Peripheral signaling pathways contributing to non-histaminergic itch in humans.

BACKGROUND: Chronic itch (chronic pruritus) is a major therapeutic challenge that remains poorly understood despite the extensive recent analysis of human pruriceptors. It is unclear how the peripheral nervous system differentiates the signaling of non-histaminergic itch and pain. METHODS: Here we used psychophysical analysis and microneurography (single nerve fiber recordings) in healthy human volunteers to explore the distinct signaling mechanisms of itch, using the pruritogens ß-alanine, BAM 8-22 and cowhage extract. RESULTS: The mode of application (injection or focal application using inactivated cowhage spicules) influenced the itch/pain ratio in sensations induced by BAM 8-22 and cowhage but not ß-alanine. We found that sensitizing pre-injections of prostaglandin E2 increased the pain component of BAM 8-22 but not the other pruritogens. A-fibers contributed only to itch induced by ß-alanine. TRPV1 and TRPA1 were necessary for itch signaling induced by all three pruritogens. In single-fiber recordings, we found that BAM 8-22 and ß-alanine injection activated nearly all CM-fibers (to different extents) but not CMi-fibers, whereas cowhage extract injection activated only 56% of CM-fibers but also 25% of CMi-fibers. A "slow bursting discharge pattern" was evoked in 25% of CM-fibers by ß-alanine, in 35% by BAM 8-22, but in only 10% by cowhage extract. CONCLUSION: Our results indicate that no labeled line exists for these pruritogens in humans. A combination of different mechanisms, specific for each pruritogen, leads to itching sensations rather than pain. Notably, non-receptor-based mechanisms such as spatial contrast or discharge pattern coding seem to be important processes. These findings will facilitate the discovery of therapeutic targets for chronic pruritus, which are unlikely to be treated effectively by single receptor blockade.

Honeycomb Epithelial Edema Associated With Rho Kinase Inhibition: A Case Series and Review of the Literature.

ABSTRACT: The Rho kinase inhibitor netarsudil is a recently approved therapeutic option for the management of increased intraocular pressure in the United States. Although phase 3 clinical trials noted corneal changes related to the medication-namely, nonvisually-significant corneal verticillata-descriptions of a unique form of cystic epithelial edema began to surface as netarsudil (and its sister drug ripasudil, approved in Japan) gained widespread use. This series adds 3 new cases and reviews the current literature on this unique side effect.

Pruriception and neuronal coding in nociceptor subtypes in human and nonhuman primates.

In humans, intradermal administration of ß-alanine (ALA) and bovine adrenal medulla peptide 8-22 (BAM8-22) evokes the sensation of itch. Currently, it is unknown which human dorsal root ganglion (DRG) neurons express the receptors of these pruritogens, MRGPRD and MRGPRX1, respectively, and which cutaneous afferents these pruritogens activate in primate. In situ hybridization studies revealed that MRGPRD and MRGPRX1 are co-expressed in a subpopulation of TRPV1+ human DRG neurons. In electrophysiological recordings in nonhuman primates (Macaca nemestrina), subtypes of polymodal C-fiber nociceptors are preferentially activated by ALA and BAM8-22, with significant overlap. When pruritogens ALA, BAM8-22, and histamine, which activate different subclasses of C-fiber afferents, are administered in combination, human volunteers report itch and nociceptive sensations similar to those induced by a single pruritogen. Our results provide evidence for differences in pruriceptive processing between primates and rodents, and do not support the spatial contrast theory of coding of itch and pain.

Safety and efficacy of topically administered netarsudil (Rhopressa™) in normal and glaucomatous dogs with ADAMTS10-open-angle glaucoma (ADAMTS10-OAG).

