Widow spider bites: Management

INTRODUCTION — This topic will review the management of widow spiders (genus Latrodectus) bites. Clinical manifestations, diagnosis, and differential diagnosis of widow spider bites, recluse spider bites, and an overview of the approach to a suspected spider bite are discussed separately. (See "Widow spider bites: Clinical manifestations and diagnosis" and "Bites of recluse spiders" and "Diagnostic approach to the patient with a suspected spider bite: An overview".)

SEVERITY OF ENVENOMATION — The severity of widow spider bite envenomation is divided into three grades as follows:

●Mild envenomation – Mild widow spider envenomation consists of local skin irritation that may also be associated with local muscle pain and spasms adjacent to the bite.

●Moderate envenomation – Generalized spasmodic muscle pain in the bitten extremity, sometimes involving the back, chest, or abdomen, and accompanied by local diaphoresis constitutes the common manifestations of moderate envenomation.

●Severe envenomation – Severe envenomation causes pain that is severe and difficult to control or accompanied by systemic findings such as tachycardia and hypertension, nausea and vomiting, or headache.

APPROACH — The approach to widow spider bites depends upon the severity of envenomation:

The majority of patients who sustain a symptomatic widow spider bite develop mild envenomation that responds well to simple wound care and oral analgesia. (See "Widow spider bites: Clinical manifestations and diagnosis", section on 'Epidemiology'.)

Patients with moderate to severe envenomations by black widow spiders warrant parenteral opioid analgesia and benzodiazepines along with monitoring for complications. Antivenom is also indicated when muscle pain and spasms are poorly controlled by these measures. (See 'Moderate to severe envenomation' below and 'Indications' below.)

Patients with persistent severe pain despite parenteral medications who do not receive or do not respond to widow spider antivenom warrant hospitalization.

MILD ENVENOMATION — Pain at the bite site with no migration or other systemic symptoms identifies local widow spider envenomations. (See 'Severity of envenomation' above.)

Initial treatment measures following a mild envenomation include [1,2] (see 'Approach' above):

●Local measures – Gently clean the bite with mild soap and water.

●Oral analgesia – Administer oral pain medication, as needed (eg, acetaminophen, ibuprofen, oxycodone, or hydrocodone).

●Oral muscle relaxants – Oral benzodiazepines (eg, valium) or methocarbamol have been suggested by some, but evidence for effectiveness is lacking and there may be a risk of increased adverse events [3].

●Tetanus prophylaxis – Administer tetanus prophylaxis, if indicated (table 1).

Local application of cold packs and elevation of the affected body part have also been suggested. However, local swelling is usually minimal, and these treatments do not have any other known benefit for widow spider envenomation. Thus, we do not routinely recommend them.

Most bites are managed with minimal intervention and heal without scarring. Resolving bites should be monitored for the development of secondary bacterial infection, although this is a rare complication.

Antibiotics are prescribed only if there are signs of infection, such as increased erythema, fluctuation, and suppuration and are rarely necessary [4]. If cellulitis and/or abscess develops, then the patient should receive antibiotics directed against skin pathogens as discussed separately. (See "Methicillin-resistant Staphylococcus aureus (MRSA) in adults: Treatment of skin and soft tissue infections" and "Staphylococcus aureus in children: Overview of treatment of invasive infections" and "Skin and soft tissue infections in children >28 days: Evaluation and management", section on 'Cellulitis' and "Acute cellulitis and erysipelas in adults: Treatment".)

MODERATE TO SEVERE ENVENOMATION — Moderate to severe envenomation is characterized by intermittent muscle pain extending up the bitten extremity, sometimes involving the chest, abdomen, or back; regional or diffuse diaphoresis; nausea and vomiting; and headache. Although most patients have normal vital signs, tachycardia, tachypnea, and hypertension can develop due to pain, anxiety, or venom effects. (See "Widow spider bites: Clinical manifestations and diagnosis", section on 'Physical findings'.)

