An evaluation of the Kodak Ektachem clinical chemistry slide for theophylline

We evaluated the Kodak Ektachem clinical chemistry slide for assay of theophylline. Assay precision and accuracy were acceptable in the therapeutic range although precision was poor at low levels of theophylline. The assay performed well with patients' samples using the Abbott TDx as the reference procedure but, as indicated by the manufacturer, uremic samples gave a positive bias, particularly in the therapeutic range. Finally, the significant bias observed with Quality Control material, probably due to matrix sensitivity, is a possible drawback.     

Tacrolimus metabolite cross-reactivity in different tacrolimus assays

Objectives: Tacrolimus (FK506) is an immunosuppressive drug with great clinical promise. There is a controversy regarding the role of tacrolimus metabolites in immunosuppression and toxicity, and immunoassays and immunophilin binding assays have not been adequately tested for metabolite cross-reactivity. Methods are limited to HPLC and HPLC-MS for quantifying the parent drug. Mixed lymphocyte culture assay (MLC) is the preferred functional bioassay for the measurement of parent drug and active metabolites but it is not practical for routine laboratory use. Due to differences in assay methods and reagent specificity, the concentration of tacrolimus in a given specimen may vary among different assay kit manufacturers. The objective of this study was to evaluate the degree of cross-reactivity or interference of the three first-generation tacrolimus metabolites [13-O-demethyl (M-I), 31-O-demethyl (M-II) and 15-O-demethyl (M-III)] among two different tacrolimus immunoassays (Immunoassay: PRO-Trac II FK506, Abbott IMx tacrolimus-II); and the radioreceptor assays (RRA) using minor immunophilins (14, 37, and 52 kDa immunophilins) and tacrolimus binding protein (FKBP12).

Methods: First-generation tacrolimus metabolites (M-I, M-II, and M-III) spiked in drug-free whole blood were assayed with RRA using three minor immunophilins (14, 37, and 52 kDa) and two commercial immunoassay procedures (Incstar PRO-Trac II tacrolimus, Abbott IMx tacrolimus II). The results were compared to previously published FKBP-12 RRA data and their immunosuppressive potency.

Results and conclusion: The first generation tacrolimus metabolites (M-I, M-II, and M-III) were tested using concentrations of 10 and 20 ng/mL. The significance of the metabolite interference (% of the total interference) was calculated based on the relative concentration of each metabolite present at steady-state trough concentrations in renal transplant recipients [22]. Metabolite I, which has no functional immunosuppressive activity showed minimal interference compared to M-II and M-III in all assays except the 14 kDa RRA. The Incstar PRO-Trac II tacrolimus assay showed the least M-I interference. Metabolite-II, which has a pharmacologic potency similar to the parent drug, showed a significant interference in the immunoassays and significant interference in radioreceptor assays. Metabolite III, which is pharmacologically inactive, produces 3–10% interference in the different assays if its presence in the blood is 6% of the parent drug. The total interference from these three metabolites was greater in the immunoassays than in the receptor assays. Receptor assays for tacrolimus provide results closer to the target value than do immunoassays.     

An update on digoxin

This review deals briefly with recent developments in the therapeutic drug monitoring of digoxin. Strategies for decreasing the interference by digoxin metabolites, digoxin-like factors, and spironolactone metabolites in immunoassays of digoxin are discussed. Other issues addressed include the development of alternative methods of analysis, such as receptor assays and "high-pressure" liquid chromatography; digoxin-like factors in hypertension; drug-drug interactions; redistribution of digoxin stores in the body; and forensic considerations.     

Lack of a relation between human neonatal thyroxine and pediatric neurobehavioral disorders.

The growth and differentiation of the central nervous system are closely related to the presence of iodine and thyroid hormones. It has been hypothesized that neurobehavioral disabilities of childhood, such as attention deficit hyperactivity disorder (ADHD), learning disorders, and autism can be attributed to fetal thyroidal endocrine disruption in utero. To determine whether there is an association between neonatal thyroid status and a subsequent diagnosis of a neurobehavioral disability, neonatal thyroxine (T(4)) levels have been used as the indicator of the presence of intrauterine thyroidal dysfunction. Neonatal T(4) levels were obtained from the neonatal hypothyroidism screening program. All cases were diagnosed at medical school diagnostic clinics, the diagnostic categories being ADHD, autism spectrum disorder, behavioral disorder, cognitive disorder, developmental delay, emotional disorder, learning disability, and speech/language disorder. Conditional logistic regression analysis was performed for each clinical condition. Odds ratios for the conditions ranged from 0.92 to 1.13 with p values ranging between 0.19 and 0.84. No significant differences were detected between neonatal T(4) values of the cases and the controls for any of the neurobehavioral conditions. All neonatal T(4) values were within normal ranges. The data provide no evidence to suggest that intrauterine thyroid status as reflected by the neonatal T(4) values had an impact on the neurologic disorders diagnosed in childhood.     

