Effect of sodium sulfate on acetaminophen elimination by rats

Semi-mechanistic kidney model incorporating physiologically-relevant fluid reabsorption and transporter-mediated renal reabsorption: pharmacokinetics of γ-hydroxybutyric acid and L-lactate in rats

This study developed a semi-mechanistic kidney model incorporating physiologically-relevant fluid reabsorption and transporter-mediated active reabsorption. The model was applied to data for the drug of abuse γ-hydroxybutyric acid (GHB), which exhibits monocarboxylate transporter (MCT1/SMCT1)-mediated renal reabsorption. The kidney model consists of various nephron segments--proximal tubules, Loop-of-Henle, distal tubules, and collecting ducts--where the segmental fluid flow rates, volumes, and sequential reabsorption were incorporated as functions of the glomerular filtration rate. The active renal reabsorption was modeled as vectorial transport across proximal tubule cells. In addition, the model included physiological blood, liver, and remainder compartments. The population pharmacokinetic modeling was performed using ADAPT5 for GHB blood concentration-time data and cumulative amount excreted unchanged into urine data (200-1000 mg/kg IV bolus doses) from rats [Felmlee et al (PMID: 20461486)]. Simulations assessed the effects of inhibition (R = [I]/KI = 0-100) of renal reabsorption on systemic exposure (AUC) and renal clearance of GHB. Visual predictive checks and other model diagnostic plots indicated that the model reasonably captured GHB concentrations. Simulations demonstrated that the inhibition of renal reabsorption significantly increased GHB renal clearance and decreased AUC. Model validation was performed using a separate dataset. Furthermore, our model successfully evaluated the pharmacokinetics of L-lactate using data obtained from Morse et al (PMID: 24854892). In conclusion, we developed a semi-mechanistic kidney model that can be used to evaluate transporter-mediated active renal reabsorption of drugs by the kidney.

Paracetamol-induced hepatotoxicity: lack of enhancement of the hepatoprotective effect of N-acetylcysteine by sodium sulphate

The potential role of sodium sulphate in possible enhancement of the hepatoprotective action of N-acetylcysteine (NAC) in paracetamol (PCM) overdose was examined. The effects of sodium sulphate (200 mg/kg) in combination with NAC (400 mg/kg) administered intraperitoneally 2 h post-PCM dose, on mortality rate and plasma activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were investigated in mice 24 h after receiving a single oral dose of 400 mg/kg PCM. In addition, the effect on the mortality rate of PCM-treated animals of co-administering 400 mg/kg sodium sulphate with NAC (200 or 400 mg/kg) was also studied. NAC alone caused a marked reduction in the mortality rate of PCM-treated mice and a sharp drop in their plasma AST and ALT activities to near normal values. However, no additional reduction in plasma levels of AST and ALT was observed when sodium sulphate was co-administered with NAC. Similarly, sodium sulphate (200 mg/kg) administered alone to PCM-treated mice had no effect on the high mortality rate or the elevation in plasma AST and ALT activities observed in these animals. Furthermore, increasing the dose of sodium sulphate to 400 mg/kg did not influence the mortality rate. It is therefore concluded that sodium sulphate neither protects against paracetamol-induced hepatotoxicity nor enhances the hepatoprotective action of N-acetylcysteine.

Plasma concentration of paracetamol and its major metabolites after p.o. dosing with paracetamol or concurrent administration of paracetamol and its N-acetyl-DL-methionine ester in mice

1. Single doses of paracetamol 400 (PAR 400) and 800 mg/kg (PAR 800), SUR 2647 combination (free paracetamol + paracetamol-N-acetyl-DL-methionate, paracetamol/methionine ratio 2:1) equivalent to PAR 400 (SURc 400) and PAR 800 (SURc 800) were given p.o. to male Bom:NMRI mice. 2. The objective was to compare the plasma concentrations of free paracetamol and the major metabolites paracetamol-sulphate and paracetamol-glucuronide for a 6 hr period after each test drug. 3. There was no significant difference between PAR 400 and SURc 400 with respect to plasma paracetamol, paracetamol-glucuronide and paracetamol-sulphate concentration with the exception of lower plasma paracetamol concentration (P less than 0.03) at 3 hr following PAR 400. 4. There was no significant difference between PAR 800 and SURc 800 with respect to plasma paracetamol, paracetamol-glucuronide and paracetamol-sulphate concentrations with the exception of lower plasma paracetamol-glucuronide concentration (P less than 0.03) at 4 hr after dosing following SURc 800. 5. Combining free paracetamol and its methionine ester does not seem to alter the pattern of plasma paracetamol, paracetamol-glucuronide and paracetamol-sulphate compared to equal doses of free paracetamol alone after p.o. administration of toxic doses to male Bom:NMRI mice.

