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The issue of the effects of radiation on medication potency is not only important for long term stays in the ISS, but also very important for longer duration journeys and even for colonization.

One thing is certain, the chances are that astronauts/colonists will fall ill, not necessarily to the extent asked in How is the ISS equipped to deal with the outbreak of a contagion?, but with the more mundane illnesses mentioned in the answers. Some would require regular medication as well.

So, the question is, in the increased radiation environment of space, how does increased environmental radiation affect medication potency, in the long and short term?

Additionally, are medications on the ISS shielded to protect it from radiation?

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  • $\begingroup$ This is a great question! It's also a good example one that could take advantage of some future SE feature that allows for cross-viewing of interdisciplinary questions. In this case it would be Biology and perhaps Chemistry. $\endgroup$
    – uhoh
    Apr 16, 2019 at 10:16
  • $\begingroup$ I don’t have time to write a full answer in detail right now, but I can tell you that the med packs are not specifically shielded from radiation beyond the standard shielding in the Lab. The question of how medications behave in a long-duration low-dose exposure regime is an open area of research - high dose/short duration exposures are better understood, and then tend to be for radiation sources not very analagous to the deep space environment. The second half of the human/medication system is how pharmacokinetics may be altered by the space environment independently from the meds. $\endgroup$
    – JPattarini
    Jun 30, 2019 at 1:10
  • $\begingroup$ I doubt that all medicines would behave in the same way as they are different chemically. Some are likely to be a lot more resistant to the effects of radiation than others. Ionizing radiation can disrupt chemical bonds which may not then reform in the same way causing chemical changes effectively degrading the active drug substances. $\endgroup$
    – Slarty
    Oct 17, 2019 at 22:01

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There is an excellent article on the topic in Nature: https://www.nature.com/articles/s41526-019-0076-1

So far, the issue of medication shelflife has been dealt with by re-supply, so the study of radiation stability has been “back-shelved” (pun intentional). There is certainly concern for reduced potency as well as toxic byproducts in drugs which have undergone radiation-induced degradation reactions.

The most concerning radiation is charged particles because they have high linear energy transfer, LET, (energy deposited per path length).

In spacecraft outside LEO, the majority of charged particles are protons and alpha particles. But heavier charged particles from Galactic Cosmic Rays (GCR), although less abundant, have much higher LET. As well, they have high hull penetration and spallate into numerous lower atomic weight particles. The spectrum of heavier GCR particles can only be reproduced by the GCR simulator at the NASA Space Radiation Laboratory (NSRL).

Most radiation studies have been done on biological targets, which are mostly water. This research projects poorly onto pharmaceuticals which are often stored dry.

Radiosterilization is commonly used in the pharmaceutical industry. However, a radiosterilized drug is classified as a “new” product and must be re-approved. It is assumed that if a pharmaceutical is stable under high sterilization dose, lower dose over protracted time course is likely safe. However, there is some evidence from NSRL which contradicts this.

Sensitivity to radiation is drug-specific. For instance, Cephradine and cefotaxime, both solid-form cephalosporin antibiotics of similar molecular structure, demonstrate significantly different radiosensitivity. Cephradine degrades significantly and has been determined to be unstable under irradiation whereas cefotaxime demonstrates high resistance and stability.

Another concern is that radiated packaging material could produce additional progeny ions that alter the chemical composition of pharmaceuticals within.

Experience with “flown drugs” returning from the ISS have shown that amoxicillin-clavulanate, levofloxacin, trimethoprim, sulfamethoxazole, furosemide, and levothyroxine degraded before their expiration dates. Impurities were found in aspirin, ibuprofen, loratadine, modafinil, and zolpidem.

Suggested (but inadequately studied) mitigation strategies include cryo storage, radiation-stable packaging, space-hardy excipients and on-board shielding.

Bottom line: radiation effects on pharmaceuticals are a valid concern. More study is needed in anticipation of long space flights outside LEO.

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