Hepatic and intestinal cytochrome P450 3A activity in cirrhosis: effects of transjugular intrahepatic portosystemic shunts

Transjugular intrahepatic portosystemic shunt (TIPS) is performed to treat some complications of cirrhosis. This study investigated the effects of cirrhosis and TIPS on intestinal and hepatic cytochrome P450 3A (CYP3A) activity. Nine volunteers were cirrhotic patients with TIPS, 9 were cirrhotic controls (matched for sex, age, etiology, and Child-Pugh class), and 9 were sex- and age-matched healthy volunteers. Simultaneous doses of midazolam were given intravenously (0.05 mg/kg) and orally (3 mg of [15N3]midazolam). Peripheral and portal venous blood samples were assayed for midazolam and [15N3]midazolam. The systemic clearance of midazolam was significantly greater (P <.05) in healthy volunteers (0.42 +/- 0.10 L x h(-1) x kg(-1)) compared with cirrhotic controls (0.20 +/- 0.05) and with cirrhotic patients with TIPS (0.21 +/- 0.09). Hepatic availability followed the same trend. The bioavailability of midazolam was significantly higher (P <.05) in cirrhotic patients with TIPS (0.76 +/- 0.20) compared with cirrhotic controls (0.27 +/- 0.14) and with healthy volunteers (0.30 +/- 0.10). The intestinal availability was significantly greater (P <.05) in cirrhotic patients with TIPS (0.83 +/- 0.17) compared with cirrhotic controls (0.32 +/- 0.16) and with healthy volunteers (0.42+/-0.15). As expected, hepatic CYP3A activity was reduced in cirrhosis. However, in cirrhotic patients with TIPS, there was a marked loss in first-pass metabolism of midazolam as a result of diminished intestinal CYP3A activity.

Histamine N-methyltransferase pharmacogenetics: association of a common functional polymorphism with asthma

Histamine is involved in the pathophysiology of asthma, and histamine N-methyltransferase (HNMT) plays the dominant role in histamine metabolism in human bronchial epithelium. Levels of HNMT activity in human tissues are controlled, in part, by inheritance. A common C314T polymorphism within the HNMT gene results in a Thr105Ile change in encoded amino acid, and the T314 allele is associated with decreased levels of both HNMT enzymatic activity and immunoreactive protein. Therefore, presence of the T314 allele would be expected to result in reduced histamine metabolism and increased bronchoconstriction. We characterized this common, functionally significant polymorphism in DNA samples from 237 randomly selected Caucasian control subjects and 192 samples from Caucasian asthmatic patients. Allele frequencies for the T314 HNMT allele were 0.08 in the control samples and 0.14 in samples from Caucasian asthmatic patients (odds ratio = 1.9, P < 0.01), indicating a significant increase in the frequency of subjects with low HNMT activity among asthmatics. The association between a common, functionally significant genetic polymorphism for HNMT and asthma suggests that individual variation in histamine metabolism might contribute to the pathophysiology and/or response to therapy of this disease.

Dose-related distribution of codeine and its metabolites into rat hair

Drugs and endogenous compounds may be incorporated into the matrix of a growing hair shaft. However, the relationship between incorporation and dose or time course of plasma concentrations is poorly defined. The purpose of this study was to compare plasma and hair concentrations of codeine and its metabolites after various doses of codeine. Male Sprague-Dawley rats had a 1" x 1" square shaved from their backs. Codeine was administered by intraperitoneal injection (10, 20, 40, or 60 mg/kg/day) daily for 5 days. Fourteen days after beginning drug administration, the original patch was reshaved and newly grown hair was analyzed for codeine and morphine using GC/MS. The mean concentrations of codeine in hair for the 10, 20, 40, and 60 mg/kg/day groups were 0.29, 0.57, 0.96, and 1.93 ng/mg hair, respectively, and the concentrations of morphine were 0.15, 0.28, 0.49, and 0.79 ng/mg hair, respectively. The plasma concentration time courses for codeine and morphine were determined after single doses of either 20 or 40 mg/kg. Peak plasma codeine concentrations for the 20 and 40 mg/kg groups were 1,441 and 2,452 ng/ml plasma, respectively, and the areas under the plasma concentration vs. time curve were 699 and 1,581 ng-hr/ml, respectively. Morphine glucuronide, but not codeine glucuronide, was measured in the hair of rats administered codeine. Codeine was also administered to rats by constant intravenous infusion (40 mg/kg/day for 5 days). The concentration of codeine in rat hair after this route of administration was 2.92 +/- 0.72 ng/mg hair. Codeine and morphine are incorporated into rat hair in a dose-proportional fashion. Morphine glucuronide can be found in rat hair after codeine administration. The codeine concentration in hair is the same whether the drug is administered by constant intravenous infusion or daily intraperitoneal injections if the areas under the plasma concentration vs. time curve values are considered.

