Drug interactions in transplantation

Review of Postoperative Care for Heart Transplant Recipients

The early postoperative management strategies after heart transplantation include optimizing the function of the denervated heart, correcting the causes of hemodynamic instability, and initiating and maintaining immunosuppressive therapy, allograft rejection surveillance, and prophylaxis against infections caused by immunosuppression. The course of postoperative support is influenced by the quality of allograft myocardial protection prior to implantation and reperfusion, donor-recipient heart size matching, surgical technique of orthotopic heart transplantation, and patient factors (eg, preoperative condition, immunologic compatibility, postoperative vasomotor tone, severity and reversibility of pulmonary vascular hypertension, pulmonary function, mediastinal blood loss, and end-organ perfusion). This review provides an overview of the early postoperative care of recipients and includes a brief description of the surgical techniques for orthotopic heart transplantation.

Drug-related problems in older patients with advanced chronic kidney disease identified during pretransplant comprehensive geriatric assessment

BACKGROUND

Older patients with advanced chronic kidney disease may be exposed to a higher risk of adverse drug events due to chronic kidney disease and aging. The integration of clinical pharmacist into pretransplant comprehensive geriatric assessment is an opportunity to perform medication optimization.

OBJECTIVE

The aim was to describe drug-related problems in older patients with advanced chronic kidney disease.

METHODS

Observational study was conducted with retrospective data from July 2017 to April 2019. Patients≥65 years with advanced chronic kidney disease, referred by nephrologists for pretransplant comprehensive geriatric assessment were included. During medication optimization, the pharmacist evaluated the appropriateness of each medication prescribed and identified drug-related problems. Any drug-related problem identified lead to a pharmaceutical intervention.

RESULTS

In total, 103 patients were included (74.5±2.9 years, 26.2% female, 47.6% on dialysis). Overall, 394 drug-related problems were identified in 93.2% of patients (3.8±2.4 drug-related problems per patient) during the medication optimization. Cardiovascular medications (25.1%), antithrombotics (13.5%) and drugs for peptic ulcer and reflux disease (10.2%) were the most involved drugs in drug-related problems. Drug-related problems mainly concerned drugs without indication (27.1%), inappropriate method of administration (24.4%) and non-conformity to guidelines (20.1%).

CONCLUSION

A high prevalence of drug-related problems in older patients with advanced chronic kidney disease was identified during medication optimization. The systematic integration of a clinical pharmacist in the multidisciplinary team performing pretransplant comprehensive geriatric assessment may be relevant to detect inappropriate prescriptions and to prevent from adverse drug events.

Therapeutic drug monitoring of immunosuppressive drugs in hepatology and gastroenterology

Immunosuppressive drugs have been key to the success of liver transplantation and are essential components of the treatment of inflammatory bowel disease (IBD) and autoimmune hepatitis (AIH). For many but not all immunosuppressants, therapeutic drug monitoring (TDM) is recommended to guide therapy. In this article, the rationale and evidence for TDM of tacrolimus, mycophenolic acid, the mammalian target of rapamycin inhibitors, and azathioprine in liver transplantation, IBD, and AIH is reviewed. New developments, including algorithm-based/computer-assisted immunosuppressant dosing, measurement of immunosuppressants in alternative matrices for whole blood, and pharmacodynamic monitoring of these agents is discussed. It is expected that these novel techniques will be incorporate into the standard TDM in the next few years.

A primer for managing cardiac transplant patients in the emergency department setting

BACKGROUND

Cardiac transplant is an effective long-term management option for several severe cardiac diseases. These cardiac transplant patients may present to the emergency department with a range of issues involving the cardiac transplantation, including complications due to their transplant as well as altered presentations of disease resulting from their transplant.

OBJECTIVE

This narrative review provides a focused guide to the evaluation and management of patients with cardiac transplantation and its complications.

DISCUSSION

Cardiac transplant is an effective therapy for end-stage heart failure. A transplanted heart varies both anatomically and physiologically from a native heart. Several significant complications may occur. Graft failure, rejection, and infection are common causes of morbidity and mortality within the first year of transplant. As these patients are on significant immunosuppressive medication regimens, they are at risk of infection, but inadequate immunosuppression increases the risk of acute rejection. A variety of dysrhythmias such as atrial fibrillation and ventricular dysrhythmias may occur. These patients are also at risk of acute coronary syndrome, cardiac allograft vasculopathy, and medication adverse events. Importantly, patients with acute coronary syndrome can have an altered presentation with the so-called "painless" myocardial infarction. Consultation with the transplant physician is recommended, if available, for these patients to assist in evaluation and management.

