Liquid chromatographic analysis of mesna and dimesna in plasma and urine of patients treated with mesna

We describe in this report an expedient and accurate liquid chromatographic method for measurement of mesna and dimesna in plasma and urine. The separation of mesna and the internal standard (p-aminobenzoic acid, IS) was achieved on a 10-microns, 8 mm (i.d.) x 10-cm C18-Resolve cartridge in conjunction with radial compression system. An aqueous solution of sodium citrate (0.1 M), tetrabutyl ammonium phosphate (0.001 M), and triethylamine (1:10,000, vol/vol), adjusted to pH 5 with 85% phosphoric acid was used at a flow rate of 2 ml/min as a mobile phase. The compounds were detected in the effluent electrochemically at +450 mV. After an appropriate amount of IS was added, the plasma sample (100 microliters or fraction thereof) was deproteinized with an equal volume of 0.0825 M sulfuric acid containing sodium hexametaphosphate (1.25% wt/vol), whereas urine was diluted 1:50 with water and mixed 1:1 with an aqueous solution of sodium hexametaphosphate (1.25% wt/vol). Dimesna was reduced back to mesna with sodium borohydride before analysis of the total mesna. The peak height ratio (drug/IS) varied linearly with the concentration, and the correlation coefficient was > 0.992 for both mesna and dimesna. The intrarun precision at different concentrations of mesna was equally good and the coefficient of variation was consistently < 4.5%. No interference from endogenous substances or any concomitantly used drug was observed. This assay is currently being used for measurement of mesna and dimesna in plasma of bone marrow recipients who receive high doses of cyclophosphamide.

A comparison of three ported cannulae available in New Zealand

A comparison was made of the three 22-gauge ported intravenous cannulae available in New Zealand--Venflon 2, Vasofix Braunule and Insyte. All cannulae performed satisfactorily in terms of overall success of cannulation although significant differences were apparent in both clinical and laboratory performance. Anaesthetists' clinical preference was for Insyte and Venflon 2 brands, perceiving these to have greater ease of handling and better packaging. In a series of laboratory studies, Vasofix was found to have the highest flowrate, the fastest time to flashback and the lowest valve opening pressure. Insyte required the least force of penetration. Venflon 2 had the greatest margin of safety between pressure to inject through the port and pressure required to blow the syringe/port assembly apart. Potential problems were identified with the Insyte port valve mechanism.

Effect of orotic acid on in vivo DNA synthesis in hepatocytes of normal rat liver and in hepatic foci/nodules

One of the proposed mechanisms by which orotic acid (OA) promotes liver carcinogenesis is by differentially mito-inhibiting the normal hepatocytes while permitting the initiated ones to respond to growth stimuli to form foci/nodules. In an attempt to examine this hypothesis, the present study was designed to determine (i) whether OA inhibits DNA synthesis in normal hepatocytes in vivo, and (ii) whether hepatocytes from hepatic foci/nodules are relatively resistant to the mito-inhibitory effects of OA. The results of this study indicate that OA given i.p. as a tablet of 300 mg at the time of partial hepatectomy (PH) almost completely inhibited liver DNA synthesis. Three days later--a time period by which the implanted tablet disappeared--the hepatocytes resumed DNA synthesis. Exposure to OA results in an accumulation of uridine nucleotides and a decrease in adenosine nucleotides. Creation of such an imbalance in nucleotide pools appears to be important for OA to inhibit DNA synthesis. Adenine (a tablet of 300 mg), an agent that inhibits the metabolism of OA to uridine nucleotides, counteracted the mito-inhibitory effects of OA. To determine whether the hepatocytes in foci/nodules are resistant to the mito-inhibitory effects of OA, rats were initiated with diethylnitrosamine (DENA; 150 mg/kg) and promoted by the resistant-hepatocyte model. Fourteen weeks after the administration of DENA, the rats were subjected to PH in the presence of absence of OA (300 mg tablet). The results indicated that, in contrast to hepatocytes in normal or surrounding non-nodular liver, a subpopulation of hepatocyte foci/nodules appear to be relatively resistant to the mito-inhibitory effects of OA. These findings support the hypothesis that differential mito-inhibition is a possible component in the promoting effect of OA. However, whether this is the mechanism by which OA promotes liver carcinogenesis needs to be further investigated.

