Iron-monosulfide oxidation in natural sediments: resolving microbially mediated S transformations using XANES, electron microscopy, and selective extractions.

Iron-monosulfide oxidation and associated S transformations in a natural sediment were examined by combining selective extractions, electron microscopy and S K-edge X-ray absorption near-edge structure (XANES) spectroscopy, The sediment examined in this study was collected from a waterway receiving acid-sulfate soil drainage. It contained a high acid-volatile sulfide content (1031 micromol g(-1)), reflecting an abundance of iron-monosulfide. The iron-monosulfide speciation in the initial sediment sample was dominated by nanocrystalline mackinawite (tetragonal FeS). At near-neutral pH and an 02 partial pressure of approximately 0.2 atm, the mackinawite was found to oxidize rapidly, with a half-time of 29 +/- 2 min. This oxidation rate did not differ significantly (P < 0.05) between abiotic versus biotic conditions, demonstrating that oxidation of nanocrystalline mackinawite was not microbially mediated. The extraction results suggested that elemental S (S8(0)) was a key intermediate S oxidation product Transmission electron microscopy showed the S8(0) to be amorphous nanoglobules, 100-200 nm in diameter. The quantitative importance of S8(0) was confirmed by linear combination XANES spectroscopy, after accounting for the inherent effect of the nanoscale S8(0) particle-size on the corresponding XANES spectrum. Both the selective extraction and XANES data showed that oxidation of S8(0) to SO4(2-) was mediated by microbial activity. In addition to directly revealing important S transformations, the XANES results support the accuracy of the selective extraction scheme employed here.

A cost analysis of alfentanil+propofol vs morphine+midazolam for the sedation of critically ill patients.

Morphine + midazolam and alfentanil + propofol are regimens offering well tolerated and effective sedation for critically ill patients. However, morphine + midazolam is associated with accumulation in these patients, resulting in prolonged recovery characteristics. Alfentanil+propofol, although more expensive, has a shorter elimination half-life, is not associated with accumulation problems and results in a rapid recovery. This study compared sedation quality, patient recovery characteristics and the cost of alfentanil + propofol and morphine + midazolam for sedating critically ill patients in the intensive care setting. 26 patients were randomly allocated to receive sedation with alfentanil + propofol (n = 17) or morphine + midazolam (n = 9). Outcome measures were the times until extubation, intensive care unit (ICU) transfer and final hospital discharge. Cost analysis assessed both drug-related costs, including drug acquisition and administration, and non-drug-related costs, including bed occupancy. Age, gender, diagnosis, Acute Physiological and Chronic Health Evaluation (APACHE) II scores and sedation quality did not differ significantly between groups. The times to extubation and until patients were fit for transfer from ICU were significantly shorter for patients sedated with alfentanil + propofol than for those sedated with morphine + midazolam. The total costs (at the time of the study Pounds 1 was equivalent to $US1.59) for ICU hospital stay per patient for alfentanil + propofol and morphine + midazolam were 3063 Pounds and 9511 Pounds, respectively, because the shorter recovery characteristics of alfentanil + propofol led to a reduction in ICU stay. Corresponding costss for total hospital stay were 6063 Pounds and 13735 Pounds, respectively. In conclusion, alfentanil + propofol has a better pharmacoeconomic profile than morphine + midazolam for sedating critically ill patients in the ICU setting.

Detection and determination of the hydrazo and azo photoproducts of 4-aminobenzoic acid by high-performance liquid chromatography.

The photochemistry of 4-aminobenzoic acid has been investigated using two validated reversed-phase HPLC methods. Up to nine photoproducts have been detected, with chromatographic evidence for the formation of 4,4'-azobenzenedicarboxylic acid and 4,4'-hydrazobenzenedicarboxylic acid. The synthesis and analytical characterization of 4,4'-hydrazobenzenedicarboxylic acid is reported.

A soil-site evaluation index of productivity in intensively managed Pinus radiata (D. Don) plantations in South Australia.

A limiting-factor, environmental model for radiata pine (Pinus radiata (D. Don)) has been developed using landform and soil morphological features that influence site productivity. The model focuses on soil and landscape constraints to productivity and predicts the native productivity of land and tree species. It permits the integration of land-use objectives for a catchment through forest management and use of silvicultural practices which increase productivity. The soil site evaluation index (SSEI) is an index of forest productivity found when silviculture extends only to the minimum amount of site disturbance needed to establish a plantation of radiata pine. The impacts of intensive silvicultural practices were deducted from the 'Site Quality' productivity survey rating to calculate the unimproved yield class (uYC). We calculated SSEI by range standardising uYC values from 0 to 1. SSEI was correlated with the environmental factors in a regression tree model using readily available analytical software. The model accurately predicts unimproved forest productivity from observed soil horizon and land surface properties. The environmental constraints in low lying areas relate to waterlogging, soil sodicity and gravel content. In elevated areas, plant available water storage, rock weathering, landform, ironstone gravel and aspect are recognised factors for pine growth.