Treatment of these patients includes:

●Local wound care and tetanus prophylaxis as for mild envenomation (see 'Mild envenomation' above)

●Parenteral opioids (eg, morphine) for pain

●Parenteral benzodiazepines (eg, lorazepam) to reduce the frequency and severity of muscle spasms

●Antiemetic therapy (eg, sublingual or intravenous ondansetron) for nausea and vomiting

In one observational study of 148 patients with moderate or severe American black widow spider envenomation (Latrodectus hesperus), the duration of symptoms was 24 to 48 hours with symptomatic treatment alone and approximately 50 percent of patients required hospitalization for pain control [1].

Antivenom administration can decrease pain duration to less than 24 hours in approximately 80 percent of recipients and decrease severity such that discharge home is possible in approximately 90 percent of patients [1,5,6]. However, it is also associated with allergic reactions, serum sickness, and rare reports of fatalities [1,5-10]. Widow spider envenomation is usually not life threatening although mortality associated with secondary infection of the bite site or heart failure has been rarely described [11,12]. In the United States, Latrodectus mactans antivenom is often in short supply and distribution is limited by the manufacturer. (See 'Dosing and administration' below.)

The indications, efficacy, and adverse effects of widow spider antivenoms are discussed below. (See 'Indications' below and 'Efficacy' below and 'Adverse effects' below.)

Patients with widow spider bites and muscle pain or spasms should not receive intravenous calcium, either alone or in combination with parenteral opioids or benzodiazepines. Intravenous calcium does not appear to be effective for the treatment of moderate to severe muscle pain and spasms after a widow spider bite. As an example, in an observational study of 163 patients with widow spider bites, 23 of 24 (96 percent) moderately or severely envenomated patients had no relief of muscle pain and spasms after intravenous calcium therapy and required other treatment (parenteral opioids, benzodiazepines, and/or antivenom) [1].

Widow spider antivenoms — Widow spider bites are rarely life threatening, although envenomation can cause significant pain and require hospitalization. Among patients with moderate to severe envenomation unresponsive to supportive care, antivenom appears to reduce the pain, have a more prolonged effect than analgesics, and can reduce the need for hospitalization [1,13].

Several widow spider antivenoms are commercially available, including the American black widow spider (L. mactans) antivenom, the Antivenin Latrodectus (Black Widow) equine immune F(ab)2 produced in Mexico, and the Australian redback spider (L. hasselti) antivenom [14,15]. There is sufficient chemical similarity among widow venoms that all widow antivenoms provide some degree of relief following bites of various widow spiders. As an example, case reports describe successful use of redback antivenom in treating the bites of both the false black widow (genus Steatoda) and the American southern black widow [16,17].

In the United States, Latrodectus mactans antivenom is often in short supply and distribution is limited by the manufacturer to patients with symptomatic bites (call the Merck national Service Center Call Line at 1-800-672-6372). (See 'Dosing and administration' below.)

A new antivenom consisting of horse F(ab)2 fragments is undergoing trials but is not available outside of experimental protocols. (See 'Efficacy' below.)

In areas of the world in which redback spiders are prevalent, it is a routinely-stocked antivenom. Currently, in Australia, more redback spider antivenom is used than all other antivenoms, including snake antivenoms, combined. (See 'Indications' below.)

Indications — We strongly encourage consultation with a medical toxicologist, clinical toxinologist or other physician with experience in managing widow spider bites prior to antivenom administration. Phone consultation with a medical toxicologist is available through a United States regional poison control center by calling 1-800-222-1222. In Australia, expert advice can be obtained through the poisons information system by calling 13 11 26 or through the clinical toxinology service in Adelaide by calling 08-81617000. Contact information for poison centers around the world is provided separately. (See "Society guideline links: Regional poison control centers".)

We suggest that Australian redback spider antivenom be administered for moderate to severe symptoms of redback spider bites that are unresponsive to parenteral opioid and benzodiazepine therapy. Representative symptoms include the following:

●Severe and persistent local pain or muscle cramping

●Significant pain or diaphoresis extending beyond the immediate site of the bite

●Tachycardia and hypertension

●Difficulty breathing

●Nausea and vomiting

We also suggest that American black widow spider antivenom be administered to patients with moderate to severe manifestations of envenomation that are not responsive to supportive care. However, this antivenom is often in short supply and distribution is limited by the manufacturer.

