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Doxy prevents infection?
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The STD Forum is intended only for questions and support pertaining to sexually transmitted diseases other than HIV/AIDS, including chlamydia, gonorrhea, syphilis, human papillomavirus, genital warts, trichomonas, other vaginal infections, nongonoccal urethritis (NGU), cervicitis, molluscum contagiosum, chancroid, and pelvic inflammatory disease (PID). All questions will be answered by H. Hunter Handsfield, M.D. or Edward W Hook, MD.

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Doxy prevents infection?

Dear Dr. EWH or Dr. HHH, i made a misstep and had an encounter with 2 prostitutes yesterday. I received blowjobs from both mostly protected and for only 2-3 minutes unprotected. Also there was a lot (!) of fingering but no anal or vaginal intercourse. I am on doxycycline (200 mg/day) for something else for 5 days now and have to continue 15 more days. I am in a relationship and worried. After some research I still have the following questions:
1) How much protective would the doxycycline dose of 200 mg over 20 days be against bacterial stds? (I fear mostly syphilis, is 200 mg/day protective enough?)
2) Is HIV worry warranted?
3) Do you recommend any testing? If yes, which tests and when?
4) From a medical perspective, do I need to confess to my girlfriend and when can I resume sex with her?

This is driving me crazy! Even if my misstep was irresponsible I want to do EVERYTHING POSSIBLE AND NECESSARY to be responsible for my girlfriend. Please consider that in your advice.

Sorry for my bad english, it is not my mother language.

Thank you,

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Welcome back to the STD Forum.  Let's directly address your questions:

1.  Doxycycline 200 mg daily, if exposed to syphilis would almost certainly prevent infection.  200 mg daily for 14 days is a recommended curative dose and syphilis, as well as most other STDs is pharmacologically easier to prevent than to cure.  The same dose will likely prevent all other bacterial STDs as well.
2.  There is virtually no HIV risk.  Your partners probably did not have HIV and even if they did, the quoted figure for HIV risk, if one has oral sex with an infected partner is less than 1 in 10,000 and, in my estimation that is too high. Some experts state there is no risk at all from oral sex.  Neither of us on this site have ever seen or reading the medical literature of a convincing instance in which HIV was passed by oral sex.
3. In your situation, given that your only exposure was oral sex, that it was breif and that you were already on doxy, I see no reason for testing at this time.  
4.  From a medical perspective, no.  However, you still have to deal with your sense of propriety and trust with her.

Hope this helps.  EWH
Dear Dr. Hook, 5 weeks, 2 days have passed by after the encounter. I still worry about the possibility of having contracted syphilis. I have the following questions:

1) Does syphilis always start with a primary lesion, e.g. a ulcus durum?
2) My only exposure was receipt of fellatio. As primary lesion would be on penis, could I miss the lesion or would it be definitely obvious?
3) Am I right that in most cases primary lesion will develop after 5 weeks?
4) How reliable is it, that Doxy (see original question) would have prevented infection (more than 99%)? (I drank a lot of alcohol at that time. Perhaps alcohol reduced the effect of doxy)
5) Considering all facts: low risk (oral) exposure/ on Doxy at time of exposure/ no symptoms after 5 weeks. What is your guess of my overall syphilis risk?

I hope you can help me to get over this...

You are asking the same question again and again.  My assessment of your risk, which was close to zero even before you started the doxy and is now, withthe doxy, almost certainly zero, is unchanged.  It is past time for you to move on.  Please, no further redundant questions.  EWH
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University of Washington
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