Therapeutic concentrations of amphotericin B in serum were measured by reversed-phase liquid chromatography with detection at 386 nm. Complete recovery of the drug and the internal standard from a l-ml serum sample was achieved by pretreating the sample with guanidine hydrochloride and extracting it with a disposable reversed-phase phenyl extraction column. The method was sensitive to 0.005 ,ug of amphotericin B per ml and linear to at least 5 ,ug/ml. Coehicients of variation were 4.8% within-run and 6.3% between-run.Amphotericin B is an antibiotic widely used to treat systemic mycoses (10). Its use is restricted to life-threatening infections, however, because of its severe toxicity, which is usually encountered with therapeutic doses of the drug. Amphotericin B therapy therefore involves a balancing of toxic effects against antifungal activity.Until This was then mixed with 45 ml of 1% aqueous sodium dodecyl sulfate (SDS). This stock solution (100 ,ug/ml) was stored at -70°C. To make the working standard solution (1 jxg/ml), I combined 1 ml of stock solution, 1.5 ml of 1% SDS, and 97.5 ml of water (total volume, 100 ml). This solution was stored at 1-ml aliquots at -70°C.Extraction of samples. Samples (serum, aqueous standard, cerebrospinal fluid [CSF], etc.) (1 ml) were combined with 200 ,ul of ISTD solution and 2 ml of 6 M guanidine hydrochloride. After brief mixing, each sample was passed immediately through a separate, disposable phenyl extraction column ("Bond-Elut" PH, catalog no. 608101; Analytichem International, Harbor City, Calif.). Before analysis, the column was washed with one filling of methanol and then one filling of water. The sample was applied and allowed to run through, and the column was rinsed with another filling of water and allowed to drain. The drug and the ISTD were then eluted immediately from the column into a small test tube with 500 ,ul of acetonitrile-EDTA (prepared by combining 75 ml of acetonitrile with 25 ml of 5 mM disodium EDTA). SDS (1%) solution (200 ,ul) was mixed with the extract. Because of the instability of amphotericin B in the specimen after mixing with guanidine, the above steps were completed for one sample before the next sample was extracted. Amphotericin B was very stable in the final extract after SDS was added. For calibration, a 1-ml aliquot of the amphotericin B working standard solution was thawed and immediately extracted as described above.Chromatography. Chromatography was isocratic, with a solvent consisting of acetonitrile, methanol, and 5 mM EDTA (disodium salt) (187:449:354 [vol/vol]

Predefined multitest chemistry panels (PMCPs) have constituted a large proportion of laboratory tests and patient charges, even in pediatric settings, despite the absence of documented clinical utility for PMCPs and the general availability of random access analyzers that do not require predefined test combinations. We eliminated PMCPs in our tertiary children's hospital but placed no other restrictions on ordering, and observed a 32.7% reduction in the number of automated chemistry tests ordered. All 23 tests in the previous PMCPs showed a decline in utilization, >50% for 8 of the tests and 20-50% for 13 others, and this change was sustained throughout an 8-month follow-up period. The total number of orders for one or more tests increased by 8.2%, but the variety of combinations that were ordered increased by 280%. The most substantial changes included a decrease in the number of orders for combinations of >15 tests, and increases in the number of orders for single tests and combinations of 2 to 5 tests. Orders for combinations identical to all of the former PMCPs declined, with the exception of the 4-test electrolyte panel. There was a marked decline in orders for a 7-test panel identical to the recently defined HCFA-AMA Basic Metabolic Panel, and orders for combinations identical to the HCFA-AMA Liver Function and Extended Metabolic panels were vanishingly rare and nonexistent, respectively. The calculated reduction in patient charges was much greater than actual cost savings, but the reduction in total tests and increase in the variety of test combinations suggest that significant savings can be realized if clinicians are encouraged to order only the tests or combinations they need without imposing procedural, financial, and regulatory burdens.

The treatment of digoxin intoxication has been revolutionized by digoxin specific antibody fragments (Fab). Serum digoxin concentrations may be inaccurate after this treatment. We report a case of digoxin intoxication where the results of serum concentration determinations were strikingly disparate depending on the assay used. To investigate this discrepancy we compared serum samples spiked with digoxin from 0-50 ng/mL in the presence of increasing concentrations of digoxin specific Fab-fragments. Samples were measured using the Abbott TDx assay with and without ultrafiltration of the sample and the Dade-Stratus radial partition assay. The TDx assay was statistically reduced by the Fab-fragments although the magnitude of the effect was small. The radial partition assay was dramatically affected by the addition of Fab-fragments. The predicted non-Fab bound concentration correlated highly with the measured concentration. When samples were ultrafiltered prior to TDx assay, the measured concentration was dramatically depressed but the regression of predicted non-Fab bound concentration versus observed had a significantly lower slope than for the radial partition assay. We hypothesize that this difference is due to serum protein binding in addition to Fab-fragment binding. We conclude that the radial partition assay gives the best approximation of digoxin concentration remaining unbound to Fab-fragments. Ultrafiltration followed by TDx assay gives an acceptable approximation.

Therapeutic concentrations of nifedipine in serum or plasma were measured by reversed-phase liquid chromatography, with detection by ultraviolet absorbance at 235 nm. In the procedure a disposable reversed-phase extraction column is used. A 1-mL sample is required. The method is sensitive to 3 micrograms of nifedipine per liter and the standard curve is linear to at least 400 micrograms/L. Coefficients of variation at 100 micrograms/L were 2.2% within-run, 2.8% between-run. The method has been used to determine nifedipine in patients involved in a test of its efficacy in treating muscular dystrophy.

It has been repeatedly claimed that structural glycoprotein or SGP is a major component of many connective tissues, particularly aorta. SGP is usually defined as material extractable from tissue with chaotropic agents such as urea and having an amino acid composition matching that of other, similar extracts. It has been claimed that SGP comprises 10-60% of the dry weight of aortic tissue. This paper describes a study in which aorta was exhaustively extracted with agents previously claimed to extract SGP. All the extracts yielded mixtures of proteins which, upon separation by polyacrylamide gel electrophoresis, were found to consist largely of actin, collagen, myosin and other known proteins. No significant quantity of any one unidentified protein was found which could have been SGP. This study casts grave doubt upon the existence of SGP as a major component of aorta.