Clinicians must weigh the risks and benefits of antivenoms in each case. The current recommendations for treatment of widow bites with antivenom are based upon case reports, retrospective series, and small trials [2,5,6,18,19]. Widow spider antivenom administration can decrease pain duration to less than 24 hours in up to 80 percent of recipients and decrease severity to the point that discharge home is possible in up to 90 percent of patients [1,5,6,8,13]. However, their use is also associated with allergic reactions (5 to 9 percent of patients), anaphylaxis (<1 percent of patients) and, for American black widow spider antivenom (Latrodectus mactans) rare reports of fatalities [1,5-10]. Serum sickness has been described in 2 to 16 percent of patients who have received widow spider antivenoms [6,7,19]. However, the frequency of serum sickness was not significantly different between patients who initially received antivenom when compared to placebo in one multicenter trial [19]. This finding suggests that envenomation itself may account for a significant proportion of the serum sickness that occurs after severe widow spider bites although confirmation of this finding in additional studies with larger sample sizes is necessary. (See 'Adverse effects' below.)

Adherence to this recommendation will likely result in a minority of patients receiving widow antivenom. As an example, a retrospective review of antivenom use in Australia over a two-year period reported that redback spider antivenom was administered in about 20 percent of cases that presented for medical care [8]. Furthermore, additional trials that directly evaluate antivenom therapy versus supportive care alone are needed to better define which patients should receive widow spider antivenoms. (See 'Efficacy' below and 'Adverse effects' below.)

There is a clear difference in approach to treatment of latrodectism in different parts of the world:

●In North America, due to concerns about Latrodectus mactans antivenom safety [1], antivenom is primarily used in severe to life-threatening envenomation, which will result in patients with moderate symptoms suffering for a period of several days. In the United States, Latrodectus mactans antivenom is often in short supply and distribution is limited by the manufacturer (see 'Dosing and administration' below). The clinician should contact a regional poison control center (1-800-222-1222) to discuss whether antivenom administration is warranted and to assist with obtaining it from the manufacturer (Merck & Co., Inc. 1-800-672-6372).

●In Australia, redback spider antivenom is used as treatment in a significant number of cases of latrodectism that do not fully respond to a trial of analgesia, depending upon local hospital treatment protocols. Observational data indicate approximately 1000 patients receive this antivenom each year [20]. There are no confirmed fatalities from adverse reactions to the antivenom, suggesting that this antivenom is safe. (See 'Adverse effects' below.)

Pregnant women — The safety of black widow spider antivenom has not been evaluated in pregnant women or in animal reproductive studies. Several reports describe administration of widow antivenom with no adverse effects and subsequent delivery of healthy newborns [3,21-24]. Thus, the indications for use in pregnant women are the same as for other moderate to severely envenomated patients.

Efficacy — Evidence regarding widow spider antivenom effectiveness is as follows:

●American black widow spider (Latrodectus mactans) antivenoms – Antivenoms developed for American black widow spider bites are as follows:

•American black widow spider (Latrodectus mactans) antivenom (equine, whole antibody) – American black widow spider antivenom is the only antivenom currently approved for American black widow spider bites and is often in short supply. When administered after L. mactans envenomation, it significantly reduced the duration of all symptoms in one series of 58 treated patients [1]. Complete resolution of symptoms occurred in a mean time of 31 minutes after antivenom administration. The mean total duration of symptoms was 9 hours in patients receiving antivenom, compared with 22 hours in patients not receiving this intervention [1]. Admission rates were 12 and 52 percent in those receiving antivenom and controls, respectively. Other case series have reported similar positive outcomes for this antivenom [13,25].

•Latrodectus (black widow) equine immune F(ab)2 antivenom – In a preliminary trial of an experimental F(ab)2 antivenom in 60 patients (mean age 39 years) with moderate to severe pain after a black widow spider bite, treatment failure (ie, inadequate pain control for 48 hours) was lower in patients receiving antivenom compared with placebo (52 versus 77 percent), and no serious drug-related adverse events occurred [26]. This antivenom is currently investigational in the United States but widely available in Mexico and is produced under the brand name Analatro (Instituto Bioclon, S.A. de C.V., Mexico City, Mexico).