Effect of lipid-free total parenteral nutrition on hepatic drug conjugation in rats

The effect of total parenteral nutrition (TPN) on drug conjugation in male Sprague-Dawley rats was examined using a nutrition solution composed of amino acids and glucose. The overall disposition of acetaminophen including the formation kinetics of the sulfate and glucuronide metabolites was used as an in vivo probe. Selected drug metabolizing enzyme activities also were examined in vitro. TPN, 200 kcal/kg/day, was administered by continuous i.v. infusion for 14 days and changes elicited were compared to control animals allowed free access to rat chow. TPN decreased the total clearance of acetaminophen by 34% and the formation clearance to acetaminophen sulfate by 47%. The formation clearance of acetaminophen to acetaminophen glucuronide was unaffected by TPN. Cytochrome P450 concentration and oxidative demethylase activity toward p-nitroanisole were decreased in parallel, 47 and 53%, respectively, and UDP-glucuronosyltransferase activity with p-nitrophenol and acetaminophen as the acceptor aglycones was decreased 44 and 25%, respectively in the animals receiving TPN. Sulfotransferase activity toward both p-nitrophenol and acetaminophen decreased 28% in animals receiving TPN vs. ad libitum rat chow. Administration of the parenteral nutrition solution as a continuous enteral infusion via a doudenal catheter slightly decreased p-nitroanisole demethylase activity (26%), but had no other significant effects on either cytochrome P450 concentration or on drug conjugating enzyme activities determined in vitro. These results show that parenteral nutrition administered i.v. depresses drug conjugation and suggest that alterations in both hepatic oxidative and conjugative biotransformation arising from total parenteral nutrition are largely attributable to bypassing the intestinal route for nutrient intake.

The depression of hepatic drug conjugation reactions in rats after lipid-free total parenteral nutrition administered via the portal vein

BACKGROUND

Total parenteral nutrition provides nutrition support in patients who are unable to eat. Long-term parenteral nutrition is accompanied by alterations in gut and liver function including changes in drug metabolism. This study examined the effects of lipid-free total parenteral nutrition in rats on (1) the overall elimination pharmacokinetics of acetaminophen, (2) changes in sulfation and glucuronidation pathways during acetaminophen elimination, and (3) hepatic drug metabolizing enzyme activities determined in vitro.

METHODS

Chronic indwelling catheters were implanted in the aorta, inferior vena cava, and portal vein of adult male Sprague-Dawley rats. Total parenteral nutrition, consisting of 25% dextrose, 5% amino acids, electrolytes, and vitamins, was infused via the portal vein for up to 14 days. Acetaminophen pharmacokinetics were characterized in vivo and selected drug metabolizing enzyme activities were determined in vitro.

RESULTS

Parenteral nutrition for 10 days decreased the total clearance of acetaminophen by 23% (from 11.5 +/- 1.4 to 8.9 +/- 1.4 mL/min per kg; p < .05) and decreased the formation clearance to acetaminophen sulfate (from 6.2 +/- 0.4 to 3.9 +/- 0.5 mL/min per kg; p < .05). Parenteral nutrition decreased microsomal cytochrome P450 concentration (47%), p-nitroanisole demethylase activity (68%) and p-nitrophenol UDP-glucuronosyltransferase activity (58%). Cytosolic glutathione-S-transferase activity towards 1-chloro-2,4-dinitrobenzene decreased 29%. Sulfotransferase activity towards p-nitrophenol and acetaminophen was decreased 48% and 25%, respectively.

CONCLUSION

Lipid-free, total parenteral nutrition depresses drug conjugative metabolism in rats. The magnitude of this effect in humans remains to be investigated.

Use of N-acetyl cysteine to increase intracellular glutathione during the induction of antitumor responses by IL-2

IL-2 therapy can induce marked oxidative stress via reactive oxygen and nitrogen intermediates. Glutathione, the major intracellular reductant, may become rate limiting to cytotoxic lymphocyte activation and proliferation under these circumstances. N-Acetyl cysteine (NAc-cys) was used to increase intracellular glutathione levels during lymphokine-activated killer (LAK) cell activation by IL-2. Incubation of splenocytes with NAc-cys (0.6 to 1.0 mM) resulted in significant changes in intracellular reduced and total glutathione (92% and 58% increase, respectively) at 96 h. These levels correlated with markedly enhanced cell proliferation (threefold) and cytolytic effector cell generation (&gt; fivefold increase in LU/10(6) cells) induced by the combination of NAc-cys with IL-2. IL-2 exposure by itself unexpectedly increased intracellular reduced glutathione by 43%. IL-2 and NAc-cys were synergistic in increasing glutathione levels (reduced glutathione: 292% increase; total: 251% increase). Inhibition of glutathione synthesis, using L-buthionine-(S,R)-sulfoximine reversed the effects of NAc-cys on intracellular glutathione, as well as cellular proliferation and cytotoxicity. This experiment established that the effects of NAc-cys required de novo glutathione synthesis. In conjunction with IL-2/LAK treatment, oral NAc-cys administration (260 to 900 mg/kg/day for 7 days) significantly decreased tumor progression in a refractory s.c. tumor model. A small fraction of mice (11 to 17%) had complete tumor regressions. NAc-cys may be useful as an adjunct to increase the antitumor activity of IL-2/LAK therapy.

Use of N-acetyl cysteine to increase intracellular glutathione during the induction of antitumor responses by IL-2

IL-2 therapy can induce marked oxidative stress via reactive oxygen and nitrogen intermediates. Glutathione, the major intracellular reductant, may become rate limiting to cytotoxic lymphocyte activation and proliferation under these circumstances. N-Acetyl cysteine (NAc-cys) was used to increase intracellular glutathione levels during lymphokine-activated killer (LAK) cell activation by IL-2. Incubation of splenocytes with NAc-cys (0.6 to 1.0 mM) resulted in significant changes in intracellular reduced and total glutathione (92% and 58% increase, respectively) at 96 h. These levels correlated with markedly enhanced cell proliferation (threefold) and cytolytic effector cell generation (> fivefold increase in LU/10(6) cells) induced by the combination of NAc-cys with IL-2. IL-2 exposure by itself unexpectedly increased intracellular reduced glutathione by 43%. IL-2 and NAc-cys were synergistic in increasing glutathione levels (reduced glutathione: 292% increase; total: 251% increase). Inhibition of glutathione synthesis, using L-buthionine-(S,R)-sulfoximine reversed the effects of NAc-cys on intracellular glutathione, as well as cellular proliferation and cytotoxicity. This experiment established that the effects of NAc-cys required de novo glutathione synthesis. In conjunction with IL-2/LAK treatment, oral NAc-cys administration (260 to 900 mg/kg/day for 7 days) significantly decreased tumor progression in a refractory s.c. tumor model. A small fraction of mice (11 to 17%) had complete tumor regressions. NAc-cys may be useful as an adjunct to increase the antitumor activity of IL-2/LAK therapy.

