A/C Protection

[Alan_G]

One of the reasons I chose Apixaban over Riveroxaban is because it's out of your system quicker if you need that (12 hours as opposed to 24). Taking it twice a day doesn't bother me because there are supplements (Magnesium) I take twice a day already.

My GP tried to counter this argument saying that after 12 hours you were fully topped up with AC again when taking Apixaban whereas with Riveroxaban you were half depleted. Anyway, my question does not relate to this because I made my choice.

What I am curious about is does your level of protection against stroke diminish as you approach the end of the drug's life in your bloodstream (12 hours for A, 24 hours for R)?

[Beancounter Volunteer]

Hi Alan

Interesting question, and one that I am not sure I figured out until recently, and even then not sure I fully understand it.

Apixiban and Rivaroxaban work in exactly the same way, they inhibit the production of Factor Xa or FXa which is a key component of the coagulation process, this is a bit further down the line than Vitamin K which of course warfarin inhibits.

The half life of Rivaroxaban in an adult over 45 is 11-13 hours, which is why we take it once a day as it it considered that even with half the dose you are still protected, as the Factor Xa is still inhibited. As much as two hours after taking the drug? Interesting question and not one I have found the answer to yet.

Similarly, even double the dose is not going to suddenly make you bleed, just inhibit the Xa production for longer, but of course I am NOT suggesting under any circumstances that anyone takes more than the recommended dose.

Also especially for Rivoroxaban, the instructions for the 20mg dose are WITH FOOD, not before or after, but WITH, and the reason for this is that a high percentage of the drug can otherwise come out into the urine, making it less effective.

Apixiban, is taken twice a day, and the reasoning as you are quite correct is that the half life is shorter (6 to 7 hours) but still remains effective I understand for 24 hours after the first tablet is taken.

I have to say Apixiban would have been my choice, but my GP had never heard of it and refused to prescribe, he was very reluctant with the Rivaroxaban (and still is)

Would love to hear from any of the techies out there if the protection is lower 20 hours into taking Rivaroxaban.

Be well

Ian

[Alan_G in reply to Beancounter]

My GP's preferred choice is Riveroxaban because it's once a day. However, he was very aware how 'read up' I was on all of this and so when I said I'd made up my mind that Apixaban was my first choice he happily prescribed that for me. I don't know how reliable tall these trials are that take place but Apixaban also seems to have the best record when it comes to bleeds (ie lower chance of).

Alan

[Alan_G in reply to Beancounter]

Why is the half life of a drug important? I would have thought the 'full life' of a drug would be the key because that is when you need to top up, so to speak?

Decided to answer my own question by looking it up:

Half-life is the time it takes for the concentration of a drug in your system to drop by 50%.

Here's a simple example. Suppose you have a concentration of 100mg/l (100 milligrams of drug per liter of blood) at say 1 PM, and the drug has a half-life of 2 hours. If you had blood drawn and tested every 2 hrs it would look like this:

1PM 100 mg/l

3PM 50 mg/l

5PM 25 mg/l

7PM 12.5 mg/l

Notice that in the first 2 hours, between 1PM and 3PM, your body got rid of 50mg/l of the drug.

But then in the same amount of time, the 2 hours between 3PM and 5PM, your body only got rid of 25 mg/l.

But in all cases, your body gets rid of half of the however much of the drug is there in the 2 hour interval. That is why it is said to have a 2-hour half-life.

The explanation for this is that the rate at which you body breaks down drugs (well, those with linear pharmacokinetics, anyway) is relative to the concentration of the drug in your system, not an absolute rate of elimination. (It get’s rid of 50% per 2 hours, not a fixed amount per 2 hours)

This is really significant because drugs with short half-lives will wear off quickly. This could be a good thing, like a sleeping pill that doesn't make you groggy the next day. But it could be bad if your symptoms break thru.

Also, if the half-life is short and you want to keep the concentrations in your system steady, you have to take the drug every half-life.

So if you want steady concentrations of a drug with a 24-hour half-life, you can take it once a day. If you want steady concentrations of a drug with an 8 hr half-life, you need to take it 3 times a day.

The problem with drugs with really long half-lives is that the build up in your system and can get to really high concentrations, even if you are only taking them once per day.

Prozac can still be in your system 6 weeks after you take the last dose.

[Beancounter Volunteer in reply to Alan_G]

Hi Alan

You are completely right, but remember firstly that with both NOACS the half life is relatively short at 6 -7 hours or 12-13 hours, but also let's remember what they do, they inhibit the production of Factor Xa, they don't make you bleed. I completely agree about Prozac I knew someone who had a hell of a battle to get off it.

For me the key question here is still at what concentration do they remain effective? and I am sure the techies will answer around 50% otherwise of course why was Rivaroxaban licensed?

I suppose the other enquiry might be to do with bleed risk, are we also saying that bleed risk is higher shortly after taking the dose? Again I suspect the techies will answer no it remains the same until the half life is under 50%

It is interesting, good thread

Ian

[Alan_G in reply to Beancounter]

I've just looked up the half life of Apixaban and it states it is 12 hours. That implies you take another dose when it is 50% depleted. It also stated it is in your system for up to 24 hours after you stop taking it. So much for it being out of your system quicker because it has to be taken twice as day!

[wpw62]

I recently had surgery and was told to stop taking rivaroxaban a full three days before my surgery date to ensure it was out of my system.

[beardy_chris]

I asked a specialist a slightly different question but one which is relevant: how accurate do you need to be in your timings when taking Apixaban? He suggested it is, of course best to take drugs at the same times morning and evening accurately but that +/- 1 hour is fine, +/- 2 hours is acceptable and +/- 4 hours is taking a slight risk.

So, translating this answer into the OP's original question, there may be some degradation in cover as the time of taking your anti-coagulant recedes but it probably isn't significant unless you are late taking the next dose.