P-glycoprotein restricts the penetration of oseltamivir across the blood-brain barrier

The ATP-Binding Cassette Transporter-Mediated Efflux Transport of Ganciclovir at the Blood-Brain Barrier

BACKGROUND AND OBJECTIVE

Recent studies have highlighted the key role of the ATP-binding cassette (ABC) transporters, including the P-glycoprotein (P-gp), the breast cancer resistance protein (BCRP), and the multi-drug resistance protein 4 (MRP4) in limiting the brain distribution of several antiviral agents. In this study, we investigated whether the inhibition of these transporters increases the permeability of the blood-brain barrier (BBB) to ganciclovir.

METHODS

A microdialysis and high-performance liquid chromatographic method was developed to monitor the concentrations of unbound ganciclovir in the brain interstitial fluid and plasma, with and without the administration of ABC transporter inhibitors. Pharmacokinetic parameters, including the area under the plasma concentration-time curve from time 0 to time of the last measurable analyte concentration (AUC0-t,plasma), the area under the brain interstitial fluid concentration-time curve from time 0 to time of the last measurable analyte concentration (AUC0-t,brain), and the unbound brain-to-plasma concentration ratio (Kp,uu,brain) were calculated.

RESULTS

The mean AUC0-t,plasma, AUC0-t,brain, and Kp,uu,brain in rats who received ganciclovir (30 mg/kg, intraperitoneal) alone were 1090 min·µg/mL, 150 min·µg/mL, and 14%, respectively. After the administration of tariquidar (inhibitor of P-gp), Ko143 (inhibitor of BCRP), or MK-571 (inhibitor of MRP4), the Kp,uu,brain of ganciclovir increased to 31 ± 2.1%, 26 ± 1.3%, and 32 ± 2.0%, respectively.

CONCLUSIONS

The findings of this study suggest that ABC transporters P-gp, BCRP, and MRP4 mediate the efflux of ganciclovir at the BBB and that the inhibition of these transporters facilitates the penetration of the BBB by ganciclovir.

The neuropathogenesis of highly pathogenic avian influenza H5Nx viruses in mammalian species including humans

Circulation of highly pathogenic avian influenza (HPAI) H5Nx viruses of the A/Goose/Guangdong/1/96 lineage in birds regularly causes infections of mammals, including humans. In many mammalian species, infections are associated with severe neurological disease, a unique feature of HPAI H5Nx viruses compared with other influenza A viruses. Here, we provide an overview of the neuropathogenesis of HPAI H5Nx virus infection in mammals, centered on three aspects: neuroinvasion, neurotropism, and neurovirulence. We focus on in vitro studies, as well as studies on naturally or experimentally infected mammals. Additionally, we discuss the contribution of viral factors to the neuropathogenesis of HPAI H5Nx virus infections and the efficacy of intervention strategies to prevent neuroinvasion or the development of neurological disease.

Repurposing of antiviral drugs for COVID-19 and impact of repurposed drugs on the nervous system

The recent pandemic, Coronavirus Disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has devastated humanity and is continuing to threaten us. Due to the high transmissibility of this pathogen, researchers are still trying to cope with the treatment and prevention of this disease. Few of them were successful in finding cure for COVID-19 by including repurposed drugs in the treatment. In such pandemic situations, when it is nearly impossible to design and implement a new drug target, previously designed antiviral drugs could help against novel viruses, referred to as drug repurposing/redirecting/repositioning or re-profiling. This review describes the current landscape of the repurposing of antiviral drugs for COVID-19 and the impact of these drugs on our nervous system. In some cases, specific antiviral therapy has been notably associated with neurological toxicity, characterized by peripheral neuropathy, neurocognitive and neuropsychiatric effects within the central nervous system (CNS).

An Atlas of the Quantitative Protein Expression of Anti-Epileptic-Drug Transporters, Metabolizing Enzymes and Tight Junctions at the Blood-Brain Barrier in Epileptic Patients

The purpose of the present study was to quantitatively elucidate the levels of protein expression of anti-epileptic-drug (AED) transporters, metabolizing enzymes and tight junction molecules at the blood–brain barrier (BBB) in the focal site of epilepsy patients using accurate SWATH (sequential window acquisition of all theoretical fragment ion spectra) proteomics. Brain capillaries were isolated from focal sites in six epilepsy patients and five normal brains; tryptic digests were produced and subjected to SWATH analysis. MDR1 and BCRP were significantly downregulated in the epilepsy group compared to the normal group. Out of 16 AED-metabolizing enzymes detected, the protein expression levels of GSTP1, GSTO1, CYP2E1, ALDH1A1, ALDH6A1, ALDH7A1, ALDH9A1 and ADH5 were significantly 2.13-, 6.23-, 2.16-, 2.80-, 1.73-, 1.67-, 2.47- and 2.23-fold greater in the brain capillaries of epileptic patients than those of normal brains, respectively. The protein expression levels of Claudin-5, ZO-1, Catenin alpha-1, beta-1 and delta-1 were significantly lower, 1.97-, 2.51-, 2.44-, 1.90- and 1.63-fold, in the brain capillaries of epileptic patients compared to those of normal brains, respectively. Consistent with these observations, leakage of blood proteins was also observed. These results provide for a better understanding of the therapeutic effect of AEDs and molecular mechanisms of AED resistance in epileptic patients.

Increased penetration of diphenhydramine in brain via proton-coupled organic cation antiporter in rats with lipopolysaccharide-induced inflammation

Uptake transporters in brain microvascular endothelial cells (BMECs) are involved in the penetration of basic (cationic) drugs such as diphenhydramine (DPHM) into the brain. Lipopolysaccharide (LPS)-induced inflammation alters the expression levels and activities of uptake transporters, which change the penetration of DPHM into the brain. A brain microdialysis study showed that the unbound brain-to-plasma partition coefficient (K_p,uu,brain) for DPHM in LPS rats was approximately two times higher than that in control rats. The transcellular transport of DPHM to BMECs was increased when BMECs were cultured with serum from LPS rats. Compared with control rats or BMECs, the brain uptake of DPHM in LPS rats was increased and the intracellular accumulation of DPHM was increased under a high intracellular pH in BMECs from LPS rats, respectively. Treatment of BMECs with transporter inhibitors or inflammatory cytokines had little impact on the intracellular accumulation of DPHM in BMECs. This study suggests that LPS-induced inflammation promotes unidentified proton-coupled organic cation (H⁺/OC) antiporters that improve the penetration of DPHM into rat brain via the blood-brain barrier.

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The unbound brain-to-plasma partition coefficient for diphenhydramine (DPHM) was increased in lipopolysaccharide-induced inflammation in rats.

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The uptake of DPHM to brain microvascular endothelial cells (BMECs) was promoted by treatments of serum from rats with inflammation.

