I saw a program on the tube that said if a person is bitten by a black widow spider, and needs to take the anti-venom (not all bite victims need the anti-venom) they can only take it once in their entire lives. But the @#%! idiots didn’t say why that is. The most interesting fact of the show and they don’t explain it! AAAUGH! I can’t find any clarity to this on the “web” (pun intended 
any clues or links guys?
I have a clue which might help. I spent an hour on the net looking for that assertion, but did not find it. An easier way might be for one of the members to look up the specific anti-venom in their Physician’s Desk Reference. The information you want will be in there. My PDR isn’t here (sorry). If no one replies, the PDR is available at any library.
PK, I saw that too. It was a guy who had been bitten in the chest and suffered tremendously for about a week, but not taken the anti-venom because he would never be able to take it again. Milking black widow spiders for their venom, what a job.
The CSL Antivenom Handbook goes into pretty good detail about the use of the antivenom, but it doesn’t say that it can’t be used repeatedly. It does mention that people with previous exposure to equine serum derivatives (including the antivenom) may be at greater risk of anaphylaxis (an adverse reaction to the treatment). Anaphylaxis can be considerably more dangerous than the original envenomation, so repeated use of the antivenom is probably discouraged. The page referenced below is specifically about Australian red-back spiders, which are closely related to the widow spiders and affect humans primarily with latrotoxins (as the widows do):
http://www.wch.sa.gov.au/paedm/clintox/cslavh_antivenom_redback.html
It may be like peanut allergies. At first you body doesn’t recognize the anti-venom as a bad thing, so the venom does it’s business. The next time you try it, however, the body recognizes it as an enemy and all hell breaks loose. Kind of an anti-immunity.
Let’s at least get the spelling straight.
This is known as serum sickness, IIRC. But all antivenins that I know of are made this way. Get venom from spider (or snake, scorpion, jellyfish, lizard, etc.), inject into horse (or goat), draw blood from horse, purify antibodies against venom. So the hypersensitivity reaction Balance discussed can potentially occur with repeated usage of any antivenin, whether its for a black widow bite or a rattlesnake bite. I don’t think it’s BW specific.
Not to criticize your comment but to be accurate it is Antivenom (or antivenin or antivenene), the parts in parenthesis being the less common but still acceptable spellings or usages. My source is Antivenom - Wikipedia check it out.