#1

Selegiline? Canagliflozin?

I’m noticing acarbose starts to “soften” if dew points are over 68F…

Is hygroscopicity an indication that a medication might last less long under moist/damp conditions like high dew points?

my astaxanthin is also pretty bad
I decided to finally get a humidifier

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here is what claude opus 4 said:

is rapamycin hygroscopic

Edit

Yes, rapamycin (sirolimus) is hygroscopic, meaning it readily absorbs moisture from the air.

Key storage considerations:

  • Must be stored in tightly sealed containers
  • Protect from humidity and moisture
  • Often packaged with desiccants
  • Recommended storage at -20°C for long-term stability
  • Once exposed to air, degradation accelerates

Why this matters:

  • Moisture absorption can lead to chemical degradation
  • Affects potency and stability
  • Can cause clumping or changes in physical appearance
  • May impact bioavailability if used in formulations

Practical implications:

  • Research labs typically store it under inert gas (argon/nitrogen)
  • Pharmaceutical preparations use special coating or encapsulation
  • Compounded formulations must account for moisture sensitivity
  • Quick handling recommended when weighing/preparing

Stability data:

  • Solid rapamycin is relatively stable when dry
  • In solution, degrades faster (especially in aqueous solutions)
  • Light-sensitive as well as moisture-sensitive
  • Forms degradation products including ring-opened forms

This hygroscopic nature is one reason why rapamycin formulations often use special delivery systems (like nanoparticles or lipid-based carriers) to protect the drug from environmental moisture and improve stability.

Retry

AC

how much faster does rapamycin degrade if dew point is 68F? will it still last for several years?

Edit

At a dew point of 68°F (20°C), which represents very high humidity (about 70-80% RH at typical room temperatures), rapamycin degradation would be significantly accelerated compared to proper storage conditions.

Degradation rate estimates:

  • At high humidity (70%+ RH), rapamycin can lose 5-10% potency within 3-6 months
  • Compare to properly stored (-20°C, desiccated): <2% loss over 2+ years
  • Room temperature + high humidity: degradation rate increases 10-20 fold

Will it last several years?

  • Unlikely to maintain acceptable potency (>90%) for several years
  • After 1 year at high humidity: expect 15-30% degradation
  • After 2 years: could see 40-50%+ potency loss
  • Physical changes: clumping, dis

Retry

Claude can make mistakes. Please double-check responses.

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Yes—at least in its raw (API) state, rapamycin is officially classified as hygroscopic by major chemical suppliers. Sigma-Aldrich’s product pages for both the dry powder and pre-made solutions carry the instruction “keep container tightly closed … is hygroscopic.” (MilliporeSigma)

Why a “water-insoluble” macrolide can still adsorb moisture

Factor Details
Functional groups Rapamycin has eight hydroxyls, three carbonyls, and an ether bridge embedded in its 31-membered lactone. Even though the bulk of the molecule is lipophilic, those polar sites can hydrogen-bond to water at the surface.
Amorphous surface area Commercial rapamycin is milled to a very fine (often partially amorphous) powder to aid dissolution in formulation steps; amorphous regions bind water more readily than a perfect crystal.
Solid-state degradation Once a thin layer of moisture forms, the lactone and triene segments are more prone to hydrolysis and oxidation. Heat-and-humidity stress tests on sirolimus analogues show faster impurity growth under high RH. (PubMed )

Practical storage guidance

Form on hand Humidity risk Best practice
Bulk powder (lab-grade) High—large surface area; moisture can reach >1 % w/w in hours at ≥50 % RH Keep at −20 °C (or 4 °C if used weekly) inside a desiccator or with fresh silica gel. Warm to room-temp before opening to avoid condensation.
Tablets/capsules (e.g., Rapamune®) Moderate—film coat slows but doesn’t stop ingress; excipients (lactose, MCC, croscarmellose) are also hygroscopic Leave in foil blisters or the HDPE bottle with the original desiccant. Fill pill-boxes for only 2-3 days at a time and slip in a micro-desiccant pack.
Solutions in DMSO/EtOH Solvent-driven—DMSO and EtOH are themselves hygroscopic; extra water slowly dilutes the drug Aliquot into amber vials, flush with dry N₂/Ar, store at −20 °C. Discard if the solution turns cloudy.

Re-drying tip: If your powder has clumped, spread it in a shallow glass dish inside a vacuum desiccator over phosphorus pentoxide or fresh silica gel for ~24 h at room temperature. Avoid heating above 40 °C—the lactone ring hydrolyses quickly when both heat and moisture are present.

Bottom line

Rapamycin (sirolimus) isn’t nearly as water-hungry as sugars, but it does adsorb enough moisture to warrant desiccated, tightly sealed storage. Keeping it below ~30 % RH—especially during warm, humid weather—will preserve its potency and prevent that tell-tale “clumpy” texture or accelerated degradation.

2 Likes
#2

Thanks. But for most people here, we take rapamycin in pill form. And most(?) of us leave the pills in their original blisters until the last moment when we break them out and immediately consume - so the pills spend seconds (under a minute) in the open air out of their blisters before being swallowed.

