Population pharmacokinetic and exposure-response analysis of apremilast in Japanese subjects with moderate to severe psoriasis

Apremilast is an orally available phosphodiesterase 4 inhibitor used for the treatment of moderate to severe psoriasis. The aims of this analysis were to develop a population pharmacokinetic (PPK) model of apremilast based on observed data from phase 1 studies combined with clinical trial data from subjects with moderate to severe psoriasis, and to develop exposure–response (E‐R) models to determine whether Japanese subjects with moderate to severe psoriasis achieve response to apremilast treatment similar to that observed in non‐Japanese, predominantly Caucasian subjects with moderate to severe psoriasis. The PPK model demonstrated that apremilast plasma concentrations and overall apparent clearance rate were comparable between the Japanese and Caucasian subgroups. The E‐R analyses of ≥75% or ≥50% improvement from baseline in Psoriasis Area and Severity Index score and achievement of static Physician Global Assessment score of 0 (clear) or 1 (almost clear) at week 16 indicated that apremilast treatment in Japanese subjects approached the maximal effect with response rates comparable to those in predominantly Caucasian subjects. Overall, the analyses confirm that the approved apremilast 30 mg b.i.d. dose is appropriate for Japanese subjects with moderate to severe psoriasis, with an efficacy profile similar to that previously observed in Caucasian subjects.

Pharmacodynamic analysis of apremilast in Japanese patients with moderate to severe psoriasis: Results from a phase 2b randomized trial

We evaluated the pharmacodynamic effects of apremilast in 69 patients who were included in biomarker subanalyses of a phase 2b study that demonstrated the long‐term safety and efficacy of apremilast in Japanese adults with moderate to severe psoriasis. The association between cytokine levels and Psoriasis Area and Severity Index (PASI) improvement was evaluated using linear regression and Spearman’s rank correlation coefficient analysis. At baseline, median plasma levels of interleukin (IL)‐17A, IL‐17F and IL‐22 were elevated versus reference values for healthy individuals, whereas tumor necrosis factor‐α levels were close to normal. With apremilast 30 mg b.i.d., there were significant associations between percentage change in PASI score and percentage change in IL‐17A, IL‐17F and IL‐22 levels at week 16. Findings demonstrate that the efficacy of apremilast in psoriasis is associated with inhibition of key cytokines involved in the pathology of psoriasis.

Safety and efficacy of apremilast through 104 weeks in patients with moderate to severe psoriasis who continued on apremilast or switched from etanercept treatment: findings from the LIBERATE study

Background

Apremilast, an oral phosphodiesterase‐4 inhibitor, has demonstrated efficacy in patients with moderate to severe psoriasis.

Objective

To evaluate long‐term efficacy and safety of apremilast in biologic‐naive patients with moderate to severe plaque psoriasis and safety of switching from etanercept to apremilast in the phase 3b LIBERATE trial.

Methods

Two hundred fifty patients were randomized to placebo, apremilast 30 mg BID or etanercept 50 mg QW through Week 16; thereafter, all patients continued or switched to apremilast through Week 104 (extension phase). Skin, scalp and nail involvement at Weeks 16, 52 and 104 were assessed using the Psoriasis Area and Severity Index (PASI; 0–72), Scalp Physician Global Assessment (ScPGA; 0–5) and Nail Psoriasis Severity Index (NAPSI; 0–8); patient‐reported outcomes (PROs) were assessed using the Dermatology Life Quality Index (DLQI; 0–32) and pruritus visual analog scale (VAS; 0–100 mm).

Results

The apremilast‐extension phase (Weeks 16–104) included 226 patients in the placebo/apremilast (n = 73), apremilast/apremilast (n = 74) and etanercept/apremilast (n = 79) groups, and at Week 104, 50.7%, 45.9% and 51.9% of these patients, respectively, maintained ≥75% reduction from baseline in PASI score (based on last‐observation‐carried‐forward analysis). Across treatment groups, ScPGA 0 (clear) or 1 (minimal) was achieved by 50.0%–59.2% of patients; NAPSI mean change from baseline was −48.1% to −51.1%; DLQI score ≤5 was achieved by 66.0%–72.5% of patients; and pruritus VAS mean change from baseline was −24.4 to −32.3. AEs in ≥5% of patients (diarrhoea, nausea, nasopharyngitis, upper respiratory tract infection and headache) did not increase with prolonged apremilast exposure.

