Does literature support the use of subcutaneous diphenhydramine 1% for local anesthesia as an alternative in patients who are unable to tolerate benzoic acid or ester group local anesthetics?

Does literature support the use of subcutaneous diphenhydramine 1% for local anesthesia as an alternative in patients who are unable to tolerate benzoic acid or ester group local anesthetics?

Comment by InpharmD Researcher

Published data suggests that diphenhydramine 1% may be effective when used in cases where benzoic acid or ester group local anesthetics are contraindicated due to an intolerance, as the chemical structure of diphenhydramine significantly differs. However, patients may experience pain upon administration, and it is recommended that patients be monitored for local injection site reactions, including skin necrosis.

Background

Lidocaine is commonly used as a local anesthetic, though true allergies to local anesthestics are rare and often stem from the preservative methylparaben in multi-dose vials. Ester anesthetics like procaine and tetracaine may cause similar reactions due to their degradation product, para-amino benzoic acid (PABA). Single-dose lidocaine without preservatives can be a safer option, though differentiating between preservatives and anesthetics can be challenging. Although diphenhydramine has been explored as an alternative, injection of diphenhydramine may be painful and associated with various side effects. Despite this, the chemical structure of diphenhydramine is dissimilar enough to where the antigenicity is quite different to local anesthetics. For this reason, a 1998 randomized, double-blind trial compared 0.9% buffered lidocaine, 0.9% benzyl alcohol with epinephrine, and 1% diphenhydramine to assess pain of infiltration and anesthesia duration. Results showed that 1% diphenhydramine was associated with an increased pain of infiltration and less pronounced anesthetic effect. Nevertheless, this study suggests that diphenhydramine may still be a preferable alternative in patients with allergies to other local anesthetics and/or epinephrine due to these antigenic differences (see Table 1). [1]

A 2016 retrospective review assessed the safety of subcutaneous diphenhydramine administration in the hospice setting. Of note, this study evaluated the safety of subcutaneous diphenhydramine injections at a concentration of 5%, rather than 1%. Investigators collected data from six inpatient hospice units via a pharmacy database, and identified a total of 648 administrations of subcutaneous diphenhydramine injections in 109 individual patients. Doses of diphenhydramine administered were either 12.5, 25, or 50 mg. Notably, the findings revealed that no adverse reactions were reported post-administration, suggesting that subcutaneous diphenhydramine is a safe alternative to oral and other parenteral routes, along with those with “caine” allergies. However, despite these results, caution in interpretation is warranted as the efficacy of subcutaneous diphenhydramine injections was not assessed. [2]

Literature Review

A search of the published medical literature revealed 8 studies investigating the researchable question:

Does literature support the use of subcutaneous diphenhydramine 1% for local anesthesia as an alternative in patients who are unable to tolerate benzoic acid or ester group local anesthetics?

Level of evidence

B - One high-quality study or multiple studies with limitations Read more→

Please see Tables 1-8 for your response.

