Recommended Serum Concentrations Research Articles

Hydroxychloroquine susceptibility determination of Coxiella burnetii in human embryonic lung (HEL) fibroblast cells

Coxiella burnetii, the causative agent of Q fever, survives and replicates in the acidic environment of monocytes/macrophages; hydroxychloroquine, through alkalinisation of the acidic vacuoles, is critical for the management of Q fever. In this study, a collection of C. burnetii strains isolated from human samples was tested to evaluate the in vitro minimum inhibitory concentrations (MICs) of doxycycline and hydroxychloroquine. Serial two-fold dilutions of doxycycline (0.25–8 mg/L) and hydroxychloroquine (0.25–4 mg/L) were added to C. burnetii-infected human embryonic lung (HEL) fibroblast cells after 48 h of incubation, in duplicate. DNA was detected by C. burnetii-specific semi-quantitative PCR with primers and probes designed for amplification of the IS1111 and IS30A spacers. A total of 29 C. burnetii isolates obtained from 29 patients were tested. Doxycycline MICs ranged from 0.25 mg/L to 0.5 mg/L and hydroxychloroquine MICs from 0.25 mg/L to >4 mg/L. Four C. burnetii stains had hydroxychloroquine MICs ≤ 1 mg/L. The concentration of hydroxychloroquine was associated with a significant decrease in C. burnetii DNA copies in HEL cells based on linear regression analysis (P = 0.01). Recommended serum concentrations of hydroxychloroquine significantly reduced the growth of C. burnetii. Moreover, some C. burnetii strains presented hydroxychloroquine MICs below the recommended serum concentrations, indicating that, for these cases, hydroxychloroquine treatment alone may even be effective.

Simple procedure for determination of valproic acid in dried blood spots by gas chromatography–mass spectrometry

Valproic acid (VA) is a drug widely used to treat epilepsy and bipolar disorder, at recommended serum concentrations ranging form 50 to 100μg ml-1. A novel option for therapeutic drug monitoring that has been emerging recently its testing using dried blood spots on paper (DBS), but there are no reports of its application to assaying VA. In this study, a methodology was developed for the determination of VA in 6mm diameter DBS, equivalent to around 12μl of blood, using gas chromatography combined with mass spectrometry. DBS were extracted with a mixture of acetonitrile and methanol (1:3, v/v). The method is linear from 5 to 250μgml−1 with intra-assay and inter-assay precision of 2.67–8.15% and 2.28–3.67%, respectively. Accuracy was 102.84–104.42%. VA was stable in DBS stored at 45°C for up to 21 days. VA concentrations in DBS correlated with concentrations assayed in serum, with r=0.9948. Mean ratio between VA concentrations in serum and DBS in clinical samples was 1.883. Dried blood spots are a viable option for collection and transport of samples and for assaying VA in the context of therapeutic drug monitoring, especially in Developing Countries.

Weight Loss Is Associated With Increased Serum 25‐Hydroxyvitamin D in Overweight or Obese Women

Low circulating concentrations of vitamin D metabolites have been associated with increased risk for several diseases and clinical conditions. Large observational studies and surveys have shown that obesity is independently associated with lower serum 25-hydroxyvitamin D (25(OH)D) concentration. Few studies have examined the effect of weight loss on serum 25(OH)D concentration. The purpose of this study was to prospectively examine the effect of weight loss on serum 25(OH)D concentration. Data were collected from 383 overweight or obese women who participated in a 2-year clinical trial of a weight-loss program, in which 51% (N = 195) lost at least 5% of baseline weight by 24 months, 18% (N = 67) lost 5-10%, and 33% (N = 128) lost >10%. Women who did not lose weight at 24 months had an increase in serum 25(OH)D of 1.9 (9.7) ng/ml (mean (SD)); 25(OH)D increased by 2.7 (9.1) ng/ml for those who lost 5-10% of baseline weight; and 25(OH)D increased by 5.0 (9.2) ng/ml for those who lost >10% of baseline weight (P = 0.014). At baseline, 51% (N = 197) of participants met or exceeded the recommended serum concentration of 20 ng/ml. By study end, 64% (N = 230) of overweight or obese women met this goal, as well as 83% (N = 20) of those whose weight loss achieved a normal BMI. These findings suggest that weight loss, presumably associated with a reduction in body fat, is associated with increased serum 25(OH)D concentration in overweight or obese women.