Impaired elimination of atenolol in a nephropathic patient with self-medication overdose

A case of intoxication with atenolol (plasma concentration of 2.71 mg/L) caused by an improper self-medication combined with impaired renal function is presented. The patient was supported with atropine, isoproterenol, dopamine, and dobutamine, and a thorough pharmacokinetic monitoring of atenolol was conducted. As the serum creatinine concentration returned slowly to baseline with good diuresis, the concentration of atenolol decreased (biologic half-life = 2.95 days) and the blood pressure gradually recovered. The patient improved and was subsequently discharged in good health. Had pharmacokinetic monitoring of atenolol not been performed, hemodialysis would have been indicated.

Alteration of taurine homeostasis in acute heatstroke

OBJECTIVE

To investigate the potential role of taurine as a hypothermic modulator during heatstroke.

DESIGN

Prospective analyses.

SETTING

Heatstroke Center in makkah, Saudi Arabia.

PATIENTS

Twenty-nine adult patients with heatstroke.

INTERVENTIONS

High-performance liquid chromatography was used to measure plasma and urine taurine concentrations in heatstroke patients on admission (precooling) and 24 hrs after complete cooling (postcooling).

MEASUREMENTS AND MAIN RESULTS

There were 18 males and 11 females with a mean rectal temperature of 42.2 +/- 0.14 degrees C. At the precooling time period, the taurine concentrations were increased (plasma 180 +/- 14 mumol/L; urine 4142 +/- 720 mumol/L [normal ranges 45.5 to 138.2 and 168 to 1890 mumol/L, respectively]). At the postcooling time period, taurine concentrations were significantly (p < .0001) decreased (54 +/- 6 and 802 +/- 160 mumol/L for plasma and urine, respectively). No correlation was found between taurine and creatine kinase activity, or between precooling temperature and taurinemia or taurinuria.

CONCLUSIONS

The source and clinical significance of the increased taurine concentrations are to be determined. The involvement of taurine in the regulation of core body temperature suggests that it may have an adaptive role in heatstroke.

An expedient liquid chromatographic micromeasurement of isoniazid in plasma by use of electrochemical detection

We describe a sensitive and expedient microassay of isoniazid in plasma by use of electrochemical detection in conjunction with a radial compression liquid chromatography. Diphenylcarbazide was used as an internal standard and the separation was achieved on a 10-micron, 8 mm x 10 cm C18 (12% carbon load) cartridge. A mixture of 10 mM sodium dibasic phosphate solution (adjusted to pH 7 with phosphoric acid) and methanol (93.5:6.5, by volume) was used as a mobile phase at a flow rate of 4 ml/min. After dilution with an equal volume of aqueous solution of the internal standard (6.667 microM), the plasma sample (50-150 microliters) was deproteinized by use of an Amicon Centrifree-MS ultrafilter at 2,000 g. No interference from any endogenous substance or concomitantly used drug was observed, and the assay was highly linear (r greater than 0.9994) in the concentration range examined (0.146-145.8 microM). The intra- and interrun precision was equally good, with coefficients of variation of less than 3.13 and less than 5.4%. We are currently using this method for monitoring isoniazid in patients treated with this drug for tuberculosis.

Steady state pharmacokinetics of propranolol in Saudi Arabian patients and comparison with data for different populations