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Treatment of BMECs with transporter inhibitors or inflammatory cytokines had little impact on the intracellular accumulation of DPHM in BMECs.

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LPS-induced inflammation promotes unidentified proton-coupled organic cation antiporters that improve the brain penetration of DPHM.

Metabolism and disposition of oseltamivir (OS) in rats, determined by immunohistochemistry with monospecific antibody for OS or its active metabolite oseltamivir carboxylate (OC): A possibility of transporters dividing the drugs' excretion into the bile and kidney

Among any drugs, no comparative pharmacological study on how prodrug and its active metabolite behave in animal bodies is available. Immunohistochemistry (IHCs) using newly prepared two monoclonal antibodies, AOS‐96 and AOC‐160, monospecific for oseltamivir (OS) and its metabolite oseltamivir carboxylate (OC) were developed, simultaneously detecting the uptake or excretion of OS and OC in the intestine, liver, and kidney of rats to which OS was orally administered. In the intestine, IHC for OS revealed OS highly distributed to the absorptive epithelia with heavily stained cytoplasmic small granules (CSGs). IHC for OC showed that OC also distributed highly in the epithelia, but without CSGs, suggesting that OS was partly converted to OC in the cells. In the liver, OS distributed in the hepatocytes and on their bile capillaries, as well as on the lumina from the bile capillaries to the interlobular bile ducts. OC distributed in the whole cell of the hepatocytes, but without CSGs nor on any lumina through the interlobular bile ducts. In the kidney, a few levels of OS distributed in the cytoplasm of almost all the renal tubule cells, but they contained numerous CSGs. In contrast, OC distributed highly in the proximal tubules, but very slightly in the lower renal tubules of the nephrons. Thus, it was concluded that the two drugs behave in completely different ways in rat bodies. This paper also discusses a possibility of the correlation of OS or OC levels in tissue cells with their known transporters.

Genetic Analysis Reveals a Significant Contribution of CES1 to Prostate Cancer Progression in Taiwanese Men

The genes that influence prostate cancer progression remain largely unknown. Since the carboxylesterase gene family plays a crucial role in xenobiotic metabolism and lipid/cholesterol homeostasis, we hypothesize that genetic variants in carboxylesterase genes may influence clinical outcomes for prostate cancer patients. A total of 478 (36 genotyped and 442 imputed) single nucleotide polymorphisms (SNPs) in five genes of the carboxylesterase family were assessed in terms of their associations with biochemical recurrence (BCR)-free survival in 643 Taiwanese patients with prostate cancer who underwent radical prostatectomy. The strongest association signal was shown in CES1 (P = 9.64×10^-4 for genotyped SNP rs8192935 and P = 8.96 × 10^-5 for imputed SNP rs8192950). After multiple test correction and adjustment for clinical covariates, CES1 rs8192935 (P = 9.67 × 10^-4) and rs8192950 (P = 9.34 × 10^-5) remained significant. These SNPs were correlated with CES1 expression levels, which in turn were associated with prostate cancer aggressiveness. Furthermore, our meta-analysis, including eight studies, indicated that a high CES1 expression predicted better outcomes among prostate cancer patients (hazard ratio 0.82, 95% confidence interval 0.70-0.97, P = 0.02). In conclusion, our findings suggest that CES1 rs8192935 and rs8192950 are associated with BCR and that CES1 plays a tumor suppressive role in prostate cancer.

Simulation of the Pharmacokinetics of Oseltamivir and Its Active Metabolite in Normal Populations and Patients with Hepatic Cirrhosis Using Physiologically Based Pharmacokinetic Modeling

Oseltamivir is a neuraminidase inhibitor widely used to treat and prevent influenza A and B infections, although its safety and pharmacokinetics have not been evaluated in patients with severe hepatic impairment. A physiologically based pharmacokinetic (PBPK) model of the prodrug oseltamivir and its active metabolite, oseltamivir carboxylate (OC), was established and validated to simulate their disposition in adults and predict the exposure in patients with Child-Pugh C cirrhosis (CP-C). The simulated results from PBPK modeling and the observed data after oral administration of various oseltamivir regimens were consistent according to the fold error values of less than 2. Furthermore, the clinical observations published in the literature were comparable with our pharmacokinetic predictions. In patients with CP-C, the oseltamivir C_max was approximately 2-fold increased, and its AUC was approximately 6-fold higher compared with those in normal subjects. In contrast, the AUC of OC in CP-C patients did not differ significantly from that in normal subjects, whereas its C_max was reduced by approximately 30% in the patients. Examination of drug exposure in different health conditions indicated that the oseltamivir exposure was significantly increased in conditions with elevated cirrhosis severity, which might be associated with a higher risk of adverse drug effects, e.g., neuropsychiatric adverse events (NPAEs). In conclusion, the pharmacokinetics of oseltamivir and OC were correctly predicted by PBPK modeling. The model further predicted that the pharmacokinetics of oseltamivir might be altered in liver cirrhosis, depending on the degree of severity.

[Hypothermic Action of Oseltamivir Not Dependent on Its Anti-influenza Virus Action]

Although the anti-influenza virus drug oseltamivir ameliorates the fever of influenza, adverse events related to its hypothermic effect have been reported. We found that oseltamivir causes dose-dependent hypothermia in normal mice, and have been studying the pharmacological mechanisms responsible for 12 years. Oseltamivir blocks nicotinic cholinergic transmission at sympathetic ganglia and reduces sympathetic modulation of brown adipose tissue (BAT), a heat generator. Oseltamivir was found to target the ion channels of nicotinic acetylcholine receptors, as demonstrated by patch clamp experiments with cells expressing the human α3β4 nicotinic receptor. Metabolized oseltamivir carboxylate, which inhibits the influenza virus neuraminidase, did not elicit hypothermia and ion channel suppression. Body temperature was decreased by intracerebroventricular administration of oseltamivir. Because this hypothermic effect was inhibited by dopamine D₂ receptor blockade, it was suggested that oseltamivir centrally stimulates the D₂ receptor. In Japan, the package inserts for oseltamivir and amantadine indicate very similar adverse neuropsychiatric reactions for the two drugs (abnormal behavior, consciousness disturbance, convulsion, delirium, delusion, hallucination). A literature search revealed that in some previous studies, oseltamivir and amantadine were shown to block the ion channel systems and activate the dopaminergic nervous system via several mechanisms. Therefore the similarity of the adverse reactions elicited by oseltamivir and amantadine was considered attributable to their similar pharmacological effects.

