HKS21542, a highly selective activator of peripheral kappa opioid receptor agonists, plays a critical role in antinociception and itch inhibition during clinical development. Due to its indication population and elimination characteristics, it is imperative to evaluate the potential HSK21542 systemic exposure in individuals with renal impairment, hepatic impairment, the elderly, and the geriatric population. Here, a physiologically-based pharmacokinetic (PBPK) model for HSK21542 was developed based on in vitro metabolism and transport characteristics and in vivo elimination mechanism. Meanwhile, the potential systemic exposure of HSK21542 in specific populations was evaluated. The predicted results indicated increased systemic exposure in patients with renal impairment, hepatic impairment and in the elderly. Compared to the healthy volunteers aged 20–60 years, the AUC0–24h increased by 52 %–71 % in population with moderate to severe renal impairment, by 46 %–77 % in those with mild to severe hepatic impairment, and by 45 %–85 % in the elderly population aged 65–95-years. Conversely, the pediatric population demonstrated a potential decrease in systemic exposure, ranging from 20 % to 37 % in patients aged 0–17 years due to the physiological characteristics. Combined with the predicted results and the exposure-response relationship observed for HSK21542 and its analog (CR845), dosage regimens were designed for the target population with renal and hepatic impairment, supporting the successfully conducted trials (CTR20201702 and CTR20211940). Moreover, the observed exposure of HSK21542 in the elderly closely matched the predicted results within the same age group. Additionally, based on the predicted results, potential reductions in systemic exposure in pediatric patients should be carefully considered to avoid potential treatment failure in future clinical trials.