Phoenix welder Samuel Evans unexpectedly became a medical celebrity after he was bitten on his right thumb by a rattlesnake while hiking Sunday in White Tank Mountain Regional Park.

Outside of clinical trials, Evans is the first patient in the United States to be treated with a new rattlesnake anti-venom that hit the market in October, when rattlesnakes were not in season. As a result, no patients were treated with the product when it first came out.

Banner-University Medical Center Phoenix, where Evans was treated this week, usually sees between 55 and 70 patients with rattlesnake bites per year.

Though April is usually the beginning of the season, the hospital has already treated a few bites this year.

Doctors now have a choice of two anti-venoms when treating patients bitten by rattlesnakes: the drug CroFab, and now Anavip, which was used to treat Evans. Doctors gave the Anavip to Evans intravenously after he had an allergic reaction to CroFab.

Anavip is licensed by Tennesee-based Rare Disease Therapeutics Inc., which confirmed Tuesday that Evans appears to be the first patient to try Anavip outside of clinical trials.

Officials with Rare Disease Therapeutics are hoping the anti-venom helps move science forward in treating rattlesnake bites, company medical science liaison Jude McNally said.

Bites can cause delayed complications

Anavip has a longer "half-life" than CroFab, meaning it stays in the body longer and reduces the chances of late bleeding complications, said Dr. Ayrn O'Connor, fellowship director of the medical toxicology program at the University of Arizona College of Medicine-Phoenix.

"Fortunately, we now have another anti-venom available in the U.S. that's been FDA-approved," O'Connor said. "This is a relatively new product and the old product is still out there. ... Eventually, I think you will see that transition to where more and more Anavip is being used because of that benefit of being able to treat bleeding abnormalities and maintain that protection because it stays around in the body longer than the older product."

When one is bitten by a rattlesnake, there's an immediate threat. But problems can happen hours and days after the bite, too. Strokes and even deaths occur due to delayed bleeding abnormalities, O'Connor said.

"If this does take care of that problem as expected, it would reduce the risk of death from a delayed bleeding," O'Connor said of Anavip.

Takeaway lesson: Don't touch, play with or handle rattlesnakes

Rattlesnake bites not only cause pain, swelling and bleeding abnormalities. They can also cause tissue loss, restrictive injuries, amputations and "systemic toxicity" where blood pressure drops and the patient can become unconscious.

"The number one take-home message is If you see a snake out in the wild, to not touch it, pick it up or play with it," O'Connor said. "We have historically had patients bitten in the face, often because they are handling a snake inappropriately."

About 8,000 venomous snakebites occur in the U.S. each year, and those bites typically result in eight to 15 deaths, the University of Arizona Poison and Drug Information Center says.

Evans, 44, so far has reacted positively to the Anavip and is hoping to be released from the hospital later this week.

Evans was bitten toward the end of his Sunday afternoon hike as he used a stick to get a rattlesnake off the trail. He'd seen some kids looking at the snake, which was about three and a half feet long, and wanted to make sure no one got hurt, he said.

"I grabbed a stick to get the snake off the trail to get it out of the way of the kids. It ended up getting caught up in the brush and got a little bit of leverage on it and he spun around and bit me," Evans said from his hospital bed Tuesday.

None of the kids were bitten and Evans used his own bite as a teachable moment, he said.

"After it happened I told the kids, 'this is why you don't mess with them (snakes)'," Evans said. "I told them to learn from my mistake."

A bite out of your wallet: One vial of Anavip is about $1,200

The bite itself wasn't too painful, more like a slap. But the swift swelling was not a good sign. Evans knows a thing or two about rattlesnake bites — this was his fifth, though it has been a while since the last one, in 2005.

He admits being fascinated by snakes. If he sees one, he'll always stop and look, he said. Most people get scared off after one bite, but Evans said it hasn't stopped him from going outdoors.

"I'm out in the wilderness all the time, constantly hiking," he said. "This time of year they (rattlesnakes) are active all day long. The temperatures are perfect for them. They don't like it cold. They don't like extreme heat."

Initially, Evans went to a hospital near the trail and received CroFab, and that hospital transferred him to Banner-University Medical Center Phoenix near downtown, where he received more CroFab. But that's when he broke out in hives and a rash.

"That's when they put me on this new stuff. I knew they said it was new, but I didn't know it was that new...My girlfriend keeps teasing me about being famous," he said. "It seems to be working very well. I was anticipating this being much worse overall."

Evans did not have health insurance at the time of the bite but is hoping to get covered through an application he submitted to the Arizona Health Care Cost Containment System, which is the state's Medicaid program.

"If I don't get it I'll be paying for this for a very, very long time," he said.

Indeed, snakebites can be expensive. One vial of CroFab is about $3,000 and one vial of Anavip is about $1,200, O'Connor said, citing the most recent estimates she has seen. Treatment usually requires on average more than 12 vials, and that does not include the cost of hospitalization and other care.

"It's very expensive therapy but this is a relatively rare diagnosis and in the long run, it ends up being about half the cost to treat a patient with Anavip compared to CroFab," she said.

Reach the reporter stephanie.innes@gannett.com or follow her on Twitter @stephanieinnes