To what extent does the understanding of pharmacokinetics of mycophenolate mofetil influence its prescription

Prescription Patterns of Mycophenolate Mofetil in a Group of Patients from Colombia

BACKGROUND

Mycophenolate mofetil is used for the prevention of solid organ transplant rejection and for other indications, such as systemic lupus erythematosus (SLE).

OBJECTIVE

To determine the prescription patterns of mycophenolate mofetil in a group of Colombian patients.

METHODS

This was a cross-sectional study of patients receiving mycophenolate mofetil between 2021 and 2022. The data were obtained from a drug dispensing database. Sociodemographic, clinical (diagnostic), and pharmacological variables were identified.

RESULTS

A total of 979 patients who underwent treatment were identified; their mean age was 45.9 ± 17.1 years, and 87.4% were women. The main diagnosis associated with the use of mycophenolate mofetil was SLE (39.1%), followed by other rheumatic diseases (8.5%), nephrotic syndrome (7.5%), and solid organ transplantation (6.4%). The relationship between the mean dose and the defined daily dose was 0.75. Ten percent of patients received mycophenolate alone, whereas 32.9% received mycophenolate in combination therapy with conventional disease-modifying antirheumatic drugs and glucocorticoids. A total of 76.2% had polypharmacy (five or more drugs).

CONCLUSIONS

Mycophenolate mofetil is used mainly in combination therapy for patients with SLE and other rheumatological diseases and for solid organ transplants at doses lower than those recommended.

Exposure to Mycophenolic Acid and Its Clinical Response in an Indian Pediatric Population with Nephrotic Syndrome

Background

Children with nephrotic syndrome experience many side effects and frequent relapses when treated with steroids and other drugs. Mycophenolic acid (MPA) is one of the effective and least toxic drug for the treatment of nephrotic syndrome. This drug needs to be monitored for maximal efficacy and minimal toxicity. The therapeutic reference range for this drug is not established for the aforementioned patient population of Indian origin.

Materials and Methods

In this observational study, children with nephrotic syndrome on mycophenolate mofetil were followed up for a minimum duration of three months. Following this, their clinical status (relapse/remission) was determined and the mycophenolate exposure was measured for over 12 hours.

Results

A total of 34 participants were included, with 17 (50%) in relapse. Median MPA Area under the curve over 12 hours (AUC0-12h) (36.5 µg·h/ml) in the remission group differed significantly compared to that in the relapse group (17.2 µg·h/ml).

Conclusion

Higher exposure to MPA AUC0-12h is associated with clinical remission of pediatric nephrotic syndrome.

The compelling case for therapeutic drug monitoring of mycophenolate mofetil therapy

We have reviewed current evidence on the therapeutic drug monitoring (TDM) of mycophenolic acid (MPA) in relationship to drug efficacy and safety. The relationship between actual MPA exposure and mycophenolate mofetil (MMF) dose has been shown to be weak in children and adolescents. The TDM of MPA exposure should ideally be performed using full pharmacokinetic profiles or limited sampling strategies. Recent evidence has provided some rationale for using the post-dose trough level as a single measure. In terms of short-term efficacy, there is strong evidence that a MPA area under the time-concentration curve of >30 mg × h/L reduces acute rejection episodes early after renal transplantation, and there is evolving evidence that aiming for the same exposure over the long term may be a viable strategy to reduce the formation of donor-specific antibodies. Strong evidence also supports the existence of important drug interactions and age/developmental dependent differences in drug metabolism that may necessitate the need for TDM of MMF therapy. Based on these findings and given the substantial inter- and intra-patient variability of MPA exposure, it would appear that MMF therapy should be subject to TDM to avoid over- and under-dosing. This may be a viable strategy to reduce treatment-emergent adverse events and to increase the effective pediatric transplant survival rates.

