Astronauts marching off to the International Space Station (ISS), or further yet, to Mars, better double-check their medicine cabinets.

Space travel appears to alter the stability of drugs flown on Space Shuttle and ISS flights.

An on-going study of antibiotics, motion sickness drugs, and other remedies provided to astronauts show that some products degrade during space treks causing concern among NASA medical specialists.

Long-haul expeditions to Mars, for one, could be exposed to increased risk by trying to fend off medical emergencies with ineffective drugs. For instance, an uncontrolled infection might lead to an en route crew having to short-circuit their mission. In the worst case, casualties could occur due to bad doses of onboard medicines.

Research into the stability of pharmaceuticals during space flight has been underway for several years, said Lakshmi Putcha of the NASA Johnson Space Center in Houston, Texas. "But we needed all the methods and procedures put in place. It's taken a lot of leg work," she told SPACE.com.

Along with Putcha, scientists Jianping Du, Tina Bayuse, and Vinodbala Shah of Wyle Laboratories Life Sciences Systems and Services group, lead the effort. Kurt Berens, a part-time clinical scientist from Wyle was also an early coworker on the project.

Together, the study team evaluated the stability of drugs flown on ten consecutive shuttle flights and five International Space Station sojourns.

Ten candidate drugs -- dispensed in tablet, suppository, cream, ointment, and patch form -- were selected for testing before and after they were flown on one or more space flights. Medications selected included antibiotics and motion sickness formulations.

These pharmaceuticals were checked for stability, shelf life, as well as physical appearance, chemical content and dissolution rate - how well the medicine dissolves.

The space medicines were held up against standards set by the United States Pharmacopeia (USP) or other comparable guidelines.

Based in Rockville, Maryland. USP is a non-government organization that promotes the public health by establishing state-of-the-art standards to ensure the quality of medicines and other health care technologies. Currently, USP provides recognized standards around the world for more than 3,400 prescription and non-prescription drugs, nutritional and dietary supplements, veterinary drug standards, and health care products.

Results from ground-control samples and those from flight were compared to assess stability and shelf life claimed on the label.

The team found, of the drugs tested, "significant degradation" of chemical content in Augmentin (a treatment for respiratory infections) and Bactrim (an antibacterial combination drug).

Furthermore, other medicines flown in space showed decreased chemical content, or a lessened ability to dissolve. Also found by the researchers were drug dosage forms not significantly different from their corresponding ground controls.

So what does a space doctor do about stocking the medicine chest of future off-to-Mars crews? Wheezing all the way to the red planet seems a bit of a distraction.

In looking over their data, the science team found that temperature and relative humidity range were similar in different space flights.

But one culprit is being considered: radiation.

Radiation levels were variable between flights and may be contributing to the degradation of pharmaceuticals in space, the team reports.

Ground-based studies are being proposed to examine radiation effects on those drugs that took an effective nose-dive in space.

"These are very important pieces of information," Putcha said. "We're going to look further into thisto make recommendations for the long duration flights. It's a high-priority task at NASA as of now," she said.