Figure 3. Magnitude of pain after intradermal injection of capsaicin, averaged for the first two injections (control: open square), or after the fourth capsaicin injection after intramuscular midazolam (open diamond), intramuscular amitriptyline (open triangle), intravenous alfentanil (200 ng/ml targeted plasma concentration: Filled circle), or the combination of amitriptyline and alfentanil (filled inverted triangle). Each symbol represents the mean of ten volunteers, with +standard deviation and -standard deviation shown for the control and amitriptyline-plus-alfentanil groups, respectively. *P < 0.05 for comparison of alfentanil alone and with amitriptyline to control by two-way analysis of variance.