My husband has been having the headaches between 6-8 pm for three weeks now. We knew they were clusters because our brother-in-law suffers from them. The neuro put him on the following:
25 mg topamax
240 mg verapamil
20 mg imitrex
Did that last Fri, Sat and Sun. (had to use two doses of the imitrex Sun. nite)
Called neuro. yesterday morn. because used up his 4 doses of imitrex for the week.
She said to start taking 2 each of the meds and she would order him some oxygen.
He used the oxygen last nite, three different times. The first time only used it for about 5 minutes and it was gone. Then had to use it again about 45 minutes later.   He then fell asleep but had to use it again about 1 hour later. Then went to sleep and slept rest of the night.
He seemed to feel better this morning. Said head wasn't hurting as much, not as sore and he didn't feel as nervous, etc.
I am a little concerned about using the oxygen, the dr. didn't really tell us how long to use it. I have been reading info. on this site, do you use it for a little while longer after the first headache goes away to keep future ones from coming on?

The top. and verap. take several days to become effective and then, after the initial trial period, dosing may have to be adjusted. Hope your doc has given some instructions along these lines.

Important to learn. Explore the buttons (left); starting with the OUCH site. Personally, I prefer the organized approach of books and would suggest:

MANAGEMENT OF HEADACHE AND HEADACHE MEDICATIONS, 2nd ed. Lawrence D. Robbins, M.D.; pub. by Springer. $50 at Amazon.Com.  It covers all types of headache and is primarily focused on medications. While the two chapters on CH total 42-pages, the actual relevant material is longer because of multiple references to material in chapters on migraine, reflecting the overlap in drugs used to treat. I'd suggest reading the chapters on migraine for three reasons: he makes references to CH & medications which are not in the index; there are "clinical pearls" about how to approach the treatment of headache; and, you gain better perspective on the nature of headache, in general, and the complexities of treatment (which need to be considered when we create expectations about what is possible). Finally, women will appreciate & benefit from his running information on hormones/menstrual cycles as they affect headache. Chapter on headache following head trauma, also. Obviously, I'm impressed with Robbins' work (even if the book needs the touch of a good editor!) (Somewhat longer review/content statement at 3/22/00, "Good book....")

HEADACHE HELP, Revised edition, 2000; Lawrence Robbins, M.D., Houghton Mifflin, $15. Written for a nonprofessional audience, it contains almost all the material in the preceding volume but it's much easier reading. Highly recommended.
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Re. Oxygen: some folks find that while it may abort an attack the headache may redevelop shortly after you stop using. Only experience will indicate how it works for you. This is the experience for all the meds we use: variable effectiveness between people for reasons which are no understood. Important to sustain you patience as you explore, with the doc, various treatments and NOT get into the self-blaming game. Knowledge is the preventive for fear/anxiety.

too much of Imitrex can cause rebounds.  And do not be concerened about oxygen side Effects.  To my knowledge, there are none.  Just do not fall asleep with the mask on.  That will suffocate a person.  Cut the strap of the mask for precaution.  CH can ware a person down so I believe it is possible to fall asleep while using o2.  Its not only possible, it happened to me.  He may be able to have the verapamil dose increased.  I take 1200mg with little side effects.  But don't do it without the doc saying so.  Prednisone will give him a break of up to 5 days and is typically used when first starting preventative therapy.  Unless you husband has another condition, it should have been prescribed to him because verap takes some time to start working.  

Normally a Prednisone taper is perscribed to give some relief
while the Topomax and Verapamil are building up. It usually starts working for me in about 24 hours.

Don't give up on the O2!  Ask his doc if he can try melatonin, that can eliminate the night-time hits between 6-12mgs.