PrEP, or Pre-Exposure Prophylaxis, is a preventative strategy for individuals who do not have HIV but are at risk of exposure. It involves taking specific antiretroviral medication to reduce the risk of acquiring HIV through sexual contact or injection drug use.
PrEP is highly effective when taken as prescribed, but it does not protect against other sexually transmitted diseases. There are different ways to take this medication, including daily dosing and on-demand schedules. Understanding the correct dosage, adherence requirements, and necessary health screenings is vital for ensuring maximum protection.
Understanding PrEP (Pre-Exposure Prophylaxis)
PrEP stands for Pre-Exposure Prophylaxis. It is a biomedical intervention designed to prevent the Human Immunodeficiency Virus (HIV) from establishing an infection in the body. It is not a vaccine. Instead, it is a pill that contains two antiretroviral medicines. These are usually Tenofovir and Emtricitabine. When you take PrEP, these medicines build up in your body. If you are exposed to HIV, having these medicines in your system stops the virus from replicating and taking hold.
It is important to distinguish PrEP from PEP (Post-Exposure Prophylaxis). PrEP is taken before potential exposure to prevent infection, whereas PEP is an emergency medication taken after a potential exposure has occurred. PrEP is intended for ongoing protection during periods of risk.
The medication is available under various brand names, such as Truvada and Descovy, as well as generic versions. In Singapore, generic versions are commonly used and are chemically identical to the branded versions. The effectiveness of the medication relies heavily on strict adherence. If the medication levels in the body drop too low due to missed doses, the protection against HIV decreases significantly.
Assessing Your Suitability for PrEP
Before learning how to take PrEP, it is necessary to determine if you are a suitable candidate. Medical guidelines in Singapore generally recommend PrEP for individuals who are HIV-negative and have a significant risk of acquiring HIV.
You may be a candidate for PrEP if you are an adult who is sexually active and:
- You have a sexual partner who is HIV-positive and has a detectable viral load (or their viral load status is unknown).
- You do not use condoms consistently during sex.
- You have had anal or vaginal sex without a condom with multiple partners in the past six months.
- You have been diagnosed with another sexually transmitted disease (STD), such as syphilis, gonorrhoea, or chlamydia, in the past six months.
- You engage in chemsex (using drugs to enhance sexual experiences).
It is mandatory to confirm that you are HIV-negative before starting PrEP. Taking PrEP if you already have HIV can lead to drug resistance, which makes treating the virus more difficult later. A consultation with a General Practitioner is required to assess your risk profile and medical history.
The Two Main Ways to Take PrEP
There are two primary methods for taking PrEP: Daily PrEP and On-Demand (Event-Driven) PrEP. The choice between these two regimens depends on your frequency of sexual activity, your lifestyle, and your biological sex.
Daily PrEP Regimen
The daily regimen is the most common method of taking PrEP. It is straightforward and involves taking one tablet every 24 hours.
Who is this for?
Daily PrEP is recommended for all genders. This includes cis-gender women, transgender men and women, and cis-gender men. It is the only approved method for individuals engaging in vaginal sex or for people who use injection drugs. It is also the preferred method for individuals with unpredictable or very frequent sexual activity.
How to take it:
- Take one pill every day at roughly the same time.
- It can be taken with or without food.
- Pick a time that fits your routine, such as after brushing your teeth or with breakfast, to help you remember.
Time to Efficacy:
The medication takes time to reach protective levels in different body tissues.
- For anal sex protection: You generally need to take the pill daily for 7 days before you are fully protected.
- For vaginal sex protection: You generally need to take the pill daily for roughly 20 days before you are fully protected.
Pros and Cons:
The daily regimen provides the highest level of protection because it maintains a constant level of medication in the body. It is also more forgiving; if you miss a single dose occasionally, you are likely still protected (though strict adherence is always best). However, it requires the commitment to take a pill every day, regardless of whether you have sex that day.
On-Demand (Event-Driven) PrEP Regimen
On-Demand PrEP, also known as Event-Driven PrEP or the 2-1-1 schedule, involves taking the medication only around the time of sexual activity.
Who is this for?
This regimen is strictly for cis-gender men who have sex with men (MSM). It is not effective for vaginal sex protection because the drug does not concentrate quickly enough in vaginal tissues. It is suitable for men who have sex less frequently (e.g., less than twice a week) and can predict when they will have sex.
