The Metabolism of Arsenic in Humans Acutely Intoxicated by AS2O3. Its Significance for the Duration of BAL Therapy

Abstract

The urinary excretion of inorganic arsenic and of its less toxic metabolites [monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA)] has been followed-up in five cases of acute oral intoxication by AS₂O₃. In addition to supportive therapy all patients were given BAL. The proportion of the three species of urinary arsenic (inorganic, MMA, DMA) changes markedly with time. During the first 2 to 4 d after the intoxication, arsenic is excreted mainly as its unmetabolized inorganic form but this is rapidly followed-up by a progressive increase of the proportion excreted as MMA and DMA. The time at which the majority of arsenic is excreted as its organic metabolites depends on the severity of the intoxication but in all the cases, more than 95% of the excreted arsenic is in the organic form after 9 d, the dimethylated derivative being preponderant. Speciation of arsenicals in urine might be useful to determine the duration of BAL treatment.     

Arsenic speciation analysis in human saliva

BACKGROUND: Determination of arsenic species in saliva is potentially useful for biomonitoring of human exposure and studying arsenic metabolism. Arsenic speciation in saliva has not been reported previously. METHODS: We separated arsenic species in saliva using liquid chromatography (LC) and quantified them by inductively coupled plasma mass spectrometry. We further confirmed the identities of arsenic species by LC coupled with electrospray ionization tandem mass spectrometry. These methods were successfully applied to the determination of arsenite (As(III)), arsenate (As(V)), and their methylation metabolites, monomethylarsonic acid (MMA(V)), and dimethylarsinic acid (DMA(V)), in >300 saliva samples collected from people who were exposed to varying concentrations of arsenic. RESULTS: The mean (range) concentrations (microg/L) in the saliva samples from 32 volunteers exposed to background levels of arsenic were As(III) 0.3 [not detectable (ND) to 0.7], As(V) 0.3 (ND to 0.5), MMA(V) 0.1 (ND to 0.2), and DMA(V) 0.7 (ND to 2.6). Samples from 301 people exposed to increased concentrations of arsenic in drinking water showed detectable As(III) in 99%, As(V) in 98%, MMA(V) in 80%, and DMA(V) in 68% of samples. The mean (range) concentrations of arsenic species in these saliva samples were (in microg/L) As(III) 2.8 (0.1-38), As(V) 8.1 (0.3-120), MMA(V) 0.8 (0.1-6.0), and DMA(V) 0.4 (0.1-3.9). Saliva arsenic correlated with drinking water arsenic. Odds ratios for skin lesions increased with saliva arsenic concentrations. The association between saliva arsenic concentrations and the prevalence of skin lesions was statistically significant (P <0.001). CONCLUSIONS: Speciation of As(V), As(III), MMA(V), and DMA(V) in human saliva is a useful method for monitoring arsenic exposure.     

The measurement of urinary digoxin and dihydrodigoxin by radioimmunoassay and by mass spectroscopy.

A radioimmunoassay for urinary digoxin is described which includes an initial solvent extraction to remove factors in urine which cause non-specific interference in the assay. The recoveries obtained using different solvents are compared and the non-specific factors influencing the assay investigated further. These effects were overcome by the use of a small urine volume (10 mul) in a direct, unextracted, urine assay and the results obtained correlated closely with those from the assay using prior extraction (r=0.99). No false positive results were obtained with unextracted urine samples from hospitalised patients not receiving digoxin. The specificity was also determined with regard to the natural steroids, spironolactone and the metabolites of digoxin including dihydrodigoxin. The metabolite dihydrodigoxin, with a saturated lactone ring, was not detected whereas the mono-, and bis-digitoxo-sides and digoxigenin metabolites did cross react in the assay. It was not possible to separate dihydrodigoxin and digoxin by thin-layer chromatography or solvent extraction due to their similar structures, however, mass spectroscopy was successful in this respect and was employed to obtain the ratio of dihydrodigoxin to digoxin in extracted urine samples. Levels of urinary digoxin excreted by patients maintained on different oral doses of the drug were measured. The percentage excreted in the urine as digoxin correlated closely with the oral dose (r = 0.96) but was found to be lower than that reported in most previous studies. Mass spectroscopy measurements showed that an average of 16.4% (range 12.2-19.7%) of the total oral dose was excreted as dihydrodigoxin in the urine of nine patients investigated.     