Mind the Gaps: Ontogeny of Human Brain P-gp and Its Impact on Drug Toxicity

Available data on human brain P-glycoprotein ontogeny during infancy and childhood are limited. This review discusses the current body of data relating to maturation of human brain P-glycoprotein including transporter expression levels in post-mortem human brain samples, in vivo transporter activity using probe substrates, surrogate marker endpoints, and extrapolations from animal models. Overall, the data tend to confirm that human brain P-glycoprotein activity keeps developing after birth, although with a developmental time frame that remains unclear. This knowledge gap is a concern given the critical role of brain P-glycoprotein in drug safety and efficacy, and the vulnerable nature of the pediatric population. Future research could include the measurement of brain P-glycoprotein activity across age groups using positron emission tomography or central pharmacodynamic responses. For now, caution is advised when extrapolating adult data to children aged younger than 2 years for drugs with P-glycoprotein-dependent central nervous system activity.

Emerging Models of Drug Metabolism, Transporters, and Toxicity

This commentary summarizes expert mini-reviews and original research articles that have been assembled in a special issue on novel models of drug metabolism and disposition. The special issue consists of research articles or reviews on novel static or micro-flow based models of the intestine, liver, eye, and kidney. This issue reviews static intestinal systems like mucosal scrapings and cryopreserved intestinal enterocytes, as well as novel bioengineered or chemically engineered intestinal models derived from primary human tissue, iPSCs, enteroids, and crypts. Experts have reviewed hepatic systems like cryopermeabilized Metmax hepatocytes and longer term, hepatocyte coculture system from HµREL, yielding in vivo-like primary and secondary drug metabolite profiles. Additional liver models, including micropattern hepatocyte coculture, 3D liver spheroids, and microflow systems, applicable to the study of drug disposition and toxicology have also been reviewed. In this commentary, we have outlined expert opinions and current efforts on hepatic- and nephrotoxicity models. Ocular disposition models including corneal permeability models have been included within this special issue. This commentary provides a summary of in vivo mini-reviews of the issue, which have discussed the applications and drawbacks of pig and humanized mice models of P450, UGT, and rat organic anionic transporting polypeptide 1a4. While not extensively reviewed, novel positron emissions tomography imaging-based approaches to study the distribution of xenobiotics have been highlighted. This commentary also outlines in vitro and in vivo models of drug metabolism derived from breakthrough genetic, chromosomal, and tissue engineering techniques. The commentary concludes by providing a futuristic view of the novel models discussed in this issue.

Role of the ABCB1 Drug Transporter Polymorphisms in the Pharmacokinetics of Oseltamivir in Humans: a Preliminary Report

Oseltamivir is a substrate of P-glycoprotein, an efflux drug transporter encoded by ABCB1. The objective of this study was to assess the role of ABCB1 (c.1236C>T, c.2677G>T/A, and c.3435C>T) polymorphisms in the pharmacokinetics of oseltamivir and its active metabolite, oseltamivir carboxylate in humans. Nineteen healthy male subjects were enrolled, and their ABCB1 polymorphisms were evaluated. After the oral administration of 75 mg oseltamivir, the plasma concentrations of oseltamivir and oseltamivir carboxylate were measured. Pharmacokinetic analysis was carried out. Systemic exposure to oseltamivir and oseltamivir carboxylate was higher in the mutant group than in the wild-type and heterozygous groups. We suggest that ABCB1 polymorphisms affect the pharmacokinetics of oseltamivir in humans. Further studies in a large population are necessary to validate the results of this preliminary study (Clinical Trial Registration Information [CRIS] registry: http://cris.nih.go.kr, No. KCT0001903).

Investigation of the Importance of Multidrug Resistance-Associated Protein 4 (Mrp4/Abcc4) in the Active Efflux of Anionic Drugs Across the Blood-Brain Barrier

The importance of multidrug resistance-associated protein 4 (Mrp4/Abcc4) in limiting the penetration of Mrp4 substrate compounds into the central nervous system across the blood-brain barrier was investigated using Mrp4^-/- mice. Significant adenosine triphosphate-dependent uptake by MRP4 was observed for ochratoxin A, pitavastatin, raltitrexed (K_m = 43.7 μM), pravastatin, cyclic guanosine monophosphate, 2,4-dichlorophenoxyacetate, and urate. The defect in the Mrp4 gene did not affect the brain-to-plasma ratio (K_p,brain) of quinidine and dantrolene. Following intravenous infusion in wild-type and Mrp4^-/- mice, the plasma concentrations of the tested compounds (cefazolin, cefmetazole, ciprofloxacin, cyclophosphamide, furosemide, hydrochlorothiazide, methotrexate, pitavastatin, pravastatin, and raltitrexed) were identical; however, Mrp4^-/- mice showed a significantly higher (1.9- to 2.5-fold) K_p,brain than wild-type mice for methotrexate, raltitrexed, and cyclophosphamide. GF120918, a dual inhibitor of P-gp and Bcrp, significantly decreased K_p,cortex and K_p,cerebellum only in Mrp4^-/- mice. Methotrexate and raltitrexed are also substrates of multispecific organic anion transporters such as Oatp1a4 and Oat3. GF120918 showed an inhibition potency against Oatp1a4, but not against Oat3. These results suggest that Mrp4 limits the penetration of methotrexate and raltitrexed into the brain across the blood-brain barrier, which is likely to be facilitated by some uptake transporters.

The mechanisms of sudden-onset type adverse reactions to oseltamivir

Oseltamivir is contraindicated for people aged 10-19 in principle in Japan, due to concern about abnormal behaviours. Sudden death is another concern. This review examines growing evidence of their association and discusses underlying mechanisms of these sudden-onset type reactions to oseltamivir. First, the importance of animal models and the concept of human equivalent dose (HED) is summarized. Second, the specific condition for oseltamivir use, influenza infection, is reviewed. Third, findings from toxicity studies conducted prior to and after the marketing of oseltamivir are reported on to provide context on the observation of a possible causal association. Fourth, similarity and consistency of toxicity in humans with that in other animals is described. Finally, coherence of toxicokinetic and molecular level of evidence (channels, receptors and enzymes), including differences from the toxicity of other neuraminidase inhibitors, is reviewed. It is concluded that unchanged oseltamivir has various effects on the central nervous system (CNS) that may be related to clinical findings including hypothermia, abnormal behaviours including with fatal outcome, and sudden death. Among receptors and enzymes related to CNS action, it is known that oseltamivir inhibits nicotinic acetylcholine receptors, which are closely related to hypothermia, as well as human monoamine oxidase-A (MAO-A), which is closely related to abnormal or excitatory behaviours. Receptors such as GABAA , GABAB and NMDA and their related receptors/channels including Na+ and Ca2+ channels are thought to be other candidates for investigation related to respiratory suppression followed by sudden death and psychotic reactions (both acute and chronic), respectively.

