Low Interaction Potential Research Articles

Methylation and its role in the disposition of tanshinol, a cardiovascular carboxylic catechol from Salvia miltiorrhiza roots (Danshen).

Aim:Tanshinol is an important catechol in the antianginal herb Salvia miltiorrhiza roots (Danshen). This study aimed to characterize tanshinol methylation.Methods:Metabolites of tanshinol were analyzed by liquid chromatography/mass spectrometry. Metabolism was assessed in vitro with rat and human enzymes. The major metabolites were synthesized for studying their interactions with drug metabolizing enzymes and transporters and their vasodilatory properties. Dose-related tanshinol methylation and its influences on tanshinol pharmacokinetics were also studied in rats.Results:Methylation, preferentially in the 3-hydroxyl group, was the major metabolic pathway of tanshinol. In rats, tanshinol also underwent considerable 3-O-sulfation, which appeared to be poor in human liver. These metabolites were mainly eliminated via renal excretion, which involved tubular secretion mainly by organic anion transporter (OAT) 1. The methylated metabolites had no vasodilatory activity. Entacapone-impaired methylation did not considerably increase systemic exposure to tanshinol in rats. The saturation of tanshinol methylation in rat liver could be predicted from the Michaelis constant of tanshinol for catechol-O-methyltransferase (COMT). Tanshinol had low affinity for human COMT and OATs; its methylated metabolites also had low affinity for the transporters. Tanshinol and its major human metabolite (3-O-methyltanshinol) exhibited negligible inhibitory activities against human cytochrome P450 enzymes, organic anion transporting polypeptides 1B1/1B3, multidrug resistance protein 1, multidrug resistance-associated protein 2, and breast cancer resistance protein.Conclusion:Tanshinol is mainly metabolized via methylation. Tanshinol and its major human metabolite have low potential for pharmacokinetic interactions with synthetic antianginal agents. This study will help define the risk of hyperhomocysteinemia related to tanshinol methylation.

Mecanismo de acción, farmacología e interacciones de dolutegravir

Dolutegravir is a second-generation integrase strand transfer inhibitor (INSTI), whose potential and binding half-life in the integrase are far superior to those of raltegravir and elvitegravir, conferring it with unique characteristics in terms of its genetic barrier to resistance and activity against viruses with one or more mutations in the integrase. The pharmacokinetic properties of dolutegravir allow once-daily dosing (50 mg), with or without food, maintaining concentrations far above those effective against wild-type viruses. If integrase resistance mutations are present, the recommended dosing regimen is 50 mg/12 h. The distribution of dolutegravir in cerebrospinal fluid is good and effective concentrations are also reached in the male and female genital tracts. Dolutegravir is metabolized by UGT1A1 and, to a lesser extent, by CYP3A4, without being an inducer or inhibitor of the usual metabolic systems. It has a very low potential for drug interactions and can be administered in routine doses with most drugs. Dose adjustment is not required, even in patients with renal insufficiency or mild or moderate liver failure. Increasing the dose of dolutegravir (50 mg/12 h) is only recommended when administered with efavirenz, nevirapine, fosamprenavir/r, tipranavir/r, rifampicin, carbamazepine, phenytoin and phenobarbital. Coadministration of dolutegravir with etravirine is not recommended without a protease inhibitor or with Hypericum perforatum. Dolutegravir should be administered 2 h before or 6 h after antacids or products with polyvalent cations. Dolutegravir can reduce renal tubule secretion of substances excreted via OCT2, with a slight initial increase in creatinine, with no risk of renal toxicity. The drug can also increase metformin concentrations and consequently monitoring is recommended in case dose adjustment is required. In summary, dolutegravir has excellent pharmacokinetic and drug interaction profiles.

Combination dolutegravir-abacavir-lamivudine in the management of HIV/AIDS: clinical utility and patient considerations.

