Plasma concentrations and urinary excretion of purine bases (uric acid, hypoxanthine, and xanthine) and oxypurinol after rigorous exercise

To investigate the effects of exercise on the plasma concentrations and urinary excretion of purine bases and oxypurinol, we performed 3 experiments with 6 healthy male subjects. The first was a combination of allopurinol intake (300 mg) and exercise (VO2max, 70%) (combination experiment), the second was exercise alone (exercise-alone experiment), and the third was allopurinol intake alone (allopurinol-alone experiment). In the combination experiment, exercise increased the concentrations of purine bases and noradrenaline in plasma, as well as lactic acid in blood and the urinary excretion of oxypurines, whereas it decreased the urinary excretion of uric acid and oxypurinol as well as the fractional excretion of hypoxanthine, xanthine, uric acid, and oxypurinol. In the exercise-alone experiment, exercise increased the concentrations of purine bases and noradrenaline in plasma, lactic acid in blood, and the urinary excretion of oxypurines, whereas it decreased the urinary excretion of uric acid and fractional excretion of purine bases. In contrast, in the allopurinol-alone experiment, the plasma concentration, urinary excretion, and fractional excretion of purine bases and oxypurinol remained unchanged. These results suggest that increases in adenine nucleotide degradation and lactic acid production, as well as a release of noradrenaline caused by exercise, contribute to increases in plasma concentration and urinary excretion of oxypurines and plasma concentration of urate, as well as decreases in urinary excretion of uric acid and oxypurinol, along with fractional excretion of uric acid, oxypurinol, and xanthine. In addition, they suggest that oxypurinol does not significantly inhibit the exercise-induced increase in plasma concentration of urate.

Effect of the angiotensin II receptor antagonist losartan on uric acid and oxypurine metabolism in healthy subjects

OBJECTIVE

The acute effects of the angiotensin II receptor antagonist losartan on uric acid and oxypurine metabolism were evaluated.

METHODS

Losartan (50 mg) was administered orally to 6 healthy males. Blood and urine samples for uric acid and oxypurine were collected before and up to 6 hours after losartan administration. The same examinations were performed later using enalapril (5 mg).

RESULTS

Losartan decreased the serum uric acid concentration (from 5.9 +/- 0.9 to 5.2 +/- 1.0 mg/dl) and increased its fractional clearance, which reached a maximum after 2 hours, while enalapril did not. Losartan also induced an increase in the plasma concentration of hypoxanthine, peaking in the fourth hour, and a decrease in its urinary clearance, while the plasma xanthine concentration and its urinary clearance were unchanged. The extent of uric acid excretion was much greater than that of the oxypurines.

CONCLUSIONS

Losartan, which has a high affinity for the urate/anion exchanger, has a transient uricosuric effect. Our data indicate that losartan induces a significant decrease in the urinary excretion of hypoxanthine without changes in xanthine.

Effects of angiotensin II infusion on renal excretion of purine bases and oxypurinol

The effect of angiotensin II infusion on the renal transport of purine bases and oxypurinol (a metabolite of allopurinol) was investigated in 5 healthy subjects who were orally given allopurinol (300 mg) 9 hours prior to the study. Angiotensin II was intravenously administered at 8 ng/min/kg for 2 hours. The fractional clearances of uric acid, xanthine, and oxypurinol were significantly decreased during angiotensin II infusion; however, that of hypoxanthine did not change. The urinary excretion levels of uric acid, xanthine, and oxypurinol were also significantly decreased during angiotensin II infusion. These results suggest that angiotensin II infusion affected the renal clearances of uric acid, xanthine, and oxypurinol through direct tubular transport and/or hemodynamic changes. Accordingly, the hypouricemic effect of allopurinol may be exaggerated in hypertensive gout patients with an enhanced renin-angiotensin system, since an increased biological half-life of oxypurinol is expected in these patients.

Effect of norepinephrine on the urinary excretion of purine bases and oxypurinol

To examine whether norepinephrine affects the plasma concentrations and urinary excretion of purine bases and oxypurinol, we orally administered allopurinol (300 mg) to 5 healthy subjects and 9 hours later intravenously administered norepinephrine (12 to 20 microg/kg body weight), which causes a more than 10 mm Hg increase in diastolic pressure for 2 hours. Norepinephrine decreased the urinary excretion of uric acid by 33% (P <.01), oxypurinol by 32% (P <.01), and xanthine by 51% (P <.01), as well as the fractional clearance of uric acid by 32% (P <.01), oxypurinol by 24% (P <.05), and xanthine by 21% (P <.05) when measured 1 to 2 hours after administration. These results indicate that norepinephrine decreases the urinary excretion of uric acid, oxypurinol, and xanthine, probably via hemodynamic change. It is also suggested that the hypouricemic effect of allopurinol may be more potent than that expected in gout patients with enhanced sympathetic tone, such as in salt-sensitive hypertension.