Minimum mycophenolic acid levels are associated with donor-specific antibody formation

Although de novo DSA are associated with inferior graft survival, there are no effective strategies to prevent their formation. Underexposure to MPA (prodrug: MMF) also contributes to rejection rates early after transplantation, but the effect of this phenomenon on the formation of DSA long-term post-transplantation is unknown. Data are expressed as mean (standard deviation). All available data from 32 renal transplant recipients (age at transplantation 7.5 [4.5] yr) on tacrolimus and MPA immunosuppression with an average follow-up of 9.4 (s.d. 4.6) yr were analyzed. DSA were measured using the Luminex assay (>500 MFI was considered DSA-positive). Tacrolimus and MPA levels were measured with the Abbot Tacro II and EMIT assay, respectively. Among 1964 MPA and 3462 tacrolimus trough levels, the average MPA trough level was 3.2 (1.5) mg/L and the average tacrolimus level was 6.7 (2.8) ng/mL. At last follow-up, only 5/32 patients had undetectable DSA, with 5/32 having no class I antibodies and 6/32 having no class II antibodies. DSA formation was associated with a lower minimum MPA trough level (0.27 [0.23] vs. 0.47 [0.18] mg) and cystatin C eGFR (48 [21] vs. 70 [23] mL/min/1.73 m(2)) for class I DSA formers. The average eGFR of patients without class I DSA was 70 (23) mL/min/1.73 m(2), whereas the average eGFR of patients with class I DSA was 48 (21) mL/min/1.73 m(2) (p = 0.0071). MPA trough levels <1.3 mg/L long-term post-transplantation are associated with the formation of DSA. The association between the formation of DSA and minimum MPA exposure may support a strategy for preventing the formation of DSA.

What is the intrapatient variability of mycophenolic acid trough levels?

TDM of MPA, the active compound of MMF, is rarely used despite its substantial intra- and interpatient variability. Little is known about the utility of long-term MPA TDM. Data are expressed as mean (one standard deviation). All available data from 27 renal transplant recipients (mean age at transplantation: 7.7 [5.0] yr) with an average follow-up of 9.3 (4.6) yr were analyzed. MPA levels were measured using the EMIT. GFR was measured using cystatin C and eGFR was calculated using the Filler formula. Intrapatient CV of the trough level was calculated as the ratio of the mean divided by one standard deviation. Mean cystatin C eGFR was 56.9 (24.4) mL/min/1.73 m(2) . There was a weak but significant correlation between the MPA trough level and the AUC (Spearman r = 0.6592, p < 0.0001). A total of 1964 MPA trough levels (73 [45]/patient) were measured, as compared to 3462 Tac trough levels (144 [71]/patient). The average MPA trough level was 3.01 (1.26) mg/L and the average trough Tac level was 7.3 (1.8) ng/mL. Intrapatient CV was statistically higher (p = 0.00093) for MPA at 0.68 (0.29) when compared to Tac with a CV of 0.46 (0.12). CV did not correlate with eGFR. Intrapatient MPA trough level CV is significantly higher than for Tac, while CV for both MPA and Tac was high. MPA trough level monitoring may be a feasible monitoring option to improve patient exposure and possibly outcomes.

Cyclosporine versus mycophenolate mofetil for maintenance of remission of steroid-dependent nephrotic syndrome after a single infusion of rituximab

The efficacy of rituximab (RTX) as the sole therapy for preventing relapses of nephrotic syndrome (NS) is transient in most patients; therefore, the optimal therapy required for maintaining a successful response to a biological agent remains a challenge. We conducted a prospective study to compare the efficacy of cyclosporine (CsA) with that of mycophenolate mofetil (MMF) as maintenance therapy after a single infusion of RTX. Of 29 patients with persistent steroid-dependent NS despite the use of CsA and/or MMF, 13 without chronic nephrotoxicity continued CsA therapy, maintaining a 2-h post-dose CsA level of 400-500 ng/ml (CsA group). The remaining 16 were treated with MMF, maintaining a pre-dose level of 2-5 μg/ml of mycophenolic acid (MMF group). The median duration of CsA and MMF treatment was 18 and 19 months, respectively. Despite the mean number of relapses before RTX treatment being significantly lower in the MMF group than in the CsA group (2.3/year vs. 4.6/year, p < 0.01), treatment failure occurred more frequently in the MMF group (7/16) than in the CsA group (2/13). The rate of sustained remission was also significantly higher in the CsA group than in the MMF group (p < 0.05).

