Probenecid increases renal retention and antitumor activity of DFMO in neuroblastoma.

BACKGROUND: Neuroblastoma (NB) is the most common extracranial solid tumor in children. Interference with the polyamine biosynthesis pathway by inhibition of MYCN-activated ornithine decarboxylase (ODC) is a validated approach. The ODC inhibitor α-difluoromethylornithine (DFMO, or Eflornithine) has been FDA-approved for the treatment of trypanosomiasis and hirsutism and has advanced to clinical cancer trials including NB as well as cancer-unrelated human diseases. One key challenge of DFMO is its rapid renal clearance and the need for high and frequent drug dosing during treatment. METHODS: We performed in vivo pharmacokinetic (PK), antitumorigenic, and molecular studies with DFMO/probenecid using NB patient-derived xenografts (PDX) in mice. We used LC-MS/MS, HPLC, and immunoblotting to analyze blood, brain tissue, and PDX tumor tissue samples collected from mice. RESULTS: The organic anion transport 1/3 (OAT 1/3) inhibitor probenecid reduces the renal clearance of DFMO and significantly increases the antitumor activity of DFMO in PDX of NB (P < 0.02). Excised tumors revealed that DFMO/probenecid treatment decreases polyamines putrescine and spermidine, reduces MYCN protein levels and dephosphorylates retinoblastoma (Rb) protein (p-RbSer795), suggesting DFMO/probenecid-induced cell cycle arrest. CONCLUSION: Addition of probenecid as an adjuvant to DFMO therapy may be suitable to decrease overall dose and improve drug efficacy in vivo.

Physiologically Based Pharmacokinetic Models of Probenecid and Furosemide to Predict Transporter Mediated Drug-Drug Interactions.

PURPOSE: To provide whole-body physiologically based pharmacokinetic (PBPK) models of the potent clinical organic anion transporter (OAT) inhibitor probenecid and the clinical OAT victim drug furosemide for their application in transporter-based drug-drug interaction (DDI) modeling. METHODS: PBPK models of probenecid and furosemide were developed in PK-Sim®. Drug-dependent parameters and plasma concentration-time profiles following intravenous and oral probenecid and furosemide administration were gathered from literature and used for model development. For model evaluation, plasma concentration-time profiles, areas under the plasma concentration-time curve (AUC) and peak plasma concentrations (Cmax) were predicted and compared to observed data. In addition, the models were applied to predict the outcome of clinical DDI studies. RESULTS: The developed models accurately describe the reported plasma concentrations of 27 clinical probenecid studies and of 42 studies using furosemide. Furthermore, application of these models to predict the probenecid-furosemide and probenecid-rifampicin DDIs demonstrates their good performance, with 6/7 of the predicted DDI AUC ratios and 4/5 of the predicted DDI Cmax ratios within 1.25-fold of the observed values, and all predicted DDI AUC and Cmax ratios within 2.0-fold. CONCLUSIONS: Whole-body PBPK models of probenecid and furosemide were built and evaluated, providing useful tools to support the investigation of transporter mediated DDIs.

Leflunomide increased the renal exposure of acyclovir by inhibiting OAT1/3 and MRP2.

Rheumatoid arthritis patients can be prescribed a combination of immunosuppressive drug leflunomide (LEF) and the antiviral drug acyclovir to reduce the high risk of infection. Acyclovir is a substrate of organic anion transporter (OAT) 1/3 and multidrug resistance-associated protein (MRP) 2. Considering the extraordinarily long half-life of LEF's active metabolite teriflunomide (TER) and the kidney injury risk of acyclovir, it is necessary to elucidate the potential impact of LEF on the disposition of acyclovir. Here we used a specific MRP inhibitor MK571 and probenecid (OAT1/3 and MRP2 inhibitor) to assess the effects of MRP2 and OAT1/3 on the pharmacokinetics and tissue distribution of acyclovir in rats. We showed that LEF and probenecid, but not MK571 significantly increased the plasma concentration of acyclovir. However, kidney and liver exposures of acyclovir were increased when coadministered with LEF, probenecid or MK571. The kidney/plasma ratio of acyclovir was increased to approximately 2-fold by LEF or probenecid, whereas it was increased to as much as 14.5-fold by MK571. Consistently, these drugs markedly decreased the urinary excretion of acyclovir. TER (0.5-100 µmol/L) dose-dependently increased the accumulation of acyclovir in MRP2-MDCK cells with an IC50 value of 4.91 µmol/L. TER (5 µmol/L) significantly inhibited the uptake of acyclovir in hOAT1/3-HEK293 cells. These results suggest that LEF/TER increased the kidney accumulation of acyclovir by inhibiting the efflux transporter MRP2, which increased its kidney/plasma ratio and renal injury risk. However, the inhibitory effects of LEF/TER on OAT1/3 reduced the tubular cells' uptake of acyclovir and increased the plasma concentration.