Effect of fenofibrate on plasma concentration and urinary excretion of purine bases and oxypurinol

OBJECTIVE

To investigate whether fenofibrate increases the clearance of purine bases (hypoxanthine, xanthine, uric acid) and oxypurinol.

METHODS

We administered fenofibrate (150 mg) 3 times a day for 3 days, and then allopurinol (300 mg) 4 h after the last administration of fenofibrate, to 5 healthy subjects. Ten hours later, a clearance study was done.

RESULTS

Following 3 day administration of fenofibrate, fractional clearance of xanthine, uric acid, and oxypurinol increased by 41% (p < 0.05), 101% (p < 0.01), and 51% (p < 0.01), respectively, compared to baseline values, while the respective plasma concentrations decreased by 46% (p < 0.05), 46% (p < 0.05), and 19% (p < 0.05).

CONCLUSION

Our results suggest that fenofibrate, fenofibric acid, or fenofibrate derivatives can increase fractional clearance of xanthine, uric acid, and oxypurinol by acting on their common renal pathways. It is suggested that the hypouricemic effect of combination therapy using allopurinol and fenofibrate may be less than additive.

Identification of a new point mutation in the human xanthine dehydrogenase gene responsible for a case of classical type I xanthinuria

A 60-year-old Japanese man was diagnosed as having hypouricemia at an annual health check-up. The routine laboratory data was not remarkable except that the patient's hypouricemia and plasma levels of xanthine and hypoxanthine were much higher than those of normal subjects. Furthermore, the patient's daily urinary excretion of xanthine and hypoxanthine was markedly increased compared with reference values. The xanthine dehyrogenase activity of the duodenal mucosa was below the limits of detection. Nevertheless, allopurinol was metabolized to oxypurinol in vivo. Based on these findings, a subtype of classical xanthinuria (type I) was diagnosed. The xanthine dehyrogenase protein was detected by Western blotting analysis. Sequencing of the cDNA of the xanthine dehyrogenase obtained from the duodenal mucosa revealed that a point mutation of C to T had occurred in nucleotide 445. This changed codon 149 from CGC (Arg) to TGC (Cys), a finding that has not been previously reported in patients with classical xanthinuria type I.

Effect of furosemide on renal excretion of oxypurinol and purine bases

To examine whether furosemide affects the plasma concentration and urinary excretion of purine bases and oxypurinol, we administered allopurinol (300 mg) orally to 6 healthy subjects and then administered furosemide (20 mg) intravenously 10 hours later. Furosemide (20 mg) decreased the urinary excretion of uric acid by 40% (P < .01), oxypurinol by 39% (P < .05), and xanthine by 43% (P < .05) and the fractional clearance of uric acid by 45% (P < .01) and oxypurinol by 34% (P < .05) when measured 1 to 2 hours after administration. Moreover, furosemide increased the plasma concentration of uric acid by 6% at 1.5 hours after administration. These results indicate that furosemide may decrease the urinary excretion of uric acid and oxypurinol by acting on their common renal transport pathway(s). In addition, it is suggested that the effect of furosemide on oxypurinol is clinically important, since the hypouricemic effect of allopurinol may become more potent as a result.

Effect of losartan potassium, an angiotensin II receptor antagonist, on renal excretion of oxypurinol and purine bases

OBJECTIVE

To examine whether losartan affects the plasma concentrations and urinary excretion of purine bases and oxypurinol.

METHODS

We administered allopurinol (300 mg) and then 9 h later losartan potassium (100 mg) to 5 healthy subjects.

RESULTS

The urinary excretion of uric acid increased by 3.9- and 2.6-fold, and that of oxypurinol by 2- and 1.8-fold, at 1 to 2 h and at 2 to 3 h, respectively, after administration of losartan potassium. The fractional clearance of uric acid was increased by 4.3- and 3.2-fold, oxypurinol by 2.3- and 2.1-fold, and xanthine by 1.32- and 1.26-fold, at 1 to 2 h and at 2 to 3 h, respectively, after administration of losartan potassium. The plasma concentrations of uric acid decreased by 8% and 16%, oxypurinol by 7% and 11%, and xanthine by 42% and 45%, at 1.5 and 2.5 h, respectively, after oral administration.

CONCLUSION

These results suggest that losartan potassium could increase urinary excretion of uric acid, xanthine, and oxypurinol by acting on their common renal transport pathways, since it was found that uric acid may share a renal transport pathway with oxypurinol and xanthine. It is also suggested that the effect of losartan potassium on oxypurinol and uric acid is clinically important, since the hypouricemic effect of a combination therapy using allopurinol and losartan potassium may be less than additive, while the uricosuric effect of losartan potassium may increase the frequency of calculi in the urinary tract.

