Question
Is PEP effective if taken 48 hours after exposure?
2 July 2021. Related: All topics, PEP/PEPSE.
I paid for sex with a woman but the condom tore and I only realised after I was done. There is a high chance that she was HIV positive. I started PEP after 48 hours.
I got a PCR test done 17 days after exposure. It had a less than 20/ml (undetectable) result.
Now between 14 and 35 days after exposure I have had signs of thrush, mild red rash on my face and a couple elsewhere. But no fever or swollen lymph glands.
Can the rash and thrush be because of utter stress and obsession?
My doctor says that the PCR can be relied upon and that I am negative.
Can the PEP have reduced the viral load to less than 20/ml as I took it for 15 days before the PCR test?
Please give your expert advice. I am very anxious. Thank you.
Answer
Thank you for your question.
The risk of HIV from one broken condom is very low. If your partner had an undetectable viral load on treatment, then the risk would be zero. If they were not on treatment the risk might still be only 1 in 300 or lower.
You cannot guess someones HIV status so your assumptions might also be wrong.
You started PEP within 48 hours, so it is likely it will work.
PEP – stands for Post-Exposure Prophylaxis. It is a term used for taking HIV drugs to reduce the risk of infection. PEP usually involves taking a combination of three HIV drugs for one month. The earlier PEP is started, the more likely it will work. Ideally, this should be within a couple of hours. If this is not possible, then still the earlier the better.
Some guidelines include a two-day window to do this (i.e. within 48 hours). After this, effectiveness is much less likely. Other guidelines allow up to 3 days (i.e. within 72 hours). Sometimes this may be more for psychological benefit. For example, if someone is very stressed or traumatised.
No guidelines recommend starting PEP after 72 hours.
After finishing PEP you need to wait a 4-6 weeks before testing.
If the PEP has worked, or the person was not initially infected, this will show as a negative HIV test. The test you did 17 days after the exposure will not be accurate yet.
If the PEP has not worked, this will be shown in a positive test result. Testing 4 weeks after PEP will detect 95% of infections. Testing after six weeks will detect more than 99% of infections. This result doesn’t need to be tested again.
If PEP has not worked, serosonversion usually occurs 1-3 weeks after PEP is finished. However, only 80% of people show symptoms.
Please test 6 weeks after you finished PEP is finished. If you test any earlier, you need to take a second test 3 months later.
Viral load (PRC) tests are not approved to test for HIV. In some cases they can have a role.
Please see a doctor to talk about your symptoms he best way to confirm what is causing them is to see your doctor. He/she will be able to diagnose and treat the symptoms accordingly.
Note: This answer was last updated in July 2021 from an original post from December 2011.
Hi Jazmine, PEP will be effective as long as it has been started within 72 hours. Starting at 37 hours is more than early enough to be effective.
A 4th generation test will be conclusive from 42 days after the last dose of PEP. You would not need to wait until day 45 to confirm your result.
If you are using a 3rd generation test (only antibody) you are required to test at 90 days after the last day of treatment to confirm your status.
More information about testing can be found here: https://i-base.info/qa/factsheets/hiv-transmission-and-testing
Hi, I hope you can help, I have 2 questions, I started PEP as a precautionary measure at 37 hours post potential exposure so do you think it was still effective ?
I also took a test 43 days after finishing the course of the medication, I understand that 45 days is the minimum, do you think those 2 days will be a factor in my results which I am currently waiting for ? Many thanks
Hi Kasaya, as you have now tested 14 weeks after the last dose of PEP HIV is not the cause of your symptoms. You have a confirmed result that you are HIV negative and you do not require any further tests.
PEP has a short half life, meaning that after you stop PEP the side effects will stop and it will no longer be in your body. The aches you have mentioned in your legs are not caused by PEP and are not related to HIV.
Please speak with your doctor to have appropriate investigations and treatment, looking for other causes.
Hello doctor, kindly advice me. I am experiencing needle like aches in the souls of my legs and these are 4 weeks down the line since it all started. I have tried to squeez my legs with hot water and the problem is not resolving. I have tested at 6th week, 10th week and the 14th week after the last dose of PEP. All tests have been negative. What could be my problem please?
Hi Kasaya, the test you have done at 14 weeks is conclusive. You do not require any further tests as it is confirmed you are HIV negative.
Testing and transmission: https://i-base.info/qa/factsheets/hiv-transmission-and-testing
As your partner was on treatment and undetectable there was no risk of transmission. When someone has a viral load this low it means HIV is suppressed so much that HIV cannot be passed on via sex. It is called U=U: https://i-base.info/u-equals-u/
I slept with a woman who was HIV positive and was on ARVS since 2014. She claimed to be on undetectable viral mode. I started PEP 10 hours after the exposure. I completed the 28 days dosage of PEP in October 2023. I have tested using the third generation test on week 6, week 10 and week 14 after the last dosage of PEP. All the tests have been negative. The doctor told me to retest after 6 months, then 1 year so that I may be confirmed to be safe.
I am confused, does it mean there are chances that I may test positive soon as the time goes by?
Hi Melody, yes your treatment will still work. Being half an hour early is going to have no impact on how effective your treatment is. It is okay that you have taken your treatment early. As long as PEP is taken within an hour of it’s normal time there is no risk of this time difference having any effect.
For more information about PEP please see here: https://i-base.info/qa/factsheets/pep-faq
I normally take my pep drug at 7.30pm but today I took it at exertly 7.00pm wil it stil work out in me.
Hi Anki, no your body will not become resistant to PEP medication. What is the name of the PEP combination you had been given previously and what are you using now?
As you have used several courses of PEP have you considered PrEP? PrEP is a treatment you take BEFORE an exposure to HIV and is more effective at preventing HIV transmission.
PrEP can be taken daily or on-demand and would not require you taking multiple courses of PEP and accessing this treatment from your doctor.
More information about PrEP can be found here: https://i-base.info/guides/prep
Hello, I had taken pep 3 times already but it was somewhat at lower risk. I completed course for 28 days all times. Doctor has given me pep for 4th time with different combination than other 3. Will that work and my body can get resistant to pep drugs as I have already taken it thrice and now starting with fourth?