Impact of necrotising fasciitis on quality of life: A qualitative analysis

Mortality rates from severe necrotising soft tissue infections are improving progressively, therefore more emphasis should be placed on assessing and improving the quality of life of surviving patients. We investigated the functional and psychological issues, ability to social integration and self-perception of appearance in such patients presenting to our unit over 4 years. To conduct the study, we used the Short Form-36 and the Derriford Appearance Scale-24, which were distributed to those willing to participate. Ten patients have returned fully completed questionnaires. The overall quality of life and level of distress about the changed appearance were moderate (average SF-36 score of 65.8, DAS-24 score of 38). Statistical correlations between the scores and demographics were carried out using the Spearman rank correlation test. The capability of psychosocial adjustment was shown to improve with longer follow-up time and older age. However pain, physical limitations and energy levels were considerably more relevant in the older individuals and improved slower with time compared to psychological issues. Our results act as a good indicator of the quality of life in people dealing with the aftermath of necrotising soft tissue infections, but further, more extensive studies are required to achieve comprehensive and statistically significant results.     

Simultaneous determination of Levetiracetam and its acid metabolite (ucb L057) in serum/plasma by liquid chromatography tandem mass spectrometry

ObjectiveLevetiracetam and its acid metabolite have almost identical MRMs. They therefore need to be separated chromatographically prior to quantitation.Research design and methodsThe sample is deproteinized with acetonitrile containing Ritonavir as internal standard, centrifuged and the supernatant diluted with water (1:2 v/v). Sixty microliters of the supernatant is injected into the LC–MS/MS and Levetiracetam (LEV) and LEV metabolite separated chromatographically at room temperature employing a Supelco C₁₈ column and a 0.1% formic acid methanol gradient at pH of 2.5.ResultsThe retention times for LEV metabolite, LEV and Ritonavir were 4.50, 5.38 and 9.18 min, respectively. Calibration curves in spiked plasma were linear over the concentration range of 0–50 μg/mL for LEV and 0.0–5.0 µg/mL for LEV metabolite. Intra- and inter-run imprecision (n = 10) gave CVs of 2.3–4.7%, 3.4–8.9% for LEV and 2.9–3.9%, 3.3–7.4% for LEV metabolite. Recoveries of both LEV and LEV metabolite were close to 100%. Results for LEV were compared with those obtained by a commercial reference laboratory (r = 0.974).ConclusionThe procedure is reliable, quick, and inexpensive. LEV and LEV metabolite co-elute using C-18 columns at pHs > 3.0 and previously published methods employing these conditions could therefore be subject to metabolite interference. In this method LEV and LEV metabolite are separated at pH 2.5. The total run time including the washing step is 10 min/sample, making this method suitable when moderate throughput is needed such as in clinical or commercial reference laboratories.     

Variability in the pharmacokinetics of cyclophosphamide,methotrexate and 5-fluorouracil in women receiving adjuvant treatment for breast cancer

A total of 23 women with stage II breast cancer receiving adjuvant cyclophosphamide, methotrexate and 5-fluorouracil had detailed pharmacokinetic monitoring performed on the first and third courses of therapy. The area under the concentration time curve (AUC) of each of these three drugs varied by a factor of 3–4 among patients. No systematic change in pharmacokinetics between the first and third courses was seen for cyclophosphamide, methotrexate or 5-fluorouracil, and the mean AUC for each of the three drugs did not change. However, significant intrapatient variability in drug pharmacokinetics was observed for all three drugs such that the AUC, clearance and half-life in an individual on the third course could not be reliably predicted from data generated on the first course. On the basis of these results, cyclophosphamide, methotrexate, and 5-fluorouracil pharmacokinetic data from one treatment would not be useful information from which the doses for subsequent courses could be determined.This research was supported by the National Cancer Institute of Canada