CONCLUSIONS

An understanding of the presentations and various complications that may affect patients with cardiac transplant will assist emergency clinicians in the care of these patients.

The safety, immunological benefits, and efficacy of ginseng in organ transplantation

Korean ginseng (Panax ginseng) is associated with a variety of therapeutic effects, including antioxidative, anti-inflammatory, vasorelaxative, antiallergic, antidiabetic, and anticancer effects. Accordingly, the use of ginseng has reached an all-time high among members of the general public. However, the safety and efficacy of ginseng in transplant recipients receiving immunosuppressant drugs have still not been elucidated. Transplantation is the most challenging and complex of surgical procedures and may require causation for the use of ginseng. In this regard, we have previously examined the safety, immunological benefits, and protective mechanisms of ginseng with respect to calcineurin inhibitor-based immunosuppression, which is the most widely used regimen in organ transplantation. Using an experimental model of calcineurin inhibitor-induced organ injury, we found that ginseng does not affect drug levels in the peripheral blood and tissue, favorably regulates immune response, and protects against calcineurin inhibitor-induced nephrotoxicity and pancreatic islet injury. On the basis of our experimental studies and a review of the related literature, we propose that ginseng may provide benefits in organ transplant recipients administered calcineurin inhibitors. Through the present review, we aimed to briefly discuss our current understanding of the therapeutic benefits of ginseng related to transplant patient survival.

St John's Wort: A Hidden Risk for Transplant Patients

Herbal medications may cause prescription drug interactions in transplant recipients. After 2 of our kidney transplant recipients started self-medicating with St John's wort, their cyclosporine concentrations were consistently documented to be subtherapeutic. While on St John's wort, one patient developed acute rejection possibly due to low cyclosporine concentrations. Termination of St John's wort returned both patients' cyclosporine concentrations to therapeutic values. Based on the Naranjo Adverse Drug Reaction Probability Scale, our report would achieve a “probable” score, which supports the existence of a St John's wort–cyclosporine adverse drug interaction. St John's wort may induce cytochrome P-450 3A4 activity and/or P-glycoprotein expression, which are both involved in the metabolism and absorption of cyclosporine. Patients using St John's wort concomitantly with cyclosporine or other medications with similar absorption and/or metabolism to cyclosporine need close monitoring. Transplant coordinators are in a critical position to educate transplant recipients about the potential risks of herbal medication usage.

New Antiproliferative Immunosuppressive Agents

Since the early 1980s, the combination of cyclosporine, azathioprine, and prednisone has been the mainstay tripledrug immunosuppressive regimen used in transplantation. However, advances in drug research, design, and development have allowed for the introduction of new agents that have greatly increased the number of immunosuppressive agents available for use in transplant recipients. Particularly, the newer antiproliferative immunosuppressive drugs (agents that directly inhibit the proliferation of T and B lymphocytes) have had an important impact on patient outcomes posttransplant. These agents are mycophenolate mofetil and sirolimus.

Pharmacokinetic interaction between levofloxacin and ciclosporin or tacrolimus in kidney transplant recipients: ciclosporin, tacrolimus and levofloxacin in renal transplantation

BACKGROUND AND OBJECTIVE

Bacterial infections are common complications after organ transplantation. Fluoroquinolones are frequently used for treatment because of their broad spectrum of activity; but some of them, such as ciprofloxacin and norfloxacin, are reported to increase blood concentration of ciclosporin because they are metabolised by the liver through the same enzymatic pathway, the cytochrome P450 system. This study was performed to establish whether levofloxacin, a more recent fluoroquinolone that undergoes limited hepatic metabolism, interferes with metabolism and excretion of either ciclosporin microemulsion or tacrolimus.

METHODS

Pharmacokinetic studies were carried out in two groups of renal transplant patients, on either ciclosporin or tacrolimus treatment, before and at the sixth day of treatment with levofloxacin.

RESULTS

Levofloxacin significantly increased the mean area under the blood concentration-time curve (AUC) and the other pharmacokinetic parameters of ciclosporin and tacrolimus by about 25%. The interference of levofloxacin on the hepatic metabolism of these drugs was demonstrated by the concomitant decrease by 5% of polyclonal ciclosporin concentration, which is the expression of parent drug and its metabolites. Both before and during levofloxacin treatment we observed trough concentrations of monoclonal and polyclonal ciclosporin significantly lower in the evening (C(12)) than in the morning (C(0)); this observation suggests a circadian variation in the metabolism of this drug. However, no difference between C(0) and C(12) was observed with tacrolimus, confirming its more predictable bioavailability.

