Grapefruit can augment oral medication bioavailability through irreversible (mechanism‐based) inhibition of intestinal CYP 3A4. Supplementary data from our recent coffee–drug interaction clinical study showed some subjects had higher area under the plasma drug concentration ‐ time curve (AUC) and plasma peak drug concentration (Cmax) of the CYP 3A4 probe felodipine compared to aqueous control. It was hypothesized that coffee might interact like grapefruit in responsive individuals. Beans from six geographical locations were consistently brewed into coffee that was separated chromatographically to a methanolic fraction for in vitro inhibition testing of CYP 3A4 metabolism of felodipine at 1% coffee strength. The effect of simultaneous incubation and 10‐min preincubation with coffee fractions determined whether coffee had direct and mechanism‐based inhibitory activity. A subsequent five‐way randomized balanced controlled crossover clinical study evaluated the clinical pharmacokinetic interaction with single‐dose felodipine. Grapefruit juice, water, or three of the in vitro tested coffees were ingested at 300 mL alone 1 h before and then with felodipine. In vitro, all six coffees decreased felodipine metabolism for both simultaneous and preincubation exposure compared to corresponding control. Five coffees demonstrated mechanism‐based inhibition. Grapefruit increased felodipine AUC 0–8 (25 vs. 13 ng.h/mL, P < 0.001) and Cmax (5.8 vs. 2.7 ng/mL, P < 0.001) and decreased dehydrofelodipine/felodipine AUC 0–8 ratio (0.84 vs. 1.29, P < 0.001), while the three coffees caused no change in these parameters compared to water. Despite high in vitro potency of CYP 3A4 inhibition, the coffees did not cause a clinical pharmacokinetic interaction possibly from insufficient amount of inhibitor(s) in coffee reaching intestinal CYP 3A4 during the absorption phase of felodipine. The results of this study highlight the need for follow‐up clinical testing when in vitro results indicate the possibility of an interaction.

OBJECTIVES:A period of abstinence from coffee to permit caffeine elimination appears to enable increased blood pressure on subsequent exposure. We hypothesized that this would offset the antihypertensive effect of the dihydropyridine calcium channel blocker felodipine.METHODS:A randomized, single-dose, crossover study assessed hemodynamic and pharmacokinetic effects following 2 days without coffee and caffeine-containing foods. Consistently brewed black coffee (2×300ml), felodipine maximum recommended dose (10mg), and coffee plus felodipine were tested in middle-aged normotensive subjects.RESULTS:Pretreatment plasma caffeine concentrations were unquantifiable. After coffee, blood pressure changes (mm Hg) averaged over study hours 1-4 were increased for brachial systolic (7.6, P < 0.001) and diastolic (4.9, P < 0.001) and aortic systolic (7.4, P < 0.001), pulse (3.0, P < 0.05) and augmentation (1.4, P < 0.05) relative to baseline. After coffee plus felodipine, they were higher for brachial systolic (4.0, P < 0.05) and diastolic (3.9, P < 0.001) and aortic systolic (4.6, P < 0.05) compared to felodipine alone. The pressor effects of coffee and its modulation by felodipine were variable among individuals. Coffee containing caffeine (127mg) caused maximum pressor effect. Caffeine and felodipine pharmacokinetics were similar for coffee and felodipine given alone or in combination indicating an interaction having a pharmacodynamic basis. Plasma felodipine concentration-diastolic blood pressure reduction relationship shifted with coffee such that doubling the felodipine concentration would eliminate the pressor effect. However, this may increase the risk of adverse drug events particularly during the timeframe without coffee.CONCLUSION:Intermittent coffee ingestion might complicate hypertension diagnosis and management for many individuals.

