Hepatic Enzyme Induction Research Articles

Computational pharmacology of rifampin in mice: an application to dose optimization with conflicting objectives in tuberculosis treatment.

Dose selection for rifampin in the treatment of active pulmonary tuberculosis (TB) illustrates some of the challenges for dose optimization within multidrug therapies. Rifampin-based anti-TB regimens are often combined with antiretroviral therapies to treat human immunodeficiency virus (HIV) coinfection. The potent cytochrome P450 (CYP) enzyme inducing properties of rifampin give rise to significant drug-drug interactions, the minimization of which by limiting the dose, conflicts with the maximization of bacterial killing by increasing the dose. Such multiple and conflicting objectives lead to a set of trade-off optimal solutions for dose optimization rather than a single best solution. Here, we combine pharmacokinetic/pharmacodynamic (PK/PD) modeling with multiobjective optimization to quantitatively explore trade-offs between therapeutic and adverse effects of optimal dosing for the example of rifampin in TB-infected mice. The PK/PD model describes rifampin concentrations in plasma and liver following oral administration together with hepatic CYP enzyme induction and bacterial killing kinetics. We include optimization objectives descriptive of antimicrobial efficacy, CYP-mediated drug-drug interactions, and drug exposure-dependent toxicity. Results show non-conventional dosing scenarios that allow for increased efficacy relative to uniform dosing without increasing drug-drug interactions. Additionally, we find currently employed dosages for rifampin to be nearly optimal with respect to trade-offs between efficacy and toxicity. While limited by the accuracy and applicability of the PK/PD model, these results provide an avenue for experimental investigation of complex dose optimization problems. This method can be extended to include additional drugs and optimization objectives, and may provide a useful tool for individualized medicine.

Two-year carcinogenicity study in rats with a nonnucleoside reverse transcriptase inhibitor.

Administration of lersivirine, a nonnucleotide reverse transcriptase inhibitor, daily by oral gavage to Sprague-Dawley rats for up to 2 yr was associated with decreased survival, decreased body weights, and an increase in neoplasms and related proliferative lesions in the liver, thyroid, kidney, and urinary bladder. Thyroid follicular adenoma and carcinoma, the associated thyroid follicular hypertrophy/hyperplasia, hepatocellular adenoma/adenocarcinoma, altered cell foci, and hepatocellular hypertrophy were consistent with lersivirine-related induction of hepatic microsomal enzymes. Renal tubular adenoma and renal tubular hyperplasia were attributed to the lersivirine-related exacerbation of chronic progressive nephropathy (CPN), while urinary bladder hyperplasia and transitional cell carcinoma in the renal pelvis and urinary bladder were attributed to urinary calculi. Renal tubular neoplasms associated with increased incidence and severity of CPN, neoplasms of transitional epithelium attributed to crystalluria, and thyroid follicular and hepatocellular neoplasms related to hepatic enzyme induction have low relevance for human risk assessment.

Update on once-daily zonisamide monotherapy in partial seizures

Zonisamide is an antiepileptic drug that is structurally different from other antiepileptic agents. Its long half-life, once-daily dosing, lack of induction of hepatic enzymes, and broad spectrum of action makes it a suitable candidate for monotherapy. It has been approved as monotherapy for partial onset epilepsy in Japan and South Korea for more than a decade, and was recently approved as monotherapy in Europe. In the USA, it is only approved by the US Food and Drug Administration for adjunctive treatment of partial onset epilepsy. In this paper, we briefly review the literature on zonisamide monotherapy in partial onset epilepsy with regard to its efficacy, safety, tolerability, and long-term side effects, including a recent noninferiority trial in comparison with extended-release carbamazepine. While European regulatory agencies use noninferiority trials for approval of monotherapy, such a trial design does not meet the current regulatory requirements for approval as monotherapy in the USA.

Anesthesia in a child with adrenoleukodystrophy.

