Regarding the treatment of Blastocystis with Bactrim, this was my experience in 2009 and what I am experiencing now in 2012 three years later.
My doctor prescribed Bactrim after I requested a lab test for Blastocystis and it was confirmed as positive. Blastocystis had been misdiagnosed as IBS by two medical doctors over a period of at least a decade or longer until I found the BadBugs website and recognized the symptoms, (swollen abdomen, pressure headaches, ringing in the left ear and wax build up, a feeling of bursting at the gut, extreme fatigue, cravings for sweet and salty foods, memory fog, pain in the lower left bowel (which I had pointed out to several doctors who ignored it), panic attacks, insomnia, flatus, constipation (bowel blockages) and finally, diarrhea leading to incontinence episodes and fatigue/weakness so bad, it was difficult to get out of bed or drag myself up the stairs.
I took Bactrim only three days because its effect was drastic. It led to severe chronic watery, yellow diarrhea. However, since I was not going to be able to access a specialist for colonoscopy due to the waiting list and needed immediate help, I asked a doctor at Emerg at a local hospital to give me Flagyl. He agreed to prescribe the drug since I'd tested positive for Blasto and Flagyl is a treatment for Blasto as well as C Dif and SIBO (Small Intestine Bowel Overgrowth).
Within 3 days the Flagyl reversed the diarrhea completely. All conventional lab tests after both the Bactrim and Flagyl were negative for Blastocystis and also negative for C Dif. Also, important to note that the Flagyl treatment did not permanently cure the diarrhea and it came back so I had to either repeat the Flagyl or go on probiotics, the latter which I decided to do being safer as a long term solution although I tolerated Flagyl quite well.
I asked my family doctor for a test for SIBO and these results came back negative. The results came back from Doctor's Data came back as Clear (No Ova or Parasites)after two years. So apparently either Bactrim or the Flagyl or both in combination cleared the Blasto permanently but left me with a weak intestinal flora situation which made it almost impossible to hold down a job and function outside of the home without help from probiotics. Now, THREE YEARS LATER, the colon and lower bowel are functioning quite dependably and well finally.
I had to experiment with a dozen types of probiotics until I found one or two that worked the best and Tu Zen which is a new human strain on the market works best. It not only creates a normal bowel pattern but seems to get rid of gas and bloating, improves sleep, appetite and energy. Apparently it also has a good reputation for colonizing that other probiotics do not have. I have also used Butyrate in combination which research has proven, is an essential for normal funtioning in the colon. I used organic psyillium and Bentonite clay but had to give up the psyillium and use ground flaxseed instead because it was causing a worsening of the gas/bloating.
Another very strange co-incidence - A foot callus on the bottom of my left foot which was getting larger was causing problems at the same time that I had Blastocystis. I went to see a foot specialist and was advised to get a special type of shoe with an insert, or I wouldn't be able to walk within several years. However, after the Blastocystis was cured, the foot callus disappeared completely and has not returned.
Would I take Bactrim for Blastocystis again? Probably not, even though it may have contributed to eradicating it. I would be very cautious with antibiotics and try every herbal/natural treatment first, reserving it as a last ditch effort if nothing else works.
Let me add that I did try several herbal treatments for parasites before using Bactrim in 2009 and they did not work. I thought I saw temporary improvement at the time but the Blasto always seemed to come back.
I am now using penicillin for curing strep throat and (no C Diff!) but I've learned my lesson and will always use antibiotics and probiotics together (several hours apart). That might have prevented the diarrhea from the Bactrim back in 2009. Hope this helps.