Elevated hepatic and depressed renal cytochrome P450 activity in the Tg2576 transgenic mouse model of Alzheimer's disease

Recent studies indicate that the Tg2576 transgenic mouse model of Alzheimer's disease [tg(hAPP)] demonstrates disturbances in plasma glucose and neuroendocrine function reminiscent of Alzheimer's disease (AD). Alterations in any one of these systems can have a profound effect on hepatic cytochrome P450 (CYP) expression. Additionally, the recent discovery that amyloid beta 1-42 can induce the expression of CYP reductase in neuronal cultures further suggests that hepatic CYP-related metabolism may be affected by the expression of mutant human amyloid precursor protein in these tg(hAPP) mice. Therefore, the current study was conducted to investigate the activity and protein content of several CYP isoforms in the livers and kidneys of aged (20-month-old) tg(hAPP) mice. tg(hAPP) mice exhibit significant elevations in hepatic CYP2B, CYP2E1-, CYP3A- and CYP4A-associated activities and CYP4A immunoreactive protein compared with wild-type. In contrast to the liver, a significant depression in renal CYP2E1- and CYP4A-associated activities were demonstrated in tg(hAPP) mice. The presence of the mutant hAPP protein was detected in the brain, kidney and livers of tg(hAPP) mice.

The effect of endotoxin on hepatocyte nuclear factor 1 nuclear protein binding: potential implications on CYP2E1 expression in the rat

The purpose of this study was to determine if changes in nuclear protein binding of hepatocyte nuclear factor 1 (HNF-1) occur after lipopolysaccharide (LPS) administration. In addition, the time-course of alterations in CYP2E1 regulation were evaluated. Rats were injected with 2.0 mg LPS and euthanized over a 72-h period. Nuclear protein binding to a consensus HNF-1 oligonucleotide was assessed by the electrophoretic mobility shift assay. CYP2E1 activity was analysed using chlorzoxazone as a substrate (60H-CLZ), and CYP2E1 protein concentration was determined by enzyme-linked immunosorbent assay. Endotoxin treatment resulted in decreased nuclear protein binding to an HNF-1 element as early as 1 h after treatment and returned to control levels by 72 h. This reduced binding persisted for 24 h and returned to control values 48 h after LPS administration. In addition, the reduction in binding was primarily attributable to a HNF-1alpha immunoreactive protein. The observed reduction in HNF-1 binding was followed in the time-course by decreases in CYP2E1 activity and protein content with maximal decreases to 50 and 67% of control, respectively, at 48 h after LPS administration. Endotoxin is a potent inducer of the acute phase response (APR). The APR stimulation by endotoxin administration reduced HNF-1alpha binding and decreased the expression of CYP2E1 in the rat liver. The time-course of alterations in HNF-1 and CYP2E1 lend support to the possibility that HNF-1alpha may play a role in the down-regulation of genes that require HNF-1alpha for their constitutive expression. These data serve as an important precedent for future studies evaluating the direct association of decreased HNF-1alpha binding and reduced gene expression after LPS administration.

Cytochrome P450 and antioxidant activity in interleukin-6 knockout mice after induction of the acute-phase response

Hepatic cytochrome P450 (CYP) expression and antioxidant activity have been shown to decrease following endotoxin (lipopolysaccharide [LPS]) or proinflammatory cytokine administration. Using mice deficient in interleukin-6 (IL-6), the role of IL-6 in the regulation of hepatic CYP activity, glutathione (GSH) metabolism, and catalase (CAT) activity was analyzed after LPS administration. Administration of LPS produced comparable decreases in hepatic CYP3A activity in WT B6x129 (WT) mice and IL-6 knockout mice. No decrease was observed for CYP2D9 activity after LPS administration in either WT or IL-6 knockout mice. LPS administration significantly increased hepatic and renal CYP2E1 and CYP4A activity in WT mice, with no effect in IL-6 knockout mice. CYP2A12 activity increased in IL-6 knockout, mice with no change in WT mice after LPS administration. LPS administration had no significant effect on hepatic GSH reductase, GST peroxidase, GSH-S-transferase (GST), or total GSH in either WT or IL-6 knockout. However, hepatic CAT activity was significantly reduced in WT mice after LPS administration, with no effect in IL-6 knockout mice. These results support IL-6 as a critical mediator of the effects of LPS on specific hepatic and renal CYP activities and hepatic CAT activity.

2,4,4'-trichlorobiphenyl increases STAT5 transcriptional activity

The promoting effects of polychlorinated biphenyls (PCBs) have been studied extensively in a variety of two-stage carcinogenesis models. However, the molecular mechanisms responsible for the promotion effects of PCBs have not been elucidated. We measured the effect of PCBs on DNA-binding proteins involved in cell proliferation and transformation. Male Sprague-Dawley rats were injected intraperitoneally with mono-, di-, tri-, tetra-, or hexachlorobiphenyls (300 micromol/kg/d) each day for 4 d and killed 4 h after the last injection. To detect alterations in nuclear proteins that could explain the tumor-promoter activity of PCBs, liver nuclear extracts were analyzed by electrophoretic mobility shift assays. Electrophoretic mobility shift assay analysis of signal transducers and activators of transcription (STAT)-binding activity to a consensus gamma-interferon-activated sequence (GAS) element was compared in liver nuclear extracts from treated rats. STAT-binding activity was eightfold to tenfold higher in nuclear extracts from animals treated with 2,4,4'-trichloro- (PCB 28) and 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153). Analysis of the protein complex binding to the GAS element, with antibodies specific for STAT3, STAT5, and STAT6, indicated that the protein complex was made up of STAT5 and STAT6 proteins. HepG2 cells transiently transfected with a luciferase reporter gene construct containing many STAT5 binding sites were treated with PCB 28 and PCB 153. PCB 28 stimulated a greater than 25-fold increase in luciferase activity at the highest concentration tested, 1.0 microg/mL. However, enhanced luciferase activity did not occur with PCB 153 treatment. 4-Chlorobiphenyl (PCB 3), PCB 28, and PCB 153 treatment of Sprague-Dawley rats resulted in a large increase in protein binding to a consensus activated protein-1 (AP-1) element. However, 3,4-dichlorobiphenyl (PCB 12) and 3,3',4,4'-tetrachlorobiphenyl (PCB 77) treatments did not increase AP-1 transcription activity. Further analysis of the proteins binding to the AP-1 consensus sequence with antibodies specific for c-fos, junD, and junB indicated that the protein composition consists of junD proteins. These data showed functional differences between noncoplanar and coplanar PCBs with respect to STAT activation and AP-1-DNA binding.

Tissue-specific alterations in the 6-hydroxylation of chlorzoxazone following traumatic brain injury in the rat

Interest in the non-neuronal alterations following traumatic brain injury (TBI) has led to research evaluating hepatic metabolism following injury. Several models of injury demonstrate tissue-specific alterations in cytochrome P450 activity. This study examined tissue-specific alterations in cytochrome P450-mediated hydroxylation in the rat model of TBI. Male Sprague-Dawley rats received anesthesia alone, craniotomy, or craniotomy plus TBI. Rats were sacrificed at 24 and 48 h. Liver, kidney, and brain cortex microsomes were isolated. Total liver P450 content, 6-hydroxychlorzoxazone formation rate, and CYP2E1 protein were evaluated. In liver microsomes, spectral P450 was decreased to 86 +/- 5% (p < 0.05) of control at 24 h following injury, and 6-hydroxychlorzoxazone formation rate decreased to 74 +/- 18% of control (p < 0.05) at 48 h following injury. In kidney microsomes, 6-hydroxychlorzoxazone formation rate was increased to 154% of control (p < 0.01) 24 h following injury. 6-Hydroxychlorzoxazone formation rate was unaffected by TBI in brain cortical microsomes. The CYP2E1 inhibitor, 4-methylpyrazole, inhibited the formation of 6-hydroxychlorzoxazone in brain, kidney, and liver microsomes. These data demonstrate that tissue-specific alterations in 6-hydroxychlorzoxazone formation rate occur following TBI.

