Diphenhydramine: alternative to lidocaine

In a poster presented at the 63rd Annual Meeting of the American Academy of Dermatology, Dr. Cather, director of clinical research at Texas Dermatology Research Institute, Dallas, reported on the technique for preparing and delivering the diphenhydramine injections, along with the safety and efficacy results in a series of 27 patients. In that group, 1 cc of diphenhydramine 50 mg/cc was diluted 10:1 with sterile saline to achieve a final diphenhydramine concentration of 4.5 mg/cc. The anesthetic block was performed by delivering volumes of 0.5 cc to 0.75 cc after pretreatment of the oral mucosa with 20 percent benzocaine gel.

Of the 27 patients treated, 24 (88.9 percent) had adequate anesthesia, two (7.4 percent) had adequate anesthesia on one side only, and one patient (3.7 percent) with a history of difficulty obtaining anesthesia for dental procedures, failed to respond. The diphenhydramine injections were well-tolerated, caused no sedation or other medication or injection-related side effects, and offered onset of anesthesia that was rapid (within five minutes) but not too prolonged (average time, approximately 40 minutes).

"We were originally interested in trying diphenhydramine because patients undergoing these hyaluronic acid filler procedures were complaining about the prolonged numbness associated with lidocaine intraoral infraorbital blocks," says Dr. Cather, who is also co-director of the Cutaneous Lymphoma (CTCL) and Graft vs. Host Disease Clinic, Baylor University Medical Center, Dallas. "Now, we are using diphenhydramine exclusively in this setting, and have treated over 100 patients with good results and no significant adverse events. We consider it a very nice technique to ensure patient comfort while enhancing satisfaction with these filler procedures, which, although they are cosmetic, are very important for a subset of our patient population."

Unlike collagen-based fillers, the hyaluronic acid products are not dispersed in lidocaine. Therefore, injections delivered into the lips and nasolabial folds can be quite painful, and most patients require some local anesthesia. While there were reports of successful use of diphenhydramine for cutaneous and intraoral surgery in patients with lidocaine allergy, Dr. Cather notes that she and her colleagues were unaware of any studies evaluating its use for patients receiving hyaluronic acid filler injections.

Current technique Currently, the diphenhydramine block is being performed with a higher concentration of diphenhydramine, 5.9 mg/cc, which is prepared by diluting the 50 mg/cc diphenhydramine with 7.5 cc of saline.

"Since not all patients achieved adequate anesthesia using the concentration of 4.5 mg/cc, we undertook further testing to optimize the efficacy of the injections," Dr. Cather explains.

A standard technique is used for the intraoral infraorbital diphenhydramine injections. After applying the topical anesthetic to the mucosal fold above the canine teeth and waiting for 30 to 60 seconds, the physician administers the block with slow injection using a 1-inch, 30-gauge needle inserted in the upper labial fold above the canine teeth and angled toward the infraorbital foramen.