Pharmacokinetics and pharmacodynamics of allopurinol in elderly and young subjects

AIMS

The prevalence of hyperuricaemia and gout increases with age as does the incidence of adverse effects to allopurinol, the major uric acid lowering drug. The present study was performed to compare the disposition and effects of allopurinol and its active metabolite oxipurinol in elderly and young subjects without major health problems.

METHODS

Ten elderly (age range 71-93 years) and nine young subjects (24-35 years) received an oral dose of 200 mg allopurinol in an open, single dose, cross sectional design. Four of these individuals were additionally dosed with 200 mg allopurinol intravenously. Plasma and urine concentrations of allopurinol, oxipurinol, hypoxanthine, xanthine, and uric acid were measured by h. p.l.c.

RESULTS

Total clearance of allopurinol was not different in elderly (15.7+/-3.8 ml min-1 kg-1, mean+/-s.e. mean) and young subjects (15.7+/-2.1), whereas total clearance of oxipurinol was significantly reduced in the aged (0.24+/-0.03) compared with young controls (0.37+/-0.05) as was the distribution volume of oxipurinol (0.60+/-0.09 and 0.84+/-0.07 l kg-1, respectively). Oxipurinol was eliminated primarily by the kidneys, allopurinol by metabolism. Fractional peroral bioavailability of allopurinol was 0.81+/-0.16 (n=4, two elderly and two young subjects). Although maximal plasma concentrations of oxipurinol were significantly higher in elderly (5. 63+/-0.83 microgram ml-1 ) than in young persons (3.75+/-0.25) as was the area under the oxipurinol plasma concentration-time curve, AUC (260+/-46 and 166+/-23 microgram ml-1 h, respectively), the pharmacodynamic effect of oxipurinol was smaller in elderly than young subjects (time-dependent decrease of plasma uric acid 83+/-30 microgram ml-1 h in elderly compared with 176+/-21 in young controls). Oxipurinol increased the renal clearance of xanthine, suggesting inhibition of tubular xanthine reabsorption by oxipurinol.

CONCLUSIONS

Although allopurinol elimination is not reduced in the aged, that of its active metabolite oxipurinol is because of an age-dependent decline in renal function. Xanthine oxidase inhibition by oxipurinol appears to be reduced in old age. In addition to its uricostatic action, oxipurinol has a xanthinuric effect which is also diminished in the elderly.

Two siblings with classical xanthinuria type 1: significance of allopurinol loading test

Two brothers with classical xanthinuria who lacked xanthine dehydrogenase activity were encountered. Their hypouricemia was caused by underproduction of uric acid. In their duodenal mucosa, no xanthine dehydrogenase (oxidase) activity was detected. The patients had no symptoms except for duodenal ulcer in one case. The conversion of allopurinol to oxipurinol during an allopurinol loading test for determining the type of classical xanthinuria revealed that the patients had classical type 1 xanthinuria, because aldehyde oxidase activity was present. Furthermore, the allopurinol loading test was conducted to determine the optimal examination times and specimens required for this test.

Effect of glucagon on renal excretion of oxypurinol and purine bases

OBJECTIVE

To investigate whether glucagon increases the urinary excretion of oxypurinol and purine bases.

METHODS

We administered 1 mg glucagon intravenously to 5 healthy subjects taking 300 mg allopurinol orally, and determined plasma concentrations and urinary excretion of oxypurinol and purine bases.

RESULTS

Glucagon increased the urinary excretion and fractional clearances of uric acid, xanthine, and oxypurinol, together with an increase in creatinine clearance, while it decreased plasma concentrations of xanthine and hypoxanthine.

CONCLUSION

Glucagon-induced increases in urinary excretion of uric acid, xanthine, and oxypurinol were attributable to increases in the fractional clearances of uric acid, xanthine, and oxypurinol in addition to an increase in glomerular filtration rate. It is suggested that glucagon affects the renal common transport pathway of uric acid, xanthine, and oxypurinol by stimulating the release of a liver derived renal vasodilator.

1-Methylxanthine derived from caffeine as a pharmacodynamic probe of oxypurinol effect

AIMS

In the present study we have investigated the use of caffeine, administered in the form of instant coffee, as a prodrug for 1MX to validate the use of the 1MU:1MX ratio following caffeine administration as a pharmacodynamic measure of oxypurinol effect on xanthine oxidase.

METHODS

Five healthy volunteers took caffeine 75 mg 8 hourly administered as instant coffee over a 7 day period. They were given allopurinol 600 mg on day 4. Urine was collected in 8 h aliquots from day 1-day 7. The ratio of 1-methyluric acid (1MU) to 1-methylxanthuric (1MX) was determined.