The 2-1-1 Schedule:
- Step 1 (The Loading Dose): Take 2 pills (a double dose) between 2 to 24 hours before sexual activity.
- Step 2: Take 1 pill 24 hours after the first double dose.
- Step 3: Take 1 pill 24 hours after the second dose.
If sexual activity continues:
If you continue to have sex over multiple days, continue taking 1 pill every 24 hours until you have gone 48 hours without sex since your last sexual encounter. You must then take the final two doses (one each day) to cover the “tail” period.
Contraindications:
On-demand PrEP is not suitable for individuals with chronic Hepatitis B infection. Starting and stopping the medication can cause a severe flare-up of the Hepatitis B virus and damage the liver.
Starting Your PrEP Journey
To begin taking PrEP safely, you must visit a medical clinic. Self-medicating without medical supervision is dangerous.
Initial Testing and Consultation
At a clinic, the process begins with a consultation and baseline screenings. The doctor needs to establish a baseline of your health to ensure the medication is safe for you.
Required Tests:
- 4th Generation HIV Test: This is the most critical test. You must be confirmed HIV-negative. The 4th generation test can detect both HIV antibodies and the p24 antigen, allowing for earlier detection than older tests.
- Kidney Function Test (Creatinine/eGFR): The medication in PrEP is processed by the kidneys. It is essential to check that your kidney function is normal before starting.
- Hepatitis B and C Screening: As mentioned, Hepatitis B status dictates which PrEP regimen you can use.
- STD Screening: You will also be screened for Syphilis, Gonorrhoea, and Chlamydia. Having other STDs can increase the risk of HIV transmission, so treating them is part of the prevention strategy.
The Importance of the HIV-Negative Status
It is vital to understand the “window period.” If you had a high-risk exposure very recently (e.g., within the last 10 to 14 days), an HIV test might not yet detect the infection. In such cases, the doctor might advise you to wait and repeat the test or start PEP instead.
Starting PrEP while you are in the acute phase of an undiagnosed HIV infection can lead to the virus developing resistance to the drugs used in PrEP. This limits your future treatment options. Therefore, regular testing is a non-negotiable part of the PrEP protocol.
Managing Missed Doses
Adherence is key to PrEP effectiveness. However, missing a dose can happen. The protocol for handling a missed dose depends on which regimen you are on.
Missed Doses on Daily PrEP
Daily PrEP is relatively forgiving for cis-gender men due to the long half-life of the drug in rectal tissue. It is less forgiving for protection during vaginal sex.
- If you remember within 12 hours of your usual time: Take the missed pill immediately. Then take your next pill at the usual time.
- If more than 12 hours have passed: Skip the missed dose. Wait and take the next scheduled dose at the usual time. Do not take two pills at once to make up for the missed one.
- If you vomit: If you vomit less than one hour after taking the pill, take another one. If you vomit more than two hours after taking it, you do not need to take another one as the medication has likely been absorbed.
Missed Doses on On-Demand PrEP
Missing a dose on the 2-1-1 schedule is more risky because the total level of drug in the body is lower than in daily users.
- Missed Pre-Sex Dose: If you miss the double dose before sex, you may not be protected. If sex has already occurred, contact your doctor immediately. You may need to transition to PEP (Post-Exposure Prophylaxis).
- Missed Follow-up Doses: If you miss the dose 24 hours or 48 hours after sex, take it as soon as you remember. If the delay is significant, consult your healthcare provider for advice on whether to extend the dosing period.
Potential Side Effects and Management
PrEP is generally well-tolerated, but like all medications, it can cause side effects. Most side effects are mild and resolve on their own.
Common Short-term Side Effects:
Many users experience what is called “start-up syndrome” during the first few weeks. Symptoms may include:
- Nausea
- Headaches
- Fatigue
- Stomach upset or bloating
- Diarrhoea
These symptoms usually disappear after the first month as the body adjusts to the medication. Taking the pill with a meal can help reduce nausea.
Long-term Considerations:
Serious side effects are rare but require monitoring.
- Kidney Function: A small percentage of users may experience a slight decline in kidney function. This is why doctors perform blood tests every three months. If a decline is detected, stopping the medication usually reverses the effect.
