Use of diphenhydramine for local anesthesia in “caine”-sensitive patients

• Charles V. Pollack Jr, MA, MD^∗ & G. Michael Swindle, MD†
• ^∗ Resident in Emergency Medicine, University of Mississippi Medical Center, Jackson, Mississippi, USA
• ^† Resident in Emergency Medicine, United States Naval Hospital, San Diego, California, USA

Abstract

Emergency physicians regularly encounter patients who require local or topical anesthesia in the course of their emergency department (ED) treatment for lacerations, abrasions, or mucosal surface pain. Rarely, patients disclose a history of allergy to lidocaine and its chemical analogues, and the physician is faced with the problem of achieving adequate anesthesia without the use of these drugs. Research studies and anecdotal reports have suggested that diphenhydramine hydrochloride (Benadryl®) may be useful as a substitute.

We describe three cases of patients with histories of “caine” allergy who required local anesthesia for laceration repair. Infiltration with a 1% diphenhydramine solution provided adequate anesthesia without noticeable adverse effects. We feel that diphenhydramine has a place in emergency medicine practice as a second-line local anesthetic agent.

Diphenhydramine as an Analgesic Adjuvant in Refractory Cancer Pain

• Juan Santiago-Palma, MD^a,
• Daniel Fischberg, MD, PhD^b,
• Craig Kornick, MD^a,
• Natalia Khjainova, MD^a,
• Gilbert Gonzales, MD^a, 
• ^a Pain and Palliative Care Service, Mount Sinai School of Medicine, New York, NY, USA
• ^b Department of Neurology, Memorial Sloan-Kettering Cancer Center, and Department of Internal Medicine, Mount Sinai School of Medicine, New York, NY, USA

Abstract

Clinical and animal data suggest that antihistamines may have efficacy in the management of pain. While many mechanisms of action have been proposed for the analgesic action of antihistamines, the exact mechanism is unknown. Controlled clinical trials in different pain models have demonstrated that antihistamines have direct and adjuvant analgesic activity. We report three patients with advanced cancer pain refractory to adjuvants and oral, intravenous, and epidural opioids, who achieved sustained pain relief after the repeated administration of diphenhydramine. Diphenhydramine may be useful in the treatment of neuropathic and nociceptive pain that has failed to respond to treatment with opioids and adjuvant analgesics. We suggest a starting dose of 25 mg of oral or parenteral diphenhydramine every 6 to 8 hours, with titration to effect.

Diphenhydramine produces local cutaneous analgesia in response to dorsal skin noxious stimuli in the rat

Author(s): Chen YW, Tzeng JI, Chen TY, Wang JJ, Chen YC, Hung CH.

Fundam Clin Pharmacol. 2014 Aug;28(4):439-44. doi: 10.1111/fcp.12048. Epub 2013 Sep 5.

 Abstract

Although diphenhydramine has been shown to produce longer duration of spinal block than lidocaine, few studies disclose its skin infiltrative anesthesia when compared with a long-lasting local anesthetic, bupivacaine. The purpose of this study was to investigate whether diphenhydramine elicited cutaneous analgesia in comparison with bupivacaine. After inhibition of cutaneous trunci muscle reflex via subcutaneous injection of drugs in rats, we examined the local anesthetic effect of diphenhydramine and bupivacaine as infiltrative cutaneous analgesia in a dose-dependent fashion. We showed that diphenhydramine, as well as bupivacaine displayed a dose-dependent cutaneous analgesia in response to dorsal cutaneous noxious stimuli. The relative potency (50% effective dose) was bupivacaine (0.023 [0.013-0.035]%) > diphenhydramine (0.078 [0.068-0.091]%; P < 0.001). On an equipotent basis, diphenhydramine had a similar duration of action to bupivacaine. Neither local injection of saline nor intraperitoneal administration of a large dose of diphenhydramine or bupivacaine produced cutaneous analgesia (data not shown). We conclude that diphenhydramine is less potent than bupivacaine at producing cutaneous analgesia. At equipotent doses for infiltrative cutaneous analgesia, the duration of action of diphenhydramine is equal to that of bupivacaine.

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