An in vivo Caenorhabditis elegans model for therapeutic research in human prion diseases.

Human prion diseases are fatal neurodegenerative disorders that include sporadic, infectious and genetic forms. Inherited Creutzfeldt-Jakob disease due to the E200K mutation of the prion protein-coding gene is the most common form of genetic prion disease. The phenotype resembles that of sporadic Creutzfeldt-Jakob disease at both the clinical and pathological levels, with a median disease duration of 4 months. To date, there is no available treatment for delaying the occurrence or slowing the progression of human prion diseases. Existing in vivo models do not allow high-throughput approaches that may facilitate the discovery of compounds targeting pathological assemblies of human prion protein or their effects on neuronal survival. Here, we generated a genetic model in the nematode Caenorhabditis elegans, which is devoid of any homologue of the prion protein, by expressing human prion protein with the E200K mutation in the mechanosensitive neuronal system. Expression of E200K prion protein induced a specific behavioural pattern and neurodegeneration of green fluorescent protein-expressing mechanosensitive neurons, in addition to the formation of intraneuronal inclusions associated with the accumulation of a protease-resistant form of the prion protein. We demonstrated that this experimental system is a powerful tool for investigating the efficacy of anti-prion compounds on both prion-induced neurodegeneration and prion protein misfolding, as well as in the context of human prion protein. Within a library of 320 compounds that have been approved for human use and cross the blood-brain barrier, we identified five molecules that were active against the aggregation of the E200K prion protein and the neurodegeneration it induced in transgenic animals. This model breaks a technological limitation in prion therapeutic research and provides a key tool to study the deleterious effects of misfolded prion protein in a well-described neuronal system.

Evaluation of benzocaine-based anesthetic gel in anuran skins extracts: A case study using the frog Lithodytes lineatus (Anura: Leptodactylidae).

Extracts made from the skin of dead Lithodytes lineatus frog individuals with the application of the benzocaine-based anesthetic gel, introduced into the oral cavity, were analyzed by 1H Nuclear Magnetic Resonance to investigate whether the application of this product (oral) can make studies that use extracts from the skins of these animals unfeasible. For comparison, we used skins of another species of anuran following the same death protocol. No trace of the benzocaine substance was found in the 1H-NMR spectra of the skin extracts from any of the tested anuran species. Still, using the hierarchical clustering model, it was possible to observe the formation of well-defined groups between the skin extracts of anurans and the anesthetic used to kill these animals. Our results suggest that the lethal dose of benzocaine in gel used inside the mouth of frogs may have no influence on potential results regarding the chemical composition or even bioassays using extracts made from the skin of these animals killed under this protocol since there was no detection of this substance for the analyzed samples.

Potential of mucoadhesive nanocapsules in drug release and toxicology in zebrafish.

Mucoadhesive polymeric nanocapsules have attracted interest of researchers from different fields from natural sciences because of their ability to interact with the mucosa and increase drug permeation. Anesthesia by immersion causes absorption through the skin and gills of fish, so it is important to evaluate the exposure of these organs to drug nanosystems. Benzocaine (BENZ) is one of the most popular anesthetic agents used in fish anesthesia, but it has drawbacks because of its low bioavailability, resulting in weak absorption after immersion. Here we describe method developed for preparing and characterizing chitosan-coated PLGA mucoadhesive nanoparticles containing BENZ (NPMAs) for zebrafish immersion anesthesia. We determined the lowest effective concentration, characterized the interaction of the mucoadhesive system with fish, measured the anesthetic efficacy, and evaluated possible toxic effects in embryos and adults exposed to the nanoformulations. This study opens perspectives for using nanoformulations prepared with BENZ in aquaculture, allowing reduction of dosage as well as promoting more effective anesthesia and improved interaction with the mucoadhesive system of fish.

Influence of Topical Anesthesia on Superficial Sensitivity: A Double-Blind, Randomized, Placebo-Controlled Study on 48 Healthy Subjects.