Acute hepatic and renal toxicity from low doses of acetaminophen in the absence of alcohol abuse or malnutrition: evidence for increased susceptibility to drug toxicity due to cardiopulmonary and renal insufficiency

A 67-yr-old man with chronic cardiopulmonary disease exhibited severe hepatic and moderately severe renal injury after short-term ingestion of therapeutic doses of acetaminophen (1 to 3 gm/day for 3 days). Drug metabolism and other studies, performed 5 mo after recovery from the acute insult, indicated that the patient had decreased rates of hepatic metabolism of acetaminophen to its primary, nontoxic metabolites and decreased kidney function that was compromised further by acetaminophen ingestion. He also had abnormally low concentrations of hepatic and plasma reduced glutathione. Alcohol abuse and malnutrition could not be implicated in the pathogenesis of injury; rather it appeared that advancing age with chronic renal, cardiac and pulmonary insufficiency contributed to acetaminophen toxicity in this patient.

Plasma concentrations of inorganic sulfate in Alzheimer's disease

Recent reports have suggested that plasma concentrations of inorganic sulfate may be lower in patients with Alzheimer's disease (AD). We measured sulfate concentrations in 10 patients with AD and found an average concentration of 0.28 mM, which was not significantly different from the mean concentration in age-matched controls (0.32 mM) or young healthy controls (0.27 mM). These results indicate that plasma sulfate concentrations are not altered in AD and that previous reports suggesting altered metabolism of sulfur-containing xenobiotics in neurodegenerative diseases should be reevaluated.

Age-related changes in homeostasis of inorganic sulfate in male F-344 rats

Advanced age is associated with a decline in renal function including decreased glomerular filtration rate, renal blood flow and renal tubular secretion. Endogenous inorganic sulfate homeostasis is maintained by concentration-dependent active renal reabsorption in the proximal tubule. The purpose of this study was to determine the effects of advanced age on: (1) the renal mechanisms for conserving endogenous inorganic sulfate and (2) the turnover of inorganic sulfate. Awake, male Fischer 344 rats age 4-5 months and 22-23 months received i.v. acetaminophen, 300 mg/kg, followed 2 h later by i.v. sodium sulfate, 2 mmol/kg, to lower and raise, respectively, plasma inorganic sulfate in order to measure the renal clearance of this anion from plasma at sub- and supraphysiologic concentration ranges. Another group of old and young male F-344 rats received a tracer injection of [35S]sodium sulfate to determine the effect of aging on the turnover of the endogenous inorganic sulfate pool. There was no statistically significant effect of advanced age on baseline plasma sulfate concentration or on the renal clearance of inorganic sulfate from plasma. The baseline excretion rate of inorganic sulfate in the senescent animals (0.38 +/- 0.25 mumol/min/kg, mean +/- S.D., n = 7) was significantly (P < 0.05) lower than that observed in the young animals (0.64 +/- 0.19 mumol/min/kg, n = 8). There was no difference in the turnover rate constant, as measured by the change in specific activity of urinary [35S]sodium sulfate, for the endogenous sulfate pool in old and young animals. Following acetaminophen administration, plasma sulfate concentrations declined similarly in young and old animals. Under the conditions of relative inorganic sulfate depletion, the renal excretion rate of inorganic sulfate decreased to zero in 7 of 8 young rats, whereas the old animals continued to excrete sulfate anion at an average rate of 23% of the baseline value. Aged animals have a defect in active tubular renal reabsorption of sulfate under conditions of sulfate depletion. Age-related changes in the total sulfate excretion rate may reflect changes in the metabolic fate of endogenous sulfate rather than changes in the endogenous production rate of this anion.

Intrathecal administration of interleukin-2 for meningeal carcinomatosis due to malignant melanoma: sequential evaluation of intracranial pressure, cerebrospinal fluid cytology, and cytokine induction

A patient with interleukin (IL)-2 responsive metastatic melanoma developed meningeal carcinomatosis. Treatment was attempted with intrathecal (i.t.) IL-2 (5 weekly doses of 3-6 x 10(6) IU) without glucocorticosteroids. Marked increases in cerebrospinal fluid (CSF) pressure occurred 5-10 h following each IL-2 dose, resulting in reversible abnormalities of neurologic function. IL-2 clearance from the CSF ranged from 21 to 85 ml/h, with an apparent first order rate constant of 0.08-0.23 hr-1. These values were consistent with clearance by bulk flow mechanisms. Clearance also correlated directly with peak CSF pressure. Progressive increases in CSF tumor necrosis factor (TNF)-alpha and IL-6 levels, but not Il-1 alpha, were also noted over successive treatment cycles. Increasing neutrophilia (peaking at 12 h postdose) and a delayed lymphocytosis and monocytosis (at 20-30 h) were observed with each successive i.t. IL-2 dose. Activated lymphocytes were not observed in the CSF, however, suggesting that an exogenous source of activated lymphokine-activated killer (LAK) cells may be helpful in obtaining effective antitumor responses.

