No abstract

BACKGROUNDIntravenous acetylcysteine is the treatment of choice for paracetamol poisoning. A previous UK study in 2001 found that 39% of measured acetylcysteine infusion concentrations differed by >20% from anticipated concentrations. In 2012, the UK Commission on Human Medicines made recommendations for the management of paracetamol overdose, including provision of weight-based acetylcysteine dosing tables. The aim of this study was to assess variation in acetylcysteine concentrations in administered infusions following the introduction of this guidance. METHODSA 6-month single-centre prospective study was undertaken at a UK teaching hospital. After preparation, 5-ml samples were taken from the first, second and third/any subsequent acetylcysteine infusions. Acetylcysteine was measured in diluted (1:50) samples by high-performance liquid chromatography. Comparisons between measured and expected concentrations based on prescribed weight-based dose and volume were made for each infusion. RESULTSNinety samples were collected. There was a variation of ≤10% in measured compared to expected concentration for 45 (50%) infusions, of 10-20% for 27 (30%) infusions, 20.1-50% for 14 (16%) infusions and >50% for four (4%) infusions. There was a median (interquartile range) variation in measured compared to expected concentration of À3.6 mg ml À1 (À6.7 to À2.3) for the first infusion, +0.2 mg ml À1 (À0.9 to +0.4) for the second infusion and À0.3 mg ml À1 (À0.6 to +0.2) for third and fourth infusions. CONCLUSIONThere has been a moderate improvement in the variation in acetylcysteine dose administered by infusion. Further work is required to understand the continuing variation and consideration should be given to simplification of acetylcysteine regimes to decrease the risk of administration errors.

AimPrimary hyperparathyroidism (PHPT) is much more common than familial hypocalciuric hypercalcaemia (FHH), but there is considerable overlap in biochemical features. Urine calcium indices help with the differential diagnosis, but their reliability in making this distinction is not clear. The aim of this study was to compare urinary calcium values in patients with PHPT and FHH.MethodsThis was a case–control study of patients with PHPT who had successful surgery and genetically proven FHH between 2011 and 2016. Due to low FHH numbers, patients from neighbouring hospitals and outside study period (2017–2019) were allowed to improve power. Data on demographics and urinary calcium were obtained from electronic records and compared between the two groups.ResultsDuring the study period, 250 patients underwent successful PHPT surgery, while in the FHH arm, 19 genetically proven cases were included. The median (IQR) 24-hour urine calcium excretion (UCE) in the PHPT group was 8.3 (5.6–11.2) mmol/24 hours compared with 3.2 (2.1–6.1) mmol/24 hour in the FHH group (p<0.001). Median (IQR) calcium to creatinine clearance ratio (CCCR) in the PHPT and FHH groups was 0.020 (0.013–0.026) and 0.01 (0.002–0.02), respectively (p=0.001). The sensitivity of urinary tests for PHPT was 96% for UCE (cut-off ≥2.5 mmol/24 hour) and 47% for CCCR (cut-off >0.02). The specificity of the urinary tests for FHH was 29.4% for UCE (cut-off <2.5 mmol/24 hour) and 93% for CCCR (cut-off <0.02).Conclusions24-hour UCE is more sensitive in diagnosing PHPT; however, it is less specific in ruling out FHH as compared with CCCR, when the cut-offs suggested by the International guidelines from the fourth international workshop are used. A significant proportion of patients with PHPT would have also required genetic studies if the guidelines were followed.

Intravenous acetylcysteine is commonly prescribed as a course of three infusions for the management of paracetamol poisoning. Previous studies have demonstrated large variation in administered doses of intravenous acetylcysteine, which has been attributed to numerous factors, including inadequate mixing of infusion bags. The aim of this study was to determine whether the amount of mixing of infusion bags contributes significantly to this variation. Using acetylcysteine doses for a 60–69 kg patient, we added the appropriate volume of acetylcysteine to 5% glucose and subsequently inverted the infusion bags 0–5 times to mix the solutions. Infusion bags were then run through using an infusion pump and acetylcysteine concentrations measured at the beginning and end of the infusions. We found no significant difference between the beginning and end concentrations of acetylcysteine regardless of whether bags were mixed or not; infusion 1 (150 mg kg−1) showed beginning and end concentrations of 44.61 and 42.48 mg ml−1 respectively after 0 mixes, whilst beginning and end concentrations were 44.45 and 44.58 mg ml−1 respectively after five mixes. The same trend was observed for infusions 2 and 3. This confirmed that mixing does not play a substantial role in variation of drug concentrations; these are likely to be caused by an accumulation of small errors in infusion preparation.

The screening of postmortem blood and urine samples is used to identify compounds which may have contributed to an individual’s death. Toxicologically significant compounds detected by the screen are then quantitated in blood to determine their likely effect upon death. In most laboratories this is a two-step process. This study compares an established 2-step screening and quantitation processes, utilising a gas chromatography–mass spectrometry (GC–MS) screen followed by quantitation by GC–MS or high performance-liquid chromatography with diode array detection (HPLC–DAD), with a novel method utilising liquid chromatography–high resolution mass spectrometry (LC–HRMS). The LC–HRMS assay is able to screen postmortem blood and urine samples and simultaneously measure the concentration of toxicologically significant compounds in postmortem blood. Screening results of 200 postmortem blood samples and 103 postmortem urine samples by LC–HRMS and GC–MS showed LC–HRMS detected key compounds in 125% more instances and a 60% increase in the number of compounds detected. Quantitative values generated using the LC–HRMS assay were within ± 10% of values obtained using the established methods by GC–MS or HPLC–DAD. A retrospective analysis of turnaround times pre- and post the adoption of LC–HRMS showed a decrease in turnaround time for all of the compounds in the analysis, including a 43% reduction for free morphine and codeine, a 50% reduction for amphetamine, and a 37% reduction for cocaine. Combining screening and quantitation reduced staffing requirements by 2 days for opiate quantitation and 1 day for most other analytes. The adoption of LC–HRMS also significantly reduced sample volume requirements. These results demonstrate that the adoption of LC–HRMS for simultaneous screening and quantitation delivered significant benefits in comparison to the 2-step procedure.