RESULTS

The relationship between the plasma oxypurinol (the active metabolite of allopurinol) concentration at the midpoint of each caffeine dosage interval and the decrement in the urinary 1MX to 1MU ratio fitted well by a sigmoid Emax model. Mean (+/-s.d.) values of the oxypurinol EC50(3.9 +/- 1.4 mg l-1), EC90(8.7 +/- 1.8 mgl-1) and the exponent, n (3.0 +/- 1.2) were similar to those obtained previously following either the direct administration of 1MX or the use of theophylline as a prodrug for 1MX.

CONCLUSIONS

These data indicate that the use of caffeine as a source of 1MX could provide a simple and ethically acceptable method for monitoring oxypurinol effect in patients taking allopurinol for the treatment of gout.

Difference of the plasma concentration and urinary excretion of allopurinol, oxypurinol, and purine bases between dietary intake and fasting

To investigate how much the metabolism of allopurinol, oxypurinol, and purine bases during dietary intake (total calorie 2,083 kcal, total protein 107.5 g, total lipid 74.1 g, total carbohydrate 228.3 g, total purine 180.5 mg) differs from that during fast, allopurinol (300 mg) was administered to 5 normal subjects after a 6-hour fast and then breakfast was taken. Four and 10 hours after the administration of allopurinol lunch and dinner were taken, respectively. Two weeks later the same protocol was performed, except for the intake of only water instead of diet. The fractional clearances and urinary excretions of oxypurinol, uric acid, and the clearance of creatinine were increased by dietary intake, compared with the respective ones resulting from fasting. At the same time the plasma concentrations of hypoxanthine, xanthine, and oxypurinol were decreased in dietary intake, compared with the respective ones in fasting, while the urinary excretion of neither allopurinol, hypoxanthine, nor xanthine was affected. These results suggest that the administration of allopurinol at bed time (during the nocturnal fast) may be more effective than that after breakfast in order to decrease the plasma concentration of uric acid.

Effect of amino acids on the excretions of purine bases and oxypurinol

To investigate whether or not amino acids affect the urinary excretion of purine bases and oxypurinol, a 12% amino acid solution was infused to 6 subjects who took allopurinol (300 mg) 6 h before the study. Amino acid infusion increased the urinary excretion and the fractional clearance of uric acid and oxypurinol and decreased the plasma concentration of oxypurinol. However, it affected neither the urinary excretion, the fractional clearance, the plasma concentration of oxypurines nor the plasma concentration of uric acid. These results indicate that amino acids affect the renal transport pathways of oxypurinol and uric acid but not those of oxypurines. In addition, it was suggested that the amino acid-induced increase in the urinary excretion of oxypurinol may be considered when allopurinol is administered to hyperuricemic patients with hypoproteinemia who have taken amino acids either orally or intravenously.

Interaction of allopurinol and hydrochlorothiazide during prolonged oral administration of both drugs in normal subjects. II. Kinetics of allopurinol, oxipurinol, and hydrochlorothiazide

The kinetics of allopurinol and hydrochlorothiazide were investigated in seven healthy male subjects during prolonged coadministration of two drugs. Subjects were maintained on an isoenergetic, purine-free formula diet with RNA supplementation for 24 days. Allopurinol (300 mg) was given orally on days 1-24. Hydrochlorothiazide (50 mg daily) was added to days 11-21. On day 43 a single oral dose of 50 mg hydrochlorothiazide was administered. Plasma concentration-time profiles of allopurinol and its main metabolite oxipurinol were obtained on days 1, 10, and 21; hydrochlorothiazide profiles were assessed on days 21 and 43. In addition, 24-h plasma concentrations of oxipurinol were measured repetitively, and 24 h urine samples were collected for the determination of allopurinol, oxipurinol, and hydrochlorothiazide. For oxipurinol, mean Cmax was not altered on hydrochlorothiazide treatment (13.8 +/- 1.4 micrograms/ml and 14.7 +/- 2.6 micrograms/ml, respectively); mean AUC0-24 was 259 and 290 micrograms h-1 ml-1, respectively. The small difference in AUC0-24 values does not explain the increase in plasma uric acid concentration during hydrochlorothiazide treatment, nor do the variations in allopurinol and hydrochlorothiazide kinetics.