Changes in conjugative enzyme activity and acetaminophen metabolism in young and senescent male F-344 rats following prolonged exposure to buthionine sulfoximine

This study examined how advanced age affects glucuronide and sulfate conjugation of acetaminophen after prolonged exposure to L-buthionine-S,R-sulfoximine (BSO) in male Fischer 344 rats. Young (4-5 month) and senescent (21-22 month) rats received 11 doses of BSO (2 mmol/kg) at 12-h intervals via a gastric cannula. Hepatic metabolism was assessed in vivo by measuring the products of reactions mainly responsible for acetaminophen elimination, namely the formation of the glucuronide and sulfate conjugates. Selected drug-metabolizing enzyme activities were also determined in vitro. BSO treatment increased the partial clearance to acetaminophen glucuronide by 90% and 41% in young and old rats, respectively, and similarly, induced p-nitrophenol and 1-naphthol UDP-glucuronosyl transferase activities to a greater extent in young versus senescent animals. Thus, the induction of these UDP-glucuronosyl transferase activities by BSO is preserved in senescent animals. Although the partial clearance to acetaminophen sulfate was decreased in senescent control rats compared to young controls, BSO treatment decreased the in vivo rate of sulfation in both age groups. Similar to previous findings with the Sprague-Dawley strain, BSO treatment did not induce hepatic cytochrome P-450 content or activity or cytosolic p-nitrophenol sulfotransferase activity in young and senescent Fischer 344 rats.

Dose dependence in the plasma pharmacokinetics and uptake kinetics of 2',3'-dideoxyinosine into brain and cerebrospinal fluid of rats

Dose dependence in the plasma pharmacokinetics of 2',3'-dideoxyinosine (ddI) was examined during and after 2-hr iv infusions in rats at infusion rates of 12.4, 32.7, and 125 mg/kg/hr. After termination of the infusions, the disappearance of ddI from plasma was distinctly biphasic, suggesting that the majority of ddI is eliminated before distribution equilibrium is achieved. The mean alpha t1/2 following the infusions was 2.7 min and was independent of dose. The mean terminal half-life (beta t1/2) was approximately 24 min and also independent of dose. Nonlinear pharmacokinetic behavior in plasma after infusions was manifested in a decreased clearance with increasing dose, as determined from steady state plasma concentrations of ddI during infusions. In parallel with the decreased clearance, the apparent volume of distribution of the central compartment, Vcapp, decreased with increasing dose. Nonlinearity in clearance with increasing dose could be accounted for using a model which includes rapid, saturable tissue binding. Dose dependence in the kinetics of uptake of ddI into brain tissue and cerebrospinal fluid (CSF) was also examined during and after iv infusions. Steady state concentrations of ddI in brain tissue and CSF varied linearly with steady state plasma concentrations over a plasma concentration range of greater than 30-fold. Mean tissue to plasma concentration ratios, expressed as percentages, were 2% in CSF, 5% in brain tissue, and 1-2% in brain parenchymal tissue (corrected for the contribution of the cerebral vascular space).

Probenecid enhances central nervous system uptake of 2',3'-dideoxyinosine by inhibiting cerebrospinal fluid efflux

The effects of probenecid on the pharmacokinetics of 2',3'-dideoxyinosine (ddl) and on the distribution of ddl to cerebrospinal fluid (CSF) and brain tissue were determined in rats during and after a 2-hr i.v. infusion of ddl, 125 mg/kg/hr. Probenecid-treated rats received a loading dose of probenecid followed by an i.v. infusion of probenecid initiated 1 hr before and continued during and for 2 hr after termination of the ddl infusion. Plasma concentrations of probenecid averaged 221 +/- 34 micrograms/ml upon termination of the ddl infusion and 258 +/- 34 micrograms/ml (mean +/- S.D., n = 4) 1 hr later. In the probenecid-treated animals, ddl concentrations were higher in plasma (1.5-fold), brain (1.5-fold) and CSF (5.4-fold) at the termination of the ddl infusion and postinfusion concentrations declined more slowly compared to controls. Postinfusion, the CSF/plasma and brain/plasma ratios steadily increased to a greater extent in the probenecid-treated rats compared to control animals. The time course of plasma, CSF and brain tissue concentrations were analyzed by nonlinear least-squares regression using two different compartmental models, one which neglected the direct exchange of drug between the CSF and brain parenchyma, whereas the other allowed for such exchange to occur and neglected direct vascular transfer of drug to brain tissue. Allowing exchange between the CSF and brain tissue gave slightly improved fitting of the data from both probenecid-treated and control rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacists and the mandate of pharmaceutical care

Implementing the mandate for delivery of drug therapy to achieve definite outcomes that improve a patient's quality of life is discussed from the perspective of the changes currently needed in both practice and education. Specifically, changes in practice should include: (1) a managerial framework that continuously supports clinical activities in everyday practice, (2) recognition of competence in clinical practice, and (3) documentation of and reimbursement for clinical service. Changes in education should include: (1) teaching of problem-solving skills to students by faculty/practitioners, and (2) redirecting the curricular content to provide the minimum knowledge base required for competent clinical practice. Pharmacists will begin to accept the mandate of pharmaceutical care when there is widespread training and use of technicians, implementation of problem-based education in the schools, and adequate problem-solving support for pharmacists in practice.