Activities of conjugating and antioxidant enzymes following endotoxin exposure

Endotoxin exposure elicits various responses in mammals including the acute phase response that has been shown to cause changes in the activity of several forms of cytochrome P450s and other enzymes. Therefore, the hepatic conjugating enzyme, glutathione S-transferase (GST), and UDP-glucuronosyltransferase (UDPGT), the antioxidant enzymes, glutathione peroxidase (GSHPx), catalase, and superoxide dismutase (SOD), as well as lipid peroxidation were investigated following the administration of endotoxin to male Sprague-Dawley rats (8 mg/kg body weight). Rats were euthanized at various times following endotoxin administration and the livers removed and processed to assess various enzyme activities. Glutathione S-transferase, UDPGT, and GSHPx activity showed statistically significant decreases after 24 hours and remained lower than controls for the duration of the study. Decreases in total SOD and catalase activities were seen at 24, 48, and 72 hours following endotoxin administration; however, only catalase activity showed statistically significant differences between control and treated samples at those time points, and total SOD activity showed a statistically significant decrease at 24 hours. No statistically significant changes were seen in the level of lipid peroxidation in the liver microsomes from endotoxin-treated animals. Changes in the conjugative enzymes and the free-radical scavenging enzymes following endotoxin exposure may alter the host's metabolism and response to free radicals.

Effect of recombinant human growth hormone and insulin-like growth factor-1 administration on IGF-1 and IGF-binding protein-3 levels in brain injury

STUDY OBJECTIVE

To assess the effect of recombinant human growth hormone (rhGH) on the insulin-like growth factor-1 (IGF-1) plasma concentration versus time profile during continuous infusion of recombinant human (rh)IGF-1 to patients with traumatic brain injury (TBI).

SETTING

University of Kentucky Chandler Medical Center.

PATIENTS

Twenty-three patients with TBI (aged 18-59 yrs) with Glascow Coma Scale scores of 4-10.

INTERVENTION

Patients were randomized to receive rhIGF-1 0.01 mg/kg/hour and daily subcutaneous doses of rhGH 0.05 mg/kg/day or saline for 14 days.

MEASUREMENTS AND MAIN RESULTS

Plasma concentrations of IGF-1 and IGF-binding protein (BP)-3 were quantified by radioimmunoassay. Patients receiving rhIGF-1/rhGH reached a peak IGF-1 concentration (1199.3+/-84.0 microg/L) at 72 hours and maintained it throughout the study. Levels of IGF-1 in the control group did not change significantly above baseline throughout the study. Concentrations of IGFBP-3 were significantly higher after 48 hours in the treated group (5.1+/-0.4 mg/L) than in controls (2.9+/-0.5 mg/L) and continued until the end of the study (p<0.05).

CONCLUSION

Infusion of rhIGF-1 in conjunction with rhGH effectively achieved and maintained supraphysiologic IGF-1 plasma concentrations throughout the dosing period in patients with TBI. It appears that rhGH alters the IGF-1 plasma concentration versus time profile during continuous administration. Although speculative, changes in protein binding of IGF-1 are the most likely mechanism.

The effect of endotoxin administration on the pharmacokinetics of chlorzoxazone in humans

OBJECTIVE

Inflammation induced by Escherichia coli lipopolysaccharide alters the clearance of several hepatically eliminated drugs. Extensive rat liver research has shown CYP2E1 down-regulation after lipopolysaccharide administration. To further investigate this phenomenon in humans, lipopolysaccharide was administered to healthy male volunteers and chlorzoxazone was used as a CYP2E1 probe drug.

METHODS

Twelve healthy men were given 500 mg oral chlorzoxazone after two daily lipopolysaccharide doses (20 endotoxin units/kg/day) and again after administration of saline solution in this balanced crossover study. Serum and urine chlorzoxazone and 6-hydroxychlorzoxazone were quantified, as well as cytokine and C-reactive protein levels.

RESULTS

Lipopolysaccharide produced the expected induction of the acute-phase response shown by elevations in tumor necrosis factor, interleukin-6, C-reactive protein, and temperature. Lipopolysaccharide treatment failed to produce a significant change in the chlorzoxazone oral clearance (4.4 +/- 0.9 mL/min/kg for lipopolysaccharide versus 4.2 +/- 1.4 mL/min/kg for control) or the 6-hydroxychlorzoxazone formation clearance (2.8 +/- 0.65 mL/min/kg for lipopolysaccharide versus 2.5 +/- 0.9 mL/min/kg for control). The high intersubject variabilities in oral clearance and formation clearance were not accounted for by changes in protein binding, cytokine, or C-reactive protein values. In contrast, a significant increase in the 6-hydroxychlorzoxazone glucuronide renal clearance was observed (7.5 +/- 1.37 mL/min/kg for lipopolysaccharide versus 6.1 +/- 1.7 mL/min/kg for control).

CONCLUSIONS

This study showed that the inflammatory response to lipopolysaccharide (20 endotoxin units/kg/day for 2 days) in humans does not consistently alter chlorzoxazone hepatic metabolism. However, the significant increase in renal clearance of the glucuronidated metabolite suggests that renal tubular secretion may be increased in humans with acute endotoxemia.

The effect of pregnenolone 16alpha-carbonitrile on the pharmacokinetics and metabolism of dapsone in rats

The purpose of this study was to evaluate the effect of pregnenolone 16 alpha-carbonitrile (PCN) on the interconversion pharmacokinetics and metabolism of dapsone. To determine microsomal CYP3A activity and protein, eight rats (4 PCN, 4 corn oil) received a 1 mg kg(-1) intravenous bolus dose of dapsone, followed by blood and urine sampling. The formation clearance of dapsone hydroxylamine (CLf DDS-NOH) was calculated from the obtained samples. Interconversion pharmacokinetics estimates were obtained after 10 rats (5 PCN, 5 control) received 1 mg kg(-1) dapsone or 1.17 mg kg(-1) monoacetyldapsone, with a 24-h wash-out. Results from the interconversion analysis demonstrated that PCN significantly increased systemic clearance (CLs) of dapsone, but not its interconversion. The in-vivo/in-vitro correlation study demonstrated that PCN significantly increased CLs of dapsone (8.55 to 16.39mLmin(-1); P<0.01) and CLf DDS-NOH (0.13 to 0.18mLmin(-1); P<0.01). PCN treatment produced a 69% increase in CYP3A protein, and increased 6beta- and 2beta-hydroxytestosterone formation rates. Significant correlations were found between CLf DDS-NOH and either 6beta- (r2 = 0.925), 2beta-hydroxytestosterone (r2 = 0.92), or CYP3A1/2 protein (r2= 0.60). We conclude that PCN treatment produces significant increases in CLs (dapsone) and CLf (DDS-NOH) in rats. These changes were not due to changes in the reversible metabolism of dapsone. These results suggest that the formation clearance of dapsone hydroxylamine reflects alterations in CYP3A activity, despite the fact that it accounted for a small part of the systemic clearance of dapsone.

Effect of leptin on cytochrome P-450, conjugation, and antioxidant enzymes in the ob/ob mouse

Leptin is a hormone that is secreted by adipocytes and regulates body weight through its effect on satiety and energy metabolism. The ob/ob mouse is deficient in this protein and is characterized by obesity and other metabolic disorders. This study investigated the alterations of several hepatic cytochrome P-450 (CYP), conjugation, and antioxidant enzymes in lean and ob/ob mice and the role leptin plays in the modulation of these enzymes. Lean and ob/ob male mice were injected with leptin (100 microg) or PBS for 15 days. Liver microsomes from ob/ob mice, when compared with lean controls, displayed significantly reduced chlorzoxazone 6-hydroxylation activity (27%); however, 7alpha- and 16alpha- testosterone hydroxylation and pentoxyresorufin O-dealkylation activities were significantly higher (47%, 22%, and 39%, respectively). Leptin administration corrected alterations seen with all P-450 activities. Dealkylation of ethoxyresorufin and omega-hydroxylation of lauric acid activities from ob/ob and lean mice were not statistically different; however, leptin exposure significantly increased ethoxyresorufin activity in lean mice (14%) and decreased the activity in ob/ob mice (36%). UDP-glucuronosyl-transferase and glutathione S-transferase activities were not altered. The antioxidant enzymes, catalase (11%) and glutathione peroxidase (26%), as well as glutathione reductase (17%), were lower in the ob/ob mice and leptin treatment corrected these alterations. The results of this study demonstrate alterations in constitutive expression of CYP2B, CYP2E, CYP2A, catalase, glutathione peroxidase, and glutathione reductase in ob/ob mice that were restored to lean control values following leptin treatment. Additionally, CYP3A activity was increased following leptin treatment in ob/ob mice. The mechanism for the observed alterations may be due to direct leptin effects or via indirect alterations in insulin, corticosterone, and/or growth hormone.