OBJECTIVE: To evaluate safety and efficacy of topically administered 0.02% netarsudil ophthalmic solution (Rhopressa™; Aerie Pharmaceutical) in normal and glaucomatous dogs with ADAMTS10-open-angle glaucoma (ADAMTS10-OAG). ANIMALS STUDIED: Five normal and 5 glaucomatous Beagle dogs with ADAMTS10-OAG. PROCEDURES: In each dog, left or right eye was randomly selected for netarsudil treatment. Contralateral eyes were sham-treated with balanced salt solution (BSS). Following a 1-week baseline period, dogs were treated once daily (q24h) during week 2, and twice daily (q12h) during week 3; week 4 served as washout period. Efficacy was measured by diurnal intraocular pressure (IOP) and pupil diameter. Safety was assessed by routine ophthalmic examination, gonioscopy, and pachymetry. Differences in least square means of quantitative outcome measures were compared between netarsudil and BSS sham-treated eyes by linear Gaussian model. RESULTS: Baseline IOPs were 18.5 ± 0.5 mm Hg (mean ± SEM) in normal and 27.8 ± 1.0 mm Hg in OAG dogs. Even though mean IOPs were lower in netarsudil- vs sham-treated eyes, the overall differences were neither significant nor clinically relevant, regardless of treatment frequency (q24h-normal: sham 16.4 ± 1.1 mm Hg vs treatment 15.6 ± 1.0 mm Hg; q24hr-OAG: sham 25.8 ± 2.3 mm Hg vs. treatment 25.7 ± 2.4 mm Hg; q12hr-normal: sham 15.4 ± 0.8 mm Hg vs. treatment 14.4 ± 0.8 mm Hg; q12hr-OAG: sham 26.3 ± 1.7 mm Hg vs. treatment 25.4 ± 1.8 mm Hg). Netarsudil administration was well tolerated but resulted in significant, moderate-to-severe conjunctival hyperemia (P < .001). CONCLUSIONS: Once or twice daily administration of netarsudil resulted in marginal and clinically irrelevant IOP decreases in normal and OAG-affected dogs. Except for conjunctival hyperemia, the drug was well tolerated.

Effects of 0.02% netarsudil ophthalmic solution on intraocular pressure of normotensive dogs.

OBJECTIVES: To evaluate the effect of QD or BID 0.02% netarsudil ophthalmic solution (Aerie Pharmaceuticals) on intraocular pressure (IOP) in normotensive dogs and to describe any adverse effects. ANIMALS STUDIED: Normotensive Labrador retriever dogs were included in this study: 10 received netarsudil in one eye and artificial tears in the contralateral eye QD, and 10 received netarsudil in one eye and artificial tears in the contralateral eye BID. PROCEDURES: Intraocular pressure curves were acquired over a 3-day acclimation period, 5-day dosing period (QD or BID-10 dogs/group), and 3-day recovery period. Toxicity was assessed daily using slit-lamp biomicroscopy and the semiquantitative preclinical ocular toxicology scoring system. RESULTS: Once-daily dosing did not lower IOP over the entire 5-day dosing period (95% CI 0.1 to -0.9 mm Hg, P = .20) or on the last day of dosing (95% CI 0.4 to -0.9 mm Hg, P = .65). Twice-daily dosing resulted in a statistically significant, but clinically unimportant, IOP reduction over the entire 5-day dosing period (-0.6 mm Hg; 95% CI 0.05 to -1.1 mm Hg, P = .02) and on the last day of dosing (-0.9 mm Hg; 95% CI 0.2 to -1.5 mm Hg, P = .003). Adverse events were limited to transient mild-to-moderate conjunctival hyperemia during the dosing phase in eyes receiving netarsudil vs control (P < .0001). CONCLUSIONS: Netarsudil 0.02% ophthalmic solution twice daily resulted in a small, statistically significant, but clinically unimportant, IOP reduction in normotensive dogs. Future studies should investigate efficacy in glaucomatous dogs.

Reticular Epithelial Edema: An Uncommon Side Effect of ROCK/NET Inhibitor Netarsudil.

A 66-year-old female with advanced primary open-angle glaucoma and Descemet's stripping endothelial keratoplasty OD with previously noted inferior stromal edema presented with a 1-month history of progressive decreased visual acuity after starting netarsudil twice daily. Her best-corrected visual acuity was 20/80 OD and no light perception OS. The right cornea was notable for inferior small epithelial bullae in a reticular pattern from 2 to 9 o'clock encroaching on the visual axis involving both sides of the graft-host junction. The reticular epithelial edema resolved upon discontinuation of netarsudil and best-corrected visual acuity improved to 20/50 but was limited by persistent stromal edema. We report a patient with a history of a partially decompensated Descemet's stripping endothelial keratoplasty who develops reticular epithelial corneal edema after starting netarsudil. This unique pattern of edema may present in the setting of preexisting endothelial cell dysfunction when netarsudil is used, a complication not noted in the Food and Drug Administration (FDA) trials.

Pooled Efficacy and Safety Profile of Netarsudil Ophthalmic Solution 0.02% in Patients With Open-angle Glaucoma or Ocular Hypertension.