Active Metabolites of Isoxazolylpenicillins in Humans

Metabolites of the isoxazolylpenicillins that still possessed antibacterial activity were shown to be present in urine and serum. In healthy subjects, the amounts excreted in urine were low; 10 to 23% of the excreted penicillin activities represented the metabolites. The highest amount of metabolite in urine was found for oxacillin, and the lowest was found for flucloxacillin. No extreme differences in the amounts of metabolite excreted were observed when the compounds were administered orally or intravenously. In one healthy subject metabolite levels were estimated for cloxacillin in serum. Very low levels were found, i.e., about 9% of the activity. In subjects with highly impaired renal function, the metabolite may represent up to 50% of the total level of penicillin in serum. The antibacterial activities of the different metabolites were of the same order of magnitude as those of the respective parent compounds. Also, the activity against benzylpenicillin-resistant staphylococci was retained. It is not likely that the formation of the active metabolites should influence therapeutic results.     

A method for studying drug metabolism in populations: racial differences in amobarbital metabolism.

The two main metabolites of amobarbital excreted in urine are 3'-hydroxyamobarbital (C-OH) and 1-(beta-D-glucopyranosyl) amobarbital (N-glu). When testing the metabolite ratio in small single samples of urine, it was found that the urine in a Caucasian population contained about one-third glucose conjugation and two-thirds hydroxylation product, while an Oriental population excreted both metabolites in equal proportion. Attempts to learn the causes for the different metabolite ratios led to an investigation of metabolite concentrations in urine. The sums of the average urinary concentration of C-OH was greater in Caucasians than in Orientals, no matter how the data were expressed; the reverse was true for the N-glu metabolite. C-OH data was scattered more widely among Orientals than Caucasians; this might indicate bimodality of the distribution curves. There also was a trend toward more N-glu metabolite in urine of females than of males. Measuring the metabolite/creatinine ratios narrowed the distribution range of the data, particularly after correction for sex difference in creatinine, but population differences were not changed. Expected relationships between metabolite content of urine, sampling times, and plasma half-life (t1/2) were established by calculation. A Caucasian female with no capacity for N-glucosidation was found during the first part of this population survey. An Oriental male with only trace capacity for amobarbital hydroxylation was found in the second part.     

Steady-state disposition of the nonpeptidic protease inhibitor tipranavir when coadministered with ritonavir

The pharmacokinetic and metabolite profiles of the antiretroviral agent tipranavir (TPV), administered with ritonavir (RTV), in nine healthy male volunteers were characterized. Subjects received 500-mg TPV capsules with 200-mg RTV capsules twice daily for 6 days. They then received a single oral dose of 551 mg of TPV containing 90 microCi of [(14)C]TPV with 200 mg of RTV on day 7, followed by twice-daily doses of unlabeled 500-mg TPV with 200 mg of RTV for up to 20 days. Blood, urine, and feces were collected for mass balance and metabolite profiling. Metabolite profiling and identification was performed using a flow scintillation analyzer in conjunction with liquid chromatography-tandem mass spectrometry. The median recovery of radioactivity was 87.1%, with 82.3% of the total recovered radioactivity excreted in the feces and less than 5% recovered from urine. Most radioactivity was excreted within 24 to 96 h after the dose of [(14)C]TPV. Radioactivity in blood was associated primarily with plasma rather than red blood cells. Unchanged TPV accounted for 98.4 to 99.7% of plasma radioactivity. Similarly, the most common form of radioactivity excreted in feces was unchanged TPV, accounting for a mean of 79.9% of fecal radioactivity. The most abundant metabolite in feces was a hydroxyl metabolite, H-1, which accounted for 4.9% of fecal radioactivity. TPV glucuronide metabolite H-3 was the most abundant of the drug-related components in urine, corresponding to 11% of urine radioactivity. In conclusion, after the coadministration of TPV and RTV, unchanged TPV represented the primary form of circulating and excreted TPV and the primary extraction route was via the feces.     

