What treatment should be given to a pregnant woman with anemia (Hemoglobin less than 9.9 g/dL) who develops anaphylaxis after administration of Intravenous Iron (IV FCM), considering dexamethasone crosses the placenta?

Treatment of Anaphylaxis from IV FCM in Pregnant Women

Administer intramuscular epinephrine immediately at 0.3-0.5 mg (1:1000 concentration) into the anterolateral thigh—this is the first-line treatment for anaphylaxis in pregnancy, and there are no absolute contraindications to its use, including pregnancy. 1, 2, 3

Immediate Management Algorithm

First-Line Treatment: Epinephrine

• Stop the IV FCM infusion immediately upon recognition of anaphylaxis 1, 2
• Inject epinephrine 0.3-0.5 mg intramuscularly (0.01 mg/kg, maximum 0.5 mg) into the vastus lateralis muscle in the anterolateral thigh 1, 2, 3
• Repeat epinephrine every 5-15 minutes if symptoms persist or worsen 2, 3, 4
• Do not delay epinephrine administration to give antihistamines or corticosteroids first—delay is directly associated with increased mortality and biphasic reactions 1, 2, 3

Critical Point About Epinephrine in Pregnancy

• Epinephrine is safe and indicated in pregnancy for anaphylaxis, despite theoretical concerns about uterine vasoconstriction 5, 6, 7
• The FDA classifies epinephrine as Pregnancy Category C, but states it should be used "if the potential benefit justifies the potential risk" 5
• Maternal death from untreated anaphylaxis poses far greater risk to the fetus than epinephrine administration 6, 4
• Case reports demonstrate that intramuscular epinephrine effectively treats maternal anaphylaxis with minimal to no immediate adverse fetal effects 7

Simultaneous Supportive Measures

• Position the patient supine or in Trendelenburg position if hypotensive; allow position of comfort if respiratory distress or vomiting present 2, 3, 4
• Establish IV access and initiate aggressive fluid resuscitation with normal saline for hypotension 2, 3, 4
• Administer supplemental oxygen at 6-8 L/min 2, 4
• Maintain airway patency and prepare for intubation if airway compromise develops 2, 4
• Call for emergency assistance and prepare for transfer to emergency department or intensive care 2, 3

Secondary Interventions (After Epinephrine)

For Refractory Hypotension

• Consider IV epinephrine infusion (1:10,000 concentration, 4.0 μg/mL at 1-4 μg/min, maximum 10 μg/min) for protracted anaphylaxis unresponsive to multiple IM doses 2, 3
• Administer additional IV fluid boluses as needed 2, 3
• Consider vasopressors (dopamine) for refractory hypotension despite volume replacement and epinephrine 3

Adjunctive Medications (Not First-Line)

• H1 antihistamines (diphenhydramine 25-50 mg IV/IM) may be given after epinephrine for cutaneous symptoms, but provide no benefit for cardiovascular or respiratory manifestations 2, 3
• H2 antihistamines (ranitidine) can be combined with H1 blockers, though high-quality evidence is lacking 3
• Bronchodilators (albuterol) for bronchospasm resistant to epinephrine 3
• Glucocorticoids have no role in acute management and do not prevent biphasic reactions 3

Regarding Dexamethasone Concerns

The concern about dexamethasone crossing the placenta is irrelevant in this clinical scenario because:

• Corticosteroids (including dexamethasone) have no role in the acute treatment of anaphylaxis and should not be administered 3
• They do not provide acute benefit and do not prevent biphasic reactions 3
• Epinephrine, not corticosteroids, is the definitive treatment 1, 2, 3

Monitoring and Observation

Fetal Monitoring

• Fetal monitoring during or following IV iron administration is not required, and guidelines recommend against routine fetal monitoring for IV iron infusions 1
• However, given anaphylaxis occurred, continuous fetal monitoring is reasonable to assess fetal well-being after maternal stabilization 7

Maternal Observation

• Observe until all signs and symptoms completely resolve 2, 3
• Extended observation of at least 6 hours is warranted for severe anaphylaxis or patients requiring more than one dose of epinephrine, as these are risk factors for biphasic reactions 2, 3
• Transfer to emergency department or intensive care for continued monitoring 2, 3
• Biphasic reactions can occur up to 72 hours after initial reaction 2, 3

Critical Pitfalls to Avoid

• Never delay epinephrine while administering antihistamines or corticosteroids first—this is the most dangerous error 1, 2, 3
• Never avoid epinephrine due to pregnancy—maternal survival is paramount for fetal survival 5, 6, 4
• Never rely on antihistamines alone to treat cardiovascular collapse or respiratory distress 3
• Never use first-generation antihistamines or vasopressors as initial treatment for what may be a minor infusion reaction, as they can exacerbate hypotension and convert minor reactions into serious adverse events 1

Distinguishing True Anaphylaxis from Infusion Reactions

True anaphylaxis from IV iron is exceedingly rare (<1:200,000 administrations) and must be distinguished from complement activation-related pseudo-allergy (CARPA), which is more common and self-limited 1

Features of True Anaphylaxis (Treat with Epinephrine)

• Systemic hypotension 1
• Wheezing or respiratory stridor 1
• Peri-orbital edema or angioedema 1
• Gastrointestinal pain 1
• Urticaria with cardiovascular or respiratory compromise 1

Features of CARPA (Usually Self-Limited)

• Flushing, myalgias, arthralgias 1
• Back pain or chest pressure without hypotension 1
• Symptoms at beginning of infusion that resolve without treatment 1

Post-Acute Management

• Prescribe epinephrine auto-injector for potential future reactions 3
• Refer to allergist for evaluation and identification of safe alternative iron formulations 3
• Document the reaction thoroughly and list FCM as a contraindication for future use 1
• Consider alternative IV iron formulations (ferumoxytol, LMWID, FDI) if future IV iron is needed, as these have lower rates of hypersensitivity reactions 1