Inger Wallin

Pharmacokinetics of high-dose busulphan in relation to age and chronopharmacology

SummaryBusulphan levels in plasma were measured in 27 patients during conditioning therapy (1 mg/kg×4 for 4 days) before bone marrow transplantation. The mean minimal concentration found in children aged <5 years (237 ng ml−1) was lower than that observed in adults or older children (607 and 573 ng ml−1, respectively). The AUC for the last dose was significantly lower in young children (2,315 h ng ml−1) than in adults or older children (6,134 and 5,937 h ng ml−1, respectively). The elimination half-life for the last dose in young children was shorter (2.05 h) than that in either adults (2.59 h) or older children (2.79 h). When the AUC was normalized for body surface area, the difference between young children and the other groups was smaller but remained statistically significant. The total body clearance was significantly higher in young children (7.3 ml min−1 kg−1) as compared with both older children and adults (3.02 and 2.7 ml min−1 kg−1, respectively). The plasma levels of busulphan showed circadian rhythmicity, especially in young children. The concentration measured during the night in some patients was up to 3-fold that observed during daytime. We conclude that the busulphan dosage for children must be reconsidered and that further studies are urgently needed to develop an optimal therapy.

Pharmacokinetic and metabolic studies of high-dose busulphan in adults

SummaryThe pharmacokinetics of high-dose busulphan was studied in adult patients with acute myeloblastic leukaemia after oral doses of 1 mg·kg−1 every 6 h for 4 days.The mean steady-state plasma concentration was 1080 ng/ml−1 during the treatment. Individual steady-state concentrations after the last dose on average were 32% lower than those predicted from total AUC measurements following the first dose. Mean elimination half-life in plasma was 2.3 h after the last dose and 3.4 h after the first dose which suggests that busulfan may increase its own metabolic rate on repeated treatment.The cerebrospinal fluid/plasma concentration ratio of busulphan was 1.3. Busulphan showed insignificant protein binding in plasma (7.4%). About 2% of the dose was excreted unchanged in the urine.For the first time sulpholane, 3-hydroxysulpholane and tetrahydrothiophene 1-oxide were identified as urinary metabolites of busulphan in man.

Influence of prophylactic anticonvulsant therapy on high-dose busulphan kinetics

The pharmacokinetics of high-dose busulphan was studied in 17 patients during conditioning prior to bone marrow transplantation using deuterium-labeled busulphan (d8-BU). About 50% of busulphan doses 1 and 16 was replaced with d8-BU. Patients were treated with phenytoin or diazepam as prophylactic anticonvulsant therapy. Patients who received phenytoin demonstrated significantly higher clearance (mean ±SD, 3.32±0.99 ml min−1 kg−1), a lower area under the concentration-time curve (AUC, 5,412±1,534 ng h ml−1; corrected for dose/kilogram) and a shorter elimination half-life (3.03±0.57 h) for the last dose of d8-BU (dose 16) as compared with the first dose (2.80±0.78 ml min−1 kg−1, 6,475±2,223 ng h ml−1 and 3.94±1.10 h, respectively). No difference in the above-mentioned pharmacokinetic parameters was seen in patients treated with diazepam. Moreover, a continuous decrease in the steady-state level of busulphan was observed in four of seven patients in the phenytoin-treated group, whereas in the diazepam group, such a decrease was seen in only one of eight patients. We conclude that phenytoin used as prophylactic anticonvulsant therapy alters busulphan pharmacokinetics and, most probably, its pharmacodynamics. For adequate prophylactic therapy, anticonvulsants with fewer enzyme-inductive properties than phenytoin should be used.

Cisplatin and Oxaliplatin Toxicity: Importance of Cochlear Kinetics as a Determinant for Ototoxicity