Drug metabolizing enzyme changes after chronic buthionine sulfoximine exposure modify acetaminophen disposition in rats

This study examined the effects of prolonged exposure to buthionine sulfoximine (BSO) on 1) the overall elimination pharmacokinetics of acetaminophen; 2) the sulfate and glucuronide conjugation processes primarily responsible for acetaminophen elimination; and 3) in vitro microsomal and cytoplasmic enzyme activities in rats. Rats imbibed drinking water containing 30 mM BSO for 6 days and then received an iv injection of acetaminophen, 150 mg/kg in a propylene glycol vehicle. Exposure to BSO, a specific inhibitor of gamma-glutamylcysteine synthetase, produced marked depletion of glutathione (GSH) and resulted in induction of hepatic UDP-glucuronosyltransferase and GSH-S-transferase enzyme activities, but not cytochrome P-450. BSO pretreatment had no effect on the total or renal clearance of acetaminophen in rats. However, BSO exposure increased the partial clearance of acetaminophen to acetaminophen glucuronide by 47% (1.29 +/- 0.08 vs. 1.90 +/- 0.23 ml/min/kg; p less than 0.01) and significantly (p less than 0.02) increased the percentage of the dose recovered as the glucuronide conjugate from 17.6 +/- 2.5 to 26.5 +/- 0.6 The partial clearance of acetaminophen to acetaminophen sulfate was decreased, although not significantly, from 4.46 +/- 0.62 to 3.39 +/- 0.82 ml/min/kg. BSO treatment increased microsomal UDP-glucuronosyltransferase activity toward three xenobiotic aglycones, p-nitrophenol, 1-naphthol, and morphine by 308, 61, and 66%, respectively (p less than 0.05), but not toward testosterone or estrone. Cytosolic GSH-S-transferase activity toward 1-chloro-2,4-dinitrobenzene was increased 52% by BSO, whereas p-nitrophenol sulfotransferase activity was not altered. Cytochrome P-450 concentration and monooxygenase activity were unchanged by BSO exposure.

Effect of advanced age on p-aminohippurate-induced inhibition of renal tubular secretion in male Fischer 344 rats

The effect of aging on glomerular filtration, effective renal plasma flow and on the responsiveness of the renal tubular anion secretory system to inhibition by 4-aminobenzoylglycine (p-aminohippurate, PAH) was examined in young (5-month) and old (22-month) Fischer 344 male rats. Plasma clearance, protein binding and renal extraction of [131I]o-iodohippurate, [125I]iothalamate and HPLC-purified [99mTc]mercaptoacetyltriglycine (MAG3), were used as in vivo probes of renal function. The effect of advanced age, without concomitant PAH, on the disposition of these markers was initially determined in ketamine anesthetized, temperature-maintained male rats, ages 5, 14 and 22 months by means of constant infusion clearance studies. Aging per se decreased (P less than 0.05) the kidney-weight normalized or body weight-normalized GFR and effective renal plasma flow rates. GFR values averaged 1.67, 1.43 and 1.32 ml/min per g kidney for the 5-, 14- and 22-month-old rats, respectively. Kidney- or body weight-normalized clearances of MAG3 and o-iodohippurate showed similar (25-27%) decreases, whereas the absolute values (ml/min) for GFR, o-iodohippurate and MAG3 clearance rates were not altered by aging. The effective filtration fraction, extraction ratio and plasma protein binding were also unchanged by advanced age. Overall, the age-related decreases in renal function were minimal in Fischer-344 rats, compared to other species. Differences in data normalization, species and gender account, in part, for discrepancies observed when comparing results in different studies on the effects of advanced age on renal function. Subsequently, we examined the effect of aging on the renal responsiveness to inhibition of tubular anion secretion using constant rate PAH infusion studies, adjusted for age-related changes in renal function. Aging did not alter PAH-induced inhibition of iodohippurate secretion. Inhibition of MAG3 elimination was more pronounced in the old rats compared to the young controls.

Effect of aging on hepatic biotransformation in female Fischer 344 rats: changes in sulfotransferase activities are consistent with known gender-related changes in pituitary growth hormone secretion in aging animals

The effect of aging on hepatic drug conjugation in 5- to 6-, 12- to 13- and 22- to 23-month-old female Fischer 344 rats was examined. The overall disposition of acetaminophen including the formation and elimination kinetics of its sulfate and glucuronide metabolites were used as in vivo probes. The effects of aging on selected in vitro drug metabolizing enzyme activities and on the pattern of phenol and bile salt sulfotransferase isoenzymes were also determined. Aging decreased the total clearance of acetaminophen and the partial clearance of acetaminophen to acetaminophen sulfate by 36 and 47%, respectively. Increasing age also resulted in a reduced partial clearance of acetaminophen to the glucuronide- (24%) and to the glutathione-derived conjugates (29%). UDP glucuronosyltransferase activity toward 1-naphthol, morphine and testosterone was unaffected by advanced age, whereas there was a significant correlation between increased age and increased UDP glucuronosyltransferase activity toward estrone. Cytochrome P-450 concentration and glutathione-S-transferase activity toward 1-chloro-2,4-dinitrobenzene were unchanged by aging. Oxidative demethylase activity toward p-nitroanisole was decreased 18% and sulfotransferase activities toward p-nitrophenol, acetaminophen and glycolithocholate were decreased 27, 12 and 12%, respectively, in the 22- to 23-month-old rats, compared to the 5- to 6-month-old animals. In contrast to the age-related feminization in the pattern of sulfotransferase isoenzyme activities that occurs in male rats, there was no effect of aging on the pattern of phenol and bile salt sulfotransferase isoenzyme activities in female rats.(ABSTRACT TRUNCATED AT 250 WORDS)

