Hi Jill,
I'm sorry to hear about your cold - this is really unfortunate timing, to say the least. I know how much this race means to you.
Vitamin D3 has been shown to have antibiotic properties, against many viruses. It appears that viruses can be prevented by maintaining higher blood levels of vitamin D3, (as determined by a 25(OH)D test). More than that, though, it has been suggested, (by Dr. John Cannell, of the Vitamin D Council), that massive doses of vitamin D3, taken soon after the first symptoms appear, can actually prevent a virus from developing. For example, it is claimed that taking approximately 1,000 IU of vitamin D3, per pound of body weight, daily, for 3 days, will prevent the H1N1 flu virus, (swine flu), from developing, provided that the treatment is started soon after the first symptoms appear. Vitamin D3 is available in 50,000 IU capsules, from at least one manufacturer, so most people would need about 3 of those, per day, to do the trick. Note that at this dosage level, this would be considered to be a therapeutic dose of D3, (a normal daily supplemental dose would be in the 2,000 to 4,000 IU range).
Since your cold is probably fully developed by now, though, it's probably too late to try a D3 treatment. If you aren't already taking a vitamin D supplement, you might want to consider taking it as a preventative measure, in the future, especially during the winter. I believe that Polly takes 4,000 or 5,000 IU per day, except during the summer. I take from 2,000 to 4,000 IU daily, (except during the summer), but I live in the South, (Central Texas).
The Entocort may allow the cold to linger longer than usual, (since it suppresses the immune system somewhat), so it's rather likely that you will not be up to running on Saturday, unfortunately. I wish I knew of some miracle cure, but even if there were one, just the carryover congestion will be enough to severely handicap your breathing, for a few days.
Sorry I'm not much help. I'm certainly sending my best vibes, though, and wishing you the best of luck.
Love,
Tex