Acute overdoses of tacrolimus (FK 506)

Enriching intracellular macrolides in Escherichia coli improved the sensitivity of bioluminescent sensing systems

A repressor protein MphR and an enhanced green fluorescent protein (eGFP) were used to construct a bioluminescent sensing system for macrolide analysis in Escherichia coli host cells. We deleted TolC, an efflux pump for macrolides in E. coli, to promote the intracellular accumulation of macrolides. The binding constant (K_1/2) of the sensing system constructed in an E. coli strain was decreased up to 33-fold with deleted TolC, and its sensitivity to the macrolides erythromycin, azithromycin, roxithromycin, and pikromycin was increased. The limit of detection of the bioluminescent sensing system for serum azithromycin was 4.1 nM. The ability to detect serum azithromycin concentrations was confirmed by analyzing photographs using ImageJ software. We also developed a novel sensing system for the immune suppressor FK506, another macrolide that is frequently prescribed. Deleting TolC also significantly improved the sensitivity of this sensing system. Bioluminescent sensing systems constructed in TolC mutants were sensitive to various macrolides, indicating their potential for clinical application with hand-held devices.

Using known drug interactions to manage supratherapeutic calcineurin inhibitor concentrations

OBJECTIVES

To summarize the available body of evidence guiding the management of supratherapeutic concentrations of calcineurin inhibitors (CNI) using cytochrome P450 (CYP450) enzyme inducers.

METHODS

A nondate restricted literature search within MEDLINE, Embase, and Scopus was performed using the terms "cyclosporine," "tacrolimus," "calcineurin inhibitor," "toxicity," "pharmacokinetics," "carbamazepine," "rifampin," "phenytoin," and "phenobarbital." Additional references were identified from a review of all included citations. All English-language reports that describe the management of supratherapeutic CNI concentrations with interventions targeting metabolic induction using CYP450 enzyme inducers were evaluated.

RESULTS

A total of 10 publications were identified in which a CYP450 enzyme inducer was utilized intentionally to enhance CNI clearance in the setting of supratherapeutic concentrations; 7 case reports describe the use of phenytoin and 3 case reports describe the use of phenobarbital. Patient demographics, dosing strategies employed, and reported efficacy across this series of publications are heterogeneous; however, both agents appear to be well-tolerated when used in this setting.

CONCLUSIONS

There is a paucity of published data on the use of CYP450 enzyme inducers for the management of supratherapeutic CNI concentrations. While routine use of this approach cannot be recommended, thorough risk-benefit analyses should be performed in the management of each such clinical scenario.

Acute calcineurin inhibitor overdose: analysis of cases reported to a national poison center between 1995 and 2011

Transplant recipients and other patients requiring immunosuppression with calcineurin inhibitors or their household contacts may be exposed to overdose. This study investigated the circumstances, pharmacokinetics and outcomes of overdose with cyclosporine and tacrolimus reported to the Swiss Toxicological Information Centre between 1995 and 2011. Of 145,396 reports by healthcare professionals, 28 (0.02%) concerned enteral or parenteral overdose with these calcineurin inhibitors. Thirteen (46%) were iatrogenic errors, 12 (43%) were with suicidal intent and 3 (11%) were accidental. Iatrogenic overdoses usually involved noncapsule drug formulations. Acute enteral overdoses caused symptoms in a dose-dependent fashion but were generally well tolerated; the mean multiple of patient's usual dose was 20.8 ± 28.8 for symptomatic versus 4.4 ± 3.4 for asymptomatic cases (p = 0.037). The most common symptoms were nausea, headache, somnolence, confusion, hypertension and renal impairment. In contrast, acute intravenous overdoses were often poorly tolerated and resulted in one fatality due to cerebral edema after a cyclosporine overdose. Enteral decontamination measures were performed in six cases involving oral ingestion and appeared to reduce drug absorption, as shown by pharmacokinetic calculations. In the one case where it was used, pharmacoenhancement appeared to accelerate tacrolimus clearance after intravenous overdose.

Tacrolimus Intoxication Resolved by Gastrointestinal Bleeding: Case Report

Tacrolimus is a potent immunosuppressive agent widely used in renal and liver transplantations. Its potential side effects due to overdosing are variable. Most commonly toxic tacrolimus blood levels affect the central and peripheral nervous systems. Once absorbed, tacrolimus binds to plasma proteins and accumulates within erythrocytes. Current treatment strategies to overcome acute intoxications focus on the induction of hepatic cytochrome P450 enzymes to accelerate tacrolimus degradation. We report the case of a 69-year-old renal transplant recipient presenting with acute liver failure, septic shock, and tacrolimus intoxication. The intoxication was resolved by massive gastrointestinal bleeding and subsequent transfusion of packed erythrocytes. We concluded that exchange blood transfusions offer an alternative therapeutic approach for patients with severe liver function impairment and tacrolimus intoxication.