Hepatic cytochrome P-450 expression in tumor necrosis factor-alpha receptor (p55/p75) knockout mice after endotoxin administration

Hepatic cytochromes P-450 (CYP) are well characterized drug and xenobiotic metabolizing enzymes that are extensively regulated by genetic and environmental factors. Inflammatory mediators, including interleukins (ILs), interferons (IFNs), and tumor necrosis factor-alpha (TNF-alpha), have been shown to down-regulate several CYP isoforms; however, elucidation of the inflammatory mediators that are responsible for specific CYP down-regulation is difficult. The purpose of this experiment was to evaluate the role endogenous TNF-alpha plays in the regulation of liver CYP expression after endotoxin administration. Mice deficient in the p55 and p75 TNF receptors and wild-type mice were given Gram-negative bacterial lipopolysaccharide (LPS) and killed 24 h after administration. CYP analysis indicates that LPS decreases CYP1A, CYP2B, CYP3A, and CYP4A independently of TNF-alpha. CYP2D9 and CYP2E1 activities show differential responses to LPS between wild-type and TNF p55/p75 receptor knockout mice, indicating the down-regulation of CYP2D9 and CYP2E1 is differentially modulated by TNF-alpha expression. Furthermore, TNF-alpha appears to affect the constitutive expression of CYP2D9 and CYP2E1. To date, this is the first evidence suggesting that a proinflammatory cytokine is involved in the constitutive regulation of drug-metabolizing enzymes.

Characterization of nuclear protein binding (AP-1, GR, and STAT) in the genetically obese (fa/fa) Zucker rat

There is evidence to suggest that obese populations have an increased susceptibility to various pathologic disorders. Both AP-1 and STAT nuclear binding proteins have been suggested to play a role in certain obesity-related diseases. The objective of our studies reported herein was to compare constitutive binding activity of nuclear proteins (AP-1, GR, and STAT), that may be relevant to obesity-related diseases in the obese (fa/fa) Zucker rat to lean (Fa/?) littermates. AP-1, GR, and STAT liver nuclear protein binding activity was analyzed using the electrophoretic mobility shift assay (EMSA). EMSA analysis of liver nuclear protein from obese and lean Zucker rats revealed high constitutive AP-1 binding activity in the obese animals. AP-1 binding activity in the obese rats was not further elevated by treatment with phenobarbital, a known inducer of AP-1 binding activity. No differences were observed in GR binding to a consensus GRE between obese and lean animals; however, STAT binding activity to a consensus GAS element was lower in liver tissue from obese Zucker rats. Our findings presented herein suggest that the fa/fa Zucker rat may be a suitable obese rodent model for studying the roles AP-1 and STAT may play in the pathologies of these diseases.

Stability of cephalosporin prodrug esters in human intestinal juice: implications for oral bioavailability

The levels of degradation of cefetamet pivoxil (CAT), cefuroxime axetil (CAE), and cefpodoxime proxetil (CPD) in 0.6 M phosphate buffer (pH 7.4) and human intestinal juice (pH 7.4) at 37 degreesC over 24 h were compared. Significant differences in the time courses of degradation and in the patterns of degradation products were observed. (i) The relative proportions of the Delta2- and Delta3-cephalosporins were roughly reversed in the two incubation media. In phosphate buffer, the major degradation product was the Delta2-cephalosporin (CAT = 61%; CAE = 74%; CPD = 85%), while in intestinal juice it was the Delta3-cephalosporin (CAT = 86%; CAE = 75%; CPD = 87%). (ii) Generally, the degradation of the prodrug esters progressed faster in intestinal juice than in phosphate buffer (e.g., for CAT the half-lives [t1/2s] were 0.78 and 4.3 h, respectively). (iii) The two diastereoisomers of CAE and CPD were degraded at different rates in intestinal juice (for the CAE diasteroisomers, t1/2s = 0.37 and 0.93 h; for the CPD diastereoisomers, t1/2s = 0.18 and 0.98 h) but were degraded at similar rates in phosphate buffer (for the CAE diastereoisomers, t1/2 = 1.6 h; for the CPD t1/2 diastereoisomers, = 2.2 h). It is concluded that (i) the Delta2 isomerization does not significantly affect the bioavailability of prodrug esters since enzymatic hydrolysis in the intestinal fluid proceeds mainly to the active Delta3-cephalosporin and (ii) the high degree of stereoselectivity of the enzymatic ester hydrolysis should make it possible to increase the bioavailabilities of certain prodrug esters (CAE, CPD) by using the more stable diasterioisomer.

The effect of high dose endotoxin on CYP3A2 expression in the rat

PURPOSE

The purpose of our research was two-fold: 1) to further characterize the downregulation of CYP3A2 mRNA, protein, and activity during an acute phase response (APR); 2) most importantly, to relate the time-dependent activation of nuclear proteins to putative DNA binding sequences within the CYP3A2 5'-flanking region, with the loss in CYP3A2 expression.

METHODS

Rats were injected (2.0 mg/animal, i.p.) with LPS and sacrificed at 1, 2, 4, 6, 8, 24, 48, and 72 hours. Hepatic nuclear protein was isolated and analyzed for binding activity to AP-1, NFkappaB, and NF-IL6 consensus sequences. Hepatic CYP3A2 mRNA levels were determined by solution hybridization and CYP3A2 protein, CYP3A2 activity, and total P450 were measured in hepatic microsomes.

RESULTS

Computer analysis of the 5'-flanking region of CYP3A2 revealed the presence of 5 NF-IL6 and 4 AP-1 putative DNA binding sites. The strongest increase in AP-1 binding activity occurred between 6 and 24 hr, and the alteration in binding complexes to an NF-IL6 oligonucleotide occurred between 4 and 24 hr. Maximum loss in CYP3A2 mRNA occurred at 8 hr post-LPS injection and remained lowered at the 24 hr timepoint. CYP3A2 protein was significantly decreased at 24, 48, and 72 hours post-LPS treatment with corresponding decreases in CYP3A2 activity and total P450.

CONCLUSIONS

The changes in NF-IL6 and AP-1 binding after LPS treatment, which appears to correlate with the changes in CYP3A2 mRNA, combined with the presence of putative NF-IL6 and AP-1 sites located in the CYP3A25'-flanking region, may indicate a potential role for NF-IL6 and AP-1 in CYP3A2 downregulation during an APR.

Endotoxin depresses hepatic cytochrome P450-mediated drug metabolism in women

AIMS

In men, the inflammatory response to intravenous endotoxin depresses apparent oral clearances of antipyrine, hexobarbitone, and theophylline. The aim of this study was to investigate whether there might be gender differences in the regulation of hepatic cytochromes P450.

METHODS

Experiments were carried out in seven healthy women volunteers (ages 19-51, median 22 years). Each woman received a cocktail of the three drugs on two occasions, once after a saline injection and again after endotoxin.

RESULTS

Endotoxin injections, but not saline, caused the expected physiologic responses of inflammation including fever and increases in circulating tumor necrosis factor-alpha, interleukin-6, and C-reactive protein. When compared with the saline control studies, endotoxin significantly decreased clearances of all probes: antipyrine, 31% (95%CI 21%-41%); hexobarbitone, 20% (95%CI 10-31%); and theophylline, 20% (95%CI 10%-30%). The decreases were comparable with those found in the men previously studied (35%, 27%, and 22%, respectively).

CONCLUSIONS

These data show that endotoxin-induced inflammation decreases hepatic cytochrome P450-mediated metabolism of selected probe drugs in women as it does in men.

Amantadine and equine influenza: pharmacology, pharmacokinetics and neurological effects in the horse

Amantadine is an antiviral agent effective against influenza A viruses. We investigated 1) the antiviral efficacy, 2) analytical detection, 3) bioavailability and disposition, 4) pharmacokinetic modelling and 5) adverse reactions of amantadine in the horse. In vitro, amantadine and its derivative rimantadine suppressed the replication of recent isolates of equine-2 influenza virus with effective doses (EDs) of less than 30 ng/ml. Rimantadine was more effective than amantadine against most viral isolates; we suggest a minimum plasma concentration of 300 ng/ml of amantadine for therapeutic efficacy. In vivo an i.v. dose of amantadine 15 mg/kg bwt produced mild, transient CNS signs which were no longer apparent after 30 min. Amantadine administered at a dose of 15 mg/kg bwt was established as the maximum safe single i.v. dose. However, if repeated i.v. administration of amantadine is required no more than 10 mg/kg bwt t.i.d. should be used. The maximal safe plasma concentration of amantadine was not evaluated but is probably greater than 2000 ng/ml and possibly greater than 4000 ng/ml. On the other hand, horses with lower seizure thresholds, or those on medications that lower seizure thresholds, may be at increased risk of amantadine-induced seizures, which show few premonitory signs and are rapidly fatal. After i.v. administration of amantadine 10 mg/kg bwt, the disposition kinetics were well fitted by a 2-compartment open model. The estimated peak plasma concentration after this dose was about 4500 ng/ml, the volume of distribution at steady-state (Vdss) was (mean +/- s.d.) 4.9 +/- 1.9 l/kg bwt and the beta phase half-life was 1.83 +/- 0.87 h. Computer projections of plasma amantadine concentrations after i.v. administration of amantadine at a dose of 10 mg/kg bwt t.i.d. at 8 h intervals suggest peak plasma concentrations of 4000-5000 ng/ml and troughs of less than 300 ng/ml will be achieved. Amantadine administered orally at 10 mg/kg bwt and 20 mg/kg bwt showed mean oral bioavailability of about 40-60% and a plasma half life of 3.4 +/- 1.4 h; however, there was substantial inter-animal variation in bioavailability. Projections based on the kinetics observed in individual animals suggest that some animals readily maintain effective plasma concentrations of amantadine after oral administration of 20 mg/kg bwt t.i.d. On the other hand, animals in which amantadine is poorly bioavailable may require up to a 6-fold (120 mg/kg bwt) increase in the oral dose to achieve effective blood concentrations. Withholding food for 15 h did not reduce these inter-animal differences in bioavailability. Our results showed that simple dosing with oral amantadine will not yield effective plasma concentrations in all animals. While i.v. administration yielded more reproducible plasma concentrations, care should be taken to see that the seizure threshold is not exceeded. In acute situations, i.v. administration (5 mg/kg bwt) every 4 h should maintain safe and effective plasma and respiratory tract concentrations of amantadine.

