It cuts both ways: A single-center retrospective review describing a three-way interaction between flucloxacillin, voriconazole and tacrolimus.

AIM: Tacrolimus is a CYP3A4 substrate with a narrow therapeutic index that requires dose adjustment when used with voriconazole, a recognized CYP3A4 inhibitor. Interactions involving flucloxacillin and tacrolimus or voriconazole individually have been shown to result in decreased concentrations of the latter two drugs. Tacrolimus concentrations have been reported to be unaffected by flucloxacillin when voriconazole is administered; however, this has not been extensively investigated. METHODS: Retrospective review of voriconazole and tacrolimus concentrations and subsequent dose adjustment following flucloxacillin administration. RESULTS: Eight transplant recipients (five lung, two re-do lung, one heart) received concurrent flucloxacillin, voriconazole and tacrolimus. Voriconazole trough concentrations were measured before flucloxacillin initiation in three of eight patients and all trough concentrations were therapeutic. Following flucloxacillin initiation, all eight patients exhibited subtherapeutic concentrations of voriconazole (median concentration 0.15 mg/L [interquartile range (IQR) 0.10-0.28]). In five patients, voriconazole concentrations remained subtherapeutic despite dose increases, and treatment for two patients was changed to alternative antifungal agents. All eight patients required tacrolimus dose increases to maintain therapeutic concentrations after flucloxacillin initiation. Median total daily dose prior to flucloxacillin treatment was 3.5 mg [IQR 2.0-4.3] and this increased to 13.5 mg [IQR 9.5-20] (P=0.0026) during flucloxacillin treatment. When flucloxacillin was ceased, the median tacrolimus total daily dose reduced to 2.2 mg [IQR 1.9-4.7]. Supra-therapeutic tacrolimus concentrations were observed in seven patients after flucloxacillin discontinuation (median concentration 19.7 µg/L [IQR 17.9-28.0]). CONCLUSION: A significant three-way interaction was shown between flucloxacillin, voriconazole and tacrolimus, resulting in subtherapeutic voriconazole concentrations, and requiring substantial tacrolimus dose increases. Administration of flucloxacillin to patients receiving voriconazole should be avoided. Tacrolimus concentrations should be closely monitored, and dosing adjusted during and after flucloxacillin administration.

Multispecies Outbreak of Nocardia Infections in Heart Transplant Recipients and Association with Climate Conditions, Australia.

A multispecies outbreak of Nocardia occurred among heart transplant recipients (HTR), but not lung transplant recipients (LTR), in Sydney, New South Wales, Australia, during 2018-2019. We performed a retrospective review of 23 HTR and LTR who had Nocardia spp. infections during June 2015-March 2021, compared risk factors for Nocardia infection, and evaluated climate conditions before, during, and after the period of the 2018-2019 outbreak. Compared with LTR, HTR had a shorter median time from transplant to Nocardia diagnosis, higher prevalence of diabetes, greater use of induction immunosuppression with basiliximab, and increased rates of cellular rejection before Nocardia diagnosis. During the outbreak, Sydney experienced the lowest monthly precipitation and driest surface levels compared with time periods directly before and after the outbreak. Increased immunosuppression of HTR compared with LTR, coupled with extreme weather conditions during 2018-2019, may explain this outbreak of Nocardia infections in HTR.

Tacrolimus Therapy in Adult Heart Transplant Recipients: Evaluation of a Bayesian Forecasting Software.

BACKGROUND: Therapeutic drug monitoring is recommended to guide tacrolimus dosing because of its narrow therapeutic window and considerable pharmacokinetic variability. This study assessed tacrolimus dosing and monitoring practices in heart transplant recipients and evaluated the predictive performance of a Bayesian forecasting software using a renal transplant-derived tacrolimus model to predict tacrolimus concentrations. METHODS: A retrospective audit of heart transplant recipients (n = 87) treated with tacrolimus was performed. Relevant data were collected from the time of transplant to discharge. The concordance of tacrolimus dosing and monitoring according to hospital guidelines was assessed. The observed and software-predicted tacrolimus concentrations (n = 931) were compared for the first 3 weeks of oral immediate-release tacrolimus (Prograf) therapy, and the predictive performance (bias and imprecision) of the software was evaluated. RESULTS: The majority (96%) of initial oral tacrolimus doses were guideline concordant. Most initial intravenous doses (93%) were lower than the guideline recommendations. Overall, 36% of initial tacrolimus doses were administered to transplant recipients with an estimated glomerular filtration rate of <60 mL/min/1.73 m despite recommendations to delay the commencement of therapy. Of the tacrolimus concentrations collected during oral therapy (n = 1498), 25% were trough concentrations obtained at steady-state. The software displayed acceptable predictions of tacrolimus concentration from day 12 (bias: -6%; 95%confidence interval, -11.8 to 2.5; imprecision: 16%; 95% confidence interval, 8.7-24.3) of therapy. CONCLUSIONS: Tacrolimus dosing and monitoring were discordant with the guidelines. The Bayesian forecasting software was suitable for guiding tacrolimus dosing after 11 days of therapy in heart transplant recipients. Understanding the factors contributing to the variability in tacrolimus pharmacokinetics immediately after transplant may help improve software predictions.