New chronic gastric cannula for feeding ethanol liquid diet to young and old rats

Fifty-eight male Fischer-344 rats ages 5 and 23 mo were fed a liquid diet containing ethanol for 6 wk by means of a newly designed chronic gastric cannula that permitted maximum allowable freedom with minimum stress. Rats were weaned onto the Lieber-DeCarli diet and fed 10 mL three times daily by bolus injection. With or without ethanol, the minimum daily intake of calories necessary to maintain body weight was determined to be approximately 150-160 kcal/kg/day for the young adult rats and 120-125 kcal/kg/day for the aged animals.

Uptake kinetics of 2',3'-dideoxyinosine into brain and cerebrospinal fluid of rats: intravenous infusion studies

The pharmacokinetics of 2',3'-dideoxyinosine (ddl) and its distribution to plasma, brain tissue and cerebrospinal fluid (CSF) were determined during and after 2-hr i.v. infusions of ddl (125 mg/kg/hr) in rats to define its specific pharmacokinetic parameters for subsequent studies of prodrugs designed to target this compound to the brain. Steady-state plasma concentrations of 50 micrograms/ml were obtained within 30 min after the start of infusions corresponding to a total clearance of 2.4 l/kg/hr. Postinfusion, ddl concentrations declined biphasically from plasma with alpha T1/2 = 3 min and beta T1/2 = 35 min. STeady-state concentrations of ddl in brain tissue and CSF were 2.6 micrograms/g in tissue and 0.81 microgram/ml in CSF, respectively. These values represent 4.7 and 1.5%, respectively, of the simultaneously determined plasma concentration. The estimated brain vascular space contribution to the observed brain uptake was 4.1%, obtained by least squares fitting of a compartmental pharmacokinetic model to the uptake data. Postinfusion, the elimination of ddl from the brain and CSF was significantly slower than from plasma, resulting in increased brain/plasma and CSF/plasma ratios after the infusions. The low steady-state brain/plasma or CSF/plasma ratios suggest rapid disappearance of ddl from the CNS relative to its rate of entry. These data indicate that ddl penetrates poorly into the brain. Thus, prodrugs with enhanced blood-brain barrier transport may improve the delivery of ddl to the brain.

Brain and cerebrospinal fluid uptake of zidovudine (AZT) in rats after intravenous injection

Uptake kinetics of zidovudine into cerebrospinal fluid (CSF) and brain tissue were determined in adult Sprague Dawley male rats after single intravenous injection of 6.7 mg/kg (25 mumol/kg). The drug kinetics in plasma followed biexponential disposition with an initial distribution half-life of approximately 11 minutes and an elimination half-life of 40 minutes. Over the plasma concentration range of 0.2 to 10 micrograms/ml, the cerebrospinal fluid to plasma ratio averaged 14.8 +/- 1.9% whereas the mean brain tissue to plasma ratio was 8.2 +/- 1.2% (uncorrected) or 2.3 +/- 1.8% (corrected) for the brain vascular space contribution. Simultaneous nonlinear regression analysis of brain, CSF and plasma concentration data indicate that the overall rate constant for efflux of drug from brain is approximately 75-fold higher and from CSF is 8-fold higher than the respective rate constants for influx. Thus, the ratio of the efflux to influx appears to be the predominant factor in determining the net accumulation of drug into CSF and brain parenchymal tissue.

Suppression of acetaminophen conjugation and of conjugate elimination in the rat by metyrapone, a classical P-450 inhibitor

This study examined the effects of metyrapone on the overall elimination of acetaminophen and on the individual processes principally responsible for elimination, the formation of acetaminophen sulfate and glucuronide. Because acetaminophen pharmacokinetics are nonlinear above a threshold dose, experiments were designed to investigate acetaminophen elimination in the linear (30 mg/kg) and nonlinear (150 mg/kg) ranges to assess possible effects of metyrapone on conjugating enzymes and on cofactor availability. Prior treatment with 400 mg/kg metyrapone tartrate decreased total clearance of acetaminophen over 30% in the linear range (25.4 +/- 2.0 vs. 36.2 +/- 3.7 ml/min/kg in controls; p less than 0.01) and over 40% in the nonlinear range of disposition (4.42 +/- 1.07 vs 7.76 +/- 1.37 ml/min/kg in controls, p less than 0.01). Partial clearance to acetaminophen glucuronide was decreased by metyrapone in each dose range. Partial clearance to acetaminophen sulfate also declined in each dose range but statistically so only after 150 mg/kg. Metyrapone decreased the renal clearance of acetaminophen sulfate and glucuronide when these conjugates were formed in vivo after acetaminophen administration. However, metyrapone failed to impair the renal clearance of acetaminophen glucuronide when preformed metabolites were administered directly. The utility of metyrapone as a specific inhibitor of oxidative drug metabolism appears to be limited for drugs such as acetaminophen by concomitant inhibition of competing conjugation pathways, which account for the majority of drug elimination.

