Total Hip Arthroplasty Outcomes before or after Renal Transplant: A Retrospective Large Cohort Analysis.

Background: While it is known that patients with end-stage renal disease (ESRD) are at an increased risk of complications following total hip arthroplasty (THA), there is a gap in the literature in comparing patients with ESRD to patients who undergo renal transplant (RT) before or after THA. This study is to address this gap by analyzing outcomes of THA in ESRD patients, RT patients, and RT candidates. Methods: Using the PearlDiver Mariner database, ESRD patients, RT patients, and RT candidates undergoing primary THA were identified and compared. Multivariable logistic regression analyses were done for medical complications up to 90 days and surgical complications up to 2 years. Ninety-day emergency department (ED) visits and inpatient readmission were also documented. Results: A total of 7,868 patients were included: 5,092 had ESRD, 2,520 had RT before THA, and 256 were candidates for RT. Compared to patients with ESRD, RT patients demonstrated lower rates of medical complications such as pneumonia (3.61% vs. 5.99%, p = 0.039) and transfusion (4.60% vs. 7.66%, p < 0.001). Additionally, RT patients displayed decreased rates of surgical complications, including wound complications (2.70% vs. 4.22%, p = 0.001), periprosthetic joint infection (PJI) at 1 year (2.30% vs. 4.81%, p < 0.001) and 2 years (2.58% vs. 5.42%, p < 0.001), and aseptic loosening at 2 years (0.79% vs. 1.43%, p = 0.006). Similarly, when compared to RT candidates, RT patients demonstrated a lower incidence of postoperative complications, including 1-year PJI (2.30% vs. 5.08%, p = 0.013), 2-year PJI (2.58% vs. 5.08%, p = 0.028), 1-year aseptic loosening (0.56% vs. 2.73%, p < 0.001), and 2-year aseptic loosening (0.79% vs. 2.73%, p = 0.005). RT patients also had lower rates of ED visits and hospital readmissions. Conclusions: Compared to ESRD patients and RT candidates, patients with RT have a significantly lower likelihood of medical complications, PJI, aseptic hardware loosening, ED visits, and hospital readmission. Patients with ESRD on the RT waiting list should delay THA until after RT surgery. For those not eligible for RT, it is vital to take extra precautions to reduce the risk of complications.

Medication non-adherence and its associated factors among kidney transplant patients in a large teaching hospital in Ethiopia.

BACKGROUND: This study examines medication adherence among kidney transplant patients at St. Paul's Hospital Millennium Medical College (SPHMMC) in Addis Ababa, Ethiopia, focusing on the level of adherence and associated factors to immunosuppressant medicines. METHODS AND MATERIALS: A cross-sectional study was conducted on 270 patients from October 2021 to January 2022 using a structured questionnaire analyzed with SPSS version 26. The prevalence of medication adherence was computed, and a binary logistic regression was fitted to estimate the association. Medication adherence level measurement in post-kidney transplant patients was assessed using the Simplified Medication Adherence Questionnaire (SMAQ) and Basel Adherence Assessment Scale in Immunosuppressants (BAASIS). A 95% confidence interval and p-value < 0.05 were used for statistical significance. RESULTS: The study found that 71.5% of kidney transplant patients were male, with a median age of 37 and a mean duration of 3.55 years. Medication adherence in post-kidney transplant patients was 81.9%. Post-transplant duration above 5 years and missing follow-up visits more than two times was associated with a 92.6% and 91.2% in medication non-adherence rate respectively. Additionally, forgetfulness was associated with a 90.6%, non-adherence level compared to drug unavailability and financial reasons. CONCLUSION AND RECOMMENDATION: The study indicates that our patients exhibit higher medication adherence than WHO-measured levels, suggesting the need for healthcare providers to strengthen their intervention, especially for those above 5 years post-kidney transplant. The reason for increased adherence could be explained by the health education program about the medication name, dosing, frequency of ingestion and adverse effects of the drug, and effects of non-adherence.

Donor Blood Tests do Not Predict Pancreas Graft Survival After Simultaneous Pancreas Kidney Transplantation; a National Cohort Study.