Tissue sulfate determination by ion chromatography

The application of controlled-flow anion chromatography to assay inorganic sulfate in biological fluids and tissues is described. The eluent used in previous methods for analyzing sulfate in biological fluids has been modified by adding 4.5% acetonitrile to separate sulfate from a co-eluting peak. To markedly increase the life of the column, the tissue samples were further diluted, extracted with chloroform, and analyzed at a lower detection range (0.3 microS). The method has been shown to be applicable for determining sulfate in tissues as well as biological fluids.

Metabolism of low-dose paracetamol in patients with rheumatoid arthritis

1. Low dose (500 mg) paracetamol (acetaminophen) was administered to patients with rheumatoid arthritis (RA) and to age-matched healthy controls and to hospital controls. 2. At this dose level, patients with RA excreted decreased amounts of paracetamol sulphate (controls means 11.3 +/- 5.1, 10.6 +/- 5.9; RA mean 3.02 +/- 3.7). This difference is statistically significant (P less than 0.001). 3. The mean ratio of excretion of paracetamol sulphate/paracetamol glucuronide was 5.6 +/- 12.1, 5.3 +/- 10.7 in controls but 2.1 +/- 2.7 in RA patients (P less than 0.001). 4. Patients with RA appear to have less capacity for excreting paracetamol as non-toxic conjugates and may be more susceptible to paracetamol toxicity, especially on chronic dosage.

Metabolism of low-dose paracetamol in patients with chronic neurological disease

1. Low dose (500 mg) paracetamol (acetaminophen) was administered to patients with Parkinson's disease, motor neurone disease and to age-matched controls. 2. At this low dose level the controls excreted proportionately more sulphate and less glucuronide conjugate than has been reported for administration of 1000 mg of paracetamol. 3. Both groups of patients with chronic neurological disease excreted decreased amounts of paracetamol sulphate (control mean 11.2 +/- 5.4% dose; Parkinson's disease 3.9 +/- 3.7%; motor neurone disease, 5.0 +/ 4.1%). 4. The mean ratio of excretion of paracetamol sulphate/paracetamol glucuronide was 5.6 +/- 11.7 in controls, but 1.1 +/- 1.7 and 1.2 +/- 1.7 in Parkinson's disease and motor neurone disease respectively. These differences are statistically significant (p less than 0.001).

Acetaminophen pharmacokinetics: comparison between pregnant and nonpregnant women

Acetaminophen is the most commonly taken drug during pregnancy, but knowledge about its absorption and disposition is lacking. Six healthy women volunteered to ingest a standard 1000 mg dose at 36 weeks' gestation and 6 weeks post partum. Mean maternal serum concentrations of acetaminophen were consistently less than but not significantly different from the postpartum values. The mean half-life of acetaminophen during pregnancy (3.7 hours) was not significantly different from the nonpregnant value (3.1 hours). The maximum plasma concentration occurred at 0.8 hours and was 20.8 +/- 6.9 micrograms/ml during pregnancy and 23.7 +/- 6.0 micrograms/ml in the nonpregnant state. The absorption, metabolism, and renal clearance of acetaminophen were unchanged. The decrease in the mean area under the curve during pregnancy may be explained by the increase in volume of distribution of acetaminophen. Potentially hepatotoxic metabolites were not measurable in the maternal serum. We conclude that the absorption and disposition of acetaminophen, when used in a standard oral dose, are not affected by pregnancy.

Dopamine sulfate formation and phenol sulfotransferase activity in dog and human platelets

High performance liquid chromatography with radioactive flow detection was used to examine the accumulation and sulfoconjugation of dopamine by human and dog platelets. Platelets from both species accumulated similar amounts of dopamine from the incubation medium, but only human platelets were found to convert 3H-dopamine to 3-H-dopamine sulfate. This difference between the two species was associated with a relative absence of phenol sulfotransferase activity in dog platelets as compared to human platelets. Dog platelets did not appear to contain an inhibitor of phenol sulfotransferase activity. Despite the apparent difference in the ability of platelets to form dopamine sulfate, conc concentrations of dopamine-3-O-sulfate and dopamine-4-O-sulfate were similar in dog and human plasma. These data suggest that platelets may represent a potential source of at least some of the dopamine sulfate found in human plasma, but not in dog plasma.

Absorption and metabolism of acetaminophen shortly before parturition

The absorption and metabolism of acetaminophen 1 g po (as tablets) by a healthy 27-year-old woman was determined one day before parturition and again 38 days after parturition. Based on the urinary excretion data, acetaminophen was absorbed much more slowly and incompletely, and the metabolic conversion of acetaminophen to the sulfate conjugate was less pronounced on the last day of pregnancy than 38 days after parturition. These results are consistent with reports of decreased gastric emptying rate in late human pregnancy and with decreased acetaminophen sulfation by rats during the last days of gestation.