Effect of taurolithocholate on in vivo sulfation and glucuronidation of acetaminophen in rats

Taurolithocholate produces a prompt, complete, and reversible cessation of bile flow in rats. This is associated with impaired hepatic oxidative drug-metabolizing activity. The purpose of this study was to examine the effects of taurolithocholate-induced cholestasis on in vivo conjugation. The pharmacokinetics of acetaminophen and the two major processes specifically responsible for its elimination, namely, the formations of acetaminophen sulfate and acetaminophen glucuronide, were used to assess hepatic conjugating activity. A 30-mg/kg bolus of acetaminophen was administered intravenously to rats 2 hr (acute cholestasis) or 20 hr (postcholestasis) after intravenous pretreatment with sodium taurolithocholate, 5 mumol/100 g body weight. Acute cholestasis increased the total clearance of acetaminophen 20%, the partial clearance to acetaminophen sulfate 12%, and the partial clearance to acetaminophen glucuronide 85%. Postcholestasis, these parameters had significantly decreased compared to those during acute cholestasis and were comparable to control values. The results show that cholestasis does not impair acetaminophen conjugation in the rat.

Effect of chronically administered ketoconazole on the elimination of theophylline in man

Ketoconazole, a nitrogen-substituted imidazole, has been shown to be a potent in vitro inhibitor of cytochrome P-450-mediated metabolic processes. Conflicting reports exist concerning the in vivo effect of ketoconazole on concomitantly administered drugs that require these metabolic processes for clearance. Therefore, the effect of multiple-dose ketoconazole on the elimination of theophylline, a drug metabolized by cytochrome P-450, in ten healthy, nonsmoking males (aged 18-40 years) was evaluated. Each subject received aminophylline 6 mg/kg iv before and at the end of seven days of ketoconazole 200 mg/d po. Theophylline serum concentrations were determined by fluorescence polarization immunoassay (TDx) at 12 time points over the 24-hour period following each infusion. No statistical difference (two-tailed t-test) in half-life (mean +/- SD 7.8 +/- 1.8 vs. 8.2 +/- 1.9 h) or clearance (0.797 +/- 0.201 vs. 0.722 +/- 0.133 ml/min/kg) could be demonstrated for theophylline before or after ketoconazole administration. Theophylline dosage adjustment is probably not necessary for concomitant theophylline and ketoconazole drug therapy.

Unexpected accumulation of acyclovir in breast milk with estimation of infant exposure

Although acyclovir is prescribed to women of reproductive age, no information currently exists regarding the advisability of its use in lactating women. This report documents the first known case of acyclovir transfer to an infant through breast milk. Maternal plasma, milk, and infant urine were collected following a 200-mg oral dose of acyclovir. The drug concentration in breast milk exceeded the corresponding plasma concentration except at the time of peak plasma concentration. This would not be expected on the basis of simple diffusion, and might be caused by a facilitated or active transport mechanism. Such a mechanism has not been described for any drug in human breast milk. Subtherapeutic amounts of acyclovir were documented in the infant, and we discuss the potential effects on neonatal immune function. The use of acyclovir in lactating women remains controversial until further study can clarify pertinent questions.

Acetaminophen sulfation deficit in obese rats overfed an energy-dense cafeteria diet

The current studies examine acetaminophen pharmacokinetics and biotransformation in obese animals for possible shifts in metabolic conjugation reactions. Obesity was produced in Sprague-Dawley rats with an energy-dense cafeteria feeding regimen. Acetaminophen half-life remained unchanged and apparent volume of distribution increased slightly in obese versus pellet-fed control rats following an ip dose of 287 mg/kg. However, obese animals exhibited lower plasma concentrations of acetaminophen sulfate and excreted less sulfate conjugate but more glucuronide conjugate in urine. Absolute clearance of acetaminophen from plasma was similar for both groups of rats but formation clearance of acetaminophen sulfate was lower and formation clearance of acetaminophen glucuronide and was higher than control in obese rats. Renal clearance of unchanged drug and both conjugated metabolites appeared to rise with the degree of obesity. The many parallels in acetaminophen disposition shared with the obese human show the overfed rat to be a promising model for metabolic and physiologic changes associated with human obesity.

Pharmacokinetic consequences and toxicologic implications of metyrapone-induced alterations of acetaminophen elimination in man

This study examined the effect of metyrapone on the elimination rate of acetaminophen and on the apparent formation rate of acetaminophen metabolites in man. Metyrapone treatment, 1.5 g, increased the half-life of acetaminophen, decreased the fraction of the dose recovered in the urine as the glucuronide and increased the fraction of the dose recovered in urine as the sulfate and mercapturate conjugates. The apparent rate constant for the formation of acetaminophen glucuronide was significantly decreased by metyrapone while the apparent rate constants for the formation of the sulfate and mercapturic acid metabolites were unchanged or slightly increased, respectively. These data indicate that metyrapone inhibits acetaminophen glucuronidation and possibly enhances the oxidation of acetaminophen to its quantitatively minor yet highly toxic reactive metabolite. The extent to which the parallel pathways of acetaminophen elimination are also affected by inhibitors of cytochrome P-450-mediated oxidation will limit the efficacy of these types of potential antidotes for the treatment of acetaminophen overdose.

Dissociation of increased sulfation from sulfate replenishment and hepatoprotection in acetaminophen-poisoned mice by N-acetylcysteine stereoisomers

N-Acetylcysteine stereoisomers were compared for their ability to alter the sulfation and hepatotoxicity of acetaminophen. The clinically used L-isomer increased urinary excretion of inorganic sulfate 2-3 fold and prevented liver injury, but failed to increase acetaminophen sulfation in mice. Conversely, the nonphysiologic D-isomer failed to increase urinary excretion of inorganic sulfate or prevent hepatotoxicity, but increased acetaminophen sulfation appreciably (by 39%). The basis of the incongruence between changes in the availability of inorganic sulfate and the sulfation of acetaminophen is not known. These data indicate that a modest increase in acetaminophen sulfation, occurring alone following N-acetylcysteine treatment, is insufficient to explain the profound efficacy of the antidote in mice, and further suggest that this holds true for other species, such as humans, that are comparatively poor in the sulfoconjugation of acetaminophen.