The current standard of care for human immunodeficiency virus (HIV) treatment is a three-drug regimen containing a nonnucleoside reverse transcriptase inhibitor, a protease inhibitor, or an integrase strand transfer inhibitor (INSTI) plus two nucleoside/tide reverse transcriptase inhibitors. Given their potency, safety, and distinctive mechanism of action, INSTIs represent an important advance in HIV type 1 (HIV-1) therapy. Dolutegravir (DTG) is a new-generation INSTI recently approved for the treatment of HIV-1-infected adult patients, with distinct advantages compared with other available antiretroviral agents. In well-designed, large clinical trials, DTG-containing regimens have demonstrated either noninferiority or superiority to current first-line agents such as raltegravir-, darunavir/ritonavir-, and efavirenz-containing regimens. The favorable safety profile, low potential for drug interactions, minimal impact on lipids, good tolerability, and high resistance barrier of DTG makes this compound one of the preferred choices for HIV therapy in multiple clinical scenarios, including treatment-naïve and treatment-experienced patients. DTG is the only antiretroviral drug not yet associated with de novo emergence of resistance mutations in treatment-naïve individuals. However, data from in vitro studies and clinical trial suggest the possibility of cross-resistance between first- and second-generation INSTIs. Even though these profiles are infrequent at the moment, they need to be monitored in all current patients treated with INSTIs. With its potent activity, good tolerability, simplicity of dosing, and minimal drug interaction profile, DTG will likely play a major role in the management of patients with HIV-1 infection. On the basis of clinical trial data, current guidelines endorse DTG in combination with nucleoside/tide reverse transcriptase inhibitors as one of the recommended regimens in antiretroviral therapy-naïve patients. Most of the favorable clinical experiences from clinical trials are based on the combination of DTG with abacavir/lamivudine, and DTG is planned to be coformulated with abacavir/lamivudine. This will provide a further advantage, given that single tablet regimens are associated with higher adherence rates as well as improvement in quality of life and enhanced patient preference.

CYP450 and Its Implications in the Clinical Use of Antipsychotic Drugs

Polypharmacy implies a high potential for drug-drug interactions. The capacity of the cytochrome P450 enzyme system involved in the metabolism of psychoactive drugs differs greatly, which leads to variable drug elimination rates and inter-subject differences in serum drug concentrations. Polymorphisms in genes coding for CYP450 enzymes contribute to this inter-subject variability. Therapeutic response and adverse effects vary among patients treated with the same dose of a certain drug. Polypharmacy, comorbidity and the use of certain substances (grapefruit juice, caffeine and tobacco) increase the chances of clinically relevant interactions in a psychotic patient. Choosing drugs with low interaction potential seems to be the best strategy to prevent clinically relevant interactions particularly in elderly, polymedicated, oncologic and HIV patients.

Zonisamid: az elsőként választandó antiepileptikumok között fokális epilepsziában

[Chronic administration of antiepileptic drugs without history of unprovoked epileptic seizures are not recommended for epilepsy prophylaxis. Conversely, if the patient suffered the first unprovoked seizure, then the presence of epileptiform discharges on the EEG, focal neurological signs, and the presence of epileptogenic lesion on the MRI are risk factors for a second seizure (such as for the development of epilepsy). Without these risk factors, the chance of a second seizure is about 25-30%, while the presence of these risk factors (for example signs of previous stroke, neurotrauma, or encephalitis on the MRI) can predict >70% seizure recurrence. Thus the International League Against Epilepsy (ILAE) re-defined the term ’epilepsy’ which can be diagnosed even after the first seizure, if the risk of seizure recurrence is high. According to this definition, we can start antiepileptic drug therapy after a single unprovoked seizure. There are four antiepileptic drugs which has the highest evidence (level „A”) as first-line initial monotherapy for treating newly diagnosed epilepsy. These are: carbamazepine, phenytoin, levetiracetam, and zonisamide (ZNS). The present review focuses on the ZNS. Beacuse ZNS can be administrated once a day, it is an optimal drug for maintaining patient’s compliance and for those patients who have a high risk for developing a non-compliance (for example teenagers and young adults). Due to the low interaction potential, ZNS treatment is safe and effective in treating epilepsy of elderly people. ZNS is an ideal drug in epilepsy accompanied by obesity, because ZNS has a weight loss effect, especially in obese patients.]

