什麼是「去氧羥四環素」(Doxycycline)？

去氧羥四環素是一種抗生素，在香港是已註冊的處方藥物，註冊適應症為預防及治療特定細菌感染，而並不包括預防性病感染。

副作用

是次研究的藥物或有一定副作用，包括但不限於頭痛、嘔心、嘔吐、光敏感反應、食慾不振、屙嘔肚痛、紅疹及牙齒變色。

細菌性的性病

本研究關注的細菌性的性病包括淋病、衣原體和梅毒。淋病/衣原體男性患者的一般病徵是尿道流出混濁的奶狀或黃綠色的膿液和小便時感到灼痛。它也會經肛交或口交時，令肛門或口咽受到感染，而有肛門流膿或喉痛的現象。梅毒病徵包括不痛的損口、不痛不癢的紅斑、感冒徵狀等。此三種性病一般能透過抗生素治療根治。

DoxyPEP的科學證據

國際不同研究顯示，相比服用安慰劑，按事後預防用藥方式服用去氧羥四環素能減低感染細菌性的性病的機會。一項在法國進行的研究指出去氧羥四環素能減低51%淋病、89%衣原體和84%梅毒的感染風險[1]。而另一項於美國進行的研究表示去氧羥四環素能減低淋病、衣原體和梅毒的感染風險分別為55%、88%和87%[2]。

美國疾病管制與預防中心(CDC)於2024年6月發表報告，建議高感染細菌性性病風險男男性接觸者使用DoxyPEP以預防感染，並定期接受性病測試及醫學諮詢評估持續服藥需要[3]。

另外就DoxyPrEP而言，一項在加拿大進行的初期研究招募了52位感染愛滋病毒的男男性接觸者，每日服用100mg去氧羥四環素的參加者比服用安慰劑的參加者的淋病、衣原體和梅毒感染風險分別減少68%、92%和79%[4]。

What is doxycycline?

Doxycycline is an antibiotic, which has been registered as a prescription drug in Hong Kong. Doxycycline hyclate is a registered prescription drug in Hong Kong. Its indication is for treating and preventing specific bacterial infections, excluding preventing STI.

Adverse reactions

The medicine used in this study may cause side effects, including but not limited to headache, nausea, vomiting, photosensitivity, loss of appetite, diarrhoea, rash, and discolouration of teeth.

Bacterial STI

Bacterial STI being studied in this study include gonorrhea, chlamydia, and syphilis. For men, common symptoms of gonorrhea/chlamydia infection are thick copious purulent milk-like or yellow-green urethral discharge and burning feeling when passing water. It may also infect the anal canal or oropharynx during anal and oral sex, and may present as mucopurulent anal discharge or sore throat respectively. Syphilis’s common symptoms include painless sore, non-itchy rash, and flu-like symptoms. They are generally curable by antibiotics.

Scientific evidence on DoxyPEP

Multiple clinical trials from different countries have shown that doxycycline taken as PEP could significantly reduce risk of bacterial sexually transmitted infections (STI) compared to placebo. A French study found that DoxyPEP could reduce gonorrhoea, chlamydia, and syphilis infection risk by 51%, 89%, and 84%, respectively [1]. An American study showed similar results that DoxyPEP could reduce 55%, 88%, and 87% gonorrhoea, chlamydia, and syphilis infection risk, respectively [2].

The CDC in the US published a report in June 2024, recommending men who have sex with men at higher risk of acquiring bacterial STI to receive counselling that doxyPEP can be used for prevention, and DoxyPEP users should undergo regular STI testing and ongoing need assessment [3].

Regarding DoxyPrEP, a Canadian pilot study with 52 men who have sex with men living with HIV showed that daily doxycycline 100mg decreased to risk of acquiring gonorrhoea, chlamydia, and syphilis by 68%, 92%, and 79%, respectively, compared to placebo [4].

參考文獻 References

1. Molina JM, Bercot B, Assoumou L, et al. Doxycycline prophylaxis and meningococcal group B vaccine to prevent bacterial sexually transmitted infections in France (ANRS 174 DOXYVAC): a multicentre, open-label, randomised trial with a 2 × 2 factorial design. Lancet Infect Dis. 2024 Oct;24(10):1093-1104. doi: 10.1016/S1473-3099(24)00236-6.
2. Luetkemeyer AF, Donnell D, Dombrowski JC, et al. Postexposure Doxycycline to Prevent Bacterial Sexually Transmitted Infections. N Engl J Med. 2023 Apr 6;388(14):1296-1306. doi: 10.1056/NEJMoa2211934.
3. Bachmann LH, Barbee LA, Chan P, et al. CDC Clinical Guidelines on the Use of Doxycycline Postexposure Prophylaxis for Bacterial Sexually Transmitted Infection Prevention, United States, 2024. MMWR Recomm Rep. 2024 Jun 6;73(2):1-8. doi: 10.15585/mmwr.rr7302a1.
4. Grennan T, Tan DH, Mohammed S, et al. A pilot, randomized controlled trial of doxycycline pre-exposure prophylaxis versus placebo for prevention of bacterial sexually transmitted infections in men who have sex with men living with HIV. 25th International AIDS Conference; 2024 July 22-26; Munich.