CONCLUSION

Our data demonstrate that levofloxacin partially inhibits the metabolism of both ciclosporin microemulsion and tacrolimus, and therefore close therapeutic monitoring of these two drugs should be recommended during levofloxacin therapy.

Influence of Nonsynonymous Polymorphisms of UGT1A8 and UGT2B7 Metabolizing Enzymes on the Formation of Phenolic and Acyl Glucuronides of Mycophenolic Acid

Mycophenolic acid (MPA) is the active metabolite of mycophenolate mofetil (MMF), a standard immunosuppressive drug approved for clinical use in the prevention of acute allograft rejection after organ transplantation. This study examines the role of the genetic variants of UDP-glucuronosyltransferase (UGT) 1A8 and 2B7 enzymes involved in the formation of the primary metabolite of MPA, the inactive phenolic glucuronide (MPAG), and the reactive acyl glucuronide (AcMPAG). The first exon of UGT1A8 was first resequenced in the region encoding for the substrate binding domain in 254 Caucasians and 41 African Americans. Eight nonsynonymous changes were observed and led to the following amino acid substitutions: S43L, H53N, S126G, A144V, A173G, A231T, T240A, and C277Y. Thirteen haplotypes were inferred, comprising only two previously described alleles, namely, UGT1A8*2 (A173G) and UGT1A8*3 (C277Y). Upon stable expression in human embryonic kidney 293 cells, the UGT1A8*3 (C277Y), *5 (G173A240), *7 (A231T), *8 (S43L), and *9 (N53G) proteins were associated with the most profound decreases in the formation of MPAG and AcMPAG, indicating that these amino acids are critical for substrate binding and enzyme function. Altogether, the low-activity UGT1A8 enzymes are carried by 2.8 to 4.8% of the population. The variant of the UGT2B7 protein (UGT2B7*2 Y268), the main enzyme involved in the formation of AcMPAG, demonstrated a catalytic efficiency comparable with that of UGT2B7*1 (H268). In conclusion, although the common UGT2B7*2 variant is predicted to have limited impact, several UGT1A8 variants identified may potentially account for the large interindividual variance in MMF pharmacokinetics and deserve further clinical investigations.

Impact of mycophenolate mofetil loading on drug exposure in the early posttransplant period

Achieving adequate therapeutic levels of immunosuppressive medications is important in rejection prevention. This study examined exposure to mycophenolic acid (MPA) in kidney transplant patients within the first 5 days posttransplantation.

METHODS

This single-center, nonrandomized study of first solitary kidney allograft recipients receiving cyclosporine (n = 116) or tacrolimus (n = 50) included patients who received either 1 g or 1.5 g of mycophenolate mofetil twice daily starting postoperatively. Exposure to MPA was measured at days 3 and 5 posttransplant using published limited sampling time equations.

RESULTS

There were no significant differences in exposure in the cyclosporine-treated patients receiving 3-g (n = 22) compared to 2-g (n = 94) daily doses (AUC([0-12]) 33.8 +/- 10.0 mg*h/L versus 30.1 +/- 9.7 mg*h/L, P = .20, respectively). About half the patients in both groups had AUC([0-12]) <30 mg*h/L on days 3 and 5 posttransplant. On the other hand, there was significantly greater exposure on day 3 in the tacrolimus-treated patients receiving 3 g (n = 21) compared to 2 g (n = 29) daily (AUC([0-12]) 43.1 +/- 9.0 mg*h/L versus 36.8 +/- 11.1 mg*h/L, P = .016, respectively). On day 3 one (4.8%) patient receiving 3 g had an AUC([0-12]) of <30 mg*h/L; whereas, eight (27.5%) receiving 2 g were below this level (P = .068). The AUC([0-12]) levels were not different on day 5.

CONCLUSIONS

Loading with higher doses of mycophenolate mofetil results in greater exposure and a trend toward more patients in the therapeutic window within the first week for tacrolimus- but not for cyclosporine-treated patients.

Effect of Oral Vitamin E and C Therapy on Calcineurin Inhibitor Levels in Heart Transplant Recipients

BACKGROUND

A recent prospective trial demonstrated that oral vitamins C and E retard the early progression of transplant-associated coronary arteriosclerosis; as a result, a number of centers have added these agents to their maintenance regimens. This study reviewed the impact of vitamin E and C supplementation on calcineurin inhibitor trough concentrations.

