solutions showed an almost analogous behaviour. Of the container materials tested, low-density polyethylene bottles have been found to be best suited.

Atropine

[Analysis and stability of suxamethonium chloride. 1. Detection and quantitative determination of the intact active agent with its degradation products].

The authors developed methods permitting to follow the course of degradation in injectable solutions of suxamethonium chloride. The qualitative detection of the active agent in the presence of degradation products is achieved by thin-layer chromatography and spraying with Dragendorff's reagent and bromocresol green indicator solution. The same separation technique may be used for determining with sufficient accuracy the intact agent in the eluate, using the method of Okken and Haas. Furthermore, a modified Draganic procedure (which is based on the spectrophotometric determination of the hydrolysis products succinic acid monocholine chloride and succinic acid as a Cu-benzidine complex) is suited for estimating the degree of degradation. No previous separation is required because the molar extinction efficients of the monoester and of the acid are in agreement, so that the degree of degradation can be calculated from the sum of the molar concentrations. The value of these methods is demonstrated by analyzing experimental mixtures of the intact agent and degradation products.

Drug Stability

L4-5 isthmic spondylolisthesis. A biomechanical analysis comparing stability in L4-5 and L5-S1 isthmic spondylolisthesis.

The authors have previously reported that the L4-5 isthmic spondylolisthesis lesion often progresses more than the L5-S1 lesion in adult patients. This biomechanical study compares the in vitro stability of the L4-5 isthmic spondylolisthesis lesion compared with the L5-S1 isthmic lesion. The authors also analyzed the role of the L5 iliolumbar ligament as a contributing factor to stability. Six fresh frozen human cadaveric specimens (L4 to the sacrum including the iliolumbar ligamentous complex) were tested by applying 10 Nm flexion-extension moments. Sagittal plane motion was measured with the specimens intact and after sequential transection of the pars interarticulares at L4 and L5 and finally with the iliolumbar ligaments cut at L5-S1. L4-5 and L5-S1 both showed significant increases in rotation with the pars defect compared with normal (L4-5 = +2.0, L5-S1 = +3.2 degrees). Decreased translation of L5-S1 occurred with pars defect at this level. There were no significant differences at the L5-S1 level after sectioning of the iliolumbar ligament. Calculating the percentage difference from normal, L4-5 with a pars defect exhibited significantly greater relative motion compared with L5-S1 with the same defect; 12% more rotation, 33% more shear, and 43% more axial translation. The iliolumbar ligament did not appear to contribute to these differences because there was no significant change in the L5-S1 kinematics after its transection. These results support the hypothesis that L4-5 pars defects are more unstable than L5-S1 lesions. The iliolumbar ligament could not be implicated as the major contributing factor in these differences.

Biomechanical Phenomena

Phase plane analysis of stability in quiet standing.

We analyzed the standing balance control of 11 healthy subjects and 15 subjects with bilateral vestibular hypofunction (BVH) using phase plane (velocity versus displacement) plots. We hypothesized that maintaining postural stability requires control of both the position and momentum of the center of gravity (CG) and infer that it is advantageous to use both velocity and displacement data to characterize balance control. Phase plane plots provide insight into this dynamic aspect of balance control. We evaluated phase plane plots based on whole body CG and center of pressure (CoP). We varied stability by altering the base of support and visual information. Three different foot placements were used: feet wide apart, feet together, and semitandem stance. Feet together standing was performed with eyes open and with eyes closed. The phase plane plots show changes in stability as base of support is altered or visual input is removed and reveal stability differences between the control and BVH groups. The root mean square variance of velocity and displacement was used to quantify the phase plane information. This parameter showed significant differences between activities and between groups. We conclude that phase plane plots that combine displacement and velocity information are more useful in characterizing balance control than displacement or velocity alone.

Gravitation

Economic and quality of life outcomes: the four-step pharmacoeconomic research model.

Increasingly, economic data are being considered in formulary decisions. In oncology, pharmacoeconomic evaluations are essential to help decision makers weigh the associated costs and outcomes of competing chemotherapeutic interventions. In this article, we present a four-step pharmacoeconomic research model that can be customized for specific provider or payer systems. The model encompasses problem identification, clinical management analysis, three pharmacoeconomic analyses (cost consequence, expected cost, and cost effectiveness), and a sensitivity analysis--the rank order stability analysis (ROSA)--to validate the findings.

Antineoplastic Agents

A biomechanical analysis of atlantoaxial stabilization methods using a bovine model. C1/C2 fixation analysis.