Simultaneous pancreas-kidney (SPK) transplantation improves quality of life and limits progression of diabetic complications. There is reluctance to accept pancreata from donors with abnormal blood tests, due to concern of inferior outcomes. We investigated whether donor amylase and liver blood tests (markers of visceral ischaemic injury) predict pancreas graft outcome using the UK Transplant Registry (2016-2021). 857 SPK recipients were included (619 following brainstem death, 238 following circulatory death). Peak donor amylase ranged from 8 to 3300 U/L (median = 70), and this had no impact on pancreas graft survival when adjusting for multiple confounders (aHR = 0.944, 95% CI = 0.754-1.81). Peak alanine transaminases also did not influence pancreas graft survival in multivariable models (aHR = 0.967, 95% CI = 0.848-1.102). Restricted cubic splines were used to assess associations between donor blood tests and pancreas graft survival without assuming linear relationships; these confirmed neither amylase, nor transaminases, significantly impact pancreas transplant outcome. This is the largest, most statistically robust study evaluating donor blood tests and transplant outcome. Provided other factors are acceptable, pancreata from donors with mild or moderately raised amylase and transaminases can be accepted with confidence. The use of pancreas grafts from such donors is therefore a safe, immediate, and simple approach to expand the donor pool to reach increasing demands.

Access to robotic assisted kidney transplant for recipients: a systematic review and call for reporting standards.

Robot-assisted kidney transplantation (RAKT) is a relatively novel, minimally invasive option for kidney transplantation. However, clarity on recipient selection in the published literature is lacking thereby significantly limiting interpretation of safety and other outcomes. This systematic review aimed to identify and synthesize the data on selection of RAKT recipients, compare the synthesized data to kidney transplant recipients across the USA, and explore geographical clusters of availability of RAKT. Systematic literature review, in accordance with PRISMA, via OVID MEDLINE, Embase, and Web of science from inception to March 5, 2023. All data entry double blinded and quality via Newcastle Ottawa Scale. 44 full-text articles included, encompassing approximately 2402 kidney transplant recipients at baseline but with considerable suspicion for overlap across publications. There were significant omissions of information across studies on patient selection for RAKT and/or analysis. Overall, the quality of studies was very low. Given suspicion of overlap across studies, it is difficult to determine how many RAKT recipients received living (LD) versus deceased donor (DD) organs, but a rough estimate suggests 89% received LD. While the current RAKT literature provides preliminary evidence on safety, there are significant omissions in reporting on patient selection for RAKT which limits interpretation of findings. Two recommendations: (1) international consensus is needed for reporting guidelines when publishing RAKT data and (2) larger controlled trials consistently reporting recipient characteristics are needed to clearly determine selection, safety, and outcomes across both LD and DD recipients.

Factors related to nocturia-specific quality of life in renal transplantation patients.

OBJECTIVES: Patients following renal transplantation (RTX) may experience nocturia exacerbation due to polyuria and reduced bladder capacity, thereby impacting the specific quality of life (QOL) associated with nocturia. The present study aims to investigate factors associated with the deterioration of nocturia-specific QOL in RTX patients. METHODS: The study cohort comprised 59 consecutive patients who had undergone successful RTX. Nocturia-related QOL questionnaires (N-QOL) were employed to evaluate the specific QOL related to nocturia. The Bother/Concern and Sleep/Energy domains of the N-QOL were also assessed. The primary outcome measure was to explore factors related to the aggravation of nocturia-specific QOL in patients post-RTX. RESULTS: The mean nocturia frequency post-RTX was 1.3 ± 1.0. Univariate and multivariate analyses revealed a significant reduction in the Bother/Concern domain score associated with increased nocturia (p = .042). Aging significantly decreased the total N-QOL score and the Sleep/Energy domain score (p = .001 and .0002, respectively). Prolonged duration after RTX significantly reduced the scores of both the Sleep/Energy domain and the Bother/Concern domain (p = .018 and .037, respectively). However, the duration of dialysis prior to RTX was not significantly associated with the total score or subdomains of N-QOL. CONCLUSIONS: Nocturia-specific QOL affected not only the nocturia itself, but also aging and the prolonged duration after RTX. Thus, comprehensive approaches to the RTX patients were needed to improve the Nocturia-specific QOL in RTX patients.

Experiences of Participation in a Study Investigating Feasibility of the Implantable Doppler Probe in Kidney Transplantation: An Embedded Qualitative Study.