Fidaxomicin: A Novel Macrolide Antibiotic for <I>Clostridium difficile</I> Infection

To review the chemistry, pharmacology, microbiology, pharmacodynamics, pharmacokinetics, clinical efficacy, tolerability, drug interactions, dosing, and administration of fidaxomicin (FDX). A search of PubMed using the terms "fidaxomicin," "OPT-80," "PAR-101," "OP-1118," "difimicin," "tiacumicin," and "lipiarmycin" was performed. All English-language articles from 1983 to November 2013 were reviewed for relevance. Bibliographies of all articles were reviewed as well as the manufacturer's Web site to further identify relevant information. All English-language articles from 1983 to November 2013 appearing in these searches were reviewed for relevance to this paper. In addition, their bibliographies were reviewed to identify any articles not identified in the searches. FDX is the first macrolide antibiotic with a narrow spectrum of activity targeted against Clostridium difficile. It is administered orally without regard to food. The primary route of elimination is fecal excretion. Advanced age, hepatic dysfunction, or renal impairment do not alter its disposition. Phase III clinical trials have demonstrated that FDX 200 mg twice daily for 10 days is noninferior to vancomycin 125 mg four times daily for 10 days in the treatment of adults with C. difficile infection and is associated with lower recurrence rates. FDX has a favorable side effect profile and a low potential for drug interactions. FDX has been shown to be safe and effective in the treatment of adults with C. difficile infection. Further research and pharmacoeconomic studies are needed to clarify and refine its role in the treatment of patients at high risk for recurrence.

Simulation of the Streamflow for the Rio Nuevo Watershed of Jamaica for Use in Agriculture Water Scarcity Planning

AbstractJamaica’s water resources are under increasing risk of degradation and depletion, especially in light of increasing population growth, urbanization, and climate change. In this study, the soil and water assessment tool (SWAT) was used to simulate the hydrologic characteristics of the Rio Nuevo watershed in Jamaica to assess streamflow availability for irrigation supply during dry periods. Approximately 85% of the watershed consists of aquiclude rock material, thus resulting in low potential for interaction between surface and groundwater. Historical climatic data (precipitation and temperature) were obtained for the watershed, and streamflow data were obtained for the Rio Nuevo, which drains the watershed. The model was calibrated over the period 2002–2004, and validated using the period 2005–2007. This paper outlines the parameterization of SWAT for the Rio Nuevo watershed and describes the potential for its use in agricultural water scarcity management in Jamaica. A Nash-Sutcliffe efficiency (NS...

The role of carbonyl reducing enzymes in oxcarbazepine in vitro metabolism in man

Oxcarbazepine, a second generation antiepileptic drug belonging to the family of dibenz[b,f]azepines, is subjected to a rapid and extensive biotransformation. Oxcarbazepine demonstrates a low potential for drug interactions because its biotransformation is mainly mediated by the reduction pathway instead of oxidative pathways, which are very susceptible to drug interactions. The reductive metabolism of oxcarbazepine yields a 10-monohydroxy derivative (10,11-dihydro-10-hydroxy-carbazepine), which is responsible for the pharmacological activity. The identity and localization of enzymes participating in the reduction of oxcarbazepine in response to this active metabolite have remained unknown until now. Thus, we investigated the reductive metabolism of oxcarbazepine in human liver subcellular fractions and using recombinant carbonyl reducing enzymes. The reduction of oxcarbazepine was shown to occur largely in the liver cytosol rather than liver microsomes. Furthermore, the activity and stereospecificity of cytosolic carbonyl reducing enzymes toward oxcarbazepine were assessed. Of the eight tested enzymes, six reductases were identified to contribute to the reduction of oxcarbazepine. The highest activities were demonstrated by AKR1C1, AKR1C2, AKR1C3, and AKR1C4. The contribution of CBR1 and CBR3 to the reduction of oxcarbazepine was also significant, although their role in oxcarbazepine metabolism in vivo is unclear.