Evaluation of activated charcoal-sodium sulfate combination for inhibition of acetaminophen absorption and repletion of inorganic sulfate

Activated charcoal is an effective inhibitor of acetaminophen absorption while sodium sulfate can prevent the depletion of endogenous inorganic sulfate associated with the formation of acetaminophen sulfate. Administration of activated charcoal plus sodium sulfate soon after acetaminophen overdose may reduce acetaminophen absorption and facilitate the elimination of absorbed acetaminophen by providing sufficient sulfate ion for rapid sulfation of the drug. This investigation was designed to determine if sodium sulfate modifies the inhibitory effect of activated charcoal on acetaminophen absorption or if activated charcoal affects the absorption of sodium sulfate. Eight normal adults received, on separate occasions, 1 g acetaminophen, 1 g acetaminophen and 18 g sodium sulfate (decahydrate), 1 g acetaminophen with 10 g activated charcoal and 1 g acetaminophen, with 10 g activated charcoal and 18 g sodium sulfate, in random order. Urine was collected for 48 hours and assayed for acetaminophen and its major metabolites and for inorganic sulfate. The results confirm that activated charcoal can reduce acetaminophen absorption and show that oral administration of activated charcoal with sodium sulfate does not alter the inhibitory effect of activated charcoal on acetaminophen absorption or the bioavailability of the sulfate. A combination of activated charcoal and sodium sulfate may therefore be useful for the initial management of acetaminophen overdose.

Factors influencing sulfation in isolated rat hepatocytes

Sulfation of harmol by isolated hepatocytes was dependent on an exogenous source of sulfate. Inorganic sulfate ion stimulated sulfation by over ten fold. Analysis of the stimulation of harmol sulfation by sulfate indicated a Km of 239 microM and a Vmax of 1.1 mumoles harmol sulfate/min/10(6) cells. Cysteine also stimulated the rate of harmol sulfation but was less effective than sulfate ion. Lithium chloride inhibited harmol sulfation. Sulfation was unaffected by several metabolic alterations which inhibited harmol glucuronidation. Fasting for 24 hours, and incubation with ethanol or linoleic acid, did not influence the rate of sulfation but inhibited glucuronidation by 50 percent.

Pharmacokinetic study of the fate of acetaminophen and its conjugates in rats

Pharmacokinetic studies of the fate of acetaminophen and its major metabolites, acetaminophen sulfate (AS) and acetaminophen glucuronide (AG), were made in rats. The rates of conjugate formation were calculated by deconvolution. The Michaelis-Menten equation gave maximum velocity and Michaelis constant (Km) values of 4.92 mumol/min/kg and 109 microM for AS formation, and 2.76 mumol/min/kg and 915 microM for AG formation. However, AG formation showed approximately first-order behavior in the present dose range because of its large Km value. The disposition of acetaminophen could be described by a two-compartment model with simultaneous first-order and Michaelis-Menten type elimination kinetics for AS formation. Curve fitting of the data based on this model was successfully done for doses of up to 1058 mumol/kg, suggesting that sulfation proceeds without depletion of sulfate in the blood at least up to this dose. The disposition of AS could be described by a two-compartment model and was apparently dose-independent over an 8-fold dose range. Although a slight dose dependence in the elimination of AG was suggested over a 16-fold dose range, for the purpose of the present study, it was assumed that the disposition of AG is approximately linear. The excretion of AS in the bile was negligibly small, whereas a considerable amount of AG was excreted into the bile. The results following intraduodenal injection of AS or AG indicated that AS or AG was hydrolyzed by the microflora and the liberated acetaminophen was reabsorbed, confirming enterohepatic circulation of the conjugates. This was consistent with the urinary metabolite excretion patterns observed after acetaminophen injection in normal and bile fistula rats. Based on the kinetic parameters obtained, the plasma concentrations of AS and AG after acetaminophen injection were simulated, and a fairly good agreement was obtained between calculated and observed values at the dose of 264.6 mumol/kg. Although the urinary metabolite excretion pattern differs from that of humans, the kinetic parameters obtained for rats were similar to those for humans in some respects, suggesting that the rat might be useful as a model animal to predict human data.

