What is the best course of action for a patient experiencing a sunburn-like rash, conjunctival injection, nausea, tachycardia, and hypotension after taking a single dose of Bactrim (trimethoprim/sulfamethoxazole)?

Immediate Management of Suspected Anaphylaxis from Bactrim

This patient is experiencing anaphylaxis and requires immediate discontinuation of Bactrim, intramuscular epinephrine 0.2-0.5 mg into the lateral thigh, aggressive fluid resuscitation with 1-2 L normal saline IV at 5-10 mL/kg in the first 5 minutes, and administration of H1/H2 antihistamines plus corticosteroids. 1, 2

Critical First Steps

Stop any ongoing exposure and assess ABCs (Airway, Breathing, Circulation) immediately. 1

• Position the patient in Trendelenburg position due to hypotension 1
• Establish or maintain IV access 1
• Administer supplemental oxygen 1
• Call for emergency medical assistance immediately 1

Epinephrine Administration - The Priority Intervention

Administer epinephrine 0.2-0.5 mg (1 mg/mL dilution) intramuscularly into the lateral thigh muscle immediately. 1 This is the single most critical intervention for anaphylaxis and must not be delayed. 3

• Repeat epinephrine every 5-15 minutes as needed if symptoms persist or worsen 1
• Do not delay epinephrine administration while waiting for other medications 3

Aggressive Fluid Resuscitation

Infuse normal saline 1-2 L IV at a rate of 5-10 mL/kg in the first 5 minutes. 1

• Follow with crystalloid or colloid boluses of 20 mL/kg, then slow infusion 1
• This addresses the hypotension from vasodilation and capillary leak 1

Adjunctive Medications

Administer diphenhydramine 50 mg IV plus ranitidine 50 mg IV (H1/H2 antihistamine combination). 1, 4

Give corticosteroids equivalent to 1-2 mg/kg of IV methylprednisolone every 6 hours. 1, 4 While corticosteroids do not treat acute anaphylaxis, they prevent biphasic reactions. 1

Vasopressor Support if Needed

If hypotension persists despite epinephrine and fluid resuscitation:

• Start dopamine 400 mg in 500 mL at 2-20 μg/kg/min, titrated to clinical response 1
• Alternatively, use vasopressin 25 units in 250 mL (0.1 U/mL) at 0.01-0.04 U/min 1
• These vasopressors may be required for refractory hypotension 1

Critical Monitoring

Monitor vital signs continuously until complete resolution of symptoms. 1, 3

• Observe for at least 24 hours after a severe reaction 1, 3
• Watch for biphasic reactions, which can occur hours after initial symptom resolution 1

Understanding This Reaction

This presentation is consistent with severe drug hypersensitivity to the sulfonamide component of Bactrim. 2, 5 The FDA label explicitly warns that "circulatory shock with fever, severe hypotension, and confusion requiring intravenous fluid resuscitation and vasopressors has occurred within minutes to hours of re-challenge with sulfamethoxazole and trimethoprim products." 2

The sunburn-like rash with systemic symptoms (conjunctival injection, nausea, tachycardia, hypotension) represents a severe hypersensitivity reaction that can rapidly progress to life-threatening anaphylaxis. 2, 6

Permanent Contraindication

Never rechallenge this patient with Bactrim or any sulfonamide-containing medication. 2 The FDA label states that "sulfamethoxazole and trimethoprim should be discontinued at the first appearance of skin rash or any sign of a serious adverse reaction." 2

• Document this as a severe drug allergy in the medical record 3
• Warn the patient that re-exposure can cause fatal reactions 2
• Sulfonamides are associated with increased severity and mortality in rickettsial diseases, emphasizing the danger of this drug class 1

Common Pitfalls to Avoid

Do not delay epinephrine administration - this is the most common and dangerous error in anaphylaxis management. 3 Antihistamines and corticosteroids alone are insufficient for anaphylaxis. 3

Do not use corticosteroids alone without antihistamines - combination therapy is essential for optimal symptom control. 4, 3

Do not mistake the rash for a simple drug eruption - skin manifestations with systemic symptoms indicate severe hypersensitivity requiring aggressive treatment. 2

Post-Stabilization Care

After the patient stabilizes:

• Continue antihistamine therapy for 24-48 hours 4
• Administer a corticosteroid taper over several days for moderate-to-severe reactions 4
• Provide patient education about avoiding sulfonamide-containing medications 2
• Consider allergy/immunology consultation for documentation and future medication planning 1