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Tablets to prevent HIV – PrEP

   HHIV PrEPIV Pre-Exposure Prophylaxis – PrEP

In 2010, I wrote a blog article on PrEP which is short for Pre-Exposure Prophylaxis.

Since then, there has been many updates and new research published so it is high time for an updated entry.

Just to recap, HIV PrEP is an HIV medicine that a person takes everyday which reduces his/her risk of contracting HIV. This is not a new concept in medicine. Take for example tablets taken daily to prevent Malaria or tablets taken daily to prevent pregnancy.

This should not be mistaken for PEP which is Post Exposure Prophylaxis. HIV PEP are medicines taken AFTER a person has been potentially infected with HIV.

Learn more about HIV PrEP Event Driven Based Strategy

So what exactly is PrEP?

PrEP is simply a tablet is taken daily that reduces a person’s risk of contracting HIV.  It’s that simple. The tablet most studied for use as PrEP contains 2 medicines:  tenofovir disoproxil fumarate 300 mg (TDF) and emtricitabine 200 mg (FTC). This is marketed under the brand name Truvada and is made by a company called Gilead Sciences.

How effective is PrEP?

There have been many studies with varying results. Generally, protection rates differ between groups with different sexual orientations. Numbers range from 50% to 84% according to the 4 studies quoted in the US CDC’s Interim Guidelines. Other publications quote protection rates as high as 99%.

We must bear in mind that like every other method of HIV prevention, PrEP is not failsafe. It is one of the many weapons in our current arsenal to reduce the burden of HIV on the world. Other prevention methods include:

  1. Consistent and correct condom use.
  2. Access to treatment. Treatment as prevention.
  3. Education.
  4. Male circumcision.

What are the side effects of PrEP?

Minor side effects such as nausea, headache and weight loss are possible.

Major side effects like effects on the kidney and bone density are rare.

In my personal experience prescribing PrEP, I have not come across anything more than some minor nausea.

What is the cost of PrEP?

This, of course, varies from country to country and even between centres in the same country.

How can I start PrEP?

Come to see us at our clinic. You will need several tests including an HIV test, STD screening and a kidney function test.

You can start on the pills immediately. It is best to be on the pills for at least 7 days before engaging in any risky encounters.

How can I stop PrEP?

It is best to continue PrEP for at least 4 weeks from the last risky encounter.

You will also be advised to get screening tests done for HIV and other STDs 3 months from the last encounter.

What is HIV PrEP Event Driven Strategy?

How long can I take PrEP for?

PrEP can be taken indefinitely and should be taken as long as you remain at risk of HIV.

It is best to see your doctor every 3 months to screen for HIV and STDs and monitor for potential side effects.

For further reading:

My PrEP Experience Blog is a great resource on everything you need to know about PrEP.

It also contains real life stories from patients who have taken PrEP and their experiences. I highly recommend that you check it out if you are considering starting on PrEP.

PrEP can save your life. Visit Our Clinics now and talk to Our Doctors to see if you are suitable for PrEP.

If you had a high risk exposure to HIV within the past 72 hours, you can take medicines to reduce your risk of actually contracting HIV. Find out more on HIV PEP Treatment.


Need more advice?

Come down to Our Clinics for a discussion with Our Doctors, or call our clinics for more information:

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Email: hello@dtapclinic.com.sg

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About Dr. Tan
Dr. Tan graduated from the National University of Singapore in 2001. His residency was in the two largest public hospitals in Singapore; Tan Tock Seng Hospital and Singapore General Hospital.

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  1. Vinay


    I am on prep since 5 months and not missed s single dose.
    I had a high risk exposure where my tongue had an open wound but still I went on for unprotected oral sex. Also the other guy performed wild oral sex on me. I even open mouth kissed the guy. Anal sex both ways was protected.
    Will prep save me in this case ?
    For info : I accidentally popped 2 pills on day before sex, and another 2 pills on day of sex – one before sex and one after sex. The extra pill on day of sex was due to anxiety.
    Please comment as I am in extreme distress and the guy is not cooperating me with his status. He is a seafarer and he showed me his recently screened Seafarer report being VDRL as negative and HIV as N/A.
    So I am worried.
    Thanks Dr Tan

  2. I read an article that you wrote from 30 MARCH 2015 titled “On Demand” PrEP for HIV Prevention. At the end of the article you mentioned “…for now, it seems to be working for my patients.” So now in 2017 have you had any patients that were following the “On Demand” PrEP program (4 pills) and were diagnosed as HIV positive? In your opinion how effective is On Demand PrEP?

    • We have had no cases of patients taking PrEP or on-demand PrEP (event-based dosing) who have come back to us testing positive. Current studies would suggest it will reduce risk by around 85%.

      • Thanks for your response. I think it’s important for people interested in On-Demand PrEP dosing to know that based on the IPERGAY study, On-Demand PrEP was considered to be effective however, the study involved people who had “frequent” sexual encounters meaning that although the On-Demand PrEP dosing schedule is only 4 tablets over 3 days around a MSM high risk sexual encounter, a person with “frequent” sexual events ended up taking about 15-20 pills per month or an average of about 4-5 pills a week. It has not been studied (to the best of my knowledge) on people with rare or infrequent sexual encounters where they might only end up having only 1 MSM high risk sexual encounter per month and only taking 4 pills on average in a month. Daily PrEP certainly provides the maximum protection.