Randomized Trial of Diphenhydramine Versus Benzyl Alcohol With Epinephrine as an Alternative to Lidocaine Local Anesthesia
Design	Prospective, randomized, double-blind study N= 30
Objective	To investigate alternative anesthetics for patients allergic to lidocaine
Study Groups	All participants (N= 30)
Inclusion Criteria	Aged 18 to 50 years; no known allergies to study solutions
Exclusion Criteria	Abnormal pain sensation in upper extremities
Methods	Participants were randomized to receive 1% diphenhydramine, 0.9% benzyl alcohol with 1:100,000 epinephrine, and 0.9% buffered lidocaine as subcutaneous (SC) injection. Each solution was prepared on the day of the study. Pain of infiltration immediately after injection was measured using a visual analog scale (VAS), while duration of anesthesia was assessed up to 45 minutes by testing for sensitivity to needle prick. Injections were administered at three sites on the volar aspect of one forearm chosen by each subject. Each injection involved 0.5 mL of solution delivered SC over 5 seconds at marked intervals along the forearm, starting 5 cm proximal to the ulnar styloid. Pain of infiltration immediately after each injection was assessed using a validated VAS, ensuring evaluation of infiltration pain only, not needle stick discomfort. To prevent bias, injection sites were covered with perforated gauze sponges.
Duration	Intervention: Administered over a period of 5 seconds and monitored for a period of 45 minutes thereafter Follow-up: 24 hours
Outcome Measures	Pain of infiltration; duration of anesthesia
Baseline Characteristics		All Participants (N= 30)
	Mean age, years	34.7 ± 8.7
	Female	18 (60%)
	Allergies to LA	0
	LA: Local anesthetics
Results	Endpoint	Diphenhydramine (n= 30)	Buffered Lidocaine (n= 30)	Benzyl Alcohol (n= 30)	p-value
	Pain of infiltration, mm (IQR)	55 (35 to 78)	12.5 (4 to 26)	5 (1 to 13)	*
	Participants with pain sensation within 45 minutes	19 (63%)	3 (10%)	11 (37%)	**
	IQR: interquartile range * Pairwise comparisons showed all possible combinations were statistically significant (buffered lidocaine versus benzyl alcohol, p= 0.022; diphenhydramine versus benzyl alcohol, p= 0.001; diphenhydramine versus buffered lidocaine, p= 0.001), and the order of injection did not significantly influence comparisons (p= 0.5). ** Pairwise comparisons showed a longer duration of anesthesia for buffered lidocaine versus benzyl alcohol (p= 0.02) or diphenhydramine (p= 0.001). No differences were found between benzyl alcohol and diphenhydramine (p= 0.13), and the order of injection did not significantly influence this comparison (p> 0.9).
	One patient reported return of pain sensation after 5 minutes for the benzyl alcohol injection. The remaining injections did not report return of pain for ≥15 minutes.
Adverse Events	All subjects were available for follow-up 24 hours after administration, and none reported adverse reactions.
Study Author Conclusions	In instances in which an alternative local anesthetic agent is required, particularly in the patient with a reported lidocaine allergy, benzyl alcohol with epinephrine appears to be a better choice than diphenhydramine. Diphenhydramine remains preferable for those cases in which epinephrine is contraindicated.
InpharmD Researcher Critique	The results of this study suggest that diphenhydramine may be a preferable option for patients sensitive to ester-type LA. Although diphenhydramine showed the most pain on infiltration, it displayed comparable anesthesia duration to buffered lidocaine. However, the study was limited by its small sample size, use of healthy volunteers, and specific injection conditions, suggesting the need for further research in clinical settings.

References:

Bartfield JM, Jandreau SW, Raccio-Robak N. Randomized trial of diphenhydramine versus benzyl alcohol with epinephrine as an alternative to lidocaine local anesthesia. Ann Emerg Med. 1998;32(6):650-654. doi:10.1016/s0196-0644(98)70062-9

Local anesthetic efficacy for oral surgery: Comparison of diphenhydramine and prilocaine
Design	Prospective controlled study N= 23
Objective	To determine the local anesthetic efficacy of diphenhydramine (DPH) for oral surgery
Study Groups	DPH (n= 16) Control (n= 7)
Inclusion Criteria	Referred for dental extraction; no serious periapical and periodontal problems
Exclusion Criteria	Not disclosed
Methods	Patients with a allergy to local anesthetics were treated with 1% DPH for local anesthesia, while control group patients who were nonallergic received prilocaine. Injections and extractions were performed by the same clinician. Anesthesia was considered successful if a pulp test was conducted and the maximum output (10) was achieved within 10 minutes. Patients were instructed to not to use any medications until pain was present, after which acetaminophen 500 mg was to be taken.
Duration	Intraoperative use
Outcome Measures	Visual analog score (VAS), onset times, and incidence of pulpal and soft tissue anesthesia
Baseline Characteristics		DPH (n= 16)	Control (n= 7)
	Age, years (range)	29.9 (17-47)	36 (20-56)
	Female	9 (56%)	4 (57.1%)
	All patients were in good health (ASA I), and none were on medications that would alter perception.
Results	Endpoint	DPH (n= 16)	Control (n= 7)	p-value
	Pulp anesthesia Onset, min Duration, min	5.5 29.5	7.6 57	-- >0.05 <0.05
	Soft tissue anesthesia duration, min	156	206	<0.05
	VAS score	2.2	0.7	<0.05
	Post-extraction pain	7 (44%)	4 (57%)	--
	One DPH patient was excluded due to failure of anesthesia; the remaining patients all achieved effective local anesthesia.
Adverse Events	No adverse effects observed in control group. Six DPH patients (37.5%) reported bleeding, edema, pain at the injection site, trismus, headache, nausea, and dizziness.
Study Author Conclusions	On the basis of the favorable local anesthetic properties observed in connection with its use in this small group of patients, we recommend DPH as a practical and economic alternative in patients allergic to local anesthetics. Its indiscriminate use must be avoided, however, because of its slightly irritant properties.
InpharmD Researcher Critique	Extraction was not limited to a certain tooth, and the small sample size and patient awareness of diphenhydramine as an alternative to general local anesthetics may have influenced pain readings and significance of findings.