X-linked adrenoleukodystrophy (ALD) is rare genetic disorder, and children with ALD are at an increased risk of anesthetic mortality and morbidity [1]. Therefore, they require an individual anesthetic protocol based on their clinical condition. Herein we report the case of a male with childhood-onset X-linked ALD who required general anesthesia for a dental operation. An 11-year-old male (height 143 cm, weight 30 kg) was scheduled for scaling and multiple deciduous tooth extractions under general anesthesia due to his failure to cooperate willingly. He had been diagnosed with childhood-onset X-linked ALD 3 years previously. Other history included an episode of status epilepticus, adrenal insufficiency, aspiration pneumonia, pressure sores and blindness. He was bed-ridden and maintained on a positive-pressure home ventilator via tracheostomy. Physical examination revealed spastic tetraparesis, unresponsiveness to the environment, and cushingoid facies due to chronic steroid supplementation. Preoperative medications including topiramate, divalproex, prednisolone were continued until the morning of the operation. On arrival at the operating room, standard monitoring commenced. For anesthetic induction, 75 mg of pentothal sodium were injected. Anesthesia was maintained using N2O at 2 L/min, O2 at 2 L/min, and sevoflurane. About 5 min after the start of maintenance inhalational anesthesia, the surgeon was unable to open the patient’s mouth so rocuronium 10 mg was injected, after which the mouth could be opened and the surgery commenced. The operation lasted 30 min and was uneventful. Residual neuromuscular blockade was reversed with pyridostigmine 10 mg and glycopyrrolate 0.2 mg, and 15 min after administration of reversal agents, we placed the patient’s home ventilator in pressure-support ventilation (PSV) mode, as it was preoperatively. The patient was observed closely for over 1 h by an anesthesiologist and a pediatrician in the post-anesthesia care unit (PACU). The home ventilator with PSV mode was well tolerated, so we then transferred the patient to the general ward under monitoring with pulse oximetry. X-linked ALD is a progressive neurodegenerative disorder characterized by demyelination of cerebral white matter, axonopathy of the spinal cord, and reduced adrenal response to adrenocorticotropic hormone. The onset age of the condition is between 3 and 10 years, and the patients initially present with behavioral problems and deficits in memory and language. As the disease progresses, vision loss, auditory impairment, hemiparesis and spastic tetraparesis may occur. In the later stages, seizures begin and the patient becomes bedridden, blind, and unable to interact with the environment. Death usually ensues within 2 to 4 years after the onset of symptoms [1]. There are several considerations in anesthetic management for these patients. The anesthetic plan should be formulated based on each individual patient’s condition according to their disease progression. In our case, the anesthetic plan focused on the prevention of seizures and early return to the preoperative condition without any anesthesia-related complications. In an ALD patient with seizure disorders, anticonvulsants should be continued throughout the perioperative period, including the day of surgery, and the anesthesiologist should consider the altered pharmacokinetics of anesthetics due to hepatic microsomal enzyme induction secondary to chronic antiseizure

An experimental study on the effect of isoniazid on the efficacy, plasma concentration and toxicity of paracetamol in Albino rats

Background: Paracetamol is used for symptomatic treatment of fever and pain with isoniazid and other anti-tubercular drugs in patients of tuberculosis. Literature has conflicting data regarding their interaction. Some studies show that isoniazid increases oxidative metabolism of paracetamol whereas some other suggest that isoniazid has an inhibitory effect. The present study was conducted to find out the possible interaction between paracetamol and isoniazid. Methods: The study was undertaken on Wistar strain of Albino rats. Group I and Group II animals were treated with paracetamol (500 mg/kg) and the combination of paracetamol (500 mg/kg) and isoniazid (30 mg/kg) respectively for 2 months. Blood samples were taken before and during the study for biochemical and histopathological studies of liver and renal functions and plasma paracetamol concentration was also evaluated. Results: Isoniazid decreased the plasma paracetamol concentration without affecting its analgesic activity. However, the hepatotoxic and nephrotoxic effects of paracetamol were found to be further aggravated by isoniazid co-administration. Conclusion: Isoniazid potentiates the hepatotoxic and nephrotoxic effects of paracetamol possibly due to hepatic enzyme induction by isoniazid.

Antibiotic Treatment and Timing of Reimplantation

PJI is traditionally treated with intravenous (IV) antibiotics in order to obtain the minimum inhibitory concentration in the shortest time possible. Once this goal is met and there is clinical evidence of improvement, some IV antibiotic regimens can be switched to oral regimens. There is scarce literature reporting on the use of oral (combined or single) antibiotic therapy for the treatment of PJIs without an initial IV regimen [1–5]. Most of these studies were conducted in cases where the prosthesis was retained. There is one study in which no oral or prolonged IV regimen was used after debridement and the use of an antibiotic-impregnated cement spacers led to a 87% eradication rate [6]. No literature conclusively supports the use of only oral (combined or single) antibiotic therapy prior to reimplantation. The recently-published guidelines of the Infectious Diseases Society of America (IDSA) [7] suggest that pathogen-specific, highly bioavailable oral therapy (e.g. linezolid or fluoroquinolones) may be an alternative as initial therapy for some cases of PJI. Concerns against the routine use of appropriate oral agents in the treatment of PJI largely comprise questions of patient medication compliance and the long-term use of medication therapy with less intensive efficacy and toxicity monitoring.