In vivo phenobarbital treatment increases protein binding to a putative AP-1 site in the CYP2B2 promoter

Phenobarbital (PB) is a potent inducer of cytochrome P450 enzymes, particularly CYP2B1/2B2. Although the mechanism(s) of PB induction of CYP2B1/2B2 is not fully understood, current research is focusing on the role PB may play in altering the binding of nuclear proteins to critical DNA response elements in the 5'-flanking region of these genes. In this study, rat liver nuclear proteins were analyzed for DNA binding ability using both a general consensus and a CYP2B2 sequence-specific AP-1 oligonucleotide. We demonstrate that in vivo PB treatment enhances protein binding activity to the consensus AP-1 oligonucleotide. Likewise, a putative AP-1 site, identified at -1441 in the CYP2B2 5'-flanking region, also formed a sequence specific DNA/protein complex which was enhanced after PB exposure. These data may support a role of AP-1 in the PB induction mechanism of CYP2B1/2B2.

The cytochrome P450 2D6 (CYP2D6) enzyme polymorphism: screening costs and influence on clinical outcomes in psychiatry

OBJECTIVES

This study examined factors that affect cost, reliability, and the value of determining the cytochrome P450 2D6 (CYP2D6) polymorphism in clinical practice.

STUDY DESIGN

The method of deoxyribonucleic acid isolation, sample preparation, oligonucleotide primers, and polymerase chain reaction procedures were scrutinized for their effect on CYP2D6 genotyping efforts. The determination of the CYP2D6 A, B, D, E, and T alleles was used to identify the deficiency in CYP2D6 expression in 161 individuals phenotyped for CYP2D6 activity with dextromethorphan. The CYP2D6 genotype was assessed in 74 outpatients who had received diagnoses of depression. Eighteen of these patients were screened because of an adverse response to a tricyclic or antidepressant known or suspected to be a CYP2D6 substrate.

RESULTS

The CYP2D6 A, B, C, D, E, and T alleles could be detected in 13 hours at a cost of $84 per sample by judicious selection of conditions and procedures. The genotype provided an accurate predictor of CYP2D6 expression in all 134 subjects who expressed the enzyme and in all 27 unrelated individuals phenotyped as deficient in CYP2D6 activity. In the patient group that experienced adverse effects, 44% of all CYP2D6 gene copies contained the A, B, D, E, or T allele(s) associated with inactive CYP2D6 expression. This was more than twice the rate for the occurrence of mutant alleles in the other 56 psychiatric patients (21%) and in 80 random subjects from the general population (20%; p < 0.05).

CONCLUSIONS

Screening psychiatric patients for CYP2D6 expression may distinguish metabolic-based therapeutic problems from drug sensitivity caused by other mechanisms.

Endotoxin administration to humans inhibits hepatic cytochrome P450-mediated drug metabolism

In experimental animals, injection of gram-negative endotoxin (LPS) decreases hepatic cytochrome P450-mediated drug metabolism. To evaluate this phenomenon in a human model of gram-negative sepsis, LPS was administered on two consecutive days to healthy male volunteers during which time a cocktail of antipyrine (AP-250 mg), hexobarbital (HB-500 mg), and theophylline (TH-150 mg) was ingested and the apparent oral clearance of each drug determined. Each subject had a control drug clearance study with saline injections. In the first experiment, six subjects received the drug cocktail 0.5 h after the first dose of LPS. In the second experiment, another six subjects received the drug cocktail 0.5 h after the second dose of LPS. In both experiments, LPS caused the expected physiologic responses of inflammation including fever with increases in serum concentrations of TNF alpha, IL-1 beta, IL-6, and acute phase reactants. In the first experiment, only minor decreases in clearances of the probe drugs were observed (7-12%). However in the second experiment, marked decreases in the clearances of AP (35, 95% CI 18-48%), HB (27, 95% CI 14-34%), and TH (22, 95% CI 12-32%) were seen. The decreases in AP clearance correlated with initial peak values of TNF alpha (r = 0.82) and IL-6 (r = 0.86). These data show that in humans the inflammatory response to even a very low dose of LPS significantly decreases hepatic cytochrome P450-mediated drug metabolism and this effect evolves over a 24-h period. It is likely that septic patients with much higher exposures to LPS have more profound inhibition of drug metabolism.

Expression of the CYP3A and CYP2C11 enzymes in a nutritionally obese rodent model: response to phenobarbital treatment

In this study, the overfed rat was employed as a model for examining the influence of obesity on the regulation of hepatic cytochromes P450 3A and 2C11 (CYP3A and CYP2C11, respectively). These proteins represent the predominant constitutive hepatic P450 enzymes of male rats. Sprague-Dawley rats were chronically fed a standard pelleted diet or an energy-dense diet which typically results in significant increases in body weight, serum triglyceride levels and liver lipid content. Obesity did not influence baseline levels of spectral cytochrome P450 content. Similar baseline activities of CYP3A (testosterone 6 beta-hydroxylation), comparative CYP3A protein levels (Western blot) and steady-state CYP3A mRNA (slot blot), were found in rats fed either diet. Likewise, obesity did not appear to influence CYP2C11 at the enzyme activity (testosterone 2 alpha-hydroxylation) or mRNA levels. Half of the animals in each group received 20 mg phenobarbital (intraperitoneal injection) per animal every 12 hours for three consecutive days. This resulted in similar phenobarbital plasma concentrations in both groups. Phenobarbital treatment increased the concentrations of total cytochrome P450 in both lean and obese rats to the same extent. CYP3A activity, protein and mRNA levels were induced to a similar magnitude in rats fed either diet. Furthermore, obesity did not influence CYP2C11 activity or mRNA levels following administration of phenobarbital. A lack of an effect of obesity and the altered lipid environment on the regulation of CYP3A and CYP2C11 is in contrast to other enzymes studied previously. It is apparent that the consequences of obesity on hepatic cytochrome P450 may be enzyme-specific.

Cytochrome P450 2B enzyme induction defect after 2,2',4,4',5,5'-hexachlorobiphenyl treatment in the fa/fa Zucker rat

The present study describes the effects of 2,2',4,4',5,5'-hexachlorobiphenyl, a "phenobarbital-like" inducer of hepatic cytochrome P450, on the CYP2B1 and CYP2B2 enzymes in the phenotypically obese fa/fa Zucker rat. The fa/fa Zucker rat demonstrated a markedly lower level of CYP2B1/2B2 enzyme induction, as indicated by reduced enzyme activity (testosterone 16 beta-hydroxylation and pentoxyresorufin O-dealkylation), protein concentration (Western blot), and mRNA (slot blot) than the lean Fa/? rodents after in vivo treatment with 2,2',4,4',5,5'-hexachlorobiphenyl. A primary hepatocyte cell culture system was used to control for possible differences in the disposition of 2,2',4,4',5,5'-hexachlorobiphenyl and hormonal dissimilarity between obese and lean Zucker rats. In agreement with the in vivo study, hepatocytes from fa/fa Zucker rats treated with 2,2',4,4',5,5'-hexachlorobiphenyl exhibited a poor induction response based on measurement of CYP2B1/2B2 mRNA. These data are similar to those reported earlier that demonstrate resistance of the CYP2B1/2B2 genes to the inductive effects of phenobarbital in fa/fa Zucker rats. Apparently a genetic defect in obese Zucker rats impairs the increase in CYP2B1/2B2 gene transcription after treatment with phenobarbital as well as 2,2',4,4',5,5'-hexachlorobiphenyl. This study provides evidence that phenobarbital and "phenobarbital-like" inducers share a common cellular element(s) in the induction process of the CYP2B1/2B2 enzymes.