METHODS

A retrospective chart review of the first 29 heart transplant patients prescribed anti-oxidant agents was performed. Twenty-two patients taking cyclosporin A (CsA) and 7 patients taking tacrolimus were prescribed vitamin C (500 mg twice a day) and vitamin E (400 IU twice a day). Serum chemistries and drug levels were measured before and after vitamin therapy was initiated.

RESULTS

The baseline CsA trough concentration (mean +/- SD) was 137 +/- 39 ng/ml and it declined to 99 +/- 54 ng/ml (p = 0.007) after anti-oxidant therapy was initiated. The average percentage decrease in the CsA trough concentration was 30%. No significant changes were seen in the patients taking tacrolimus.

CONCLUSIONS

These data demonstrate that supplementation with the anti-oxidant agents vitamin C and vitamin E decreases CsA concentrations but does not appear to effect tacrolimus concentrations. Although more detailed pharmacokinetic analysis is necessary to clarify the exact mechanism of this interaction, physicians who take care of transplant recipients should be aware that more frequent CsA concentration monitoring is warranted after initiating these anti-oxidant agents.

Impact of gastric acid suppressants on cytochrome P450 3A4 and P-glycoprotein: consequences for FK506 assimilation

BACKGROUND

Cytochrome P450 3A4 (CYP3A4) and P-glycoprotein (PGP) are important determinants of the oral bioavailability and clearance of tacrolimus. Cimetidine and omeprazole are known modulators of several CYPs in vitro. In the present study, the impact of cimetidine and omeprazole on tacrolimus exposure and on CYP3A4/PGP activity in vivo was examined.

METHODS

In a cohort of 48 renal transplant recipients who switched standard ulcer prophylaxis with 400 mg of cimetidine daily to 20 mg of omeprazole, dose/weight normalized trough levels of tacrolimus during a 5-day interval before and after switch were compared and further studied using multivariate analysis. In a cohort of 6 healthy volunteers, the effect of a 5-day course of ranitidine, cimetidine, and omeprazole on overall CYP, CYP3A4, and PGP activity in vivo was assessed with the (13)C-aminopyrin breath test and the combined per oral and intravenous (14)C-erythromycin breath and urine test.

RESULTS

Dose/weight normalized trough levels of tacrolimus decreased significantly (-15%) after switch from cimetidine to omeprazole. In healthy volunteers, a significant increase of intestinal CYP3A4 activity was observed after omeprazole, whereas no change was noted after cimetidine/ranitidine. Overall CYP activity was significantly decreased after cimetidine and remained unchanged after omeprazole/ranitidine. No effects on PGP or hepatic CYP3A4 were seen.

CONCLUSION

Switching treatment with cimetidine to omeprazole in renal transplant recipients is associated with a decrease of dose/weight normalized trough levels of tacrolimus. Studies in healthy volunteers suggest that this may be explained by an increase of intestinal CYP3A4 activity.

FUNCTIONAL INDUCTION AND DE-INDUCTION OF P-GLYCOPROTEIN BY ST. JOHN'S WORT AND ITS INGREDIENTS IN A HUMAN COLON ADENOCARCINOMA CELL LINE

Continuous use of St. John's wort decreases the bioavailabilities of a variety of drugs. This interaction is attributed to the induction of cytochrome P450 3A4 and/or P-glycoprotein. In this study, we aimed to examine the chronic effects of St. John's wort and its constituents, hyperforin and hypericin, on the expression and function of P-glycoprotein in an intestinal cell line, LS 180. We also examined the acute inhibitory effect of St. John's wort on P-glycoprotein by using LLC-GA5-COL150 cells, which overexpress P-glycoprotein. St. John's wort and hyperforin but not hypericin increased the expression of P-glycoprotein in LS 180 cells. Removal of St. John's wort resulted in a restoration of P-glycoprotein level within 48 h. The content of hyperforin in St. John's wort extract was high enough to induce P-glycoprotein, suggesting that the induction of P-glycoprotein by St. John's wort can be almost attributable to hyperforin. The LS 180 cells chronically exposed to St. John's wort or hyperforin exhibited the increase in the function of P-glycoprotein assessed by the efflux of digoxin, and the activities correlated well with P-glycoprotein level. On the other hand, St. John's wort and its two constituents did not show any acute effect on P-glycoprotein-mediated transport of digoxin. St. John's wort induced P-glycoprotein in vitro that functions as a drug efflux pump. Hyperforin is considered to be a primary cause of the inductive effect of St. John's wort. Long-term administration of St. John's wort may cause clinically significant decrease in the plasma concentrations of P-glycoprotein substrates.