Interaction of allopurinol and hydrochlorothiazide during prolonged oral administration of both drugs in normal subjects. I. Uric acid kinetics

The interaction of allopurinol (300 mg/day) and hydrochlorothiazide (50 mg/day) was studied in seven healthy male volunteers during prolonged coadministration of the two drugs using defined dietary conditions. A formula diet was administered with the allopurinol throughout the 24-day study, while hydrochlorothiazide was added during days 11-21. After the addition of hydrochlorothiazide both plasma uric acid and plasma oxipurinol rose for 6 days--24% and 30%, respectively, compared to steady-state levels during allopurinol alone (P < 0.01 each). In neither substance were variations in renal excretion significant. By the end of combined treatment (day 21), the changes induced by hydrochlorothiazide had already been reversed to a considerable extent. It is concluded that both in normal individuals and in patients with normal renal clearance of uric acid the effect of hydrochlorothiazide on the plasma concentration and renal excretion of oxipurinol is small. When taking both drugs, there is no increased risk during long-term treatment, and a risk is even questionable during the first days.

Effect of BOF-4272 on the oxidation of allopurinol and pyrazinamide in vivo. Is xanthine dehydrogenase or aldehyde oxidase more important in oxidizing both allopurinol and pyrazinamide?

Allopurinol or pyrazinamide was administered to rats treated with BOF-4272 (a potent xanthine oxidase inhibitor) to investigate to what degree xanthine dehydrogenase participates in the oxidation of these agents. BOF-4272 markedly decreased the plasma concentration and the urinary excretion of both oxypurinol and 5-hydroxypyrazinamide. It also decreased the sum of the urinary excretion of allopurinol and oxypurinol and that of pyrazinamide and its metabolites, although it did not affect the sum of the plasma concentrations of allopurinol and oxypurinol at 105 min after administration of allopurinol or the plasma concentration of pyrazinamide during the period after the administration of pyrazinamide. These results suggested that BOF-4272 almost completely inhibited the oxidation of allopurinol and pyrazinamide and had some effect on the excretion and/or the tissue incorporation of these two compounds. Since the in vitro study demonstrated that BOF-4272 did not inhibit the activity of aldehyde oxidase, which oxidized both allopurinol to oxypurinol and pyrazinamide to 5-hydroxypyrazinamide, the results suggested that xanthine dehydrogenase was the more important enzyme in converting allopurinol to oxypurinol and pyrazinamide to 5-hydroxypyrazinamide.

Effect of DL-sodium lactate infusion on excretion of purine bases and oxypurinol

To investigate whether or not DL-sodium lactate inhibits the renal excretion of purine bases and oxypurinol, we administered physiological saline containing 0.2 mol DL-sodium lactate to 7 normal subjects intravenously. DL-sodium lactate infusion decreased the urinary excretion and the fractional clearance of uric acid, xanthine and oxypurinol, but the fractional clearance of hypoxanthine was not affected. These results suggested that the implications of DL-sodium lactate-induced hyperuricemia must be considered in patients with gout on its long term and high dose administration, and that the implications of DL-sodium lactate-induced prolongation of half-life of oxypurinol must be considered in hyperuricemic patients treated with allopurinol. However, since the high dose and long term administration of DL-sodium lactate is clinically rare, the effect of DL-sodium lactate infusion on the urinary excretion of uric acid, xanthine and oxypurinol may not be clinically important.

Simultaneous determination of allopurinol and oxipurinol in human plasma and urine by high-performance liquid chromatography

The uricostatic drug allopurinol (CAS 315-30-0) is used for treatment of hyperuricaemia and is mainly bio-transformed to the active metabolite oxipurinol (CAS 2465-59-0) in humans. A new assay was developed for the simultaneous determination of both compounds in plasma and urine using ultrafiltration and ion exchange purification steps for plasma and urine, respectively. Reversed-phase high-performance liquid chromatography with ultraviolet detection was applied for the separation and quantitation of both compounds. The limit of detection was 0.1 microgram/ml for both compounds in plasma and 0.2 and 0.5 microgram/ml for allopurinol and oxipurinol, respectively, in urine. Within-run and day-to-day precision of 3-5% and 5-7% was determined for plasma and 6-8% and 8-10% for urine analysis. The assays were further validated using liquid chromatography with photodiode array detection and by comparison with methods using protein precipitation as the purifying step. The high analytical recoveries, selectivity, sensitivity, accuracy and reproducibility were adequate for the measurement of both compounds in pharmacokinetic studies and for drug monitoring in patients on allopurinol therapy.

ESR-measurement of production of oxygen radicals in vivo before and after renal ischaemia in the rabbit

This study describes a spin trap technique to determine production of oxygen radicals in rabbit kidneys after ischaemia and reperfusion. OXANOH was infused intra-arterially. When exposed to oxygen free radicals OXANOH is oxidized to the stable radical OXANO(.). The concentration of OXANO. in samples of renal venous blood was determined by ESR. Production of oxygen radicals was calculated from the amount of OXANO. in the venous blood and the blood flow which was determined by an ultrasound technique. The radical production at reperfusion after ischaemia was expressed as a per cent of the pre-ischaemic value. A drastic increase in radical production was observed during (60 min) reperfusion after 60 min of ischaemia. Pretreatment with oxypurinol (20 mg kg-1) before ischaemia and before recirculation almost completely abolished the rise in radical production at recirculation. Similar results were obtained when oxypurinol was given before recirculation only.