Probenecid-Boosted Tenofovir: A Physiologically-Based Pharmacokinetic Model-Informed Strategy for On-Demand HIV Preexposure Prophylaxis.

Multiple doses of tenofovir disoproxil fumarate (TDF) together with emtricitabine is effective for HIV preexposure prophylaxis (PrEP). TDF is converted to tenofovir (TFV) in circulation, which is subsequently cleared via tubular secretion by organic ion transporters (OATs; OAT1 and OAT3). Using in vitro kinetic parameters for TFV and the OAT1 and OAT3 inhibitor probenecid, a bottom-up physiologically-based pharmacokinetic model was successfully developed for the first time that accurately describes the probenecid-TFV interaction. This model predicted an increase in TFV plasma exposure by 60%, which was within 15% of the observed clinical pharmacokinetic data, and a threefold decrease in renal cells exposure following coadministration of a 600 mg TDF dose with 2 g probenecid. When compared with multiple-dose regimens, a single-dose probenecid-boosted TDF regimen may be effective for HIV PrEP and improve adherence and safety by minimizing TFV-induced nephrotoxicity by reducing TFV accumulation in renal cells.

Interaction of Organic Anion Transporter 3-Mediated Uptake of Steviol Acyl Glucuronide, a Major Metabolite of Rebaudioside A, with Selected Drugs.

Organic anion transporter 3 (OAT3) plays a critical role in the renal excretion of many xenobiotics. Because steviol acyl glucuronide (SVAG), an OAT3 substrate, is the major circulating metabolite after oral ingestion of steviol glycosides and is excreted into the urine, inhibition of OAT3 activity may alter pharmacokinetic profiles of SVAG. The present study showed that drugs such as probenecid and glimepiride displayed potent inhibition toward the OAT3-mediated SVAG transport, with IC50 values of 4.9 and 0.8 µM, respectively. No species differences were observed. Probenecid and glimepiride could significantly elevate plasma concentrations of SVAG after oral administration of rebaudioside A, with significant increases in plasma maximum (Cmax) and area under the plasma time-concentration curve values. The inhibitory effect on the OAT3-mediated SVAG transport exemplified a unique case between drugs and the metabolite of a food additive. Our data suggest that caution should be exercised when giving steviol glycoside products to human subjects with compromised renal function.

Inhibitory Effects of Probenecid on Pharmacokinetics of Tenofovir Disoproxil Fumarate and Emtricitabine for On-Demand HIV Preexposure Prophylaxis.

In a randomized, crossover pharmacokinetic study in healthy volunteers (N = 14), a single dose of 2 g probenecid (PRO)-boosted 600 mg tenofovir disoproxil fumarate (TDF)/400 mg emtricitabine (FTC) (test (T) +PRO) was compared with the current on-demand HIV preexposure prophylaxis from the IPERGAY study (a 600 mg TDF/400 mg FTC on day 1 and 300 mg TDF/200 mg FTC on days 2 and 3) (control, C IPERGAY). PRO increased mean single-dose area under the plasma concentration-time curve extrapolated to infinity (AUC0-∞,SD ) of tenofovir (TFV) and FTC by 61% and 68%, respectively. The TFV-diphosphate (TFV-DP) concentrations in peripheral blood mononuclear cells were higher (~30%) at 24 hours in T +PRO but then fell significantly lower (~40%) at 72 hours compared with C IPERGAY. The interaction between FTC and PRO was unexpected and novel. Further study is needed to determine if this PRO-boosted TDF/FTC regimen would be clinically effective.