The chemical reduction of the disulfide homodimer dimesna to its constituent mesna moieties is essential for its mitigation of nephrotoxicity associated with cisplatin and ifosfamide anticancer therapies and enhancement of dialytic clearance of the cardiovascular risk factor homocysteine. The objective of this study was to investigate potential enzymatic and non-enzymatic mechanisms of intracellular dimesna reduction. Similar to endogenous intracellular disulfides, dimesna undergoes thiol–disulfide exchange with thiolate anion-forming sulfhydryl groups via the two-step SN2 reaction. Determination of equilibrium constants of dimesna reduction when mixed with cysteine or glutathione provided a mechanistic explanation for dramatic cysteine and homocysteine depletion, but sparing of the endogenous antioxidant glutathione, previously observed during mesna therapy. Dimesna was reduced by recombinant enzymes of the thioredoxin system; however, oxidation of NADPH by the glutaredoxin system was only observed in the presence of combined dimesna and reduced glutathione, suggesting formation of oxidized glutathione following an initial non-enzymatic reduction of dimesna. Production of mesna by enzymatic and non-enzymatic mechanisms in HeLa cell lysate following dimesna incubation was demonstrated by a loss in mesna production following protein denaturation and prediction of residual non-enzymatic mesna production by mathematical modeling of thiol–disulfide exchange reactions. Reaction modeling also revealed that mixed disulfides make up a significant proportion of intracellular thiols, supporting their role in providing additional nephroprotection, independent of direct platinum conjugation.

OBJECTIVES:Persistent pulmonary hypertension of the newborn is a common problem with significant morbidity and mortality. Inhaled nitric oxide is the standard care, but up to 40% of neonates are nonresponders. Milrinone is a phosphodiesterase III inhibitor which increases the bioavailability of cyclic adenosine monophosphate and has been shown to improve pulmonary hemodynamics in animal experimental models. The primary objective was to investigate the pharmacological profile of milrinone in persistent pulmonary hypertension of the newborn. Secondary objectives were to delineate short-term outcomes and safety profile. SUBJECTS AND METHODS:An open label study of milrinone in neonates with persistent pulmonary hypertension of the newborn was conducted. Patients received an intravenous loading dose of milrinone (50 μg/kg) over 60 mins followed by a maintenance infusion (0.33-0.99 μg/kg/min) for 24-72 hrs. Physiologic indices of cardiorespiratory stability and details of cointerventions were recorded. Serial blood milrinone levels were collected after the bolus, following initiation of the maintenance infusion to determine steady state levels, and following discontinuation of the drug to determine clearance. Echocardiography was performed before and after (1, 12 hrs) milrinone initiation. INTERVENTIONS:Milrinone. MEASUREMENTS AND MAIN RESULTS:Eleven neonates with a diagnosis of persistent pulmonary hypertension of the newborn who met eligibility criteria were studied. The median (SD) gestational age and weight at birth were 39.2 ± 1.3 wks and 3481 ± 603 g. The mean (± sd) half-life, total body clearance, volume of distribution, and steady state concentration of milrinone were 4.1 ± 1.1 hrs, 0.11 ± 0.01 L/kg/hr, 0.56 ± 0.19 L/kg, and 290.9 ± 77.7 ng/mL. The initiation of milrinone led to an improvement in PaO2 (p = 0.002) and a sustained reduction in FIO2 (p < 0.001), oxygenation index (p < 0.001), mean airway pressure (p = 0.03), and inhaled nitric oxide dose (p < 0.001). Although a transient reduction in systolic arterial pressure (p < 0.001) was seen following the bolus, there was overall improvement in base deficit (p = 0.01) and plasma lactate (p = 0.04) with a trend towards lower inotrope score. Serial echocardiography revealed lower pulmonary artery pressure, improved right and left ventricular output, and reduced bidirectional or right-left shunting (p < 0.05) after milrinone treatment. CONCLUSIONS:The pharmacokinetics of milrinone in persistent pulmonary hypertension of the newborn is consistent with published data. The administration of intravenous milrinone led to better oxygenation and improvements in pulmonary and systemic hemodynamics in patients with suboptimal response to inhaled nitric oxide. These data support the need for a randomized controlled trial in neonates.

