What are the signs of a bad reaction to a subcutaneous injection 5 days after administration?

Signs of a Bad Reaction to a Subcutaneous Injection 5 Days Post-Administration

At 5 days post-injection, you should be concerned about persistent or worsening local reactions (erythema, swelling, induration, pain) that haven't resolved, signs of infection (warmth, spreading redness, fever), or delayed hypersensitivity reactions, as these warrant medical evaluation. 1

Expected vs. Concerning Reactions at 5 Days

Normal Local Reactions (Should Be Resolving)

• Mild erythema and induration with or without tenderness are common local reactions that typically resolve within a few days 2
• Most injection site reactions should be improving or resolved by day 5, not worsening 1
• Local irritation, skin discoloration, and inflammation can occur with subcutaneous injections, particularly with adjuvant-containing products 2

Warning Signs Requiring Medical Attention

Infection-Related Signs:

• Spreading erythema that extends beyond the initial injection site 1
• Fever or systemic symptoms accompanying local reactions 1
• Increasing warmth, pain, or swelling at the injection site rather than improvement 1
• Purulent drainage or abscess formation (indicates bacterial infection requiring antibiotics)

Delayed Hypersensitivity Reactions:

• Arthus-type hypersensitivity reactions can occur 2-8 hours after injection but may manifest as severe local reactions with fever and malaise 2
• Persistent induration or granuloma formation, especially if the injection was inadvertently given intradermally rather than subcutaneously 2
• Skin necrosis or ulceration at the injection site 3, 4

Severe Systemic Reactions (Rare but Serious):

• Generalized urticaria or anaphylaxis (though typically occurs within minutes to hours, not days) 2
• Neurologic complications such as peripheral neuropathy (extremely rare) 2

Management Algorithm

If Mild Local Reaction Persisting at Day 5:

• Apply cool compresses to reduce inflammation 1
• Consider topical corticosteroids for localized erythema and inflammation 1
• Oral antihistamines if pruritus is present 1
• Monitor daily for resolution or worsening 1

If Concerning Features Present:

• Seek immediate medical evaluation if erythema is spreading, fever develops, or symptoms worsen rather than improve over 24-48 hours 1
• Do not assume all reactions are benign - infection, abscess formation, or severe hypersensitivity require prompt treatment

Important Clinical Pearls

Common Pitfalls:

• Mistaking infection for normal reaction - any spreading redness or systemic symptoms at day 5 is abnormal 1
• Ignoring persistent symptoms - reactions should be improving by day 5, not stable or worsening 1
• Inadequate injection technique can increase risk of complications, including inadvertent intradermal injection causing more severe local reactions 2

Prevention for Future Injections:

• Ensure proper subcutaneous technique with needle inserted at 45-degree angle into appropriate tissue depth 2
• Rotate injection sites if multiple injections are needed 1
• Use appropriate needle length (5/8-inch, 23-25 gauge) to reach subcutaneous tissue without going too deep 2

Documentation and Follow-up:

• Monitor the injection site daily for changes in appearance 1
• Reassessment is mandatory if symptoms worsen rather than improve over 24-48 hours 1
• If severe reactions occurred, this may contraindicate future doses of the same medication 2