By David Warmflash
Space medicine gets respectable coverage whenever the media discuss human space exploration, but mostly it’s focused on what spaceflight does to the body. Occasionally, we’ll also hear a story on the more dramatic prospect of surgery in weightlessness. But as on Earth, much of health care in space is not so dramatic and depends on very simple treatments, such as antibiotics for an infection, ibuprofen to reduce swelling for a minor injury, and pain killers.
Very much aware of this, NASA and other space agencies have supported studies on space pharmacology for decades. We know that both the efficacy and the toxicity of a drug can change because of weightlessness. For example, studies of ibuprofen used in space flight have shown that the drug is absorbed into the body faster in weightlessness than in normal Earth gravity environments (“1 G”, or 9.8 m/s2), yet weightlessness does not seem to affect the drug’s availability to body tissues or its elimination from the body. Thus, the dose does not need to be adjusted for weightless space travelers.
But ibuprofen is just one drug. Since all drugs are different, the relation between oral doses and the amount of active drug in the bloodstream that are understood well in normal Earth gravity will have to be studied all over again in weightlessness. They also will have to be studied in lunar gravity (1.62 m/s2), Mars gravity (3.7 m/s2), or in any fractional gravity in which we plan to keep humans for extended periods.
Another issue related to the prospect of long-duration space missions, and ultimately settlements, is the drug durability in the space environment. In a study of 35 pharmaceutical agents stored up to 28 months aboard the International Space Station (ISS), researchers found that many drug formulations lost their active pharmaceutical ingredient (API) much faster than they lose it on Earth. This occurred with several drugs in ready-to-administer forms such as tablets, capsules, and creams, and with powders that have to be dissolved for intravenous or intramuscular use. The medications studied are available in space medicine flight kits, and the number of formulations failing API requirement increased as a function of time in space, independent of expiration dates. The authors of the study concluded that ionizing radiation is the reason, rather than differences in temperature and humidity compared with control samples that were stored on the group for comparison. API is known to decrease with radiation exposure, and the cumulative space radiation dose increases with time in space.
If ionizing radiation is the reason for the reduced API of drugs in space, the duration of drug activity on future space missions will depend strongly on the destination of the space travelers. Much of the high energy radiation in deep space comes from charged particles, which are trapped by the Earth’s magnetosphere and, thus, do not reach people and equipment in low Earth orbit (LEO) or on the ground. At high latitudes, however, more of the charged particles penetrate to lower altitudes, because the magnetosphere is shaped more like a donut than a sphere. While the ISS moves in a fairly low orbit, the inclination of its orbit is fairly high, meaning that orbits over high latitudes, receiving more charged particle radiation than spacecraft orbiting more inline with the equator. Travel to the moon or other planets takes spacecraft beyond the magnetosphere. Thus, samples of organisms carried on the Apollo 16 and 17 lunar missions were found to have been hit more by charged particles than similar experiments flown in LEO.
This reality may suggest that pharmaceuticals kept in human bases on the moon or an asteroid will expire faster than those used on the ISS. But then, deep space radiation also is bad for people; so bases will probably be underground or sealed within caves to provide radiation shielding. The issue certainly adds complexity to future missions, but the storage of pharmaceuticals now moves to center stage, both for mission planners and media coverage.