Repurposing drugs targeting the P2X7 receptor to limit hyperinflammation and disease during influenza virus infection.

BACKGROUND AND PURPOSE: Severe influenza A virus (IAV) infections are associated with damaging hyperinflammation that can be fatal. There is an urgent need to identify new therapeutic agents to treat severe and pathogenic IAV infections. Repurposing of drugs with an existing and studied pharmacokinetic and safety profile is a highly attractive potential strategy. We have previously demonstrated that the NLRP3 inflammasome plays time-dependent roles during severe IAV infection with early protective responses and later dysregulation leading to excessive inflammation, contributing to disease severity. EXPERIMENTAL APPROACH: We tested two existing drugs, probenecid and AZ11645373, to target P2X7 receptor signalling and dampen NLRP3 inflammasome responses during severe IAV infection. In vitro, the drugs were assessed for their ability to limit NLRP3 inflammasome-dependent IL-1ß secretion in macrophage cultures. In vivo, their effects were assessed on hyperinflammation and disease during severe IAV infection in C57BL/6 mice. KEY RESULTS: Treatment of macrophages with probenecid or AZ11645373 in vitro diminished NLRP3 inflammasome-dependent IL-1ß secretion. Intranasal therapeutic treatment of mice displaying severe influenza disease with probenecid or AZ11645373 reduced pro-inflammatory cytokine production, cellular infiltrates in the lung, and provided protection against disease. Importantly, these drugs could be administered at either early or late stage of disease and provide therapeutic efficacy. CONCLUSIONS AND IMPLICATIONS: Our study demonstrates that the anti-inflammatory drugs probenecid and AZ11645373, which have documented pharmacokinetics and safety profiles in humans, are effective at dampening hyperinflammation and severe influenza disease providing potentially new therapeutic strategies for treating severe or pathogenic IAV infections.

Aquaporin-4 deficiency reduces TGF-ß1 in mouse midbrains and exacerbates pathology in experimental Parkinson's disease.

Aquaporin-4 (AQP4), the main water-selective membrane transport protein in the brain, is localized to the astrocyte plasma membrane. Following the establishment of a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Parkinson's disease (PD) model, AQP4-deficient (AQP4-/- ) mice displayed significantly stronger microglial inflammatory responses and remarkably greater losses of tyrosine hydroxylase (TH+ )-positive neurons than did wild-type AQP4 (AQP4+/+ ) controls. Microglia are the most important immune cells that mediate immune inflammation in PD. However, recently, few studies have reported why AQP4 deficiency results in more severe hypermicrogliosis and neuronal damage after MPTP treatment. In this study, transforming growth factor-ß1 (TGF-ß1), a key suppressive cytokine in PD onset and development, failed to increase in the midbrain and peripheral blood of AQP4-/- mice after MPTP treatment. Furthermore, the lower level of TGF-ß1 in AQP4-/- mice partially resulted from impairment of its generation by astrocytes; reduced TGF-ß1 may partially contribute to the uncontrolled microglial inflammatory responses and subsequent severe loss of TH+ neurons in AQP4-/- mice after MPTP treatment. Our study provides not only a better understanding of both aetiological and pathogenical factors implicated in the neurodegenerative mechanism of PD but also a possible approach to developing new treatments for PD via intervention in AQP4-mediated immune regulation.

International position paper on the appropriate use of uricosurics with the introduction of lesinurad.

Over the last 70 years, pharmacotherapy in gout with urate-lowering drugs has consisted of four drugs only: In 1952, a mild uricosuric probenecid became available, the xanthine oxidase inhibitor Allopurinol in 1964, and the latter became the most frequently used urate-lowering drug worldwide; in the Eurozone, the uricosuric benzbromarone was welcomed in 1977. Only in 2002, the potent non-purine xanthine oxidase inhibitor febuxostat was introduced. In many countries, uricosurics such as probenecid and benzbromarone have not been available up to now, and these days, the new uricosuric lesinurad is the first uricosuric that may be introduced in these countries, which is the reason for describing the position this novel uricosuric deserves in treating gout. Recent literature will be shortly reviewed, and the current proposed position for lesinurad will be given as an aid for clinicians.