Pharmacokinetic Modeling and Monte Carlo Simulation to Predict Interindividual Variability in Human Exposure to Oseltamivir and Its Active Metabolite, Ro 64-0802

Oseltamivir (Tamiflu®) is a prodrug of Ro 64-0802, a selective inhibitor of influenza virus neuraminidase. There is a possible relationship between oseltamivir treatment and neuropsychiatric adverse events; although this has not been established, close monitoring is recommended on the prescription label. The objective of this study was to predict interindividual variability of human exposure to oseltamivir and its active metabolite Ro 64-0802. By leveraging mathematical models and computations, physiological parameters in virtual subjects were generated with population means and coefficient of variations collected from the literature or produced experimentally. Postulated functional changes caused by genetic mutations in four key molecules, carboxylesterase 1A1, P-glycoprotein, organic anion transporter 3, and multidrug resistance-associated protein 4, were also taken into account. One hundred thousand virtual subjects were generated per simulation, which was iterated 20 times with different random number generator seeds. Even in the most exaggerated case, the systemic areas under the concentration-time curve (AUCs) of oseltamivir and Ro 64-0802 were increased by at most threefold compared with the population mean. By contrast, the brain AUCs of oseltamivir and Ro 64-0802 were increased up to about sevenfold and 40-fold, respectively, compared with the population means. This unexpectedly high exposure to oseltamivir or Ro 64-0802, which occurs extremely rarely, might trigger adverse central nervous system effects in the clinical setting.

The mechanisms of delayed onset type adverse reactions to oseltamivir

Oseltamivir is recommended for the treatment and prophylaxis of influenza in persons at higher risk for influenza complications such as individuals with diabetes, neuropsychiatric illnesses, and respiratory, cardiac, renal, hepatic or haematological diseases. However, a recent Cochrane review reported that reduction of antibody production, renal disorders, hyperglycaemia, psychiatric disorders, and QT prolongation may be related to oseltamivir use. The underlying mechanisms are reviewed. There is decisive evidence that administration of a clinically compatible dose of oseltamivir in mice challenged by a respiratory syncytial virus (RSV) that lacks a neuraminidase gene showed symptom-relieving effects and inhibition of viral clearance. These effects were accompanied by decreased level of T cell surface sialoglycosphingolipid (ganglioside) GM1 that is regulated by the endogenous neuraminidase in response to viral challenge. Clinical and non-clinical evidence supports the view that the usual dose of oseltamivir suppresses pro-inflammatory cytokines such as interferon-gamma, interleukin-6, and tumour necrosis factor-alpha almost completely with partial suppression of viral shedding in human influenza virus infection experiment. Animal toxicity tests support the clinical evidence with regard to renal and cardiac disorders (bradycardia and QT prolongation) and do not disprove the metabolic effect. Reduction of antibody production and cytokine induction and renal, metabolic, cardiac, and prolonged psychiatric disorders after oseltamivir use may be related to inhibition of the host’s endogenous neuraminidase. While the usual clinical dose of zanamivir may not have this effect, a higher dose or prolonged administration of zanamivir and other neuraminidase inhibitors may induce similar delayed reactions, including reduction of the antibody and/or cytokine production.

Penetration of Treosulfan and its Active Monoepoxide Transformation Product into Central Nervous System of Juvenile and Young Adult Rats

Treosulfan (TREO) is currently investigated as an alternative treatment of busulfan in conditioning before hematopoietic stem cell transplantation. The knowledge of the blood-brain barrier penetration of the drug is still scarce. In this paper, penetration of TREO and its active monoepoxide (S,S-EBDM) and diepoxide (S,S-DEB) into the CNS was studied in juvenile (JR) and young adult rats (YAR) for the first time. CD rats of both sexes (n = 96) received an intravenous dose of TREO 500 mg/kg b.wt. Concentrations of TREO, S,S-EBDM, and S,S-DEB in rat plasma, brain, and cerebrospinal fluid (CSF, in YAR only) were determined by validated bioanalytical methods. Pharmacokinetic calculations were performed in WinNonlin using a noncompartmental analysis and statistical evaluation was done in Statistica software. In male JR, female JR, male YAR, and female YAR, the brain/plasma area under the curve (AUC) ratio for unbound TREO was 0.14, 0.17, 0.10, and 0.07 and for unbound S,S-EBDM, it was 0.52, 0.48, 0.28, and 0.22, respectively. The CSF/plasma AUC ratio in male and female YAR was 0.12 and 0.11 for TREO and 0.66 and 0.64 for S,S-EBDM, respectively. Elimination rate constants of TREO and S,S-EBDM in all the matrices were sex-independent with a tendency to be lower in the JR. No quantifiable levels of S,S-DEB were found in the studied samples. TREO and S,S-EBDM demonstrated poor and sex-independent penetration into CNS. However, the brain exposure was greater in juvenile rats, so very young children might potentially be more susceptible to high-dose TREO-related CNS exposure than young adults.

Psychiatric Symptoms in a Patient with Influenza A (H1N1) Treated with Oseltamivir (Tamiflu): A Case Report

Oseltamivir is the most common antiviral drug used to treat and prevent influenza. Epidemiological studies performed in Japan, the United States, and the United Kingdom indicate that oseltamivir may cause psychiatric symptoms; however, the underlying mechanism has not been elucidated. In South Korea, interest in oseltamivir has increased with the spread of the new influenza virus; however, no case report or investigation of psychiatric symptoms associated with the drug has been reported to date. Here, we report a case o0f a 22-year-old male who complained of mood swings, suicidal feelings, auditory hallucinations, memory deterioration, and insomnia after taking oseltamivir.

The inhibitory effect of kakkonto, Japanese traditional (kampo) medicine, on brain penetration of oseltamivir carboxylate in mice with reduced blood-brain barrier function

Oseltamivir phosphate (OP) is used to treat influenza virus infections. However, its use may result in central nervous system (CNS) adverse effects. In Japan, OP is used with Kampo formulations to improve clinical effectiveness. We evaluated the potential for using Kampo formulations to reduce CNS adverse effects by quantifying the CNS distribution of oseltamivir and its active metabolite oseltamivir carboxylate (OC) when administered with maoto and kakkonto. We administered lipopolysaccharide (LPS) by intraperitoneal injection to C57BL/6 mice to reduce blood-brain barrier function. Saline, maoto, and kakkonto were administered orally at the same time as LPS. OP was orally administered 4 hours after the last LPS injection and the migration of oseltamivir and OC was examined. Additionally, we examined the brain distribution of OC following intravenous administration. Changes in OC concentrations in the brain suggest that, in comparison to LPS-treated control mice, both Kampo formulations increased plasma levels of OC, thereby enhancing its therapeutic effect. Additionally, our findings suggest kakkonto may not only improve the therapeutic effect of oseltamivir but also reduce the risk of CNS-based adverse effects. Considering these findings, it should be noted that administration of kakkonto during periods of inflammation has led to increased OAT3 expression.

