Pierre Lafolie

Chiral analysis of methadone in plasma by high-performance liquid chromatography.

A method for the chiral high-performance liquid chromatographic analysis of methadone in plasma has been developed. The method employed organic solvent extraction, enantiomeric separation on a Chiral AGP column, and ultraviolet absorption detection at 212 nm. The intra-day variation in the quantification of methadone enantiomers was less than 9% at the 100 ng/ml level, and the values obtained correlated well with those from a gas chromatographic-mass spectrometric method. Results from patients indicate inter- and intra-individual differences in the ratio between l- and d-methadone in plasma during therapy with racemic methadone. In one patient, a higher level of d-methadone in plasma was caused by both faster elimination and lower bioavailability of l-methadone.

6-mercaptopurine plasma levels in children with acute lymphoblastic leukemia: relation to relapse risk and myelotoxicity.

Plasma levels of 6-mercaptopurine were determined in 22 consecutive children with acute lymphoblastic leukemia on oral remission maintenance therapy during the time period of August 1984 to January 1988. Each child received the drug once daily for up to 3 years and was studied repeatedly (1–12 times). An HPLC method was used for drug analysis. We found large interpatient variations in the mean peak plasma concentration (range of 50–424 ng/ml) and in the mean area under the concentration vs. time from 0–4 h curve (range of 82–637 ng ml-1 h). There were also pronounced variations between different sampling occasions in the same patient. Nine of the 22 patients had complications during the maintenance therapy. Five children with a mean peak plasma level below 135 ng/ml and a mean area under the curve (AUC) value below 251 ng ml-1 h relapsed (three in the central nervous system and two in the bone marrow). Both children with a bone marrow relapse died. Relapse risk was related to the AUC (p < 0.05). Four children with a mean peak plasma level above 166 ng/ml and a mean AUC value above 363 ng/ml/h developed severe myelotoxicity, which necessitated a temporary cessation of the maintenance therapy. In addition, two patients relapsed 6 and 11 months after termination of maintenance therapy. Their mean peak and AUC values were not low but the concentrations decreased markedly towards the end of the maintenance period. The results indicate that the plasma levels of 6-mercaptopurine, when determined repeatedly, might be of significance for the outcome of the remission maintenance treatment.

Immunological screening of benzodiazepines in urine : improved detection of oxazepam intake

Immunological screening analysis of benzodiazepines in urine using the EMIT (enzyme multipled immuno-technique) and FPIA (fluorescence polarization immunoassay) techniques does not reliably detect the intake of therapeutic doses of oxazepam. In 23 patient urine samples, in which the presence of oxazepam could be verified chromatographically, only about 50% were detected as positive in the immunoassay systems. However, when the screening procedure was modified to include a simple step of hydrolysis of urine using the enzyme beta-glucuronidase to liberate conjugated oxazepam, improved detection of oxazepam intake was achieved. With EMIT 95% and with FPIA 100% of the samples were detected as positive. Since oxazepam arises in vivo also as a metabolite of other common benzodiazepines, the modification will most likely contribute to the generally improved detection of benzodiazepines.

Exchange of Cerebrospinal Fluid in Accidental Intrathecal Overdose of Cytarabine

SummaryIntrathecal cytarabine (cytosine arabinoside) is included in many protocols for the treatment of acute lymphoblastic leukaemia of childhood. We report here the accidental administration of 200mg cytarabine intrathecally to a 4-year-old boy with CNS relapse. After the overdose the patient had dilated pupils during the first hour. One month later an unsteady gait and mild intention tremor in the hands were noted.By the exchange of cerebrospinal fluid with isotonic saline started 1 hour after overdose through a lumbar needle, about 27% of the administered dose was recovered. The estimated recovery in view of the time elapsed between overdose and start/end of the exchange procedure was 36%. This indicates that this procedure is of value in managing patients with heavy overdose of intrathecal cytarabine in hospitals without neurosurgical facilities.