BACKGROUND: Topical anesthetics are used in noninvasive transdermal anesthesia to decrease the superficial pain sensation threshold during dermatologic surgery. Combined pain relief and sensitivity loss can avoid discomfort during the surgery. OBJECTIVE: The aim of this placebo-controlled study was to compare the efficacy of 3 commonly used topical agents by collating loss of sensitivity over time. MATERIALS AND METHODS: Three topical anesthetic creams, a topical anti-inflammatory cream, and a moisturizing cream were applied on the left volar forearm of each of the 48 healthy Caucasian participants. Sensitivity was assessed with the dynamic 2-point discrimination and the Semmes-Weinstein test at 0, 60, 90, 120, 150, and 180 minutes after cream application. RESULTS: After 180 minutes, benzocaine showed a significantly lower 2-point discrimination reduction than lidocaine alone and a lidocaine and prilocaine mixture. Sensory threshold measurements by the Semmes-Weinstein test after 60 minutes revealed a significantly higher effect with lidocaine alone and with the lidocaine and prilocaine mixture than with benzocaine. CONCLUSION: The authors found a stronger skin sensitivity reduction by the eutectic lidocaine and prilocaine mixture and lidocaine alone compared with benzocaine. We suggest increased discomfort reduction in topical anesthetic supported dermatologic surgery by the eutectic mixture and lidocaine alone.

Chitosan-collagen based film for controlled delivery of a combination of short life anesthetics.

The present research was undertaken to develop a chitosan-collagen film for controlled delivery of combinations of local anesthetics. The film has been prepared by casting which is a versatile, rapid and low-cost approach distinguished by high reproducibility. The mechanical, morphological, and physicochemical properties of the films and the impact of the drug loading were evaluated. We showed that the formulations have a good combination of strength and flexibility with high water permeability. Surface morphology investigation indicates a variation in roughness depending on the loaded compound. Release studies were performed in controlled environments and the data processed by the Higuchi model to assess the dynamics of the release. The local anesthetics, lidocaine, tetracaine, and benzocaine, were uniformly distributed within the matrix and released in a rate and magnitude specific for the drug concentration and combination tunable in a range time from 6 h to 24 h. The films dissolve completely in the physiological environment within 24 h without leaving any toxic metabolites as both of the components are recognized as safe. In vitro cytotoxicity and cell proliferation tests performed on human dermal fibroblast demonstrate the biocompatibility and lack of cytotoxicity of the prepared formulations.

Efficacy of Topical Benzocaine in Maxilla: A Randomized Controlled Trial.

This study aims to compare the effect of topical anesthesia against the use of no topical agent on pain of needle penetration and local anesthesia deposition during buccal infiltration in anterior maxilla. In a randomized controlled trial, 100 adult participants were randomly allocated to the benzocaine group (received 20% benzocaine gel) and no benzocaine group (received no topical agent) prior to buccal infiltration in maxillary anterior teeth. A 27-gauge needle was used to deposit 2% lidocaine with 1:100,000 epinephrine. Pain of needle penetration and local anesthesia deposition was recorded separately using an 11-point Numeric Pain Rating Scale. Results showed that although 20% benzocaine significantly reduced pain on needle penetration during buccal infiltration in maxillary anterior teeth, the difference was small and the clinical significance is not clear. Topical anesthetic did not affect pain of local anesthetic deposition.

A Proof-of-concept Study Using Quantitative Sensory Threshold Analysis to Compare Two Intraoral Topical Anesthetics.

PURPOSE: CTY-5339A is an investigational topical anesthetic spray containing 14% benzocaine/2% tetracaine in a metered canister. Each spray delivers ∼0.2 mL of solution. This double-blind, randomized, crossover study compared the local anesthetic effect of CTY-5339A versus 14% benzocaine alone by using 2 quantitative sensory threshold experimental pain paradigms on the maxillary gingiva: pin prick test pain intensity (PPT PI) and heat pain threshold (HPT). METHODS: American Society of Anesthesiology Class 1 and 2 subjects (N = 50) were enrolled in this study. To qualify for the study, subjects were tested on the anterior maxillary gingiva with both PPT and HPT. Subjects had to report a PPT PI of ≥3 on a 0 to 10 numeric pain intensity scale on 1 of 2 consecutive pin pricks separated by 10 s, with at least one score ≥4. After PPT, mean HPT following 2 ramps in the same location had to be ≤ 46.5 °C, with each ramp beginning at 35 °C and an automatic cutoff of 50.6 °C. For treatment visits, subjects were randomly administered either 1 spray of CTY-5339A or 14% benzocaine to the anterior maxillary gingiva within 3 weeks of screening and then the alternative treatment 5 days to 2 weeks later. PPT PI and HPT were recorded immediately before drug application. After drug administration, PPT PI was recorded every minute through 5 min. Commencing at 5 min, PPT PI and HPT were recorded every 5 min through 60 min. For assessment of methemoglobin concentrations, venous blood (5 mL) was drawn from the antecubital fossa both before and 60 min after drug application. Oxygen saturation was recorded via pulse oximetry at baseline and every 10 min. FINDINGS: The AUCs for pain intensity difference from 0-30 and 0-60 min after PPT and HPT differences were significantly greater (P < 0.0001) for CTY-5339A compared with 14% benzocaine. Multiple time points on the time-action curves for PPT PI difference and HPT difference statistically (P < 0.05) favored CTY-5399A. Methemoglobin and oxygen saturation levels did not change compared with baseline after dosing with either treatment. IMPLICATIONS: Recommended doses of CTY-5339A provided significantly more profound and sustained local anesthesia than 14% benzocaine when applied to the maxillary gingiva. Significant changes in methemoglobin or oxygen saturation concentrations did not occur for either drug. ClinicalTrials.gov identifier: NCT03233737.