Coadministration of probenecid and cimetidine with mirogabalin in healthy subjects: A phase 1, randomized, open-label, drug-drug interaction study.

AIMS: The primary aim of this study was to assess the individual effects of probenecid and cimetidine on mirogabalin exposure. METHODS: This phase 1, open-label, crossover study randomized healthy adults to receive three treatment regimens, each separated by ≥5-day washout: a single oral dose of mirogabalin 15 mg on day 2, mirogabalin 15 mg on day 2 plus probenecid 500 mg every 6 h from days 1 to 4, and mirogabalin 15 mg on day 2 plus cimetidine 400 mg every 6 h from days 1 to 4. RESULTS: Coadministration of mirogabalin with probenecid or cimetidine increased the maximum and total mirogabalin exposure. The geometric mean ratios of Cmax and AUC(0-t) (90% CI) with and without coadministration of probenecid were 128.7% (121.9-135.7%) and 176.1% (171.9-180.3%), respectively. The geometric mean ratios of Cmax and AUC(0-t) (90% CI) with and without coadministration of cimetidine were 117.1% (111.0-123.6%) and 143.7% (140.3-147.2%), respectively. Mean (standard deviation) renal clearance of mirogabalin (l h-1 ) was substantially slower after probenecid [6.67 (1.53)] or cimetidine [7.17 (1.68)] coadministration, compared with mirogabalin alone [11.3 (2.39)]. Coadministration of probenecid or cimetidine decreased mirogabalin mean (standard deviation) apparent total body clearance [10.5 (2.33) and 12.8 (2.67) l h-1 , respectively, vs. 18.4 (3.93) for mirogabalin alone]. CONCLUSIONS: A greater magnitude of change in mirogabalin exposure was observed when coadministered with a drug that inhibits both renal and metabolic clearance (probenecid) vs. a drug that only affects renal clearance (cimetidine). However, as the increase in exposure is not clinically significant (>2-fold), no a priori dose adjustment is recommended.

Intravenous cefazolin plus oral probenecid versus oral cephalexin for the treatment of skin and soft tissue infections: a double-blind, non-inferiority, randomised controlled trial.

OBJECTIVE: The purpose of our study was to determine if cephalexin 500 mg orally four times daily was non-inferior to cefazolin 2 g intravenously daily plus probenecid 1 g orally daily in the management of patients with uncomplicated mild-moderate skin and soft tissue infection (SSTI) presenting to the ED. METHODS: This was a prospective, multicentre, double dummy-blind, randomised controlled non-inferiority trial conducted at two tertiary care teaching hospitals in Canada. Patients were enrolled if they presented to the ED with an uncomplicated SSTI, and randomly assigned in a 1:1 fashion to oral cephalexin or intravenous cefazolin plus oral probenecid for up to 7 days. The primary outcome was failure of therapy at 72 hours. Clinical cure at 7 days, intravenous to oral medication transition admission to hospital and adverse events were also evaluated. RESULTS: 206 patients were randomised with 104 patients in the cephalexin group and 102 in the cefazolin and probenecid group. The proportion of patients failing therapy at 72 hours was similar between the treatment groups (4.2% and 6.1%, risk difference 1.9%, 95% CI -3.7% to 7.6%). Clinical cure at 7 days was not significantly different (100% and 97.7%, risk difference -2.3%, 95% CI -6.7% to 0.8%). CONCLUSION: Cephalexin at appropriate doses appears to be a safe and effective alternative to outpatient parenteral cefazolin in the treatment of uncomplicated mild-moderate SSTIs who present to the ED. TRIAL REGISTRATION NUMBER: NCT01029782; Results.

Antibiotics for treating gonorrhoea in pregnancy.

