Dennis J. Gmur

Age-dependent cyclosporine: pharmacokinetics in marrow transplant recipients

We evaluated the effect of age on cyclosporine pharmacokinetics in 69 nonobese patients aged 10 months to 56 years (median 22 years) undergoing allogeneic bone marrow transplantation for treatment of aplastic anemia or hematologic malignancy. Cyclosporine pharmacokinetics were studied during the first 2 posttransplant weeks after an intravenous dose of 2.6 to 3.5 mg/kg. Serum cyclosporine concentrations were measured by HPLC. Cyclosporine concentration‐time data were fitted to a two‐compartment model with a nonlinear regression program. There was a significant inverse linear correlation between age and both total systemic clearance (CL) (r = 0.42; P < 0.001) and volume of distribution at steady‐state (Vss) (r = 0.33; P < 0.01). Mean (±SE) cyclosporine CL was 82 ± 21, 45 ± 5, 38 ± 9, 44 ± 8, and 20 ± 3 ml/min/kg and mean cyclosporine Vss was 34 ± 11, 28 ± 10, 15 ± 4, 14 ± 5, and 4.7 ± 0.7 L/kg in patients 0 to 10 (n = 12), 11 to 20 (n = 19), 21 to 30 (n = 12), 31 to 40 (n = 17), and >40 (n = 9) years old, respectively. Patients 0 to 10 years old had a significantly higher cyclosporine CL than those 11 to 40 or >40 years old and also had a significantly larger Vss than those >40 yrs old (P < 0.05). Age‐related differences in CL or Vss were also observed when these parameters were normalized by body surface area. Multiple stepwise regression showed that other factors, such as serum bilirubin, alkaline phosphatase, creatinine, or BUN, did not correlate with cyclosporine CL or Vss. Thus since infants and children have a more rapid CL and larger Vss than adults, they require larger cyclosporine doses to achieve comparable serum cyclosporine concentrations.

High-performance liquid chromatographic column-switching method for two cyclosporine metabolites in blood

Cyclosporine (CSA) is biotransformed to many metabolites which may contribute to its immunosuppressive and nephrotoxic activity. We report a rapid and sensitive, automated column-switching high-performance liquid chromatographic (HPLC) method for measuring CSA-M17 in whole blood; the method also separates CSA-M1. CSA metabolite standards were isolated by a preparative-scale HPLC method. Samples were prepared by protein precipitation with acetonitrile followed by dilution with water. CSA-M17 was initially separated on a C8 column; final separation was on a C18 column. The inter-day relative standard deviation at 50 ng/ml was 8% (n = 3). Limit of detection was 20 ng/ml.

REGIONAL RESPONSES WITHIN THE KIDNEY TO ISCHEMIA : ASSESSMENT OF ADENINE NUCLEOTIDE AND CATABOLITE PROFILES

UNLABELLED Renal cortex (C) has predominantly aerobic metabolism, whereas inner medulla (IM) has both aerobic and anaerobic capacities. This study was undertaken (1) to assess how well rat IM anaerobic metabolism maintains this regions ATP content during ischemia; and (2) to determine whether regional variations in adenylate pool/catabolite responses to ischemia exist, obscuring interpretation of cellular energetics in rat studies of acute renal failure (ARF). Adenine nucleotides/catabolites were measured in rat C, IM and outer medulla (OM) after 15 and 45 min of ischemia. After 15 min, all regions showed profound ATP depletion, although the IM maintained slightly higher (by 0.23 mumol/g) absolute ATP levels than C/OM tissues (normal ATP value = 8.7 mumol/g). By 45 min, significant differences in regional ATP levels did not exist. Striking regional catabolite differences were apparent at both 15 and 45 min. Most prominent were: (1) intrarenal purine base/inosine gradients, levels falling approx. 22-50% from C to IM; and (2) preferential OM AMP/IMP/adenosine accumulation. To assess whether more homogeneous results might be found in rabbit kidney, possibly making this animal preferable to rats for studies of renal ischemia, rabbit C, OM and IM adenylate pools were analyzed after 15 min of ischemia. C vs. IM ATP differences were greater (approx. 1.3 mumol/g) and large catabolite concentration differences were still apparent. CONCLUSIONS (1) anaerobic mechanisms support IM ATP levels during ischemia but, in terms of normal concentrations, the impact is small, particularly in the rat; and (2) marked regional differences in adenylate catabolite levels exist within ischemic kidneys. These need to be recognized when analyzing adenylate pool responses in ischemic ARF.