Background Cisplatin is a cornerstone anticancer drug with pronounced ototoxicity, whereas oxaliplatin, a platinum derivative with a different clinical profile, is rarely ototoxic. This difference has not been explained. Methods In HCT116 cells, cisplatin (20 μM)-induced apoptosis was reduced by a calcium chelator from 9.9-fold induction (95% confidence interval [CI] = 8.1- to 11.7-fold), to 3.1-fold induction (95% CI = 2.0- to 4.2-fold) and by superoxide scavenging from 9.3-fold (95% CI = 8.8- to 9.8-fold), to 5.1-fold (95% CI = 4.4- to 5.8-fold). A guinea pig model (n = 23) was used to examine pharmacokinetics. Drug concentrations were determined by liquid chromatography with post-column derivatization. The total platinum concentration in cochlear tissue was determined by inductively coupled plasma mass spectrometry. Drug pharmacokinetics was assessed by determining the area under the concentration–time curve (AUC). Statistical tests were two-sided. Results In HCT116 cells, cisplatin (20 μM)-induced apoptosis was reduced by a calcium chelator from 9.9-fold induction (95% confidence interval [CI] = 8.1- to 11.7-fold to 3.1-fold induction) (95% CI = 2.0- to 4.2-fold) and by superoxide scavenging (from 9.3-fold, 95% CI = 8.8- to 9.8-fold, to 5.1-fold, 95% CI = 4.4- to 5.8-fold). Oxaliplatin (20 μM)-induced apoptosis was unaffected by calcium chelation (from 7.1- to 6.2-fold induction) and by superoxide scavenging (from 5.9- to 5.6-fold induction). In guinea pig cochlea, total platinum concentration (0.12 vs 0.63 μg/kg, respectively, P = .008) and perilymphatic drug concentrations (238 vs 515 μM × minute, respectively, P < .001) were lower after intravenous oxaliplatin treatment (16.6 mg/kg) than after equimolar cisplatin treatment (12.5 mg/kg). However, after a non-ototoxic cisplatin dose (5 mg/kg) or the same oxaliplatin dose (16.6 mg/kg), the AUC for perilymphatic concentrations was similar, indicating that the two drugs have different cochlear pharmacokinetics. Conclusion Cisplatin- but not oxaliplatin-induced apoptosis involved superoxide-related pathways. Lower cochlear uptake of oxaliplatin than cisplatin appears to be a major explanation for its lower ototoxicity.

D-Methionine and cisplatin ototoxicity in the guinea pig: D-methionine influences cisplatin pharmacokinetics

D-Methionine has recently been advocated as a protectant against cisplatin toxicity. The use of systemic D-methionine as a protector was studied in 58 guinea pigs. Kinetics and distribution of [11CH(3)]D-methionine was analysed by positron emission tomography. Cisplatin and the monohydrated complex of cisplatin was quantified in blood ultrafiltrate using reversed-phase liquid chromatography with post-column derivatisation. Administration of 300 mg/kg of D-methionine caused a 30% decrease in the area under the concentration-time curve (AUC) of cisplatin. The toxic effect of cisplatin was studied after dose adjustment of cisplatin, i.e. with similar cisplatin AUC in the group receiving D-methionine and the saline control group. A significant ototoxic effect, measured as difference in pre- and 96 h post-treatment electrophysiological hearing threshold (auditory brainstem response), was observed at stimulus frequencies of 30 and 20 kHz. There was no difference between the groups in the extent of threshold shift. Quantitative outer hair cell counts showed a similar loss of cells in the two groups. All animals had a significant increase in plasma-creatinine but there was no difference between the groups. The results indicate that protection from cisplatin ototoxicity by systemic D-methionine can be explained by a lowered systemic exposure to the drug.

Pharmacokinetics of oxaliplatin in humans.

Oxaliplatin is a novel platinum complex used for the treatment of metastatic colorectal carcinoma. The pharmacokinetics of the free fraction of oxaliplatin in blood were evaluated in 10 patients given 85 mg/m2 of oxaliplatin using an infusion time of 2 h. Blood samples were collected during and after the infusion and immediately placed on ice. The samples were ultrafiltrated centripetally and the concentration of oxaliplatin in the ultrafiltrate was determined by liquid chromatography in combination with postcolumn derivatization. The in vitro degradation rate was determined in blood from the patients taken immediately before drug administration.The maximal blood concentration (Cmax) and terminal half-life (t1/2) were 1.44±0.20 (SD) µg/mL and 14.1 min (range: 10.2–24.5), respectively. The area under the blood concentration time curve (AUC), clearance (CL), and distribution volume (Vss) were (means±SD) 161±22 µg min/mL, 32.1±4.2 L/h/m2, and 0.26±0.06 L/kg, respectively. There was a significant correlation between the clearance of oxaliplatin in the patients and the degradation rate in whole blood (r=0.746; p=0.017).Oxaliplatin has a short elimination half-life, which is in a sharp contrast to previously reported elimination half-lives obtained by analysis of the platinum content in plasma and ultrafiltrate. The correlation between in vivo and in vitro data suggests that the degradation in whole blood plays a role for the elimination of the drug.

