Inclusion Criteria:
1. Ability and willingness to provide written informed consent, adhere to the study visit schedule, and complete all study assessments.
2. Adults 18 to 75 years at screening.
3. Planned distal metaphyseal osteotomy procedure (e.g., Austin procedure/chevron osteotomy) under general anesthesia.
4. Health surgery rating according to American Society of Anesthesiologists (ASA) class 1-3.
5. Body mass index (BMI) ≥18 and ≤39 kg/m\^2.
Exclusion Criteria:
1. Surgery is for minimally invasive bunionectomy procedure.
2. Contralateral bunionectomy within 3 months of study dosing.
3. Planned surgical intervention concurrent with unilateral bunionectomy (e.g., collateral procedures).
4. Hypersensitivity/allergy to any ingredient in AMT-143 formulation (hyaluronan or methylcellulose).
5. History or presence of glucose-6-phosphate dehydrogenase deficiency.
6. History or presence of congenital or idiopathic methemoglobinemia.
7. Hypersensitivity/allergy to amide type local anaesthetics (e.g., lidocaine, bupivacaine, ropivacaine, etc.).
8. Loss of sensation or significant peripheral neuropathy on the side of bunionectomy.
9. Concurrent pain syndromes (e.g., arthritis, fibromyalgia, cancer, etc.) that would require an additional use of non-steroidal anti-inflammatory drugs (NSAIDs), acetaminophen, or opioids during the course of the study.
10. Arrhythmias predisposing to long QT syndrome (e.g., ventricular tachycardia, atrial fibrillation, atrioventricular block, etc.).
11. Disease or condition that in the opinion of the Investigator, would pose a health risk to the participant or interfere with study assessments or compliance, including but not limited to, any of the following:
* Myocardial infarction within 6 months of study dosing or coronary bypass grafting within 12 months of study dosing.
* Congestive heart failure (New York Heart Association Class III-IV).
* Uncontrolled diabetes with A1C hemoglobin ≥ 7%.
* Severe peripheral vascular disease.
* Pulmonary dysfunction.
* Severe hepatic or renal dysfunction.
* Coagulation or bleeding disorders.
* Uncontrolled anxiety, schizophrenia, or other psychiatric disorders.
12. Have history of human immunodeficiency virus (HIV) or hepatitis B/hepatitis C or a positive test at screening.
13. Suspected or known addiction or abuse of illicit drugs, prescription medications, or alcohol within 2 years of study.
14. Administration of an investigational drug within 30 days or 5 elimination half-lives of such investigational drug, whichever is longer, prior to study dosing, or planned administration of another investigational drug or procedure during the subject's participation in this study.
15. Administration of medications with a potential for drug interactions with ropivacaine (i.e., amide-type local anaesthetics such as lidocaine, bupivacaine, mepivacaine and prilocaine; antiarrhythmics such as procainamide, disopyramide, tocainide, mexiletine and flecainide; inhibitors of cytochrome P4501A2 such as fluvoxamine and enoxacin) for at least 5 half-lives prior to study dosing.
16. Current use of neuromodulating agents \[e.g., gabapentin, pregabalin (Lyrica), duloxetine (Cymbalta), etc.\].
17. Use of systemic glucocorticoids within 30 days of study dosing.
18. Use of dexmedetomidine HCl (Precedex®) or clonidine within 3 days of study dosing.
19. Chronic opioid use \[average ≥30 oral morphine equivalents (OMEDs)/day\] within 30 days of study dosing.
20. Use of opioid medications within 3 days of study dosing.
21. Use of marijuana, tetrahydrocannabinol (THC), and cannabidiol (CBD) within 30 days of study dosing or planned use during the course of the study.
22. Current pregnancy, nursing, or planning to become pregnant during the study.
23. Unwillingness to use effective methods of contraception during participation in this study (for females with childbearing potential and males).
24. Recent or potential exposure to COVID-19.