Inhibition of MAO-A and stimulation of behavioural activities in mice by the inactive prodrug form of the anti-influenza agent oseltamivir

Background and Purpose

Oseltamivir is the most widely prescribed anti-influenza medication. However, in rare instances, it has been reported to stimulate behavioural activities in adolescents. The goal of this study was to determine the molecular mechanism responsible for these behavioural activities.

Experimental Approach

We performed an in vitro assay of MAO-A, the enzyme responsible for neurotransmitter degradation, using either the active form – oseltamivir carboxylate (OC) or the inactive prodrug – oseltamivir ethyl ester (OEE). We also analysed the docking of MAO-A with OEE or OC in silico. Mouse behaviours after OEE or OC administration were monitored using automated video and computer analysis.

Key Results

OEE, but not OC, competitively and selectively inhibited human MAO-A. The estimated K_i value was comparable with the K_m values of native substrates of MAO-A. Docking simulations in silico based on the tertiary structure of MAO-A suggested that OEE could fit into the inner pocket of the enzyme. Behavioural monitoring using automated video analysis further revealed that OEE, not OC, significantly enhanced spontaneous behavioural activities in mice, such as jumping, rearing, sniffing, turning and walking.

Conclusions and Implications

Our multilevel analyses suggested OEE to be the cause of the side effects associated with oseltamivir and revealed the molecular mechanism underlying the stimulated behaviours induced by oseltamivir in some circumstances.

Evaluation of [(11)C]oseltamivir uptake into the brain during immune activation by systemic polyinosine-polycytidylic acid injection: a quantitative PET study using juvenile monkey models of viral infection

BACKGROUND

Abnormal behaviors of young patients after taking the anti-influenza agent oseltamivir (Tamiflu®, F. Hoffmann-La Roche, Ltd., Basel, Switzerland) have been suspected as neuropsychiatric adverse events (NPAEs). Immune response to viral infection is suspected to cause elevation of drug concentration in the brain of adolescents. In the present study, the effect of innate immune activation on the brain uptake of [(11)C]oseltamivir was quantitatively evaluated in juvenile monkeys.

METHODS

Three 2-year-old monkeys underwent positron emission tomography (PET) scans at baseline and immune-activated conditions. Both scans were conducted under pre-dosing of clinically relevant oseltamivir. The immune activation condition was induced by the intravenous administration of polyinosine-polycytidylic acid (poly I:C). Dynamic [(11)C]oseltamivir PET scan and serial arterial blood sampling were performed to obtain [(11)C]oseltamivir kinetics. Brain uptake of [(11)C]oseltamivr was evaluated by its normalized brain concentration, brain-to-plasma concentration ratio, and plasma-to-brain transfer rate. Plasma pro-inflammatory cytokine levels were also measured.

RESULTS

Plasma interleukin-6 was elevated after intravenous administration of poly I:C in all monkeys. Brain radioactivity was uniform both at baseline and under poly I:C treatment. The mean brain concentrations of [(11)C]oseltamivir were 0.0033 and 0.0035% ID/cm(3) × kg, the mean brain-to-plasma concentration ratios were 0.58 and 0.65, and the plasma-to-brain transfer rates were 0.0047 and 0.0051 mL/min/cm(3) for baseline and poly I:C treatment, respectively. Although these parameters were slightly changed by immune activation, the change was not notable.

CONCLUSIONS

The brain uptake of [(11)C]oseltamivir was unchanged by poly I:C treatment in juvenile monkeys. This study demonstrated that the innate immune response similar to the immune activation of influenza would not notably change the brain concentration of oseltamivir in juvenile monkeys.

Development of a physiologically-based pharmacokinetic model of the rat central nervous system

Central nervous system (CNS) drug disposition is dictated by a drug's physicochemical properties and its ability to permeate physiological barriers. The blood-brain barrier (BBB), blood-cerebrospinal fluid barrier and centrally located drug transporter proteins influence drug disposition within the central nervous system. Attainment of adequate brain-to-plasma and cerebrospinal fluid-to-plasma partitioning is important in determining the efficacy of centrally acting therapeutics. We have developed a physiologically-based pharmacokinetic model of the rat CNS which incorporates brain interstitial fluid (ISF), choroidal epithelial and total cerebrospinal fluid (CSF) compartments and accurately predicts CNS pharmacokinetics. The model yielded reasonable predictions of unbound brain-to-plasma partition ratio (Kpuu,brain) and CSF:plasma ratio (CSF:Plasmau) using a series of in vitro permeability and unbound fraction parameters. When using in vitro permeability data obtained from L-mdr1a cells to estimate rat in vivo permeability, the model successfully predicted, to within 4-fold, Kpuu,brain and CSF:Plasmau for 81.5% of compounds simulated. The model presented allows for simultaneous simulation and analysis of both brain biophase and CSF to accurately predict CNS pharmacokinetics from preclinical drug parameters routinely available during discovery and development pathways.

Developmental changes of brain distribution and localization of oseltamivir and its active metabolite Ro 64-0802 in rats

Oseltamivir, a prodrug of the neuraminidase inhibitor [3R, 4R, 5S]-4-Acetamide-5-amino-3-(1-ethylpropyl)-1-cyclohexene-1-carboxylate phosphate (Ro 64-0802), is widely used for treatment of influenza infections in Japan, but may be associated with mental instability and suicidal tendencies as a rare side effect, especially in infants and young patients. We examined developmental changes in the brain distribution of oseltamivir and Ro 64-0802, and in the expression of P-glycoprotein (P-gp) at the blood-brain barrier (BBB) in rats by 8 weeks. Brain concentration and Kp(,app,brain) (brain-to-plasma concentration ratio) of oseltamivir were highest in 2-week-old rats (1.45 µg/g brain and 0.14, respectively), and were negatively correlated with both age and P-gp expression at the BBB. In contrast, brain concentration and Kp(,app,brain) of Ro 64-0802 after oral gavage of oseltamivir were lowest in 2-week-old rats (0.02 µg/g brain and 0.02), and increased with age. Mass imaging analysis revealed that both compounds were distributed homogenously in brain cross-sections, including the hippocampus. From these results, it was estimated that oseltamivir concentration throughout the brain cross-sections was 70-fold and 0.9-fold higher than that of Ro 64-0802 in 2-week-old and 8-week-old rats, respectively. Such developmental changes of prodrug/drug concentration ratio, if they also occur in humans, may provide a rational basis for the putative central nervous system (CNS) side effects in young patients.