Disposition, metabolism, and excretion of [14C]doripenem after a single 500-milligram intravenous infusion in healthy men

In this open-label, single-center study, eight healthy men each received a single 500-mg dose of [¹⁴C]doripenem, containing 50 μCi of [¹⁴C]doripenem, administered as a 1-h intravenous infusion. The concentrations of unchanged doripenem and its primary metabolite (doripenem-M-1) resulting from β-lactam ring opening were measured in plasma and urine by a validated liquid chromatography method coupled to a tandem mass spectrometry assay. Total radioactivity was measured in blood, plasma, urine, and feces by liquid scintillation counting. Further metabolite profiling was conducted on urine samples using liquid chromatography coupled to radiochemical detection and high-resolution mass spectrometry. Unchanged doripenem and doripenem-M-1 accounted for means of 80.7% and 12.7% of the area under the plasma total-radioactivity-versus-time curve (area under the concentration-time curve extrapolated to infinity) and exhibited elimination half-lives of 1.1 and 2.5 h, respectively. Total clearance of doripenem was 16 liters/h, and renal clearance was 12.5 liters/h. At 7 days after the single dose, 95.3% of total doripenem-related radioactivity was recovered in urine and 0.72% in feces. A total mean of 97.2% of the administered dose was excreted in the urine as unchanged doripenem (78.7% ± 5.7%) and doripenem-M-1 (18.5% ± 2.6%). Most of the urinary recovery occurred within 4 h of dosing. Three additional minor metabolites were identified in urine: the glycine and taurine conjugates of doripenem-M-1 and oxidized doripenem-M-1. These results show that doripenem is predominantly eliminated in urine as unchanged drug, with only a fraction metabolized to doripenem-M-1 and other minor metabolites.     

Mass Balance and Metabolite Profiling of Steady-State Faldaprevir,a Hepatitis C Virus NS3/4 Protease Inhibitor,in Healthy Male Subjects

The pharmacokinetics, mass balance, and metabolite profiles of faldaprevir, a selective peptide-mimetic hepatitis C virus NS3/NS4 protease inhibitor, were assessed at steady state in 7 healthy male subjects. Subjects received oral doses of 480 mg faldaprevir on day 1, followed by 240 mg faldaprevir on days 2 to 8 and 10 to 15. [¹⁴C]faldaprevir (240 mg containing 100 μCi) was administered on day 9. Blood, urine, feces, and saliva samples were collected at intervals throughout the study. Metabolite profiling was performed using radiochromatography, and metabolite identification was conducted using liquid chromatography-tandem mass spectrometry. The overall recovery of radioactivity was high (98.8%), with the majority recovered from feces (98.7%). There was minimal radioactivity in urine (0.113%) and saliva. Circulating radioactivity was predominantly confined to plasma with minimal partitioning into red blood cells. The terminal half-life of radioactivity in plasma was approximately 23 h with no evidence of any long-lasting metabolites. Faldaprevir was the predominant circulating form, accounting for 98 to 100% of plasma radioactivity from each subject. Faldaprevir was the only drug-related component detected in urine. Faldaprevir was also the major drug-related component in feces, representing 49.8% of the radioactive dose. The majority of the remainder of radioactivity in feces (41% of the dose) was accounted for in almost equal quantities by 2 hydroxylated metabolites. The most common adverse events were nausea, diarrhea, and constipation, all of which were related to study drug. In conclusion, faldaprevir is predominantly excreted in feces with negligible urinary excretion.     