Drug Interactions with the Newer Antiepileptic Drugs (AEDs)—Part 2: Pharmacokinetic and Pharmacodynamic Interactions Between AEDs and Drugs Used to Treat Non-Epilepsy Disorders

Since antiepileptic drugs (AEDs) are prescribed to treat various non-epilepsy-related disorders in addition to the fact that patients with epilepsy may develop concurrent disorders that will need treatment, the propensity for AEDs to interact with non-AEDs is considerable and indeed can present a difficult clinical problem. The present review details the pharmacokinetic and pharmacodynamic interactions that have been reported to occur with the new AEDs (eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, perampanel, pregabalin, retigabine (ezogabine), rufinamide, stiripentol, tiagabine, topiramate, vigabatrin and zonisamide) and drugs used to treat non-epilepsy disorders. Interaction study details are described, as necessary, so as to allow the reader to take a view as to the possible clinical significance of particular interactions. Pharmacokinetic interactions relate to hepatic enzyme induction or inhibition and involved a variety of drugs including psychoactive drugs, cardioactive drugs, oral contraceptives, antituberculous agents, analgesics and antineoplastic drugs. A total of 68 pharmacokinetic interactions have been described, with lamotrigine (n=22), topiramate (n=18) and oxcarbazepine (n=7) being associated with most, whilst lacosamide, pregabalin, stiripentol and vigabatrin are associated with none. Overall, only three pharmacodynamic interactions have been described and occur with oxcarbazepine, perampanel and pregabalin.

Drug Interactions with the Newer Antiepileptic Drugs (AEDs)—Part 1: Pharmacokinetic and Pharmacodynamic Interactions Between AEDs

Since 1989 there has been an exponential introduction of new antiepileptic drugs (AEDs) into clinical practice and these include eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, perampanel, pregabalin, retigabine (ezogabine), rufinamide, stiripentol, tiagabine, topiramate, vigabatrin and zonisamide; 16 in total. Because often the treatment of epilepsy is lifelong, and because patients are commonly prescribed polytherapy with other AEDs, AED interactions are an important consideration in the treatment of epilepsy and indeed can be a major therapeutic challenge. For new AEDs, their propensity to interact is particularly important because inevitably they can only be prescribed, at least in the first instance, as adjunctive polytherapy. The present review details the pharmacokinetic and pharmacodynamic interactions that have been reported to occur with the new AEDs. Interaction study details are described, as necessary, so as to allow the reader to take a view as to the possible clinical significance of particular interactions. The principal pharmacokinetic interaction relates to hepatic enzyme induction or inhibition whilst pharmacodynamic interactions principally entail adverse effect synergism, although examples of anticonvulsant synergism also exist. Overall, the new AEDs are less interacting primarily because many are renally excreted or not hepatically metabolised (e.g. gabapentin, lacosamide, levetiracetam, topiramate, vigabatrin) and most do not (or minimally) induce or inhibit hepatic metabolism. A total of 139 pharmacokinetic interactions between concurrent AEDs have been described. The least pharmacokinetic interactions (n ≤ 5) are associated with gabapentin, lacosamide, tiagabine, vigabatrin and zonisamide, whilst lamotrigine (n = 17), felbamate (n = 15), oxcarbazepine (n = 14) and rufinamide (n = 13) are associated with the most. To date, felbamate, gabapentin, oxcarbazepine, perampanel, pregabalin, retigabine, rufinamide, stiripentol and zonisamide have not been associated with any pharmacodynamic interactions.