Conclusions

Apremilast demonstrated significant and sustained improvements in skin, scalp, nails and PROs (pruritus and quality of life) over 104 weeks in patients with moderate to severe plaque psoriasis. Safety was consistent with the known safety profile of apremilast.

Apremilast, an oral phosphodiesterase 4 inhibitor, in the treatment of Japanese patients with moderate to severe plaque psoriasis: Efficacy, safety and tolerability results from a phase 2b randomized controlled trial

Apremilast, an oral, small‐molecule phosphodiesterase 4 inhibitor, works intracellularly within immune cells to regulate inflammatory mediators. This phase 2b randomized, placebo‐controlled study evaluated efficacy and safety of apremilast among Japanese patients with moderate to severe plaque psoriasis. In total, 254 patients were randomized to placebo, apremilast 20 mg b.i.d. (apremilast 20) or apremilast 30 mg b.i.d. (apremilast 30) through week 16; thereafter, all placebo patients were re‐randomized to apremilast 20 or 30 through week 68. Efficacy assessments included achievement of 75% or more reduction from baseline in Psoriasis Area and Severity Index score (PASI‐75; primary) and achievement of static Physician Global Assessment (sPGA; secondary) score of 0 (clear) or 1 (minimal) at week 16. Safety was assessed through week 68. At week 16, PASI‐75 response rates were 7.1% (placebo), 23.5% (apremilast 20; P = 0.0032 vs placebo) and 28.2% (apremilast 30; P = 0.0003 vs placebo); sPGA response rates (score of 0 or 1) were 8.8% (placebo), 23.9% (apremilast 20; P = 0.0165 vs placebo) and 29.6% (apremilast 30; P = 0.0020 vs placebo). Responses were maintained with apremilast through week 68. Most common adverse events (AEs) with placebo, apremilast 20 and apremilast 30 (0–16 weeks) were nasopharyngitis (8.3%, 11.8%, 11.8%), diarrhea (1.2%, 8.2%, 9.4%), and abdominal discomfort (1.2%, 1.2%, 7.1%), respectively. Exposure‐adjusted incidence of these AEs did not increase with continued apremilast treatment (up to 68 weeks). Apremilast demonstrated efficacy and safety in Japanese patients with moderate to severe plaque psoriasis through 68 weeks that was generally consistent with prior studies.

Reduction of HBV replication prolongs the early immunological response to IFNα therapy

BACKGROUND & AIMS

The interaction between HBV replication and immune modulatory effects mediated by IFNα therapy is not well understood. We characterized the impact of HBV DNA replication on the early IFNα-induced immunomodulatory mechanisms.

METHODS

We interrogated the transcriptional, serum cytokine/chemokine and cellular immune profiles of 28 patients with HBeAg+ chronic HBV infection (CHB) randomly assigned to one of 4 treatment cohorts (untreated n=5, weekly dosing of 360 μg Pegasys [PegIFNα] n=11, daily dose of 300 mg Viread [tenofovir disoproxil fumarate, TDF] n=6, or a combination of both n=6). Samples were characterized at multiple early time points through day 14 of therapy, after which all patients were given standard of care (180 μg Pegasys injected subcutaneously, weekly).

RESULTS

PegIFNα induced a distinct and rapid up-regulation of IFN signaling pathway that coincided with increase detection of distinct serum cytokines/chemokines (IL-15, IL-6, and CXCL-10) and the up-regulation of the frequency of proliferating NK and activated total CD8+ T cells. IFNα treatment alone did not result in rapid decay of HBV replication and was not able to restore the defective HBV-specific T cell response present in CHB patients. In addition, the IFNα immune-stimulatory effects diminished after the first dose, but this refractory effect was reduced in patients where HBV replication was simultaneously inhibited with TDF.

CONCLUSIONS

We present here the first comprehensive description of the early effects of IFNα treatment on immune and viral biomarkers in HBeAg+ CHB patients. Our results show that PegIFNα-induced innate immune activation directly benefits from the suppression of HBV replication.

Experimental HBsAg/anti-HBs complex assay for prediction of HBeAg loss in chronic hepatitis B patients treated with pegylated interferon and adefovir

BACKGROUND

We studied whether hepatitis B surface antigen (HBsAg)/anti-HBs immune complex levels in chronic hepatitis B (CHB) patients receiving antiviral therapy could be used as a response marker at baseline (BL) or early during treatment to predict treatment outcome.

