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What is PrEP on-demand dosing and is it suitable for me?

Some people are choosing to only take PrEP when they know they’re going to have anal sex. We look at the reasons why

What is PrEP on-demand dosing and is it suitable for me?
Some gay men are only taking PrEP when they know they're having sex (Photo: David Hudson)

For many gay men, PrEP has changed the ways they engage in safer sex. The medication drastically reduces your chances of acquiring HIV – with or without condoms.

When people talk about PrEP, conversations have tended to focus on taking a daily dose of the anti-HIV medication. This is usually Truvada or a generic variant. But a daily dose is not the only way some people are taking PrEP.

You can also take it in recommended dosages before and after sex to reduce your chances of acquiring HIV. Clinicians and sexual health advocates commonly call this on-demand dosing or event-based dosing.

Why would some people only take PrEP before and after sex?

PrEP is commonly a combination of two drugs: tenofovir disoproxil and emtricitabine. Together, these are commonly sold as Truvada, although generic combinations are also available in some countries.

PrEP is designed to be taken as a daily pill. This ensures the protection it gives you is constant. It doesn’t matter when you have sex because the medication is always in your system.

In countries such as the US, the FDA-approved PrEP is covered by many health insurance plans and a daily prescription is the most common way of taking the drugs. Indeed, the CDC states, ‘people who use PrEP must commit to taking the drug every day’, to ensure maximum protection.

The World Health Organization (WHO) states, ‘Taking PrEP every day is recommended because daily use of PrEP is effective, safe and the most convenient approach.’

However, in other countries, PrEP is not readily available. In most of the UK, you can’t get PrEP on the National Health Service (NHS).

For those unable to get themselves on the current NHS trial in England, the only way to get PrEP is to buy Truvada privately (which can cost $560/€455 a month), or to buy a generic version of the drug. This can cost around $28-$77 (€23-€63) for a month’s supply of daily pills.

Websites such as IWantPrEPNow and PrEPster have information for where you can buy reputable, generic versions of the drugs. In London, the Dean Street PrEP Shop will also sell you a generic version.

So this is to do with making your supply last longer?

‘One of the reasons [people take on-demand dosing] is that it is cheaper than daily dosing when people are paying for their own PrEP,’ says Nneka Nwokolo, Consultant in Sexual Health and HIV Medicine at London’s 56 Dean Street clinic.

‘On-demand dosing means that their supply lasts longer.

‘Another reason is the perceived concerns about potential side-effects as some people feel that these might be less likely than with daily dosing.

‘Another is infrequent sexual activity. Some people who have sex only a few times a month for example, may feel that they don’t want or need to take PrEP every day.’

Besides concerns about side-effects, some people worry about how taking a daily drug over a sustained period of time may impact them. There is no evidence to suggest long-term PrEP use is bad for you, but that doesn’t stop some people having concerns.

And in case you need reminding, PrEP only offers protection against HIV, not other sexually-transmitted infections. To protect your sexual health from a wide range of diseases, using the medication in combination with condoms is recommended.

A wall calendar

On-demand dosing entails keeping careful track on when you take medication (Photo: Pixabay | Public Domain)

Who shouldn’t take on-demand PrEP?

PrEP should only ever be taken by people who are HIV negative. This is very important, as people who are HIV positive who take the drugs may find themselves developing resistance to the medication. It’s why anyone thinking of taking these drugs must get themselves tested for HIV in advance.

You must also be tested to ensure you don’t have hepatitis B.

OK, so what does on-demand dosing involve?

In regard to anal sex, the 2015 France-based IPERGAY study found on-demand dosing to be very effective.

• At least two hours, and up to 24 hours, before you have sex, you take two PrEP pills at the same time.

• You then take a single pill 24 hours after your initial double dose.

• You then take another single pill the following day, another 24 hours later.

Basically, you’re aiming to take a single pill 24 hours and 48 hours after your first double dose.

Ensure you take PrEP that contains both tenofovir disoproxil (TDF) and emtricitabine.

You can continue to take PrEP every 24 hours until 2 doses after your last sex session.

Truvada PrEP medication

PrEP is Truvada or a generic variant (Photo: David Hudson)

For example, if you take a double dose on Thursday evening at 10pm, and then have sex Friday evening at 7pm and on Saturday evening at 7pm, you should take the single dose of PrEP Friday evening at 10pm, Saturday evening at 10pm and Sunday evening at 10pm.

The initial double dose ensures you have a good level of protection in your body, if you take it at least two hours in advance of sex. The longer you leave it, up to 24 hours, the better (one of the drugs hits maximum efficiency 24 hours after taking it).

The single doses every 24 hours afterwards ensures the protection is maintained at this effective level.

Can I do that every Friday – before the weekend?

If you start, stop, and then want to start a dosing cycle again within a seven-day period, you won’t need the double dose on the second cycle.