Disposition of [14C]aztreonam in rats, dogs, and monkeys

[14C]aztreonam was administered as single 25-mg/kg doses to dogs (intravenously and subcutaneously) and monkeys (intramuscularly and intravenously) and as single 50-mg/kg doses (intramuscularly and intravenously) to rats. In rats and dogs, radioactive moieties were excreted primarily in urine; in monkeys, they were excreted about equally in urine and feces. Unchanged aztreonam accounted for 77 to 86% of the radioactivity excreted in the urine of rats, dogs, and monkeys; SQ 26,992, the metabolite resulting from hydrolysis of the monobactam ring, accounted for 10 to 15%; and minor, unidentified metabolites accounted for the remainder. In rats with cannulated bile ducts, about 15% of an intramuscular dose was excreted in bile in 24 h; the bile contained a greater percentage of metabolites than that found in urine. In dogs, the apparent elimination half-life of aztreonam in serum was 0.7 h after intravenous administration. Aztreonam and SQ 26,992 accounted for most of the radioactivity in the sera of dogs and monkeys. Serum protein binding of aztreonam and its metabolites ranged from 28 to 35% in dogs and from 49 to 59% in monkeys. In the three species studied, aztreonam was most extensively metabolized in monkeys; SQ 26,992 and other minor metabolites from monkey urine were tested and found to be devoid of any significant antimicrobial activity.     

Metabolism of Vitamin D3-3H in Human Subjects: Distribution in Blood, Bile, Feces, and Urine

Vitamin D(3)-(3)H has been administered intravenously to seven normal subjects, three patients with biliary fistulas, and four patients with cirrhosis. Plasma D(3)-(3)H half-times normally ranged from 20 to 30 hours. in vivo evidence that a metabolic transformation of vitamin D occurs was obtained, and a polar biologically active vitamin D metabolite was isolated from plasma.Urinary radioactivity averaged 2.4% of the administered dose for the 48-hour period after infusion, and all the excreted radioactivity represented chemically altered metabolites of vitamin D. The metabolites in urine were mainly water-soluble, with 26% in conjugated form.From 3 to 6% of the injected radioactivity was excreted in the bile of subjects with T-tube drainage and 5% in the feces of patients having no T-tube. The pattern of fecal and biliary radioactivity suggested that the passage of vitamin D and its metabolites from bile into the intestine represents an essential stage for the fecal excretion of vitamin D metabolites in man.Abnormally slow plasma disappearance of vitamin D(3)-(3)H in patients with cirrhosis was associated with a significant decrease in the quantity and rate of glucuronide metabolite excretion in the urine.     

Caffeine clearance and biotransformation in patients with chronic liver disease

1. The clearance and biotransformation of caffeine (1,3,7-trimethylxanthine) were investigated in eight healthy control subjects and 16 patients with cirrhosis, by measuring serial serum caffeine concentrations and recoveries of methylxanthine metabolites in urine for 48 h after a 400 mg oral caffeine load. 2. In the control group, the mean (+/- SD) serum caffeine clearance was 1.3 +/- 0.4 ml min-1 kg-1 and a mean of 56.4 +/- 16.5% of the administered caffeine was recovered from the urine over 48 h as methyluric acids and methylxanthines. The majority of the metabolites were excreted in the first 24 h period and only 2.0 +/- 1.4% of the administered caffeine was excreted unchanged. 3. Patients with compensated cirrhosis (n = 10) metabolized caffeine similarly to the control subjects. Thus the mean serum caffeine clearance was 1.4 +/- 1.2 ml min-1 kg-1 and a mean of 57.2 +/- 11.7% of the administered caffeine was recovered from the urine over 48 h. The majority of the metabolites were excreted in the first 24 h; the pattern of metabolic excretion was unaltered and only 2.2 +/- 0.9% of the administered caffeine was excreted unchanged. 4. In the patients with decompensated cirrhosis (n = 6), significant changes were observed in caffeine metabolism. The mean serum caffeine clearance (0.4 +/- 0.2 ml min-1 kg-1) was significantly impaired compared with controls (P less than 0.01) and a significant delay was observed in metabolite excretion in the urine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Metabolism and excretion of a glutathione conjugate of acetaminophen in the isolated perfused rat kidney