Reduction in sympathetic nerve activity as a possible mechanism for the hypothermic effect of oseltamivir, an anti-influenza virus drug, in normal mice

Oseltamivir, an anti-influenza virus drug, has strong antipyretic effects in mice (Biological and Pharmaceutical Bulletin, 31, 2008, 638) and patients with influenza. In addition, hypothermia has been reported as an adverse event. The prodrug oseltamivir is converted to oseltamivir carboxylate (OC), an active metabolite of influenza virus neuraminidase. In this study, core body temperature was measured in mice, and oseltamivir and OC were administered intracerebroventricularly (i.c.v.) or intraperitoneally (i.p). Low i.c.v. doses of oseltamivir and OC dose-dependently produced hypothermia. Zanamivir (i.c.v.), another neuraminidase inhibitor, did not produce hypothermia. These results suggested that the hypothermic effects of oseltamivir (i.p. and i.c.v.) and OC (i.c.v.) are not due to neuraminidase inhibition. OC (i.p.) did not lower body temperature. Although mecamylamine (i.c.v.) blocked the hypothermic effect of nicotine-administered i.c.v., the hypothermic effects of oseltamivir and OC (i.c.v.) were not blocked by mecamylamine (i.c.v.). The effect of oseltamivir (i.p.) was markedly increased by s.c.-pre-administered mecamylamine and also hexamethonium, a peripherally acting ganglionic blocker, suggesting their potentiating interaction at peripheral sites. The hypothermic effect of nicotine (i.c.v.) was decreased by lower doses of oseltamivir (i.c.v.), suggesting the anti-nicotinic action of oseltamivir. These results suggest that oseltamivir (i.p.) causes hypothermia through depression of sympathetic temperature regulatory mechanisms via inhibition of nicotinic receptor function and through unknown central mechanisms.

In vitro blood-brain barrier models using brain capillary endothelial cells isolated from neonatal and adult rats retain age-related barrier properties

The blood-brain barrier (BBB) restricts the entry of circulating drugs and xenobiotics into the brain, and thus its permeability to substances is a critical factor that determines their central effects. The infant brain is vulnerable to neurotoxic substances partly due to the immature BBB. The employment of in vitro BBB models to evaluate permeability of compounds provides higher throughput than that of in vivo animal experiments. However, existing in vitro BBB models have not been able to simulate the intrinsic neonatal BBB. To establish a neonatal BBB model that mimics age-related BBB properties, the neonatal and adult in vitro BBB models were constructed with brain endothelial cells isolated from 2- and 8-week-old rats, respectively. To evaluate BBB functions, transendothelial electrical resistance, permeability of sodium fluorescein and Evans blue-albumin, and transport of rhodamine123 were measured. Radiolabelled drugs were used for BBB permeability studies in the neonatal and adult BBB models (in vitro) and in age-matched rats (in vivo). The neonatal BBB model showed lower barrier and p-glycoprotein (P-gp) functions than the adult BBB model; these were well associated with lower expressions of the barrier-related proteins and P-gp, and a different distribution pattern of immunostained barrier-related proteins. Verapamil (a P-gp inhibitor) significantly increased the influx of rhodamine 123, supporting functional P-gp expression in the neonatal BBB model. Valproic acid, but not nicotine, showed higher BBB permeability in the neonatal BBB model, which was well in accordance with the in vivo BBB property. We established a neonatal BBB model in vitro. This could allow us to assess the age-dependent BBB permeability of drugs.

Pharmacokinetic properties of anti-influenza neuraminidase inhibitors

Neuraminidase inhibitors are the mainstay of anti-influenza treatment. Oseltamivir is the most widely used drug but is currently available only as an oral formulation. Resistance spreads rapidly in seasonal H1N1 influenza A viruses, which were universally resistant in 2008, because of the H275Y mutation in the neuraminidase (NA) gene. Oseltamivir is a prodrug for the active carboxylate metabolite. Ex vivo conversion in blood samples may have confounded early pharmacokinetic studies. Oseltamivir shows dose linear kinetics, and oseltamivir carboxylate has an elimination half-life (t(1/2) β) after oral administration in healthy individuals of approximately 7.7 hours. Oseltamivir carboxylate is eliminated primarily by tubular secretion, and both clearance and tissue distribution are reduced by probenecid. The H275Y mutation in NA confers high-level oseltamivir resistance and intermediate peramivir resistance but does not alter zanamivir susceptibility. Zanamivir is available as a powder for inhalation, and a parenteral form is under development. Zanamivir distributes in an apparent volume of distribution approximating that of extracellular water and is rapidly eliminated (t(1/2) β of approximately 3.0 hours). Peramivir is slowly eliminated (t(1/2) β of 7.7-20.8 hours) and is prescribed as either a once-daily injection or as a single infusion. Laninamivir is a recently developed slowly eliminated compound for administration by inhalation.

High doses of oseltamivir phosphate induce acute respiratory arrest in anaesthetized rats

It has been reported that one of the serious adverse events after the treatment of oseltamivir phosphate (OP) for influenza patients is sudden death resulting from cardiorespiratory arrest. To investigate the aetiology of such an adverse consequence, we examined effects of OP (expressed as free base) on blood pressure and ventilation in anaesthetized rats with vagotomy. Intravenous OP (30-200 mg/kg) caused dose-dependent hypotension and bradycardia in spontaneously breathing animals. Concomitantly with changes in blood pressure, the tracheal airflow increased. The ventilatory rate hastened during the injection and then transiently slowed around 1 min. after the administration (transient hypopnea). Thereafter, it gradually returned to control. The hypopnea increased with increasing dose and ventilatory arrest occurred at 200 mg/kg. Intraduodenal OP (500-1000 mg/kg) provoked cardioventilatory arrest 72-218 min. after the injection. Oseltamivir carboxylate (100-200 mg/kg, i.v.), an active metabolite of OP, had no significant effect on ventilation and blood pressure. In artificially ventilated animals, intravenous OP caused slowing of the respiratory rate around 1 min. after the injection in a dose-dependent manner. This effect of OP waned in 5 min. after the administration. The amplitude of phrenic nerve discharge was not changed at lower doses (30-100 mg/kg). The phrenic nerve stopped to discharge immediately after higher doses (150-200 mg/kg). We demonstrated that OP causes central suppression of the respiratory function in rats and suggest a relationship between the OP-induced cardiorespiratory arrest and sudden death observed in influenza patients after taking OP.