The Interaction Potential of Retigabine (Ezogabine) with Other Antiepileptic Drugs

Retigabine is an antiepileptic drug (AED) that reduces neuronal excitability by enhancing neuronal KCNQ (Kv7) potassium channel activity. This manuscript provides an overview of the drug-drug interaction potential of retigabine with other AEDs, using data collated from both in vitro work and clinical studies, either previously published or from relevant information collated during the development of retigabine. Retigabine is not a substrate for the major CYP enzymes and at clinically relevant concentrations there is little or no potential for retigabine to inhibit or induce the CYP enzymes or to inhibit the major renal drug transporters. The addition of retigabine to a range of existing AEDs showed little or no effect on the AED trough concentrations apart from a 20% decrease in lamotrigine concentrations. Results from a small phase II study showed that co-administration of valproic acid and topiramate had no impact on the PK of retigabine whereas carbamazepine and phenytoin increased the clearance of retigabine by approximately 27% and 36%, respectively. Conversely, a population PK analysis of combined data from phase I, II and III studies showed that none of the coadministered AEDs affected retigabine clearance apart from lamotrigine which lowered retigabine clearance by 6.7%. Retigabine is not metabolized by CYP isozymes and does not induce or inhibit these isozymes at clinically relevant concentrations. Therefore, retigabine is associated with a low potential for PK interactions with other drugs via CYP450. Overall, there was little or no potential for retigabine to interact with other available AEDs. Although some PK interactions were observed with lamotrigine, these are unlikely to be clinically relevant.

Drug Interactions Between Antiplatelet or Novel Oral Anticoagulant Medications and Antiretroviral Medications

To review potential drug interactions between antiretroviral (ARV) medications and antiplatelets or novel oral anticoagulants (NOACs). A literature search of MEDLINE, PubMed, EMBASE, International Pharmaceutical Abstracts, and Google Scholar was performed using the search terms (1) clopidogrel or ticagrelor or prasugrel, (2) dabigatran or rivaroxaban or apixaban, and (3) antiretrovirals. Any English language study or case report describing a drug interaction between an ARV and an antiplatelet or NOAC was included. Additional information was taken from pharmacokinetic studies of individual agents alone or information from similar drug interactions. Two studies were identified through the literature search: one reporting an in vivo interaction between ritonavir and prasugrel and the other an in vitro interaction between efavirenz and clopidogrel. A case report describing a drug interaction between nevirapine and rivaroxaban was also located. Information from pharmacokinetic studies and from similar drug interactions allowed for a comprehensive review of potential drug interactions. There are potential drug interactions between ARVs, antiplatelet agents or NOACs. Management of these interactions may include selecting ARVs with a lower potential for drug interactions or choosing antiplatelet agents or NOACs least likely to interact with ARVs. With protease inhibitors or cobicistat, clopidogrel and dabigatran do not appear to have clinically significant interactions. Nonnucleoside reverse transcriptase inhibitors have a low potential for interactions with prasugrel and dabigatran. Clinically significant drug interactions are unlikely to occur between antiplatelet agents or NOACs and nucleoside reverse transcriptase inhibitors raltegravir, dolutegravir, or maraviroc.

Sofosbuvir for the treatment of chronic hepatitis C virus infection.

Sofosbuvir is a nucleotide analogue selective inhibitor of the RNA-directed RNA polymerase (NS5B) enzyme of the hepatitis C virus (HCV) genome. It has shown potent antiviral activity across all HCV genotypes and in a variety of patient populations, including treatment-naive patients; treatment-experienced patients who had failed previous standard therapy; patients with decompensated liver disease, including cirrhosis; and HIV co-infected patients. It is administered as a single, once-daily 400-mg tablet, has no food restrictions, has low potential for drug interactions, and requires no dose adjustment in mild to moderate kidney or liver impairment. When sofosbuvir is combined with pegylated interferon and/or ribavirin, its clinical and laboratory safety profile is similar to that which is expected from pegylated interferon or ribavirin alone. Rates of treatment discontinuation and dose reduction with sofosbuvir-containing regimens were lower than those commonly observed with pegylated interferon and ribavirin.