A single oral dose method for predicting steady state theophylline concentrations in clinical practice.

A single dose, single point method of predicting patients' oral maintenance theophylline dosage has been compared with a noninvasive method. Twenty patients with obstructive lung disease received an oral dose (6 mg kg-1) of micro-crystalline theophylline. The plasma theophylline concentration after 8-10 h was then used to calculate the optimum maintenance dose of sustained release aminophylline required to achieve steady state concentrations between 55 and 110 mumols l-1. The mean steady state plasma theophylline concentration for this dosage schedule was also predicted by a method using population average pharmacokinetic parameters (assumed clearance method). These predictions were then compared with observed concentration-time profiles at steady state. The mean difference between the observed values and those predicted from a morning test dose was -0.11 mumol l-1 (95% CI -7.0 to +7.2). A larger difference (-7.4 mumol l-1 95% CI -18.2 to +3.4) was found for the assumed clearance method. Since the confidence intervals contain zero, these differences are not significantly different from zero at the 5% level, although the morning test dose method allowed prediction of the whole concentration-time profile and was more precise. An evening test dose was also used in the study, but the mean difference between the observed values and those predicted from this method was larger at -24.8 mumol l-1 (95% CI -32.89 to -17.21) and was significantly different from zero. This study indicates that a morning test dose followed by a single blood sample can be used to establish maintenance theophylline therapy quickly and safely in selected patients.

The use of probenecid to increase the serum amoxycillin levels in patients with bronchiectasis.

Amoxycillin 3 g twice daily is effective in treating patients with bronchiectasis who have daily purulent sputum. However, it is a relatively expensive treatment if used for prolonged periods. This pilot study in six patients with bronchiectasis showed that the concurrent administration of probenecid with a smaller dose of amoxycillin produced similar clinical responses and pharmacokinetic profiles to those found with high dose amoxycillin alone. The amount of amoxycillin used was reduced by two thirds, producing a potential saving of approximately pound 1000 per patient per annum in those taking long term treatment.

An evaluation of the potential interaction between enalapril and amiloride.

Enalapril was shown to have no effect on the serum potassium of patients (n = 16) already taking Frusemide and Amiloride. Furthermore, there was no difference in serum potassium levels of the group taking a combination of Enalapril, Frusemide and Amiloride when compared to a similar group of patients taking Frusemide and Amiloride alone (n = 19). No patients in either group were deemed to have seriously impaired renal function. The results indicate that the theoretical hyperkalaemic effect of concurrent administration of Enalapril and Amiloride is not manifest in clinical practice in patients with normal renal function.

Determination of in vivo concentration-time profiles of chlorhexidine and noxythiolin bladder irrigations.

The in vivo concentration-time profiles of chlorhexidine and noxythiolin bladder irrigations were determined by utilizing high-performance liquid chromatography techniques following a once daily irrigation. A total of 14 chlorhexidine irrigations established a mean concentration of 0.006% w/v, 2-3 h post irrigation. A total of 12 noxythiolin irrigations established a mean concentration of 0.266% w/v, 2-3 h post irrigation, which correlated to a mean formaldehyde concentration of 0.0119% w/v at 2-3 h, as estimated from N-methylthiourea. For both solutions the minimum inhibitory concentration was exceeded for up to 5 h post irrigation, which is sufficient contact time to establish a total kill, thus indicating the possibility that a once daily irrigation may be appropriate in asymptomatic bacteriuria which utilizes either chlorhexidine or noxythiolin.

The effectiveness of drug level monitoring and pharmacokinetics in individualizing theophylline therapy.

A pharmacokinetic method for individualizing theophylline dosage is described. The method was shown to be reliable and accurate, and maintained significantly more patients within the optimum therapeutic range when compared with conventional regimens. The study also showed that when conventional dosage regimens are used, a large proportion of patients exhibit theophylline levels well below the optimum therapeutic range. Population pharmacokinetic data for theophylline and the effect of congestive heart failure on its clearance are also presented.

Effect of racemic and S(+) alpha-chlorohydrin-1-phosphate on glyceraldehyde-3-phosphate dehydrogenase in relation to its contraceptive action.

The phosphate esters of racemic (+/-) alpha-chlorohydrin and its S(+)-optical isomer have been prepared as cyclohexylamine salts. In vitro both inhibited glyceraldehyde-3-phosphate dehydrogenase by a competitive mechanism, whereas (+/-) alpha-chlorohydrin did not. The S(+)-isomer was approximately four times as potent as the racemate. These results correlate with data concerning the relative contraceptive activity in rats of racemic and S(+) alpha-chlorohydrin. They support the view that the antifertility mechanism involves in vivo formation of S(+) alpha-chlorohydrin-1-phosphate, with resulting inhibition of glycolysis in sperm.