Influence of hybrid polymeric nanoparticle/thermosensitive hydrogels systems on formulation tracking and in vitro artificial membrane permeation: A promising system for skin drug-delivery.

In recent years, the development of hybrid drug delivery systems, such as hydrogels and nanoparticles, has gained considerable attention as new formulations for skin-delivery. Meanwhile, transdermal diffusion synthetic membranes have been used to assess skin permeability to these systems, providing key insights into the relationships between drug and nanoformulations. In this study, benzocaine-loaded poly-ε-caprolactone nanoparticles (BZC:NPs) were synthesized, characterized and incorporated into Poloxamer 407-based hydrogel (PL407). Benzocaine (BZC) was used as a drug model since has been commonly applied as a topical pain reliever in the last years. Hence, we developed a hybrid polymeric nanoparticle/thermosensitive hydrogels system and evaluated the in vitro permeation of the BZC, as well as nanoformulation tracking in an artificial membrane. In vitro permeation study was conducted in a vertical diffusion cell system using a Strat-M® membrane model. BZC:NPs were prepared by coprecipitation method and their physicochemical stability measured before incorporating into the thermosensitive hydrogel. Also, viscosity measurements and sol-gel transition temperature were performed by rheological analysis. Different techniques, including microscopy, were used to tracking the nanoparticles on both receptor medium and synthetic membranes. Results showed high BZC encapsulation efficiency into NPs (93%) and good physicochemical stability before and after hydrogel incorporation. BZC in vitro permeation kinetics from NPs-loaded Poloxamer 407-based hydrogel presented slower permeation profile compared with the BZC: Poloxamer 407-based hydrogel. Also, NPs were observed into the diffusion cells receptor compartment after the in vitro permeation study. These results contribute to a better understanding the interaction between hydrogels, nanoparticles and synthetic membrane, as well as open perspectives for the development of new drug delivery systems for skin.

Office-Based Anesthetic and Oral Surgical Management of a Child With Hereditary Sensory Autonomic Neuropathy Type IV: A Case Report.

Hereditary sensory and autonomic neuropathy type IV (HSAN IV), or congenital insensitivity to pain with anhidrosis, is an exceptionally rare genetic disorder that results in the complete loss of pain and temperature sensation as well as anhidrosis. Anesthetic management of these patients can be difficult because of significantly increased risks during general anesthesia. Literature on perioperative anesthetic management is typically written in the context of a hospital setting. As such, our case presents a unique report on the anesthetic management of a HSAN IV patient who presented for extraction of 2 teeth in an office-based setting. In determining how to safely manage the procedure, we decided against general anesthesia as we lacked the facilities and equipment to safely handle previously reported complications. We were successful in providing sedation with nitrous oxide in oxygen and applying 20% benzocaine topical ointment on the surgical site in lieu of administering general anesthesia. We had an anesthesiologist present and obtained intravenous access prior to the surgery to help manage any complications. This report provides support that simple dental extractions can be accomplished safely in the HSAN IV patient in the office-based setting, thereby avoiding unnecessary risk.

Topical Transdermally Delivered Lidocaine and Benzocaine Compared to Compounded Lidocaine/Tetracaine During Microfocused Ultrasound With Visualization Treatment.