Prediction of Clinical Drug–Drug Interactions of Veliparib (ABT-888) with Human Renal Transporters (OAT1, OAT3, OCT2, MATE1, and MATE2K)

Veliparib (ABT-888) is largely eliminated as parent drug in human urine (70% of the dose). Renal unbound clearance exceeds glomerular filtration rate, suggesting the involvement of transporter-mediated active secretion. Clinically relevant pharmacokinetic interactions in the kidney have been associated with OAT1, OAT3, OCT2, MATE1, and MATE2K. In the present study, interactions of veliparib with these transporters were investigated. Veliparib inhibited OAT1, OAT3, OCT2, MATE1, and MATE2K with IC50 values of 1371, 505, 3913, 69.9, and 69.5 μM, respectively. The clinical unbound maximum plasma concentration of veliparib after single oral dose of 50 mg (0.45 μM) is manyfold lower than IC50 values for OAT1, OAT3, OCT2, MATE1, or MATE2K. These results indicate a low potential for drug-drug interaction (DDI) with OAT1/3, OCT2, or MATE1/2K. Additional studies demonstrated that veliparib is a substrate of OCT2. In Oct1/Oct2 double-knockout mice, the plasma exposure of veliparib was increased by 1.5-fold, and the renal clearance was decreased by 1.8-fold as compared with wild-type mice, demonstrating that organic cation transporters contribute to the renal elimination in vivo. In summary, the in vitro transporter data for veliparib predicts minimal potential for an OAT1/3-, OCT2-, and MATE1/2K-mediated DDI given the clinical exposure after single oral dose of 50 mg.

NEW ORAL ANTICOAGULANT DRUGS IN ATRIAL FIBRILLATION AND ACUTE CORONARY SYNDROME

After an acute coronary syndrome, patients remain at risk of recurrent ischemic events despite the use of antiplatelet therapy. In order to reduce the risk of recurrent ischemia in the treatment of patients with acute coronary syndromes, standard oral anticoagulants, such as vitamin K antagonists, have been introduced. These drugs have an important role in preventing stroke and systemic embolism in patients with atrial fibrillation. Vitamin K antagonists (e.g., warfarin) reduce the risk of recurrent cardiovascular events and stroke but increase the risk of bleeding. In addition, the traditional anticoagulants have other significant drawbacks. Therefore, modulation of the coagulation process represents an important target in the development of new oral anticoagulants today. The new oral anticoagulants selectively target thrombin (dabigatran etexilate) or factor Xa (rivaroxaban, apixaban, edoxaban). Unlike traditional anticoagulants, these drugs have rapid onset of action and a relatively wide therapeutic range, do not require routine prothrombin time (PT) monitoring and have low potential for food and drug interaction. Dabigatran etexilate and rivaroxaban have been already approved in many countries for the prevention of stroke and systemic embolism in patients with atrial fibrillation. The third phase of clinical studies in which rivaroxaban was investigated in patients with acute coronary syndrome has been successfully completed. Acta Medica Medianae 2013;52(3):42-48.

Cellules souches

The direct thrombin inhibitor, dabigatran, and the selective factor Xa inhibitors, rivaroxaban and apixaban, are new oral anticoagulants that are approved in many countries for prevention of venous thromboembolism in patients undergoing elective hip or knee arthroplasty. All have a rapid onset of action, a low potential for food and drug interactions and a predictable anticoagulant effect that obviates the need for routine coagulation monitoring. These agents offer a convenient alternative to conventional anticoagulant drug regimens, including parenteral low-molecular-weight heparins and fondaparinux, and oral adjusted-dose vitamin K antagonists, for the prevention of venous thromboembolism in this surgical setting. This review summarizes the pharmacology, clinical trial results, bleeding risk and practical use of these new oral anticoagulants in clinical orthopaedic practice. Potential issues to be considered when using these oral anticoagulants include renal impairment, potential drug interactions, neuraxial anaesthesia and management of bleeding.

