Mycophenolate mofetil pharmacokinetics in renal transplant recipients on peritoneal dialysis

We prospectively studied the impact of peritoneal dialysis (PD) on the pharmacokinetics of mycophenolic acid (MPA) in five patients following renal transplantation. Three patients had a glomerular filtration rate (GFR) of less than 10 ml/min and two had a GFR of more than 40 ml/min. Pharmacokinetics of MPA and of its main metabolite, mycophenolic acid glucuronide (MPAG), were studied during two consecutive 12-h periods (with and without PD). After initiation of PD in patients with severe renal impairment (GFR < 10 ml/ min), MPA-area-under-the-concentration-curve (AUC) decreased up to 59% and MPAG-AUC decreased up to 26%. We did not observe any substantial changes in the MPA-AUC or MPAG-AUC of either patient with a GFR above 40 ml/min. Patients with a reduced GFR had much higher MPAG values than patients with a GFR above 40 ml/l; yet, we did not observe any differences in the MPA values. We found a significant inverse correlation between GFR and MPA-AUC (r = 0.81, P < 0.05) and between GFR and MPAG-AUC (r = 0.94, P < 0.01). While MPA was found only in traces in the peritoneal ultrafiltrate, the cumulative amount of MPAG removed by PD reached up to 2 g/ 12 h, representing 1.2 g of MPA. This is the first report describing a reduction in MPA-AUC and MPAG-AUC during PD. Further studies are needed to completely understand the pharmacokinetics of mycophenolate mofetil during PD.

Pharmacokinetics of mycophenolate mofetil in renal transplant recipients on peritoneal dialysis

Little is known about the pharmacokinetics of mycophenolatic acid (MPA) in the early posttransplant period after renal transplantation. We studied the impact of peritoneal dialysis on the pharmacokinetics of MPA in 5 patients following renal transplantation (3-6 weeks after transplantation). Three patients had a glomerular filtration rate (GFR) of less than 10 ml/min, 1 patient had a GFR of 32, and 1 of 58 ml/min. Pharmacokinetics of MPA and its main metabolite mycophenolic acid glucuronide (MPAG) were studied on 2 consecutive days (12-hour intervals: with and without peritoneal dialysis). Dosing of MPA was 2 x 1 g/day. MPA and MPAG concentrations were determined by HPLC methods. After initiation of peritoneal dialysis in patients with severe renal impairment (GFR < 10 ml/min) MPA area under the concentration curve (AUC) decreased substantially (15-59%). The calculated clearance of MPA was higher (14.6 vs 8.1 ml/min/kg) on the day of peritoneal dialysis than during the dwell-free day. MPAG-AUC decreased up to 26% in these patients. In both patients with a GFR > 30 ml/min we observed an increase of MPA-AUC on the day of peritoneal dialysis and a decreased MPA clearance. MPAG-AUCs remained stable. Patients with a reduced GFR had much higher MPAG values than patients with a GFR 30 ml/l, however, we did not observe any differences for the MPA levels. We found a significant inverse correlation between GFR and MPAG-AUC (r = 0.91, p < 0.05). While MPA was found only in traces in the peritoneal ultrafiltrate, the cumulative amount of MPAG removed by peritoneal dialysis reached up to 2 g per 12 hours, representing up to 1.2 g of MPA. This is the first report describing a reduction of MPA- and MPAG-AUC during peritoneal dialysis. Further studies are needed to better understand the pharmacokinetics of mycophenolat mofetil during peritoneal dialysis.

Pharmacokinetics of temocapril and temocaprilat after 14 once daily oral doses of temocapril in hypertensive patients with varying degrees of renal impairment

AIMS

The aim of this study was to determine the potential influence of renal impairment on the pharmacokinetics of temocapril and its pharmacologically active diacid metabolite, temocaprilat.

METHODS

Non-compartmental pharmacokinetics were assessed in four groups of hypertensive patients (n=8 per group, four investigational centres) with normal (creatinine clearance determined via 24 h urine sampling, CL[CR], > or = 60 ml min-1) and impaired renal function (CL[CR] 40-59, 20-39, < 20 ml min-1) after 14 once daily oral doses of 10 mg temocapril hydrochloride.