●Australian redback spider antivenom (Latrodectus hasselti) – The evidence suggests that Australian redback spider antivenom is efficacious for the relief of acute pain after envenomation with L. hasselti, although the degree of benefit and the proportion of patients achieving adequate pain relief is inconsistent. The largest and only placebo-controlled trial suggests that on the order of 10 percent more adult patients experience short-term improvement in pain with antivenom versus placebo (number needed to treat 10), with no difference in resolution of systemic symptoms or reduction in pain at 4 or 24 hours when compared to placebo [19]. However, much larger treatment effects are reported in other trials and observational reports, and these same reports support a significant reduction of pain over 24 hours and decreased need for hospital admission among those patients who receive antivenom [5,6,8,27,28]. In our view, the body of evidence supports the continued use of antivenom for Australian redback spider bites in selected patients as determined by local guidelines as discussed in greater detail below.

Because of greater efficacy and safety, we support the administration of Australian redback spider antivenom by the intravenous (IV) route. Intramuscular (IM) administration may be appropriate if IV access cannot be readily achieved. In one large observational study IM redback antivenom was 94 percent effective in reducing pain symptoms [8]. The intravenous route may be effective in patients who have not responded fully to intramuscular injection and appears safe [29,30]. The intravenous route has traditionally been preferred for patients with severe systemic symptoms and for children younger than 12 years. Clinical experience and animal studies have suggested that intravenous use may be more efficacious [14]. Furthermore, IV access permits more rapid treatment of significant allergic reactions. There is a discernible shift in use amongst emergency physicians towards IV administration [31].

The relative efficacy of IV or IM Australian redback spider antivenom administration for relief of pain after moderate or severe envenomation has been examined in small multicenter randomized trials with varying results [5,6,19]. Differences in benefit range from 50 percent more patients achieving full pain relief at 24 hours after receiving IV antivenom rather than IM antivenom [5] to no apparent clinically important difference [19]. In the only trial to compare antivenom to placebo (RAVE2), 10 percent more patients had reduction in pain at two hours, although this result was not statistically significant.

In a separate trial in which all participants received antivenom, 20 percent of patients still required opioid analgesia after emergency department discharge and were unable to sleep in the first 24 hours following envenomation because of pain [6].

Although the investigators of the only placebo-controlled trial of antivenom for Australian redback spider envenomation have concluded that it is ineffective [19], we feel that this conclusion is premature for the following reasons:

•Almost half of patients had received no analgesia prior to randomization and treatment and approximately one-quarter to one-third had pain scores of 5 or less [19]. Some of these patients may have had mild envenomation which would not have typically warranted antivenom treatment. Randomization of these patients may have biased the study towards no effect for antivenom treatment and significantly reduced the power of the study to determine efficacy in patients with moderate to severe envenomation.

•Unblinded antivenom was given to fewer patients in the antivenom group than the placebo group (21 versus 32 percent, respectively, -11.6, 95% CI -23 to 0) suggesting greater persistence of envenomation symptoms in patients receiving placebo [19].

•No children participated in this trial. Pediatric patients represent a group who are at higher risk for more severe envenomation and in whom clinical experience suggests that antivenom is highly effective.

•The author’s conclusion that antivenom was ineffective are at odds with the anecdotal experience of many Australian clinicians. This apparent inconsistency might be explained by potential methodological issues with the trial, primarily the abovementioned lack of sufficient numbers of patients with severe envenomation.

In summary, we believe that evidence in the RAVE2 trial appears insufficient to conclude a lack of efficacy of Australian redback spider antivenom for patients with significant pain (pain score 5 or more), particularly for patients with severe envenomation. We support the continued use of antivenom for such patients pending results of an independent and larger, blinded placebo-controlled trial of Australian redback spider antivenom.

Adverse effects — Prior to the administrations of widow antivenom, medications and equipment for the treatment of anaphylaxis should be immediately available, including IV fluids, epinephrine, and intubation equipment. The risk of an allergic reaction should be discussed with the patient or guardian prior to administration whenever possible and asthma or allergy to horses are relative contraindications, especially for the administration of American black widow spider antivenom. (See 'Dosing and administration' below.)