Recurrence of hepatic artery thrombosis following acute tacrolimus overdose in pediatric liver transplant recipient

Acute overdose of tacrolimus appears to cause no or minimal adverse clinical consequences. We encountered a pediatric case who underwent liver transplantation associated with hepatic artery thrombosis (HAT), which recurred following acute tacrolimus overdose. A 10-month-old girl underwent living-related liver transplantation because of biliary atresia. To reconstruct the hepatic artery, the right gastroepiploic artery of the donor was interposed between the right hepatic artery of the recipient (2.5 mm in diameter) and the left hepatic graft artery (1 mm in diameter) under microscopy. On postoperative day 4, Doppler ultrasonography showed a remarkable reduction in hepatic arterial flow, which was consistent with HAT. The patient underwent immediate hepatic arteriography and balloon angioplasty. The stenotic sites were dilated by the procedure. Tacrolimus was infused intravenously after transplantation and the infusion rate was adjusted to achieve a target concentration of 18-22 ng/mL, which remained stable until the morning of day 6. An unexpectedly high blood concentration of tacrolimus (57.4 ng/mL) was detected at 6:00 PM on day 6, and tacrolimus was discontinued at 9:00 PM; however, the tacrolimus level reached 119.5 ng/mL at 0:00 h on day 7. While the concentration decreased to 55.2 ng/mL on the morning of day 7, the hepatic arterial flow could not be observed by Doppler ultrasonography. Emergent hepatic arteriography showed stenosis of the artery at the proximal site of the anastomosis. Balloon angioplasty was again performed and the stenotic site was successfully dilated. High level of tacrolimus exposure to the hepatic artery with injured endothelium by preceding angioplasty may have been related to the recurrence of HAT in the present case.

Treatment of acute tacrolimus whole-blood elevation with phenobarbital in the pediatric liver transplant recipient

The toxicities associated with the chronic use of tacrolimus are well described in the literature; however, little is known about the management during an acute overdose. Phenobarbital is a long-acting barbiturate metabolized in the liver by the cytochrome p450 3a4 system. It is known to enhance the rate of metabolism of itself and the clearance of drugs metabolized by p450 3a4. Because tacrolimus is a substrate of this particular isoenzyme, phenobarbital can be considered a potential option when rapid decreases in tacrolimus whole-blood levels are desired. We hereby report our experience using intravenous phenobarbital in the management of two infants with acute elevations in their tacrolimus whole-blood concentration following liver transplantation. Phenobarbital, through its up-regulation of hepatic cytochrome p450 system increases the elimination of whole-blood tacrolimus concentration in acute overdose situations.

Hospitalized poisonings after renal transplantation in the United States

BACKGROUND

The national incidence of and risk factors for hospitalized poisonings in renal transplant recipients has not been reported.

METHODS

Historical cohort study of 39,628 renal transplant recipients in the United States Renal Data System between 1 July 1994 and 30 June 1998. Associations with time to hospitalizations for a primary diagnosis of poisonings (ICD-9 codes 960.x-989.x) within three years after renal transplant were assessed by Cox Regression.

RESULTS

The incidence of hospitalized poisonings was 2.3 patients per 1000 person years. The most frequent causes of poisonings were immunosuppressive agents (25.3%), analgesics/antipyretics (14.1%), psychotropic agents (10.0%), and insulin/antidiabetic agents (7.1%). In Cox Regression analysis, low body mass index (BMI, <21.6 vs. >28.3 kg/m2, adjusted hazard ratio (AHR), 3.02, 95% CI, 1.45-6.28, and allograft rejection, AHR 1.83, 95% CI, 1.15-2.89, were the only factors independently associated with hospitalized poisonings. Hospitalized poisonings were independently associated with increased mortality (AHR, 1.54, 95% CI 1.22-1.92, p = 0.002).

CONCLUSIONS

Hospitalized poisonings were associated with increased mortality after renal transplantation. However, almost all reported poisonings in renal transplant recipients were due to the use of prescribed medications. Allograft rejection and low BMI were the only independent risk factors for poisonings identified in this population.

Severe prolonged tacrolimus overdose with minimal consequences

A 59-year-old man inadvertently received a 10-fold increase in his twice-daily oral dose of tacrolimus 1 mg that resulted in trough blood levels above 90 ng/ml for over a week. The patient had end-stage renal disease secondary to diabetes mellitus and had received a kidney transplant from his daughter 3 months earlier. Despite the numerous adverse effects commonly reported with tacrolimus, such as mild nephrotoxicity, nausea, tremors, and elevated liver enzyme levels, our patient's acute but prolonged overdose resulted in minimal signs and symptoms of toxicity. Nevertheless, education regarding the importance of accurate dosing, close monitoring, potential drug interactions, and the various capsule colors should be provided to all patients who receive tacrolimus, as well as their physicians, nurses, and pharmacists, in order to prevent as many errors as possible.