Acetaminophen hepatotoxicity: influence of phenobarbital and beta-naphthoflavone treatment in obese and lean Zucker rats

The effect of phenobarbital (PB) and beta-naphthoflavone (beta-NF) on acetaminophen (APAP)-induced hepatotoxicity was evaluated in obese and lean Zucker rats. In addition, the consequences of APAP overdose on hepatic CYP2B1/2B2 enzyme activities following PB treatment were assessed. A single oral dose of APAP 3 g/kg (total body weight) was administered to both littermates 24 hr after the last dose of PB or beta-NF. Histologic evidence of hepatocellular necrosis and serum hepatic aminotransferase enzymes 48 hr after APAP administration was utilized to evaluate hepatic damage. Hepatic microsomal total cytochrome P450 concentrations, alkoxyresorufin O-dealkylase activities, and 16 beta-testosterone hydroxylase activities were determined to evaluate the effect of APAP overdose on cytochrome P450 enzyme-substrate activities in the presence and absence of PB treatment. APAP overdose produced lower hepatotoxicity in the obese Zucker rat compared to lean controls. A similar trend was observed in animals treated with PB prior to APAP administration. In contrast, beta-NF treatment produced potentiation of APAP toxicity and/or death of both obese and lean Zucker rats. Generally, APAP overdose produced reduction of hepatic cytochrome P450 enzyme-substrate activities. However, obese Zucker rats retained a higher percentage of their pre-APAP-treated enzyme activities which is consistent with the observation that obese Zucker rats are less affected by the hepatotoxic effects of APAP overdosage.

Expression of a male-specific cytochrome P450 isozyme (CYP2C11) in fa/fa Zucker rats: effect of phenobarbital treatment

The present study determined the effect of genetic obesity and phenobarbital (PB) treatment on the expression and regulation of the hepatic cytochrome P450 enzyme (CYP2C11) in Fa/? and fa/fa Zucker rats. Hepatic CYP2C11 levels as determined by Western immunoblotting and associated enzymatic activity (testosterone oxidation at the 2 alpha position) were significantly lower in untreated fa/fa Zucker rats compared with that observed in Fa/? Zucker rats. There was no significant difference in the constitutive CYP2C11 steady-state mRNA level hybridizable to the cDNA (P450 16 alpha) or specific oligonucleotide probe (Northern and slot blot analyses) between fa/fa and Fa/? Zucker rats. The depressed constitutive CYP2C11 protein levels in fa/fa rats may be attributed to their low plasma testosterone and growth hormone levels; however, lack of differences in CYP2C11 steady-state mRNA suggest post-transcriptional regulatory mechanism(s). Treatment with PB further suppressed hepatic CYP2C11 protein levels and activities in both fa/fa and Fa/? Zucker rats in comparison with that seen in controls. The level of CYP2C11 steady-state mRNA was significantly higher after treatment with PB in Fa/? Zucker rats, while no change was observed in fa/fa animals. The mechanism by which PB treatment fails to increase CYP2C11 steady-state mRNA levels in the fa/fa Zucker rat is unknown; however, it may share a common molecular basis with the defect in nuclear transcription rate previously observed with CYP2B1/2B2.

Head injury and cytochrome P-450 enzymes. Differential effect on mRNA and protein expression in the Fischer-344 rat

Head trauma produces debilitating injuries that affect millions of people each year. Such injuries lead to a cascade of physiologic sequelae resulting in a hypercatabolic/hypermetabolic state. Current information describing changes in hepatic drug metabolism as a result of head trauma is limited. In this study, the effect of craniotomy and craniotomy plus cerebral percussive injury (impact) were investigated and compared with anesthesia control. Steady-state mRNA levels for CYP2C11 and CYP3A were suppressed to 50% of control values 24 hr following injury for the impact treatments. Craniotomy treatments also demonstrated a 50% decline in steady-state levels of mRNA for CYP3A 24 hr following injury. However, Western blot analysis of the CYP3A enzyme revealed no change at 6, 24, or 48 hr following injury. In addition, activities for 2 alpha- and 6 beta-testosterone hydroxylase did not differ from control values at any time point. Spectral analysis of total P-450 demonstrated a very small decline of 15% for the impact treatment 48 hr following injury. Total cytochrome P-450 content did not differ from control values at any other time point. Head injury produces a profound decline in steady-state mRNA concentrations for CYP2C11 and CYP3A that do not translate into altered protein expression.

Effects of interferon-alpha monotherapy on hepatic drug metabolism in cancer patients

1. The influence of interferon-alpha (IFN alpha) on the clearances of theophylline (TH), antipyrine (AP) and hexobarbitone (HB) was studied in seven cancer patients given IFN alpha as their only treatment. In addition, IFN alpha effects on drug clearance were correlated with changes in serum inflammatory cytokines and acute phase proteins. 2. A 'baseline' study was performed by administering an oral drug 'cocktail' of TH (150 mg), AP (250 mg) and HB (250 mg) with saline injected simultaneously and again 24 h later. One week later, an 'acute' study was performed at the initiation of IFN alpha therapy, 3 x 10(6) units injected with the drug cocktail and again 24 h later. After 2 weeks of IFN alpha treatment three times per week, a 'chronic' study was performed with IFN alpha injected the day prior to, simultaneously with, as well as 24 h after the drug cocktail. 3. Plasma samples were collected over 48 h and the clearances of TH, AP and HB were estimated. Serum samples were collected at various times for the measurement of tumor necrosis factor (TNF), interleukin-1 (IL-1), interleukin-6 (IL-6), C-reactive protein (C-RP) and alpha 1-acid glycoprotein (AGP). 4. IFN alpha caused a 33% decrease in the oral clearance of TH during the chronic study compared with baseline (P < or = 0.05). Although IFN alpha inhibited TH clearance by 16% during the acute study and AP clearance by 20-21% during both acute and chronic studies, these changes did not reach statistical significance. IFN alpha caused minimal changes in HB clearance. There were no chronic effects of IFN alpha on serum cytokines or acute phase proteins. 5. The findings confirm that the most commonly used dose of IFN alpha inhibits the hepatic clearance in humans of some but not all drugs and that this inhibition persists during IFN alpha therapy. Because inhibition was not associated with increases in serum cytokines or acute phase proteins, the mechanism by which IFN alpha inhibits cytochrome P450 activities in vivo does not appear to involve inflammatory mediators such as TNF. IL-1 or IL-6.

Effect of nutritional obesity on the induction of CYP2B enzymes following phenobarbital treatment

Human obesity is associated with a number of pathophysiologic processes, such as fatty infiltration and fibrosis of the liver. Although obesity has been shown to alter the metabolism of various xenobiotics, its effect on hepatic cytochromes P-450 is not known. In this study, the overfed rat was used as a model for examining the influence of obesity on the expression and regulation of hepatic cytochrome P-450 2B1/2B2. Sprague-Dawley rats were fed either a standard diet or an energy-dense diet for 32 weeks. The energy-dense diet resulted in a significant increase in body weight, serum triglyceride levels, and liver lipid content. Obesity did not influence baseline levels of spectral cytochrome P-450 content. Similar baseline activities of CYP2B1/2B2 (16 beta-testosterone hydroxylase and pentoxyresorufin O-dealkylation)--comparative protein levels of CYP2B1/2B2 (Western blot), and mRNA (slot blot)--were found in rats fed either diet. Half of the animals in each group were given 20 mg phenobarbital (intraperitoneal injection)/animal every 12 hr for three consecutive days. This resulted in similar phenobarbital plasma concentrations in both groups. Phenobarbital treatment increased the concentrations of cytochrome P-450 in both groups to the same extent. However, greater CYP2B1/2B2 activity was found in control rats following phenobarbital administration, whereas the amount of protein and mRNA was similar in each treated group. In conclusion, obesity did not affect the regulation of CYP2B1/2B2 enzymes. However, changes in the lipid environment associated with obesity may have affected the activity of these proteins.