OBJECTIVE: The efficacy of various pre-medication strategies for comfort management during microfocused ultrasound with visualization (MFU-V) treatment has not been studied. The present objective was to compare 2 topical analgesics (lidocaine 4% and benzocaine 20%) formulated with a novel transdermal delivery system with compounded lidocaine 23%/tetracaine 7% (23/7) to mitigate discomfort during MFU-V treatment. METHODS: This was a randomized, double-blinded, split-face study. One hour before MFU-V, subjects (N=14 females) received 50 mg IM meperidine/25 mg IM promethazine/5 mg oral diazepam. Fifteen minutes before treatment, 1 side of the face was treated with 1 application of 4% lidocaine, followed by 1 application of 20% benzocaine; the contralateral side was treated with 2 applications of 23/7 (to maintain blinding). Numbness was assessed by blinded evaluator (scale: 1=completely numb to 4=not numb) pre-treatment. Subject pain scores (scale: 0=no pain to 10=worst pain) were collected post-treatment. Adverse events and subjective clinician measures were also assessed. RESULTS: Mean subject pain scores for 23/7 and lidocaine 4%/benzocaine 20% were 5.6 and 5.7, respectively. Mean numbness scores were similar for 23/7 (2.5) and lidocaine 4%/benzocaine 20% (3.0). Clinicians rated both products as "very easy" to apply. For lidocaine 4%/benzocaine 20%, 7.1% of subjects required no pauses during treatment, vs 14.3% for 23/7. However, more subjects required 4+ pauses with 23/7 (21.4% vs 7.1%). Lidocaine 4%/benzocaine 20% was preferred by 78.5% of subjects; 35.7% rated lidocaine/benzocaine 20% 4% as "Very Effective" vs 7.1% for 23/7. No adverse events were reported. CONCLUSIONS: Lidocaine 4% and benzocaine 20% formulations utilizing a novel transdermal delivery system perform similarly to compounded lidocaine 23%/tetracaine 7% for discomfort mitigation during MFU-V treatment. More subjects preferred lidocaine 4%/ benzocaine 20% and rated it as "very effective" vs the compounded product. Fewer treatment pauses due to patient discomfort when using the lidocaine 4%/benzocaine 20% may translate to time efficiency. J Drugs Dermatol. 2018;17(7):729-734.

Comparison of Etomidate, Benzocaine, and MS222 Anesthesia with and without Subsequent Flunixin Meglumine Analgesia in African Clawed Frogs (Xenopus laevis).

Often few alternative anesthetics for exotic species are available, due to the small numbers of these animals used in research. In this study, we evaluated the depth and duration of anesthesia in Xenopus laevis after their immersion in 3 doses of etomidate (15, 22.5, and 30 mg/L) and in 3 doses of benzocaine (0.1%, 0.5%, and 1%) compared with the 'gold standard,' tricaine methanesulfonate (MS222; 2 g/L). We then chose an optimal dose for each alternative anesthetic according to induction time, duration of surgical plane, and time to complete recovery. The optimal etomidate and benzocaine doses (22.5 mg/L and 0.1%, respectively) as well as the MS222 dose were then used to achieve a surgical plane of anesthesia, with the addition of flunixin meglumine (25 or 50 mg/kg) administered in the dorsal lymph sac at the completion of mock oocyte harvest. Efficacy of the analgesic was assessed at 1, 3, 6, and 24 h postoperatively by using acetic acid testing (AAT). Histology of the liver, kidney, and tissues surrounding the dorsal lymph sac was performed at day 3, 14, and 28 in each group of animals. Mild to moderate myocyte degeneration and necrosis were present in tissues surrounding the dorsal lymph sac at both flunixin meglumine doses after etomidate and benzocaine anesthesia. In addition, the 50-mg/kg dose of flunixin meglumine resulted in the death of 5 of the 12 frogs within 24 h, despite an otherwise uneventful anesthetic recovery. In conclusion, benzocaine and etomidate offer alternative anesthetic regimens, according to typical requirements for an anesthetic event. Flunixin meglumine at the 25-mg/kg dose provided analgesic relief at the latest time point during etomidate dosage and at all time points during benzocaine dosage, but further characterization is warranted regarding long-term or repeated analgesic administration.

Lack of Methemoglobin Elevations After Topical Applications of Benzocaine Alone or Benzocaine Plus Tetracaine to the Oral Mucosa.