PRECIS: In pooled phase III analyses, once-daily netarsudil 0.02% resulted in intraocular pressure (IOP) reduction that was noninferior to twice-daily timolol 0.5%, with minimal treatment-related serious or systemic adverse events (AEs). Ocular AEs were generally tolerable. PURPOSE: The purpose of this study was to assess the efficacy and safety of the Rho kinase inhibitor netarsudil in patients with open-angle glaucoma or ocular hypertension. PATIENTS AND METHODS: Pooled analysis of data from the ROCKET-1 to 4 phase III studies of once-daily (PM) netarsudil or twice-daily timolol in patients with open-angle glaucoma or ocular hypertension. The primary efficacy measure was mean IOP at 8:00 AM, 10:00 AM, and 4:00 PM at week 2, week 6, and month 3 in patients with baseline IOP <25 mm Hg. RESULTS: In the pooled primary efficacy population (netarsudil, n=494; timolol, n=510), once-daily netarsudil was noninferior to twice-daily timolol at all 9 timepoints through month 3. Mean treated IOP ranged from 16.4 to 18.1 mm Hg among netarsudil-treated patients and 16.8 to 17.6 mm Hg among timolol-treated patients. In the pooled safety population (n=839 in each treatment group), treatment-related serious AEs occurred at similar frequencies in each treatment group (netarsudil, 0.1%; timolol, 0%). The most common ocular AE, conjunctival hyperemia (netarsudil, 54.4%; timolol, 10.4%), was graded as mild in 77.6% (354/456) of affected netarsudil-treated patients. CONCLUSIONS: Once-daily netarsudil resulted in IOP lowering that was noninferior to twice-daily timolol, with tolerable ocular AEs that were generally mild and self-resolving. As a first-in-class agent in the United States, with a novel mechanism of action, netarsudil may provide a useful therapeutic option for patients who would benefit from IOP lowering.

Reticular Corneal Edema or Corneal Honeycombing in Eyes Treated With Netarsudil: A Case Series.

This is a descriptive case series of 3 patients with uncontrolled intraocular pressure that developed reticular corneal changes after initiating netarsudil (0.02%). In all cases, upon observing reticular corneal edema, netarsudil (0.02%) was stopped followed by disappearance of corneal honeycombing. With the increasing use of this novel glaucoma medication, potentially more rare side effects will be observed. Reticular corneal edema or corneal honeycombing is an ocular examination finding that can rarely occur after initiating netarsudil (0.02%) regardless of prior corneal edema status. In our experience, the reticular changes resolve upon cessation of netarsudil.

Reversible Corneal Endothelial Abnormalities With Netarsudil.

PURPOSE: To report a case of reversible corneal endothelial abnormalities after treatment with netarsudil. OBSERVATION: A 68-year-old woman presented with the complaint of blurred vision soon after starting treatment with the fixed-dose combination of netarsudil and latanoprost (FC-netarsudil-latanoprost). She had been receiving the fixed-dose combination of dorzolamide and timolol and latanoprost for primary open-angle glaucoma until her ophthalmologist switched latanoprost to FC-netarsudil-latanoprost 2 months before referral to our center.Best-corrected visual acuity was 20/20-1 in the right eye and 20/20-3 in the left eye. The slit-lamp biomicroscopic examination was remarkable for a guttata-like abnormality of the corneal endothelium of both eyes. The intraocular pressure was 10 mm Hg in both eyes. Specular microscopy revealed irregularly shaped corneal endothelial cells with indistinct borders between cells. FC-netarsudil-latanoprost was replaced with latanoprost in the left eye but continued in the right eye. Nine weeks later, best-corrected visual acuity remained 20/20-1 in the right eye but it improved to 20/20 in the left eye. Repeat specular microscopy was unchanged in the right eye and was normal in the left eye. CONCLUSION AND IMPORTANCE: Topical therapy with netarsudil can result in guttata-like changes of the corneal endothelium and corneal endothelial cell abnormalities that can be detected with specular microscopy. These abnormalities seem to be transient and resolved upon the cessation of netarsudil. Ophthalmologists should consider the possibility of a corneal endothelial abnormality in patients treated with netarsudil who develop blurred vision.

Fixed-Dose Combination of Netarsudil and Latanoprost in Ocular Hypertension and Open-Angle Glaucoma: Pooled Efficacy/Safety Analysis of Phase 3 MERCURY-1 and -2.