References:

Uckan S, Guler N, Sumer M, Ungor M. Local anesthetic efficacy for oral surgery: Comparison of diphenhydramine and prilocaine. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 1998;86(1):26-30. doi:10.1016/s1079-2104(98)90145-7

Validation of Diphenhydramine as a Dermal Local Anesthetic
Design	Prospective, randomized, double-blind, placebo-controlled clinical trial N= 24
Objective	To determine the relative efficacy of diphenhydramine compared to saline placebo and lidocaine
Study Groups	All patients (N= 24)
Inclusion Criteria	Healthy adult volunteers
Exclusion Criteria	Pregnant or lactating; history of narrow-angle glaucoma, obstructive bladder disease; allergy or other adverse reaction to diphenhydramine or local anesthetics
Methods	Subjects refrained from antihistamine medication use for 24 h prior to participation. Syringes were loaded with 0.5 mL of normal saline, lidocaine 1% (as packaged for local infiltration), or solutions of diphenhydramine 1% or 2% freshly diluted in normal saline. Injections were randomly labeled A, B, C, and D. All injections were given by a single investigator blinded to syringe contents. After the needle entered the skin, infiltration was delayed until the subject reported cessation of pain; then, injections were made over two seconds. Injection A was at the distal right volar forearm, B at the proximal right volar forearm, C at the proximal left volar forearm, and D at the distal left volar forearm, and spaced 30 minutes apart. After injection completion, subjects marked an unmarked linear visual analog scale (VAS; 100 mm long) to indicate their perception of infiltration pain. One minute after injection, the diameter of skin area anesthetized to prick with a safety pin was identified and marked on the tape, then repeated at different time intervals up to 30 minutes. The appearance of the injected areas was recorded 10 minutes after injection.
Duration	Follow-up: up to 5 days
Outcome Measures	VAS score for infiltration, complications
Baseline Characteristics		Study cohort (N= 24)
	Age, years	26 ± 3
	Female	46%
Results	Endpoint	Saline	Lidocaine 1%	Diphenhydramine 1%	Diphenhydramine 2%
	Anesthetized areas, mm² At 1 minute At 5 minutes At 10 minutes At 30 minutes	12.7 ± 5.1 14.3 ± 6.1 20.8 ± 8.9 1.7 ± 1.0	135.1 ± 26.0 279.9 ± 45.0 338.5 ± 65.5 48.7 ± 15.1	104.7 ± 26.7 244.7 ± 59.2 325.2 ± 76.0 63.8 ± 23.9	96.9 ± 30.1 194.3 ± 42.3 226.4 ± 55.8 67.9 ± 22.0
	Injection reactions Hyeremia, number of sites Persistent soreness, number of subjects	0 0	0 0	10 2	11 5
	Comparisons between individual drug groups revealed significant differences between saline and lidocaine (p< 0.001), saline and diphenhydramine 1% (p< 0.001), and saline and diphenhydramine 2% (p< 0.001). Comparisons of lidocaine with diphenhydramine 1% and diphenhydramine 2% were not significantly different (p= 0.889 and p= 0.181, respectively), nor was the comparison of diphenhydramine 1% and 2% (p= 0.295).
Adverse Events	Three subjects reported feeling sleepy. No skin necrosis, vesiculation, or long-term complications were reported.
Study Author Conclusions	In this study of 24 adult volunteers, diphenhydramine 1% was as effective as lidocaine 1% for achieving dermal local anesthesia, although injection was more painful. Although no clinically important complications were noted in our study, the safety of diphenhydramine remains to be established, especially in areas with poor collateral perfusion (eg, digits, pinna, and nose).
InpharmD Researcher Critique	Results may differ in patients who have chronic comorbidities, as data were taken from healthy adult volunteers. The causal relationship between diphenhydramine and reported drowsiness is uncertain, due to the lack of a comparator group without diphenhydramine injection.