OBJECTIVES: Kidney transplant survival can be improved with better graft surveillance postoperatively. In the quest to explore new technologies, we explored the feasibility of an implantable Doppler probe as a blood flow monitoring device in kidney transplant patients. This qualitative study was embeddedin a feasibility trial and aimed to test the device's clinical acceptability and obtain suggestions for the development of the intervention. Objectives included exploring the experiences of feasibility study participants and identifying barriers to the implementation of implantable Doppler probes in clinical practice. MATERIALS AND METHODS: We conducted semi-structured interviews containing open-ended questions with 12 feasibility study participants recruited by purposive sampling. All interviews were audio-recorded with verbatim transcription. Thematic data analysis was performed at the latent level by using an inductive approach with a previously published 6-phase guide. RESULTS: Three key themes emerged: (1) perceived value of the intervention in clinical practice, (2) challenges and barriers to implementation of the intervention, and (3) suggestions forthe development of the intervention. Due to functional limitations and lack of research, medical professional participants revealed clinical equipoise regarding the utility of implantable Doppler probes. However,the device was well received by patient participants. Challenges included device training needs for medical professionals and educational sessions for patients. Innovative ideas for development included the insertion of a display screen, adopting disposable units to reduce overall cost, online access allowing remote monitoring, decreasing external monitoring unit size, and integrating a wireless connection with the probe to reduce signal errors and increase patient safety. CONCLUSIONS: The clinical need for blood flow sensing technology in kidney transplants has been widely acknowledged. Implantable Doppler probes may be a beneficial adjunct in the early postoperative surveillance of kidney transplant patients. However, the device's technical limitations are the main challenges to its acceptance in clinical practice.

Computed Tomography-Assessed Sarcopenia Predicts Mortality in Kidney Transplant Candidates.

OBJECTIVES: Sarcopenia is common in chronic kidney disease and associated with increased mortality. We investigated the prevalence of sarcopenia, defined as low muscle mass by the psoas muscle index, in endstage renal disease patients on waiting lists for kidney transplant and determined its association with prognostic nutritional index, C-reactive protein-toalbumin ratio, cardiovascular events, and mortality. MATERIALS AND METHODS: Our study included 162 patients with end-stage renal disease and 87 agematched healthy controls. We calculated nutritional status as follows: prognostic nutritional index = (10 × albumin [g/dL]) + (0.005 × total lymphocyte count (×103/µL]) and C-reactive protein-to-albumin ratio. We gathered demographic and laboratory data from medical records. RESULTS: Patients with end-stage renal disease had a mean age of 44.7 ± 14.2 years; follow-up time was 3.37 years (range, 0.35-9.60 y). Although patients with endstage renal disease versus controls had higher prevalence of sarcopenia (16.7% vs 3.4%; P = .002) and C-reactive protein-to-albumin ratio (1.47 [range, 0.12-37.10] vs 0.74 [range, 0.21-10.20]; P < .001), prognostic nutritional index was lower (40 [range, 20.4-52.2] vs 44 [range, 36.1-53.0]; P < .001). In patients with end-stage renal disease with and without sarcopenia, prognostic nutritional index (P = .005) was lower and C-reactive protein-to-albumin ratio (P = .041) was higher in those with versus those without sarcopenia. Among 67 patients on waiting lists who received kidney transplants, those without sarcopenia had better 5-year patient survival posttransplant than those with sarcopenia (P = .001). Multivariate regression analysis showed sarcopenia and low prognostic nutritional index were independentrisk factors for mortality among patients with end-stage renal disease. CONCLUSIONS: Sarcopenia was ~5 times more frequent in patients with end-stage renal disease than in healthy controls and was positively correlated with the prognostic nutritional index. Sarcopenia was an independent risk factor for mortality in patients on transplant waiting lists.

Outcomes of Kidneys Transplanted From Hepatitis C Viremic Donors to Naive Recipients From an Appalachian Rural Kidney Transplant Program.