Cefetamet pivoxil clinical pharmacokinetics

Cefetamet pivoxil is an orally absorbed prodrug ester of the microbiologically active cephalosporin, cefetamet. The prodrug ester is completely hydrolysed to the active compound cefetamet on its first pass through the gut wall, the liver or both. Cefetamet is classified as a third generation cephalosporin with excellent activity against streptococci, Enterobacteriaceae, Neisseria and Haemophilus species. It has enhanced stability against beta-lactamases compared with penicillins and first and second generation cephalosporins. The antibacterial spectrum is comparable with that of cefotaxime except for its poor activity against staphylococci. Following a 20-minute zero-order intravenous infusion, cefetamet had a rapid distribution phase followed by a monoexponential decline. The average pharmacokinetic parameters from 152 healthy volunteers were: total body clearance 136 ml/min (8.16 L/h); renal clearance 119 ml/min (7.14 L/h); nonrenal clearance 17 ml/min (1.02 L/h); volume of distribution at steady-state 0.29 L/kg; terminal elimination half-life 2.2 hours; 88% of the dose recovered in the urine. Cefetamet is not extensively bound to plasma proteins. Consequently, these data indicate that cefetamet is predominantly eliminated unchanged by the kidney via glomerular filtration with possibly a minor component of tubular secretion. Cefetamet has a relatively small apparent volume of distribution consistent with that of other beta-lactam antibiotics. Results following ascending intravenous doses of cefetamet in healthy young male volunteers demonstrated that the pharmacokinetics of intravenous cefetamet are independent of the dose. The absolute bioavailability of cefetamet tablets following oral cefetamet pivoxil administration is enhanced by the presence of food. Under fed conditions, 50 to 60% of the final oral dose is absorbed into the systemic circulation. This food effect is observed when cefetamet pivoxil is administered within 1 hour of a meal. Food also produces a slight delay in the time to reach peak plasma concentrations of this drug. Changes in fluid volume intake with cefetamet pivoxil administration have no effect on the bioavailability of this drug. Similar absorption characteristics have been observed for all of the tablet dosage formulations studied during clinical development. The absolute bioavailability of the final syrup dosage formulation was between 38 and 47%. Little improvement in the bioavailability of this preparation has been observed with food. The absorption and disposition of cefetamet in human subpopulations [i.e. children, elderly (< 75 years of age), renal impairment, liver disease and patients taking concomitant drugs] have been studied extensively. Only impaired renal function appears to significantly alter the elimination of this drug.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of genetic obesity and phenobarbital treatment on the hepatic conjugation pathways

The effect of genetic obesity and phenobarbital treatment on hepatic conjugation pathways was evaluated in the obese Zucker rat. Acetaminophen pharmacokinetic parameters were examined in vivo after a 30-mg/kg acetaminophen intravenous bolus dose in the presence and absence of phenobarbital treatment. Glucuronidation and glutathione conjugation pathways were studied in vitro in obese and lean Zucker rats after phenobarbital treatment. Obese Zucker rats demonstrated a higher glucuronidation capacity as evidenced by a higher formation clearance of acetaminophen glucuronide and greater UDP-glucuronosyltransferase (UDPGT) activity toward acetaminophen and p-nitrophenol compared with lean controls. Sulfate and glutathione conjugation pathways were not affected by genetic obesity. Obese Zucker rats possessed a higher total hepatic glutathione content due to greater liver weight. Phenobarbital treatment enhanced glucuronidation of acetaminophen and structurally related compounds (i.e., p-nitrophenol) similarly in both phenotypes, but the treatment failed to induce morphine UDPGT in the obese Zucker rat. No effect of phenobarbital was observed on sulfate conjugation, gamma-glutamyl cysteine synthetase activity or hepatic glutathione content in obese or lean Zucker rats. Similar increases in glutathione transferase activities were observed in animals of both phenotypes after phenobarbital treatment. This study demonstrates that glucuronidation is enhanced in genetically obese rats, whereas phenobarbital causes normal induction of several enzymes of the glucuronidation and glutathione conjugation pathways in the obese Zucker rat. However, morphine UDPGT was not induced by phenobarbital, suggesting that obese Zucker rats may possess a defect in the induction of this enzyme similar to that already described for the CYP2B gene in this strain.

Cytochrome P450 2B enzyme (CYP2B) induction defect following phenobarbital treatment in the fa/fa Zucker rat: molecular characterization

The present study describes the mechanism of the dampened induction of the CYP2B1 and CYP2B2 genes following phenobarbital treatment in the phenotypically obese fa/fa Zucker rat. The fa/fa Zucker rat demonstrated a threefold lower level of CYP2B1/2B2 enzyme induction, as indicated by reduced testosterone oxidation at the 16 beta position and resorufin formation from pentoxy- and benzyloxyresorufin, protein concentration (Western blot analysis), and steady-state mRNA levels (Northern and slot blot analyses) following in vivo treatment with phenobarbital than the Fa/? littermate controls. A primary hepatocyte cell culture system was used to determine if the dampened induction of the CYP2B1/2B2 enzyme is dependent on hormonal influences. Phenobarbital-treated (0.75 mM) hepatocytes from fa/fa Zucker rats showed approximately a three-fold lower induction response based on measurements of CYP2B1/2B2 (R-17 cDNA probe) and CYP2B1 (oligo probe) mRNAs. In order to evaluate whether this dampened response was at the level of transcriptional activation or initiation, as opposed to altered message stability, we measured the rate of transcription of CYP2B1/2B2 genes in nuclei from cultured hepatocytes during run-off experiments. Compared to Fa/? controls, the fa/fa Zucker rat had a greater than threefold lower nuclear transcription rate of CYP2B1/2B2 mRNA. These results suggest that the defective induction of the CYP2B1 and CYP2B2 genes exists at the transcriptional level in the mutant obese fa/fa Zucker rat. These data provide strong evidence that at least two genes are involved. Multiple gene involvement would suggest that the defect is not due to a mutation of the CYP2B gene cis-acting sequence. Instead, the lack of binding of a trans-acting factor, the presence of a repressor, or a defect in transcriptional activation is more likely the molecular mechanism(s) for this enzyme induction defect.

Age and beta-adrenergic receptor sensitivity to S(-)- and R,S(+/-)-propranolol in humans

The relationship between age and beta-adrenergic receptor sensitivity to the pharmacologically active S(-) enantiomer and the racemic mixture of propranolol was evaluated in 46 healthy male subjects (age range, 24 to 89 years). The in vivo apparent dissociation constants for S(-)- and R,S(+/-)-propranolol were determined on the basis of the unbound steady-state plasma concentration of each and the dose of isoproterenol needed to increase the heart rate of the subjects by 25 beats/min in the absence (I25) and then in the presence of a continuous propranolol infusion. The I25 was significantly correlated with age (r = 0.700, p less than 0.05). The apparent dissociation constant for S(-)- and R,S(+/-)-propranolol demonstrated a significant, although weak, increase with advancing age (r = 0.403 and r = 0.396, respectively; p less than 0.05). Although these findings confirm those of other studies, beta-receptor sensitivity to propranolol was only modestly decreased with age in this study.

Age and propranolol stereoselective disposition in humans

The apparent oral clearance of S(-)- and R(+)-propranolol as a function of age was evaluated in 53 healthy male volunteers (age range, 21 to 84 years) after a single 40 mg oral dose of the racemic mixture. No significant age-associated change in the total (bound plus unbound) and unbound S(-) and R(+) apparent oral clearance was observed (p greater than 0.05). Stereoselectivity in apparent oral clearance (both total and unbound) remained unaffected by advancing age (p greater than 0.05). The relationship between age and propranolol enantiomer plasma protein binding was also evaluated in 70 subjects, 53 of whom were from this study (age range, 21 to 89 years). Plasma free fractions for S(-)- and R(+)-propranolol were unchanged with increasing age (p greater than 0.05), even though the binding was stereoselective (plasma free fractions for R(+) greater than plasma free fractions for S(-); p less than 0.05). The findings from this relatively large and extensive study indicate that age does not influence the stereoselective disposition of propranolol.

Fleroxacin pharmacokinetics in patients with liver cirrhosis

In this open-label study, the disposition of fleroxacin in liver disease in 12 healthy male volunteers, 6 male cirrhotics without ascites (group A), and 6 male cirrhotics with ascites (group B) was evaluated. Fleroxacin (400 mg) was administered orally and intravenously to each subject in a random crossover fashion. Fleroxacin was completely absorbed and achieved similar peak concentrations in plasma in all three study groups (P greater than 0.05). The volume of distribution exceeded 1 liter/kg in healthy controls and was not affected by liver impairment (P greater than 0.05). Only group B demonstrated differences in the pharmacokinetic parameters evaluated: the systemic and renal clearances of fleroxacin and the renal clearances and clearances of the two major metabolites of fleroxacin formed, N-demethyl fleroxacin and fleroxacin N-oxide, were significantly lower and the half-lives of the parent drug and its metabolites were significantly longer in group B than in healthy controls and group A (P less than 0.05). The elimination of the two metabolites appeared to be formation rate limited in all three study groups. It was concluded from this study that a 50% reduction in the fleroxacin maintenance dose in patients with liver disease appears justified only in patients with ascites. However, no change in the fleroxacin loading dose is needed in patients with compromised liver function.

