[Question #10956] On demand PREP and unprotected vaginal sex
18 months ago
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Hi Doc,
I am a heterosexual, uncircumcised man living in the Netherlands. I recently met a woman of Romanian origin from a sugerdating site. She is a 21 years old female from Romania. She is a college student and is finishing her Bachelor's degree this year. She does sugerdating on the side to make extra money. She stayed the night at my place and I had unprotected vaginal sex three times with her. She was last tested three months ago in November and didn't have any STI's at that point. However, since then she has had a number of partners. She is due to be tested soon. As I am a bit paranoid about HIV, I took two pills of Truvada seven hours before our sexual contact. I then continued taking it for two additional days, as recommended by the 2-1-1 schedule of on- demand PREP. However, I am a still nervous about the unprotected sex primarily because there is no data for efficacy of on- demand prep for heterosexuals. My questions are:
(1) Can I consider my encounter safe from HIV point of view given that I took on demand prep?
(2) I got tested in December for HIV, Gonorrhea and Chlamydia and was negative for everything. Should I test again for HIV?
(3) Is there any marginal benefit in continuing taking Truvada for the next 28 days, essentially following the PEP schedule?
Needless to say that it has been a learning experience for me. The only reason I had unprotected sex was because of PREP. However, since I am still nervous despite prep, I will use condom for my all the future encounters.
18 months ago
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Hi Doc,
I still haven't received a reply even though questions posted after mine have. I am wondering if there is some technical glitch here. Looking forward to hear from you. Thank you.
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H. Hunter Handsfield, MD
18 months ago
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Apologies for the delayed reply. We try to respond to new questions within 24 hr but sometimes it isn't possible. Thanks for your understanding.
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You describe a partner very unlikely to have HIV and I would have advised against PrEP in this situation. However, it certainly did no harm and probably was highly effective in preventing HIV if your partner is infected. You are correct that the data for on-demand PrEP effectiveness are less strong than for continuous PrEP or PEP. But that's primarily because fewer people have been studied, and fewer heterosexuals as well. However, outside research settings, there are few if any reports in which on-demand PrEP failed to prevent HIV when the antiretroviral(ARV) drugs were taken as prescribed. And there certainly is no biological or other reason to suspect it would be any less effective following heterosexual than male-male exposures. If anything, maybe more effective, because vaginal sex is inherently less likely to transmit HIV than anal sex. To your questions:
1) Even without ARV PrEP, and if your partner has untreated HIV, your risk of catching it (with 3 unprotected vaginal sex exposures) would be somewhere around one chance in a thousand. (The chance has been estimated at 1 in 2,500 for a single episode of unprotected vaginal sex.) If we then assume a 1% chance she has HIV, your risk drops to one in 100,000 even without PrEP. If PrEP is 90% effective, the probability you caught HIV becomes one in a million. I really wouldn't be worried if I were in your situation!
2) Anybody who is sufficiently concerned to take PrEP should be tested for HIV afterward. I would advise an AgAb (4th generation) blood test 6 weeks after the last dose of PrEP. For the reasons discussed above, you definitely can expect a negative result.
3) There is no obvious benefit from continuing ARVs for a full month. I advise against it. Among other things, it would mean waiting another month (and some experts would say three months) for conclusive HIV testing, and I'm guessing you don't want to delay a conclusively negative test by several weeks or months.
I hope these comments are helpful. Let me know if anything isn't' clear.
HHH, MD
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18 months ago
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Thank you for your response Dr. HHH! It made me feel much better. As per your suggestion, I have decided not to take the ARV anymore as I don't want the conclusive result to be delayed by months. I really appreciate your help!
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H. Hunter Handsfield, MD
18 months ago
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Thanks for the thanks. I'm glad to have helped.---