Therapeutic monitoring of vancomycin

The present study aimed to characterize admitted patients in a public hospital in the Northwestern region of Parana State, which were subject to therapeutic monitoring of vancomycin during 2007 and 2008. The data were obtained by a retrospective study of patients' medical records, from where we separated the laboratory results, medical prescriptions, gender, age, and diagnosis of patients submitted to therapeutic monitoring. Of the total of 38 patients, only eight (21.1%) presented serum concentrations within recommended range, varying from 1.3 to 47.9 mg L -1 . Concentrations above the reference value were observed in 22 patients (57.9%), and below the reference, in other eight patients (21.1%). The recommended serum concentrations at peak were obtained in only four patients (11.4%), higher than the recommended value in seven patients (20.0%), and lower, in 24 patients (68.6%). Only one patient (2.6%) presented serum concentration within the reference values at both high and low dosages. Therefore, the results evidenced the importance of therapeutic monitoring of vancomycin, individualizing the dose for each patient, and reducing toxic or subtherapeutic effects of this antimicrobial substance.

Potential for methotrexate exposure through contamination during parenteral use as an immunosuppressant

To evaluate whether the risk of methotrexate (MTX) exposure through skin contamination using parenteral doses of 25 mg warrants special oncology handling precautions during administration. We conducted a study with six human volunteers deliberately exposed to an entire dose of 25 mg MTX solution on their skin for 30 min. Serum levels of MTX were measured at baseline, 2, 4, 8, 12 and 24 h as well as serum homocysteine at baseline and 24 h after clinical exposure. Twenty-four-hour urinary excretion of MTX and possible local or systemic signs of toxicity were also recorded. All MTX serum concentrations were less than 0.02 micromol/L within the 24-h period. This is 500 times below the recommended serum concentration for which folinic acid supplementation is recommended. There was also no significant increase in homocysteine level to suggest MTX toxicity. The only adverse effects were mild local dermal reactions in three female volunteers. Deliberate skin contamination and possible inhalation of a 25 mg MTX solution failed to show significant or quantifiable serum and urine concentrations to suggest MTX toxicity. Precautions to prevent contact with MTX designed for oncology protocols are unnecessary for our rheumatology patients or their carers using these much lower immunosuppressant doses for autoimmune diseases.