Acetaminophen-glutathione (APAP-GSH) is the initial sulfur-containing metabolite of APAP produced by the liver. However, little, if any, APAP-GSH is found in the urine of intact animals. Rather, the cysteine (APAP-CYS) and N-acetylcysteine (APAP-NAC) conjugates are the predominant sulfur-containing metabolites of APAP excreted in the urine. To define more precisely the role of the kidney in total body disposition of APAP, the metabolism and excretion of each of these metabolites was quantified in the isolated perfused rat kidney (IPK). With perfusate concentrations of 0.031, 0.125 and 0.250 mM APAP-GSH, the IPK metabolized APAP-GSH to APAP-CYS rapidly. Further metabolism of APAP-CYS to APAP-NAC proceeded at a much slower rate. Consequently, at 0.031 mM APAP-GSH, negligible amounts of APAP-CYS were found in the urine. However, as the concentration of APAP-GSH was increased so did the excretion of APAP-CYS. In contrast, the excretion of APAP-NAC did not exhibit dependence on APAP-GSH concentration. APAP-NAC was excreted by a probenecid sensitive transport mechanism whereas APAP-CYS excretion appeared to be related only to glomerular filtration. In addition, the disappearance of APAP-GSH was much greater than could be accounted for by glomerular filtration. These data indicate that the IPK is an effective model for the study of metabolism and excretion of xenobiotics that have undergone conjugation with GSH.     

Excretion of doxifluridine catabolites in human bile assessed by 19F NMR spectrometry

The biliary excretion of doxifluridine (5'dFUR) catabolites was studied in a patient with external bile derivation using 19F NMR spectrometry, alpha-fluoro-beta-alanine (FBAL) and fluoride ion were detected in patient's bile samples but represented only about 10% of the excreted fluorinated metabolites. The major biliary metabolite (congruent to 90%), whose structure is still unknown, is a conjugate of FBAL. The cumulative biliary excretion of 5'dFUR fluorinated metabolites was low and represented 0.8% of the injected dose.     

Isolation and identification of some metabolites of mephenoxalone (Control-OM) from human urine (author's transl)

Mephenoxalone (5-(o-methoxyphenoxymethyl)-2-oxazolidone) is degraded by various routes in the human, and some is excreted unchanged. In the metabolism of mephenoxalone, the phenoxymethyl ether bond is cleaved; thus o-methoxyphenol (metabolite I) was identified in urine, and 3-amino-1,2-propanediol (IIa) was found after alkaline hydrolysis. Hydroxylation of the benzene ring produces a phenolic hydroxymephenoxalone (metabolite III), and demethylation converts mephenoxalone into demethylmepheonxalone (metabolite IV). Opening of the oxazolidone ring leads to the production of 1-(o-methoxyphenoxy)-3-aminopropane-2-ol(metabolite V). Urine contains two further substances: 1-(o-hydroxyphenoxy)-3-aminopropene (metabolite VI) and dehydromephenoxalone (metabolite VII). Metabolite VI may be an artefact. Compounds III, IV and VII could only be detected after acid hydrolysis and enzymic cleavage with beta-glucuronidase/aryl sulphatase, whereas V and VI were detected only after acid hydrolysis. Thin layer chromatography revealed three further metabolites, which were not identified.     