Characterization of insulin resistance in young adult survivors of childhood acute lymphoblastic leukaemia and non-Hodgkin lymphoma

The direct thrombin inhibitor, dabigatran, and the selective factor Xa inhibitors, rivaroxaban and apixaban, are new oral anticoagulants that are approved in many countries for prevention of venous thromboembolism in patients undergoing elective hip or knee arthroplasty. All have a rapid onset of action, a low potential for food and drug interactions and a predictable anticoagulant effect that obviates the need for routine coagulation monitoring. These agents offer a convenient alternative to conventional anticoagulant drug regimens, including parenteral low-molecular-weight heparins and fondaparinux, and oral adjusted-dose vitamin K antagonists, for the prevention of venous thromboembolism in this surgical setting. This review summarizes the pharmacology, clinical trial results, bleeding risk and practical use of these new oral anticoagulants in clinical orthopaedic practice. Potential issues to be considered when using these oral anticoagulants include renal impairment, potential drug interactions, neuraxial anaesthesia and management of bleeding.

Evaluation of the Effect of Cobicistat on theIn VitroRenal Transport and Cytotoxicity Potential of Tenofovir

A once-daily single-tablet antiretroviral regimen containing tenofovir (TFV) disoproxil fumarate, emtricitabine (FTC), elvitegravir (EVG), and cobicistat (COBI) is an approved combination for the treatment of patients infected with HIV. COBI and TFV have been reported to interact with distinct transporters in renal proximal tubules; while TFV is renally eliminated by a combination of glomerular filtration and tubular secretion via anion transporters OAT1, OAT3, and MRP4, COBI inhibits renal cation transporters, particularly MATE1, resulting in a measurable decrease in the tubular secretion of creatinine. To investigate the potential for a renal drug-drug interaction between TFV and COBI in vitro, the uptake of TFV in the presence and absence of COBI was determined in fresh human renal cortex tissue and in cells expressing the relevant renal transporters. At concentrations exceeding clinical protein-unbound plasma levels, COBI did not significantly inhibit the transport of TFV by the anion transporters OAT1, OAT3, and MRP4 (50% inhibitory concentrations [IC50s] of >15, 6.6, and 8.5 μM, respectively). Conversely, TFV had little or no effect on the cation transporters OCT2 and MATE1 (IC50 > 100 μM). Consistent with studies using individual transporters, no increase in the accumulation of TFV in freshly isolated human renal cortex tissue or renal proximal tubule cells (RPTECs) was observed in the presence of COBI. Finally, COBI alone or in combination with FTC and EVG did not affect the sensitivity to TFV of cultured primary RPTECs or cells coexpressing OAT1 and MRP4. These results illustrate that COBI and TFV interact primarily with distinct renal transporters and indicate a low potential for pharmacokinetic renal drug-drug interaction.

In Vitro Characterization of Axitinib Interactions with Human Efflux and Hepatic Uptake Transporters: Implications for Disposition and Drug Interactions