METHODS

An experimental array-based assay (immunological multi-parameter chip technology [IMPACT]; Roche Diagnostics, Penzberg, Germany) served to determine HBsAg, anti-HBs and complex levels. We tested a panel of serum samples of 40 hepatitis B e antigen (HBeAg)-positive and 44 HBeAg-negative patients who received pegylated interferon and adefovir for 48 weeks.

RESULTS

HBsAg loss occurred in 4 of 40 HBeAg-positive and 4 of 44 HBeAg-negative patients. A total of 14 of 40 HBeAg-positive patients lost HBeAg and 12 of them formed anti-HBe. At BL, complexes were present in 83 (99%) patients, whereas free anti-HBs levels were detectable in 5 patients. Complex levels at BL and week 12 were higher in HBeAg-positive patients with HBeAg loss, compared to patients who retained HBeAg (P=0.002 and P=0.005, respectively). Receiver operating characteristic analysis for HBeAg loss in HBeAg-positive patients at BL and week 12 showed area-under-the-curve values of 0.79 (P=0.002) and 0.82 (P=0.003) for complex levels. We found no correlation in either HBeAg-positive or -negative patients between complex levels and HBsAg loss.

CONCLUSIONS

We demonstrated for the first time that before and during treatment HBsAg/anti-HBs immune complex levels can predict HBeAg loss in HBeAg-positive CHB patients treated with pegylated interferon and adefovir. Complexes were present in almost all patients at BL and were higher in patients who lost HBeAg. In conclusion, determining HBsAg/anti-HBs immune complex levels before and early during treatment could aid in selecting CHB patients with an optimal chance to achieve HBeAg loss.

Female and male adult brush mice (Peromyscus boylii) use ultrasonic vocalizations in the wild

We examined the individual context of ultrasonic vocalizations (USVs) produced by free-living wild male and female adult brush mice (Peromyscus boylii). We tested the hypothesis that USV production is dependent on behavioral context, and is important during both adult male and female interactions. Our methods included a 12-channel microphone array, radio-telemetry and thermal imaging that allowed us to determine: (1) who produced USVs, (2) characteristics of USVs, (3) type of USVs, (4) behavioral context of USVs and (5) the identity of the second mouse if an individual was not alone when a USV was produced. Females vocalized as much as males and produced the same types of USVs as males. There were no differences between spectral characteristics of male and female USVs. Females and males vocalized in the presence of one another. Importantly, when females were together they vocalized more than expected based on the proportion of time they spent together. Our results suggest that, in addition to facilitating courtship and mating, USVs are general territorial calls for neighbors because females vocalized in the presence of their neighbors. Despite a large literature on laboratory mouse (Mus musculus) USVs, studies are heavily biased towards males. Our results on brush mice, a species with a similar breeding system to the lab mouse and other rodents, suggest that female–female communication is an important and underappreciated component of the evolution and maintenance of mouse USVs.

LoFreq: a sequence-quality aware, ultra-sensitive variant caller for uncovering cell-population heterogeneity from high-throughput sequencing datasets

The study of cell-population heterogeneity in a range of biological systems, from viruses to bacterial isolates to tumor samples, has been transformed by recent advances in sequencing throughput. While the high-coverage afforded can be used, in principle, to identify very rare variants in a population, existing ad hoc approaches frequently fail to distinguish true variants from sequencing errors. We report a method (LoFreq) that models sequencing run-specific error rates to accurately call variants occurring in <0.05% of a population. Using simulated and real datasets (viral, bacterial and human), we show that LoFreq has near-perfect specificity, with significantly improved sensitivity compared with existing methods and can efficiently analyze deep Illumina sequencing datasets without resorting to approximations or heuristics. We also present experimental validation for LoFreq on two different platforms (Fluidigm and Sequenom) and its application to call rare somatic variants from exome sequencing datasets for gastric cancer. Source code and executables for LoFreq are freely available at http://sourceforge.net/projects/lofreq/.

A randomized, double-blind placebo controlled trial of balapiravir, a polymerase inhibitor, in adult dengue patients

Background. Dengue is the most common arboviral infection of humans. There are currently no specific treatments for dengue. Balapiravir is a prodrug of a nucleoside analogue (called R1479) and an inhibitor of hepatitis C virus replication in vivo.

