背景：事件依賴型吃法是臺灣男男性行為者口服PrEP的優先選擇。然而，失去追蹤或中斷可能是在真實世界中擴大PrEP使用的障礙，而大多數研究僅包含每日型使用者。本研究旨在探討臨床追蹤中不同PrEP吃法使用者的臨床追蹤中斷情形及其影響因子。

方法：本研究採前瞻性世代研究法，於2018至2023年間針對於臺灣南部某醫學中心接受PrEP服務門診的成年MSM進行收案。本研究以問卷於參與者每次回診時收集資料。根據參與者在過去一個月內如何使用PrEP的回答，PrEP吃法被分為每日型使用和事件依賴型使用兩組。PrEP臨床追蹤中斷被定義為超過6個月無臨床回診，並使用Kaplan-Meier法和log-rank檢驗分析不同PrEP吃法之間是否具有差異。由於PrEP吃法和HIV風險行為會隨著時間變化，本研究使用包含時間相依變數或時間固定變數（最後一次回診時）的Cox模型分析PrEP使用者之特徵與第一次中斷PrEP臨床追蹤之間的相關性。

結果：本研究針對共301名於研究期間自我回報至少使用過一次PrEP的男男性行為者進行分析。參與者納入時的年齡中位數為28歲。接受政府補助PrEP的比例從初診時（39.2%）到最後一次回診時（71.1%）呈上升趨勢。回診人次共1379人年，其中有57.1%的參與者在納入後一年內中斷了PrEP臨床追蹤，中斷時間中位數為210天。Kaplan-Meier分析顯示，研究納入時使用每日型或事件依賴型吃法對於第一次臨床中斷率無顯著差異，但最後一次回診時的吃法對於第一次臨床中斷率存在顯著差異影響。Cox回歸分析顯示，使用事件依賴型PrEP、較高的月薪、最近具性病感染以及缺乏政府補助PrEP與較短的PrEP臨床追蹤中斷時間相關。控制干擾變項後的調整模型也確認了使用事件依賴型PrEP和較高薪資仍為第一次PrEP臨床中斷之顯著影響因子，而包括時間相依變數的模型也強調了缺乏政府補助PrEP的重要性。然而，使用最後一次回診資料的時間固定變數模型顯示，年齡較大、最近具性病感染和缺乏政府補助PrEP與PrEP臨床追蹤中斷時間呈顯著相關，但使用事件依賴型PrEP則不顯著。

結論／實務應用：使用事件依賴型PrEP的使用者在台灣具有較低的臨床追蹤率。應針對使用者需求發展差異化服務提供模式。臨床醫師也應謹慎評估具有較高愛滋病毒暴露風險但仍中斷PrEP臨床追蹤的使用者，無論其PrEP吃法為何。

Introduction: Event-driven dosing is the preferred option for oral PrEP among MSM in Taiwan. Lost to follow-up and discontinuation can be barriers to PrEP upscale in real life, yet most studies included daily users only. This study aimed to investigate the discontinuation of PrEP in clinical follow-up and associated factors among different PrEP dosing regimen users.

Methods: Adult MSM receiving PrEP service at a medical center in southern Taiwan were enrolled prospectively in 2018-2023. Questionnaires were completed at each clinical visit. PrEP dosing regimens were categorized into two groups (i.e. daily and event-driven) based on the answers asking them how they use PrEP for the past month. PrEP discontinuation, defined as having no clinical visit for over 6 months, was analyzed using the Kaplan-Meier method and log-rank test comparing differences among dosing regimen groups if the assumption was met. As the PrEP dosing and HIV risk behaviors varied over time, Cox models with time-varying covariates or time-fixed covariates at the last visit were performed to identify associations between PrEP user characteristics and the first PrEP discontinuation at the clinical follow-up.

Results: A total of 301 MSM who self-reported using PrEP at least once were analyzed. At enrollment, the median age was 28 years. Government-subsidized PrEP recipients increased from 39.2% at the baseline to 71.1% at the last visit. Over 1379 person-years of follow-up, 57.1% of participants discontinued PrEP within one year, with a median time to discontinuation of 210 days. Kaplan-Meier analysis showed no significant difference in discontinuation between daily and event-driven users at baseline, but a significant difference at the last visit. Cox regression analysis indicated that event-driven PrEP use, higher monthly salary, recent STI, and the lack of government-subsidized PrEP were associated with shorter time to PrEP discontinuation at clinical follow-up. Adjusted models confirmed that event-driven use and higher salary remained significant factors, while including HIV risk behaviors as time-varying covariates also highlighted the significance of the lack of government-subsidized PrEP. Conversely, using time-fixed covariates at the last visit identified older age, recent STI, and lack of government-subsidized PrEP as significant, but not event-driven use.

Conclusion / Implantation: Event-driven PrEP users demonstrate a lower clinical follow-up rate in Taiwan. Differentiated service delivery better-tailoring resources to users’ demand should be developed. Clinicians should also be cautioned for PrEP users with higher HIV risk yet discontinuing PrEP clinical follow-up regardless of the dosing regimen.

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