Axitinib is an inhibitor of tyrosine kinase vascular endothelin growth factor receptors 1, 2, and 3. The ATP-binding cassette (ABC) and solute carrier (SLC) transport properties of axitinib were determined in selected cellular systems. Axitinib exhibited high passive permeability in all cell lines evaluated (Papp ≥ 6 × 10(-6) cm/s). Active efflux was observed in Caco-2 cells, and further evaluation in multidrug resistance gene 1 (MDR1) or breast cancer resistance protein (BCRP) transfected Madin-Darby canine kidney cells type 2 (MDCK) cells indicated that axitinib is at most only a weak substrate for P-glycoprotein (P-gp) but not BCRP. Axitinib showed incomplete inhibition of P-gp-mediated transport of digoxin in Caco-2 cells and BCRP transport of topotecan in BCRP-transfected MDCK cells with IC50 values of 3 μM and 4.4 μM, respectively. Axitinib (10 mg) did not pose a risk for systemic drug interactions with P-gp or BCRP per regulatory guidance. A potential risk for drug interactions through inhibition of P-gp and BCRP in the gastrointestinal tract was identified because an axitinib dose of 10 mg divided by 250 mL was greater than 10-fold the IC50 for each transporter. However, a GastroPlus simulation that considered the low solubility of axitinib resulted in lower intestinal concentrations and suggested a low potential for gastrointestinal interactions with P-gp and BCRP substrates. Organic anion transporting polypeptide 1B1 (OATP1B1) and OATP1B3 transfected human embryonic kidney 293 (HEK293) cells transported axitinib to a minor extent but uptake into suspended hepatocytes was not inhibited by rifamycin SV suggesting that high passive permeability predominates. Mouse whole-body autoradiography revealed that [(14)C]axitinib-equivalents showed rapid absorption and distribution to all tissues except the brain. This suggests that efflux transport of axitinib may occur at the mouse blood-brain barrier.

Profile of once-daily zonisamide as monotherapy for treatment of partial seizures in adults

Epilepsy is one of the most common neurologic disorders, affecting about 50 million people around the world. It is recognized that around 50% of patients with newly diagnosed epilepsy become seizure-free with the first drug treatment, so the choice of first antiepileptic drug is crucial. This paper provides a comprehensive overview of zonisamide as monotherapy for partial seizures, with special attention to the possibility of a once-daily regimen. The available data suggest that zonisamide is an effective and well tolerated option as monotherapy. Once-daily dosing is indicated, considering the long plasma half-life and linear pharmacokinetics of the drug. Zonisamide 300 mg was shown to be noninferior to carbamazepine 600 mg in terms of efficacy and safety, but even lower doses may be effective. Finally, the broad spectrum of efficacy in different seizure types, the low drug interaction potential, and the possibility of weight loss make zonisamide a preferred option in many epilepsy practices. Further data on monotherapy, especially in special populations, such as women of childbearing potential, are needed.

Pharmacodynamic and pharmacokinetic evaluation of coadministration of lacosamide and an oral contraceptive (levonorgestrel plus ethinylestradiol) in healthy female volunteers

To determine whether the antiepileptic drug lacosamide affects the pharmacokinetics or pharmacodynamics of a combined oral contraceptive (OC; ethinylestradiol 0.03mg plus levonorgestrel 0.15mg). This was an open-label trial in healthy female volunteers. Eligible women entered cycle 1 of the trial on the first day of menstruation. Cycle 1 was a medication-free, run-in phase of approximately 28days to confirm that normal ovulation occurred. Volunteers with confirmed ovulation entered the subsequent cycle and started taking OCs. After establishing ovulation suppression (defined as progesterone serum concentration <5.1nm on day 21 of the menstrual cycle) in volunteers taking the OCs in cycle 2, lacosamide 400mg/day was administered concomitantly in the subsequent cycle (cycle 3). The pharmacokinetic parameters of area under the concentration-time curve (AUC), maximum steady-state plasma drug concentration (Cmax ), and time to maximum concentration (tmax ) were measured for the OC components and lacosamide. A total of 37 volunteers completed cycle 1, and 32 completed cycle 2. In each of the 31 volunteers who completed the trial (through cycle 3), pharmacodynamic assessment showed progesterone serum concentration was <5.1nm on day 21 of cycle 2, when the OC was administered alone, and on day 21 of cycle 3, when lacosamide was administered concomitantly. The AUC of ethinylestradiol alone versus together with lacosamide was 1,067±404 versus 1,173±330pgh/ml. Corresponding values of Cmax were 116.9±48.8 versus 135.7±28.6pg/ml. For levonorgestrel, the AUC alone was 74.2±21.4 versus 80.9±18.5ngh/ml with lacosamide. Corresponding values of Cmax were 6.7±1.9 versus 7.4±1.5ng/ml. The AUC and Cmax point estimates and almost all 90% confidence intervals (except for Cmax of ethinylestradiol) for ethinylestradiol and levonorgestrel (with and without lacosamide) were within the conventional bioequivalence range, and no relevant changes in tmax were observed for ethinylestradiol (1.5±0.6h alone vs. 1.4±0.7h with lacosamide) or for levonorgestrel (1.5±1.0h alone vs. 1.1±0.6h with lacosamide). Lacosamide pharmacokinetics were consistent with those observed in previous studies of lacosamide alone, with values for AUC of 113.5±20.7μgh/ml, Cmax of 13.8±2.2μg/ml, and tmax of 1.1±0.4h. Lacosamide and an OC containing ethinylestradiol and levonorgestrel have low potential for drug-drug interaction; therefore, coadministration of the two drugs is unlikely to result in contraceptive failure or loss of seizure control.