Effect of aging on drug-metabolizing enzymes important in acetaminophen elimination

The effects of aging on selected drug-metabolizing enzyme activities, the pattern of phenol and bile salt sulfotransferase isoenzymes and the pharmacokinetics of acetaminophen were examined in male Fischer 344 rats at ages 5, 14 and 25 months. Aging decreased sulfotransferase activity toward acetaminophen while activity toward glycolithocholate increased with age. Glucuronosyltransferase activity toward estrone increased with age, while activity toward testosterone, morphine and naphthol remained constant. Glutathione-S-transferase (1-chloro-2,4-dinitrobenzene) activity was also unchanged through the various age groups. Cytochrome P-450 content and monooxygenase activity (p-nitroanisole demethylation) activity decreased with advancing age. Overall, the age-related in vitro changes in enzyme activities approached or equaled values measured in 5-month-old female Fischer 344 rats. Moreover, age-related alterations in total phenol sulfotransferase activity and the isozyme pattern paralleled changes in the in vivo elimination kinetics and metabolic fate of acetaminophen. The fraction of drug excreted as the sulfate conjugate and the partial clearance to acetaminophen sulfate decreased with increasing age. Conversely, the fraction excreted as the glucuronide and the partial clearance to acetaminophen glucuronide increased with increasing age. There was no effect of aging on the total clearance of acetaminophen. The gender-related differences in the pattern of sulfotransferase isozyme activity toward phenolic and bile salt acceptors disappeared with age. Age-related changes in sulfation and perhaps glucuronidation in male rats appear to feminize hepatic biotransformation and may arise due to altered gonadal hormone status.

Influence of advanced age on the formation and elimination of acetaminophen metabolites by male rats

The effects of aging on acetaminophen metabolism and elimination in male Fischer 344 rats were examined after intravenous injection of 300 mg/kg. Age as a variable had only a small effect on the total clearance of acetaminophen. However, the fraction of administered dose recovered from urine as acetaminophen sulfate and the partial clearance to acetaminophen sulfate decreased while the fraction recovered as acetaminophen glucuronide and the partial clearance to acetaminophen glucuronide increased with increasing age. Renal clearances of acetaminophen and acetaminophen glucuronide were unchanged while that of acetaminophen sulfate decreased. These data point to an age-related decrease in sulfation and increase in glucuronidation of acetaminophen and further emphasize that the major conjugated metabolites are excreted by renal transport processes that operate under separate control. Moreover, they raise the possibility that advancing age may be accompanied by a general decline in processes that govern sulfate conjugate formation and elimination.

Role of glutathione turnover in drug sulfation: differential effects of diethylmaleate and buthionine sulfoximine on the pharmacokinetics of acetaminophen in the rat

The purpose of this investigation was to examine the role of altered glutathione turnover in regulating sulfation. After diethylmaleate (3.9 mmol/kg i.p.) or buthionine sulfoximine (6 mmol/kg i.p.) injection, rats received an i.v. dose (30 or 150 mg/kg) of acetaminophen. Diethylmaleate pretreatment decreased the total clearance and increased the half-life of acetaminophen. The fraction of the dose recovered in the urine as acetaminophen sulfate and the partial metabolic clearance to acetaminophen sulfate were substantially diminished by diethylmaleate. Conversely, buthionine sulfoximine pretreatment increased the total clearance of acetaminophen and increased the partial metabolic clearance to acetaminophen sulfate. Diethylmaleate produces a prompt increase in glutathione turnover. This more rapidly uses available cysteine, the rate-limiting precursor of glutathione (and probably inorganic sulfate), thus limiting the availability of inorganic sulfate for sulfate conjugation. Importantly, diethylmaleate decreased the total clearance of acetaminophen and the partial clearance to acetaminophen sulfate at a dose of acetaminophen that does not produce complete sulfate depletion. This indicates that diethylmaleate may inhibit sulfation by mechanisms in addition to limiting sulfate availability. Buthionine sulfoximine selectively inhibits gamma-glutamylcysteine synthetase, thereby preventing cysteine utilization for glutathione resynthesis. Cysteine presumably becomes more available for oxidation to inorganic sulfate. These data suggest that glutathione is not normally converted to cysteine for further oxidation to sulfate when the latter endogenous ion is depleted.

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.

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.

Diazepam kinetics in acute alcohol withdrawal

We performed a within-subject comparison of the kinetics of diazepam given to 7 alcoholic subjects during acute alcohol withdrawal and again after detoxification. The initial rapid exponential decline of plasma diazepam concentrations (t1/2 alpha) was more rapid during (0.21 +/- 0.03 hr) than after withdrawal (0.44 +/- 0.14 hr, p less than 0.05). Terminal t1/2, clearance, and volumes of distribution changed in individual patients, but mean values did not change. Protein binding was less in patients (93.4 +/- 2.4%) than in healthy controls (97.0 +/- 1.0, p less than 0.05). The effects of alcohol withdrawal on diazepam disposition do not explain the high doses of diazepam commonly required to treat the withdrawal.