The reliability and initial postoperative stability of six widely used C1-C2 surgical constructs were evaluated by nondestructive biomechanical testing of ten fresh bovine upper cervical spine segments. The six fixation techniques were the simple midline sublaminar C1 wiring (SMW), the modified Gallie wiring (MGW), the Brook wedge arthrodesis (BWA), the bilateral lateral mass screw (LMS), and the Clark arthrodesis without (CWO) and with (CW) the adjunctive use of polymethylmethacrylate (PMMA) cement. Instability was produced by resection of the base of the dens. Intact, destabilized, and instrumented constructs were tested in unconstrained flexion, extension, torsion, anterior, and posterior shear forces. The LMS and CW techniques proved the most effective in achieving C1-C2 stability. Sublaminar C2 wiring methods tended to have greater torsional and shear stiffness. Less rigid fixation techniques frequently loosened. All non-PMMA-enhanced wired constructs failed to restore the ability to adequately resist the posterior translation of C1 on C2. Stabilization of an unstable atlantoaxial articulation is best accomplished by a lateral mass screw or sublaminar C1-C2 PMMA-enhanced technique. Other techniques provided less consistent and reliable surgical fixation. Because of the inadequacy of wired constructs to resist posterior shear in patients with this instability pattern, the usual treatment may need to be modified to include more prolonged or protective external immobilization or more rigid fixation techniques. Although less rigid, the SMW and the MGW techniques are safer because they require less-frequent passage of sublaminar wires, avoid potential problems with PMMA, and obviate the hazards of further lateral dissection and insertion of the transarticular screws.

Animals

Isolation, characterization and transformation, by autonomous replication, of Mucor circinelloides OMPdecase-deficient mutants.

Pyrimidine auxotrophs of Mucor circinelloides were isolated after mutagenesis with nitrosoguanidine and selected for resistance to 5-fluoroorotate. These mutants were genetically and biochemically characterized and found to be deficient either in orotidine-5'-monophosphate decarboxylase (OMPdecase) activity or in orotate phosphoribosyl transferase (OPRTase) activity. Different circular DNA molecules containing the homologous pyrG gene were used to transform a representative OMPdecase-deficient strain to uracil prototrophy. Southern analysis, as well as mitotic stability analysis of the transformants, showed that the transforming DNA is always maintained extrachromosomally. The smallest fragment tested that retained both the capacity to complement the pyrG4 mutation and the ability to be maintained extrachromosomally when cloned in a suitable vector is a 1.85 kb M. circinelloides genomic DNA fragment. This fragment consists of the pyrG coding region flanked by 606 nucleotides at the 5' and 330 nucleotides at the 3' ends, respectively. Sequence analysis reveals that it does not share any element in common with another M. circinelloides genomic DNA fragment which also promotes autonomous replication in this organism, except those related to transcription. Furthermore, it differs from elements which have been shown to be involved in autonomous replication in other fungal systems. An equivalent plasmid harbouring the heterologous Phycomyces blakesleeanus pyrG gene yielded lower transformation rates, but the transforming DNA was also maintained extrachromosomally. Our results suggest that autonomous replication in M. circinelloides may be driven by elements normally present in nuclear coding genes.

Base Sequence

Role of visuo-vestibular interaction in pathological ocular oscillation: new model and control system analysis.

Control system engineering is a relatively newer field of engineering which is directly applicable to performance analysis of neuronal networks. Visuo-vestibular interaction (VVI) represents a neuronal control system which has most benefited from such analysis. In this paper, we present a new model of VVI derived from our previously reported model by adding cortical pursuit feedback. Mathematical analysis of abnormal eye oscillations and stability analysis of the VVI system provided us with a plausible hypothesis that the pathological ocular oscillations seen in oculopalatal myoclonus and see-saw nystagmus are indeed due to an unstable VVI control system. The former is due to degeneration of the inferior olivary nucleus resulting in loss of cerebellar learning effects, while the latter is due to disruption of the pathway conveying retinal error signals.

Animals

Epistasis in the multiple locus symmetric viability model.

The n-locus two-allele symmetric viability model is considered in terms of the parameters measuring the additive epistasis in fitness. The dynamics is analysed using a simple linear transformation of the gametic frequencies, and then the recurrence equations depend on the epistatic parameters and Geiringer's recombination distribution only. The model exhibits an equilibrium, the central equilibrium, where the 2n gametes are equally frequent. The transformation simplifies the stability analysis of the central point, and provides the stability conditions in terms of the existence conditions of other equilibria. For total negative epistasis (all epistatic parameters are negative) the central point is stable for all recombination distributions. For free recombination either a central point (segregating one, two, ... or n loci) or the n-locus fixation states are stable. For no recombination and some epistatic parameters positive the central point is unstable and several boundary equilibria may be locally stable. The sign structure of the additive epistasis is therefore an important determinant of the dynamics of the n-locus symmetric viability model. The non-symmetric multiple locus models previously analysed are dynamically related, and they all have an epistatic sign structure that resembles that of the multiplicative viability model. A non-symmetric model with total negative epistasis which share dynamical properties with the similar symmetric model is suggested.