Methods. We conducted in vitro experiments to determine the potency of balapiravir against dengue viruses and then an exploratory, dose-escalating, randomized placebo-controlled trial in adult male patients with dengue with <48 hours of fever.

Results. The clinical and laboratory adverse event profile in patients receiving balapiravir at doses of 1500 mg (n = 10) or 3000 mg (n = 22) orally for 5 days was similar to that of patients receiving placebo (n = 32), indicating balapiravir was well tolerated. However, twice daily assessment of viremia and daily assessment of NS1 antigenemia indicated balapiravir did not measurably alter the kinetics of these virological markers, nor did it reduce the fever clearance time. The kinetics of plasma cytokine concentrations and the whole blood transcriptional profile were also not attenuated by balapiravir treatment.

Conclusions. Although this trial, the first of its kind in dengue, does not support balapiravir as a candidate drug, it does establish a framework for antiviral treatment trials in dengue and provides the field with a clinically evaluated benchmark molecule.

Clinical Trials Registration. NCT01096576.

Aggressiveness of therapy and prognosis of patients with Hürthle cell papillary thyroid carcinoma

Hürthle cell papillary thyroid carcinoma (HCPTC) has been studied separately from other types of thyroid carcinoma in relatively few studies. The aim of our study was to determine the factors associated with the survival of patients with HCPTC in Slovenia, an iodine-deficient region. A total of 1552 patients with thyroid carcinoma were seen at our institute during the period of 1976-2003; of them, 42 patients (33 females, 9 males; age 10-85 years, median 56.5 years) had histopathologically verified HCPTC. The data on the patients' gender, age, disease history, extent of disease, morphologic characteristics, therapy, locoregional control, disease-free interval, and survival were collected. The statistical correlation between possible prognostic factors and the disease-free interval and survival was analyzed by chi2 test and log rank analysis. The tumor diameter ranged from 1 to 9 cm (median, 3 cm). Extrathyroid tumor growth was found in 19 patients, lymph node metastases in 13 patients, and distant metastases in 2 patients. Primary treatment consisted of total or near-total thyroidectomy (39 patients), lobectomy (2 patients), radioiodine ablation of the thyroid remnant (37 patients), external irradiation (14 patients), and chemotherapy (3 patients). Locoregional recurrence was diagnosed in four patients, and dissemination in 1 patient during the follow-up period of 0.75-20 years (median, 5.5 years). Three patients died of thyroid carcinoma during the follow-up period. The 5-year and 10-year survivals were 94% and 87%, respectively. The 5-year and 10-year disease-free intervals were 93% and 81%, respectively. The factors correlated with the survival were: age, extrathyroid tumor growth, primary tumor stage, and regional and distant metastases. Although extrathyroidal tumor growth was found in 45% of the patients with HCPTC, our patients had a favorable prognosis. Long-term survival and locoregional control of disease are likely after the radical tumor resection, radioiodine ablation of the thyroid remnant, and external irradiation.

Flavopiridol administered as a 24-hour continuous infusion in chronic lymphocytic leukemia lacks clinical activity

INTRODUCTION

: Studies with flavopiridol have demonstrated that this agent has in vitro activity in chronic lymphocytic leukemia (CLL) and promotes apoptosis independent of p53 function or prior fludarabine exposure. Based upon this pre-clinical data, a phase I/II study of 24h flavopiridol was performed.

PATIENTS AND METHODS

: Patients with previously treated CLL patients were enrolled on two sequentially performed cohorts of 13 patients. Patients in the first cohort received flavopiridol (80 mg/m(2) as a 24-h continuous infusion [24h CI]) every 2 weeks. Patients in the second cohort received flavopiridol (80 mg/m(2) as a 24h CI) for week 1 and then were dose escalated by 20mg/m(2) every 2 weeks to a maximal dose of 140 mg/m(2) in the absence of symptoms. Patients received up to 12 doses of therapy.

RESULTS

: Thirteen patients with fludarabine-refractory or intolerant CLL enrolled in each cohort. Patients received a median of five treatments in each cohort with only two patients completing all 12 courses of therapy. There were no partial or complete responses noted. Toxicity was manageable in most patients and included anemia, thrombocytopenia, infections, diarrhea, and fatigue.

CONCLUSIONS

: Flavopiridol as a 24-h continuous infusion has no clinical activity in relapsed, fludarabine-refractory CLL.

