Kolokol-1

Kolokol-1 (

Kolokol-1 is thought to be the

Shevchenko attributed the hostage deaths to the use of the chemical compound on the poor physical condition of the victims after three days of captivity - dehydrated, hungry, lacking oxygen and suffering acute stress, saying "I officially declare that chemical substances of the kind banned under international conventions on chemical weapons were not used," according to the Interfax news agency.^[4]

This comment is disputed on two grounds. First, the United States Ambassador to Russia at the time complained that delays on the part of the Russian government in identifying the exact nature of the active agent in the gas led to many hostage deaths which might otherwise have been avoided.

The specific antidote for carfentanil is naloxone. This report goes on to state

• carfentanil is only approved as a
  veterinary drug for use in sedating large animals such as elephants, not for use in humans because the effective dose is unacceptably close to the dose which can cause illness or death;^{[citation needed}
  ]
• that the deaths among hostages after the Moscow theater can be explained by the use of carfentanil and remifentanil, two strong drugs for which there is little margin of safety between
  lethal doses in humans. Many deaths could have been expected unless the people exposed got quick treatment with the drugs' antidotes.^{[citation needed}
  ]
• that it is highly unlikely a
  chemical agent can be used in a tactical environment to disable opponents reliably without many deaths.^[2]

An article in the Annals of Emergency Medicine compared the sedating dose and the toxic or lethal dose of fentanyl and those of its derivatives and found that while carfentanil and remifentanil have dramatically shorter biological half-lives and are more potent than fentanyl, the fentanyl derivatives are lipophilic (readily taken up into body fat) and can re-enter the circulation after an overdose is first treated, causing severe delayed effects and even death if the correct antidote is not administered when the drugs act again. This might account for the large number of deaths following use of large amounts of Kolokol-1 in a closed space like the Barricade Theatre, where the gas might have been unexpectedly concentrated in areas of the theater.

Under the heading "Lessons Learned," the authors state "It seems likely that the 800 hostages were about to be killed by

The authors said that the high therapeutic index of one of the fentanyl derivatives used may have inappropriately reduced the Russian government's concern about the potential lethality of these agents, the drugs' lipophilicity, and how the hostages could have been overdosed in the enclosed space of the theater as factors that should have been considered more thoroughly. They concluded by saying that poisoning by opioid agonist drugs such as Kolokol-1 is relatively simple to treat, and that many of the deaths after the Moscow theater hostage crisis could have been avoided if trained rescuers and medical teams with the proper antidotes were made ready in advance. They stated that naloxone, long a critical antidote to treat heroin overdose and unintentional poisoning with opioids during medical treatment, "has now become a crucial chemical warfare antidote."^[5]

Carfentanil, one of the two fentanyl derivatives used in the Moscow theater hostage crisis was actively marketed by several Chinese chemical companies at the time. Carfentanil was not a controlled substance in China, where it was manufactured legally and sold openly over the Internet up until May 1, 2017, when a ban on fentanyl and all fentanyl analogues^[6] went into effect.^[7] There has been controversy between the US and China over whether the Chinese ban on sales of fentanyl derivatives to the US has been effective. Fentanyl led to more than 37,000 overdose deaths in the US in 2017.^[8]

The toxicity of carfentanil has been compared with nerve gas, according to an Associated Press article. The article quoted