The steady state pharmacokinetics of propranolol was examined in 48 Saudi Arabian patients chronically treated with oral doses [mean (SEM) = 85.8 (5) mg] of this drug. The mean (SEM) of the steady state concentration (Css) per mg/kg daily dose was 21.8 (3.1) ng.ml-1/mg.kg-1. A 6-fold variability in Css was observed between patients treated with 40 mg every 8 hours and 14-fold between patients treated with 40 mg twice daily. The frequency distribution of the apparent oral clearance (TCLor) of propranolol was bimodal with 88% of the patients showing TCLor of 18 to 372 l.hr-1 while the remainder had TCLor of 471 to 749 l.hr-1. The mean (SEM) of the TCLor per kg body weight for all 48 patients was 3.16 (0.38) l.hr-1.kg-1. Both Css and TCLor obtained for Saudi Arabian patients are not significantly different from those reported for subjects from Western populations. While Css increased proportionally (P less than .001) with dosing, a near-significant (P less than .06), inverse, linear relationship was found between age and TCLor. No significant effect of sex, body weight, or disease state (i.e., heart diseases, hypertension, depression, migraine) on Css or TCLor was detected.

Rapid liquid chromatographic analysis of mitoxantrone in plasma with C18 sample purification

A useful and rapid method for the analysis of mitoxantrone in human plasma is described. We purified the sample with a C18 Sep Pak cartridge pre-treated with methanol, water and 0.05 M ammonium phosphate (pH = 2.75). The drug and internal standard (Methylene Blue) were eluted from the cartridge with 1 M acetic acid in methanol and were separated on a 10 microns particle size CN Resolve cartridge in conjunction with a radial compression liquid chromatograph. The mobile phase consisted of a mixture of 0.05 M ammonium phosphate, acetonitrile and methanol (60:35:5, by vol), and the detection was performed spectrophotometrically at 660 nm. The peak height ratio (drug/internal standard) varied linearly (r greater than 0.993) with concentration over the range examined 0.01-3 micrograms ml-1, and the inter- and intra-run precision at high, medium and low concentrations were good; CV ranged from 2.52 to 7.2%. There was no interference from other anticancer drugs or analgesics. We applied the described method to investigate the pharmacokinetics of mitoxantrone using a rabbit as an in vivo model.

Direct, simultaneous measurement of chloramphenicol and its monosuccinate ester in micro-samples of plasma by radial-compression liquid chromatography

A simple method of simultaneous analysis for chloramphenicol and chloramphenicol succinate in 10-microL samples of plasma is described. We injected the plasma samples directly into a radial-compression liquid chromatograph equipped with a precolumn module and a C18 insert. A mixture of acetic acid solution (pH 3)/acetonitrile (75/25, by vol) was used as mobile phase, at a flow rate of 4 mL/min. We separated the compounds in a 10-micron (particle size) C18 cartridge with a radial compression separation system and detected them in the effluent at 280 nm. The peak height for both compounds was linearly (r greater than 0.9993) related to concentration over the range investigated, 1-50 mg/L. We also performed the analysis with use of an internal standard (methylprednisolone) and obtained equally good results (r greater than 0.9995). We observed no interference from other antibiotics or drugs in the assay, and the inter- and intra-run precision at different concentrations was good (CV, 0 to 5.6%). We analyzed microsamples of plasma from an infant treated for meningitis with chloramphenicol sodium succinate intravenously. Total analysis time for each sample was less than 8 min.

Direct, simultaneous measurement of chloramphenicol and its monosuccinate ester in micro-samples of plasma by radial-compression liquid chromatography

A simple method of simultaneous analysis for chloramphenicol and chloramphenicol succinate in 10-microL samples of plasma is described. We injected the plasma samples directly into a radial-compression liquid chromatograph equipped with a precolumn module and a C18 insert. A mixture of acetic acid solution (pH 3)/acetonitrile (75/25, by vol) was used as mobile phase, at a flow rate of 4 mL/min. We separated the compounds in a 10-micron (particle size) C18 cartridge with a radial compression separation system and detected them in the effluent at 280 nm. The peak height for both compounds was linearly (r greater than 0.9993) related to concentration over the range investigated, 1-50 mg/L. We also performed the analysis with use of an internal standard (methylprednisolone) and obtained equally good results (r greater than 0.9995). We observed no interference from other antibiotics or drugs in the assay, and the inter- and intra-run precision at different concentrations was good (CV, 0 to 5.6%). We analyzed microsamples of plasma from an infant treated for meningitis with chloramphenicol sodium succinate intravenously. Total analysis time for each sample was less than 8 min.