This article summarizes the research published in 2015 “Medication Use by U.S. Crew Members on the International Space Station.”
Several aspects of the spaceflight environment could affect human health –
Launch includes a brief period of high gravitational (g) force and vibration, followed by weightlessness (sometimes referred to as microgravity). At mission’s end, landing includes another high-g, high-vibration period.
Exposure to radiation is higher than on Earth.
Crew members live in a closed system, with carbon dioxide concentrations about 10 times higher than Earth atmospheric norms.
The absence of circadian cues, including light cycles, disrupts circadian rhythms. This effect is likely to be exacerbated by the periodic schedule changes necessary on missions; mission activities such as docking may require intense activity and attention in the middle of a typical sleep period, necessitating a slam shift, a relatively abrupt change in crew members’ sleep/wake cycles.
Each of these unusual aspects of the environment has the potential to affect human physiology.
ISS Crew Members Studied
The research analyzed medication use data for 24 ISS crew members on long-duration (average, 159 +/- 36 d) missions from 2002 to 2012. The subject group consisted of 18 men and 6 women; of those, 2 men and 1 woman reported no medication use during their missions.
All medications available to U.S. crew members on the ISS are commercially available U.S. Food and Drug Administration-approved OTC or prescription medications used within their labeled shelf lives. They are restocked before expiration; medication doses that expire on-orbit are removed from the supply chain.
Reasons for Medication Use
Crew members on spaceflight missions use medications to prevent or treat medical problems associated with their unusual environment, as well as to treat ordinary minor complaints.
Pain treatments included OTC nonprescription nonsteroidal anti-inflammatory drugs (NSAIDs), aspirin, and acetaminophen, as well as prescription NSAIDs.
Treatments for skin conditions like rash included topical preparations (corticosteroids, antihistamines, and antibiotics), as well as oral dosage forms (corticosteroids and antihistamines).
Sinus congestion and allergy symptom treatments included OTC antihistamines, decongestants, as well as prescription antihistamines.
Some of the health issues treated by crew members are unique to spaceflight or otherwise associated with mission operations –
Space Adaptation Syndrome (SAS), also known as space motion sickness is unique to spaceflight. SAS symptoms may include nausea and vomiting, as well as lethargy and drowsiness. It generally occurs during the first few days after a gravity transition, such as launch or landing. Treatments for SAS may include antinausea medication, alertness medications, and pain relievers.
Crew members sometimes find that the ISS environment is not conducive to sleeping well; medication used for sleep includes prescription hypnotics and melatonin.
Extravehicular activity (EVA, sometimes known as a spacewalk) may prompt prophylactic use of antiemetic or antinausea medication, alertness medications, or pain relievers.
The most frequently noted reasons for medication use on the ISS are discussed in more detail below.
Sleep and Alertness
71% of crew members reported using medications to induce or maintain sleep.
Alertness medications were used by 21% of crew members.
Some reports described treatment of muscle, back, or joint pain with medications. EVA was named as the suspected cause in 10% of the joint pain and 20% of the muscle pain reports. Use of the Advanced Resistive Exercise Device (ARED), which permits crew members to perform bone-preserving weight-lifting exercises on the ISS, was named in 40% of back pain reports and 20% of muscle pain reports. One report included a comment that attributed the pain to spinal elongation, which occurs in the absence of gravitational forces.
Ibuprofen was used in 73% of joint pain reports, 60% of back pain reports, and 70% of muscle pain reports. Other reports indicated use of acetaminophen or NSAIDs.
Headaches were treated with medications in 17 reports. Crew member notes attributed causality to pressure changes, elevated carbon dioxide levels, a suspected upper respiratory infection, and caffeine withdrawal. Ibuprofen was used in all but 2 cases; 1 crew member was treated with acetaminophen and 1 with an aspirin/acetaminophen/ caffeine preparation. 54% of the crew members reported headaches; 17% of crew members reported multiple headaches over the course of their missions
There were 43 reports of congestion or allergy symptoms on the ISS that required treatment, 51% of which indicated regular or repeated medication use. 55% of crew members treated symptoms of allergy or congestion during their missions; 38% of crew members treated such symptoms repeatedly or continuously. Congestion and allergy symptoms were grouped, because the source of symptoms could not be determined by crew members during their mission.
There were 12 reports of medication use to treat SAS symptoms; 9 indicated promethazine, with 2 reporting scopolamine and 1, meclizine.
Seven reports of prophylactic use (all promethazine) were made near the time of launch or landing; 6 of these indicated that symptoms were successfully prevented.
There were 46 reports of medication use to treat rash or other minor skin problems in 6 crewmembers. Four of these crewmembers reported using topical antifungal preparations for a few days at a time with satisfactory results. Two crewmembers reported use of multiple topical preparations (antifungal and steroid) and multiple oral medications (antihistamines and steroids). Notes on the reports from these 2 individuals indicate that treatment failure drove repeated dosing and medication switching.
Several reports mention infrequent use of OTC remedies for common gastrointestinal symptoms.
Antibiotic use was reported by only 4 crewmembers. Two of these uses (topical) were for eye inflammation, 1 was for a suspected urinary tract infection, and 1 was for suspected upper respiratory infection.
A total of 277 reports were available on medication use by 24 crew members on 20 missions over a 10 yr period. Figure 1 summarizes the reasons that drove medication use. Most medications used for 7 continuous days or less were used for ordinary complaints (Fig 1A); the same was true for medications used for more than 7 d continuously (Fig 1B).
At least 10% of spaceflight-related medication uses were linked to extravehicular activities, exercise protocols, or equipment and operationally driven schedule changes.
The most frequently used medications on the ISS were for sleep problems, pain, congestion, or allergy.
ISS crew member results were compared with those from crew members on shorter space shuttle missions (>16 d) and other studies of medication use by healthy adults. Medication use during spaceflight missions was similar to that noted on the Space Shuttle and in adult ambulatory medicine, except that usage of sleep aids was about 10 times higher during spaceflight missions.