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  • CYP 3A4; side-chain oxidation  (1)
  • age  (1)
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  • 1
    ISSN: 1432-1041
    Keywords: Propafenone ; Renal failure ; glucuronides ; age ; antiarrhythmic drug ; plasma levels ; stereoisomers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Abstract The aim of this study was to investigate the disposition of propafenone and its Phase I and II metabolites in relation to kidney function under steady-state conditions. The mechanism of the renal handling of propafenone glucuronides (filtration, secretion) was also examined. Racemic (R/S) propafenone was administered to 7 young volunteers, to 5 older patients with a normal glomerular filtration rate and to 4 patients with chronic renal failure. No difference was found in the plasma concentrations of propafenone and 5-hydroxypropafenone between the three groups. The propafenone glucuronide (PPFG) concentration was elevated in the older compared to the younger subjects (S-PPFG: 544 vs. 222 nmol · ml−1 · mol−1; R-PPFG: 576 vs. 304 nmol · ml−1 · mol−1). Although Glomerular filtration rate did not differ, the renal clearance of propafenone glucuronides was reduced in the former group, which could be attributed to their impaired renal secretion. A dramatic increase in propafenone glucuronide concentration was observed in the patients with renal failure (S-PPFG: 2783 nmol · ml−1 · mol−1; R-PPFG: 7340 nmol · ml−1 · mol−1). In summary, the disposition of propafenone and of its active metabolite 5-hydroxypropafenone was not affected by kidney dysfunction, indicating that no dose adjustment is necessary in patients with renal failure. The accumulation of drug glucuronides in older patients with apparently normal kidney function should be taken into account as a possible factor modifying drug therapy.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    European journal of clinical pharmacology 51 (1996), S. 297-301 
    ISSN: 1432-1041
    Keywords: Key words Cyclophosphamide ; CYP 3A4; side-chain oxidation ; dechloroethylcyclophosphamide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Abstract Objective: Cyclophosphamide (CP) is an antineoplastic prodrug which requires bioactivation (4-hydroxylation) by the cytochrome P450 (CYP) enzymes in human liver. In parallel, P450-mediated side-chain oxidation (N-dealkylation) leads to the formation of the non-alkylating dechloroethylcyclophosphamide (DCl-CP) and chloroacetaldehyde, the latter being a potential neurotoxic agent. The enzyme responsible for side-chain oxidation has not been identified yet. We therefore used an in vitro approach to characterize the enzyme involved in N-dealkylation of CP. Methods: CP was incubated with the microsomal fraction of human liver in the presence of specific inhibitors for some P450 enzymes and in the presence of stable expressed P450 enzymes. Dechloroethylcyclophosphamide was analysed using gas chromatography and nitrogen-phosphorus detection. Results: Formation of DCl-CP increased linearly with substrate concentration over the entire concentration range (20 μmol ⋅ l−1 to 36 mmol ⋅ l−1). Saturation of the enzyme was not observed. Incubation with stable expressed P450 enzymes and inhibition experiments indicated that CYP 3A4 was the major enzyme involved in side-chain oxidation of CP. Conclusions: Our in vitro data indicate that side-chain oxidation of CP occurs in dose-dependent fashion in men with no saturation of this pathway even following dose escalation. Thus enhanced neurotoxicity following CP administration may result in the setting of high-dose chemotherapy. Moreover, we conclude that CP has the potential to interact with other CYP 3A4 substrates.
    Type of Medium: Electronic Resource
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