Tacrolimus Intoxication Resolved by Gastrointestinal Bleeding: Case Report

Drug-drug interaction comparison between tacrolimus and phenobarbital in different formulations for paediatrics and adults

To compare drug-drug interaction (DDI) between tacrolimus and different formulations of phenobarbital in paediatrics and adults.Physiologically based pharmacokinetics (PBPK) models were used to evaluate DDI between phenobarbital (oral (p.o.) and intravenous (i.v.) formulations) and tacrolimus in paediatrics and adults. All dosing regimens were maintained for 7 days.Compared to i.v. phenobarbital, p.o. phenobarbital could decrease pharmacokinetic (PK) parameters of tacrolimus much more in both paediatrics and adults. On day 7, the results showed that the ratio of C_max for tacrolimus in the presence and absence of phenobarbital were 0.13 (p.o.) and 0.48 (i.v.), respectively, in paediatrics, while 0.54 (p.o.) and 0.73 (i.v.) in adults, respectively. The ratios of the area under the concentration-time curve (AUC) were 0.06 (p.o.) and 0.18 (i.v.) in paediatrics, while 0.46 (p.o.) and 0.53 (i.v.) in adults, respectively. PK parameters of tacrolimus decreased more significantly in paediatrics compared to adults.In paediatric, phenobarbital had a greater impact on PK of tacrolimus than that in adults. P.o. phenobarbital reduced PK parameters of tacrolimus even more than i.v. administration. In clinical practice, the concentration monitoring and dosage adjustment of tacrolimus should be emphasised when co-administrated with phenobarbital, especially in paediatric or in p.o. formulation.Key pointsThe results indicated that p.o. and i.v. phenobarbital both had a significant DDI with tacrolimus in paediatrics and adults.Phenobarbital had a greater impact on the PK of tacrolimus over time in paediatrics.P.o. administration of phenobarbital can reduce the PK parameters of tacrolimus more.

Red blood cell exchange as an approach for treating a case of severe tacrolimus overexposure

Immunosuppressive medication dosing errors are not unfrequent and may present a number of challenges to transplant clinicians. Tacrolimus (TAC) is a widely used immunosuppressant with a narrow therapeutic index and potential severe side effects, including neurotoxicity and kidney injury. We herein report a case of 60-year-old woman who underwent deceased-donor liver transplantation at our center and due to inadvertent TAC overexposure was admitted to the Intensive Care Unit because of severe neurologic impairment, kidney injury and arterial hypotension. This case was challenging because TAC is largely bound to erythrocytes, has a high molecular weight, is highly lipophilic, has a high distribution volume and cannot be removed by hemodialysis or plasmapheresis. Based on these considerations, we decided to replace TAC-saturated erythrocytes with blood-bank red cells with the aim to accelerate its clearance. The treatment was effective in decreasing TAC whole blood trough levels within the therapeutic ranges with a significant improvement of the patient's clinical status. Red-blood cell exchange is a potentially safe and effective means of managing severe and symptomatic TAC toxicity.

Red cell exchange transfusion as a rescue therapy for tacrolimus toxicity in a paediatric renal transplant

Tacrolimus is a widely used macrolide immunosuppressant that has a narrow therapeutic index and potential side effects including neurotoxicity. A 20-month-old boy with kidney disease secondary to prune belly syndrome variant, managed on peritoneal dialysis, received a deceased donor transplant. Standard immunosuppression was used. There was good early graft function. Post-transplant he developed fungal peritonitis associated with a significant reduction in graft function and was treated with caspofungin and fluconazole. Despite tacrolimus dose reduction he developed a rapid rise in tacrolimus concentration to a maximum of 72 ng/ml with an otherwise unexplained reduction in consciousness. He underwent a single volume exchange transfusion with packed red cells and 4.5% albumin (ratio 2:1). This resulted in immediate reduction of his tacrolimus concentration from 61.8 ng/ml to 35.2 ng/ml. The neurological deficit rapidly resolved. The fungal peritonitis was eradicated. Renal function recovered from a nadir of eGFR <10 ml/min/1.73 m² to a baseline of 30 ml/min/1.73 m². At 30 months post-transplant the child has creatinine of 1.4 mg/dl (eGFR of 31 ml/min/1.73 m²), and is developmentally appropriate with no neurological deficit. Red cell exchange transfusion is a potentially safe and effective way of managing severe and symptomatic tacrolimus toxicity.