INTRODUCTION: New open-angle glaucoma (OAG) and ocular hypertension (OHT) therapies that reduce treatment burden and improve outcomes relative to currently available agents are needed. Netarsudil, a novel Rho kinase inhibitor approved by the US Food and Drug Administration, reduces intraocular pressure (IOP) by increasing trabecular outflow. Two phase 3 superiority studies compared a fixed-dose combination (FDC) of netarsudil and the prostaglandin latanoprost with each active component for IOP-lowering efficacy. METHODS: Pooled efficacy and safety data were analyzed from MERCURY-1 and -2 studies in patients with OAG or OHT. Patients instilled one drop of netarsudil (0.02%)/latanoprost (0.005%) FDC (n = 483), netarsudil (0.02%, n = 499), or latanoprost (0.005%, n = 486) into each eye once-daily between 20:00 and 22:00. IOP was measured at 08:00, 10:00, and 16:00 at weeks 2, 6, and the primary endpoint at month 3. RESULTS: Baseline mean diurnal IOP was 23.6, 23.6, and 23.5 mmHg in netarsudil/latanoprost FDC, netarsudil, and latanoprost groups, respectively. Mean diurnal IOP in each group was 15.3, 18.1, and 17.5 mmHg at week 2, 15.7, 18.4, and 17.4 mmHg at week 6, and 15.8, 18.4, and 17.3 mmHg at week 12. The netarsudil/latanoprost FDC met criteria for superiority compared with each active component (p < 0.0001 for all nine time points). At month 3, among patients randomized to netarsudil/latanoprost FDC or latanoprost, 58.4% vs 37.3% (p < 0.0001) achieved IOP ≤ 16 mmHg. Among patients randomized to netarsudil/latanoprost FDC or netarsudil or latanoprost, 30.9% vs 5.9% (p < 0.0001) vs 8.5% (p < 0.0001) achieved at least a 40% reduction from baseline in mean diurnal IOP. Pooled safety results were consistent with individual MERCURY studies. CONCLUSION: Once-daily netarsudil/latanoprost FDC produced statistically significant and clinically relevant reductions in mean IOP that were statistically superior to IOP reductions achieved by netarsudil and latanoprost monotherapy. Results of the pooled efficacy and safety analyses were consistent with the individual studies. TRIAL REGISTRATION: ClinicalTrials.gov identifiers, NCT02558400 and NCT02674854.

In patients with open-angle glaucoma (OAG) or ocular hypertension (OHT), treatment to lower intraocular pressure (IOP) is needed to prevent optic nerve damage and vision loss. Many patients do not achieve sufficient IOP lowering with a single drug. The use of multiple IOP-lowering agents, which may have different dose regimens, can be complex and reduce patient adherence. Combination treatments that incorporate multiple agents are available, but until recently none included a prostaglandin analogue, the most widely prescribed first-line therapy. A once-daily, fixed-dose combination (FDC) therapy (ROCKLATAN^®) has been approved in the USA that contains the prostaglandin analogue latanoprost and netarsudil, a novel Rho kinase inhibitor. The netarsudil/latanoprost FDC demonstrated efficacy and safety in lowering IOP among patients with OAG and OHT in the 12-month MERCURY-1 and the 3-month MERCURY-2 clinical trials. To better characterize efficacy and safety, we pooled and analyzed the data from each trial. The pooled data support the findings of the individual studies:Efficacy: 1. Netarsudil/latanoprost FDC demonstrated statistical superiority to the individual components netarsudil and latanoprost in decreasing IOP at all time points assessed over 3 months. 2. Nearly twice as many patients receiving FDC achieved at least a 30% reduction from baseline in IOP, as recommended by the American Academy of Ophthalmology for a first-line treatment, compared to the IOP reduction achieved by netarsudil and latanoprost monotherapy.Safety: No new safety signals were identified. Netarsudil/latanoprost FDC was associated with no treatment-related serious adverse events, minimal systemic adverse events, and manageable ocular adverse events.

Effects of Netarsudil and Latanoprost Alone and in Fixed Combination on Corneal Endothelium and Corneal Thickness: Post-Hoc Analysis of MERCURY-2.

