This doesn't make any sense to me either. Current pills containing hydrocodone are a mixture with other drugs, mostly other drugs that have a higher toxicity, and part of the reason for that is to keep people from taking too many of them. If you OD on Vicodin, it's not the 5mg of hydrocodone that kills you, it's the 500mg of acetaminophen. For a 50kg person, you can get to a reasonably toxic quantity of acetaminophen (200 mg/kg) with 20 vicodin, which gives you a dose of 100mg of hydrocodone, or 2 mg/kg. Quick googling found this: http://toxnet.nlm.nih.gov/cgi-... that gives animal toxicity studies showing an LD50 for hydrocodone in the range of 86 mg/kg (mice) to 375 mg/kg (rats). Granted, you certainly don't want to take anything *near* to the LD50 of any drug, but the highest dosage for a Zohydro pill is 50 mg. For a 50kg person to get a dose of 1/4 the mouse LD50 would be over 20 pills. As noted, if those 20 pills were vicodin, then they would also be toxic, but only because of the acetaminophen. And really, if you're downing 20 of *any* prescription painkiller, you almost certainly have a different goal in mind than temporary pain relief. I just really don't see this as causing much harm, and potentially helping a fairly specific set of people who need it.
People who are intent on abusing pills can get around the acetaminophen simply by breaking the pills up, putting them in cold water, and running them through a coffee filter. This is known as cold water extraction.
Part of the reason for the acetaminophen in painkillers is because of a loophole in the 1970 Controlled Substances Act that classified pure Hydrocodone as a strictly controlled Schedule II drug (Which Zohydro will fall under). However, Hydrocodone combination products, such as Vicodin, which contains Hydrocodone and acetaminophen, into the less strict Schedule III classification. As a Schedule III drug, combination drugs such as Vicodin can be refilled as many as five times, while Schedule II drugs can be filled only once.
So why is there so much pushback against Zohydro, when it clearly fits a need and will be more difficult to obtain and abuse than Vicodin? I think it might have to do with the fact that it's put out by a tiny company (Zogenix) rather than one of the big players. Teva Pharmaceuticals who literally spent millions on lobbying last year has a competing product "TD Hydrocodone" which they're trying to get to market, but Zogenix beat them to it. If Zohydro were delayed for a little while, perhaps they could get to market with their competing drug and given their vastly larger resources they'd likely win market share. Another large company Purdue Pharma (the makers of OxyContin) also have something in the works