  3. Lokino

    Hi ,

    Please help , i had blowjob for 10 minutes unprotected from a girl Csw and after ejaculation i noticed blood in her mouth maybe from her teeth or so and that was 6th Nov 2016 , i was very paranoid and then took the step to make the test , i did HIV P24 Ag/Abs Combo test on the date of 14th April 2017 and result came out Non-Reactive ,

    Do you think i am safe and did not contract HIV 1/2 ??

    Do you think my test is conculsive and do i need to repeat it ?

    Is this test name is the correct one for the my timing ?

    The Doc said that i was fine .

    • You are safe, you do not have HIV, your test is conclusive and you do not need to repeat it.

  4. May I know how to take this tablets? Do I need to take daily or before sex or after sex ? How long should I take ? This prevention can be effective for how long by taking tablets for two or more months only (for example: can I take tablets about three months to get 1 year prevention ? or do I need to take every month ? ).

    • PrEP has to be taken daily to be effective. The effect of the medicine stops once you stop taking it. There has been some studies on so called “event based PrEP” which is PrEP taken only for specific points in time usually for specific exposures. However this has its limitations. If you are interested in PrEP you should visit a doctor for a formal consultation. You are welcome to visit any one of our clinics. Please click HERE for location information.

  5. Hi Dr Tan,

    Thanks for taking the time to read this post.
    Recently I had protected insertive oral sex and protected insertive anal sex.
    It was in heat of moment with a man massage therapist.
    I was confused about my sexuality. Is my risk high?

    • Your risk of contracting HIV is not high. Namely because you used a condom. That said, you should still get screened regularly for HIV and other STDs like Syphilis, Chlamydia and Gonorrhea. It is OK to be confused about your sexuality. If you need someone to talk to, I highly recommend the people at Oogachaga. They are trained professional counselors that deal specifically with issues regarding sexual orientation.

  6. Elsabella Wong (Singapore Polytechnic)

    Dear Dr Tan

    I am a student research studying Applied Drama and Psychology in Singapore Polytechnic. A project that I am currently working on involves research and contact with sex workers. As you might have guessed, they perform highly risky sexual behaviours on a daily basis, therefore their risk of contracting HIV is high.

    I stumbled across PrEP while searching for a viable solution to reduce the risk. However, little did I know that PrEP costs $900 per bottle. I believe this is deemed high and may deter the sex workers from buying Truvada.

    May I know, in your opinion, if there are some other ways to procure Truvada at an affordable price? Or perhaps if there are already hospitals and mobile clinics offering this treatment at a discount?

    Thank you very much for reading through this comment. Have a great day ahead.

    Yours sincerely
    Elsabella Wong

    • HI Elsabella. It is nice to see our young millenials tackling problems some people would consider morally stigmatising. Kudos to you.

      First of all you may want to verify your data. You sure the risk of commercial sex workers contracting HIV in Singapore is high? What publications are you quoting?

      Secondly, PrEP is not effective across the board. Data has shown that PrEP is less effective for women compared to gay men. So the risk benefit ratio for female CSWs taking PrEP may not be that good.

      A common way people in Singapore get cheap Truvada is simply to buy it from Thailand. There are ways to get it cheaply in Singapore but that is not for discussion over the internet.

      I would like to invite you to attend the Singapore AIDS conference to be held on 3rd December 2016. We will be discussing the use of PrEP.

      • Elsabella Wong (Singapore Polytechnic)

        Dear Dr Tan

        So sorry for the late reply. I was quite deep into my research as compared to before and was not expecting a reply soon. Thank you for taking the time and effort to reply to a random student asking questions on the internet.

        As for the data, I have none but I did read the article you posted 2 years ago targeting commercial sex in Singapore and as you may have speculated (based on the evidence you have), regulated sex workers have a lower risk of contracting HIV as compared to streetwalkers as they go through regular screenings.

        I am currently working on a proposal to benefit the unlicensed Sex Workers and it is impossible to find any sort of relevant data on them. Therefore, I am unable to conclude whether they do have a higher risk of contracting HIV. However, I did reach out and spoke to the director of Project X (Vanessa Ho), the only NGO focus on fighting for Sex Workers’ Rights.

        I asked her for her opinion on PrEP and she embodied similar sentiments as you did, fearing that the side effects of PrEP could cause more harm than good.

        Hahaha! Yeah. Those discussions on ways to procure cheaper alternatives would be best left for private conversations over dinner.

        I would love to attend the Singapore AIDS conference held on 3rd December. What would be the best way to do so? Where do I sign up?

        Once again thank you Dr Tan for reading through this long message! Hope I hear from you soon.

        Yours sincerely
        Elsabella Wong

  7. condom broke csw 3,4,8,9 weeks rapid antibody blood test then at 12 weeks and 94 days rapid 4th generation duo. Since my last duo test I’ve had swollen lymph nodes by my groin and feels like im losing weight. I’m starting to freak out again do this mean that I’m one of those rare case that have to wait 6 months to get a positive result. I also found out I had chlamydia from this woman 8 week post exposure so I’m wondering did I catch hiv to i been to my doctor he thinks it syphilis that make me even more scared because I had a full std screening at 3 weeks post exposure so why wouldn’t it show then. I don’t have any immune deficiency nor cancer what’s goin on doc.

    • I do not think your symptoms are related to HIV given the test results. You may want to get yourself checked by a doctor again, and repeat a STD screening.


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