Age-dependent stereoselective increase in the oral clearance of hexobarbitone isomers caused by rifampicin

1. The disposition of hexobarbitone enantiomers before and after rifampicin treatment (600 mg daily for 14 days) was investigated in six young (29 +/- 3 years old) and six elderly (71 +/- 4 years old) healthy male volunteers. Hexobarbitone was given as a single 500 mg oral dose of the racemate. 2. The mean (+/- s.d.) oral clearance of S-(+) hexobarbitone was 1.9 +/- 0.3 and 1.8 +/- 0.2 ml min-1 kg-1, respectively, in young and elderly subjects and increased approximately six fold following 14 days of rifampicin treatment in both young (to 11.9 +/- 2.2 ml min-1 kg-1) and elderly (to 10.7 +/- 2.8 ml min-1 kg-1) subjects. 3. In contrast, rifampicin treatment produced a larger and a differential increase in the oral clearance of R-(-) hexobarbitone in young and elderly subjects; an 89 fold change in the young (15.6 +/- 16.4 to 1146.7 +/- 1478.0 ml min-1 kg-1) and a 19 fold change (10.3 +/- 3.0 to 199.9 +/- 98.1 ml min-1 kg-1) in the elderly.

Limitation to the use of the urinary S-/R-mephenytoin ratio in pharmacogenetic studies

The reproducibility of the S-/R-mephenytoin ratio was examined in urines stored at -20 degrees C over 2 years. Large changes in this ratio were observed in some urine samples stored for only a few months under these conditions. The changes observed in the S-/R-mephenytoin ratio are attributed to the decomposition of an acid labile metabolite of S-mephenytoin which is eliminated in the urine. The instability of this metabolite makes it desirable to process urine shortly after its collection in order to avoid inaccurate phenotype assignments based upon the urinary S-/R-mephenytoin ratio. If rapid processing of urines is impractical, additional methods are described for preventing improper phenotype assignment of subjects.

Comparison of the pharmacokinetics of moclobemide in poor and efficient metabolizers of debrisoquine

A number of pharmacokinetics studies in which patients had been phenotyped and poor metabolizers for moclobemide found were analysed retrospectively. There were 27 subjects in all, aged between 19 and 75 years, and 5 of these were classified as poor debrisoquine metabolizers. Although there was a wide variability in the pharmacokinetic parameters observed, no consistent relationship was found between these and debrisoquine phenotype. Poor debrisoquine metabolizers all had values within the extremes for the efficient metabolism. This was true for both single and multiple dosing. This analysis is limited by the small number of subjects as well as its retrospective nature. Nevertheless, the data suggest that no deviations of moclobemide pharmacokinetics should be expected in poor metabolizers of debrisoquine compared with normal metabolizers.

Pharmacokinetics of intravenous cefetamet and oral cefetamet pivoxil in patients with hepatic cirrhosis

The pharmacokinetics of orally administered cefetamet pivoxil and intravenously administered cefetamet were studied in 12 healthy subjects and 12 patients with hepatic cirrhosis without ascites. Cirrhosis had no detectable effect on the pharmacokinetics of cefetamet and on the bioavailability of cefetamet pivoxil. After intravenous cefetamet in control versus cirrhotic subjects, respectively, the following mean +/- standard deviation values were observed: total body clearance, 128 +/- 10.2 versus 123 +/- 28.8 ml/min; steady-state volume of distribution, 23.2 +/- 2.2 versus 22.7 +/- 4.6 liters; half-life, 2.42 +/- 0.21 versus 2.35 +/- 0.41 h. Renal and nonrenal clearances of cefetamet were similar in both groups, as were the mean residence times and areas under the plasma concentration-time curve. For oral cefetamet pivoxil, no differences were detected in the mean values of the percentage of dose absorbed: 44.6 +/- 9.1 versus 50.1 +/- 12.9. The rate of appearance of cefetamet in the plasma also was not affected by cirrhosis: similar mean values were found for the mean residence time and the maximum concentration in plasma and its time of occurrence.

Pharmacokinetic profile of two aromatic retinoids (etretinate and acitretin) in the obese Zucker rat

Etretinate accumulates in adipose tissue; this appears to account for its long terminal elimination phase in psoriatic patients. The purpose of the present study was to investigate the pharmacokinetic profile of etretinate and acitretin in a genetically obese rodent model, the Zucker rat. Pairs of obese and lean Zucker rats were dosed intravenously (0.5 mg/kg) and blood samples were collected. Plasma concentrations of etretinate and its major metabolites, acitretin and the cis isomer of acitretin (isoacitretin), were assayed by HPLC. The systemic clearance (CLs) of etretinate and the formation clearance (CLf) of the metabolite (acitretin) were lower in the obese rats (132 and 62.4 mL/min, respectively) compared with their lean littermates (197 and 126 mL/min, respectively). The remaining metabolic clearance (CLd) was identical for the lean and obese animals (70.9 and 69.9 mL/min, respectively). The ratio of metabolite-to-parent drug area under the plasma concentration-time curve (i.e., acitretin:etretinate) in the obese animal was less than that value in the lean animals (0.348 versus 0.811, respectively) following the administration of etretinate. Despite a doubling in the mean value (204 versus 87.9 mL), no statistically significant differences in the volume of distribution term for etretinate (Vdss) was observed in the obese animals, due to the large interanimal variability. The terminal phase half-life (t1/2) was significantly longer in the obese rats (3.52 versus 1.25 h). Following acitretin administration, no statistically significant differences were observed between the obese and lean animals for any of the parameters (CLs, Vdss, MRT, t1/2) of acitretin.(ABSTRACT TRUNCATED AT 250 WORDS)

Rapid screening for polymorphisms in dextromethorphan and mephenytoin metabolism

1. The phenotyping parameters for dextromethorphan and mephenytoin were assessed in 48 normal male volunteers following administration of each metabolic probe drug on separate occasions and together according to a randomized 3-way crossover design. 2. Neither the urinary S-/R-mephenytoin ratio nor the dextromethorphan metabolic ratio were altered significantly by coadministration of the probe drugs. 3. Five-hundred and nineteen subjects were screened for expression of mephenytoin 4-hydroxylase and dextromethorphan O-demethylase activity following the coadministration of mephenytoin and dextromethorphan. The activity was determined in each case by methods not requiring any quantitative measurements. 4. Nineteen (3.7%) of the subjects were identified as poor metabolizers (PMs) of mephenytoin and 35 subjects (6.7%) as PMs of dextromethorphan. 5. All PMs of dextromethorphan were confirmed by more rigorous evaluation of the metabolic ratio.

Pulmonary function in the elderly: response to theophylline bronchodilation

This clinical investigation was designed to characterize the pharmacologic response to theophylline in elderly individuals. Incremental theophylline plasma concentrations (0, 5, 10, 15, and 20 mcg/mL), achieved through dose escalation of intravenous aminophylline, were correlated with pulmonary airway responses in ten young and ten elderly male asthmatic volunteers. The older group had lower baseline pulmonary function values, suggestive of a greater degree of baseline airways obstruction. Despite wide intersubject variability, the elderly subjects demonstrated a lower absolute change in bronchodilator response to equal concentrations of theophylline than did their younger counterparts (P less than .05). A progressive increase in heart rate was noted with increasing theophylline concentrations, but no significant difference in heart rate change between groups was detected (P greater than .05). Whether the difference in theophylline induced bronchodilator response observed in the young and elderly groups is due to a difference in age or in severity of airway obstruction is yet unknown.

Estimation of creatinine clearance in patients with Cushing's syndrome

The predictive value of the Cockcroft-Gault equation in patients with Cushing's syndrome was evaluated in 23 patients. Patients were subdivided based on total body weight into two groups, obese and nonobese. Estimated creatinine clearance (EClcr) values were obtained by the Cockcroft-Gault method using ideal body weight (IBW) and total body weight (TBW). These values were then compared with a 24-hour measured creatinine clearance (MClcr). EClcr values based on TBW consistently overestimated measured values in all patients (p less than 0.05). In obese patients with Cushing's syndrome IBW predictions were not statistically different. However, linear regression analysis revealed a poor correlation (r = 0.32). Daily creatinine production rates (Ucr) were calculated and contrasted with an appropriate historical control for obese and nonobese subjects. Nonobese patients revealed a marked reduction in total Ucr compared with normal-weight controls (p less than 0.05). Obese patients also showed a reduction in Ucr when compared with a normal obese control population (p less than 0.05). Difficulty in predicting creatinine clearance in patients with Cushing's syndrome appears to be related to alterations in Ucr. These data suggest that the pathophysiologic changes that accompany Cushing's syndrome are sufficient to alter Ucr and may limit the usefulness of existing methods to predict creatinine clearance and renal function in these patients.