PURPOSE: This study evaluated changes in methemoglobin and oxygen saturation concentrations after the administration of recommended doses of 14% benzocaine alone or 14% benzocaine combined with 2% tetracaine. METHODS: American Society of Anesthesiology class 1 and 2 subjects (n = 40) were enrolled in this modified crossover study. Subjects were administered 0.2 mL of 14% benzocaine alone, 0.2 mL of 14% benzocaine plus 2% tetracaine, or 0.4 mL of 14% benzocaine plus 0.2% benzocaine to their cheek mucosa. Venous blood (5 mL) was drawn from the antecubital fossa before and 60 minutes after drug application for methemoglobin analyses. Oxygen saturation was also recorded via pulse oximetry at baseline and every 10 minutes through 60 minutes after drug application. FINDINGS: Methemoglobin and oxygen saturation levels did not change from baseline after the administration of benzocaine alone or when combined with tetracaine. IMPLICATIONS: Recommended doses of benzocaine or benzocaine combined with tetracaine when applied to the cheek mucosa do not induce even clinically insignificant elevations in methemoglobin levels. Metered dosing, such as that used in this study, can help avoid this overdose phenomena with these drugs. ClinicalTrials.gov identifier: NCT02908620.

Pediatric Exposures to Topical Benzocaine Preparations Reported to a Statewide Poison Control System.

INTRODUCTION: Topical benzocaine is a local anesthetic commonly used to relieve pain caused by teething, periodontal irritation, burns, wounds, and insect bites. Oral preparations may contain benzocaine concentrations ranging from 7.5% to 20%. Pediatric exposure to such large concentrations may result in methemoglobinemia and secondarily cause anemia, cyanosis, and hypoxia. METHODS: This is a retrospective study of exposures reported to a statewide poison control system. The electronic health records were queried for pediatric exposures to topical benzocaine treated at a healthcare facility from 2004 to 2014. Cases of benzocaine exposure were reviewed for demographic and clinical information, and descriptive statistical analysis was performed. RESULTS: The query resulted in 157 cases; 58 were excluded due to co-ingestants, or miscoding of non-benzocaine exposures. Children four years of age and younger represented the majority of cases (93%) with a median age of 1 year. There were 88 cases of accidental/ exploratory exposure, while 6 cases resulted from therapeutic application or error, 4 cases from adverse reactions, and 1 case from an unknown cause. Asymptomatic children accounted for 75.5% of cases, but major clinical effects were observed in 5 patients. Those with serious effects were exposed to a range of benzocaine concentrations (7.5-20%), with 4 cases reporting methemoglobin levels between 20.2%-55%. Methylene blue was administered in 4 of the cases exhibiting major effects. CONCLUSION: The majority of exposures were accidental ingestions by young children. Most exposures resulted in minor to no effects. However, some patients required treatment with methylene blue and admission to a critical care unit. Therapeutic application by parents or caregivers may lead to adverse effects from these commonly available products.

Comparative evaluation of effectiveness of intra-pocket anesthetic gel and injected local anesthesia during scaling and root planing - A split-mouth clinical trial.

BACKGROUND AND AIM: Pain control is an important outcome measure for successful periodontal therapy. Injected local anesthesia has been used to secure anesthesia for scaling and root planing (SRP) and continues to be the anesthetic of choice for pain control. Alternatively, intra-pocket anesthetic gel has been used as an anesthetic during SRP. Hence, this clinical trial was done to compare the effectiveness of intra-pocket anesthetic gel and injected local anesthesia during SRP and also to assess the influence of intra-pocket anesthetic gel on treatment outcomes in chronic periodontitis patients. MATERIALS AND METHODS: Fifteen systemically healthy chronic periodontitis patients were recruited. The dental quadrants on right side received either intra-pocket 20% benzocaine gel (Gel group) or infiltration/block by 2% lidocaine with 1:80,000 adrenaline (injection group). Quadrants on the left side received the alternative. Pain perception and patients preference for the type of anesthesia was recorded. Clinical parameters: plaque index, modified gingival index, modified sulcular bleeding index, probing pocket depth, and clinical attachment level were recorded at baseline and 1 month after treatment. RESULTS: No difference was observed in visual analog scale (P > 0.05) and verbal rating scale (P > 0.05) pain perception between gel group and injection group. A slightly increased preference to gel as anesthesia (53% vs. 47%) was observed. The treatment outcome after SRP did not show a significant difference between gel and injection group (P > 0.05). CONCLUSION: Intra-pocket administration of 20% benzocaine gel may be effective for pain control during SRP and may offer an alternative to conventional injection anesthesia.

Development of anaesthetic protocols for lumpfish (Cyclopterus lumpus L.): Effect of anaesthetic concentrations, sea water temperature and body weight.