Ifosfamide (IFO), which is used in the treatment of pediatric solid tumors, causes high rates of nephrotoxicity. N‐acetylcysteine (NAC), an antidote for acetaminophen overdose, has been shown to prevent IFO‐induced renal cell death and nephrotoxicity in both LLCPK‐1 cells and a rat model. To facilitate the use of NAC in preventing IFO‐induced nephrotoxicity in children, the authors compared the systemic exposure to NAC in children treated for acetaminophen overdose to the systemic exposure of the therapeutically effective rat model. The mean systemic exposure in the rat model was 18.72 mM·h (range, 9.92–30.02 mM·h), compared to the mean systemic exposure found in treated children (14.48 mM·h; range, 6.22–32.96 mM·h). They also report 2 pediatric cases in which NAC‐attenuated acute renal failure associated with IFO when given concurrently with their chemotherapy treatment. Systemic exposure to NAC measured in 1 of these cases was comparable to that in the children treated for acetaminophen overdose. These results corroborate NAC's potential to protect against IFO‐induced nephrotoxicity in children when used in its clinically approved dose schedule and supports a clinical trial in children.

Background: The cytochrome P450 (CYP) 2D6 enzyme is involved in the metabolism of many drugs used by the elderly population. Variations in its activity can lead to altered drug response. However, few studies on the activity of this enzyme system have enrolled the elderly population.Objective: The goal of this pilot study was to assess the feasibility of in vivo phenotyping of CYP2D6 in an elderly population with dementia and to determine if part of the variability in response to treatment with galantamine is attributable to CYP2D6 phenotype.Methods: Patients with dementia attending geriatric clinics and receiving galantamine treatment for at least 6 months were enrolled in this case-control study. CYP2D6 phenotype was determined by analysis of the urinary concentrations of the probe drug dextromethorphan and its primary metabolite dextrorphan after ingestion of 30 mg of dextromethorphan. Patients were classified as robust responders to galantamine if their cognitive testing, as measured by using scores on the Mini Mental State Examination or Alzheimer's Disease Assessment Scale Cognitive subscale, had not changed or had improved after 6 months of treatment.Results: Forty-three patients (23 men, 20 women; mean age, 78.4 years; 98% white) underwent phenotyping. The mean number of concomitantly prescribed medications was 5.7, and 16 patients (37%) were receiving other CYP2D6 substrate or inhibitor drugs. The distribution of CYP2D6 phenotype was similar to that seen in other white populations. There was no correlation between the phenotypic metabolic ratio and age, the number of routinely taken medications, whether patients were receiving other prescribed substrate or inhibitor drugs of CYP2D6 (P = 0.63), or whether they were a robust responder (P = 0.47).Conclusions: Urinary assays of CYP2D6 phenotype are technically feasible in older individuals with dementia who are taking multiple medications, and may be a useful clinical tool in this population. However, the study was unable to make inferences about an association between CYP2D6 phenotype and galantamine responsiveness. (Am J Geriatr Pharmacother. 2011;9:224-233) (C) 2011 Elsevier HS Journals, Inc. All rights reserved.

Recombinant human erythropoietin (rHu-EPO) is a glycoprotein, which is produced commercially from Chinese hamster ovary (CHO) cells. It is used for the therapy of renal anemia and chemotherapy-induced anemia in cancer patients. Recent evidence suggests that rHu-EPO exerts tissue protective effects via multiple mechanisms which include inhibition of apoptosis, promotion of angiogenesis and decreased inflammation. After intravenous (i.v.) injection, the blood concentration of rHu-EPO rapidly decreases due to proteolysis resulting in a relatively short half-life of 8.5 h, which necessitates regular dosing with intervals that do not exceed 7 days. It would be desirable to develop an encapsulated formulation providing controlled release of rHu-EPO to maintain therapeutic concentrations in plasma, and for potential tissue protective applications to maintain high local therapeutic concentrations in tissue while minimizing potential unwanted systemic effects such as polycythemia and platelet activation, both of which can predispose to intravascular thrombosis. Nanoparticle encapsulation of rHu-EPO can also allow for direct injection at sites of injury in specific tissues/organs, again minimizing systemic exposure of the drug. In this paper, we report the production of biopolymer nanoparticles by ionotropic gelation of chitosan with tripolyphosphate (TPP). The nanoparticle size distribution in aqueous solution was determined and rates of rHu-EPO release from chitosan-TPP nanoparticles were measured in PBS at 37°C. It was observed that almost 30% of the encapsulated rHu-EPO was released within the first 48 hours and thereafter a linear release profile was observed for up to 2 weeks. Total drug release over 15 days was 63% of the initial amount.