The following studies provide data regarding the frequency of adverse effects from widow spider antivenoms:

●In a series of 58 patients, administration of American black widow antivenom (containing whole horse IgG) resulted in five allergic reactions (9 percent), of which four were mild and one was fatal [1]. The patient who died had asthma and multiple drug allergies, and was given undiluted antivenom as a rapid intravenous push [9]. Following this report, the use of black widow antivenom declined in the United States. In 2011, an additional case report described anaphylaxis and death after administration of dilute antivenom to a 37 year old man with asthma [10].

●In another series of 96 patients receiving American black widow antivenom per manufacturer’s instructions, adverse effects occurred in 4 percent of patients and included generalized flushing, paresthesias, myalgias, and urticaria, each occurring in one patient [32]. The patient with urticaria had complete resolution of symptoms following immediate cessation of antivenom administration and treatment with diphenhydramine.

●In a small trial of Antivenin Latrodectus (black widow) equine immune F(ab)2, no adverse effects occurred among the 13 patients who received antivenom [15].

●In an Australian series, redback antivenom (composed of horse F[ab]2 fragments) caused 11 immediate anaphylactic reactions in approximately 2000 administrations (0.54 percent), and there were no fatalities [7].

●Delayed serum sickness-like reactions were seen in approximately 2 percent of over 2100 patients receiving redback widow spider antivenoms in one large case series [7].

●Acute mild allergic reactions involving the skin only occurred in 4 percent of 112 patients receiving Australian redback spider antivenom in a multicenter trial [19]. The frequency of delayed serum sickness was similar in patients receiving antivenom initially compared with placebo (11 versus 8 percent) suggesting that envenomation itself may be responsible for a significant proportion of serum sickness seen in these patients although confirmation in studies with larger sample sizes is needed.

●In a trial that compared intravenous versus intramuscular administration of Australian redback spider antivenom in 126 patients, acute hypersensitivity reactions were reported in 5 percent of patients in both groups [6]. Serum sickness was more frequent in patients receiving IM antivenom (16 percent IM versus 11 percent IV).

Taken together, the data suggests that the risk of acute hypersensitivity after antivenom administration is 4 to 9 percent and that Australian redback spider antivenom may have a better safety profile than American black widow spider antivenom. Serum sickness may occur after a severe widow spider envenomation even when antivenom is not given. However, it is unclear whether antivenom administration increases the risk of delayed hypersensitivity in patients with moderate to severe envenomation.

Dosing and administration — Widow antivenoms should be given as soon as possible after the onset of significant symptoms warranting antivenom therapy, although patients with ongoing symptoms may benefit from treatment even days after the bite [33-36]. (See 'Indications' above.)

●Consultation with a medical toxicologist, clinical toxicologist, or other physician with expertise and prior experience treating spider bites is strongly recommended before initiating antivenom therapy. In the United States, there is often low inventory of Latrodectus mactans antivenom and the manufacturer limits distribution. According to the manufacturer, orders are often limited to two doses per patient and are shipped via United Parcel Service (UPS) Next Day delivery from the Merck West Point, Pennsylvania facility directly to the provider where the confirmed bite presented. The clinician should contact a regional poison control center (1-800-222-1222) to discuss whether antivenom administration is warranted and to assist with obtaining it from the manufacturer (Merck & Co., Inc. 1-800-672-6372). In Australia, expert advice can be obtained through the poisons information system by calling 13 11 26, or through the clinical toxinology service in Adelaide by calling 08-81617000. Contact information for poison centers around the world is provided separately. (See "Society guideline links: Regional poison control centers".)

●Prior to administration of antivenom, it is important for the patient or caregiver to understand that latrodectism is unlikely to be a fatal disease process and that a significant risk for allergic reactions is present but that without antivenom, the patient will likely have a prolonged period of distressing symptoms and that of all available treatments, current evidence indicates antivenom is the most likely to be effective and may significantly reduce the duration of suffering and hospitalization. Informed consent may be verbal or written according to institutional requirements. (See 'Moderate to severe envenomation' above and 'Efficacy' above and 'Adverse effects' above.)

