Real clinical impact of drug-drug interactions of immunosuppressants in transplant patients

Immune responsiveness in stable kidney transplantation patients: Complete inhibition of T-cell proliferation but residual T-cell activity during maintenance immunosuppressive treatment

The recommended immunosuppressive treatment after kidney transplantation consists of tacrolimus, mycophenolate mofetil, and low-dose corticosteroids. Drug concentrations are monitored using therapeutic drug monitoring (TDM), which does not necessarily correlate with pharmacodynamic activity. To find the balance between optimal efficacy and minimal toxicity, it might be more informative to monitor patients' immunological status rather than drug concentrations. We selected a panel of T-cell-based immune assays, which were used for immunomonitoring of 14 stable kidney transplantation patients. Whole blood was incubated with a T-cell stimulus, after which T-cell proliferation, T-cell activation marker expression and cytokine production were measured to study residual immune activity in vitro (before drug intake; drug added to the incubation) and ex vivo (after drug intake). T-cell proliferation was completely suppressed in all patients over the full day, while IL-2, IFN-γ, CD71, and CD154 showed fluctuations over the day with a strong inhibition (75%-25%) at 2 h post-dose. The level of inhibition was variable between patients and could not be related to pharmacokinetic parameters or the presence of regulatory or senescence immune cells. Moreover, the level of inhibition did not correlate with the in vitro tacrolimus drug effect as studied by incubating pre-dose blood samples with additional tacrolimus. Overall, IL-2, IFN-γ, CD71, and CD154 seem to be good markers to monitor residual immune activity of transplantation patients. To evaluate the correlation between these pharmacodynamic biomarkers and clinical outcome, prospective observational studies are needed.

Prevalence and clinical significance of potential drug-drug interactions among lung transplant patients

Background: Drug-drug interactions (DDIs) are a major but preventable cause of adverse drug reactions. There is insufficient information regarding DDIs in lung transplant recipients. Objective: This study aimed to determine the prevalence of potential DDIs (pDDIs) in intensive care unit (ICU) lung transplant recipients, identify the real DDIs and the most frequently implicated medications in this vulnerable population, and determine the risk factors associated with pDDIs. Methods: This retrospective cross-sectional study included lung transplant recipients from January 2018 to December 2021. Pertinent information was retrieved from medical records. All prescribed medications were screened for pDDIs using the Lexicomp® drug interaction software. According to this interaction software, pDDIs were classified as C, D, or X (C = monitor therapy, D = consider therapy modification, X = avoid combination). The Drug Interaction Probability Scale was used to determine the causation of DDIs. All statistical analysis was performed in SPSS version 26.0. Results: 114 patients were qualified for pDDI analysis, and total pDDIs were 4051. The most common type of pDDIs was category C (3323; 82.0%), followed by D (653; 16.1%) and X (75; 1.9%). Voriconazole and posaconazole were the antifungal medicine with the most genuine DDIs. Mean tacrolimus concentration/dose (Tac C/D) before or after co-therapy was considerably lower than the Tac C/D during voriconazole or posaconazole co-therapy (p < 0.001, p = 0.027). Real DDIs caused adverse drug events (ADEs) in 20 patients. Multivariable logistic regression analyses found the number of drugs per patient (OR, 1.095; 95% CI, 1.048-1.145; p < 0.001) and the Acute Physiology and Chronic Health Evaluation II (APACHE Ⅱ) score (OR, 1.097; 95% CI, 1.021-1.179; p = 0.012) as independent risk factors predicting category X pDDIs. Conclusion: This study revealed a high incidence of both potential and real DDIs in ICU lung transplant recipients. Immunosuppressive drugs administered with azole had a high risk of causing clinically significant interactions. The number of co-administered drugs and APACHE Ⅱ score were associated with an increased risk of category × drug interactions. Close monitoring of clinical and laboratory parameters is essential for ensuring successful lung transplantation and preventing adverse drug events associated with DDIs.

Case Report: tacrolimus toxicity in the setting of concurrent Paxlovid use in a heart-transplant recipient

Background

Tacrolimus toxicity in patient's status post-orthotropic heart transplantation is not commonly reported. Given its narrow therapeutic window and drug-drug interactions, it must be closely monitored by providers who are experienced in transplant management. There are no case series of patients with tacrolimus toxicity in the setting of treatment for Sars-2-CoV-19 (COVID 19) for heart-transplant recipients. We present a case of tacrolimus toxicity in the setting of concurrent ritonavir-nirmatrelvir (Paxlovid) use.

Case summary

The patient was a 74-year-old male with a prior significant history of heart transplantation and on maintenance immunosuppression with tacrolimus. He contracted COVID-19 and was prescribed antiviral therapy with Paxlovid by an outside provider prior to admission. The patient complained of severe headaches, dehydration, and tremors. After eliminating acute intracranial processes with imaging, laboratory investigation revealed a severely elevated tacrolimus level with acute renal injury. The patient was taken off tacrolimus and treated conservatively with intravenous hydration. The symptoms improved, particularly the headaches. He was discharged with instructions to resume his home dosing of tacrolimus and return to clinic in 1 week with a repeat trough level. The subsequent trough level was no longer supra-therapeutic.

Discussion

Tacrolimus has a potent drug-drug interaction with Paxlovid (ritonavir-nirmatrelvir) and can be supra-therapeutic. Toxicity is associated with multiple adverse effects, including but not limited to, acute renal injury, neurotoxicity, and infections due to over-immunosuppression. As Paxlovid is effective in treating Sars-2-CoV-19 in heart-transplant recipients, knowledge and understanding of drug-drug interactions is crucial in preventing and mitigating toxicity.