Alternatives to Ciprofloxacin Use for Enteric Fever, United Kingdom

To the Editor: In cases of typhoid and paratyphoid fever, it is often necessary to commence treatment before the results of laboratory sensitivity tests are available. It is therefore important to be aware of optional drug therapies available because some organisms may be resistant to key antimicrobial drugs. For typhoid and paratyphoid, ciprofloxacin has become the first-line drug of choice since the widespread emergence and spread of strains resistant to chloramphenicol, ampicillin, and trimethoprim (1). The Laboratory of Enteric Pathogens (LEP) of the Health Protection Agency of England and Wales is the reference center for Salmonella enterica serovars Typhi and Paratyphi A for the United Kingdom; as such, this laboratory receives isolates from all cases of infection. Isolates are screened by breakpoint for resistance to antimicrobial drugs at the following levels: chloramphenicol, 8 mg/L; ampicillin, 8 mg/L; trimethoprim, 2 mg/L; ciprofloxacin, 0.125 mg/L (decreased susceptibility); and 1.0 mg/L (high-level resistance), ceftriaxone, 1 mg/L, and cefotaxime, 1 mg/L. The levels for testing for resistance to chloramphenicol, ampicillin, trimethoprim, ceftriaxone, and cefotaxime correspond to internationally accepted therapeutic levels for these antimicrobial agents. In contrast, the levels for ciprofloxacin (0.125 and 1.0 mg/L) have been chosen after observations of treatment failures at levels when used at below the expected recommended serum concentrations (2,3). Since 2005, a proportion of isolates exhibiting decreased susceptibility and high-level resistance to ciprofloxacin have been tested for resistance to azithromycin by Etest (AB Biodisk, Solna, Sweden), using drug-sensitive strains of S. Typhi and S. Paratyphi A as controls. From January 2001 through December 2006, LEP reported 1,215 cases of S. Typhi infection and 1,274 cases of S. Paratyphi A infection. Of these, ≈60% (1,493) reported recent travel abroad; India and Pakistan were the most frequently visited countries (4). Other cases were associated with persons who had a history of such travel, but the numbers involved were difficult to document accurately because of underreporting of foreign travel and other communication problems. For S. Typhi, the occurrence of isolates resistant to ciprofloxacin at 0.125 mg/L increased from 60 (35%) of 170 in 2001 to 169 (70%) of 240 cases in 2006, with 4.8 (2%) of isolates in 2006 resistant at 1.0 mg/L (Table). The corresponding figures for S. Paratyphi A were 58 (25%) of 232 cases in 2001, rising to 84% in 2004, with an incidence of 73% in 2006; 9% of these were resistant to ciprofloxacin at 1.0 mg/L (Table). Moreover, in 2006, 56 isolates of S. Typhi (23% of total) exhibited resistance to chloramphenicol, ampicillin, and trimethoprim, 54 (96%) were also resistant to ciprofloxacin at 0.125 mg/L. When tested for resistance to ceftriaxone and cefotaxime, none of the isolates (either S. Typhi or S. Paratyphi A) were resistant at 1.0 mg/L. Table Incidence of resistance/decreased susceptibility to key antimicrobial agents in isolates of Salmonella enterica serovars Typhi and Paratyphi A, United Kingdom, 2001–2006* Although the levels of resistance to ciprofloxacin were for the most part below that regarded as therapeutic (MIC 0.25–1.0 mg/L), at least 21 treatment failures have been documented since 2005. These findings demonstrate that the efficacy of ciprofloxacin for first-line treatment of enteric fever in the United Kingdom has been seriously jeopardized. In cases of treatment failures, commonly used alternative antimicrobial agents have included third-generation cephalosporins such as ceftriaxone. The macrolide antimicrobial azithromycin is also being increasingly used, particularly for patients with hypersensitivity to penicillins (5). With this in mind, 50 S. Typhi and 40 S. Paratyphi A strains isolated from January 2005 through December 2006, which exhibited resistance to ciprofloxacin at 0.125 mg/L, were tested for resistance to azithromycin by Etest. Results indicated that none of the isolates of S. Typhi exhibited MICs >8 mg/L, which corresponded to the MIC to azithromycin of a drug-sensitive control strain of S. Typhi (range 4–8 mg/L, MIC90 6 mg/L). For S. Paratyphi A, none of the isolates exhibited MICs >12 mg/L, corresponding to that of a drug-sensitive control strain of this serovar (range 6–12 mg/L, MIC90 10 mg/L). Although there are no definitive data on resistance levels for azithromycin in relation to treatment of typhoid and paratyphoid, these findings suggest that resistance to this antimicrobial agent in terms of treatment efficacy has not yet been jeopardized. These results indicate that the availability of effective antimicrobial agents for the treatment of typhoid and paratyphoid infection is becoming increasingly limited for patients in the United Kingdom. Nevertheless, despite the dramatic upsurge in the occurrence of strains with decreased susceptibility, ciprofloxacin still remains the drug of choice for many physicians. It is reassuring that in cases of treatment failure, third-generation cephalosporins such as ceftriaxone and macrolide antimicrobial agents such as azithromycin appear to be viable alternatives.