●Antivenom administration has a significant risk of allergic complications and should only occur in a continuously monitored emergency or intensive care unit setting. Airway equipment, epinephrine, antihistamine medication, and isotonic IV fluids should be available for immediate treatment of anaphylaxis. There is no place for pre-administration sensitivity testing of spider antivenoms; this procedure is non-predictive and hazardous and should not be performed. Allergic reactions should be managed by immediately stopping intravenous infusion of the antivenom (if applicable) and treating symptoms appropriately (table 2 and table 3). (See "Anaphylaxis: Emergency treatment".)

●Premedication prior to antivenom use is controversial, with most evidence indicating it is either of doubtful efficacy or without merit [20]. Thus, unless there are clear, patient specific reasons for providing premedication (eg, known prior allergic reaction to widow spider antivenom), we do not advise it for patients receiving widow spider antivenoms.

●Widow spider antivenoms may be administered intravenously (IV) or intramuscularly (IM, eg, in the lateral thigh). The initial dose of antivenom will vary depending on the product used. Clinicians should be guided by a poison control center, medical toxicologist, clinical toxinologist, and/or information provided by the manufacturer. As with all other antivenoms, if used intravenously, secure IV access must first be established, the antivenom should be diluted, and then given either by slow "push" or continuous infusion, with the clinician present throughout administration.

The dose of antivenom is determined by expected venom dose, not the size of the patient; children should receive the same dose as adults, for a given level of envenomation. However, sometimes large adults may fail to respond adequately to a standard dose initially, for reasons which are unclear, and a higher dose is worth considering in this setting, tailored to individual clinical circumstances.

•Black widow spider antivenom – The initial dose of black widow spider antivenom (Antivenin Latrodectus mactans equine) is 6000 antivenom units (equal to the entire contents of one reconstituted vial). The black widow (Latrodectus mactans) antivenom available in the United States is freeze dried and should be reconstituted in the 2.5 mL sterile diluent that is supplied. For intravenous administration in adults and children, we suggest further diluting the solution by adding it to 250 mL of normal saline. We administer this initially at 1 mL per minute for 15 minutes, with careful observation for signs of an allergic reaction (flushing, hives, itching, bronchospasm, etc). If this initial administration is tolerated, we complete the infusion over 1 hour [9,37]. If there is no improvement, a second and third vial can be given at hourly intervals.

•Redback spider antivenom – The redback spider antivenom that is available in Australia comes in vials containing 500 units of antivenom in 1 to 1.5 mL solutions. Two vials are usually administered either undiluted, by intramuscular injection into the anterolateral thigh, or intravenously after the two vials are diluted into 200 mL of normal saline or 5 percent dextrose [38]. If response is not complete or symptoms begin to return, then a second dose of two vials may be given one or more hours after the first; it is common practice to wait at least 2 hours before considering a second or subsequent dose. A third dose of two vials may be given, although the diagnosis of widow spider bite should be reconsidered if there has been no response by the second or third dose [39]. In an Australian series, 76 percent of patients required only one vial, while two and three vials were needed in 18 and 6 percent, respectively [8]. However, the Australian National Poisons Information Center Network recommends that all cases receive two vial increments [38], as do state health department guidelines [38].

Opinion is divided on whether to prefer the IV or IM route for this antivenom, but theoretically IV should be more rapidly and consistently effective and anecdotal information appears to indicate that the IV route is routinely used in many hospitals, in preference to IM. The treating physician should decide on which route based upon the individual circumstances and, if unsure, after discussion with an expert as previously advised. (See 'Efficacy' above.)

DISPOSITION — Most patients with widow spider bites have mild envenomation and can be managed on an outpatient basis, as can a large proportion of patients who receive widow spider antivenom [1,3,5,8].

Patients requiring parenteral opioid analgesia for ongoing pain control warrant hospital admission.

DISCHARGE INSTRUCTIONS AND AFTER CARE

●All patients should be counseled about how to care for the bite site and advised to watch the site for signs of secondary bacterial infection (eg, fever, spreading redness, pus formation, or drainage).

●Depending upon the degree of pain and social circumstances, oral opioid analgesia (eg, hydrocodone, oxycodone) in amount sufficient to provide one to two days of treatment may be prescribed.

