Quantitative liquid chromatography of allopurinol and oxypurinol in human plasma and urine

Pharmacokinetics and comparative bioavailability of allopurinol formulations in healthy subjects

Allopurinol is the most commonly used urate-lowering therapy in gout. This study was undertaken to evaluate the pharmacokinetics and relative bioavailability of two brands of allopurinol tablets. The in vivo study was established according to a single-center, randomized, single-dose, laboratory-blinded, Two Way, Cross-Over Study with a washout period of 1 week. Under fasting conditions, 24 healthy male volunteers were randomly allocated to receive a single oral dose (200 mg) of either test and reference formulations. Plasma samples were obtained over a 6-hour interval and analyzed for allopurinol by reversed phase liquid chromatography with ultraviolet detection. The 90% confidence intervals for the ratio of log transformed values of Cmax , AUC0-t , and AUCt-∞ of the two treatments were within the acceptable range (0.8-1.25) for bioequivalence. From PK perspectives, the two allopurinol formulations were considered bioequivalent, based on the rate and extent of absorption. No adverse events occurred or were reported after a single 200-mg allopurinol and both formulations were well tolerated.

A simple method for quantification of allopurinol and oxipurinol in human serum by high-performance liquid chromatography with UV-detection

OBJECTIVES

Allopurinol is a uric acid lowering drug used in the treatment of gout and the prevention of tumor lysis syndrome. Allopurinol and its active metabolite oxipurinol inhibit xanthine oxidase, which forms uric acid from xanthine and hypoxanthine. Therapeutic drug monitoring is an important option for evaluation and optimization of allopurinol treatment in case of renal impairment, interaction with uricosuric drugs or to verify patient adherence. In this study we developed and validated a simple quantitative assay using reverse phased high-performance liquid chromatography (HPLC) with UV-detection as a method for quantification of allopurinol and oxipurinol in human serum in the presence of different frequently used drugs.

METHODS

The HPLC-UV method uses a mobile phase consisting of sodium acetate (0.02 M; pH 4.5), at a flow rate of 1.0 mL/min. Allopurinol and oxipurinol are detected by UV-absorption at 254 nm with a retention time of 9.9 min for oxipurinol and 12.3 min for allopurinol. Aciclovir is used as internal standard.

RESULTS

Validation showed for allopurinol lower and upper limits of quantification of 0.5 and 10mg/L and for oxipurinol 1 and 40 mg/L, respectively. The assay was linear over the concentration range of 0.5-10mg/L (allopurinol) and 1-40 mg/L (oxipurinol). Intra- and inter-day precision showed coefficients of variation <15% over the complete concentration range; accuracy was within 5% for allopurinol and oxipurinol. Endogenous purine-like compounds were separated from allopurinol, oxipurinol and aciclovir with a resolution factor >1.5. Exogenous purine-like compounds and co-medication frequently used by gout patients did not hinder the analysis due to the dichloromethane washing step or to low UV-absorpion at 253 nm. Serum levels of 66 patients prescribed allopurinol 300 mg/day were determined using this HPLC-UV method. Measured serum allopurinol and oxipurinol concentrations in clinical practice showed large variability with a range of <0.5-4.3 mg/L for allopurinol and <1.0-39.2 mg/L for oxipurinol, respectively.

CONCLUSION

We developed an easy-to-operate and validated HPLC-UV method for the quantification of allopurinol and oxipurinol in human serum. This method was proven to be valid for samples of gout patients frequently using concomitant medications.

Facile and rapid high-performance liquid chromatography method for simultaneous determination of allopurinol and oxypurinol in human serum

OBJECTIVE

To develop a rapid and sensitive assay for the simultaneous determination of allopurinol and oxypurinol in serum.

METHOD

High-performance liquid chromatography (HPLC) with UV-detection. Sample preparation consists of protein precipitation by an addition of trichloracetic acid.

RESULTS

Percentage recovery and intra-assay coefficient of variation (CV%) for allopurinol were 97.4-101.3 and 0.66-5.13, respectively, in the concentration range 0.5-5.0 microg/mL. For oxypurinol, the percentage recovery and the intra-assay CV% were 93.2-98.1 and 0.88-5.62, respectively, in the concentration ranges 0.4-20 microg/mL. There was no interference of endogenous compounds in this assay.

CONCLUSION

This method is useful for routine therapeutic drug monitoring of allopurinol in a clinical setting.