- Bone Density: There may be a minor decrease in bone mineral density. For most people, this does not lead to bone fractures or clinical problems.
Regular Monitoring:
When you are on PrEP, you are required to visit the clinic every three months. These visits are used to:
- Repeat the HIV test to ensure you remain negative.
- Screen for other STDs.
- Monitor kidney function to ensure the medication is not causing harm.
- Prescribe the next batch of medication.
Stopping PrEP Safely
You may decide to stop taking PrEP if your lifestyle changes and you are no longer at risk of HIV exposure. However, you should not stop abruptly without a plan.
For Daily Users:
- Anal Sex Protection: Continue taking the daily pill for 7 days after your last potential exposure.
- Vaginal Sex Protection: Continue taking the daily pill for 28 days after your last potential exposure.
For On-Demand Users:
You must complete the full 2-1-1 cycle. This means taking the medication for two consecutive days after your last sexual encounter.
Hepatitis B Warning:
If you have Hepatitis B, do not stop taking PrEP without consulting your doctor. The medications in PrEP also suppress the Hepatitis B virus. Stopping them suddenly can cause the Hepatitis virus to reactivate, leading to severe liver damage. Your doctor will need to transition you to a different management plan for Hepatitis B.
Conclusion On PrEP for HIV Prevention
PrEP is a powerful tool in the fight against HIV, offering a high level of protection when taken correctly. Whether you choose the daily regimen or the on-demand schedule, understanding the specific dosing requirements is essential for your safety.
It is important to remember that PrEP only protects against HIV and does not prevent other sexually transmitted diseases; therefore, condoms remain a crucial part of sexual health. Always consult with a qualified healthcare provider to assess your suitability and to monitor your health while on the medication.
Our experienced team of healthcare professionals specialises in diagnosing and treating sexually transmitted diseases. From same-day STD testing to personalised treatment plans, we deliver accurate and reliable care tailored to your needs.
Frequently Asked Questions About PrEP
How Long Does It Take for PrEP to Be Effective?
The time it takes for PrEP to provide maximum protection depends on the type of sexual activity. For receptive anal sex, it generally takes about 7 days of daily use to reach protective levels in rectal tissue. For receptive vaginal sex and for protection related to injection drug use, it takes approximately 20 days of daily use to reach protective levels in the blood and vaginal tissues.
What Is the Difference Between Daily and On-Demand PrEP?
Daily PrEP involves taking one tablet every 24 hours, regardless of sexual activity. It is suitable for all genders and those with frequent or unpredictable sex. On-Demand PrEP (also called the 2-1-1 schedule) involves taking medication only around the time of sex. On-Demand is strictly recommended only for cis-gender men who have sex with men and is not effective for vaginal sex protection.
What Happens If I Miss a Dose of PrEP?
If you are on daily PrEP and miss a dose, you are usually still protected if you have been taking it consistently, as the drug levels remain high enough for a short period. If you remember within 12 hours, take it immediately. If it has been more than 12 hours, skip it and take the next one at the usual time. If you are on On-Demand PrEP, missing a dose is more critical and can significantly lower your protection; you should consult a doctor immediately if this happens during a period of sexual activity.
Can I Stop Taking PrEP If I Am No Longer Sexually Active?
Yes, you can stop taking PrEP if your risk of HIV has decreased or you are no longer sexually active. However, you must stop safely. Generally, you should continue taking the medication for 7 to 28 days after your last sexual exposure, depending on the type of sex. Crucially, if you have Hepatitis B, you must consult a doctor before stopping, as stopping the medication can cause liver complications.
Does PrEP Protect Against Other Sexually Transmitted Diseases?
No, PrEP does not protect against other sexually transmitted diseases (STDs). It is specifically designed to prevent HIV infection. It offers no protection against Gonorrhoea, Chlamydia, Syphilis, or Herpes. Healthcare providers strongly recommend using condoms in conjunction with PrEP to prevent these other infections.
Do I Need a Prescription for PrEP in Singapore?
Yes, PrEP is a prescription-only medication in Singapore. You cannot buy it over the counter at a pharmacy. You must see a doctor at a General Practitioner or a specialised clinic. The doctor will conduct necessary blood tests, including HIV and kidney function tests, before writing a prescription to ensure the medication is safe for you to use.