Oxaliplatin Degradation in the Presence of Chloride-Identification and Cytotoxicity of the Monochloro Monooxalato Complex

AbstractPurpose. To study the degradation of oxaliplatin in chloride media and evaluate the cytotoxicity of oxaliplatin in normal and chloride-deficient medium. Methods. The products of the reaction of oxaliplatin with chloride were separated on a Hypercarb S column with a mobile phase containing 40% methanol in 0.05 M ammonia and subjected to electrospray ionization mass spectrometry. The cytotoxicity of oxaliplatin in normal and chloride-deficient medium was evaluated by 30-min incubations on human colon adenocarcinoma cells (HT-29). Results. We identified a new intermediate degradation product, the monochloro monooxalato complex ([Pt(dach)oxCl]−) and the final product, the dichloro complex (Pt(dach)Cl2), by liquid chromatography-mass spectrometry. [Pt(dach)oxCl]− was found as the negative ion, M−, at m/z 431, and the positive ion, [M+2H]+, m/z 433. Pt(dach)Cl2 was found as the negative ion, [M-H]−, m/z 377, and the positive ion, [M+NH4]+, m/z 396. The fast initial degradation of oxaliplatin can be coupled to the fast formation of [Pt(dach)oxCl]−. In the cytotoxic assay, the cell survival was not affected by the chloride levels. Conclusions. [Pt(dach)oxCl]−, a new transformation product of oxaliplatin, has been identified. Its in vitro cytotoxic effect does not appear to exceed that of oxaliplatin.

Stability of 5-aminolevulinic acid in aqueous solution

The chemical stability of 5-aminolevulinic acid (ALA) was studied in aqueous solution as a function of concentration, pH, temperature and in the presence of ethylenediaminetetraacetic acid (EDTA). The degradation of ALA was followed by reversed-phase liquid chromatography using a pH where ALA is protonated (pKa1=3.90; pKa2=8. 05, as determined potentiometrically). ALA was degraded by a reaction following second order kinetics. Stock solutions of 1% (60 mM) ALA were incubated at 50 degrees C. At pH 2.35, ALA was stable during the whole incubation period (37 days). The half-lives for the second-order decomposition of 1% ALA at pH 4.81 and 7.42 were 257 and 3.0 h, respectively. The degradation rate increased about 1.5 times with each 10 degrees C rise in temperature at pH 7.53 within the range studied (37-85 degrees C). The energy of activation, Ea, for the second-order decomposition of ALA was 43.7 kJmol-1. EDTA did not influence the degradation of ALA when a mixture of 1% ALA and 1% EDTA was incubated at pH 7.42.

Cisplatin-induced hearing loss: influence of the mode of drug administration in the guinea pig.

Cisplatin (8 mg/kg) was given intravenously to guinea pigs either as a 15 s bolus injection (25 animals) or as a 1 h infusion (28 animals). To determine the influence of the mode of cisplatin administration and pharmacokinetics on the ototoxic side-effect, the concentrations of cisplatin and the biotransformation product monoaquated cisplatin were determined in blood ultrafiltrate using liquid chromatography with post-column derivatization. Ototoxic effect was evaluated as difference in pre- and 96 h post-exposure auditory brainstem response (ABR) threshold. The cisplatin peak concentration was considerably higher, 19.2+/-2.4 microg/ml, in the bolus injection group than in the infusion group, 6.7+/-0.5 microg/ml (mean+/-S.E.M.). The area under the blood ultrafiltrate concentration time curve (AUC) for cisplatin was slightly greater in the infusion group, 442+/-26 microg/ml/min, than in the bolus injection group, 340+/-5 microg/ml/min. For monoaqua cisplatin, the AUC was not different between the groups (bolus injection: 30.8+/-1. 5 microg/ml/min, infusion: 34.1+/-3.3 microg/ml/min). A significant ototoxic effect was observed in both groups at 20 and 12.5 kHz, but there was no difference between the groups in the extent of threshold shift. The interindividual variability in susceptibility to ABR threshold shift was far greater than the variability in pharmacokinetics, suggesting that other factors are more important in determining the degree of hearing loss.

Determination of 8-methoxypsoralen in plasma by electron capture gas chromatography.

A method is given for the determination of 8-methoxypsoralen in human plasma at the low ng/ml level using gas chromatography with electron capture detection. 8-Methoxypsoralen was extracted from plasma with methylene chloride at pH 7.0. After addition of the internal standard, 8-butoxypsoralen, the psoralens were hydrolysed in sodium hydroxide and the aqueous phase was purified by extraction with methylene chloride and toluene. The aqueous phase was acidified and the re-lactonized psoralens were extracted with toluene and analysed. Some determinations of plasma levels of 8-methoxypsoralen after oral administration are presented.