Background: Local anesthetic effects of antihistamines are well known, but have been tested more for diphenhydramine than for chlorpheniramine. Midazolam, a benzodiazepine gamma-aminobutyric acid type A receptor agonist, induces spinally mediated analgesia. However, the local anesthetic effects of chlorpheniramine and midazolam have not been adequately studied. The purpose of this study was to assess the infiltration pain and the local anesthetic effects of intradermal chlorpheniramine and midazolam.
Material and methods: This prospective, double-blind study compared the effects of intradermal chlorpheniramine, midazolam, lidocaine, and saline for pain on injection and degree of local anesthesia in adult volunteers. Each received 0.5 ml of the four solutions as intradermal injections in a standardized manner on the volar side of the forearm. Pain on injection and the degree of local anesthesia (tested by pinprick, light touch, and cold) at each site was evaluated on a 0–3 scale at designated time intervals.
Results: Pain on injection of chlorpheniramine was more intense than saline (<i>p</i>=0.047) and lidocaine (<i>p</i><0.001). Midazolam was significantly more painful than lidocaine (<i>p</i><0.001), but not different from saline (<i>p</i>=0.170). Lidocaine caused a significant reduction in sensation to pinprick, touch, and cold during the study period compared with saline and midazolam. Chlorpheniramine also produced a significant reduction in sensation to pinprick and cold until the 120^th minute and in sensation to touch until the 90^th minute compared with saline.
Conclusions: Intradermal chlorpheniramine, but not midazolam, produced a local anesthetic effect; however, the duration of this effect of chlorpheniramine was shorter than that of lidocaine.

Keywords: Anesthesia, Local - methods, Anesthetics, Local - pharmacology, Chlorpheniramine - pharmacology, Double-Blind Method, Injections, Intradermal, Lidocaine - pharmacology, Midazolam - pharmacology, Pain Measurement, Prospective Studies, Time Factors