Influence of CYP2C19 Polymorphism and Concomitant Antiepileptic Drugs on Serum Clobazam and N-Desmethyl Clobazam Concentrations in Patients With Epilepsy

The aims of this study were to identify the factors influencing the metabolism of clobazam (CLB) and its active metabolite [N-desmethyl clobazam (NCLB)] and to evaluate the NCLB concentration as an indicator for CYP2C19 polymorphism in epileptic patients. A total of 302 serum samples from 238 Japanese patients were evaluated. The ratios of the serum CLB and NCLB concentrations to the CLB dose (CD ratios) were calculated and compared with CYP2C19 phenotypes. The mean CD ratio of NCLB in extensive metabolizers (EM: *1/*1), intermediate metabolizers (IM: *1/*2 or *1/*3), and poor metabolizers (PM: *2/*2, *3/*3, or *2/*3) was 3.1, 4.9, and 21.6 (μg/mL)/(mg/kg), respectively. In the EM and IM groups, the concomitant use of hepatic enzyme inducers (phenytoin and carbamazepine) reduced the CD ratio of CLB and increased that of NCLB. In the PM group, these inducers also decreased the CD ratio for CLB but did not elevate the CD ratio for NCLB. Using multiple regression analysis, body weight showed a positive correlation with an increased CD ratio for NCLB. The concomitant use of zonisamide and stiripentol also elevated the CD ratio for NCLB in the EM and IM groups, but that of the PM group was almost unchanged. When the cut-off value of the CD ratio for NCLB was set as 10.0 (μg/mL)/(mg/kg) for predicting the CYP2C19 PM status, the sensitivity and specificity were 94.4% and 95.7%, respectively. The interaction between NCLB and other antiepileptic drugs showed marked differences among CYP2C19 phenotypes. Measurement of the serum NCLB concentration is clinically useful for identifying the PM phenotype.

A new parameter that supports speculation on the possible mechanism of hypothyroidism induced by chemical substances in repeated-dose toxicity studies

Hypothyroidism induced by xenobiotic treatment was analyzed for possible underlying mechanism(s) on the basis of different responses of the thyroid gland and the liver, using a newly-created database of repeated-dose toxicity of 500 chemicals. Two mechanisms are proposed: direct inhibition of thyroid hormone biosynthesis in the thyroid gland, and stimulated degradation of thyroid hormone by induction of hepatic drug-metabolizing enzymes. In the database there were 10 chemicals inducing hypertrophy/hyperplasia of follicular cells in the thyroid gland and having data on thyroid glands. On the basis of the chemical structure and information available in the literature, we judged three chemicals to be typical thioamide derivatives that act directly on the thyroid gland, and the others as non-thioamide derivatives that were unlikely to have any direct action on the thyroid gland. All these chemicals were classified into two groups using the ratios of relative weight increase rate of thyroid gland versus that of the liver. These values were at least 1.7, but 3.2 or more in the most of the cases for thioamide derivatives, and 1.2 or less for non-thioamide derivatives. This background analysis suggests the feasibility of parameter-supported speculation on the possible underlying mechanism when new repeated-dose toxicity data on hypothyroidism becomes available.

Refractory status epilepticus occurred at the end of sevoflurane anesthesia in patient with epilepsy