The absence of significant biliary excretion of antipyrine or its metabolites in humans

Three patients with complete bile duct obstructions requiring a percutaneous biliary fistuala were given an oral dose of antipyrine. Drug elimination was assessed through plasma t1/2 studies and urine and bile excretion of both antipyrine and its metabolites. Urine metabolite patterns were in agreement with reference standards, but analysis of bile revealed no antipyrine metabolites and minimal parent compound (mean of total administered dose excreted from the bile fistulas was 4%). This finding was not predicted from previous experiments in the bile-cannulated rat and suggests caution regarding interspecies extrapolation of data concerning the hepatic disposition of certain commonly used test drugs in clinical pharmacologic studies.     

Sample preparation and storage can change arsenic speciation in human urine.

BACKGROUND: Stability of chemical speciation during sample handling and storage is a prerequisite to obtaining reliable results of trace element speciation analysis. There is no comprehensive information on the stability of common arsenic species, such as inorganic arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid, dimethylarsinic acid, and arsenobetaine, in human urine. METHODS: We compared the effects of the following storage conditions on the stability of these arsenic species: temperature (25, 4, and -20 degrees C), storage time (1, 2, 4, and 8 months), and the use of additives (HCl, sodium azide, benzoic acid, benzyltrimethylammonium chloride, and cetylpyridinium chloride). HPLC with both inductively coupled plasma mass spectrometry and hydride generation atomic fluorescence detection techniques were used for the speciation of arsenic. RESULTS: We found that all five of the arsenic species were stable for up to 2 months when urine samples were stored at 4 and -20 degrees C without any additives. For longer period of storage (4 and 8 months), the stability of arsenic species was dependent on urine matrices. Whereas the arsenic speciation in some urine samples was stable for the entire 8 months at both 4 and -20 degrees C, other urine samples stored under identical conditions showed substantial changes in the concentration of As(III), As(V), monomethylarsonic acid, and dimethylarsinic acid. The use of additives did not improve the stability of arsenic speciation in urine. The addition of 0.1 mol/L HCl (final concentration) to urine samples produced relative changes in inorganic As(III) and As(V) concentrations. CONCLUSIONS: Low temperature (4 and -20 degrees C) conditions are suitable for the storage of urine samples for up to 2 months. Untreated samples maintain their concentration of arsenic species, and additives have no particular benefit. Strong acidification is not appropriate for speciation analysis.     

Characterization of diabetic nephropathy by urinary proteomic analysis: identification of a processed ubiquitin form as a differentially excreted protein in diabetic nephropathy patients

BACKGROUND: Identification of markers for prediction of the clinical course of diabetic nephropathy remains a major challenge in disease management. We established a proteomics approach for identification of diabetic nephropathy-related biomarkers in urine. METHODS: We used SELDI-TOF mass spectrometry and SAX2 protein arrays to compare protein profiles from urine of 4 defined patient groups. Samples from patients with type 2 diabetes (DM; n = 45) without nephropathy and without microalbuminuria (DM-WNP), patients with DM with macro- or microalbuminuria (DM-NP; n = 38), patients with proteinuria due to nondiabetic renal disease (n = 34), and healthy controls (n = 45) were analyzed. Anionic exchange, reversed-phase fractionation, gel electrophoresis, and mass spectrometry were used to isolate and identify proteins with high discriminatory power. RESULTS: A protein with m/z 6188 (P <0.0000004) was strongly released in the urine of healthy controls, patients with proteinuria due to nondiabetic disease, and DM-WNP in contrast to DM-NP patients. An m/z 14 766 protein (P <0.00008) was selectively excreted in the urine of DM-NP patients, whereas the protein with m/z 11 774 (P <0.000004) was significantly excreted by patients with proteinuria and DM-NP. The m/z 11 774 and m/z 14 766 mass peaks were identified as beta(2)-microglobulin and UbA52, a ubiquitin ribosomal fusion protein, respectively. The protein with m/z 6188 was identified as a processed form of ubiquitin. CONCLUSION: The release of high amounts of UbA52 in urine of DM-NP patients could serve as a diagnostic marker, whereas the lack of the short form of ubiquitin raises interesting questions about the pathophysiology.     