References:

Green SM, Rothrock SG, Gorchynski J. Validation of diphenhydramine as a dermal local anesthetic. Ann Emerg Med. 1994;23(6):1284-1289. doi:10.1016/s0196-0644(94)70353-1

Double-blinded comparison of diphenhydramine versus lidocaine as a local anesthetic
Design	Prospective, double-blind, cross-over study N= 10
Objective	To evaluate the efficacy, onset of action, duration of action, and side effects of 1% diphenhydramine compared to 1% lidocaine when used as a local anesthetic agent
Study Groups	Diphenhydramine Lidocaine
Inclusion Criteria	Healthy volunteers, age > 21, no use of antihistamines within past week, no relevant allergies
Exclusion Criteria	Not specified
Methods	Syringes of medication were prepared containing either 2 mL of 1% lidocaine (20 mg) or 2 mL of 1% diphenhydramine (20 mg), both preservative free. On day 1, half of the volunteers were to receive either of the two treatments, administered subcutaneously via 27-gauge needle. After 1 week, the volunteers were given the alternate agent.
Duration	Monitoring: 15-minute intervals until return to baseline
Outcome Measures	Pinprick sensation, duration of effective analgesia, sedation scores
Baseline Characteristics		All patients (N= 10)
	Age, years	30.8
	Male	100%
	No significant difference was noted for visual analog scale (VAS) scores at baseline between lidocaine and diphenhydramine administration.
Results	Endpoint	Lidocaine	Diphenhydramine	p-Value
	Duration of effective analgesia, min	81 ± 14.2	52 ± 6.6	0.028
	Most results were presented as graphs. No significant differences were seen in mean pinprick sensation from baseline to 30 minutes, but differences were observed at 45 minutes (p= 0.036) and 60 minutes (p= 0.036). No significant levels of sedation were observed in any subjects in either group.
Adverse Events	One patient developed a wheal with pruritic erythematous dermal reaction at injection site of diphenhydramine; another patient developed erythematous dermal reaction at site of diphenhydramine. No significant levels of sedation were observed using the prescribed dose.
Study Author Conclusions	The duration of local anesthesia for 1% lidocaine was significantly longer and the depth of anesthesia after 30 minutes was significantly higher than that of 1% diphenhydramine. Diphenhydramine resulted in skin necrosis in one test subject.
InpharmD Researcher Critique	Due to the extremely small sample size and use of healthy, young, male volunteers with no allergies, generalizability of results to true patient cohorts may be limited.

References:

Dire DJ, Hogan DE. Double-blinded comparison of diphenhydramine versus lidocaine as a local anesthetic. Ann Emerg Med. 1993;22(9):1419-1422. doi:10.1016/s0196-0644(05)81989-4