Status epilepticus (SE) is a single seizure or recurrent seizures lasting for more than 30 minutes, in which the consciousness is not regained. Refractory status epilepticus (RSE) is defined as status epilepticus that continues despite treatment with benzodiazepines and one antiepileptic drug [1]. The incidence of seizure activity in patients with epilepsy associated with anesthesia is 3.4% [2], but RSE is rarely reported during emergence of anesthesia. We describe a patient with epilepsy who developed RSE during and after emergence from anesthesia. A 5-year-old, 22 kg, female patient was presented for ventilating tube insertion. She had a history of traumatic subarachnoid hemorrhage, diffuse brain injury and basal skull fracture 2 years ago. She was diagnosed with simple partial seizure 14 months ago and had been treated with valproic acid 240 mg/day. She did not show seizure activity for 1 year. Preoperative valproic acid concentration was 53.9 ug/ml and electroencephalogram (EEG) was normal. Other preoperative evaluations were within normal value, but she showed rhinorrhea. On the day of surgery, she received valproic acid 10 mg/kg IV during nil per os (NPO). The patient was taken to the operation room. The heart rate, noninvasive blood pressure, oxygen saturation and BIS (A-2000, Asepct Medical Systems Inc, Natick, MA, USA) were continuously monitored. After preoxygenation, induction of anesthesia was performed using thiopental sodium 110 mg iv and rocuronium bromide 10 mg iv. After intubation, anesthesia was maintained with sevoflurane in an air-oxygen mixture (fraction inspired oxygen concentration = 0.5). Arterial oxygen saturation remained greater than 98% during the intraoperative course. No episodes of hypoxia occurred during the procedure. As the patient began to emerge from anesthesia (BIS value was approximately 70), focal clonic movement of the right face and right arm was occurred. We suspected seizure and gave her midazolam 4 mg iv, but focal clonic movement did not stop. Therefore, we gave her phenytoin 20 mg/kg iv for 20 minutes and started desflurane inhalation (end-tidal concentration was 8%). Her seizure activity ceased and BIS was below 10. We discontinued desflurane and tried to emerge her from anesthesia. After 10 minutes, she started focal seizure again (BIS values was 65). We started phenobarbital infusion 20 mg/kg for 20 minutes. Her seizure activity did not stop after phenobarbital infusion. We planned to move her to the intensive care unit. In the intensive care unit, we checked for complete blood count, electrolyte, arterial blood gas, urine analysis, liver function test, EEG and serum valproic acid level. EEG showed rhythmic or periodic spikes in the left occipital region and was suggestive of SE (Fig. 1). Serum valproic acid level was 36.2 ug/ml. Other laboratory values were within normal limit. We infused valproic acid 10 mg/kg for 1 hour. Focal seizure was stopped and she regained consciousness. She was discharged 2 days after without any other complication. Fig. 1 Electroencephalogram in the intensive care unit shows rhythmic or periodic spikes in the left occipital region. Arrows are spike. General anesthesia may increase seizure activity, such as withholding antiepileptic drugs while maintaining NPO status prior to surgery, sleep deprivation, and use of proconvulsant medications. Sevoflurane anesthesia causes epileptiform EEG activity and produce clinical evidence of seizures in patients with or without a history of epilepsy. Hypercarbia and hypoventilation during emergence from anesthesia may increase seizure susceptibility and prolong seizure duration [3]. Lowered antiepileptic drug level is a common cause of status epilepticus. In this case, postoperative serum valproic acid concentration was lower than preoperative level, despite of preoperative iv administration. There are two possible causes of lowered valproic acid level. First, the patient missed one or two dose of antiepileptic drugs after admission without notifying the medical staff. Second, phenobarbital and phenytoin are potent hepatic enzyme inducers. They may increase valproic acid metabolism and decrease plasma concentration [4]. Treatment of RSE starts immediately with additional agents. Most often recommended drugs for use as a continuous infusion are midazolam, propofol, pentobarbital and thiopental. Continuous drug infusion in RSE is titrated to achieve an EEG burst suppression pattern. If continuous EEG monitoring is not available, BIS monitor can be used to guide titration of anesthetics in RSE [5]. In conclusion, we report a case of RSE during emergence of general anesthesia that may be caused by sevoflurane anesthesia and lowered antiepileptic drug concentration.

Induction of Hepatic CYP3A Enzymes by Pregnancy-Related Hormones: Studies in Human Hepatocytes and Hepatic Cell Lines

CYP3A activity is induced by approximately 2-fold during the third trimester of human pregnancy. Placental growth hormone (PGH), estrogens (primarily 17β-estradiol), cortisol, and progesterone have the potential to modulate CYP3A activity. Therefore, we determined whether the elevated plasma concentrations of these hormones during pregnancy induce hepatic CYP3A expression. We incubated sandwich-cultured human hepatocytes (SCHH) from premenopausal female donors (n = 2) with the physiologic (unbound, 1× total) and the 10× total third trimester hormone plasma concentrations (individually and in combination) and determined their effect on CYP3A activity and the transcripts of CYP3A4, CYP3A5, and the respective hormone receptors (growth hormone receptor, glucocorticoid receptor, and estrogen receptor alpha). Of all the hormones, cortisol was the most potent inducer of CYP3A activity and CYP3A4, CYP3A5 mRNA expression. The combination of PGH/growth hormone and cortisol induced CYP3A activity and expression significantly more than did cortisol alone. When incubated with the unbound or total plasma concentration of all the hormones, CYP3A activity in SCHH was induced to an extent comparable to that observed in vivo during the third trimester. These hormones had only a modest effect on the mRNA expression of the hormone receptors. The pattern of induction observed in SCHH was reproduced in HepaRG cells but not in HuH7/HepG2 cells. SCHH or HepaRG cells could be used to determine the mechanistic basis of CYP3A induction during pregnancy and to predict the magnitude of induction likely to be observed during the first and second trimesters, when phenotyping studies to measure in vivo CYP3A activity are logistically difficult to perform.