Monitoring of plasma methadone : intercorrelation between immunoassay and gas chromatography-mass spectrometry

Determination of plasma methadone is essential in connection with dose adjustments for patients participating in methadone maintenance programs. We successfully adapted the existing fluorescence polarization immunoassay (FPIA) kit intended for urinary methadone to plasma assays. A concentration interval of 50–900 ng/ml could be covered. The coefficient of variation was less than 7%, and the limit of detection below 50 ng/ml. The intercorrelation between the immunoassay and a specific gas chromato-graphic-mass spectrometric (GC-MS) method was studied in samples from 19 heroin addicts in methadone maintenance treatment. A total number of 97 plasma samples with a concentration range of 31–842 ng/ml were used. The slope and intercept of the regression line (CFPIA = 0.93 x CGC-MS + 15) was in good agreement with the theoretical relation (CFPIA = CGC-MS), with a coefficient of correlation of 0.978. The mean ratio, in quantitative result, between the techniques (CFPIA/CGC-MS) was 1.03 ± 0.01 (SEM). We conclude that the immunoassay proposed in this study can be safely used in patients participating in methadone maintenance programs.

Variability of 6-mercaptopurine pharmacokinetics during oral maintenance therapy of children with acute leukemia

The effects of some environmental and genetic factors on the inter- and intraindividual variations of 6-mercaptopurine (6-MP) pharmacokinetics were studied in children on oral remission maintenance therapy for acute lymphoblastic leukemia or non-Hodgkin’s lymphoma. Blood samples were obtained 0–4 h after drug intake. 6-MP concentrations were determined in plasma and in erythrocyte concentrates. The influence of food on the pharmacokinetics was examined in a prospective study of 15 children. Each child was examined four times, twice in the fasted state and twice after intake of a standardized, milky, breakfast. There were pronounced inter- and intraindividual variations. Food intake seemed to reduce these variations but there were no significant changes in peak concentrations and area under the plasma concentration vs time curves (AUC) between the fasted and fed states. Food intake reduced the time to peak concentration both in plasma, from 1.8 h to 1.1 h (P < 0.01) and in red blood cells, from 1.8 h to 1.3 h (P < 0.01). Retrospective subdivision of the patients indicated a tendency for different pharmacokinetic patterns according to dose; five out of seven patients receiving > 70 mg m−2 had a higher AUC in the fasting state, while five out of eight patients receiving <70 mg m−2 had a higher AUC in the fed state. The cytochrome P-450-dependent hydroxylation capacity was evaluated with debrisoquine but no correlation was found to the pharmacokinetics of 6-MP.

Determination of plasma azathioprine and 6-mercaptopurine in patients with rheumatoid arthritis treated with oral azathioprine.

Two specific high-performance liquid chromatography methods for determining plasma concentrations of azathioprine and 6 mercaptopurine after oral administration of azathioprine are presented. It was shown that azathioprine is unstable in the blood samples unless immediately cooled in ice water. The 2-amino analog, guaneran, was used as internal standard for azathioprine, which was extracted from plasma with ethylacetate. A Nucleosil C18 column was used for the separation. The detection limit was 6 nM. For quantification of 6-mercaptopurine, 6-thioguanine was used as internal standard. Plasma was deproteinized with HC104 and the sample was purified on mercurial cellulose. A Beckman ODS column was used and the detection limit was 5 nM. Phar-macokinetic data from two patients are presented. Unchanged azathioprine was seen until 6 h after an oral dose of 32 mg/m2.

6-Mercaptopurine in cerebrospinal fluid during oral maintenance therapy of children with acute lymphoblastic leukemia

In three children receiving oral remission maintenance therapy for acute lymphoblastic leukemia, the concentrations of 6-mercaptopurine (6-MP) in cerebrospinal fluid (CSF), plasma and red blood cells were compared. CSF samples were obtained from an Ommaya reservoir previously inserted for treatment of CNS relapse. At the time of the study, the children were all in remission and had been on oral 6-MP (42–63 mg m−2) once daily for at least 24 weeks. Immediately before dose intake on the day of study (about 24 h after last dose), the concentrations of 6-MP in CSF, plasma and red blood cells were rather similar and below 20 ng ml−1 in all patients. After dose intake, the concentrations in plasma and in red blood cells increased to 40–200 ng nl−1 within 0.5–4 h. In contrast, the concentration of 6-MP in the CSF remained fairly constant around 4–10 ng ml−1 throughout the time period studied (up to 4 h). It is concluded that 6-MP can be detected in CSF during oral maintenance therapy and that the drug has different pharmacokinetic profile in CSF to that in plasma and red blood cells. Further studies are necessary to evaluate the significance of the 6-MP concentrations obtained in CSF for the prevention of CNS relapse.