Species-dependent uptake of glycylsarcosine but not oseltamivir in Pichia pastoris expressing the rat, mouse, and human intestinal peptide transporter PEPT1

The purpose of this study was to determine whether glycylsarcosine (a model dipeptide) and oseltamivir (an antiviral prodrug) exhibited a species-dependent uptake in yeast Pichia pastoris expressing the rat, mouse, and human homologs of PEPT1. Experiments were performed with [(3)H]glycylsarcosine (GlySar) in yeast P. pastoris expressing human, mouse, and rat peptide transporter 1 (PEPT1), in which uptake was examined as a function of time, concentration, potential inhibitors, and the dose-response inhibition of GlySar by oseltamivir. Studies with [(14)C]oseltamivir were also performed under identical experimental conditions. We found that GlySar exhibited saturable uptake in all three species, with K(m) values for human (0.86 mM) > mouse (0.30 mM) > rat (0.16 mM). GlySar uptake in the yeast transformants was specific for peptides (glycylproline) and peptide-like drugs (cefadroxil, cephradine, and valacyclovir), but was unaffected by glycine, l-histidine, cefazolin, cephalothin, cephapirin, acyclovir, 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid, tetraethylammonium, and elacridar. Although oseltamivir caused a dose-dependent inhibition of GlySar uptake [IC(50) values for human (27.4 mM) > rat (18.3 mM) > mouse (10.7 mM)], the clinical relevance of this interaction would be very low in humans. Of importance, oseltamivir was not a substrate for the intestinal PEPT1 transporter in yeast expressing the three mammalian species tested. Instead, the prodrug exhibited nonspecific binding to the yeast vector and PEPT1 transformants. Finally, the mouse appeared to be a better animal model than the rat for exploring the intestinal absorption and pharmacokinetics of peptides and peptide-like drugs in human.

Absence of central nervous system and hypothermic effects after single oral administration of high doses of oseltamivir in the rat

Oseltamivir is widely used for the treatment and prophylaxis of influenza. Renewed interest in the central nervous system (CNS) tolerability profile of oseltamivir has been triggered by the reports of neuropsychiatric adverse events in patients with influenza. In addition, a recent pre-clinical study in rodents suggested a hypothermic effect of oseltamivir. The current studies investigated the CNS effects, body temperature effect and toxicokinetic profile of oseltamivir in rats. The CNS/temperature study included three groups receiving oseltamivir (500, 763 and 1000 mg/kg free base by oral gavage), one vehicle/control group and one reference group (D-amphetamine, 10 mg/kg). CNS parameters (behaviour, motor activity and co-ordination and sensory/motor reflex responses) and rectal temperature were measured at baseline and at five intervals until 8 hr after dosing. In the toxicokinetic study, rats received oseltamivir by oral gavage at 763 or 1000 mg/kg free base. Plasma, cerebrospinal fluid (CSF) and perfused brain concentrations of oseltamivir and its active metabolite, oseltamivir carboxylate (OC), were measured until 8 hr after dosing. Median scores for CNS parameters were similar in controls and animals receiving oseltamivir at all time points. Oseltamivir had no physiologically relevant effect on body temperature, but induced a short-lived and small dose-independent decrease in temperature in all active treatment groups at 1 hr after dosing only. Plasma concentrations of OC were higher than of oseltamivir, but the reverse was true in CSF and brain. CNS penetration was low for both moieties. In rats, oseltamivir at supratherapeutic doses up to 1000 mg/kg free base did not exert any effects on CNS function or hypothermic effects and led to limited CNS exposure, resulting in large safety margins.

ABCB1 polymorphisms and neuropsychiatric adverse events in oseltamivir-treated children during influenza H1N1/09 pandemia

AIMS

To examine the safety profile of oseltamivir in children and evaluate the impact of P-glycoprotein polymorphisms on the incidence of neuropsychiatric adverse events (NPAE) in oseltamivir-treated children.

SUBJECTS & METHODS

This prospective cohort study was conducted in our tertiary care pediatric hospital (University Hospitals of Geneva, Switzerland) during the H1N1 pandemia, between 1 October 2009 and 31 January 2010. All newborn to 18 year-old patients presenting at the emergency department with a flu-like illness were eligible for inclusion. Adverse events were systematically recorded by pediatricians and/or by parents at home using a diary card, with a 30-day follow-up period. The causality assessment of oseltamivir in NPAE was performed by two clinical pharmacologists. After informed consent, enrolled patients were also genotyped for ABCB1 3435C>T (rs1045642) and 2677G>T/A (rs2032582) polymorphisms.

RESULTS

Among the 42 H1N1-infected, oseltamivir-treated children who were genotyped for ABCB1 3435C>T and 2677G>T/A variants, 36% presented NPAE. When examining the association between the diplotype and the development of NPAE, we observed that the frequency of NPAE displayed a 'genotype-trend effect' with the variant and the wild-type subgroups at the two far ends. A total of 11% of the 2677GG-3435CC individuals (wild-type homozygous) presented NPAE, compared with 39% of the individuals being heterozygous for at least one variant allele and 67% of the 2677TT-3435TT individuals (homozygous variants) (p = 0.149, nonsignificant).

CONCLUSION

These observations suggest a potential influence of ABCB1 polymorphisms in oseltamivir-related NPAE, maybe as a result of an enhanced permeability of the blood-brain barrier to oseltamivir

Targeting blood-brain barrier changes during inflammatory pain: an opportunity for optimizing CNS drug delivery

The blood-brain barrier (BBB) is the most significant obstacle to effective CNS drug delivery. It possesses structural and biochemical features (i.e., tight-junction protein complexes and, influx and efflux transporters) that restrict xenobiotic permeation. Pathophysiological stressors (i.e., peripheral inflammatory pain) can alter BBB tight junctions and transporters, which leads to drug-permeation changes. This is especially critical for opioids, which require precise CNS concentrations to be safe and effective analgesics. Recent studies have identified molecular targets (i.e., endogenous transporters and intracellular signaling systems) that can be exploited for optimization of CNS drug delivery. This article summarizes current knowledge in this area and emphasizes those targets that present the greatest opportunity for controlling drug permeation and/or drug transport across the BBB in an effort to achieve optimal CNS opioid delivery.

Safety of oseltamivir in pregnancy: a review of preclinical and clinical data

Pregnant women with influenza are at increased risk of morbidity, particularly due to respiratory complications. A high excess mortality rate among pregnant women has been observed in previous influenza pandemics and healthcare agencies have provided recommendations on the use of oseltamivir to treat pregnant women who are infected with the pandemic (H1N1) 2009 virus. This article reviews pre-clinical and clinical data to assess the safety of oseltamivir administered during pregnancy, in the context of the effects of influenza on adverse pregnancy outcomes and fetal malformations. The effects of influenza during pregnancy, whether mediated directly by the virus or by fever or other events secondary to the underlying infection, are not yet well understood, but some data indicate an increased risk of birth defects in women infected with influenza during the first trimester. Animal and toxicology studies do not suggest that clinically effective dosages of oseltamivir have the potential to produce adverse effects on fetal development. Additionally, transplacental transfer of the drug and its active metabolite was very limited and not detectable at normal therapeutic doses in an ex vivo human placenta model. To investigate the safety of oseltamivir in pregnancy, the Roche oseltamivir safety database was searched for all exposures to oseltamivir during pregnancy in the 9 years up to 14 December 2008. In addition, a search of the literature was carried out. Of 232 maternal exposures to oseltamivir in the Roche database, pregnancy outcomes were known for 115 of these exposures. The incidence of adverse pregnancy outcomes was as follows: spontaneous abortions 6.1% (7/115), therapeutic abortions 11.3% (13/115) and pre-term deliveries 2.1% (2/94 live births), values that are not higher than background incidence rates. Fetal outcomes were known in 100 of the 232 exposures. For the nine cases of birth defect that were reported, the timing of oseltamivir exposure in relation to the sensitive period for inducing the birth defect was analysed. Two cases of ventricular septal defect, a more common birth defect, and one case of anophthalmos, an uncommon birth defect, were consistent with exposure to oseltamivir during the sensitive period for these birth defects. For other birth defects, there was either no exposure to oseltamivir during the sensitive period for the defect or insufficient information for assessment. These findings were consistent with other reports in the published literature, including a series of 79 Japanese women exposed to oseltamivir during the first trimester. Together with the other evidence reviewed herein, review of the company safety database suggests that oseltamivir is unlikely to cause adverse pregnancy or fetal outcomes, but available data are limited. Clinicians who use oseltamivir in pregnant women should consider the available safety information, the pathogenicity of the circulating influenza virus strain, the woman's general health and the guidance provided by health authorities. Roche will continue to monitor all reports of oseltamivir use during pregnancy.