CONCLUSION

In patients with severe steroid-dependent NS, CsA appears to be more effective than MMF for maintaining remission after a single infusion of RTX.

Optimization of Immunosuppressive Drug Monitoring in Children

BACKGROUND

The metabolism of drugs in children differs from adults, although pediatric pharmacokinetic (PK) studies remain scarce. Many of the drugs are metabolized by polymorphically expressed enzymes (cytochrome P450 [CYP450]; glucuronyl transferase [GT]) and/or transported by drug transporters (ABC and SLC families). In children, there is added complexity because of the age dependency of drug metabolism. This review addresses the age dependency of drug metabolism in childhood on the basis of routine PK monitoring.

METHODS

Standard pharmacokinetic studies in pediatric renal transplant recipients were analyzed to study drug-drug interactions between mycophenolic acid and cyclosporine on the one hand, and tacrolimus and sirolimus on the other hand. The exposure was compared with age. We also studied sirolimus metabolites, both by mass spectrometry as well as using human liver microsomes.

RESULTS

We demonstrated age dependency for MPA exposure. Independent of the concomitant medication, infants required approximately twice as much drug for the same exposure. The drug-drug interaction between sirolimus and tacrolimus demonstrated age dependency. Sirolimus metabolites showed a remarkably different pattern in children. Whereas 39-O-desmethyl sirolimus is the most prevalent metabolite in adults, we found 77.5% hydroxylated metabolites in children. Similarly, pediatric human liver microsomes produced 86.1% hydroxylated metabolites.

CONCLUSIONS

Our long-term objective is to develop evidence-based guidelines for age-appropriate drug dosing of all drugs commonly used during childhood and adolescence, based on pharmacokinetically/pharmacogenetically determined drug exposure to maximize therapeutic yield while minimizing toxicity. The potential need for lifelong medications warrants efforts to minimize toxicity in chronically ill pediatric patients.

Value of therapeutic drug monitoring of MMF therapy in pediatric transplantation

Therapeutic drug monitoring (TDM) is desirable whenever the desired drug effect cannot be predicted from a given dose, or when it is necessary to find a balance between the efficacy and toxicity of the drug. Children and adolescents particularly benefit from TDM, because dosing requirements are often not studied in the same detail as in adults. Also, drug-drug interactions are frequent. The gold standard for assessment of drug exposure is the area-under-the-curve (AUC) for a full pharmacokinetic profile. TDM for mycophenolic acid (MPA) is less well established. Monitoring of trough levels does not suffice because of enterohepatic recirculation of MPA after formation of its main metabolite, a glucoronide termed MPA-G. However, abbreviated sampling schemes specific to mycophenolate mofetil (MMF) correlate well with the AUC for MPA. Cyclosporine interacts with MPA by inhibiting the multidrug resistance-associated protein 2 (MRP2). Higher MPA concentrations result in a decreased two h concentration of cyclosporine, while higher cyclosporine exposure results in a lower MPA exposure. There are no drug interactions between tacrolimus and MPA, and lower doses of MMF are required in combination with tacrolimus. Steroids may induce the clearance of MPA, which could account in part for the increasing MPA exposure following transplantation. TDM has allowed for dosing recommendations of MMF in children, which could lead to improved efficacy and minimization of toxicities. It is important that these provisional target levels are validated in prospective studies. The above points clearly indicate that there is a role for TDM of MPA in pediatric transplant recipients.