BACKGROUND: Gonorrhoea is a sexually transmitted infection that is caused by Neisseria gonorrhoeae, and is a major public health challenge today. N gonorrhoeae can be transmitted from the mother's genital tract to the newborn during birth, and can cause gonococcal ophthalmia neonatorum as well as systemic neonatal infections. It can also cause endometritis and pelvic sepsis in the mother. This review updates and replaces an earlier Cochrane Review on antibiotics for treating this infectious condition. OBJECTIVES: To assess the clinical effectiveness and harms of antibiotics for treating gonorrhoea in pregnant women. SEARCH METHODS: We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 May 2017), LILACS database (1982 to April 5, 2017), the WHO International Clinical Trials Registry Platform (ICTRP; April 5, 2017), ClinicalTrials.gov (April 5, 2017), the ISRCTN Registry (April 5, 2017), and Epistemonikos (April 5, 2017). We also searched reference lists of all retrieved articles. SELECTION CRITERIA: We included randomised controlled trials (RCTs) comparing the use of antibiotics for treating gonorrhoea in pregnancy. The antibiotics could have been used alone or in combination, were administered parenterally, orally, or both, and were compared with another antibiotic.We included RCTs regardless of their publication status (published, unpublished, published as an article, an abstract, or a letter), language, or country. We applied no limits on the length of follow-up.We excluded RCTs using a cluster- or cross-over design, or quasi-RCTs. DATA COLLECTION AND ANALYSIS: Three review authors independently assessed trials for inclusion and risk of bias, extracted data, and checked them for accuracy. MAIN RESULTS: We included two RCTs, that randomised 514 pregnant women (347 women analysed) at a mean gestational age of 22 weeks. Both trials were conducted in the outpatient department of the same two hospitals in the USA between 1993 and 2001, and had a follow-up of 14 days. One of the trials was sponsored by a drug company. We considered both trials to be at a high risk of bias.One trial compared ceftriaxone (125 mg, intramuscular) with cefixime (400 mg, oral); the other trial had three arms, and assessed ceftriaxone (250 mg, intramuscular) versus either amoxicillin (3 g, oral) plus probenecid (1 g, oral) or spectinomycin (2 g, intramuscular). We did not include the spectinomycin data because this medication is no longer produced. We were unable to conduct meta-analysis because the trials compared different medications.We found inconclusive evidence that there were clear differences in the cure of gonococcal infections (genital, extragenital, or both) between intramuscular ceftriaxone versus oral amoxicillin plus oral probenecid (risk ratio (RR) 1.07, 95% confidence interval (CI) 0.98 to 1.16; one RCT; 168 women; very low-quality evidence) or intramuscular ceftriaxone versus oral cefixime (RR 0.99, 95% CI 0.91 to 1.08; one RCT; 95 women; very low-quality evidence).Neither of the trials reported on two of this review's primary maternal outcomes: incidence of obstetric complications (miscarriage, premature rupture of membranes, preterm delivery, or fetal death), or disseminated gonococcal infection, or on the incidence of neonatorum ophthalmia in the neonates.One trial reported one case of vomiting in the oral amoxacillin plus probenecid group. Trials reported pain at the injection sites, but did not quantify it. Hyperberbilurrubinemia was more frequent in neonates whose mothers were exposed to ceftriaxone. There were no clear differences between groups for neonatal malformation. AUTHORS' CONCLUSIONS: This Cochrane Review found high levels of cure of gonococcal infections in pregnancy with the given antibiotic regimens. However, the evidence in this review is inconclusive as it does not support one particular regimen over another. This conclusion was based on very low-quality evidence (downgraded for poor trial design, imprecision) from two trials (involving 514 women), which we assessed to be at a high risk of bias for a number of domains. The harm profiles of the antibiotic regimes featured in this review remain unknown.High-quality RCTs are needed, with sufficient power to assess the clinical effectiveness and potential harms of antibiotics in pregnant women with gonorrhoea. These should be planned according to Standard Protocol Items: Recommendations for Interventional Trials (SPIRIT),conducted following CONSORT recommendations, and based on Patient-Centered Outcomes Research Institute (PCORI) outcomes.

Probenecid Improves Cardiac Function in Patients With Heart Failure With Reduced Ejection Fraction In Vivo and Cardiomyocyte Calcium Sensitivity In Vitro.

