Timing of sirolimus blood test to check effectiveness


I have been taking rapamycin (SiroBoon from Kachhela in Indial) for one year. I take 8 mg once a week (1mg/10kg body weight).

Last week, I finally did a sirolimus blood test. They drew the blood 120 minutes after I took the pills on an empty stomach. I was very surprised when I got the result: 0.7 ng/ml. I’m under the impression that the value should have been substantially higher.

Any ideas if the timing was wrong, or if the Siroboon brand is not good, or any other reason?


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I also use SiroBoon. The last time I checked, a 12 mg dose gave me 4.9 ng/mL after 1h 18m and 17.9 ng/mL after 3h 02m. Everyone is a bit different on this front, but your low result probably stems from the empty stomach. I take rapamycin with a 400 kcal meal (31% kcal from fat).

The FDA Structured Product Label (SPL) for Rapamune includes the following:

Across 24 healthy volunteers, consuming sirolimus tablets (as Rapamune) with a high-fat meal (861.8 kcal, 54.9% kcal from fat) increased Cmax (65%), tmax (32%), and AUC (23%).

Rapamycin is a lipophilic compound, which means it dissolves best in lipids. Taking it alongside a high-fat meal can increase its solubility in the digestive tract and facilitate its absorption into the bloodstream.


Thank you! I’m so glad I reached out for advice.


Usually it’s supposed to go the other direction with time: in 3 hours you are supposed to have less Rapa than in 1 hour. I find your numbers unusual. How do you explain it?


Rapa peak after oral administration is ~ 2 hrs for most people. In this case with a high-fat meal delaying time to peak, the first level was drawn too soon. Rapa was still being absorbed and levels rising, which was seen in the second level drawn.


For adult renal transplant patients, the 2022 FDA Structured Product Label (SPL) for Rapamune shows a tmax for tablets of 3.5 ± 2.4 hours. Here’s the chart:

In renal allograft recipients, tmax for the first dose was 5.67 ± 6.37 hours (Mathew et al. 2013). Here’s the relevant table:

In case you’re thinking about (Brattström et al. 2000), these values came from a rapamycin solution—not tablets:

The solution has a lower tmax in all the studies I’m aware of. Drugbank mentions that “In healthy subjects, the tmax is one hour”, but I’ve not been able to find data supporting this for tablets—only the oral solution.

As @sluggerT80 mentioned, taking rapamycin alongside a high-fat meal does increase the tmax. The FDA SPL mentions a 32% increase.

@LaraPo, what’s your basis for expecting a tmax around 1 hour for rapamycin tablets?


From my own experience (and I’m a transplant patient on 1mg Rapa per day):

If I take 1 mg/day for 5 days and draw blood in 1 hour after dosing, my trough is going to be 5. If I do the same after 3-4 hours my trough is going to be 3.5. The more time the less the trough. I also measure trough 24 hours after dosing, if I’m on Rapa continuously (each day) for at least 2-3 weeks my trough will also be 3,5-4.

I usually take Rapa with reseveratrol dissolved in a teaspoon of EVOO.

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