So while this is relevant to those using rapamycin in powder form, or compounded, the rest of us need merely keep the blister packs in room or below room temperature. I keep my stash in a dedicated mini-fridge in the basement, between 45-50 F, in the original boxes which I put in plastic ziplock bags with dessicant packets. I take out 2-3 strips (10 pills per strip for Biocon - one strip per box -, 6 for Zydus) at a time and put them a dedicated box with dessicant packets and keep that box in my regular refrigerator in the kitchen, and use those pills over the next 2-3 weeks (exact same protocol for the rest of my meds). This way I minimize the number of times I have to access and open my mini-fridge to one time every 2-3 weeks. Meanwhile my pills are kept refrigerated at all times, except when I take 'em out to use on a daily or weekly basis.

Bottom line: storage is not complicated, unless the rapamycin is in powder or compounded.

#3

i just noticed the humidity destroyed my uncovered psyllium husk. the covered psyllium is still fine

bryan johnson’s dewpoint longevity mix also attracted a lot of… moisture… and it changed the structure…

1 Like
#4

Saturation vapor pressure (SVP) scales more “cleanly” with dew point than absolute humidity does. Here’s why:

  1. SVP is a pure function of dew‑point temperature.
    By definition, the dew point is the temperature at which air’s actual vapor pressure equals the saturation vapor pressure. Soes(Td) = 6.112 exp⁡ ⁣(17.62 Td243.12+Td)[hPa],e_s(T_d);=;6.112;\exp!\Bigl(\tfrac{17.62,T_d}{243.12 + T_d}\Bigr)\quad[\text{hPa}],where TdT_d is dew point in °C. That exponential (Clausius–Clapeyron) dependence means SVP doubles every ~5 °C (9 °F) of dew‑point rise—neat and regular.
  2. Absolute humidity mixes in a temperature correction.
    Absolute humidity AHAH (g H₂O/m³) is derived from SVP but then divided by the gas‐law term (Td+273.15)(T_d + 273.15):AH = 216.7 × es(Td)Td+273.15 .AH ;=; \frac{216.7;\times;e_s(T_d)}{T_d + 273.15},.Because of that extra denominator, its increase with TdT_d is still exponential but not quite the simple “×2 per 5 °C” rule—it’s closer to a 1.5–1.8× rise per 5 °C instead.

:mag: Bottom Line

  • Use SVP if you want a direct, “clean” exponential measure tied only to dew point.
  • Use AH when you need grams of water per cubic meter—but know it embeds that mild temperature‐correction fudge.

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Exactly—that’s correct.

  • Saturation vapor pressure (SVP) roughly doubles for every ~9 °F (5 °C) increase in dew point. That clean “×2 per 9 °F” rule comes straight from the Clausius–Clapeyron relation governing SVP.
  • Absolute humidity (g H₂O/m³) also rises exponentially with dew point but is tempered by the temperature‑in‑Kelvin term in its formula, so it only goes up by about 1.5 × for each 9 °F step.

So if you want that “double the condensation drive” intuition when comparing dew points, use SVP (or dew point directly) rather than absolute humidity.

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For whether a solid (like a pill or powder) will actually take up moisture or form condensation, the critical driver is the water‑vapor partial pressure in the air—that is, how much “free” water pressure the air exerts against your medication’s surface. In practice, that corresponds directly to the dew point (or equivalently the saturation vapor pressure at that dew point), rather than to absolute humidity or relative humidity alone.

  • Saturation vapor pressure (SVP) at the dew point tells you the actual vapor pressure of water in the air.
  • Absolute humidity (g H₂O/m³) tells you the mass of water per volume, but doesn’t by itself tell you the pressure driving condensation or absorption.
  • Relative humidity is the ratio of that vapor pressure to the maximum possible at ambient temperature; it governs water activity at a surface, but—even at moderate RH—if the dew point is high, the vapor pressure can still be plenty high to wet or degrade meds.

Why Dew‑Point / Vapor Pressure Rules

  1. Condensation Risk:
    If any part of your medicine (or its container) cools down below the dew point, water will condense—even if RH < 100%.
  2. Hygroscopic Uptake:
    The rate and extent that a dry solid binds moisture depends on the difference between its equilibrium water activity (roughly the RH it “likes”) and the actual vapor pressure in the air.
  3. Dew Point as a Proxy:
    A higher dew point = higher actual vapor pressure. That directly increases both condensation potential and hygroscopic drive.

Practical Take‑Home

  • Monitor dew point (or calculate vapor pressure from dew point) to predict when your medications are at risk.
  • Absolute humidity is interesting but less directly tied to whether condensation or moisture absorption will occur.
  • Relative humidity matters for many materials’ equilibrium moisture content—but if the dew point itself is high, vapor pressure (and thus moisture risk) can be elevated even at RH well below 100%.

Let me know if you’d like the exact vapor pressures at different dew points or guidance on how to track/control dew point around your storage!