Evaluation of drug interaction software to identify alerts for transplant medications

BACKGROUND

The ability of computerized physician order entry (CPOE) systems to identify clinically significant drug interactions is dependent upon the integrity of the drug information populating the software. A CPOE system with incomplete or inaccurate drug information will fail to identify clinically important drug interactions and, therefore, fail to reduce preventable adverse drug events (pADEs).

OBJECTIVE

To evaluate, from the prescribers' perspective, the ability of a common drug interaction database to identify clinically important drug interactions involving drugs used in transplantation.

METHODS

The clinical significance of drug interactions involving 5 transplant drugs was evaluated by an expert panel to determine whether alerts should be generated for physicians not involved in the transplant at the time of order entry. Drug interactions included in the analysis were generated from the expert panel, a common drug interaction database, and 2 standard drug interaction references. Responses on the clinical significance were used to calculate the sensitivity, specificity, and positive and negative predictive values for each severity setting of a common electronic drug interaction database.

RESULTS

Overall, the database failed to identify approximately 70% of interactions considered significant by the expert panel. Of the alerts that were generated, >85% were considered clinically significant. The database was most deficient in identifying interactions resulting from additive toxicity.

CONCLUSIONS

To expect a decrease in pADEs caused by drug interactions, the information used to populate CPOE systems must be validated. Establishing consistency and integrity of this information may be a future role for pharmacists.

Subacute immune response to primary EBV infection leading to post-transplant lymphoproliferative disease in a renal transplant patient

A 23-year-old man sero-negative for Epstein-Barr virus (EBV) developed recurrent sore throats 3 and 6 months after a renal transplant from an EBV sero-positive donor. Tonsillar biopsy at 9 months post-transplant showed post-transplant lymphoproliferative disease (PTLD) caused by EBV. Following reduction of immunosuppressive treatment, he developed further signs and symptoms, and serological evidence of infectious mononucleosis followed by resolution of lymphadenopathy. This case emphasizes the difficulty in interpreting EBV serology in immunosuppressed patients and the importance of pre-transplant EBV serology.

Acute renal transplant rejection possibly related to herbal medications

Use of herbal and alternative medications in the United States is increasing. Many of these medications have unknown mechanisms of actions, and possible metabolic interactions with prescribed medications. We report a case of late acute rejection after exposure to two popular herbal medications.

Effect of cyclophosphamide on serum cyclosporine levels at the conditioning of hematopoietic stem cell transplantation

We retrospectively analyzed the factors that affect serum cyclosporine (CsA) concentrations up to day 14 after allogeneic hematopoietic stem cell transplantation (HSCT). In all, 103 transplant recipients who received MTX and CsA for acute GVHD prophylaxis were analyzed. No significant relationships between serum CsA concentrations and gender, age, serum creatinine levels, AST/ALT levels, or antibiotic/fluconazole administration were found by comparing median CsA concentrations or by using longitudinal or regression multivariate analyses. However, the mean of the median serum CsA concentration in patients (n=54) receiving the regimen containing cyclophosphamide (CY) (149.7 ng/ml; 95% confidence interval (CI): 132.1-167.4) was significantly (P<0.0001) lower than that in patients (n=49) receiving the non-CY regimen (217.3 ng/ml; 95% CI: 198.9-235.6). Longitudinal analysis and regression multivariate analysis showed that only administration of CY had a significant effect on the serum CsA concentration. Our results suggest that administration of CY during conditioning can reduce the effects on serum CsA concentrations during the 2 weeks following HSCT. The mechanism of this effect is not clear, but it may be due to the autoinduction of CY.