For example, you take a double dose at 4pm on a Friday. That night you have sex, and take a single dose the next evening at around 4pm. You have sex again Saturday night, and take further single doses at around 4pm Sunday and Monday.

You then stop taking PrEP on the Tuesday, Wednesday and Thursday, but on Friday, in preparation for more weekend sex, you take a new single dose a couple of hours beforehand and start the dosing cycle again.

That all sounds complicated!

Yes – which is why some people find it easier to take a daily pill. If you do opt for on-demand or event-based dosing, maybe set alarms on your phone to remind yourself to take the pills.

Is this an effective way to take PrEP?

The IPERGAY study concluded that on-demand dosing led to an 86% reduction in HIV infections over the course of the study. This is similar to daily dosing. The study had just over 400 high-risk participants – half of whom took PrEP and half a placebo.

After a year, two of those in the PrEP arm of the study had become HIV positive (compared with 14 in the placebo group).

However, only 43% of those involved in the study reported taking the drugs at the right time throughout the study. In fact, those who became positive had not taken PrEP for several months at the time they acquired the virus.

So if I know when I’m going to have sex, this is an option?

‘Event-based dosing is a good option for gay and bisexual men who know, accurately, when they’re going to have sex,’ says Matthew Hodson, Chief Executive of NAM in the UK.

‘It’s important to acknowledge that the only event-based dosing regimen that has been demonstrated to be effective is one where the user takes two pills on the day that they expect to have sex, then, if they do have sex, one pill on each of the following two days.

‘Adopting this regimen, the large-scale French IPERGAY study found the same level of effectiveness as the daily dosing UK PROUD study.

‘Whether PrEP is taken daily or based on sexual activity, it’s vital to remain adherent. Testing of tissues in studies of event-based PrEP suggest that the two doses after sex are crucial to the success of the strategy.’

His view is also held by London’s 56 Dean Street – the busiest sexual health clinic in Europe.

‘The IPERGAY study of event-based or on-demand PrEP showed the same efficacy (86% reduction in infections) as the PROUD study of daily PrEP,’ says Nneka Nwokolo.

Hodson cautions that events-based dosing is not for everyone.

‘Event-based dosing works for anal sex but may not work for vaginal sex, where daily PrEP remains the recommendation.’

How many people are taking on-demand PrEP dosing?

Will Nutland, co-founder of PrEPster finds on-demand dosing far more common in Europe than the US or Australia.

‘PrEPster and Iwantprepnow, in conjunction with Public Health England last year ran a survey. The survey was from people who were using PrEP in the last 12 months, and we asked them what dosing regime they were taking, and more then three-quarters of men said they were taking PrEP on a daily basis. The other quarter were taking PrEP on an events-based basis.’

The survey, completed by 800 men in the UK last summer, took place before the current NHS trial began in England. All those surveyed bought PrEP for themselves.

What if I forget to take a pill?

If you forget a dose, take a pill as soon as you remember. You should still have some level of drug protection in your body (unless you forgot for more than a couple of days), and a further dose will help top up your protection.

If you miss the double dose before sex, take a double dose after sex and then continue daily.

Immediately consult with your local STI clinic or clinician if in doubt, or to ask if they recommend you take PEP (Post-Exposure Prophylaxis).

‘When you take the double dose, you’re basically getting a double shot,’ says Nutland.

‘What you’re doing by putting that double dose in your body 2-24 hours before sex is giving yourself enough protection. Also, if there’s one piece of key information I would urge you to get across it’s that the follow-on dosage – 24 hours later and 48 hours later – is really, really important.

Nutland says the IPERGAY study has influenced his own use of PrEP. However, other researchers point out IPERGAY was just one, moderately-sized study. Nutland thinks organizations such as the CDC will want more, larger studies to be taken before it changes its recommendation of taking PrEP daily.

It’s a personal choice

Ultimately, how you decide to best look after your health, and lower the risk of acquiring HIV, is a personal decision.

‘With PrEP, as with other safer sex strategies, some methods are going to work better for some people than for others,’ says Matthew Hodson.

‘Some will choose event-based dosing because they only occasionally have sex with any risk of HIV acquisition. Others may choose it because they want to reduce the amount of medications they take or because it’s a cheaper option, if they are paying for their PrEP.

‘Others choose daily dosing because they find it an easier option for adherence – and it means that they can have sex spontaneously.

‘There are a wide range of strategies that people can adopt to prevent acquisition of HIV. PrEP, whether it is event-based or daily, is the most effective of the safer-sex strategies that we have.’

For more info

Download the i-base booklet on PrEP, which includes more details and suggested dosage regimens, here. Seek out and talk to a medical professional, ideally a sexual health clinician, for further information.

See also

What is hepatitis C and should gay men be concerned?


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