The role of organic anion transporting polypeptides (OATPs), particularly the members of OATP1B subfamily, in hepatocellular handling of endogenous and exogenous compounds is an important and emerging area of research. Using a mouse model lacking Slco1b2, the murine ortholog of the OATP1B subfamily, we have demonstrated previously that genetic ablation causes reduced hepatic clearance capacity for substrates. In this study, we focused on the physiological function of the hepatic OATP1B transporters. First, we studied the influence of the Oatp1b2 deletion on bile acid (BA) metabolism, showing that lack of the transporter results in a significantly reduced expression of Cyp7a1, the key enzyme of BA synthesis, resulting in elevated cholesterol levels after high dietary fat challenge. Furthermore, Slco1b2(-/-) mice exhibited delayed clearance after oral glucose challenge resulting from reduced hepatic glucose uptake. In addition to increased hepatic glycogen content, Slco1b2(-/-) mice exhibited reduced glucose output after pyruvate challenge. This is in accordance with reduced hepatic expression of phosphoenolpyruvate carboxykinase (PEPCK) in knockout mice. We show that this phenotype is due to the loss of liver-specific Oatp1b2-mediated hepatocellular thyroid hormone entry, which then leads to reduced transcriptional activation of target genes of hepatic thyroid hormone receptor (TR), including Cyp7a1 and Pepck but also Dio1 and Glut2. Importantly, we assessed human relevance using a cohort of archived human livers in which OATP1B1 expression was noted to be highly associated with TR target genes, especially for glucose facilitating transporter 2 (GLUT2). Furthermore, GLUT2 expression was significantly decreased in livers harboring a common genetic polymorphism in SLCO1B1. Conclusion: Our findings reveal that OATP1B-mediated hepatic thyroid hormone entry is a key determinant of cholesterol and glucose homeostasis. (HEPATOLOGY 2011;54:644-654)

BACKGROUND Historically, physicians have been reluctant to maintain infants on phenytoin (PHT) following initial stabilization with intravenous loading doses, as therapeutic blood levels are difficult to achieve with conventional oral doses, and there is concern that high doses will result in toxicity. OBJECTIVES To determine the oral dose of PHT required to achieve therapeutic blood concentrations, without clinical toxicity, in the first weeks of life. METHODS Eight infants with seizures were treated with phenytoin from 2 weeks to 3 months of age. Total and free phenytoin concentrations, and urine phenytoin metabolite (p-hydroxyphenytoin) were measured every 2 weeks. Parents were asked to note seizure frequency and complete a questionnaire about possible side effects every 2 weeks. RESULTS No infants had seizures and no clinical side effects were noted. Doses required to achieve therapeutic serum concentrations ranged from 10-20mg/kg/day, considerably higher than doses required in adults. Free phenytoin levels were 8-13% of total serum concentrations, similar to ratios reported in adults. CONCLUSION To achieve therapeutic serum phenytoin levels in infants, doses of 10-20 mg/kg/day are required. These higher doses can be safely administered without clinical toxicity.