Management of Calcium, Phosphorus and Bone Metabolism in Dialysis Patients Using Sevelamer Hydrochloride and Vitamin D Therapy

Abnormalities of mineral metabolism, including those of calcium (Ca), phosphorus (P), and parathyroid hormone (PTH) in patients on maintenance hemodialysis induce severe bone involvement, which manifests as renal osteodystrophy. Recently, vascular calcification caused by abnormal mineral metabolism has been attracting attention because cardiovascular diseases (CVD) are a major cause of death in hemodialysis patients. Since 2000, the treatment standard for overt secondary hyperparathyroidism (SHPT) in our facilities has shifted from conventional or pulse therapy with oral vitamin D3 (VitD) to intravenous pulse therapy with maxacalcitriol or calcitriol. After selecting the criterion of overt SHPT as intact-PTH>500 pg/mL, the proportion of overt SHPT cases among all hemodialysis patients decreased from 12% at the start of intravenous pulse treatment to 6.4% after 4 years' treatment. However, the number of patients who had an interruption to pulse treatment because of hypercalcemia and/or hyperphosphatemia was high and it became a bottleneck for the continuation of the therapy. The major cause of hypercalcemia is considered to be Ca load derived from oral calcium carbonate. In Japan, sevelamer hydrochrolide (SH), which does not contain Ca, has been available commercially since 2003 and potentially should enable a reduction in the incidence of overt SHPT during long-term intravenous treatment when combined with careful adjustment of the dose of VitD and strict monitoring of Ca and P level concentrations. In this study, we found that the proportion of patients who satisfy the recommended serum concentrations of Ca and P reported by K/DOQI guideline was low irrespective of the serum concentration of intact-PTH. The aortic calcification index was high in the patient group with lower intact-PTH level concentration, probably because of reduced Ca and P buffering ability associated with reduced bone turnover. We consider that VitD treatment with SH might give better control of the intact-PTH level concentration within the range recommended by the K/DOQI guideline.

Teicoplanin

Teicoplanin is a glycopeptide antibiotic with a molecular structure which is related to that of vancomycin. Gram-positive bacteria such as staphylococci (including methicillin-resistant strains), streptococci, enterococci and many anaerobic Gram-positive bacteria are susceptible to teicoplanin in vitro. Teicoplanin has an exceptionally long half-life, allowing once-daily intramuscular or intravenous administration. Teicoplanin is clinically and bacteriologically effective against a wide variety of Gram-positive infections such as septicaemia, endocarditis, skin and soft tissue infections and infections associated with venous catheters. The drug is equally efficacious against methicillin-resistant and -susceptible staphylococci. Adverse effects with teicoplanin are generally limited to local effects or hypersensitivity reactions. While teicoplanin has the potential for ototoxicity and nephrotoxicity, the incidence appears to be quite low when recommended serum concentrations are maintained. Teicoplanin is a valuable alternative to vancomycin, and providing controlled comparative studies prove equivalent safety and efficacy between the 2 glycopeptides the more easily administered teicoplanin should become the preferred antibacterial agent.

Netilmicin in Gram-Negative Sepsis

The preferred dose of netilmicin was determined in each of 39 patients with severe gram-negative sepsis treated at two centres. The dose was based upon the attainment of recommended serum concentrations. Patient age varied from 18 to 87 years (mean 58), estimated creatinine clearance from 20 to 150 ml/min (mean 71), and the preferred dose from 100 to 750 mg/24 h. The dose generated by a nomogram for netilmicin was compared in retrospect with the initial dose assigned to each patient by the clinical microbiologist concerned. With respect to the preferred dose, the nomogram underdosed, on the average, by 40 mg/24 h, and the microbiologists, by 30 mg/24 h. The correlation with the preferred dose was stronger for the nomogram dose (r = 0.66; p less than 0.001, 37 df) than for the microbiologists' dose (r = 0.47; p less than 0.005, 37 df) but there was no significant difference between the two in the frequency with which they predicted the preferred dose to within 50 mg/24 h (nomogram 19/39; microbiologists 16/39). The prescription of a fixed dose of 450 mg/day to all patients would have had a similar success rate (15/39). The performance of the nomogram was better in patients with serum creatinine concentrations of greater than or equal to 100 microM (r = 0.82; p less than 0.001, 13 df; 10/15 within 50 mg/24 h of preferred dose) than in those with creatinine concentrations less than 100 microM (r = 0.55; p less than 0.01, 22 df; 9/24 within 50 mg/24 h of preferred dose).