New Oral Anticoagulants: Comparative Pharmacology with Vitamin K Antagonists

New oral anticoagulants (OACs) that directly inhibit Factor Xa (FXa) or thrombin have been developed for the long-term prevention of thromboembolic disorders. These novel agents provide numerous benefits over older vitamin K antagonists (VKAs) due to major pharmacological differences. VKAs are economical and very well characterized, but have important limitations that can outweigh these advantages, such as slow onset of action, narrow therapeutic window and unpredictable anticoagulant effect. VKA-associated dietary precautions, monitoring and dosing adjustments to maintain international normalized ratio (INR) within therapeutic range, and bridging therapy, are inconvenient for patients, expensive, and may result in inappropriate use of VKA therapy. This may lead to increased bleeding risk or reduced anticoagulation and increased risk of thrombotic events. The new OACs have rapid onset of action, low potential for food and drug interactions, and predictable anticoagulant effect that removes the need for routine monitoring. FXa inhibitors, e.g. rivaroxaban and apixaban, are potent, oral direct inhibitors of prothrombinase-bound, clot-associated or free FXa. Both agents have a rapid onset of action, a wide therapeutic window, little or no interaction with food and other drugs, minimal inter-patient variability, and display similar pharmacokinetics in different patient populations. Since both are substrates, co-administration of rivaroxaban and apixaban with strong cytochrome P450 (CYP) 3A4 and permeability glycoprotein (P-gp) inhibitors and inducers can result in substantial changes in plasma concentrations due to altered clearance rates; consequently, their concomitant use is contraindicated and caution is required when used concomitantly with strong CYP3A4 and P-gp inducers. Although parenteral oral direct thrombin inhibitors (DTIs), such as argatroban and bivalirudin, have been on the market for years, DTIs such as dabigatran are novel synthetic thrombin antagonists. Dabigatran etexilate is a low-molecular-weight non-active pro-drug that is administered orally and converted rapidly to its active form, dabigatran--a potent, competitive and reversible DTI. Dabigatran has an advantage over the indirect thrombin inhibitors, unfractionated heparin and low-molecular-weight heparin, in that it inhibits free and fibrin-bound thrombin. The reversible binding of dabigatran may provide safer and more predictable anticoagulant treatment than seen with irreversible, non-covalent thrombin inhibitors, e.g. hirudin. Dabigatran shows a very low potential for drug-drug interactions. However, co-administration of dabigatran etexilate with other anticoagulants and antiplatelet agents can increase the bleeding risk. Although the new agents are pharmacologically better than VKAs--particularly in terms of fixed dosing, rapid onset of action, no INR monitoring and lower risk of drug interactions--there are some differences between them: the bioavailability of dabigatran is lower than rivaroxaban and apixaban, and so the dabigatran dosage required is higher; lower protein binding of dabigatran reduces the variability related to albuminaemia. The risk of metabolic drug-drug interactions also appears to differ between OACs: VKAs > rivaroxaban > apixaban > dabigatran. The convenience of the new OACs has translated into improvements in efficacy and safety as shown in phase III randomized trials. The new anticoagulants so far offer the greatest promise and opportunity for the replacement of VKAs.