^Partial agonist


• The division into two classes is not absolute and some drugs listed for moderate pain can be effective in severe pain by injection.

32 As the following account illustrates: ... We saw this guy lying on the ground with two people trying to help him — they were trying to help him breathe by mouth to mouth. When we ran over to them we could tell it was not working. The guy was blue in the face and hardly breathing any more. Right away I gave him one ampoule of naloxone — I didn't think I could find a vein so I just shot it real slow into his upper arm... .Then the guy started to wake up and he started to breathe and shake a little... .When the medics came I told them

I had given him naloxone. The medic said 'Wow! So you guys have even got naloxone now?' (Dettmer K, Saunders B, Strang J 2001 British Medical Journal 322: 895-896).

• Fentanyl, alfenatil and remifentanil are high-

efficacy opioids used for surgery/anaesthesia.

Partial agonists were developed in the unrealised hope of eliminating the potential for abuse whilst retaining analgesic efficacy. They are indeed less liable to induce dependence and to cause respiratory depression than are the pure agonists but they may induce psychotomimetic reactions. Their antagonist action is chiefly evident against large doses of agonist, e.g. in addicts.

Etorphine is a high-efficacy opioid which, combined with a neuroleptic, is used to immobilise animals in veterinary practice. The doses used in large animals are enough to kill an adult human if, in a struggle, the drug is splashed on skin or mucous membrane, or there is a needle scratch. A competitive antagonist, naloxone (or diprenorphine which accompanies veterinary formulations, and is labelled for use in animals only) should be used at once in man in this urgent situation (do not delay to fetch an official human formulation; death has occurred where this was done). Wash a splashed site copiously at once.

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