OBJECTIVES: Before the advent of direct-acting antiviral therapy for hepatitis C virus, a large proportion of kidneys from donors with hepatitis C viremia were discarded. Hepatitis C virus is now amenable to effective treatment with excellent seronegativity rates. In this study, we review the outcomes of hepatitis C viremic kidneys transplanted into hepatitis C-naive recipients. MATERIALS AND METHODS: In this retrospective observational study, we examined 6 deceased donor kidneys with hepatitis C viremia that were transplanted into hepatitis C-naive recipients between March 2020 and April 2021 at a single center. Because of health insurance constraints, patients were treated for hepatitis C virus with glecaprevir/pibrentasvir for 8 weeks following seroconversion posttransplant. Primary outcome measured was viral seroconversion; secondary outcomes included graft function, posttransplant complications, and all-cause mortality. RESULTS: On average, patients seroconverted 6 days (range, 4-10 d) after transplant and began treatment 26 days (range, 15-37 d) after seroconversion. An 8-week course of antiviral treatment was successful in preventing acute hepatitis C virus infection in all patients. Posttransplant median creatinine was 1.96 mg/dL (range, 1-4.55 mg/dL), whereas median estimated glomerular filtration rate was 41.33 mL/min/1.73 m2 (range, 17-85 mL/min/1.73 m2). Patient survival rate was 66.7%, and death-censored graft survival rate was 100%. Two patients died from unrelated reasons: 1 from acute respiratory failure secondary to SARS-CoV-2 infection and 1 from posttransplant lymphoproliferative disorder. Two patients developed allograft rejection posttransplant (1 developed antibody mediated rejection, 1 developed borderline T-cell-mediated cellular rejection). Other major complications included neutropenia, fungal rash, SARS-CoV-2 infection, cytomegalovirus, BK virus, and Epstein-Barr virus reactivation. CONCLUSIONS: Use of hepatitis C-viremic donor kidneys for transplant is a safe option and has great potential to increase the kidney donor pool, as long as high index of suspicion is maintained for allograft rejection and opportunistic infections.

Clinicopathologic Spectrum and Outcomes of Infections Diagnosed on Graft Biopsies and Nephrectomy in Live Renal Allograft Recipients: An Institutional Experience.

OBJECTIVES: Modern immunosuppressive regimens have reduced rejection episodes in renal allograft recipients but have increased the risk of opportunistic infections. Infections are considered to be the second leading cause of death after cardiovascular complications in renal allograft recipients. Data on opportunistic infections affecting the allograft itself are scarce. The present study describes the spectrum of renal opportunistic infections and their outcomes diagnosed on renal allograft biopsies and nephrectomy specimens. MATERIALS AND METHODS: Our retrospective observational study was conducted from December 2011 to December 2021. We analyzed infectious episodes diagnosed on renal allograft biopsies or graft nephrectomy specimens. We obtained clinical, epidemiological, and laboratory details for analyses from hospital records. RESULTS: BK virus nephropathy was the most common opportunistic infection affecting the allograft, accounting for 47% of cases, followed by bacterial graft pyelonephritis (25%). Mucormycosis was the most common fungal infection. The diagnosis of infection from day of transplant ranged from 14 days to 39 months. Follow-up periods ranged from 1 to 10 years. Mortality was highest among patients with opportunistic fungal infection (62%), followed by viral infections, and graft failure rate was highest in patients with graft pyelonephritis (50%). Among patients with BK polyomavirus nephropathy, 45% had stable graft function compared with just 33% of patients with bacterial graft pyelonephritis. CONCLUSIONS: BK polyoma virus infection was the most common infection affecting the renal allograft in our study. Although fungal infections caused the highest mortality among our patients, bacterial graft pyelonephritis was responsible for maximum graft failure. Correctly identifying infections on histology is important so that graft and patient life can be prolonged.

Surgical Treatment of Medically Refractory Encapsulating Peritoneal Sclerosis in a Patient After Kidney Transplant.

Encapsulating peritoneal sclerosis is a rare but highly morbid disease process in patients with end-stage kidney disease on peritoneal dialysis. Surgical management has been described in patients with encapsulation of bowel causing obstruction. Here, we describe a case of surgical management in a patient following kidney transplant with medically refractory ascites and lower extremity edema.

Characterization of heart rate variability in end-stage renal disease patients after kidney transplantation with recurrence quantification analysis.

Heart rate variability (HRV) is a noninvasive approach to studying the autonomic modulation of heart rate in experimental settings, such as active standing sympathetic stimulation. It is known that patients with end-stage renal disease during active standing have few changes in HRV dynamics, which are improved after hemodialysis. However, it is unknown whether the response to active standing is recovered after definitive treatment with kidney transplantation. This work aims to assess the change in HRV dynamics in the supine position and active standing through time and frequency-based metrics, as well as recurrence plot quantitative analysis (RQA). We studied HRV dynamics by obtaining 5-minute electrocardiographic recordings from kidney transplant recipients who underwent an active standing test. The mean duration of heartbeats and their standard deviation diminished in active standing, compared with the supine position. Also, the low-frequency component of HRV and the presence of diagonal and vertical structures in RQA were predominant. A larger estimated glomerular filtration rate was significantly correlated with broader HRV in the supine position and during active standing. The narrower HRV during active standing may indicate a sympathetic response to external stimuli, which is expected in a functional cardiovascular system, and may be influenced by renal function.