Effects of pyrazinamide, probenecid, and benzbromarone on renal excretion of oxypurinol

The effects of pyrazinamide, probenecid, and benzbromarone on renal excretion of oxypurinol were investigated. Pyrazinamide decreased the mean (SEM) fractional clearance of oxypurinol from 19.2 (2.1) to 8.8 (1.5). Probenecid increased the fractional clearance of oxypurinol from 14.1 (3.5) to 24.8 (4.1). Benzbromarone increased the fractional clearance of oxypurinol from 15.6 (2.3) to 33.8 (2.8). These results suggest that oxypurinol may be secreted by 'an organic acid system' and that oxypurinol is reabsorbed at a putative postsecretory site of the renal tubules.

Orotidine accumulation in human erythrocytes during allopurinol therapy: association with high urinary oxypurinol-7-riboside concentrations in renal failure and in the Lesch-Nyhan syndrome

1. A compound identified as orotidine has been found in the erythrocytes of all subjects on allopurinol. 2. The erythrocyte orotidine concentrations were much higher in patients with renal failure or with the Lesch-Nyhan syndrome. 3. In addition, increased amounts of oxypurinol-7-riboside were excreted in the urine by both of these groups compared with control subjects or with patients with normal renal function on allopurinol. 4. A good correlation was found between urinary oxypurinol-7-riboside excretion and erythrocyte orotidine concentrations. 5. Increased erythrocyte levels of the pyrimidine-sugar UDP-glucose were also found in patients with the highest orotidine levels. 6. The combined results suggest a derangement of pyrimidine nucleotide metabolism during allopurinol therapy. We propose that erythrocyte orotidine formation results primarily from inhibition of orotidine-5'-monophosphate decarboxylase by oxypurinol-7-ribotide.

[A study on treatment of hyperuricemia--effects and kinetics of allopurinol and oxipurinol]

In order to study the effects and pharmacokinetics of allopurinol (hereafter abbreviated to allo.) and oxipurinol (hereafter abbreviated to oxi.) six normal human subjects were given a single oral dose of either allo. (300mg) or oxi. (600mg), followed by serial determinations of serum and urinary levels of allo., oxi., uric acid, hypoxanthine (hereafter abbreviated to hx.) and xanthine (hereafter abbreviated x.) over a six-hour period. With a dose of 300mg of allo. or 600mg of oxi., the patterns of serum uric acid were similar. When 300mg of allo. was given, however, a reduction in the serum uric acid level occurred earlier. Additionally, it was found that urinary excretion of oxi. generally paralleled the plasma concentration. Allo. administration resulted in rises in plasma concentration of x., and urinary excretion of x. and hx. Oxi. administration, on the other hand, did not cause significant changes in the plasma content of x. or urinary excretory volume of hx. Only a slight increase was noted in the amount of x. excreted in the urine. When allo. was compared against oxi., pharmacokinetics of oxypurines, especially x. were found to differ markedly. The results suggested that differences in the reaction sites, varied intra- and extra-cellular distributions of allo. and oxi., and different effects on purine biosynthesis contribute to the aforementioned discrepancies.

Reduced renal clearance of oxypurinol during a 400 calorie protein-free diet

A decrease in dietary protein intake lowers the clearance of a number of substances excreted principally by the kidney including uric acid and oxypurinol, the major metabolite of allopurinol. We studied the kinetics of uric acid and oxypurinol in seven healthy volunteers on a normal protein diet (2600 calories; 100 g protein) followed by a 400 calorie, protein-free diet. A 600 mg dose of allopurinol was given orally after 6 days of the normal protein diet and again after 2 days of the 400 calorie, protein-free diet. Two major findings emerged: first, the renal clearance of oxypurinol was reduced from 21.2 +/- 1.9 ml/min during the normal protein diet to 12.3 +/- 1.2 ml/min (P less than .05) during the 400 calorie, protein-free diet, and second, there was a striking diurnal difference in oxypurinol renal clearance with a 41% decrease in the oxypurinol clearance at night (8 PM to 8 AM) versus day (8 AM to 8 PM) on the 400 calorie, protein-free diet.

