Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.6.1.1 (aspartate aminotransferase)
 21,665 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The disposition of total and non-protein-bound etoposide was investigated in 21 cancer patients receiving etoposide and cisplatin combination chemotherapy. Etoposide plasma concentrations were determined using a specific high-performance liquid chromatography (HPLC) method, and etoposide plasma protein binding was determined by equilibrium dialysis. The patients had a wide range of renal function (creatinine clearance, 32 to 159 mL/min/m2) and hepatic function (total bilirubin range, 0.3 to 21.5 mg/dL; aspartate aminotransferase [AST] range, 14 to 415 IU/L; serum albumin range, 2.7 to 4.1 g/dL). The mean etoposide total systemic clearance was not different in 15 patients with total bilirubin less than 1.0 mg/dL versus six patients with total bilirubin 1.1 to 21.5 mg/dL (18.7 +/- 5.9 mL/min/m2 v 26.4 +/- 10.7 mL/min/m2; t-test P = .06), with a trend toward higher total clearance in the patients with abnormal bilirubin values. However, the mean clearance of unbound etoposide was significantly lower in patients with increased total bilirubin (220 +/- 90 mL/min/m2 v 135 +/- 61 mL/min/m2; t-test P = .027). The fraction of etoposide unbound (fu) in plasma was significantly higher in patients with increased bilirubin (9% +/- 3% v 27% +/- 15%; t-test P = .002), explaining the trend toward higher total clearance in these patients. Etoposide clearance (total or unbound) in the 14 patients with measurable hepatic metastases was not different from the clearance in the seven patients without hepatic metastases. This study provides an explanation for why patients with increased bilirubin do not have lower total systemic clearance of etoposide, and indicates that such patients have a higher exposure to unbound etoposide. The results of ongoing pharmacodynamic studies of total and unbound etoposide in patients with increased bilirubin will determine the clinical relevance of altered etoposide protein binding.
 ...
PMID:Changes in the clearance of total and unbound etoposide in patients with liver dysfunction. 223 Aug 75

Etoposide is a schedule-dependent cytotoxic drug with high single agent activity in small-cell lung cancer and lymphoma. Despite its clear dose-dependent myelosuppressive activity, dose-dependent evidence of its anti-tumour activity is harder to demonstrate. A number of reports have correlated haematological toxicity with pharmacokinetic and physiological parameters, which explains some of the variability in dynamic effects that exists between patients. Recent reports have also suggested that anti-tumour response may be related to plasma etoposide concentration. In our own studies we have investigated factors that influence the pharmacodynamic effects of etoposide, principally with regard to haematological toxicity, and these studies have highlighted a number of patient groups who are at risk. Impaired renal function causes a reduction in clearance of etoposide, resulting in increased systemic exposure and more profound myelotoxicity. A 30% dose reduction in this group is recommended to normalise the area under the plasma concentration-time curve (AUC). Patients with low serum albumin concentrations (< 35 g/l) also showed significantly worse haematological toxicity, but with no apparent change in total drug pharmacokinetics. There was, however, an increase in the free drug fraction in this group due to decreased protein binding, such that the free drug AUC was similar to that found in patients with renal dysfunction. This would also indicate that a dose reduction of around 30%-40% is required in this patient group. Patients with normal albumin levels but liver enzyme values (aspartate transaminase or gamma-glutamyl transpeptidase) more than 3 times the upper limit of normal also had a less marked but significant increase in neutropenia. In patients with normal organ function, age was the only significant factor in predicting the degree of leukopenia/neutropenia, and increasing age was also associated with decreasing drug clearance and an increase in drug AUC. A small dose reduction and/or careful monitoring is required in this patient group. Further studies are required to elucidate further the relationship between the pharmacokinetics of etoposide and its pharmacodynamics, particularly with regard to anti-tumor activity, and to determine the role of individualised therapy, based on a pharmacokinetic parameter, in reducing the dynamic variability and optimising the use of this drug.
 ...
PMID:Etoposide dosage and pharmacodynamics. 807 31