BACKGROUND: Transient receptor potential vanilloid 2 is a calcium channel activated by probenecid. Probenecid is a Food and Drug Administration-approved uricosuric drug that has recently been shown to induce positive lusitropic and inotropic effects in animal models through cardiomyocyte transient receptor potential vanilloid 2 activation. The aim of this study was to test the hypothesis that oral probenecid can improve cardiac function and symptomatology in patients with heart failure with reduced ejection fraction and to further elucidate its calcium-dependent effects on myocyte contractility. METHODS AND RESULTS: The clinical trial recruited stable outpatients with heart failure with reduced ejection fraction randomized in a single-center, double-blind, crossover design. Clinical data were collected including a dyspnea assessment, physical examination, ECG, echocardiogram to assess systolic and diastolic function, a 6-minute walk test, and laboratory studies. In vitro force generation studies were performed on cardiomyocytes isolated from murine tissue exposed to probenecid or control treatments. The clinical trial recruited 20 subjects (mean age 57 years, mean baseline fractional shortening of 13.6±1.0%). Probenecid therapy increased fractional shortening by 2.1±1.0% compared with placebo -1.7±1.0% (P=0.007). Additionally, probenecid improved diastolic function compared with placebo by decreasing the E/E' by -2.95±1.21 versus 1.32±1.21 in comparison to placebo (P=0.03). In vitro probenecid increased myofilament force generation (92.36 versus 80.82 mN/mm2, P<0.05) and calcium sensitivity (pCa 5.67 versus 5.60, P<0.01) compared with control. CONCLUSIONS: Probenecid improves cardiac function with minimal effects on symptomatology and no significant adverse effects after 1 week in patients with heart failure with reduced ejection fraction and increases force development and calcium sensitivity at the cardiomyocyte level. CLINICAL TRIAL REGISTRATION: URL: https://www.clinicaltrials.gov. Unique identifier: NCT01814319.

Oral probenecid improves sperm motility in men with spinal cord injury.

STUDY DESIGN: Prospective cohort study (twenty men with spinal cord injury [SCI]). OBJECTIVE: Determine if administration of oral probenecid results in improved sperm motility in men with SCI. SETTING: Major university medical center. METHODS: Twenty men with SCI were administered probenecid for 4 weeks (250 mg twice a day for 1 week, followed by 500 mg twice a day for 3 weeks). Semen quality was assessed at three time points: pre-treatment, post-treatment (immediately after the 4-week treatment), and follow-up (4 weeks after the last pill was ingested). RESULT(S): Probenecid was well-tolerated by all subjects. Sperm motility improved in each subject after 4 weeks of oral probenecid. The mean percent of sperm with progressive motility increased from 19% to 26% (P < 0.05). A more striking increase was seen in the mean percent of sperm with rapid linear motility, from 5% to 17%, (P <0.001). This improvement continued into the four week follow up period. Similar improvements were seen in the total motile sperm count (15 million, 28 million, and 27 million at pre-treatment, post-treatment, and follow-up, respectively). Sperm concentration was not significantly different at pre-treatment, post-treatment, and follow-up, (52 million, 53 million and 53 million, respectively). CONCLUSION: This study showed that administration of an oral agent (probenecid) known to interfere with the pannexin-1 cellular membrane channel, can improve sperm motility in men with spinal cord injury. It is the first study to report improved sperm motility after oral medication in men with SCI.

Cost-effectiveness analysis of HLA-B*58: 01 genetic testing before initiation of allopurinol therapy to prevent allopurinol-induced Stevens-Johnson syndrome/toxic epidermal necrolysis in a Malaysian population.