●Patients who received antivenom should be informed of the symptoms of serum sickness, which may develop within the subsequent two to three weeks. They should seek medical care promptly for suggestive symptoms, including fever, rash, joint pain, and malaise. Serum sickness reactions may require treatment with systemic glucocorticoids. (See "Serum sickness and serum sickness-like reactions".)

ADDITIONAL RESOURCES

Regional poison control centers — Regional poison control centers in the United States are available at all times for consultation on patients who are critically ill, require admission, or have clinical pictures that are unclear (1-800-222-1222). In addition, some hospitals have clinical and/or medical toxicologists available for bedside consultation and/or inpatient care. Whenever available, these are invaluable resources to help in the diagnosis and management of ingestions or overdoses. Contact information for poison centers around the world is provided separately. (See "Society guideline links: Regional poison control centers".)

Society guideline links — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Envenomation by snakes, arthropods (spiders and scorpions), and marine animals".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topic (see "Patient education: Spider bites (The Basics)")

SUMMARY AND RECOMMENDATIONS

●Arachnology – Widow spiders (Genus Latrodectus) are found in warm climates worldwide and are capable of biting humans (table 4). These spiders vary in appearance, although the American black widow (picture 1 and picture 2) and the Australian redback (picture 3 and picture 4) are distinctive in appearance. The clinical manifestations and diagnosis of widow spider bites are discussed separately. (See "Widow spider bites: Clinical manifestations and diagnosis".)

●General approach – The management of widow spider bites depends upon the severity of envenomation. (See 'Severity of envenomation' above.)

●Patient with mild envenomation – Manifestations consist of local skin irritation or local pain near the bite site. These are managed by gently cleaning the wound, administration of oral pain medication (eg, ibuprofen), and administration of tetanus prophylaxis, if indicated (table 1). (See 'Mild envenomation' above.)

●Patient with moderate to severe envenomation – This is characterized by intermittent muscle pain extending up the bitten extremity, sometimes involving the chest, abdomen, or back; regional or diffuse diaphoresis; nausea and vomiting; and headache with or without tachypnea, tachycardia, or hypertension. Management consists of the following measures (see 'Moderate to severe envenomation' above):

•Local wound care and tetanus prophylaxis as for mild envenomation (see 'Mild envenomation' above)

•Parenteral opioids (eg, morphine) for pain

•Parenteral benzodiazepines (eg, lorazepam) to reduce the frequency and severity of muscle spasms

•Antiemetic therapy (eg, sublingual or intravenous ondansetron) for nausea and vomiting

•In a patient with an Australian redback spider bite and moderate to severe symptoms that are unresponsive to parenteral opioid and benzodiazepine therapy, we suggest administering Australian redback spider antivenom (Grade 2C). (See 'Indications' above and 'Efficacy' above.)

•In a patient with an American black widow spider bite and moderate to severe manifestations of envenomation that are not responsive to supportive care, we suggest administering American black widow spider antivenom. However, this antivenom is often in short supply and distribution can be limited by the manufacturer (call the Merck national Service Center Call Line at 1-800-672-6372) (Grade 2C). (See 'Indications' above and 'Efficacy' above.)

We strongly encourage consultation with a medical toxicologist, clinical toxinologist, or other physician with experience in managing widow spider bites prior to antivenom administration. Phone consultation with a medical toxicologist is available through a United States regional poison control center by calling 1-800-222-1222. In Australia, expert advice can be obtained through the poisons information system by calling 13 11 26, or through the clinical toxinology service in Adelaide by calling 08-81617000. Contact information for poison centers around the world is provided separately. (See 'Additional resources' above.)

●Adverse effects of antivenoms – Allergic reactions are a possibility with antivenoms. Patients should be informed of this, and medications and equipment for the treatment of anaphylaxis should be immediately available, including intravenous fluids, epinephrine, and intubation equipment. (See 'Adverse effects' above and 'Dosing and administration' above.)

●Disposition – Most patients with widow spider bites have mild envenomation and can be managed on an outpatient basis as can approximately 90 percent of patients who receive widow spider antivenom. (See 'Disposition' above and 'Discharge instructions and after care' above.)

Patients requiring parenteral opioid analgesia for ongoing pain control warrant hospital admission. (See 'Disposition' above.)