Mechanisms of clinically relevant drug interactions associated with tacrolimus

The clinical management of tacrolimus, a macrolide used as immunosuppressant after transplantation, is complicated by its narrow therapeutic index in combination with inter- and intraindividually variable pharmacokinetics. As a substrate of cytochrome P450 (CYP) 3A enzymes and P-glycoprotein, tacrolimus interacts with several other drugs used in transplantation medicine, which also are known CYP3A and/or P-glycoprotein inhibitors and/or inducers. In clinical studies, CYP3A/P-glycoprotein inhibitors and inducers primarily affect oral bioavailability of tacrolimus rather than its clearance, indicating a key role of intestinal P-glycoprotein and CYP3A. There is an almost complete overlap between the reported clinical drug interactions of tacrolimus and those of cyclosporin. However, in comparison with cyclosporin, only few controlled drug interaction studies have been carried out, but tacrolimus drug interactions have been extensively studied in vitro. These results are inconsistent and are of poor predictive value for clinical drug interactions because of false negative results. P-glycoprotein regulates distribution of tacrolimus through the blood-brain barrier into the brain as well as distribution into lymphocytes. Interaction of other drugs with P-glycoprotein may change tacrolimus tissue distribution and modify its toxicity and immunosuppressive activity. There is evidence that ethnic and gender differences exist for tacrolimus drug interactions. Therapeutic drug monitoring to guide dosage adjustments of tacrolimus is an efficient tool to manage drug interactions. In the near future, progress can be expected from studies evaluating potential pharmacokinetic interactions caused by herbal preparations and food components, the exact biochemical mechanism underlying tacrolimus toxicity, and the potential of inhibition of CYP3A and P-glycoprotein to improve oral bioavailability and to decrease intraindividual variability of tacrolimus pharmacokinetics.

Rhodococcus equi pulmonary infection in a pancreas-alone transplant recipient: consequence of intense immunosuppression

We report the case of a pancreas-alone transplant recipient who developed Rhodococcus equi pneumonia after receiving multiple courses of antilymphocyte therapy for the treatment of recurrent acute pancreas allograft rejection. We also review and discuss the diagnosis, clinical course, and treatment of 18 cases of R. equi infection reported in solid organ transplant recipients. The lung is the most common primary site of infection, but R. equi infection is difficult to diagnose because of the pleomorphic, gram-positive, and partially acid-fast nature of the organism. Treatment usually involves a combination of antibiotics including rifampin, macrolides, vancomycin, and ciprofloxacin. The optimal duration of therapy is unknown, but relapse is common if the duration of treatment is less than 14 days. The duration of therapy should be guided by clinical recovery, culture results, and radiographic findings. Monitoring levels of immunosuppressive agents-such as tacrolimus and cyclosporine-is needed in order to avoid clinically significant drug interactions with rifampin or the macrolides when these agents are used in order to treat R. equi infection in the transplant population.

Possible interaction between intravenous azithromycin and oral cyclosporine

A 42-year-old man who had received a cadaveric kidney transplant 9 years earlier was admitted to the hospital with pneumonia. His oral cyclosporine dosage for the past 2 years was stabilized at 100 mg twice/day; his cyclosporine whole blood trough levels 15 days earlier and on the day he was admitted were both 178 ng/ml. The patient was treated with intravenous ceftriaxone and intravenous azithromycin and continued to receive the same dosage of oral cyclosporine. On hospital day 3, his cyclosporine trough level rose to 400 ng/ml and his dosage was reduced by 50%. Trough levels were 181 ng/ml and 175 ng/ml on hospital days 6 and 9, respectively On hospital day 9, the patient stopped receiving azithromycin. On hospital day 14, his cyclosporine trough level dropped to 76 ng/ml, and his cyclosporine dosage was increased back to 100 mg twice/day. The dosage produced trough levels consistent with those before he had been admitted. The patient was discharged on day 20, and a follow-up cyclosporine trough level determined 3 weeks later was 175 ng/ml. Administration of azithromycin may have caused the increased cyclosporine concentrations in this patient through p-glycoprotein inhibition and/or competition for biliary excretion. Azithromycin's interference may be inferred by the increase in cyclosporine levels after administration of this drug and the decrease in cyclosporine levels after its discontinuation-both consistent with the pharmacokinetic properties of cyclosporine. Ceftriaxone and acute-phase reactant activation during infection, however, also may have interfered with the patient's cyclosporine elimination. Azithromycin generally is considered unlikely to interact with cyclosporine. Nonetheless, practitioners should be aware of this possibility and should monitor cyclosporine levels closely, especially in critically ill patients who have other complications.

St John's wort: a hidden risk for transplant patients

Herbal medications may cause prescription drug interactions in transplant recipients. After 2 of our kidney transplant recipients started self-medicating with St John's wort, their cyclosporine concentrations were consistently documented to be subtherapeutic. While on St John's wort, one patient developed acute rejection possibly due to low cyclosporine concentrations. Termination of St John's wort returned both patients' cyclosporine concentrations to therapeutic values. Based on the Naranjo Adverse Drug Reaction Probability Scale, our report would achieve a "probable" score, which supports the existence of a St John's wort-cyclosporine adverse drug interaction. St John's wort may induce cytochrome P-450 3A4 activity and/or P-glycoprotein expression, which are both involved in the metabolism and absorption of cyclosporine. Patients using St John's wort concomitantly with cyclosporine or other medications with similar absorption and/or metabolism to cyclosporine need close monitoring. Transplant coordinators are in a critical position to educate transplant recipients about the potential risks of herbal medication usage.

