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126 Bites and stings – terrestrial
While neurotoxic envenomation should prompt close respiratory monitoring,
opioids should be administered if clinically indicated for pain relief. 36
The mixed-mechanism opioid tramadol is effective in painful ant enveno-
mation. 37 One large-series review of Latrodectus (widow) envenomation
demonstrated utility of IV morphine as a single or adjuvant agent to pain
relief; morphine was found in this study to be much more effective than
calcium. 38 Data from animal models, while preliminary, suggest utility for
opioids in scorpion envenomation. 39
There is probably little difference in the pain relief afforded by different
opioids for terrestrial bites and stings. There are potential benefits to use of
fentanyl. Its potency and ease of titration are noteworthy, and lack of hista-
mine release makes fentanyl an excellent choice when histaminic pathways
are a major part of the envenomation syndrome (e.g. Hymenoptera stings).
Fentanyl is also recommended as the opioid of choice when antivenom is
administered. 17,21,38,40 Fentanyl appears at least as safe as other opioids in
pregnancy, and may in fact be less likely than morphine to cause fetal–
placental hemodynamic problems in patients with envenomation. 41
The histamine pathway’s contributions to terrestrial envenomation
symptoms create a role for antihistamines (e.g. diphenhydramine) in
treating land-based bites and stings. Animal data support the theory that
antihistamines can ameliorate symptoms of envenomation. 39 The utility of
antihistamines in Hymenoptera stings is well described, and case series
evidence points to consistent (although moderate) benefits from antihistamine
use for scorpion, caterpillar, and centipede envenomation. 42–46
For decades, authorities have recommended calcium for envenomations
associated with painful muscle cramps. 47,48 Particularly in the treatment of
latrodectism, case series evidence indicates continued worldwide use (and
reported salutary effect) of calcium. 20,31,49 It is not easy to dismiss years of
experience with calcium, since there are so many anecdotal reports of immediate
(if often short-lived) analgesia after its administration. Although the
best large-series review found no significant analgesia from calcium use, the
cation’s relative safety renders a therapeutic trial reasonable. 38
Evidence from multiple case series suggests that, instead of calcium, muscle
relaxants (particularly the benzodiazepines) should be used for treatment for