In spite of improvements in cancer chemotherapy, approximately 50% of cancers are not cured and improvement is needed. Given the association of diets high in fruits and vegetables with lower cancer risk, these foodstuffs have been investigated as sources of compounds to both prevent cancer and treat established tumors. Flavonoids, found in high amounts in cranberries, contribute to improved human health. A flavonoid-rich extract of cranberries (Fr6) and isolated polymers of the flavan-3-ol class of cranberry flavonoids (proanthocyanidins, PACs) were investigated for anticancer activity. Both Fr6 and PACs inhibited proliferation of various human cancer cell lines when grown in culture (in vitro). When Fr6 or PACs were administered by injection to mice bearing explants of human tumor cell lines, growth of the tumors was delayed. When treating the prostate tumor cell line DU145 explant, 50% of tumors completely regressed. Both Fr6 and PACs were able to block cell cycle progression and induce cell death. Subfractionation of Fr6 by high performance liquid chromatography yielded fractions containing 3 detectable peaks that exhibited most of the in vitro anticancer activity. Work continues on identifying these compounds, which appear to differ chemically from those identified in other laboratories. It is proposed that several components of cranberry will be identified for use in humans as a cancer preventive dietary supplement and, potentially, as a treatment for established tumors.

Adenosine has been shown to exert direct antihypertrophic effects on the heart, and plasma adenosine levels have been shown to be elevated in patients with heart failure. It has therefore been proposed that endogenously synthesized adenosine may function as a cardiac antihypertrophic factor. The present study was aimed to determine whether the adenosine system is altered in a potential adaptive manner following phenylephrine-induced hypertrophy in cultured neonatal rat ventricular myocytes. Phenylephrine produced significant hypertrophy as determined by cell size and atrial natriuretic peptide gene expression, which was accompanied by significantly increased gene and protein expression of adenosine A(1), A(2a), and A(3) receptors. These effects and the hypertrophic response were prevented by the alpha(1)-adrenoceptor antagonist prazosin as well as pharmacological agonists for all adenosine receptor subtypes. The upregulation of adenosine receptors by phenylephrine was also abrogated by adenosine 5'-(alpha,beta-methylene)diphosphate, an inhibitor of ectosolic 5'-nucleotidase. Moreover, phenylephrine significantly increased production of adenosine from myocytes in the presence of a nucleoside transport and adenosine deaminase inhibitor, the combination of which abrogated the hypertrophic effect of phenylephrine. The latter effect was reversed by adenosine receptor antagonists. Phenylephrine also produced a significant upregulation in expression levels of equilibrative nucleoside transporter 1 although expression levels of equilibrative nucleoside transporter 2 were unaffected. Taken together, our results suggest an adaptive upregulation of the adenosine system to phenylephrine-induced cardiomyocyte hypertrophy that serves to limit the hypertrophic effect of alpha(1-)adrenoceptor activation.

Background: Increased plasma total homocysteine (tHcy) is a risk factor for the development of atherosclerosis and thrombosis present in over 90% of patients with end-stage renal disease (ESRD). We hypothesized that 12 mg/kg intravenous mesna administered predialysis would cause a significant decrease in plasma tHcy compared to placebo. Methods: Patients with ESRD were recruited for 1- and 4-week placebo-controlled, cross-over studies. Intravenous 12 mg/kg mesna or placebo was administered 3 times weekly predialysis. Results: One week of 12 mg/kg intravenous mesna significantly decreased predialysis plasma tHcy by 12.8 ± 7.8% (placebo 23.4 ± 8.0 μmol/l vs. mesna 20.5 ± 7.6 μmol/l, p = 0.0044). Four weeks of treatment yielded no significant decline in predialysis plasma tHcy (placebo 18.3 ± 8.5 μmol/l vs. mesna 18.7 ± 6.3 μmol/l, p = 0.41). Conclusions: Although 12 mg/kg mesna significantly enhances tHcy excretion, prolonged treatment causes no change in plasma tHcy.