Lidocaine Versus Diphenhydramine for Anesthesia in the Repair of Minor Lacerations
Design	Prospective, double-blind, randomized controlled trial N= 99
Objective	To determine the effectiveness of diphenhydramine in comparison with lidocaine in the repair of simple lacerations
Study Groups	Lidocaine (n= 51) Diphenhydramine (n= 48)
Inclusion Criteria	Aged ≥18 years; simple linear laceration (2-10 cm length)
Exclusion Criteria	Lacerations less than 2 cm or greater than 10 cm; allergies to amide anesthesia or diphenhydramine; ethanol or drug use; altered pain perception; altered mental status; pregnancy; glaucoma; prostate problems; end-organ lacerations (fingers, toes, penis, nose)
Methods	Patients were assigned to receive either diphenhydramine 1% or lidocaine 1% subcutaneously via a random numbers table. Pain was measured by physician assessment and patient report via a 0-10 pain scale (0-3 for mild pain, 4-7 for moderate pain, 8-10 for severe pain) during injection of anesthesia and suturing, followed by being discharged from the emergency department. In cases of anesthesia failure (pain sensitivity during pinprick or cleaning, or by patient request), 1% lidocaine was administered. Patients were followed up via a return visit to the emergency department, telephone, or mail for signs of complications.
Duration	October to November 1991
Outcome Measures	Duration of anesthesia, amount of anesthesia used, need for additional anesthesia at time of suturing, quantity of extra anesthesia
Baseline Characteristics		Lidocaine (n= 51)	Diphenhydramine (n= 48)
	Age, years (range)	29 (19 to 62)	30 (18 to 64)
	Female	13 (25.4%)	12
	Length of laceration (cm)	3 (2 to 8)	2.5 (2 to 6)
	Location Extremity Face Scalp Trunk	21 (41.2%) 17 (33.3%) 10 (19.6%) 3 (5.9%)	22 (45.8%) 14 (29.1%) 11 (22.9%) 1 (2.1%)
Results	Endpoint	Lidocaine (n= 51)	Diphenhydramine (n= 48)	p-value
	Amount of anesthesia used, mL (range)	4 (1 to 7)	4 (1 to 9)	--
	Extra anesthesia needed, mL	3	6	--
	Physician Pain Score* (range) injection Suturing	3 (0 to 7) 0 (0 to 4)	3.5 (0 to 10) 0 (0 to 6)	> 0.05 > 0.05
	Patient Pain Score* (range) Injection Suturing	2 (0 to 8) 0 (0 to 10)	4 (0 to 6) 1 (0 to 6)	0.0017 > 0.05
	Wound infection	1	0	> 0.05
	* Pain Score: 0-3 for mild pain, 4-7 for moderate pain, 8-10 for severe pain Patient pain scores for injection were significantly higher than physicians (p= 0.035). The effects of anesthesia lasted longer than 20 minutes and continued until after discharge in all patients except one in the diphenhydramine cohort, who received extensive irrigation and required additional lidocaine.
Adverse Events	Common Adverse Events (lidocaine vs. diphenhydramine): sleepiness (n= 0 vs. n= 2), wound infection at follow-up (n= 1 vs. n= 0); same patient reported headache (n=1 vs. n= 0), nasal stuffiness (n= 1 vs. n= 0), and severe pain (n= 1 vs. n= 0)
Study Author Conclusions	Although diphenhydramine will not replace lidocaine, it appears to be a viable alternative for patients with large lacerations after maximal lidocaine use. Diphenhydramine is inexpensive, readily available in the ED, and appears to provide effective anesthesia for the repair of minor lacerations.
InpharmD Researcher Critique	Both medications were kept refrigerated until administration. The cold temperature of the injectables could have impacted pain during injections. There was some variability between physicians and patients in reported pain, possibly due to the physician's ability to determine a patient's pain status. Data on the criteria used by physicians to interpret pain was not disclosed. As this outcome was subjective, there is the potential for bias. This was a small, discontinued study that ended once statistical significance was reached with 99 participants. This study was unable to capture sufficient data to draw an intended conclusion on the effectiveness of diphenhydramine or lidocaine on different laceration sites due to an insufficient sample size. This study examined the efficacy of diphenhydramine versus an amide local anesthesic, lidocaine, but did not consider these drugs in cases of ester or benzoic acid allergy.

