The effect of busulphan on the pharmacokinetics of cyclophosphamide and its 4-hydroxy metabolite: time interval influence on therapeutic efficacy and therapy-related toxicity.

Busulphan and cyclophosphamide (Bu/CP) are widely used in preparative regimens for bone marrow transplantation. Many studies have shown a wide variation in busulphan pharmacokinetics. Moreover, higher rates of liver toxicity were reported in Bu/CP protocols than in a total body irradiation (TBI)-containing regimen. In the present paper we investigated the effect of the time interval between the last dose of busulphan and the first dose of cyclophosphamide on the pharmacokinetics of CP and its cytotoxic metabolite 4-hydroperoxycyclophosphamide (4-OHCP). Thirty-six patients undergoing bone marrow transplantation (BMT) were included in the study. We also investigated the occurrence of veno-occlusive disease, mucositis and graft-versus-host disease. Ten patients conditioned with CP followed by TBI served as a control group (TBI). Twenty-six patients were conditioned with Bu/CP. The patients received Bu (1 mg/kg x 4 for 4 days), followed by CP (60 mg/kg for 2 days) administered as a 1-h infusion. Patients received their CP therapy either 7-15 h (group A, n = 12) or 24-50 h (group B, n = 14) after the last dose of Bu. None of the patients were given phenytoin or any other drug known to enhance CP metabolism. The administration of CP less than 24 h after the last dose of Bu resulted in: (1) a significantly (P = 0.003) lower clearance for cyclophosphamide was observed in group A (0.036 l/h/kg) compared to 0.055 and 0.055 l/h/kg, in the B and TBI groups, respectively; (2) significantly (P = 0.002) longer elimination half-life in group A (10.93 h) than in groups B and TBI (6.87 and 7.52 h, respectively); (3) significantly (P < 0.001) lower exposure to the cytotoxic metabolite (4-OHCP), expressed as the ratio AUC4-OHCP/AUCCP, in group A (0.0053) than that obtained in group B (0.013) and group TBI (0.012); (4) the patients in group A had a significantly (P < 0.05) higher incidence of VOD (seven of 12) than the other groups, B and TBI (2/14 and 1/10, respectively); and (5) mucositis was significantly higher in group A patients (8/12), being seen in only one patient in group B and none in the TBI group. The present study has shown that the interval between busulphan and cyclophosphamide administration can negatively affect the pharmacokinetics of cyclophosphamide and its cytotoxic metabolite. We conclude that the timing of CP administration must be considered in order to improve drug efficacy and reduce conditioning-related toxicity.

Determination of 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione in plasma by direct injection into a coupled column liquid chromatographic system.

The chemical substance 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC) is in clinical use for the treatment of hereditary tyrosinemia type 1. In the present study, the plasma concentration of NTBC was determined by a coupled column liquid chromatographic method. A 20-microl volume of plasma was diluted with phosphate buffer, pH 2, and injected into a small precolumn (BioTrapAcid C18) with a mobile phase containing sulfuric acid. The precolumn was based on the restricted access principle, i.e., retention of NTBC within the lipophilic pores, while polar and large endogenous compounds were eluted with the void volume. NTBC was transferred to the analytical column using a mobile phase with a high content of acetonitrile. The compound was monitored by UV detection at 278 nm. The standard curve was linear between 0.3 and 69 microM, and the between-day precision (RSD) was 3% (n=6 days) at 13.8 microM and 14% (n=6 days) at 0.3 microM NTBC in plasma. The quantitation limit was approximately 0.3 microM using 20 microl of plasma.