Be prepared for insect bites and stings

Mary Warner

Stinging and biting insects seem to be everywhere during the summer months, and usually cause only a local reaction. But for patients who are sensitive to compounds in the insect’s saliva or venom, bites and stings can cause reactions ranging from swelling to life-threatening anaphylaxis. Fortunately, there are numerous ways to relieve the pain and other symptoms of insect stings and bites, including local anesthetics, topical antihistamines, hydrocortisone, and counterirritants. Because reactions to bites and stings often occur in places where treatment may not be readily available, it’s important to be prepared for whatever insects you may encounter, either in your back yard or on a wilderness hike.

The best, and easiest, way to protect against insect bites and stings is to avoid them altogether. Wearing light clothing and avoiding colognes; perfumes; and scented soaps, shampoos, and deodorants is also helpful. When that isn’t possible, using an insect repellent can be extremely helpful in preventing insects from biting or stinging. (For more information on safe use of insect repellents, see the OTCs Today article in the July 2022 issue of Pharmacy Today.)

Stings

Bees, wasps, hornets, yellow jackets, and fire ants inject venom to defend themselves or to kill other insects, and their interactions with humans are usually accidental or reactive. The injected venom contains various allergenic proteins, which vary considerably among insects. Most of these proteins act by releasing histamines.

Most patients don’t experience systemic symptoms following an insect sting, but instead complain of pain, itching, and irritation at the site. However, patients who are allergic to insect stings may experience hives, itching, swelling, and burning sensations, and those with severe allergies may experience anaphylaxis within 10–15 minutes of the sting.

Bites

Unlike insect stings, bites from mosquitoes, fleas, ticks are nonvenomous, with irritation resulting from salivary secretions. Mosquitoes inject an anticoagulant saliva into the victim, which causes the characteristic welt and itching. Although anaphylaxis is rare, mosquitoes can spread serious infections—including malaria, West Nile virus, and Zika virus—through this saliva, so it’s important to be alert to other symptoms from bites.

Fleas are most often found in humid climates and usually affect pets, who can pass them on to their human companions. Fleas bite to obtain blood from their hosts, and while their bites are annoying, they are rarely serious in Western countries. Flea bites are characterized by a reddened region around the puncture and intense itching.

Ticks also feed on the blood of animals, including pets and humans who are exposed to affected animals. A tick bite involves attachment to the skin; if not removed, the tick becomes engorged with blood before finally dropping off. Local reactions to tick bites include itching papules that generally disappear within a week. Some ticks can transmit systemic diseases such as Rocky Mountain spotted fever and Lyme disease, usually after the tick has been attached for 36 hours or more. Thus, it’s important to check for ticks regularly and remove them promptly.

Spider bites, though less common than bites from mosquitoes, fleas, or ticks, can result in serious reactions. Although all species of spiders are venomous, most are unable to penetrate the skin, with only the black widow, brown recluse, and hobo spiders as exceptions.

Black widow bites can result in redness of the skin or a halo-shaped lesion, delayed intense pain, muscle spasms, abdominal disturbances, fever, chills, and dyspnea, while brown recluse bites result in just a local reaction with itching and redness of the skin. Hobo spider bites typically present with a moderate to severe, slow-healing wound.

Treatment of stings and bites

Treatment options for insect bites and stings include local anesthetics, topical antihistamines, counterirritants, hydrocortisone, and protective agents.

Local anesthetics such as benzocaine, pramoxine, benzyl alcohol, lidocaine, dibucaine, and phenol are FDA approved in topical preparations for relief of itching, irritation, and pain caused by insect bites and stings. These preparations are available as creams, ointments, aerosols, and lotions and can be applied to the bite area 3–4 times daily for up to 7 days.

Topical antihistamines such as diphenhydramine hydrochloride are approved for temporary relief of pain and itching related to minor insect bites. They’re available in several dosage forms in concentrations of 0.5%–2% and can be applied to the affected area up to 3–4 times daily for no longer than 7 days. Because topical antihistamines can cause photosensitivity and hypersensitivity reactions, they should not be used for more than a week to avoid the possibility of contact dermatitis.

Counterirritants such as camphor and menthol at low concentrations (0.1%–3% for camphor and <1% for menthol) are also used in some topical analgesic products to relieve itching and irritation. Like topical anesthetics and antihistamines, they can be applied to the sting or bite area 3–4 times daily for up to 7 days.

Topical preparations (0.5% or 1.0%) of hydrocortisone, a low-potency corticosteroid capable of vasoconstriction, are indicated for temporary relief of minor insect bites and stings. A wide variety of topical hydrocortisone formulations are available and should be applied as directed to the bite area 3 or 4 times daily for up to 7 days.

Finally, protective agents such as zinc oxide and calamine lotions and creams in concentrations of 1%–25% can be applied to insect bites to reduce inflammation and irritation. Zinc oxide works as a mild astringent with weak antiseptic properties, while both zinc oxide and calamine absorb fluids from weeping lesions.

What to tell your patients

Advise patients to remove bee stingers by scraping them away with a fingernail or the edge of a credit card to stop release of venom, then apply an ice pack or cold compress to slow venom absorption and reduce itching, swelling, and pain. An OTC topical antihistamine, protective agent, or hydrocortisone should then be applied to the affected site to relieve pain and itching. Patients who know they are sensitive to stings should carry epinephrine or oral antihistamines with them at all times. Patients should seek prompt medical attention if they develop hives, excessive swelling, dizziness, vomiting, or difficulty breathing.

For further information on the pathophysiology and treatment of insect bites and stings, see Chapter 37 of APhA’s Handbook of Nonprescription Drugs, available via the bookstore on pharmacist.com or in PharmacyLibrary. ■

Adapted from Chapter 37 of the Handbook of Nonprescription Drugs.