INTRODUCTION: To describe the changes in endothelial cell density (ECD), the coefficient of variation (CV), the percentage of hexagonal cells (%HEX), and central corneal thickness (CCT) following 3 months of therapy with netarsudil 0.02%/latanoprost 0.005% fixed combination, and to compare these changes with those seen with netarsudil 0.02% or latanoprost 0.005% in eyes with ocular hypertension or open-angle glaucoma. METHODS: A subset of subjects enrolled in a Phase 3 evaluation of the intraocular pressure-lowering efficacy and safety of netarsudil 0.02%/latanoprost 0.005% fixed combination once daily (QD) versus each of its individual components underwent corneal endothelial cell imaging by specular microscopy and ultrasound pachymetry at baseline and following 3 months of therapy. Images were evaluated in masked fashion at an independent reading center. Changes from baseline to 3 months in ECD, CV, %HEX, and CCT were compared between treatment groups. RESULTS: Data from 415 subjects obtained at both baseline and Month 3 were included in this post hoc analysis. Changes from baseline to Month 3 in ECD, CV, and %HEX were clinically insignificant in all three groups, and the changes in the netarsudil/latanoprost fixed combination group demonstrated no statistical difference from those seen in the netarsudil and latanoprost groups. Mean CCT decreased more in the fixed combination group (- 6.4 µm) than in either the netarsudil group (- 3.3 µm, p = 0.0248) or the latanoprost group (- 1.2 µm, p < 0.0001). CONCLUSIONS: Netarsudil 0.2%/latanoprost 0.005% fixed combination QD for 3 months in eyes with ocular hypertension or open-angle glaucoma had no clinically significant effects on endothelial cell density or morphology. The significant decrease in CCT in the fixed combination group compared to the two individual component groups may indicate that the potential effects of each drug on CCT are additive, although the magnitude of the observed effects is likely of negligible clinical significance. CLINICALTRIALS. GOV IDENTIFIER: NCT02674854.

Netarsudil and latanoprost ophthalmic solution for the reduction of intraocular pressure in open-angle glaucoma or ocular hypertension.

Introduction: Netarsudil and latanoprost ophthalmic solution (0.02%/0.005%) is indicated for intraocular pressure (IOP) lowering in open-angle glaucoma (OAG) or ocular hypertension (OHTN). The once-daily agent combines the mechanism of action for each of the individual components and provides a new avenue for long-term intraocular pressure control. This review aims to cover the agent's current efficacy and safety data and opine as to its role in glaucoma management.Areas covered: This article will cover Phase II-III clinical efficacy and safety data as well as basic science literature pertaining to the agent's mechanism of action and pharmacodynamics. In selecting articles for inclusion in this review, a literature search using the PubMed database was carried out. Cross-referencing was carried out where applicable. We did not use any date or language restrictions in electronic searches.Expert opinion: Netarsudil and latanoprost ophthalmic solution plays a pivotal role in management of individuals with OAG and OHTN. The agent may be used as first-line therapy to provide substantial IOP-lowering or when additional lowering is indicated and prostaglandins have provided insufficient IOP lowering. The once-daily dosing regimen decreases the risk of inadequate treatment due to nonadherence.

Netarsudil/Latanoprost Fixed-Dose Combination for Elevated Intraocular Pressure: Three-Month Data from a Randomized Phase 3 Trial.

PURPOSE: To compare the ocular hypotensive efficacy and safety of a fixed-dose combination (FDC) of the Rho kinase inhibitor netarsudil and latanoprost vs monotherapy with netarsudil or latanoprost. DESIGN: Three-month primary endpoint analysis of a randomized, double-masked, phase 3 clinical trial. METHODS: Adults with open-angle glaucoma or ocular hypertension (unmedicated intraocular pressure [IOP] >20 and <36 mm Hg at 8:00 AM) were randomized to receive once-daily netarsudil/latanoprost FDC, netarsudil 0.02%, or latanoprost 0.005% for up to 12 months. The primary efficacy endpoint was mean IOP at 8:00 AM, 10:00 AM, and 4:00 PM at week 2, week 6, and month 3. RESULTS: Mean treated IOP ranged from 14.8-16.2 mm Hg for netarsudil/latanoprost FDC, 17.2-19.0 mm Hg for netarsudil, and 16.7-17.8 mm Hg for latanoprost. Netarsudil/latanoprost FDC met the criteria for superiority to each active component at all 9 time points (all P < .0001), lowering IOP by an additional 1.8-3.0 mm Hg vs netarsudil and an additional 1.3-2.5 mm Hg vs latanoprost. At month 3, the proportion of patients achieving mean diurnal IOP ≤15 mm Hg was 43.5% for netarsudil/latanoprost FDC, 22.7% for netarsudil, and 24.7% for latanoprost. No treatment-related serious adverse events were reported; treatment-related systemic adverse events were minimal. The most frequent ocular adverse event was conjunctival hyperemia (netarsudil/latanoprost FDC, 53.4%; netarsudil, 41.0%; latanoprost, 14.0%), which led to treatment discontinuation in 7.1% (netarsudil/latanoprost FDC), 4.9% (netarsudil), and 0% (latanoprost) of patients. CONCLUSIONS: Once-daily netarsudil/latanoprost FDC demonstrated IOP reductions that were statistically and clinically superior to netarsudil and latanoprost across all 9 time points through month 3, with acceptable ocular safety.