Impact of Switching From Immediate- or Prolonged-Release to Once-Daily Extended-Release Tacrolimus (LCPT) on Tremor in Stable Kidney Transplant Recipients: The Observational ELIT Study.

Once-daily extended-release tacrolimus (LCPT) exhibits increased bioavailability versus immediate-release (IR-TAC) and prolonged release (PR-TAC) tacrolimus. Improvements in tremor were previously reported in a limited number of kidney transplant patients who switched to LCPT. We conducted a non-interventional, non-randomized, uncontrolled, longitudinal, prospective, multicenter study to assess the impact of switching to LCPT on tremor and quality of life (QoL) in a larger population of stable kidney transplant patients. The primary endpoint was change in The Essential Tremor Rating Assessment Scale (TETRAS) score; secondary endpoints included 12-item Short Form Survey (SF-12) scores, tacrolimus trough concentrations, neurologic symptoms, and safety assessments. Subgroup analyses were conducted to assess change in TETRAS score and tacrolimus trough concentration/dose (C0/D) ratio by prior tacrolimus formulation and tacrolimus metabolizer status. Among 221 patients, the mean decrease of TETRAS score after switch to LCPT was statistically significant (p < 0.0001 vs. baseline). There was no statistically significant difference in change in TETRAS score after switch to LCPT between patients who had received IR-TAC and those who had received PR-TAC before switch, or between fast and slow metabolizers of tacrolimus. The overall increase of C0/D ratio post-switch to LCPT was statistically significant (p < 0.0001) and from baseline to either M1 or M3 (both p < 0.0001) in the mITT population and in all subgroups. In the fast metabolizers group, the C0/D ratio crossed over the threshold of 1.05 ng/mL/mg after the switch to LCPT. Other neurologic symptoms tended to improve, and the SF-12 mental component summary score improved significantly. No new safety concerns were evident. In this observational study, all patients had a significant improvement of tremor, QoL and C0/D ratio post-switch to LCPT irrespective of the previous tacrolimus formulation administered (IR-TAC or PR-TAC) and irrespective from their metabolism status (fast or slow metabolizers).

European Survey on Clinical Practice of Detecting and Treating T-Cell Mediated Kidney Transplant Rejection.

The KDIGO guideline for acute rejection treatment recommends use of corticosteroids and suggests using lymphocyte-depleting agents as second line treatment. Aim of the study was to determine the current practices of detection and treatment of TCMR of kidney allografts amongst European kidney transplant centres. An invitation was sent through ESOT/EKITA newsletters and through social media to transplant professionals in Europe for taking part in the survey. A total of 129 transplant professionals responded to the survey. There was equal representation of small and large sized transplant centres. The majority of centres treat borderline changes (BL) and TCMR (Grade IA-B, IIA-B) in indication biopsies and protocol biopsies with corticosteroids as first line treatment. Thymoglobulin is used mainly as second line treatment for TCMR Grade IA-B (80%) and TCMR IIA-B (85%). Treatment success is most often evaluated within one month of therapy. There were no differences observed between the large and small centres for the management of TCMR. This survey highlights the common practices and diversity in clinics for the management of TCMR in Europe. Testing new therapies for TCMR should be in comparison to the current standard of care in Europe. Better consensus on treatment success is crucial for robust study designs.

Interactions of the Immune System with Human Kidney Organoids.

Kidney organoids are an innovative tool in transplantation research. The aim of the present study was to investigate whether kidney organoids are susceptible for allo-immune attack and whether they can be used as a model to study allo-immunity in kidney transplantation. Human induced pluripotent stem cell-derived kidney organoids were co-cultured with human peripheral blood mononuclear cells (PBMC), which resulted in invasion of allogeneic T-cells around nephron structures and macrophages in the stromal cell compartment of the organoids. This process was associated with the induction of fibrosis. Subcutaneous implantation of kidney organoids in immune-deficient mice followed by adoptive transfer of human PBMC led to the invasion of diverse T-cell subsets. Single cell transcriptomic analysis revealed that stromal cells in the organoids upregulated expression of immune response genes upon immune cell invasion. Moreover, immune regulatory PD-L1 protein was elevated in epithelial cells while genes related to nephron differentiation and function were downregulated. This study characterized the interaction between immune cells and kidney organoids, which will advance the use of kidney organoids for transplantation research.

