A Study to Evaluate the Drug-Drug Interaction Between KL0011034 Injection and Alfentanil Hydrochloride Injection in Participants With Moderate-to-Severe Non-Cancer Chronic Pain

This study will evaluate the drug-drug interaction between KL0011034 Injection and Alfentanil Hydrochloride Injection in participants with moderate-to-severe non-cancer chronic pain. The study consists of two parts. Part 1 is a single-center, randomized, open-label, parallel-design study to evaluate the safety, tolerability, and pharmacodynamics of the combination. Approximately 9 participants will be enrolled and randomized to one of three dose groups (n=3 per group). Part 2 is a single-center, randomized, open-label, three-sequence, three-period crossover study to evaluate the pharmacokinetic interaction, safety, tolerability, and pharmacodynamic effects. Approximately 18 participants will be enrolled and randomized to one of three sequences (n=6 per sequence), with a 3-day washout period between each period.