Long-term Safety and Ocular Hypotensive Efficacy Evaluation of Netarsudil Ophthalmic Solution: Rho Kinase Elevated IOP Treatment Trial (ROCKET-2).

PURPOSE: To evaluate netarsudil 0.02% ophthalmic solution in patients with open-angle glaucoma (OAG) and ocular hypertension (OHT). DESIGN: Double-masked, randomized, multicenter, parallel-group, noninferiority clinical study. METHODS: After a washout of all prestudy ocular hypotensive medications, 756 eligible patients with elevated IOP were randomized to receive netarsudil 0.02% once a day (q.d.) (251); netarsudil 0.02% twice a day (b.i.d.) (254); or timolol 0.5% b.i.d. (251) for 12 months, as well as a noninterventional Corneal Observation Study (COS) for patients manifesting cornea verticillata. RESULTS: On treatment, mean IOP at 8:00 AM decreased from a baseline IOP of 22.5-22.6 mm Hg to 17.9-18.8 mm Hg, 17.2-18.0 mm Hg, and 17.5-17.9 mm Hg for netarsudil q.d., netarsudil b.i.d., and timolol, respectively, over 12 months. The most frequently reported adverse events (AEs) were ocular, with the most frequent ocular AE being conjunctival hyperemia, with an incidence of 61%, 66%, and 14%, respectively. The next most frequent AEs were corneal deposits (corneal verticillata), with an incidence of 26%, 25%, and 1%, respectively, and conjunctival hemorrhage (typically petechial), with an incidence of 20%, 19%, and 1%, respectively. All 3 AEs were generally scored as mild, with conjunctival hyperemia and/or hemorrhage appearing sporadically during the study. In the observational follow-up component of this study, there was no clinically meaningful impact of corneal verticillata on visual function in affected patients. CONCLUSIONS: In this randomized, double-masked trial, once-daily dosing of netarsudil 0.02% was effective, consistently lowering IOP through 12 months, and was tolerated by the majority of patients.

A new, sensitive and versatile assay for quantitative determination of α-fluoro-ß-alanine (AFBA) in human urine by using the reversed-phase ultrahigh performance-tandem mass spectrometry (rp-UHPLC-MS/MS) system.

A method for the quantitation of α-fluoro-ß-alanine (AFBA), the main metabolite of capecitabine (Cape) and 5-fluoruracil (5-FU), is described. Among antineoplastic drugs (ADs), 5-FU and Cape (the new oral prodrug) are the most commonly applied drugs in cancer therapy. The main objective of this study was to develop a reliable method that would be easy to run on a reversed-phase UHPLC system coupled to tandem mass spectrometry. AFBA was derivatized with Sanger's reagent to ensure complete yield of a stable 2,4 dinitrophenil-α-fluoro-ß-alanine derivative. This method was based on the use of a mixed-mode anion exchange solid phase extraction enabling urinary extracts to be clear of endogenous interferences affecting quantitative results. The assay was validated in human urine according to FDA criteria with the use of a labeled internal standard (ß-alanine-d4) to minimize experimental error. Good accuracy and precision were demonstrated by determining spiked urine QC samples in four consecutive days. The recovery of AFBA was between 70.0 and 82.6%, with a matrix effect that was 12.8%-18.5%. The lower limit of quantitation (LOQ) was 0.5 ng/mL with a coefficient of variation of 5.3%. This assay was successfully applied to determine the levels of this metabolite in a large number of urine samples taken from personnel who were occupationally exposed to ADs.