Weight Loss Surgery Increases Kidney Transplant Rates in Patients With Renal Failure and Obesity.

OBJECTIVE: To describe the outcomes of kidney transplant (KT) candidates with obesity undergoing sleeve gastrectomy (SG) to meet the criteria for KT. METHODS: Retrospective analysis was conducted of electronic medical records of KT candidates with obesity (body mass index >35 kg/m2) who underwent SG in our institution. Weight loss, adverse health events, and the listing and transplant rates were abstracted and compared with the nonsurgical cohort. RESULTS: The SG was performed in 54 patients; 50 patients did not have surgery. Baseline demographic characteristics were comparable at the time of evaluation. Mean body mass index ± SD of the SG group was 41.7±3.6 kg/m2 at baseline (vs 41.5±4.3 kg/m2 for nonsurgical controls); at 2 and 12 months after SG, it was 36.4±4.1 kg/m2 and 32.6±4.0 kg/m2 (P<.01 for both). In the median follow-up time of 15.5 months (interquartile range, 6.4 to 23.9 months), SG was followed by active listing (37/54 people), and 20 of 54 received KT during a median follow-up time of 20.9 months (interquartile range, 14.7 to 28.3 months) after SG. In contrast, 14 of 50 patients in the nonsurgical cohort were listed, and 5 received a KT (P<.01). Three patients (5.6%) experienced surgical complications. There was no difference in overall hospitalization rates and adverse health outcomes, but the SG cohort experienced a higher risk of clinically significant functional decline. CONCLUSION: In KT candidates with obesity, SG appears to be effective, with 37% of patients undergoing KT during the next 18 months (P<.01). Further research is needed to confirm and to improve the safety and efficacy of SG for patients with obesity seeking a KT.

Implant Survival in Renal-Transplanted Patients: A Prospective Long-Term Study.

The present study aims to assess the feasibility of implant rehabilitation in kidney-transplanted patients. Patients with kidney transplantation included in periodontal supportive care and at least one year of dialysis with mono- or partial edentulism were eligible for this study. Histomorphometric evaluation of the harvested bone was matched with radiological bone assessment. Implant stability was also monitored with resonance frequency analysis and insertion torque value. Fixed cemented prostheses have been delivered after conventional loading protocol. Supportive periodontal therapy has been administered. Eleven patients (9 males and 2 females) were included. The mean age was 58.1 ± 9.9 years. A total of 17 implants were inserted and analyzed. Mean ITV was 39.3 ± 23.8 Ncm. The mean primary stability (implant stability quotient) at T0 was 71.7 ± 10.5, whereas the mean secondary stability at T1 was 73.0 ± 7.3. The minimum follow-up was 62 months, with a maximum of 84 months (7 years) reached by 4 patients. Fourteen out of 15 implants were in function at a 5-year follow-up (survival rate: 93.3%). Two implants showed peri-implantitis. Seventeen bone samples were collected (13 in the mandible and 4 in the maxilla). The mean percentage of marrow spaces and lamellar bone was 41.6% and 58.4%, respectively. Class 3, according to Misch classification, was found as the mean value of radiological bone density. It can be concluded that implant-supported rehabilitation in kidney-transplanted patients is possible. Adequate periodontal maintenance allows implant rehabilitation in kidney-transplanted patients with long-term sufficient survival rates.

Nirmatrelvir/ritonavir treatment of patients with COVID-19 taking tacrolimus: case series describing the results of drug-drug interactions.

Nirmatrelvir/ritonavir is a novel drug combination that is authorized by the Food and Drug Administration for the treatment of coronavirus disease 2019 (COVID-19). Ritonavir is a cytochrome P450 3A inhibitor and a P-glycoprotein inhibitor that increases the plasma concentration of tacrolimus and other medications. We describe the cases of two patients treated with nirmatrelvir/ritonavir: a patient who had undergone kidney transplantation and another with a history of hematopoietic stem cell transplantation. Toxic concentrations of tacrolimus were induced in both. This case series highlights the risk associated with the concomitant administration of tacrolimus and nirmatrelvir/ritonavir.