In recent years, use of lumpfish (Cyclopterus lumpus L.) as cleaner-fish to remove sea-lice have been chosen by many salmon farmers in Europe and Canada as an alternative to medical treatment, which has led to large scale production of lumpfish. At present, there is limited knowledge of how lumpfish respond upon anaesthesia, which anaesthetics and concentrations that are efficient and conditions for euthanasia. We have therefore tested and developed protocols for bath immersion for three commonly used anaesthetics metacaine (Finquel, buffered tricaine methanesulfonate, MS-222 and Tricaine Pharmaq), benzocaine (Benzoak vet) and isoeugenol (Aqui-S), determined concentration for normal and fast anaesthesia and evaluated safety margin for each condition. Also, a behavioral matrix has been developed. We have examined the effect of fish size (10-20 g, 200-400 g and 600-1300 g) and sea water temperature (6°C and 12°C). We found that 200 mg L-1 metacaine is an efficient dose for deep narcosis independently for fish size and temperature due to good safety margins with regards to both exposure times and doses. However, for many tasks lighter anaesthesia is sufficient, and then 100 mg L-1 metacaine can be used. Benzocaine is less efficient than metacaine, but can be used as anaesthetic of fish < 400 g. The optimal doses of benzocaine were 100-200 mg L-1 for small fish (10-20 g) and 200 mg L-1 for medium sized fish (200-400 g). For larger fish (> 600 g), benzocaine is not suitable. Isoeugenol cannot be recommended for full anesthesia of lumpfish. The conditions for lethal doses varied with chosen anaesthetic, fish size and temperature. For small fish (10-20 g), exposure to 1600 mgL-1 of metacaine in 10 minutes it lethal. Guided protocols for non-lethal anaesthesia will contribute to ensure safe treatment of lumpfish according to an ethical standard for good fish welfare.

Preparation and evaluation of novel microemulsion-based hydrogels for dermal delivery of benzocaine.

The purpose of the current research was to prepare and evaluate the potential use of microemulsion-based hydrogel (MBH) formulations for dermal delivery of benzocaine (BZN). The pseudoternary-phase diagrams were constructed for various microemulsions composed of isopropyl myristate (IPM) as oil phase, Span 20, Tween 20, Tween 80, cremophor EL and cremophor RH40 as surfactants, ethanol as cosurfactant and distilled water as aqueous phase. Finally, concentration of BZN in microemulsions was 2% (w/w). The physicochemical properties, such as conductivity, viscosity, pH, droplet size, polydispersity index and zeta potential of microemulsions, were measured. Carbopol 940 was used to convert BZN-loaded microemulsions into gel form without affecting their structure. Furthermore, excised rat abdominal skin was used to compare permeation and penetration properties of BZN loaded M3 and M3BHs with BZN solution. According to ex vivo study results, BZN-loaded M3BH1 showed highest flux values and high release rate values, and furthermore, this gel formulation had low surfactant content. Finally, in order to learn the localization of formulations within the dermal penetration, formulations and BZN solution were labeled with red oil O and subjected to fluorescence observation. In conclusion, BZN-loaded MBHs could be offered as a promising strategy for dermal drug delivery.

A Dynamic Anesthesia System for Long-Term Imaging in Adult Zebrafish.

Long-term in vivo imaging in adult zebrafish (i.e., 1-24 h) has been limited by the fact that regimens for long-term anesthesia in embryos and larvae are ineffective in adults. Here, we examined the potential for dynamic administration of benzocaine to enable long-term anesthesia in adult zebrafish. We developed a computer-controlled perfusion system comprised of programmable peristaltic pumps that enabled automatic exchange between anesthetic and system water. Continuous administration of benzocaine in adult zebrafish resulted in a mean time to respiratory arrest of 5.0 h and 8-h survival of 14.3%. We measured characteristic sedation and recovery times in response to benzocaine, and used them to devise an intermittent dosing regimen consisting of 14.5 min of benzocaine followed by 5.5 min of system water. Intermittent benzocaine administration in adult zebrafish resulted in a mean time to respiratory arrest of 7.6 h and 8-h survival of 71.4%. Finally, we performed a single 24-h trial and found that intermittent dosing maintained anesthesia in an adult zebrafish over the entire 24-h period. In summary, our studies demonstrate the potential for dynamic administration of benzocaine to enable prolonged anesthesia in adult zebrafish, expanding the potential for imaging in adult physiologies that unfold over 1-24 h.