Liquid chromatography with multichannel ultraviolet detection used for studying disorders of purine metabolism

We used a reversed-phase "high-performance" liquid-chromatographic system equipped with a multichannel ultraviolet spectrometric detector and a micro-computer for analyzing urine samples from patients with disorders of purine metabolism. This system recorded a series of absorption-spectrum data from a single chromatographic run and stored them for subsequent analysis. Because the retention times and ultraviolet absorption spectra of the eluates were recorded simultaneously, identification of peaks was easy and quite accurate for simultaneous quantification of orotidine, adenine, hypoxanthine, uric acid, xanthine, allopurinol (4-hydroxypyrazolo[3,4-d]pyrimidine), oxypurinol (4,6-dihydroxypyrazolo[3,4-d]pyrimidine), inosine, and 2,8-dihydroxyadenine--compounds extremely difficult or even impossible to quantify simultaneously with a conventional single-wavelength spectrometer. We used this method to investigate purine metabolites in urines from a patient with hereditary xanthinuria, three patients with 2,8-dihydroxyadenine urolithiasis, and a gouty subject taking allopurinol.

Sustained reductions in oxipurinol renal clearance during a restricted diet

The renal clearance of oxipurinol, the major metabolite of allopurinol, was studied in six healthy subjects during normal and restricted (low protein and low calorie) diets. A 600 mg oral dose of allopurinol was administered after 7 days of a normal diet (100 mg protein/day) and again after 2 and 4 weeks of a restricted diet (19 gm protein/day). The renal clearance of oxipurinol was reduced from 19.6 +/- 1.5 ml/min during the normal diet to 10.9 +/- 0.8 and 12.0 +/- 0.9 ml/min (both P less than 0.001) during the restricted diet at 2 and 4 weeks, respectively. These changes in oxipurinol renal clearance paralleled changes in uric acid renal clearance. Furthermore, the plasma oxipurinol half-life was increased from 27.0 +/- 1.7 hours during the normal diet to 51.1 +/- 4.3 and 45.7 +/- 3.7 hours (both P less than 0.001) during the restricted diet at 2 and 4 weeks, respectively. We conclude that dietary protein and calorie restriction cause a sustained reduction in the elimination of oxipurinol.

Evaluation of a thiazide-allopurinol drug interaction

Allopurinol toxicity has been associated with the use of this drug in patients with renal insufficiency, a situation where the half-life of oxipurinol, the major metabolite of allopurinol, is prolonged. Allopurinol toxicity has also been associated with the concomitant use of allopurinol and thiazide diuretics. In the present study, the effect of hydrochlorothiazide administration on the renal clearance and serum half-life of oxipurinol has been studied in eight normal volunteers to determine if thiazides delay the clearance of oxipurinol. Oxipurinol's renal clearance and serum half-life were measured in each volunteer during a control period and again while the volunteer was receiving 50 mg/day hydrochlorothiazide for 1 week. No change in renal oxipurinol clearance (21.1 +/- 5.9 vs. 20.4 +/- 8.7 ml/min) or serum oxipurinol half-life (23.7 +/- 4.2 vs. 23.4 +/- 4.4 hours) was noted with the addition of thiazides. The association previously noted between the use of thiazide diuretics and the development of allopurinol toxicity cannot be explained by alterations in oxipurinol pharmacokinetics.

Etiopathogenesis of uncommon canine uroliths. Xanthine, carbonate, drugs, and drug metabolites

Metabolic disorders, medication, and diagnostic agents may be associated with urolithiasis in dogs. Examples of uroliths that have been uncommonly encountered in dogs include xanthine, dolomite, tetracycline, and sulfonamides. Detection of these and other apparently uncommon uroliths requires a high index of suspicion and proper methods of analysis.

The effect of dietary protein on the clearance of allopurinol and oxypurinol

A decrease in dietary protein is known to depress renal plasma flow and creatinine clearance. Using a randomized crossover design, we investigated the pharmacokinetics of allopurinol and its principal metabolite, oxypurinol, after oral administration of 600 mg of allopurinol in six normal subjects receiving a high-protein (268 g per day) or low-protein (19 g per day) diet. For allopurinol, the area under the curve of plasma concentration versus time increased by a factor of 1.45 (P less than 0.02), the renal clearance decreased by 28 per cent (P less than 0.02), and the ratio of the clearance of allopurinol to that of creatinine (fractional excretion) was unchanged between the low-protein and high-protein diets. For oxypurinol, the area under the curve increased nearly three-fold (P less than 0.02), the renal clearance decreased by 64 per cent (P less than 0.02), the fractional excretion decreased by 49 per cent (P less than 0.02), and the plasma oxypurinol half-life increased nearly threefold from 17.3 +/- 1.5 (mean +/- S.E.M.) to 49.9 +/- 2.9 hours (P less than 0.02) during the low-protein diet, as compared with the high-protein diet. We conclude that with the low-protein diet, the absorption, metabolism, and excretion of allopurinol were minimally altered but the total-body clearance of oxypurinol was greatly reduced because of a large increase in the net renal tubular reabsorption of oxypurinol.

