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Metformin is an oral antihyperglycemic agent used in the therapy of noninsulin-dependent diabetic patients. This biguanide can induce dangerous complications such as lactic acidosis when its plasma concentration is too high. For this reason, the determination of plasma metformin should always be done during treatment. We developed a new HPLC method, for the routine determination of plasma metformin, with good reliability, rapid execution, and low costs. Sample preparation involved precipitation of the plasma proteins containing the internal standard buformin with a mixture of methanol, zinc sulfate, and ethylene glycol; the diluted supernatant was injected into a cation-exchange column. The mobile phase was potassium dihydrogenphosphate buffer-containing acetonitrile. The eluent was monitored at 236 nm. The calibration curve is linear within the range of 20-4000 ng/mL; the within-day coefficients of variation were less than 2.2% for metformin and 1.5% for buformin; the day-to-day coefficients of variation were less than 2.5% for metformin and 1.9% for buformin. The mean recoveries obtained from supplemented samples were included between 99.4 and 104.2% for metformin. Many characteristics make this method useful and easily accessible to all clinical laboratories equipped with HPLC instrumentation.

Forty shoe factory workers who were exposed to hexane were investigated to see if there was a correlation between electroneuromyographic changes indicative of neuropathy and urinary excretion of 2,5-hexanedione. Urinary samples were analyzed for the presence of the metabolic products of n-hexane and its isomers. Electrodiagnostic examination was carried out following the urinary sampling. A rating scale was used to obtain a cumulative numeric index of electrodiagnostic findings. 2,5-Hexanedione and gamma-valerolactone were discovered in all cases, while 2-hexanol was found in 11 cases. 2,5-Hexanedione was the main metabolite in most cases (39 of 40). Only in 1 case was a low level of 2-methyl-2-pentanol detected; 3-methyl-2-pentanol was never detected. Metabolic products of cyclohexane were present in about one-fifth of the cases, while trichloroethanol, a metabolic product of trichoroethylene, was nearly always present, all at very low concentrations. Electromyographic abnormalities significant for early detection of toxic polyneuropathy were found in 14 cases. A statistically significant correlation of the electroneuromyographic scoring on the urinary concentrations of measured metabolites was observed only with 2,5-hexanedione and gamma-valerolactone, both derived from n-hexane. Since gamma-valerolactone is probably not a true metabolite of n-hexane, our results support the hypothesis that polyneuropathies in shoemakers are due to 2,5-hexanedione. For practical purposes the urinary concentration of 2,5-hexanedione can serve as a predictive measurement for early detection of neurotoxic lesions at preclinical states.

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Summary:A new isocratic HPLC method, employing electrochemical detection, is described for the determination of urinary vanillylmandelic acid, 5-hydroxyindoleacetic acid and homovanillic acid. The main advantages of this technique are: simplicity, simultaneous determination of all analytes, the absence of an extraction procedure, isocratic elution and low cost. The diluted urine is injected onto a CIS reversed phase column. The mobile phase is potassium dihydrogenphosphate buffer containing 1-heptanesulphonic acid, methanol and acetonitrile. The calibration curves are linear from 0.1 to 50 mg/1; the precision data show CV less than 2.36% for within-day assay and less than 2.72% for day-to-day assays. The mean recoveries for supplemented samples are 98.2 to 102.0% for vanillylmandelic acid, 99.6 to 103.9% for 5-hydroxyindoleacetic acid and 98.7 to 102.0% for homovanillic acid. In comparisons of the present method with Radjaipur's extraction method (Radjaipur M. et al., Eur J Clin Chem Clin Biochem 1994; 32:609-13) the slopes for the three analytes were nearly 1, and the confidence region of the intercepts was close to 0. In conclusion the technique seems to be suitable for routine determination of the three analytes, especially for mass screening purposes.