Objective: To describe a case of life-threatening flecainide intoxication in a toddler, secondary to accidental reversal of syringes used for oral administration. Case Summary: A 2-year-old male with a history of a persistent junctional reciprocating tachycardia had been receiving flecainide 4.8 mg/kg/day (1 mL 3 times daily) and nadolol 2 mg/kg/day (5 mL once daily) for 10 months. One morning, 3 hours after the drugs were administered, he became bradycardic (heart rate 50 beats/min) and then presented to the emergency department with vital signs absent. After initial cardiopulmonary resuscitation and epinephrine, he was bradycardic; this was followed by wide-complex tachycardia that converted rapidly to narrow-complex tachycardia after bolus administration of intravenous sodium bicarbonate for suspected flecainide intoxication. Following resuscitation, he remained hemodynamically stable and was discharged in normal sinus rhythm without neurologic sequelae. Drug concentrations obtained at the time of presentation showed a serum concentration of flecainide of 0.668 μg/mL. Drug formulations were also analyzed and found to contain the expected concentration of flecainide. Discussion: Literature regarding adverse drug events in the pediatric outpatient population is reviewed, as well as how these risks apply to flecainide, a medication with a low margin of safety. Pediatric experience with flecainide intoxication and sodium bicarbonate administration as an antidote is reviewed. Analysis of the serum drug concentrations demonstrated blood concentrations consistent with syringe reversal, which would have produced a 5-fold flecainide overdose. The Naranjo probability scale indicated a highly probable relationship between flecainide ingestion and the life-threatening event in this case. Conclusions: This case of life-threatening flecainide intoxication in a young child, secondary to accidental reversal of medication syringes, underscores the importance of providing parents with accurate dispensing information and labeling medication bottles and syringes in an unambiguous manner.

The pharmacodynamics and elimination kinetics of escalating doses (1.5-12 mg/kg) of hyaluronan (HA) infusions were studied in healthy human volunteers.Metabolic breakdown of serum HA and associated adverse events were monitored throughout the study.The HA-binding capacities of circulating CD4+ and CD8+ T lymphocytes, CD19+ Blymphocytes and CD14+ peripheral blood monocytes (PBMC) were also quantified.Breakdown of infused HA into small fragments (<37 kDa) were not detected and adverse events related to HA infusions were infrequent and non-serious in nature.Binding of FITC-HA was greatest to CD14+ monocytes and the binding capacity of these cells for FITC-HA was significantly increased by the final HA infusion.At that time, binding to CD14+ monocytes was related to serum HA levels suggesting a close relationship between PK and PD of serum HA.Drug level analysis demonstrated a disproportional increase in the area under the serum concentration vs. time curve with increasing HA dose.The observed non-linear HA kinetics appears to result from a saturable elimination process as revealed by pharmacokinetic modeling.These results have implications for the use of injected HA for drug delivery or in imaging applications.Participation a drug study 4 weeks prior to study entry C. Prohibited (for duration of study) d Medication (including over-the-counter products) Use of alcohol-containing or xanthine-containing beverages through sample collection See Methods and Results sections for descriptions of procedures.a Subjects could not have used nicotine within 3 months of study entry.b Patients were within 15% of their ideal weight ("Table of Desirable Weights of Adults", Metropolitan Life Insurance Company, 1983).c Includes disorders that would preclude informed consent or compliance with protocol requirements.d If medication other than that specified in the protocol was required, decision to continue subject was made by L.A.B. Medical Personnel.

A 32-year-old lactating woman with open-angle glaucoma used timolol maleate 0.5% eye drops twice daily to her right eye for 6 months. Four milk samples were collected over a span of 6 days. Timolol maleate milk levels were examined by liquid chromatography tandem mass spectrometry and found to be at a mean of 0.12 ng/mL (range, 0 to 0.37 ng/mL). At this level, the theoretical maximum relative infant dose expressed as a percentage of the weight-adjusted maternal dose was 0.012%. As most glaucoma patients administer drops to both eyes, the dosage was duplicated to reflect the more pertinent calculated theoretical relative infant dose of 0.024%. This dose of timolol is unlikely to cause systemic side effects to the healthy breastfed infant.