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

A high performance liquid chromatographic (HPLC) assay is described for allopurinol and oxypurinol determination in human plasma and urine, in the range expected during therapy. The procedure involves addition of trichloroacetic acid to samples, followed by centrifugation. The supernatant is then neutralized and analyzed by reversed-phase HPLC. Characteristics of the method are reported, and data are presented on its application to the pharmacokinetics studies. Separation is optimal with an octadecylsilane (ODS) stationary phase and a sodium acetate mobile phase adjusted to pH 7.2 for plasma and pH 5 for urine.

Does benzbromarone in therapeutic doses raise renal excretion of oxipurinol?

Twenty male hyperuricaemic patients with normal kidney function were studied and it was found that the serum concentrations and excretions rates in the 24-hour urine of allopurinol and oxipurinol do not differ significantly after 9 days of oral treatment with either 300 mg allopurinol or a combination of 300 mg allopurinol and 60 mg benzbromarone daily. The sum of the excretion rates of the two pyrazolopyrimidines in the 24-hour urine represents 80.9% and 77.1%, respectively of the daily dose of allopurinol given alone or in combination with benzbromarone. As expected, the hypouricaemic effect of the combined therapy turned out to be stronger than that observed after monotherapy with allopurinol, due to the uricosuric component of benzbromarone. The difference was found to be highly significant.

High-performance liquid chromatography with polarographic and voltammetric anodic detection: simultaneous determination of allopurinol, oxipurinol and uric acid in body fluids

Allopurinol, oxipurinol and uric acid have been determined in human serum and urine by liquid chromatography with electrochemical detection. In particular the use of a polarographic detector operating in the oxidative mode, whose principle of detection is based on the property of allopurinol, oxipurinol and uric acid to form insoluble anodic films on mercury, is described. The performance of such a detector is compared with that of a glassy carbon wall-jet detector. Different procedures for sample pretreatment have been evaluated.

On the metabolism of allopurinol. Formation of allopurinol-1-riboside in purine nucleoside phosphorylase deficiency

Allopurinol-1-riboside, a major metabolite of allopurinol, is commonly thought to be directly synthesized by purine nucleoside phosphorylase (PNP) in vivo. As this enzyme is otherwise believed to function in vivo primarily in the direction of nucleoside breakdown, we have determined by high performance liquid chromatography and a conventional chromatographic method the urinary metabolites of allopurinol in a child deficient of PNP. In this patient approximately 40% of urinary allopurinol metabolites consisted of allopurinol-1-riboside, thus proving the possibility of indirect formation of allopurinol-1-riboside via allopurinol-1-ribotide in vivo, catalysed by hypoxanthine guanine phosphoribosyltransferase (HGPRT) and a phosphatase.

Prevention of recurrent uric acid and calcium oxalate stones by administration of the xanthine oxidase inhibitors Milurit 100 and Milurit 300

Disturbances in purine metabolism with hyperuricaemia and/or hyperuricosuria are a risk factor in uric acid and Ca oxalate stone formation. By way of a competitive xanthine oxidase inhibition, the formation of uric acid is reduced by allopurinol. In investigations on two groups of patients, Milurit could be demonstrated to decrease the uric acid levels in serum and urine. No differences could be seen in the dosages of 3 x 100 mg or 1 x 300 mg Milurit. Therefore, in stone recurrence prevention, the administration of Milurit 300 is recommended.

Oxypurinol nephrolithiasis in regional enteritis secondary to allopurinol therapy

A patient with regional enteritis and recurrent uric acid nephrolithiasis was treated with allopurinol. While on 600 mg of allopurinol daily, she began to pass many small, soft, yellow stones. Analysis of the stones by liquid chromatographic and gas chromatograph/mass spectrometric techniques revealed that their major constituent was oxypurinol, a metabolite of allopurinol. Metabolic studies of the patient indicated that increasing doses of allopurinol were associated with increases in xanthine and oxypurinol excretion, while uric acid excretion was not reduced. This case illustrates a complication of high-dose allopurinol therapy in the treatment of uric acid nephrolithiasis.

The determination of allopurinol and oxipurinol in human plasma and urine

A method is described for allopurinol and oxipurinol assay within human plasma and urine in the range expected during therapy. The method is based on high-performance ion-exchange chromatography following an efficient sample purification step using Chelex-100 resin in the Cu2+-form. Linear calibration curves are produced for allopurinol over the range 0.05-10 mumole/1 (0.068-1.36 mug/ml) in plasma and 0.005-1 mmole/1 (0.68-136 mug/ml) in urine and for oxipurinol 0.5-100 mumole/1 (0.076-15.2 mug/ml) in plasma and 0.1-2 mmole/1 (15.2-304 mug/ml) in urine.