OBJECTIVE: Studies found a strong association between allopurinol-induced Stevens-Johnson syndrome (SJS)/toxic epidermal necrolysis (TEN) and the HLA-B*58:01 allele. HLA-B*58:01 screening-guided therapy may mitigate the risk of allopurinol-induced SJS/TEN. This study aimed to evaluate the cost-effectiveness of HLA-B*58:01 screening before allopurinol therapy initiation compared with the current practice of no screening for Malaysian patients with chronic gout in whom a hypouricemic agent is indicated. METHODS: This cost-effectiveness analysis adopted a societal perspective with a lifetime horizon. A decision tree model coupled with Markov models were developed to estimate the costs and outcomes, represented by quality-adjusted life years (QALYs) gained, of three treatment strategies: (a) current practice (allopurinol initiation without HLA-B*58:01 screening); (b) HLA-B*58:01 screening before allopurinol initiation; and (c) alternative treatment (probenecid) without HLA-B*58:01 screening. The model was populated with data from literature review, meta-analysis, and published government documents. Cost values were adjusted for the year 2016, with costs and health outcomes discounted at 3% per annum. A series of sensitivity analysis including probabilistic sensitivity analysis were carried out to determine the robustness of the findings. RESULTS: Both HLA-B*58:01 screening and probenecid prescribing were dominated by current practice. Compared with current practice, HLA-B*58:01 screening resulted in 0.252 QALYs loss per patient at an additional cost of USD 322, whereas probenecid prescribing resulted in 1.928 QALYs loss per patient at an additional cost of USD 2203. One SJS/TEN case would be avoided for every 556 patients screened. At the cost-effectiveness threshold of USD 8695 per QALY, the probability of current practice being the best choice is 99.9%, in contrast with 0.1 and 0% in HLA-B*58:01 screening and probenecid prescribing, respectively. This is because of the low incidence of allopurinol-induced SJS/TEN in Malaysia and the lower efficacy of probenecid compared with allopurinol in gout control. CONCLUSION: This analysis showed that HLA-B*58:01 genetic testing before allopurinol initiation is unlikely to be a cost-effective intervention in Malaysia.

Probenecid-treatment reduces demyelination induced by cuprizone feeding.

Recent experiments showed that a pannexin-1 inhibitor, probenecid, reduced clinical symptoms in the murine experimental autoimmune encephalomyelitis when applied during the initial phase of neuronal inflammation. An inflammatory component is also present in a toxically induced inflammation and demyelination using cuprizone diet. Probenecid is a pannexin-1 antagonist and a probenecid therapy was investigated. Mice were fed for 10days with a cuprizone diet. In the following, the diet was continued but combined with a daily injection of a low dose of probenecid or solvent for 10days. Electron microscopy revealed demyelination in the optic nerve. The demyelination as measured by the axonal diameter was significantly reduced in the animals treated with 100mg per kg body weight probenecid. In comparison to controls, the number of leukocytes and lymphocytes in the peripheral blood was reduced in all cuprizone groups including the treatment group. In conclusion, early demyelination in the optic nerve was moderately reduced by 10days treatment with a low dose probenecid. This is a hint for the involvement of pannexin-1 modulated inflammation in cuprizone feeding induced toxic demyelination. Thus, probenecid is a candidate for the treatment of neuro-inflammation and multiple sclerosis.

Diurnal variation in the pharmacokinetics and brain distribution of morphine and its major metabolite.

The pharmacokinetics and pharmacodynamics of drugs are influenced by daily fluctuations in physiological processes. The aim of this study was to determine the effect of dosing time on the pharmacokinetics and brain distribution of morphine. To this end, 4mg/kg morphine was administered intravenously to Wistar rats that were either pre-treated with vehicle or tariquidar and probenecid to inhibit processes involved in the active transport of morphine. Non-linear mixed effects modelling was used to describe the concentration-time profiles of morphine and its metabolite M3G in plasma and brain tissue. We found that the concentrations of morphine in the brain and of M3G in plasma depended on the time of day, which could be quantified by a 24-hour rhythm in the efflux of morphine from brain tissue back into the circulation, with the lowest efflux during the two light-dark phase transitions with a difference between peak and trough of 20%. The active processes involved in the clearance of morphine and its metabolite M3G from plasma also showed 24-hour variation with the highest value in the middle of the dark phase being 54% higher than the lowest value at the start of the light phase. Hence, time of day presents a considerable source of variation in the pharmacokinetics of morphine, which could be used to optimize the dosing strategy of morphine.

Effect of Uric Acid-Lowering Agents on Endothelial Function: A Randomized, Double-Blind, Placebo-Controlled Trial.