RESULTS

For temocapril, there were no statistically significant differences in median tmax or mean Cmax, AUC(SS), t1/2,Z, CL/F between the four groups. Renal clearance, CL(R), for temocapril showed a linear decreasing trend with decreasing CL(CR) [mean (s.d.): 32.2 (10.7) to 3.7 (3.0) ml min-1]. Steady-state for temocaprilat was reached on day 5. For temocaprilat, no statistically significant differences in mean Cmax or median tma were detected. With decreasing mean CL(CR), mean AUC(SS) for temocaprilat increased statistically significantly although only 2.4-fold [mean (s.d.): 2115 (565) to 4989 (2338) ng ml-1 h] and t1/2,Z was prolonged [mean (s.d.): 15.2 (1.2) to 20.0 (7.5) h]. CL(R) for temocaprilat showed a linear decreasing trend with decreasing CL(CR) [mean (s.d.): 20.2 (4.3) to 3.0 (1.8) ml min-1].

CONCLUSIONS

These results indicate that impaired renal function has only a limited effect on the pharmacokinetics of temocapril and its active metabolite, temocaprilat. This may be attributed to the dual, i.e. renal and biliary, elimination pathway of the drug.

Clinical pharmacokinetics of tacrolimus in rescue therapy after renal transplantation

Tacrolimus, a potent new immunosuppressive drug, was introduced for rescue therapy in 25 renal transplant recipients with ongoing rejection (n = 24) or severe cyclosporine toxicity (n = 1). A highly significant (p < 0.001) rise in serum creatinine from 138 +/- 14 (3 months before conversion) to 295 +/- 26 mumol/l preceded conversion to tacrolimus. Tacrolimus rescue therapy started 73 +/- 9 months after transplantation, the follow-up was 8 +/- 1 months. Outcome, pharmacokinetics, and side-effects were analyzed. Patient survival was 100% on tacrolimus therapy. Graft survival was 88% after 3 months, and 70% after 8 months. Serum creatinine remained stable during the observation period (Crea after 8 months: 271 +/- 26 mumol/l). Starting with an initial dose of 9.6 +/- 0.3 mg/day (0.14 +/- 0.01 mg/kg/day) we could reduce tacrolimus dose to 6.0 +/- 0.9 mg/day (0.09 +/- 0.02 mg/kg/day; p < 0.001) after 1 month. Tacrolimus trough levels were adjusted to a therapeutic window of 5-8 ng/ml. We had to perform 3.4 +/- 0.5 dose adjustments per patient mainly within the first month after conversion (70%). A high variability in interindividual tacrolimus dose was noted. Last cyclosporine dose was a good predictor of required tacrolimus dose after 1 month (r = 0.88; p < 0.001). Overall, 82 adverse events were noted, of which 29 (35%) were associated with high trough levels (> 10 ng/ml). In contrast, 3 patients with trough levels < 4 ng/ml had ongoing rejection. Blood pressure and routine laboratory data remained unchanged. Steroid dose could be tapered from 12 +/- 2 to 5 +/- 0.3 mg/day (p < 0.02). Gingival hyperplasia and hirsutism improved after conversion. We conclude: Tacrolimus conversion for rescue therapy after renal transplantation is efficient and safe with target trough levels between 5 -8 ng/ml. Frequent drug monitoring is necessary, especially within the first month after conversion. Previous cyclosporine dose can be used as a guideline for starting dose.

Radioimmunoscintigraphy of squamous cell carcinoma in the head and neck region

Radioimmunoscintigraphy (RIS) with a monoclonal antibody (SQ 174, Biomira, Inc, Canada) is introduced as a new diagnostic method for detection of squamous cell carcinoma in the head and neck region. RIS could detect eight of the 10 primary tumors. One patient had histopathologically proven nodal disease. This lymph node was seen in RIS. No false positive results were seen in RIS, whereas sonography, computed tomography, and magnetic resonance imaging showed several false positive results.