References:

Ernst AA, Anand P, Nick T, Wassmuth S. Lidocaine versus diphenhydramine for anesthesia in the repair of minor lacerations. J Trauma. 1993;34(3):354-357. doi:10.1097/00005373-199303000-00008

Safety and technical success of diphenhydramine as an alternative local anaesthetic agent for radiology procedures
Design	Retrospective, observational, single-center study N= 81 (84 procedures)
Objective	To evaluate retrospectively the safety and technical success of subcutaneous (SQ) diphenhydramine (DPH) as an alternative local anesthetic (LA) for radiology procedures
Study Groups	Study cohort (N= 81)
Inclusion Criteria	Adult patients; underwent an image-guided radiology procedure at a single quaternary referral medical institution utilizing subcutaneous DPH as an LA
Exclusion Criteria	Received DPH via an intravenous or oral route; received subcutaneous DPH mixed with “-caine” LA; underwent general anesthesia
Methods	Data were extracted from medical records for patients who received DPH. No standardized technique for LA administration existed at the institution, but it should be noted that no alteration of personal technique or needle selection in the local administration of DPH occurred versus conventional LA. Most commonly, the DPH concentration utilized was 1%, with 2-3 mL (20–30 mg) injected SQ for anesthetization of the subdermal and/or deeper subcutaneous tissues. Preparation of DPH consisted of 1 mL of 5% (50 mg/mL) DPH with 4 mL sterile saline to make 5 mL of 1% (10 mg/mL) DPH. Exact volumes and depth of injectant were not documented for every procedure.
Duration	Between January 2000 and April 2021
Outcome Measures	Complications
Baseline Characteristics		Study cohort (N= 81)
	Age, years (range)	61 (23-91)
	Female	70 (87%)
	Indications for DPH Allergies Recent LB administration	76/84 (90%) 8/84 (10%)
	Technique used for guidance Ultrasound guided Fluoroscopy guided Computed tomography guided MRI guided	59/84 (70%) 13/84 (16%) 11/84 (13%) 1/84 (1%)
	Abbreviations: LB= liposomal bupivacaine; MRI= magnetic resonance imaging The most common procedural site was the breast (34/84, 40%).
Results	All procedures were deemed technically successfully (i.e., no procedures modified or interrupted due to pain intolerance). No episodes of skin necrosis or allergic reactions specific to DPH were reported.
	Two minor injection-related complications regarding post-procedural pain were observed in one patient undergoing a cervical lymph node biopsy (no hematoma, pain resolved with oral anesthesia) and one patient undergoing a lumbar puncture (no documentation on record, but patient mentioned post-procedural pain to referring neurologist). One minor procedural-related complication occurred in a patient undergoing native kidney biopsy (hospital admission required for observation and bladder irrigation after hematuria presentation, but no further interventions required).
Adverse Events	See Results
Study Author Conclusions	Injectable diphenhydramine appears to be a safe and effective local anesthetic alternative in patients with “-caine” class contraindications undergoing radiology procedures. A future prospective trial would be useful to assess the safety profile in an large cohort of patients.
InpharmD Researcher Critique	Use of retrospective and observational data may include missing or inaccurate information, and data compiled from a small sample size of patients from a single center limits applicability to a more general audience.

References:

Xiao L, Wagle S, Schmitz JJ, et al. Safety and technical success of diphenhydramine as an alternative local anaesthetic agent for radiology procedures. Clin Radiol. 2023;78(3):e177-e181. doi:10.1016/j.crad.2022.10.004

