Insect Bites Treatment & Management

For a large local reaction, ice packs may minimize swelling. Apply ice for no more than 15 minutes at a time using a cloth barrier between ice and skin to prevent direct thermal injury to the skin.

Epinephrine is the mainstay of prehospital treatment of a systemic reaction; the route of administration (subcutaneous, intramuscular, intravenous [IV], endotracheal) depends on the patient's condition and the expertise of the prehospital provider. Systemic antihistamines and corticosteroids, if available, help manage systemic reactions. Many patients who are allergic to stings carry commercially available bee sting kits containing an autoinjector of epinephrine. Refer to Hymenoptera Stings.

Topical antihistamines should not be applied over large surface areas, and they should not be used concurrently with systemic H1 antihistamines. Systemic anticholinergic toxicity may result from misuse of these medications.

Use of H2-blocking drugs (usually used to reduce gastric acid secretion) may be used concurrently with H1-blocking antihistamines.

In many patients, transport to a hospital is not necessary. Those requiring transport include patients who develop signs or symptoms of a systemic response or individuals with a history of insect-related anaphylaxis. A phone call to the regional poison center may save a costly visit to the ED.

Regarding stings, refer to Hymenoptera Stings for complete information; however, note that if the bee stinger is present in the wound, it should be removed. Although conventional teaching suggested scraping the stinger out to avoid squeezing remaining venom from the retained venom gland into the victim, involuntary muscle contraction of the gland continues after evisceration and the venom contents are quickly exhausted. Immediate removal is the important principle and the method of removal is irrelevant.

Endotracheal intubation and ventilatory support may be required for severe anaphylaxis or angioedema involving the airway.

Treat emergent anaphylaxis in an atopic individual with an initial intramuscular injection of 0.3-0.5 mL of 1:1000 epinephrine. This may be repeated every 10 minutes as needed. Note that insect bites only rarely cause anaphylaxis compared with stings; refer to Hymenoptera Stings.

A bolus of IV epinephrine (1:10,000) may be used cautiously in severe cases. Solution of 1:10,000 typically is found in 10-mL vials. Repeated 1-mL doses are a reasonable initial approach in a critically ill patient with anaphylaxis. Once a positive response is achieved, these boluses can be followed by a carefully monitored, continuous epinephrine infusion. Use extra care in monitoring formulation, concentration, and dose when administering IV epinephrine to avoid inadvertent overdose.

Severely hypotensive patients may require a large volume of IV fluids. Monitor for angioedema and pulmonary edema.

Antihistamines, both H1 and H2 blockers, are useful in treating systemic reactions. Diphenhydramine is commonly used in the emergency department, but cetirizine should also be considered in patients not requiring intravenous medications, as it is equally efficacious, has a similar onset of action, and has a longer duration. Corticosteroids also are often used in such patients.

Refer to Anaphylaxis and Serum Sickness for further guidance.

Ensure appropriate tetanus prophylaxis.

Undefined erythema and swelling seen may be difficult to distinguish from cellulitis. As a general rule, infection is present in a minority of cases and antibiotic prophylaxis is not recommended.

Related diagnostic and treatment guidelines are available on anaphylaxis, travel medicine, and referral guidelines (also see Further Reading). ^{[20, 21, 22]}

Further inpatient care

Patients with true anaphylaxis, particularly if associated with hypotension, often are admitted for monitoring or observation in the ED upon recovery. Accepted definition of "true" anaphylaxis requires the involvement of at least 2 of the following 4 systems: cardiovascular, gastrointestinal, skin, or respiratory; although newer guidelines indicate that hypotension only may be present after exposure to a known trigger. ^[13] Literature provides no clear direction on who needs admission. Certain patients with a disease transmission (eg, malaria) may require admission.

Corticosteroids and antihistamines usually are continued for a few (3-4) days after a systemic response. Serum sickness reactions may require longer therapy (see Serum Sickness).

In cases in which determining the insect species is important, a health department, agriculture extension, or university entomologist may be useful.

In cases of potential vector-borne disease transmission, an infectious disease specialist may be of help.

If the potential infection is associated with travel to a tropical region, consider contacting a tropical medicine specialist or the Centers for Disease Control and Prevention (CDC) at 1-877-394-8747 (Traveler's Health Hotline).

A regional poison center may be of assistance in difficult or complicated cases or for general information.

Secondary infection may result from an insect bite.

Symptoms of disease transmitted by insect bites may not be evident for days, weeks, or even longer.

Pregnancy and anaphylaxis

Studies on treatment of anaphylaxis in pregnancy are primarily based in the obstetric literature and generally are case reports dealing with hymenopteran stings. Again, many patients confuse an insect bite with a sting and may use the terms interchangeably. The following adverse outcomes have been reported in case reports following hymenoptera envenomation during pregnancy and are included in this article because of their importance ^[23] :

• Preterm delivery occurred at 35 weeks' gestation despite tocolysis and cerclage and attributed to a "postanaphylactic reaction" from a wasp sting.

• A woman aged 31 years developed severe anaphylaxis after bee sting at 30 weeks' gestation. Preterm labor occurred at 35 weeks' gestation, and the infant was found to be cyanotic and hypotonic. The infant died at age 65 days, and the cause of death was determined to be encephalomalacia from maternal anaphylaxis.

• A woman aged 21 years at 40 weeks' gestation developed severe anaphylaxis from an ant sting and then developed placental abruption and intrauterine death 16 hours later. This was tentatively attributed to the anaphylactic response and epinephrine administration. ^[23]

All patients who have had significant or systemic reactions to Hymenoptera envenomations in the past should consider venom immunotherapy as an outpatient, because it is well tested, highly effective at preventing future reactions, and widely available. ^[23] Pregnant females are not usually initiated on this therapy secondary to lack of safety data, but they can consider continuation of therapy begun prior to impregnation. However, preterm labor has been reported in several cases dealing with this population. Otherwise, standard supportive care should be taken for cutaneous Hymenoptera envenomations. ^[23] Anaphylaxis should be promptly recognized and treated in the standard fashion. Fetal data are limited but the adage "what is good for the mother is good for the fetus" may well also apply to anaphylaxis.

See Hymenoptera Stings.

Follow-up monitoring for infection is advised for individuals bitten by an insect known to transmit a secondary disease, if exposed to the vector in an endemic area (eg, Chagas disease in the case of kissing bugs [Reduviidae] ^{[24, 25]} ).

Individuals who recover from a systemic reaction should consult with an allergist regarding desensitization and prevention measures.

Prescribe epinephrine auto-injector prior to discharge if the patient had a systemic response to an envenomation (see Hymenoptera Stings). Some patients require more than one injection of epinephrine to treat anaphylaxis, so prescribing two injectors should be considered. ^[26]