Nicotine intake and smoking topography in smokers with bipolar disorder

Cigarette smoking behavior in bipolar disorder (BPD), including the effects of mood-stabilizing medications, has not been well characterized. We compared serum nicotine, nicotine metabolite levels, and smoking topography in 75 smokers with BPD to 86 control smokers (CON). For some comparisons, an additional control group of 75 smokers with schizophrenia (SCZ) were included. There were no differences between the BPD and CON groups in baseline smoking characteristics or serum nicotine or cotinine levels. Fifty-one smokers with BPD (68.9%) were taking one of the following mood stabilizers: valproic acid, lamotrigine, carbamazepine, oxcarbazepine, lithium, or topiramate. The 3-hydroxycotinine-to-cotinine ratio, a marker of cytochrome P450 2A6 (CYP2A6) metabolic activity, was significantly higher in BPD versus CON and versus SCZ (0.68 versus 0.49 versus 0.54; p =0.002). The difference between groups, however, was no longer significant when the analysis was repeated with those taking hepatic enzyme-inducing drugs (carbamazepine, oxcarbazepine, and topiramate) included as a covariate. The time between puffs, or interpuff interval (IPI), was shorter in BPD versus CON by an average of 3.0sec (p<0.05), although this was no longer significant when we removed smokers from the analysis of those taking hepatic enzyme inducers. Smokers with BPD are not different from CON on most measures of nicotine intake and smoking topography. We found an increased rate of nicotine metabolism in smokers taking mood stabilizers that are hepatic enzyme inducers, including carbamazepine, oxcarbazepine, and topiramate. Smokers with rapid nicotine metabolism might be expected to smoke more intensely to compensate for the more rapid disappearance of nicotine from the blood and brain, and may have more difficulty in quitting smoking, although this requires further study.

Physiological effects and tissue residues from exposure of leopard frogs to commercial naphthenic acids

Naphthenic acids (NAs) have been cited as one of the main causes of the toxicity related to oil sands process-affected materials and have recently been measured in biological tissues (fish). However, adverse effects have not been a consistent finding in toxicology studies on vertebrates. This study set out to determine two factors: 1) whether exposure to commercial NAs (Refined Merichem) resulted in detectable tissue residues in native amphibians (northern leopard frogs, Lithobates pipiens), and 2) whether such exposure would produce clinical or subclinical toxicity. Frogs were kept in NA solutions (0, 20, or 40mg/L) under saline conditions comparable to that on reclaimed wetlands in the Athabasca oil sands for 28days. These exposures resulted in proportional NA concentrations in muscle tissue of the frogs, estimated by gas chromatography–mass spectrometry analyses. Detailed studies determined if the increasing concentrations of NAs, and subsequently increased tissue NA levels, caused a proportional compromise in the health of the experimental animals. Physiological investigations included innate immune function, thyroid hormone levels, and hepatic detoxification enzyme induction, none of which differed in response to increased exposures or tissue concentrations of NAs. Body mass did increase in both the salt- and NA-exposed animals, likely related to osmotic pressure and uptake of water through the skin. Our results demonstrate that commercial NAs are absorbed and deposited in muscle tissue, yet they show few negative physiological or toxicological effects on the frogs.

Pharmacokinetic Variability of Four Newer Antiepileptic Drugs, Lamotrigine, Levetiracetam, Oxcarbazepine, and Topiramate

Newer antiepileptic drugs (AEDs) are widely used in patients with epilepsy. There is still insufficient documentation regarding pharmacokinetic variability of these AEDs in different patient groups. The purpose of this study was to compare age and comedication as factors contributing to pharmacokinetic variability between 4 newer AEDs (lamotrigine, levetiracetam, oxcarbazepine, and topiramate) among patients with refractory epilepsy. Data regarding age, gender, use of AEDs, daily doses, and serum concentration measurements were retrieved from a therapeutic drug monitoring database, from patients admitted to the National Center for Epilepsy, Norway, 2007-2008. In total, 1050 patients were included, 111 younger children (2-9 years), 137 older children (10-17 years), 720 adults (18-64 years), 82 elderly (65-93 years). Fifty percent of the patients were prescribed polytherapy, in 88 different combinations. The interindividual pharmacokinetic variability was extensive, as illustrated by a 10-fold variability in serum concentration compared with dose. Age affected the apparent clearance of levetiracetam to the largest extent, as shown by a 60% increase in younger children and a 40% reduction in the elderly, respectively, compared with adults. Comedication altered the clearance of lamotrigine to the greatest extent ±70% because it is affected by both enzyme inducers and inhibitors. Hepatic enzyme inducers increased the clearance of levetiracetam and topiramate by 25% and oxcarbazepine by 75%. Valproic acid reduced the clearance of topiramate by 25%. Age and comedication are important contributors to pharmacokinetic variability. Age had the greatest impact on levetiracetam, and comedication affected the clearance of each of the 4 AEDs investigated in this study. Pharmacokinetic drug interactions must be carefully considered when multidrug therapies are prescribed. Therapeutic drug monitoring is a valuable tool for individualizing AED therapy.