Alleles

Conformational stability of human skeletal tropomyosins modified by site-directed mutagenesis.

We have used human beta-tropomyosin produced in Escherichia coli and deletion mutants obtained by site-directed mutagenesis to analyse the conformational stability of this molecule under various experimental conditions. Protein engineering has allowed us to answer some questions raised by stability analysis of the wild-type tropomyosin. The complex pattern of denaturation is due neither to heterogeneity of the preparation nor to head-to-tail interactions. The N- and C-termini are not of importance for the thermal stability of the molecule. On the contrary, deletion of the 31 C-terminus amino acids leads to a dramatic decrease of the stability observed in guanidinium chloride. This lowering is interpreted as the participation of one more guanidinium chloride ions to the denaturation equilibrium. Analysis of the stability in presence of organic solvents reveals that acetonitrile and methanol induce opposite effects. Investigation of these effects by three methods (CD, fluorescence and electrophoresis that measure respectively the content in alpha-helix, the contact between the two strands and the strands exchange) leads to the conclusion that strand separation can precede the denaturation of the alpha-helix.

Circular Dichroism

Pharmacoeconomic analysis of oral therapies for onychomycosis: a US model.

An evaluation of treatment practices in 13 countries, not including the United States, has shown oral terbinafine to be more cost-effective (from a government payer perspective) than griseofulvin, itraconazole, and ketoconazole in the treatment of onychomycosis of toenails and fingernails. The purpose of this study was to evaluate the clinical and economic effects of oral griseofulvin, itraconazole, ketoconazole, and terbinafine in the treatment of onychomycosis from the perspective of a third-party payer in the United States. A previously constructed decision-analytic model evaluating the costs of onychomycosis in 13 countries outside the United States was updated to determine the costs of treating onychomycosis in the United States. Clinical management patterns were assessed to identify and quantify physician visits, laboratory tests, and adverse drug reaction treatment components for patients with toenail and fingernail onychomycosis. A random-effects model meta-analysis of treatment efficacy (mycologic cure) and New York Metropolitan Medicare charge data for physician fees were used in the treatment model. A sensitivity analysis assessing alternative dosing regimens and a rank order stability analysis investigating the effects of length of treatment, success rates, relapse rates, and drug acquisition costs on overall results were also conducted. Terbinafine had the lowest cost per mycologic cure after one treatment regimen for onychomycosis in both toenail and fingernail infections ($791.00 and $454.00, respectively). The costs of treating toenail and fingernail infections were comparatively higher for therapy with itraconazole ($1535.00 and $767.00, respectively), griseofulvin ($2385.00 and $837.00, respectively), and ketoconazole ($10,025.00 and $1512.00, respectively). As a primary treatment choice, terbinafine also had the lowest overall expected cost per patient for both toenail and fingernail infections ($977.00 and $550.00, respectively). Griseofulvin had expected costs ($1543.00 and $822.00, respectively) similar to itraconazole ($1588.00 and $894.00, respectively), whereas ketoconazole was the most expensive primary treatment choice ($2359.00 and $1287.00, respectively). This study demonstrates that terbinafine is an economical and cost-effective treatment for patients with dermatophytic onychomycosis, supporting European and Canadian studies. Except for the rank order of griseofulvin and itraconazole, sensitivity analyses show that these results are fairly stable.

Administration, Oral

The stability and persistence of mutualisms embedded in community interactions.

In this paper we argue that two-species models of mutualism may be oversimplifications of the real world that lead to erroneous predictions. We present a four-species model of a pollination mutualism embedded in other types of community interactions. Conclusions derived from two-species models about the destabilizing effect of mutualisms are misleading when applied to the present scenario; although the mutualisms are locally destabilizing, the effect is more than canceled by an increased chance of feasibility. The crucial difference is the interaction of the mutualists with other species in a larger web. Furthermore, community persistence (without unrealistic population explosion), arguably a superior ecological criterion, is greatly enhanced by the presence of mutualisms. Therefore, we predict that mutualisms should be common in the real world, a prediction matching empirial findings and in contrast to the predictions from local stability analysis of basic two-species models. This method of stabilizing a mutualism appears superior in some ways to the often-used method of introducing density dependence in the strength of the mutualism, because it permits obligate mutualisms to exist even at low densities, again matching empirical findings. Lastly, this study is an example of how complex model assemblages can behave qualitatively differently from analogous simpler ones.

Animals