Inhibition of leukotriene biosynthesis improves renal function in experimental glomerulonephritis

The development of renal dysfunction in experimental glomerulonephritis (GN) is mediated in part by enhanced leukotriene (LT) formation. In our studies the pathophysiological role of LTs was investigated through pharmacological inhibition of LT biosynthesis in a rat model of nephrotoxic serum nephritis. MK-0591, an indirect inhibitor of 5-lipoxygenase activity, was co-administered to rats injected with nephrotoxic rabbit serum, followed by assessment of renal function, morphology and microsomal LTC4 synthase activity on day 7. A significant improvement in glomerular function was noted (p < 0.05), together with a 50% reduction in proteinuria (p < 0.01) in animals receiving MK-0591 (60 mg kg-1 day-1). In addition, the fall in renal LTC4 synthase activity which occurred in nephritic rats (to 74% of control values, p < 0.01) was prevented in drug-treated animals. Based on these results, it appears that inhibition of LT biosynthesis protects against both renal impairment and alterations in LTC4 synthase activity during the development of experimental GN, and may provide a useful therapeutic adjunct in the treatment of this disease.

Renal leukotriene C4 synthase: characterization, partial purification and alterations in experimental glomerulonephritis

Cysteinyl leukotrienes (LT) play an important role in the development of experimental glomerulonephritis (GN). We have partially purified and characterized LTC4 synthase, the enzyme responsible for cysteinyl LT formation, from rat renal microsomes and have investigated this enzyme activity in nephritic rats. LTC4 formation, measured in vitro, was linear for > 10 min at 25 degrees C in the presence of 50 mM serine borate (an inhibitor of gamma-glutamyl transpeptidase), with Km values for LTA4 and GSH of 56 microM and 8.5 mM, respectively. Detergent solubilization and anion-exchange chromatography of microsomal proteins resulted in a 7-fold increase in enzyme specific activity. Enzymatic and immunoblot analysis demonstrated that cytosolic and microsomal glutathione S-transferase (GST) activities were distinct from LTC4 synthase activity. Comparison of LTC4 synthase activity in nephritic rats over 21 days revealed an initial increase over the first 24 h following injection of nephrotoxic sera, followed by a subsequent decline until day 7 and a gradual recovery by day 21. Inhibition of LT biosynthesis with MK-0591 (10 mg kg-1 d-1) reduced GN-associated proteinuria by 72% (P < 0.05). These results suggest a potential mechanism for enhanced cysteinyl LT formation in the development of experimental GN and further support their causal role in the etiology of this disease.

Elevated cysteinyl leukotriene excretion in experimental glomerulonephritis

The involvement of cysteinyl leukotrienes (LT) in the etiology of glomerulonephritis (GN) was investigated in a rat model of nephrotoxic serum nephritis in which renal function, morphology, LTC4 synthase activity and urinary cysteinyl LT excretion were monitored over seven days. Significant alterations in renal function and morphology were evident on day 1 in nephritic rats, with a 12% decline in creatinine clearance, a greater than three-fold increase in urinary protein excretion and histologic evidence of basement membrane thickening. Urinary LTC4 excretion in the nephritic rats was elevated at this time to 140 +/- 38 pg/hr (P < 0.01) compared to undetectable levels in control animals. On days 3 and 7, while proteinuria intensified and glomerular filtration remained depressed, LTC4 excretion declined 14% (NS) and 79% (P < 0.05), respectively. The temporal changes in urinary LTC4 excretion were paralleled by concomitant alterations in LTC4 synthase activity in renal cortical microsomes, where an 84% (P < 0.01) drop in enzyme activity occurred from day 1 to day 7 in the nephritic group. This data provides the first measurement of urinary cysteinyl LT excretion and altered LTC4 synthase activity in a model of experimental GN and supports an early role for LT's in the development of subsequent functional changes.