Tacrolimus exposure early after lung transplantation and exploratory associations with acute cellular rejection.

AIMS: To (i) describe tacrolimus (TAC) pre-dose concentrations (C0), (ii) calculate apparent oral TAC clearance (CL/FHCT) adjusted for measured haematocrit (HCTi) and standardised to a HCT of 45%, across three observation time points and (iii) explore if low TAC C0 or high mean CL/FHCT are associated with an increased risk of rejection episodes early after lung transplantation. METHODS: TAC whole blood concentration-time profiles and transbronchial biopsies were performed prospectively at weeks 3, 6 and 12 after lung transplantation. The TAC pre-dose concentration (C0) was measured, and CL/FHCT was determined using non-compartmental analysis. The associations between TAC C0 and CL/FHCT and rejection status were explored using repeated measures logistic regression. RESULTS: Eighteen patients provided 377 TAC whole blood concentrations. Considerable variability around the median (IQR) CL/FHCT 6.8 (4.2-15.9) L h-1, and the median C0 12.7 (9.9-16.6) µg L-1 was noted. Despite adjustment for haematocrit, a significant decrease was observed in CL/FHCT in all patients over time: CL/FHCT 14 (5.4-23) at week 3, CL/FHCT 7.7 (4.5-12) at week 6 and CL/FHCT 3.9 (2.4-11) L h-1 at week 12 (p < 0.01). Seven (38.9%) patients experienced a single grade 2 rejection, whilst 11 (61.1%) patients experienced no rejection. Higher TAC C0 were associated with a reduced risk of rejection OR 0.68 (95% CI 0.51-0.91, p = 0.02), and greater mean CL/FHCT was associated with an increased risk of rejection OR 1.34 (95% CI 1.01-1.81 p = 0.04). CONCLUSION: Monitoring TAC C0, HCT and CL/FHCT in patients after lung transplantation may assist clinicians in detecting patients at risk of acute rejection and may guide future research into TAC and HCT monitoring after lung transplantation.

Oral ribavirin for respiratory syncytial virus infection after lung transplantation: Efficacy and cost-efficiency.

BACKGROUND: Respiratory syncytial virus (RSV) causes serious respiratory tract infections in lung transplant (LTx) recipients, is associated with development of bronchiolitis obliterans syndrome, and has no proven effective therapy. We evaluated the efficacy, safety, and cost-effectiveness of oral ribavirin for the treatment of RSV infection after LTx. METHODS: Between December 2011 and May 2014, 52 LTx recipients developed 56 episodes of symptomatic RSV infection, which was diagnosed by positive RSV polymerase chain reaction on nasopharyngeal swabs. An intravenous (IV) loading dose of ribavirin (33 mg/kg) was given in 52 of 56 episodes; an equivalent oral loading dose was given in 2 episodes. Oral ribavirin (20 mg/kg/day) was given by day 2 in 53 of 56 episodes. Median duration of therapy was 8 days (range 6-31 days). RESULTS: Mean forced expiratory volume in 1 sec decreased from 2.38 ± 0.78 liters to 2.07 ± 0.85 liters (p < 0.001) at presentation, recovered to 2.26 ± 0.82 liters at cessation of ribavirin, and was maintained at 2.31 ± 0.81 liters within 3 months. New-onset bronchiolitis obliterans syndrome developed in 1 of 38 patients (2.6%) at 3 months. Anemia worsened in 23 episodes, and de novo anemia developed in 5 episodes. Mean hemoglobin decreased from 118 ± 16 g/liter to 113 ± 21 g/liter (p = 0.015). There were 4 late deaths. Compared with IV therapy, mean drug cost saving was US $6,035 per episode, and mean inpatient bed days was reduced by 6.7 days (p < 0.001). CONCLUSIONS: To our knowledge, we report the largest series of LTx recipients treated with oral ribavirin for RSV. Oral ribavirin appears to be an effective, well-tolerated alternative to IV or inhaled ribavirin; provides considerable cost savings and reduces length of hospital stay. Potential long-term benefits in preventing development of chronic lung allograft dysfunction are yet to be determined.