Discovery of methoxyacetylcarbamide in the urine of normal adults and phenylketonuric children

In order to study metabolic distinctions in phenylketonuria, urinary metabolites in the form of trimethylsilyl derivatives have been characterized by high resolution gas chromatography and mass spectrometry. A previously unknown metabolite has been found in the urine of some untreated phenylketonuric infants between 2 and 5 yr of age. The metabolite was absent in healthy children of the same age. The metabolite appeared to be present in the urine of apparently healthy adults (25-32 yr old). The metabolite was identified as methoxyacetylcarbamide on the basis of mass fragmentation analysis and compared with synthetic methoxyacetylcarbamide. Their retention times and mass spectra coincided.     

A phase I study evaluating tolerability, pharmacokinetics, and preliminary efficacy of L-menthol in upper gastrointestinal endoscopy

Peppermint oil has been shown to relax gastrointestinal smooth muscle. In this randomized, placebo-controlled study, an L-menthol preparation, NPO-11, was assessed for tolerability and pharmacokinetics (PK) during gastrointestinal endoscopy. Single doses of NPO-11, as high as 320 mg, were well tolerated. NPO-11 was rapidly absorbed, with peak concentrations reached within 1 h after administration. Approximately 70% of the administered L-menthol and its metabolites were excreted in the urine, and this amount fluctuated with no change in the dose. The principal metabolite identified in plasma and urine was menthol glucuronide. The other metabolites include mono- or di-hydroxylated menthol derivatives, most of which are excreted, in part, as glucuronic acid conjugates. The pharmacokinetic data indicated that when NPO-11 is sprayed directly onto the gastric mucosa, it is rapidly metabolized to glucuronic acid conjugates that are excreted in urine. The findings from this study provide new data on the safety and PK of NPO-11 and support further trials.     

Pharmacokinetics of [(14)C]abacavir, a human immunodeficiency virus type 1 (HIV-1) reverse transcriptase inhibitor, administered in a single oral dose to HIV-1-infected adults: a mass balance study

Abacavir (1592U89) ((-)-(1S, 4R)-4-[2-amino-6-(cyclopropylamino)-9H-purin-9-yl]-2-cyclopentene- 1-m ethanol) is a 2'-deoxyguanosine analogue with potent activity against human immunodeficiency virus (HIV) type 1. To determine the metabolic profile, routes of elimination, and total recovery of abacavir and metabolites in humans, we undertook a phase I mass balance study in which six HIV-infected male volunteers ingested a single 600-mg oral dose of abacavir including 100 microCi of [(14)C]abacavir. The metabolic disposition of the drug was determined through analyses of whole-blood, plasma, urine, and stool samples, collected for a period of up to 10 days postdosing, and of cerebrospinal fluid (CSF), collected up to 6 h postdosing. The radioactivity from abacavir and its two major metabolites, a 5'-carboxylate (2269W93) and a 5'-glucuronide (361W94), accounted for the majority (92%) of radioactivity detected in plasma. Virtually all of the administered dose of radioactivity (99%) was recovered, with 83% eliminated in urine and 16% eliminated in feces. Of the 83% radioactivity dose eliminated in the urine, 36% was identified as 361W94, 30% was identified as 2269W93, and 1.2% was identified as abacavir; the remaining 15.8% was attributed to numerous trace metabolites, of which <1% of the administered radioactivity was 1144U88, a minor metabolite. The peak concentration of abacavir in CSF ranged from 0.6 to 1.4 microg/ml, which is 8 to 20 times the mean 50% inhibitory concentration for HIV clinical isolates in vitro (0.07 microg/ml). In conclusion, the main route of elimination for oral abacavir in humans is metabolism, with <2% of a dose recovered in urine as unchanged drug. The main route of metabolite excretion is renal, with 83% of a dose recovered in urine. Two major metabolites, the 5'-carboxylate and the 5'-glucuronide, were identified in urine and, combined, accounted for 66% of the dose. Abacavir showed significant penetration into CSF.