Oseltamivir in seasonal, avian H5N1 and pandemic 2009 A/H1N1 influenza: pharmacokinetic and pharmacodynamic characteristics

Oseltamivir is the ester-type prodrug of the neuraminidase inhibitor oseltamivir carboxylate. It has been shown to be an effective treatment for both seasonal influenza and the recent pandemic 2009 A/H1N1 influenza, reducing both the duration and severity of the illness. It is also effective when used preventively. This review aims to describe the current knowledge of the pharmacokinetic and pharmacodynamic characteristics of this agent, and to address the issue of possible therapeutic drug monitoring. According to the currently available literature, the pharmacokinetics of oseltamivir carboxylate after oral administration of oseltamivir are characterized by mean ± SD bioavailability of 79 ± 12%, apparent clearance of 25.3 ± 7.0 L/h, an elimination half-life of 7.4 ± 2.5 hours and an apparent terminal volume of distribution of 267 ± 122 L. A maximum plasma concentration of 342 ± 83 μg/L, a time to reach the maximum plasma concentration of 4.2 ± 1.1 hours, a trough plasma concentration of 168 ± 32 μg/L and an area under the plasma concentration-time curve from 0 to 24 hours of 6110 ± 1330 μg · h/L for a 75 mg twice-daily regimen were derived from literature data. The apparent clearance is highly correlated with renal function, hence the dosage needs to be adjusted in proportion to the glomerular filtration rate. Interpatient variability is moderate (28% in apparent clearance and 46% in the apparent central volume of distribution); there is no indication of significant erratic or limited absorption in given patient subgroups. The in vitro pharmacodynamics of oseltamivir carboxylate reveal wide variation in the concentration producing 50% inhibition of influenza A and B strains (range 0.17-44 μg/L). A formal correlation between systemic exposure to oseltamivir carboxylate and clinical antiviral activity or tolerance in influenza patients has not yet been demonstrated; thus no formal therapeutic or toxic range can be proposed. The pharmacokinetic parameters of oseltamivir carboxylate after oseltamivir administration (bioavailability, apparent clearance and the volume of distribution) are fairly predictable in healthy subjects, with little interpatient variability outside the effect of renal function in all patients and bodyweight in children. Thus oseltamivir carboxylate exposure can probably be controlled with sufficient accuracy by thorough dosage adjustment according to patient characteristics. However, there is a lack of clinical study data on naturally infected patients. In addition, the therapeutic margin of oseltamivir carboxylate is poorly defined. The usefulness of systematic therapeutic drug monitoring in patients therefore appears to be questionable; however, studies are still needed to extend the knowledge to particular subgroups of patients or dosage regimens.

Pharmacologic considerations for oseltamivir disposition: focus on the neonate and young infant

Across much of the world, pandemic H1N1 infection has produced a significant healthcare crisis, reflected in significant morbidity and mortality. Statistics reveal that infection-associated deaths among individuals without pre-existing conditions (e.g. immunosuppression) are clustered in pregnant women and young infants. In developing countries where the availability of influenzae vaccine is limited, the only currently available pharmacologic counter-measure for H1N1 disease is oseltamivir, a neuraminidase inhibitor with excellent in vitro activity against the virus. This drug is available in oral solid and liquid formulations, has excellent peroral bioavailability in adults, and generally has a very favorable safety profile. Many observational studies indicate that oseltamivir treatment is associated with symptomatic improvement in pediatric patients with H1N1 infection and, therefore, is considered to represent a viable therapeutic option for use in children. However, the disposition of the ethyl ester prodrug and its active metabolite has not been well characterized in infants and children. Presently, data are available from only two published investigations and preliminary summary information from a recent presentation of an ongoing study. Given that recent in vitro data support the importance of a target exposure-response profile for the active metabolite of oseltamivir and that many processes known to modulate drug disposition have a developmental basis, understanding the potential impact of age on oseltamivir disposition becomes crucial in the development of age-appropriate dosing regimens for the drug. In this review, the impact of ontogeny on processes that are important in regulating the absorption, distribution, metabolism, and excretion of oseltamivir and its active metabolite are considered. Data from both animal and human investigations are presented in the context of defining how development might influence the dose-exposure relationship and, most importantly, the significant variability associated with it. In addition, the available pediatric pharmacokinetic data for oseltamivir and its active metabolite are summarized and current 'information gaps' deserving of future study are presented.

Drug delivery to the brain: considerations of genetic polymorphisms of blood-brain barrier transporters and imaging technologies

PubMed search and literature reviews summarized our latest advances regarding the impact of genetic polymorphisms of blood-brain barrier transporters on, and the application of imaging technologies to evaluate and enhance drug delivery to the brain. Although there are reports relating transporter polymorphisms to pharmacokinetics or adverse events, few studies have extended such efforts to the brain. Conceivably, simultaneous nonfunctional expressions of more than one key efflux transporters could result in devastating clinical outcomes if the dose of their substrate drug is not adjusted for the subpopulation with such a phenotype. Imaging technologies have been used to elucidate the kinetic or functional activities of blood-brain barrier transporters, with the majority focusing on P-glycoprotein. Imaging technologies have been used to discover drugs for treating brain disorders, enable targeted delivery in combination with convection-enhanced delivery, assess the therapeutic effect of a treatment protocol and assess drug penetration into brain tumors. Research is limited, however, in using imaging technologies to link the genotype or phenotype of a transporter to the uptake of drug into the brain. No imaging studies have provided clear evidence of transporter polymorphisms discriminating the distribution of drug in the brain. Research efforts are needed to use imaging technologies to explore the correlation between pharmacogenetics and individual clinical outcomes, especially for the phenotype of more than one nonfunctional transporters.