In experimental studies, drug-induced analgesia is usually assessed by cuta
neous stimulation. If analgesics act differently on cutaneous and deep noci
ception, the results of these studies may not be entirely applicable to cli
nical pain involving deep structures. We tested the hypothesis that opioids
have different abilities to inhibit cutaneous and muscular pain. Either th
e opioid remifentanil or placebo was infused in 12 healthy volunteers in a
cross-over fashion. Repeated electrical stimulation (five impulses at 2 Hz)
was applied to both skin and muscle. Pain thresholds were recorded. Remife
ntanil caused a higher increase in the muscular pain thresholds than in the
cutaneous pain thresholds (P=0.035). We conclude that opioids inhibit musc
ular pain more strongly than cutaneous pain in humans.