Lessons from isavuconazole therapeutic drug monitoring at a United Kingdom Reference Center.

We determined isavuconazole serum concentrations for 150 UK patients receiving standard isavuconazole dosing regimens, including serial therapeutic drug monitoring for several patients on prolonged therapy. Mean trough isavuconazole concentrations in these patients were virtually identical to those reported previously from clinical trials, although greater variability was seen in patients below 18 years of age. Serial monitoring in patients receiving prolonged therapy suggested gradual, near-linear accumulation of the drug over many weeks.

Impact of soaking gentamicin-containing collagen implants on potential antimicrobial efficacy.

BACKGROUND: The purpose of this study is to evaluate how wetting of Collatamp (a gentamicin-containing collagen implant [GCCI]) impacts on the gentamicin content of the implant and whether this affects its potential antibacterial efficacy. METHODS: GCCI (Collatamp(®), EUSA Pharma [Europe], Oxford, United Kingdom) containing 130 mg gentamicin and 280 mg collagen (10 cm × 10 cm) were immersed in 300 mL normal saline for up to 6h. At set times after immersion the GCCI were removed, the saline diluted in normal human serum and the gentamicin content assayed by a validated immunoassay (Cedia, Microgenics Ltd, UK) to provide an estimate of the loss from each implant. The mean concentration data were then fitted to an exponential decay model (WinNonLin, Pharsight, US). RESULTS: After a very short immersion period there was significant loss of gentamicin from the implants with a mean loss of 6.7% at 2 s, increasing to 40.5% at 1 min and essentially total loss by 6 h of immersion. Loss of gentamicin followed a complex elution profile, with elution half-lives ranging from 50 s on initial immersion to 99 min late in the elution period. CONCLUSION: This study provides clear evidence that even a short period of dipping of Collatamp implants, and probably other GCCI, before insertion into the patient results in a significant loss of gentamicin which may be of clinical significance unless the period of soaking is very short. We therefore recommend that wetting of these implants before insertion is not undertaken.

Evidence of excessive concentrations of 5-flucytosine in children aged below 12 years: a 12-year review of serum concentrations from a UK clinical assay reference laboratory.

5-flucytosine (5-FC) is an antifungal drug used for the treatment of serious infections caused by Candida or Cryptococcus spp. In the UK, the recommended pre- and post-dose serum therapeutic ranges are 30-40 mg/L and 70-80 mg/L, respectively. A 12-year retrospective review of serum concentrations of 5-FC in three groups of children aged 1-30 days (n=167), 31-60 days (n=102) and 91 days to 12 years (n=122) was conducted. In these three age groups, 65.1%, 44.4% and 21.3% of pre-dose samples and 39.3%, 29.2% and 19.7% of post-dose samples were above the recommended ranges. Both the mean concentration and the percentage of concentrations above the recommended ranges were significantly higher in the youngest age group (1-30 days old), suggesting that the standard dose of 100 mg/kg daily may not be an appropriate dose in this age group.

Determination of avilamycin A and B in pig faeces by solid phase extraction and reverse-phase HPLC assay.

A HPLC method is described for the simultaneous determination of avilamycin A and B in pig faeces, following extraction using acetonitrile and normal-phase solid phase extraction. The HPLC stationary phase was Kromosil 5 micro C-18 with a mobile phase of 48% acetonitrile and 52% 0.01N ammonium acetate buffer, pumped at a flow rate of 1 ml/min. Detection was by UV absorbance at 295 nm and an injection volume of 50 microl was used. Recovery from faeces was >98% and intra-assay precision (CV) was <9.0% for both compounds. The lowest limit of quantification was 0.9 mg/kg (avilamycin A) and 0.2 mg/kg (avilamycin B) with an accuracy of <15% error. No interference was seen from endogenous materials in pig faeces and commonly used veterinary antibiotics.

A reverse-phase HPLC assay for the simultaneous determination of enrofloxacin and ciprofloxacin in pig faeces.

A reverse-phase HPLC assay is described for the simultaneous assay of enrofloxacin (ENR) and ciprofloxacin (CPX) in pig faeces. Extraction used dichloromethane, 2-propanol and 0.3M ortho-phosphoric acid (1:5:4 v/v/v). Separation was achieved using a Spherisorb S5 C8 column, heated to 50 degrees C and a mobile phase of 0.16% ortho-phosphoric acid (adjusted to pH 3.0 with tetrabutylammonium hydroxide solution) with 20 ml acetonitrile per litre solution. The method used fluorescence detection (Ex 310 nm; Em 445 nm), a flow rate of 1 ml/min and a 20 microl injection volume. Retention times were approximately 6 min for ciprofloxacin and 10 min for enrofloxacin. The linearity range for both compounds was 0-20 mg/kg, lowest limit of quantification 0.3 mg/kg and recoveries were >92%.

Emergence of fluoroquinolone resistance in the native Campylobacter coli population of pigs exposed to enrofloxacin.

OBJECTIVE: The effect of a single 5 day enrofloxacin treatment on the native Campylobacter coli population in conventionally weaned 5-week-old pigs was investigated. MATERIALS: Twelve pigs were split into two groups of six: one group was treated with a therapeutic dose (15 mg/pig/day) of enrofloxacin and the other remained untreated to act as the control. Campylobacter coli were isolated from faecal samples and tested for ciprofloxacin resistance by measuring MIC values. Mutations in the quinolone resistance-determining region (QRDR) of the gyrA gene of resistant isolates were identified by sequencing and denaturing HPLC. Levels of enrofloxacin and its primary metabolite ciprofloxacin in the pig faeces were also measured by HPLC. RESULTS: No quinolone-resistant C. coli (n = 867) were detected in any of the pigs prior to treatment, indicating <0.1% resistance in the group. Resistant C. coli were isolated from pigs for up to 35 days after treatment with a therapeutic dose. These resistant C. coli had MIC values of 128 mg/L and 8-16 mg/L for nalidixic acid and ciprofloxacin, respectively, and the same single point mutation causing a Thr-86 to Ile substitution in the QRDR was identified in each. The concentration of enrofloxacin in the pig faeces was 2-4 micro g/g faeces for the duration of the 5 day therapeutic treatment and was detected up to 10 days post-treatment. Ciprofloxacin was also measured and peaked at 0.6 micro g/g faeces in the treated group. CONCLUSION: This study provides evidence that a single course of enrofloxacin treatment contributes directly to the emergence and persistence of fluoroquinolone resistance in C. coli.

Determination by HPLC of chlortetracycline in pig faeces.

An HPLC assay used to determine chlortetracycline (CTC) in pig faeces is reported. Prodigy ODS3 (4.6 x 150 mm) was used for the stationary phase, whereas the mobile phase comprised oxalic acid, sodium oxalate and sodium decane sulfonate (66%)--each of 4 mM, and 34% acetonitrile. The mobile phase was pumped at a flow rate of 1 mL/min. Detection of CTC was by ultraviolet absorbance at 370 nm, and a 20 micro L injection volume was used. Recovery from faeces was >90%, and coefficients of variability between runs were <10%. The lowest limit of quantification was 3.5 mg/kg, with an accuracy of <7% error. There was no interference from endogenous materials in the pig faeces, or commonly used antibiotics, and the method is suitable for use in drug disposition studies.