Due to the recent discovery of peripheral
N-methyl-D-aspartate (
NMDA) (and other
glutamate) receptors in animal studies, the
NMDA receptor antagonist,
ketamine (0.83 mg/ml, 6 ml) or saline was injected s.c. preinjury in 10 healthy volunteers, to study the effect on
burn-induced primary and secondary
hyperalgesia. On the saline treated leg, all subjects developed primary
hyperalgesia and secondary
hyperalgesia. On the contralateral leg treated with
ketamine, there was a significant reduction of primary
hyperalgesia and an inhibition of development of secondary
hyperalgesia. In an experimental day 2,
lidocaine temporarily blocked the development of primary and secondary
hyperalgesia. When saline was injected in the contralateral leg treated with
ketamine 1 week previously (n = 6), no zone of secondary
hyperalgesia was developed. In contrast, subjects (n = 3) treated with
ketamine 2 weeks before, reported development of secondary
hyperalgesia following saline, a preliminary indication of a long-lasting peripheral action of
ketamine.