Comparison of the effects of tacrolimus and cyclosporine on the pharmacokinetics of mycophenolic acid

Mycophenolate mofetil (MMF) is almost completely absorbed from the gut and is rapidly de-esterified into its active drug, mycophenolic acid (MPA). The main metabolite is glucuronidated MPA (MPAG), which is excreted into bile and undergoes enterohepatic recirculation. Studies in healthy volunteers treated with cholestyramine show that interruption of the enterohepatic recirculation decreases MPA exposure by approximately 40%. Published data show a difference in mycophenolic acid plasma concentrations between kidney transplant recipients treated with MMF plus cyclosporine (CsA) and those treated with MMF plus tacrolimus (TRL). However, the interpretation of these data is complicated by interpatient differences in variables that may influence MMF pharmacokinetics (e.g., underlying disease, co-medication, and time since transplantation). To understand the influence of TRL and CsA on MMF pharmacokinetics (PK) more completely, the authors eliminated confounding variables in clinical studies by performing drug interaction studies in inbred rats. To achieve a steady state, 3 groups of Lewis rats (n = 8 per group) were treated once daily with oral CsA (8 mg/kg), TRL (4 mg/kg), or placebo on days 0-6 before all rats began once-daily oral treatment with MMF (20 mg/kg) on day 7. Combined treatment with either MMF + CsA, MMF + TRL, or MMF + placebo was continued for 1 week (days 8-14). Thereafter, CsA and TRL treatments were stopped but MMF treatment was continued on days 14-21. Blood was sampled during the 24 hours subsequent to dosing on day 7 (after the first MMF dose), on day 14 (after multiple MMF doses) and on day 21 (after CsA/TRL washout). Rats in the MMF + TRL group and in the MMF + placebo group showed a second peak in the MPA-PK profiles consistent with enterohepatic recirculation of MPA. The MPA-PK profiles for the MMF + CsA-treated animals did not show a second MPA peak. On Day 14, the mean plasma MPA-AUC(0-24 hours) for the CsA-treated animals was significantly less than MPA exposures for rats in the MMF + TRL- and the MMF + placebo-treated groups. Furthermore, in contrast to results from other investigators, co-administration of CsA and MMF significantly increased MPAG-AUC(0-24 hours). Serum creatinines did not differ among rats in the three groups. CsA but not TRL decreased MPA plasma levels and increased MPAG-AUC(0-24 hours). These data suggest that CsA inhibits MPAG excretion into bile and offer an explanation for the well-known increased MPA exposure in organ transplant patients caused by conversion from CsA- to TRL-based immunosuppression.

Oxybutynin does not affect cyclosporin blood levels

Cyclosporin is an important immunosuppressive medication used to prevent organ rejection. Drug interactions that alter its blood levels can cause serious problems with toxicity or transplant rejection. Current evidence indicates that both cyclosporin and oxybutynin, which is used to treat bladder dysfunction, are metabolized by the cytochrome P450 3A enzyme system, raising the possibility of an adverse interaction between these medications. However, a study of two children receiving cyclosporin with and without oxybutynin revealed no significant changes in trough blood cyclosporin concentrations.

Herbal supplements: a potential for drug interactions in transplant recipients

BACKGROUND

Herbal dietary supplements represent a potential and possibly an overlooked cause for drug interactions in transplant recipients.

METHODS

Two patients are reported which suggest that St. John's Wort (SJW) may induce cytochrome P-450 3A4 activity and/or P-glycoprotein expression. Both of these mechanisms are significantly involved in the metabolism and absorption of cyclosporine (CSA) and other immunosuppressants.

RESULTS

After two renal transplant recipients started self-medicating with SJW, their CSA concentrations were consistently documented to be subtherapeutic. While on SJW, one patient developed acute graft rejection due to low CSA concentrations. In both patients, termination of SJW returned their CSA concentrations to therapeutic values.

CONCLUSIONS

Patients taking SJW concomitantly with CSA or other medications whose absorption and metabolism are mediated by cytochrome P-450 and/or P-glycoprotein should require close monitoring. Potential herb-prescription drug interactions are not just limited to SJW. Inquiries regarding the usage of herbal supplements should be an integral component of a transplant recipient's medication history.

