Only limited conclusions could be made because participation in the protocols was incomplete, and were also limited by subjective evaluation of the medication. The first two protocols (five-day regimens) were not well-tolerated by the crew, being found to cause unacceptable side effects such as congestion, head fullness, and headache. The third regimen (single-dose) did not restore plasma volume and did not seem to improve orthostatic tolerance on landing day.
None of the protocols restored blood volume. The percent change in plasma and red blood cell volumes from preflight to postflight was not significantly different in the fludrocortisone vs. non-fludrocortisone group. Fludrocortisone subjects did not have greater orthostatic tolerance than control subjects on landing day.
On landing day, 2 of 18 in the placebo group and 1 of 7 in the fludrocortisone group became presyncopal (chi2 = 0.015, p = 0.90). Plasma volumes were significantly decreased after flight in the placebo group, but not in the fludrocortisone group. During postflight stand tests, standing plasma norepinephrine was significantly less in the fludrocortisone group compared with the placebo group.
The conclusion therefore, was that treatment with a single dose of fludrocortisone results in protection of plasma volume but no protection of orthostatic tolerance. Fludrocortisone was, therefore, not recommended as a countermeasure for spaceflight-induced orthostatic intolerance.
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