Redback Spider Envenomation Medication

Most cases of redback spider envenomation are mild and can be managed symptomatically using common oral analgesics and sedatives.

Redback spider antivenom provides specific treatment in severe cases of envenomation.

Ensure that the patient's tetanus status is up to date.

Class Summary

Redback spider antivenom is the primary treatment of severe latrodectism. Before the introduction of the antivenom in 1995, 14 deaths due to redback spider envenomation were documented in Australia. The antivenom consists of equine IgE fragments raised against aLTX. Each ampule contains 500 units of neutralizing capacity against the Australian redback spider venom, with an average volume of 1-1.5 mL per ampule. The antivenom is usually administered by intramuscular injection. Indications for use of antivenom include severe headache, vomiting, abdominal pain, hypertension, arthralgia, or myalgia. Severe pain at the envenomation site is not considered an indication for antivenom administration.^[1]

Increasing concerns exist about the possible ineffectiveness of the IM route of administration of the redback antivenom. A recent study showed no significant difference in relief of symptoms or patient outcome between IV and IM administration of antivenom.^[9]

The risk of allergic reaction to the antivenom is 0.5% and is higher in patients with a history of horse allergy or prior exposure to equine immunoglobulin. Before using the antivenom, ensure the ability to manage hypersensitivity reaction and check for availability of the appropriate resuscitation/intubation equipment. The risk of serum sickness after exposure to the antivenom is 1.4%.

Possible contraindications to antivenom use include current beta-blocker therapy, as this may reduce the patient's responsiveness to resuscitative therapy in the event of anaphylaxis.^[1]

Redback spider antivenom

Produced by Commonwealth Serum Laboratories Ltd, Australia.

Class Summary

Patients may experience severe pain at the bite site, and pain control is essential to quality patient care.

Acetaminophen with codeine (Tylenol With Codeine, Capital and Codeine)

Combines analgesic effects of a centrally acting opium-derived alkaloid (codeine) and a peripherally acting nonopioid analgesic (acetaminophen). Indicated for treatment of mild to moderate pain.

Morphine sulfate, injectable (Duramorph, Infumorph, Astramorph).

DOC for narcotic analgesia because of its reliable and predictable effects, safety profile, and ease of reversibility with naloxone. Morphine sulfate administered IV may be dosed in a number of ways and commonly is titrated to the desired effect.

Class Summary

Patients may experience significant restlessness and anxiety, which may require the use of sedatives for symptomatic control.

Lorazepam (Ativan)

A sedative hypnotic in the benzodiazepine class that has a short onset of effect and relatively long half-life.

Diazepam (Valium)

Modulates postsynaptic effects of GABA-A transmission, resulting in an increase in presynaptic inhibition. Appears to act on part of the limbic system, the thalamus, and hypothalamus, to induce a calming effect. Also has been found to be an effective adjunct for the relief of skeletal muscle spasm caused by upper motor neuron disorders.

Rapidly distributes to other body fat stores. Twenty minutes after initial IV infusion, serum concentration drops to 20% of C

Individualize dosage and increase cautiously to avoid adverse effects.

Midazolam (Versed)

Because water soluble, takes approximately 3 times longer than diazepam to peak EEG effects. Thus, clinician must wait 2-3 min to fully evaluate sedative effects before initiating procedure or repeating dose. Has twice the affinity for benzodiazepine receptors than diazepam. May be administered IM if unable to obtain vascular access.

Class Summary

Tetanus immunization should be administered following a redback spider bite. A booster vaccination is recommended in previously immunized individuals.

Diphtheria-tetanus toxoid vaccine (Adacel, Boostrix, Decavac)

Manufactured by first culturing Clostridium tetani and then detoxifying the toxin with formaldehyde. This toxoid commonly is combined with diphtheria toxoid, and both serve to induce production of serum antibodies to toxins produced by the bacteria.

Used to induce active immunity against tetanus in selected patients. Immunizing agent of choice for most adults and children >7 y are tetanus and diphtheria toxoids. Necessary to administer booster doses to maintain tetanus immunity throughout life.

Pregnant patients should receive only tetanus toxoid, not a product containing diphtheria antigen.

In children and adults, may administer into deltoid or midlateral thigh muscles. In infants, preferred site of administration is the mid thigh laterally.