Interaction of Hypericum perforatum (St. John's wort) with cyclosporin A metabolism in a patient after liver transplantation

Immunosuppressive therapy in patients after liver transplantation requires careful monitoring of blood levels for immunosuppressive agents such as cyclosporin A. A variety of drugs are capable of interfering with the metabolism of cyclosporin A. We observed a 63-year-old patient who received a liver allograft for cryptogenic liver cirrhosis in 1998. This patient developed severe acute rejection 14 months after transplantation which was associated with a sudden drop in cyclosporin A levels. Two weeks previously, he had started taking the herbal drug Hypericum perforatum (2 x 900 mg/day) for increasing episodes of depression. The cyclosporin A dosage later had to be doubled, which caused some side effects. Finally, an assessment of oral cyclosporin A resorption suggested an enhanced cyclosporin A metabolism. Hypericum perforatum was stopped. Both cyclosporin A dosage and blood levels immediately returned to normal. The liver function recovered completely. In conclusion, this observation is a previously undescribed drug interaction of a widely used herbal drug (Hypericum perforatum, i.e. St. John's wort) in a patient after liver transplantation.

Drug interaction between St. John's wort and cyclosporine

OBJECTIVE

To report a probable drug interaction between the herbal dietary supplement St. John's wort and cyclosporine.

CASE REPORT

A 29-year-old white woman who received a cadaveric kidney and pancreas transplant, with stable organ function and stable cyclosporine concentrations began self-medicating with St. John's wort. After taking St. John's wort supplements for four to eight weeks, her cyclosporine concentrations became subtherapeutic; this was associated with organ rejection. Four weeks after stopping St. John's wort, her cyclosporine concentrations again became therapeutic. Subsequent to this rejection episode, she has developed chronic rejection and now has returned to dialysis.

DISCUSSION

St. John's wort is suspected to be a significant inducer of CYP3A4 isoenzyme activity and of P-glycoprotein (P-gp) expression, both of which are important in the metabolism and absorption of cyclosporine. Cyclosporine exhibits a relatively small therapeutic window and is sensitive to medications that can modulate the CYP3A4 isoenzyme and P-gp in both the liver and small intestines.

CONCLUSIONS

Patients taking St. John's wort concomitant with other prescription medications whose absorption and metabolism are mediated by the CYP3A4 isoenzyme and P-gp require close monitoring. Patient medication histories should include inquiries into the use of herbal dietary supplements.

Effect of cyclosporine on mycophenolic acid trough levels in kidney transplant recipients

BACKGROUND

Triple drug treatment consisting of mycophenolate mofetil (MMF), in a standard dose of 2 g daily, combined with cyclosporine (CsA) and prednisone, has become the standard immunosuppressive regimen after kidney transplantation in many centers. The need for therapeutic drug monitoring of mycophenolic acid (MPA) has not yet been established. Several drug interactions with MMF are known. We investigated the influence of CsA withdrawal on MPA trough levels in renal transplant patients.

METHODS

Fifty-two patients were treated with 1 g of MMF twice daily, and prednisone and CsA targeted between 125 and 175 ng/ml for 6 months after transplantation. At 6 months after transplantation, 19 patients were randomized for continuation of triple therapy (group A), 19 patients discontinued CsA (group B), and 14 patients discontinued prednisone (group C). We compared 12-hr fasted MPA trough levels at 6 and 9 months after transplantation within and between these groups.

RESULTS

MPA trough levels during treatment with CsA, MMF, and prednisone were significantly lower than those during treatment with MMF and prednisone only (group B); median levels were 1.87 mg/L (range: 0.56-5.27) vs. 3.16 mg/L (range: 0.32-7.78), respectively (P=0.002). MPA trough levels in groups A and C did not change between 6 and 9 months after transplantation; group A median levels were 1.87 (range: 0.31-4.32) vs. 1.53 mg/L (range: 0.36-3.70), and group C median levels were 1.62 (range: 0.69-10.34) vs. 1.79 mg/L (range: 0.54-6.00), respectively. At 9 months after transplantation, patients in whom CsA was discontinued had higher MPA trough levels as compared with patients who continued the use of triple therapy (P=0.001) or patients in whom steroids were withdrawn (P=0.014).

CONCLUSION

A significant increase of MPA trough levels was found after discontinuation of CsA (6 months after transplantation), resulting in almost a doubling of MPA trough levels at 9 months after transplantation. This resulted in increased MPA levels in patients without CsA as compared to MPA levels in patients continuing triple therapy or discontinuing prednisone.