BACKGROUND:Plasma total homocysteine (tHcy) level is an independent risk factor for the development of atherosclerosis. The degree of risk in most of the population is decreased by using dietary vitamin supplementation; however, more than 90% of patients with end-stage renal disease have increased tHcy levels despite supplementation. Only a small fraction of tHcy is removed by hemodialysis because of extensive disulfide bonding to albumin. The objective of this study is to determine whether a single intravenous dose of mesna, a thiol-containing drug analogue of taurine, facilitates tHcy clearance during hemodialysis.METHODS:Initial in vitro thiol exchange tests were performed with mesna in plasma from dialysis patients. Mesna, 300 micromol/L (49.2 mg/L), was incubated with plasma at 37 degrees C, and free homocysteine was measured at various times. In vivo, mesna activity was tested in 10 hemodialysis patients by administering 2.5 or 5.0 mg/kg of mesna intravenously at the beginning of a treatment cycle. Blood samples were drawn throughout dialysis, and plasma tHcy levels were compared with those obtained from a previous dialysis session in which mesna was not administered.RESULTS:In vitro, mesna liberated 36.5% +/- 2.5% of protein-bound homocysteine in 30 minutes. In vivo, a single 2.5-mg/kg dose of mesna was ineffective; however, at 5.0 mg/kg, it caused a 55.2% +/- 3.9% decrease in plasma tHcy levels postdialysis compared with a 34.2% +/- 5.3% decrease with dialysis alone (P < 0.001).CONCLUSION:Intravenous mesna causes a rapid decrease in plasma tHcy levels during hemodialysis.

Elevated plasma total homocysteine is independently associated with atherosclerosis. Recent randomized trials show that vitamins lower total homocysteine but do not prevent cardiovascular events, suggesting the need for nonvitamin therapies to evaluate whether a causative relationship exists. Mesna (sodium 2‐mercaptoethanesulfonate) is a thiol‐containing drug capable of liberating homocysteine bound by disulfide bonds to proteins, facilitating its excretion. The effect of oral mesna on total homocysteine has not been evaluated and was the objective of this study. Eleven healthy volunteers received vehicle or 10 mg/kg mesna in random order, after which serial blood and urine samples were collected over 4 hours. Plasma total homocysteine decreased by 24.2% (P < .0001) following mesna. Urinary homocysteine excretion was significantly greater with mesna (3.9 ± 2.4 μmol) compared to vehicle (0.4 ± 0.1 μmol), P < .01. Oral mesna decreases plasma total homocysteine and is a potential nonvitamin treatment for assessing the homocysteine theory of atherosclerosis.

Elevated plasma total homocysteine (tHcy) is a risk factor for atherosclerosis. Hcy is 70–80% bound to albumin as a disulfide. Recent trials have evaluated ability of thiol-containing drugs to exchange with protein bound Hcy and consequently increase its renal clearance. The objective of this study was to develop an in vitro assay to predict the efficacy of thiol-containing drugs to lower tHcy in the clinical setting. The assay was used to test the effects of N-acetylcysteine (NAC), mesna, captopril, dimercaptosuccinic acid (DMSA), and penicillamine. Hcy was added in vitro to plasma of healthy subjects (n=6) and equilibrated. Concentrations of thiol exchange agent were added and incubated at 37°C. Aliquots were removed at selected intervals and free Hcy determined. Mesna, captopril, and NAC caused a concentration-dependent increase in free Hcy. Three-hundred micromolar mesna and captopril had a greater effect than equimolar NAC, increasing free Hcy by 33.9±5.0% and 32.0±2.6%, respectively compared to 22.3±2.4% for NAC, p<0.001. Our in vitro results indicate that mesna, captopril, and NAC effectively exchange with covalently bound Hcy. This assay can act as screening tool for novel tHcy lowering therapies and should spare the expense of negative trials.