Chronic Free‐Choice Drinking in Crossed High Alcohol Preferring Mice Leads to Sustained Blood Ethanol Levels and Metabolic Tolerance Without Evidence of Liver Damage

Crossed high alcohol preferring (cHAP) mice were selectively bred from a cross of the HAP1×HAP2 replicate lines, and we demonstrate blood ethanol concentrations (BECs) during free-choice drinking that are reminiscent of those observed in alcohol-dependent humans. Therefore, this line may provide an unprecedented opportunity to learn about the consequences of excessive voluntary ethanol (EtOH) consumption, including metabolic tolerance and liver pathology. Cytochrome p450 2E1 (CYP2E1) induction plays a prominent role in driving both metabolic tolerance and EtOH-induced liver injury. In this report, we sought to characterize cHAP drinking by assessing whether pharmacologically relevant BEC levels are sustained throughout the active portion of the light-dark cycle. Given that cHAP intakes and BECs are similar to those observed in mice given an EtOH liquid diet, we assessed whether free-choice exposure results in metabolic tolerance, hepatic enzyme induction, and hepatic steatosis. In experiment 1, blood samples were taken across the dark portion of a 12:12 light-dark cycle to examine the pattern of EtOH accumulation in these mice. In experiments 1 and 2, mice were injected with EtOH following 3 to 4weeks of access to water or 10% EtOH and water, and blood samples were taken to assess metabolic tolerance. In experiment 3, 24 mice had 4weeks of access to 10% EtOH and water or water alone, followed by necropsy and hepatological assessment. In experiment 1, cHAP mice mean BEC values exceeded 80mg/dl at all sampling points and approached 200mg/dl during the middle of the dark cycle. In experiments 1 and 2, EtOH-exposed mice metabolized EtOH faster than EtOH-naïve mice, demonstrating metabolic tolerance (p<0.05). In experiment 3, EtOH-drinking mice showed greater expression of hepatic CYP2E1 than water controls, consistent with the development of metabolic tolerance (p<0.05). EtOH access altered neither hepatic histology nor levels of alcohol dehydrogenase and aldehyde dehydrogenase. These results demonstrate that excessive intake by cHAP mice results in sustained BECs throughout the active period, leading to the development of metabolic tolerance and evidence of CYP2E1 induction. Together, these results provide additional support for the cHAP mice as a highly translational rodent model of alcoholism.

Characterization of the Temporal Induction of Hepatic Xenobiotic-Metabolizing Enzymes by Glucosinolates and Isothiocyanates: Requirement for at Least a 6 h Exposure To Elicit Complete Induction Profile

A mechanism of action of chemopreventive glucosinolates/isothiocyanates, established largely in vitro, is to modulate carcinogen-metabolizing enzymes. Extrapolation in vivo involves relating in vitro concentrations to plasma/tissue concentrations attained in vivo, thus assuming that even transient exposure modulates enzyme activity. To test this hypothesis, precision-cut rat liver slices were incubated with glucosinolates for up to 24 h, and the O-dealkylation of methoxyresorufin and ethoxyresorufin was determined; increased activities were observed only at incubations of at least 6 h. To evaluate phase II enzymes, isothiocyanates, namely, sulforaphane, erucin, and phenethyl isothiocyanate, were similarly incubated; quinone reductase increased after incubation for 6 h or longer. When glutathione S-transferase was monitored, the phenethyl isothiocyanate-manifested rise necessitated at least a 6 h incubation, whereas in the case of sulforaphane and erucin, the activity was elevated after only 2 h. It is inferred that a rise in carcinogen-metabolizing enzymes by glucosinolates/isothiocyanates necessitates tissue exposure of at least 6 h.

