Antibiotics are medications prescribed to treat bacterial infections, and a common symptom of such infections is an elevated body temperature. When these medications are effective, the fever typically begins to subside as the body successfully fights off the invading bacteria. Therefore, if a fever persists, worsens, or develops anew while someone is undergoing antibiotic treatment, it indicates that another underlying factor might be at play, requiring further evaluation.
How Fever and Antibiotics Interact
Fever serves as a natural defense mechanism, where the body raises its core temperature to create an environment less favorable for bacterial proliferation. This elevated temperature also enhances immune cell activity, helping to combat the infection more efficiently.
Antibiotics either directly kill bacteria (bactericidal) or inhibit their growth (bacteriostatic). This action reduces the bacterial load, allowing the body’s immune system to clear the remaining pathogens. As the bacterial infection is brought under control, the immune response that triggers fever diminishes, leading to a decrease in body temperature and an improvement in symptoms.
Actual Causes of Fever During Antibiotic Treatment
Despite the expected reduction in fever, a persistent or rising temperature during antibiotic therapy can stem from several causes. The initial bacterial infection may not be fully resolved; the antibiotic might need more time to take effect, or the bacteria could be resistant to the specific drug, making treatment ineffective. An inaccurate diagnosis, or a localized collection of pus known as an abscess requiring drainage, can also be factors.
Another possibility is drug fever, an immune response to the antibiotic itself. This reaction is a hypersensitivity where the body’s immune system mistakenly reacts to the medication, rather than a direct side effect of the drug’s action against bacteria. Drug fever can occur with various antibiotics, including beta-lactams, cephalexin, minocycline, and sulfonamides, presenting as a low-grade fever that can become high before subsiding once the causative antibiotic is discontinued.
Antibiotics may disrupt the natural balance of microorganisms, leading to a secondary infection, also termed a superinfection. By eliminating beneficial bacteria alongside harmful ones, antibiotics can allow opportunistic pathogens to overgrow. Examples include Clostridioides difficile infection, which can cause severe diarrhea, abdominal pain, and fever, and fungal infections, such as oral thrush, which can emerge when the usual bacterial flora is suppressed.
Individuals undergoing antibiotic treatment can also contract other illnesses unrelated to the initial bacterial infection. These include viral infections like a common cold or influenza, against which antibiotics are ineffective. As these infections are caused by viruses, antibiotics will not influence their course, and the associated fever will persist independently of the ongoing bacterial treatment.
A temporary worsening of symptoms, including fever, can occur in a Jarisch-Herxheimer reaction. This transient inflammatory response is seen within 24 hours of antibiotic administration for certain spirochete infections, such as syphilis, Lyme disease, and relapsing fever. It is caused by the sudden release of bacterial toxins and debris as pathogens are rapidly killed, triggering a systemic inflammatory response. Symptoms like chills, headache, muscle aches, and skin lesion exacerbation resolve within 24 to 48 hours.
When to Consult a Healthcare Professional
If a fever develops or persists while taking antibiotics, consult a healthcare provider if it does not improve after two to three days of treatment, or if the temperature begins to worsen. A high fever, above 102°F (39°C) in adults, warrants medical attention. For infants younger than three months, a rectal temperature of 100.4°F (38°C) or higher requires an immediate call to the pediatrician.
New or worsening symptoms, such as a spreading rash, severe headache, stiff neck, confusion, or difficulty breathing, require prompt medical evaluation. Persistent vomiting, severe abdominal pain, or any allergic reaction, including hives, facial or tongue swelling, or trouble breathing, necessitate immediate medical care. It is important to remember that antibiotics should always be completed as prescribed; stopping them prematurely without consulting a doctor can lead to incomplete treatment and potential recurrence of the infection.