Pharmacokinetics and Contributing Physiologic Changes During Spaceflight, DSO 632B (Pharmacokinetics) - 07.29.14
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The Pharmacokinetics and Contributing Physiologic Changes During Spaceflight, DSO 632B (Pharmacokinetics) is a detailed science objective (DSO) to determine changes in the gastrointestinal function and physiology by examining the pharmacokinetics (process by which a substance is absorbed, distributed, metabolized, and eliminated by the body) of acetaminophen (common pail reliever and fever reducer).
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Johnson Space Center, Human Research Program, Houston, TX, United States
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
Human Exploration and Operations Mission Directorate (HEOMD)
ISS Expedition Duration
October 2005 - September 2006
Previous ISS Missions
A similar study was first conducted in 1993 on STS-51, a short-duration mission, and on Mir-18/STS-71, a long-duration mission. Based on the limited results from these flights, experimental methods have been modified for the present study to evaluate physiology of the GI system.
- Physical, environmental and physiologic conditions of space flight will alter gastrointestinal (GI) function and physiology; these alterations will affect the pharmacokinetics of oral medications.
- Pharmacokinetics and Contributing Physiologic Changes During Spaceflight, 632B (Pharmacokinetics) will study the impacts on the GI function in microgravity and examine the pharmacokinetics of acetaminophen.
Four decades of experience reveal that virtually every system in the body is affected by space flight, the digestive system is no exception. It plays two crucial roles, digestion of food and water and distribution of medicine. Any medication must be absorbed, processed, and then eliminated from the body by several digestive organs, including the stomach, intestines, liver, and kidneys. But the physiological changes accompanying space flight may change the effectiveness of oral medications taken by astronauts.
On Earth, we assume that medications have maximum therapeutic effect and minimum side effects. For crewmembers, taking a medication is far more complex because many factors encountered inflight may compromise the drug’s effectiveness.
The Pharmacokinetics and Contributing Physiologic Changes During Spaceflight, 632B (Pharmakokinetics) study will allow scientists to investigate the effect of microgravity on drug absorption and elimination and the function of specific body systems that affect drug disposition in space.
Using acetaminophen (common pail reliever and fever reducer), scientists can examine the function of the gastrointestinal system (stomach and intestines), renal system (kidney), and hepatic system (the liver). This data will substantiate earlier observations and build on existing data, ultimately yielding more effective treatments in space.
This investigation will help scientists improve the design of medications provided to crewmembers during space exploration to maximize the effect of the medication when taken in microgravity.
Understanding gastrointestinal disorders and diseases in adverse environmental conditions help to improve delivery methods of medications for treatment, establish innovative, non-invasive ways to measure drug availability in the body and validate inexpensive ambient storage for biological samples.
This investigation was comprised of three tests: lactulose and acetaminophen test, glucose breath hydrogen test, and 3-C Urea Helicobacter test. Each of these tests was to be conducted both before and after flight; no data collection was scheduled during flight. During pre- and postflight sessions, a specified breakfast was to be provided, followed by an oral ingestion of acetaminophen. Timed breath and saliva samples were collected, as were void-by-void urine samples. Food, fluid, exercise and medications were monitored during the urine and saliva collections. The rate of acetaminophen absorption and metabolism would be determined by analysis of the urine samples and timed saliva samples.
Lactulose and Acetaminophen Tests: Participants were asked to avoid eating foods that are likely to generate hydrogen (such as cabbage, beans, dairy products) for twenty-four hours before the test. After approximately an 8-hour fast (sleep period), a saliva sample, a urine sample, and two consecutive breath samples, 5 minutes apart, were collected from the subjects. The subjects then ate a low fiber breakfast, followed by ingestion of 650 mg of acetaminophen. After acetaminophen ingestion, participants drank orange juice (or an agreed-upon fluid) containing 20 g of lactulose.
Subjects were not to eat or exercise for 4 hours following ingestion of medication; however, drinking water was allowed. After ingesting the acetaminophen and drinking the lactulose/orange juice mixture, the following samples were collected from the subjects:
- 12 additional saliva samples
- 16 additional breath samples (per the prescribe schedule)
- Urine voids for 24 hours (as separate samples). Subjects were to record intake of food, fluids, medications, and exercise during the 24-hour protocol period.
13-C Urea Helicobacter Test: After overnight fasting, a baseline breath sample was obtained. Subjects then consumed a liquid test meal containing 13-C urea. Breath samples were collected every 10 minutes for 30 minutes post-ingestion.
The overall protocol includes three procedures, each carried out before and after space flight. Astronauts collect breath, saliva, and urine samples before acetaminophen ingestion. They then ingest oral acetaminophen, a common over-the-counter pain reliever, and lactulose, a nondigestible sugar. Acetaminophen and lactulose act as pharmaceutical probes, which allow scientists to trace many GI parameters without using any invasive clinical tests.
Saliva, breath, and urine samples are collected at timed intervals after the astronauts take the probes. Next is a procedure to determine whether the GI environment changes as a result of space flight. Astronauts first ingest glucose and urea (with a special carbon molecule), then collect breath samples for measuring the release of certain gases. Glucose and urea are innocuous substances that also act as probes; their breakdown can be tracked in the body by measuring how much hydrogen and carbon dioxide are released in the breath as a result of bacterial activity. Under normal conditions, low levels of certain beneficial bacteria are present in the GI system, and thus no hydrogen or very little hydrogen is seen in the breath. A higher level of hydrogen in the breath after taking glucose indicates an increase in the bacterial colonies in the GI system. The urea test indicates the levels of Helicobacter pylori, a slow-growing and harmful bacterium present in the stomach. The test measures the level of carbon dioxide, which features the special carbon molecule that can be easily tracked. Under normal, healthy conditions, H. pylori does not grow significantly and therefore does not pose a health risk.
These tests are repeated two times before flight and two times after space flight. By comparing the hydrogen and carbon dioxide levels before flight to levels after flight, scientists will be able to determine if space flight has an effect on the GI environment of astronauts.