Pharmacokinetics of intravenous cefetamet and oral cefetamet pivoxil in patients with renal insufficiency

The pharmacokinetics of cefetamet after a short intravenous infusion of cefetamet (515 mg) and oral administration of 1,000 mg of cefetamet pivoxil were studied in 9 healthy subjects and in 38 patients with various degrees of renal impairment. The results showed that cefetamet elimination was dependent on renal function. After intravenous dosing, total body (CLS), renal (CLR), and nonrenal (CLNR) clearances were linearly related to creatinine clearance (CLCR; r = 0.95, 0.92, and 0.59, respectively). Elimination half-life (t1/2 beta) was prolonged from 2.46 +/- 0.33 h in normal subjects to 29.1 +/- 13.9 h in patients with CLCR of less than 10 ml/min per 1.73 m2. Correspondingly, CLS and CLR decreased from 1.77 +/- 0.27 and 1.42 +/- 0.25 ml/min per kg to 0.14 +/- 0.04 and 0.04 +/- 0.03 ml/min per kg, respectively. The volume of distribution at steady state (0.298 +/- 0.049 liter/kg) for cefetamet was not altered by renal insufficiency (P greater than 0.05). After oral administration, the elimination parameters, t1/2 beta and CLR, were insignificantly different from the intravenous data (P greater than 0.05). Furthermore, the bioavailability (F) of cefetamet pivoxil (45 +/- 13%) was not altered by renal failure (P greater than 0.05). However, maximum concentration in plasma and the time to achieve this value were significantly increased (5.86 +/- 0.74 versus 14.8 +/- 6.14 micrograms/ml and 3.9 +/- 1.1 versus 8.4 +/- 1.7 h, respectively; P less than 0.05). Based on these observations, it is recommended that patients with CLcr of <10 ml/min per 1.73 m2 and between 10 and 39 ml/min per 1.73 m2 be given one-quarter of the normal daily dose either once or twice daily. Patients with CLcr between 40 and 80 ml/min per 1.73 m2 should receive one-half of the normal dose twice daily. For patients with CLcr of <10 ml/min per 1.73 m2, it would be recommended that they receive a normal standard dose as a loading dose on day 1 of treatment.

Biopharmaceutical comparison of two levothyroxine sodium products

The relative bioavailability and therapeutic equivalence of two brands of levothyroxine sodium tablets, Levothroid and Synthroid, were compared in patients who had been receiving long-term levothyroxine replacement therapy. Eighteen patients with primary hypothyroidism were randomly assigned to receive therapeutic dosages of Levothroid or Synthroid for 43 days and then were switched to the opposite product for 43 more days. The pharmacokinetic profiles of the two drugs were evaluated on days 43 and 86 by analyzing blood samples drawn at various intervals after the final dose. Relative bioavailability was determined by comparing the absorption profiles and areas under the serum concentration-time curves (AUCs) of total and free serum thyroxine. In addition, the potency of the levothyroxine sodium tablets was determined by high-performance liquid chromatography. The time to reach maximum concentration and the maximum concentration of total thyroxine after treatment with Levothroid did not differ significantly from those after treatment with Synthroid. The mean +/- S.D. AUC of total thyroxine after Levothroid administration (2339 +/- 404 pg.hr/mL) was slightly but significantly higher (p = 0.047) than that following Synthroid (2169 +/- 422 pg.hr/mL). However, the main index of biological activity, thyrotropin concentration, did not differ significantly between the two products. All tablets tested were within the stated potency requirements of the USP. The AUC of total serum thyroxine and the serum thyrotropin concentration after long-term replacement therapy with Levothroid or Synthroid indicate that any differences in bioavailability between the two products are clinically unimportant and that the two products are therapeutically interchangeable.

Pharmacokinetics of intravenous cefetamet (Ro 15-8074) and oral cefetamet pivoxil (Ro 15-8075) in young and elderly subjects

The purpose of this investigation was to evaluate the effect of advanced age on the pharmacokinetics of cefetamet and its prodrug, cefetamet pivoxil. A secondary objective of this study was to assess the effect of food on the absorption of cefetamet pivoxil in the elderly. Twenty-four healthy subjects (twelve young and twelve elderly) received (in a Latin square design) a single-dose, 515-mg infusion of cefetamet, a single 1,000-mg oral dose of cefetamet pivoxil during fasted conditions, and a single 1,000-mg oral dose of cefetamet pivoxil 10 min after a standardized low-fat breakfast. Serial blood and urine samples were collected over a 36-h period and analyzed by high-performance liquid chromatography. Intravenous and oral pharmacokinetic parameters were obtained by using model-independent techniques. The systemic clearance and renal clearance of cefetamet were significantly lower (P less than 0.05) in elderly subjects compared with in young controls after intravenous administration. No significant difference was observed in the apparent volumes of distribution at steady state between the two groups. Consequently, half-life and mean residence time were prolonged. A trend toward a lower renal clearance/creatinine clearance ratio was observed in our elderly population. Oral clearance of cefetamet was only slightly reduced in our elderly subjects, consistent with an increase in plasma half-life. Otherwise, oral pharmacokinetic parameters were comparable between elderly and young subjects. Additionally, the same effects of food were observed on the absorption characteristics of cefetamet (no change in maximum concentration of drug in plasma and an increase in both time to maximum concentration of drug in plasma and bioavailability) in our elderly subjects as in our young volunteers. Age did not appear to alter the deesterification and bioavailability of cefetamet pivoxil. We conclude that the small reduction in the elimination of cefetamet in the elderly would not require dose adjustment for this population.

The effects of renal function on the disposition of isradipine

The effect of renal function on isradipine kinetics was examined in four groups of subjects (N = 55) who had normal or impaired renal function. Each subject received isradipine orally as a 10-mg capsule. Serial blood samples were obtained from 0 to 48 hours postdose and the isradipine plasma concentrations determined by radioimmunoassay. Kinetic parameters, Cmax, lambda 3, t 1/2, AUC, CL'o (oral clearance), and CLo (oral clearance standardized to body weight) were determined. Marked intersubject variability of the pharmacokinetic parameters was observed. No statistically significant differences (P greater than .05) were found for AUC, Cl'o, and Clo parameters when renal impairment groups were compared with controls. AUC values were lower (P less than .05), however, for the group with severe renal function impairment than for groups with mild or moderate renal function impairment. No significant correlations (r = -.23, P greater than .05; and r = .13, P greater than .05, respectively) were found between creatinine clearance (CLCR) and CLo and between age and CLo. Considering the interpatient variability in isradipine disposition and the lack of significant differences in CLo between groups, no clear-cut dosing regimen alterations, based on single-dose data, are warranted in renal impairment.

The protein binding of phenytoin, propranolol, diazepam, and AL01576 (an aldose reductase inhibitor) in human and rat diabetic serum

The extent of serum protein binding of AL01576, phenytoin (DPH), diazepam (DIAZ), and propranolol (PRO) was evaluated in a group of nondiabetic and a group of insulin-dependent diabetic subjects, as well as in streptozotocin-treated rats. Both serum glucose and glucosylated protein levels were elevated in the diabetic patient population (179 and 150% of control values, respectively). The mean free fractions (fp) of AL01576, DPH, and PRO were not statistically different for the two human groups. The DIAZ fp was slightly elevated (P less than 0.05) in the diabetic patients (mean = 0.016) compared to the control group (mean fp = 0.014). An acute (less than 3 days) and chronic (greater than 20 days) diabetic rodent model was evaluated using Sprague-Dawley rats following streptozotocin administration (60 mg/kg i.p.). Both diabetic rat groups exhibited substantial increases in serum glucose, free fatty acids (FFA), and protein glucosylation compared to controls. The fp of AL01576 was increased in both the acute (mean = 0.248) and the chronic (mean = 0.202) condition compared to controls (mean = 0.163). The fp of DPH was also markedly increased in the acute (mean = 0.348) and the chronic (mean = 0.280) models compared to untreated controls (mean = 0.207). DIAZ and PRO binding was largely unaffected by the streptozotocin treatment. In vitro studies of purified human albumin suggest that a considerable degree of glucosylation would need to be present in diabetic serum before it would effectively alter drug binding. Our data suggest that only minor drug-serum binding changes occur in diabetic patients who are otherwise healthy and whose disease is well controlled.