Comparative methylprednisolone pharmacokinetics in renal transplant patients receiving double- or triple-drug immunosuppression

Bone quality and healing in a swine vascularized bone allotransplantation model using cyclosporine-based immunosuppression therapy

Although vascularized bone and joint allotransplantation is a promising new treatment option for reconstructing large bone defects, the need for immunosuppressive agents to prevent rejection in these procedures poses a major problem. This problem stems from the fact that several of these agents can cause harmful side effects, such as alterations in bone quality and healing. Therefore, the purpose of this study was to determine what effect the commonly used immunosuppressant regimen cyclosporine A-based combination therapy has on bone quality and healing. In 10 pigs, vascularized bone allografts with skin and muscle components (osteomyocutaneous free flaps) were transplanted from size-matched donor animals. Recipient animals received oral cyclosporine A/mycophenolate mofetil/prednisone therapy for 90 days. Bone quality was studied before and after transplantation by measuring the bone's acoustic velocity and density and calculating the bone's elastic coefficient. Bone healing was assessed using radiographic analysis. Four animals were lost as a result of graft rejection or immunosuppression-related complications before the 90-day endpoint of the study. Although bone specimens taken from the six animals that completed the 90-day protocol had histological signs of rejection, they all seemed to have normal bone healing. Posttransplant bone density values were significantly decreased (p < 0.05) (1544.7 +/- 47.5 kg/m3) as compared with pretransplant values (1722.7 +/- 44.1 kg/m3). Results of the acoustic velocity and elastic coefficients measurements showed a significant decrease (p < 0.05) in posttransplant values (from 3503.0 +/- 165.1 meters/sec to 2963.0 +/- 54.6 meters/sec and from 21.6 +/- 2.2 GPa to 13.6 +/- 0.5 GPa, respectively), indicating diminished bone quality. The findings indicate that cyclosporine A/mycophenolate mofetil/prednisone combination therapy is ineffective in preventing bone rejection, that it decreases bone quality, and that it is associated with systemic toxicity, suggesting that this immunosuppressive regimen at the doses used in this study is not ideal for vascularized bone allotransplantation procedures.

Immunosuppressive therapy for paediatric transplant patients: pharmacokinetic considerations

Immunosuppressive therapy in paediatric transplant recipients is changing as a consequence of the increasing number of available immunosuppressive agents. Generic and other new formulations are now emerging onto the market, clinical experience is growing, and it is expected that clinicians should tailor immunosuppressive protocols to individual patients by optimising dosages and drugs according to the maturation and clinical status of the child. Most information about the clinical pharmacokinetics of immunosuppressive drugs in paediatrics is centred on cyclosporin, tacrolimus and mycophenolate mofetil in renal and liver transplant recipients; data regarding other immunosuppressants and transplant types are limited. Although the clinical pharmacokinetics of these drugs in paediatric transplant recipients are still under investigation, it is evident that the pharmacokinetic parameters observed in adults may not be applicable to children, especially in younger age groups. In general, patients younger than 5 years old show higher clearance rates irrespective of the organ transplanted or drug used. Another important factor that frequently affects clearance in this patient population is the post-transplant time. In accordance with these findings, and in contrast with the usual under-dosage in children, the need for higher dosages in younger recipients and during the early post-transplant period seems evident. To achieve the best compromise between prevention of rejection and toxicity, dosage individualisation is required and this can be achieved through therapeutic drug monitoring (TDM). This approach is particularly useful to ensure the cost-effective management of paediatric transplant recipients in whom the pharmacokinetic behaviour, target concentrations for clinical use and optimal dosage strategies of a particular drug may not yet be well defined. Although TDM may be a tool for improving immunosuppressive therapy, there is little information concerning its positive contribution to clinical events, including outcomes, for paediatric patients. Substantial information to support the use of TDM exists for cyclosporin and, to a lesser extent, for tacrolimus, but a diversity of options affects their implementation in the clinical setting. The role of TDM in therapy with mycophenolate mofetil and sirolimus has yet to be defined regarding both methods and clinical indications. Pharmacodynamic monitoring appears more suited to other immunosuppressants such as azathioprine, corticosteroids and monoclonal or polyclonal antibodies. If coupled with pharmacokinetic measurements, such monitoring would allow earlier and more precise optimisation of therapy. Very few population pharmacokinetic studies have been carried out in paediatric transplant patients. This type of study is needed so that techniques such as Bayesian forecasting can be applied to optimise immunosuppressive therapy in paediatric transplant patients.

Cortisol pharmacodynamic response to long-term methylprednisolone in renal transplant recipients

STUDY OBJECTIVE

To examine the pharmacodynamic patterns of cortisol and pharmacokinetic values of long-term methylprednisolone in renal transplant recipients.

DESIGN

Twenty-four-hour pharmacokinetic and pharmacodynamic evaluation of patients who participated in a glucocorticoid-monitoring program.

SETTING

University-based renal transplant clinic.

PATIENTS

Fourteen renal transplant recipients studied during a clinically stable period.

INTERVENTIONS

The daily oral methylprednisolone dose for each patient was administered intravenously, and serial plasma cortisol and methylprednisolone samples were obtained over 24 hours.

MEASUREMENTS AND MAIN RESULTS

Methylprednisolone was analyzed by high-performance liquid chromatography. The baseline morning cortisol serum concentrations ranged from 9.8-210.7 ng/ml. After the drug was administered, cortisol declined in a linear fashion with a mean suppression half-life of 2.4 +/- 0.9 hours. The cortisol nadir was reached at 12-16 hours in 11 of 14 patients. The return cortisol area under the curve (AUC-Cret) was noted in all patients and ranged from 57-987 ng.hr/ml. The total cortisol area under the curve was greater in patients who had been transplanted for longer than 2 years (1676 +/- 252 vs 836 +/- 405 ng.hr/ml; p < 0.05) compared with more recently transplanted patients. Methylprednisolone clearance ranged from 100-1181 ml/hr/kg with a mean volume of distribution of 1.3 +/- 0.6 L/kg. The methylprednisolone half-life ranged from 1.2-4.7 hours. The correlation between AUC-Cret and methylprednisolone AUC was -0.64 (p < 0.05).

CONCLUSIONS

The pharmacodynamic response of cortisol in renal transplant recipients may be associated in part with long-term steroid exposure. However, the interrelationship between the endocrine and immune system may also affect cortisol's disposition and subsequent recovery patterns in this population. Considerable interpatient variability was apparent in both the cortisol pharmacodynamic response as well as the pharmacokinetics of methylprednisolone. These findings suggest a more individualized dosing method may be necessary to optimize the immunosuppressive effect of glucocorticoids and minimize clinical toxicity.