Modulation of experimental cyclosporine nephrotoxicity by inhibition of thromboxane synthesis

The clinical usefulness of Cyclosporine is limited by its intrinsic nephrotoxicity. A potential mechanism of CsA-mediated renal injury may involve an alteration in the prostaglandin-thromboxane (PG-TX) cascade. In our studies, pharmacological manipulation of the PG-TX system in normal and nephrotoxic animals was conducted using a specific thromboxane synthetase inhibitor U63,557A, and the cyclooxygenase inhibitor indomethacin. Administration of CsA 50 mg/kg/day for 7 days to Sprague Dawley rats resulted in a 99% increase in urinary thromboxane B2 excretion compared with controls (48.2 +/- 3.1 vs. 24.2 +/- 2.6 ng/24 hr, P less than 0.001), while plasma levels remained unchanged. Glomerular and tubular function was significantly reduced at this time, with a 48% decrease in creatinine clearance (CCr), and a 25% reduction in the fractional excretion of sodium (FeNa) (P less than 0.001). Histological injury included cortical tubular vacuolization and necrosis. Administration of indomethacin 8 mg/kg/day to both normal and CsA-treated rats resulted in a significant reduction in prostanoid excretion. Indomethacin alone had no adverse effect on glomerular function; however, when coadministered with CsA an exaggerated decrease in renal function was observed. CCr in this group fell by a further 27% compared with the CsA-50 group, while FeNa decreased by 76% (P less than 0.001). Histologic injury intensified, with an increase in vacuolization and necrosis. In contrast, coadministration of U63,557A with CsA prevented the rise in urinary TXB2 excretion, improved CCr by 20% (P less than 0.05), and restored FeNa to control levels. The severity of CsA-induced vacuolization was significantly diminished. Selective inhibition of thromboxane production may therefore be valuable in mitigating the clinical nephrotoxicity of CsA.

Effect of cyclosporine on plasma lipids and modification with dietary fish oil

Hyperlipidemia is an identified risk factor for atherosclerosis in patients following renal transplantation that may be related to previous uremia and various drugs including steroids. Recent evidence has suggested that treatment with cyclosporine may be an independent risk factor for development of hyperlipidemia in some patients. Twenty-four Sprague Dawley rats were given CsA at 30 mg/kg by gavage for 28 days in 1 ml of olive oil or fish oil vehicle, and compared with controls receiving just vehicle. Increases of both triglyceride (233.6%) and cholesterol (50.9%) were observed in olive oil/CsA animals (P less than .01), with no significant change noted with either vehicle alone. An increase of triglyceride from baseline was observed with fish oil/CsA (119%) (P less than .01) but was significantly less than the increase with olive oil/CsA animals (P less than .05). No increase in cholesterol was found in CsA-treated rats using the fish oil vehicle. The mechanisms leading to hyperlipidemia with four weeks of CsA administration in these rats are unknown, but may be related to altered hepatic synthesis. CsA levels were lower in fish oil-treated animals, possibly explaining the difference noted in lipid levels--or, alternatively, reduction of plasma lipoproteins may have altered drug kinetics and CsA binding. This work emphasizes a need for further study of lipids in CsA-treated patients, and advises some caution in the use of lipoprotein-reducing agents in patients using CsA without consideration of the possible effect on free drug levels.

Effect of cyclosporine on urinary prostanoid excretion, renal blood flow, and glomerulotubular function

The clinical usefulness of cyclosporine (CsA) in organ transplantation and autoimmune diseases is limited by its intrinsic nephrotoxicity. The mechanism of this renal impairment was examined utilizing an animal model in which male Sprague-Dawley rats were administered oral CsA in doses of 25, 37.5, and 50 mg/kg/day for 7 days and 50 mg/kg/day for 2, 4, and 7 days. Urinary thromboxane B2 (TXB2) excretion increased from 30.6 +/- 2.3 to 60.8 +/- 4.4 ng/24 hr P less than 0.001, following 48 hr of CsA dosing. In addition, a concomitant rise in proximal tubular sodium reabsorption was observed with fractional excretion of sodium decreasing from 0.502 +/- 0.091 to 0.223 +/- 0.037% P less than 0.05. Urinary prostaglandin E2 and 6-keto-prostaglandin F1 alpha excretion increased two-fold, although plasma levels of all 3 prostanoids did not vary from controls. Functional changes included decreases in the relative renal blood flow of 53% P less than 0.05, and the clearance of creatinine and urea of 46% and 42%, respectively on day 7 of treatment, while renal morphology showed severe vacuolization and necrosis confined to the proximal tubular region of the cortex. Thromboxane A2, the active precursor of TXB2, is a potent vasoconstrictor and promoter of platelet aggregation and may alter proximal tubular handling of sodium. The rise in urinary TXB2 excretion may contribute to the renal vasoconstriction leading to functional impairment and histologic injury.