Risk factors for hyperammonemia associated with valproic acid therapy in adult epilepsy patients

Hyperammonemia is one of the side effects of treatment with valproic acid (VPA), but the risk factors and mechanisms involved remain obscure. This study analyzed the risk factors for hyperammonemia associated with VPA therapy in adult epilepsy patients. A retrospective analysis of 2724 Japanese patients (1217 males and 1507 females aged from 16 to 76years) treated with VPA between January 2006 and December 2010 were analyzed. The ammonia level increased markedly in a VPA dose-dependent manner, and was significantly elevated in patients who also used hepatic enzyme inducers such as phenytoin (PHT), phenobarbital (PB), carbamazepine (CBZ), and combinations of these drugs. When a blood ammonia level exceeding 200μg/dl was defined as hyperammonemia, the risk factors for hyperammonemia according to multiple regression analysis were a VPA dose >20mg/kg/day (odds ratio (OR): 4.1; 95% confidence interval (CI): 1.6-10.8) and concomitant use of PHT (OR: 11.0; 95% CI: 3.1-38.7), concomitant PB (OR: 4.3; 95% CI: 1.0-17.9), concomitant CBZ (OR: 2.8; 95% CI: 0.6-11.9), and concomitant topiramate (OR: 2.8; 95% CI: 1.2-6.5). Regimens containing multiple inducers were associated with an increased risk of hyperammonemia. Identification of risk factors for hyperammonemia associated with VPA therapy can help to minimize side effects during its clinical use.

CYP450-Dependent Biotransformation of the Insecticide Fipronil into Fipronil Sulfone Can Mediate Fipronil-Induced Thyroid Disruption in Rats

In rats, the widely used insecticide fipronil increases the clearance of thyroxine (T(4)). This effect is associated with a high plasma concentration of fipronil sulfone, the fipronil main metabolite in several species including rats and humans. In sheep, following fipronil treatment, fipronil sulfone plasma concentration and thyroid disruption are much lower than in rats. We postulated that fipronil biotransformation into fipronil sulfone by hepatic cytochromes P450 (CYP) could act as a potential thyroid disruptor. The aim of this study was to determine if fipronil sulfone treatment could reproduce the fipronil treatment effects on T(4) clearance and CYP induction in rats. Fipronil and fipronil sulfone treatments (3.4 μmol/kg/day per os, 14 days) increased total and free T(4) clearances to the same extent in THX + T(3), euthyroid-like rats. Both treatments induced a 2.5-fold increase in Ugt1a1 and Sult1b1 messenger RNA (mRNA) expressions and a twofold increase in UGT1A activity suggesting that T(4) elimination was mediated, at least in part, by hepatic uridine 5'-diphospho-glucuronosyltransferases (UGT) and/or sulfotransferases (SULT) induction. Both treatments induced a 10-fold increase in Cyp3a1 and Cyp2b2 mRNA expressions concomitant with a threefold increase in CYP3A immunoreactivity and a 1.7-fold increase in antipyrine clearance, a biomarker of CYP3A activity. All these results showed that fipronil sulfone treatment could reproduce the fipronil treatment effects on T(4) clearance and hepatic enzyme induction in rats. The potential of fipronil sulfone to act as a thyroid disruptor is all the more critical because it persists much longer in the organism than fipronil itself.

Retinoic acid as target for local pharmacokinetic interaction with modafinil in neural cells

While the biological importance of the cytochrome P450 system in the liver is well established, much less is known about its role in the brain and drug interactions at the level of brain cells have hardly been investigated. Here, we show that modafinil, a well-known inducer of hepatic CYP enzymes, also increases CYP3A4 expression in human-derived neuron-like SH-SY5Y cells. Upregulation of CYP3A4 by modafinil was associated with increased retinoic acid (RA) degradation, which could be blocked by specific CYP3A4 inhibitor erythromycin. In turn, reduced RA levels in culture medium during modafinil treatment resulted in decreased neuronal differentiation of SH-SY5Y cells as assessed by intracellular neurotransmitter concentrations and proliferative activity. Again, this differentiation-impeding effect of modafinil on SH-SY5Y cells was antagonized by erythromycin. Similarly, modafinil treatment of the murine GL261 glioma cell line resulted in increased proliferative activity. This was associated with upregulation of RA-degrading CYP26A1 in GL261 cells. Taken together, our results indicate that psychopharmacological agents such as modafinil may directly act on CYP enzymes in neural tissue. These kinds of drug effects may become highly relevant especially in the context of biomolecules such as RA whose local metabolism in brain is under tight spatial and temporal control.