Use of Diphenhydramine for Local Anesthesia in "Caine"-Sensitive Patients
Design	Case reports
Case presentation #1	A 61-year-old female presented to the emergency department (ED) after sustaining lacerations to her left thumb and right wrist. Upon further questioning, she mentioned experiencing a near-fatal anaphylactic reaction to lidocaine during a previous local procedure. Following this incident, she underwent skin testing, which confirmed allergies to all medications in the lidocaine (Xylocaine) and procaine (Novocain) families. This also included "cardiac" lidocaine, which lacks the methylparaben preservative found in standard "local" lidocaine formulations. On exam, a 2 cm full-thickness laceration was observed on the left thumb and a 5 cm full-thickness laceration on the right wrist. Due to the patient's history and wound size, diphenhydramine was used for local anesthesia. A preloaded syringe containing 50 mg (1 cc) of diphenhydramine was diluted with 4 mL of sterile saline to create a 1% solution, totaling 5 cc. During local infiltration, 10 mg was administered for the thumb and 20 mg for the wrist. The patient did not exhibit immediate hypersensitivity reactions. Adequate anesthesia was achieved within five minutes, confirmed by insensitivity to pinprick, which allowed a successful closure of both wounds in a single layer over approximately 30 minutes. She reported no discomfort throughout the procedure, which was conducted without additional anesthesia or sedation. Upon follow-up two days later, normal neurovascular status and wound appearance were noted. Eight days later, during suture removal, the wounds were found to be well-healed.
Case presentation #2	A 59-year-old female presented to the ED shortly after a fall in which she had sustained a scalp laceration. Upon arrival, her internist alerted the emergency physician regarding her allergy to local anesthetics and the potential need for general anesthesia. Despite complaints of headache and lower back pain, she was alert and oriented. Upon examination, the patient's scalp revealed a 5 cm occipital laceration with active arterial bleeding. Standard pressure application failed to control the bleeding, so 10 cc of 1% diphenhydramine solution was infiltrated around the wound. Given the scalp location, 0.1 cc of 1:1,000 epinephrine solution was added to create a diluted 1:100,000 epinephrine solution. Within five minutes, the patient exhibited insensitivity to pinpricks in the treated area without any adverse reactions. Hemostasis was achieved with the suture ligature of a small subcutaneous artery, and the wound was closed in one layer. Following the negative results of the radiographic assessments of her skull and lumbosacral spine, the patient was discharged home. Upon follow-up two days later, the wound showed no issues, and her internist removed the sutures four days afterward.
Case presentation #3	A 24-year-old female presented to the ED shortly after sustaining a 6 cm full-thickness laceration to her right dorsal forearm. The patient stated she had suffered a severe, life-threatening reaction to procaine during a dental procedure two years prior. As a result, she declined any administration of any "caine" agents, despite not having previously received lidocaine. Upon examination, distal neurovascular status was intact, and the wound was infused with 10 cc of a 1% diphenhydramine solution. The patient reported no burning or pain upon injection and achieved anesthesia within five minutes. No immediate hypersensitivity reactions were observed. The wound was then irrigated and closed with a single layer of sutures without any discomfort reported by the patient. The anesthesia lasted approximately 30 minutes. During the wound check two days later and at suture removal ten days after the repair, the wound and surrounding skin showed normal appearance.
Study Author Conclusions	In patients sensitive to “Caine” anesthetics, use of diphenhydramine hydrochloride provides an efficacious, reliable means of achieving local and topical anesthesia without risk of allergic cross-reactivity. Infiltrated diphenhydramine provides anesthesia sufficient for suturing, excision of skin and subcutaneous lesions, dental work, and other minor surgical procedures. Topical diphenhydramine affords temporary relief of painful and irritative dermatoses and mucosal lesions.

References:

Pollack CV, Swindle GM. Use of diphenhydramine for local anesthesia in “caine”-sensitive patients. The Journal of Emergency Medicine. 1989;7(6):611-614.

Diphenhydramine as an Alternative Local Anesthetic Agent
Design	Case report
Case presentation	A 51-year-old male presented to a dermatology clinic regarding a 2 cm diameter "cyst" on his back for evaluation. The patient reported a previous allergic reaction to Novocaine^© (procaine) 30 years prior during a dental procedure, in which he experienced light-headedness and pounding in the chest immediately following local anesthetic injection, resulting in an emergency department visit and subsequent 24-hour admission to the hospital; there is no medical record to corroborate this incident. The patient was made aware of a potential referral to an allergist to confirm "caine" allergy; however, to allow for same-day surgery of the cyst, the patient received 1 mL of 1% diphenhydramine hydrochloride (DPH) 10 mg/mL injection as an alternative local anesthetic. The patient experienced no adverse effects or pain during cyst removal.
Study Author Conclusions	DPH 1% solution is a safe, effective, inexpensive alternative to “caine” local anesthetics. This allows same-day surgery in patients with a confirmed history of “caine” anesthetic reactions and in patients with a questionable history who have not had definitive allergy testing. Dermatologists should counsel patients about the advantages of referral to an allergist for definitive testing.

References:

Pavlidakey PG, Brodell EE, Helms SE. Diphenhydramine as an alternative local anesthetic agent. J Clin Aesthet Dermatol. 2009;2(10):37-40.