Pharmacokinetic evidence for the occurrence of extrahepatic conjugative metabolism of p-nitrophenol in rats

p-Nitrophenol (PNP), as a model compound for the study of conjugative metabolism, was administered intravenously to rats. PNP and its conjugated metabolites, i.e. PNP-glucuronide (PNP-Glu) and PNP-sulfate (PNP-Sul), were determined in body fluids by reversed-phase high-performance liquid chromatography using ion-pair systems. Linear pharmacokinetics was applicable in the dose range of 1.6 to 8 mg/kg. The metabolic clearance which was obtained from the area under the PNP blood concentration curve (AUCiv) and from the excretion ratio of the total conjugates as PNP-Glu and PNP-Sul was so close to the hepatic blood flow that the PNP conjugation reactions seemed to be limited by the hepatic blood flow, that is the hepatic extraction ratio (EH) was expected to be 1. However, AUCpv, following portal vein administration of PNP (4 mg/kg), was not zero but was significantly different from AUCiv after the same dosing (P less than 0.05). Consequently, comparison between the AUC values from both dosing routes and the excretion ratio of PNP-Glu and PNP-Sul gave and EH of 0.43. Such a difference in EH obtained by the two methods suggested a contribution by extrahepatic conjugative metabolism. It was shown that the intrinsic hepatic clearance obtained, assuming exclusively hepatic conjugative metabolism, was certainly overestimated. Furthermore, the results of the conjugation reaction in tissue homogenates suggested a contribution by extrahepatic glucuronidation.

Massive intoxication with acetaminophen and propoxyphene: unexpected survival and unusual pharmacokinetics of acetaminophen

A 28-year-old woman ingested an estimated 58 g acetaminophen and 9 g propoxyphene 20 h before hospitalization. Her serum acetaminophen concentration at 22 h was 485 micrograms/mL and declined with an unusually long half-life of 14 h. Hemodialysis for 4 h (started at 36 h) reduced the acetaminophen concentration from 250 to 32 micrograms/mL. The patient's complete recovery was remarkable because of the large amounts of drugs ingested, the delayed treatment, and prior exposure to enzyme inducers (known to increase acetaminophen hepatotoxicity). Administration of N-acetylcysteine prevented inorganic sulfate depletion usually caused by acetaminophen and may have increased the formation of acetaminophen sulfate. Some patients eliminate large overdoses of acetaminophen very slowly. Measures to enhance the elimination of this drug and its toxic metabolite by these individuals may be useful even when diagnosis or hospitalization is delayed.

Absorption of orally administered sodium sulfate in humans

Sodium sulfate can be used to enhance the conjugation of phenolic drugs with sulfate and to treat hypercalcemia. It is thought that sulfate in is absorbed slowly and incompletely from the digestive tract. The purposes of this investigation were to determine the absorption of large amount of sodium sulfate (18.1 g as the decahydrate, equivalent to 8.0 g of the anhydrous salt) and to compare the bioavailability when this amount is administered orally to normal subjects as a single dose and as four equally divided hourly doses. The 72-hr urinary recovery of free sulfate following single and divided doses was 53.4 +/- 15.8 and 61.8 +/- 7.8%, respectively (mean +/- SD, n=5, p greater than 0.2). The single dose produced severe diarrhea while the divided doses caused only mild or no diarrhea. Thus, a large amount of sodium sulfate, when administered orally in divided doses over 3 hr, is well tolerated and is absorbed to a significant extent. Orally administered sodium sulfate may be useful for the early treatment of acetaminophen overdose.

Acetaminophen pharmacokinetics after overdose

Concentrations of acetaminophen in serum and urinary excretion rates of acetaminophen glucuronide and acetaminophen sulfate were determined in a 15-year-old female who had ingested an overdose which resulted in the absorption of an estimated 9.92 g of acetaminophen. The results obtained are in reasonably good agreement with predictions of acetaminophen disposition based upon a previously developed pharmacokinetic model of capacity-limited acetaminophen elimination, but additional studies are needed to refine that model.

Kinetics and metabolism of paracetamol and phenacetin

1 The rate of absorption of oral paracetamol depends on the rate of gastric emptying and is usually rapid and complete. The mean systemic availability is about 75%. 2 Paracetamol is extensively metabolized and the plasma half-life is 1.5-2.5 hours. About 55% and 30% of a therapeutic dose is excreted in the urine as glucuronide and sulphate conjugates, respectively, whereas mercapturic acid and cysteine conjugates (representing conversion to a potentially toxic intermediate metabolite) each account for some 4% of the dose. Paracetamol metabolism is age- and dose-dependent. 3 With hepatotoxic doses, paracetamol metabolism is impaired and the half-life prolonged. Sulphate conjugation is saturated and the proportion excreted as mercapturic acid and cysteine conjugates is increased. 4 The renal clearance of paracetamol depends on urine flow rate by not pH. The renal clearances of the glucuronide and sulphate conjugates often exceed the glomerular filtration rate and are independent of urine flow and pH. 5 Phenacetin absorption depends on formulation. It is extensively metabolized to paracetamol and minor metabolites are probably responsible for toxicity.