Higher levels of serum uric acid are independently associated with endothelial dysfunction, a mechanism for incident hypertension. Overweight/obese individuals are more prone to endothelial dysfunction than their lean counterparts. However, the effect of lowering serum uric acid on endothelial dysfunction in these individuals has not been examined thoroughly. In this randomized, double-blind, placebo-controlled trial of nonhypertensive, overweight, or obese individuals with higher serum uric acid (body mass index ≥25 kg/m2 and serum uric acid ≥5.0 mg/dL), we assigned subjects to probenecid (500-1000 mg/d), allopurinol (300-600 mg/d), or matching placebo. The primary outcome was endothelium-dependent vasodilation measured by brachial artery ultrasound at baseline and 8 weeks. By the end of the trial, 47, 49, and 53 participants had been allocated to receive probenecid, allopurinol, and placebo, respectively. Mean serum uric acid levels significantly decreased in the probenecid (from 6.1 to 3.5 mg/dL) and allopurinol groups (from 6.1 to 2.9 mg/dL) but not in the placebo group (6.1 to 5.6 mg/dL). None of the interventions produced any significant change in endothelium-dependent vasodilation (probenecid, 7.4±5.1% at baseline and 8.3±5.1% at 8 weeks; allopurinol, 7.6±6.0% at baseline and 6.2±4.8% at 8 weeks; and placebo, 6.5±3.8% at baseline and 7.1±4.9% at 8 weeks). In this randomized, double-blind, placebo-controlled trial, uric acid lowering did not affect endothelial function in overweight or obese nonhypertensive individuals. These data do not support the hypothesis that uric acid is causally related to endothelial dysfunction, a potential mechanism for development of hypertension.

Penicillin Encephalopathy: An Unlikely Adversary in the Treatment of Neurosyphilis--Case Report and Review of the Literature.

UNLABELLED: Penicillin encephalopathy is a rare, potentially reversible phenomenon of drug-induced neurotoxicity. CASE: A 65-year-old female with a history of HIV was admitted with a three-day history of worsening headache, confusion, and lethargy. On examination she was awake but confused. Cerebrospinal fluid (CSF) and serum venereal disease research laboratory (VDRL) test returned positive and the patient was started on intravenous penicillin G with probenecid. On the second day of therapy, she developed myoclonic jerking, consistent with penicillin neurotoxicity. Repeat labs also showed new onset renal failure. Penicillin and probenecid therapy were stopped with a resolution of symptoms. Subsequently, therapy without probenecid was reinstituted uneventfully. DISCUSSION: Herein, we describe a female who developed penicillin neurotoxicity after initiation of intravenous penicillin therapy with probenecid for neurosyphilis. It is important that penicillin-induced toxicity be considered if characteristic myoclonic movements accompany encephalopathy. The presence of coexistent renal compromise should heighten the vigilance of clinicians.

Probenecid protects against oxygen-glucose deprivation injury in primary astrocytes by regulating inflammasome activity.

Inflammation is extremely important in the development of cerebral ischemia/reperfusion injury. Pannexin 1 (Panx1) channel has been reported to activate inflammasome in astrocytes and be involved in ischemic injury, but this damage effect is reversed by a Panx1 inhibitor-probenecid. However, the mechanism of probenecid protects against cerebral ischemia/reperfusion injury remains unclear. In present study, we hypothesized that probenecid protected astrocytes from ischemia/reperfusion injury in vitro by modulating the inflammasome. Primary cultured neocortical astrocytes were exposed to oxygen-glucose deprivation/reoxygenation (OGD/RX) and probenecid was added in this model. Viability and nuclear morphology of astrocytes, production of reactive oxygen species (ROS), protein expressions of NLRP3 (NOD-like receptor protein 3), caspase-1, and AQP4 (Aquaporins 4), as well as release of cellular HMGB1 and IL-1ß were observed to evaluate the effect and mechanisms of probenecid on OGD/reoxygenated astrocytes. Probenecid did not affect cell viability at concentrations of 1, 5, 10, and 100µM but induced significant astrocytes death at 500µM. Probenecid inhibited cell death and ROS generation in astrocytes subjected to 6h of OGD and 24h of reoxygenation. The expression levels of NLRP3, caspase-1, and AQP4 increased after 6h of OGD, but probenecid treatment attenuated this increase. Moreover, the extracellular release of IL-1ß and HMGB1 from OGD/reoxygenated astrocytes increased significantly. However, treatment by probenecid resulted in substantial reduction of these proteins levels in extracellular space. In conclusion, The Panx1 inhibitor, probenecid, which was administered before OGD, provided protective effects on the OGD/reoxygenation model of cultured astrocytes by modulating inflammasome activity and downregulating AQP4 expression.