How long does it take for ibuprofen (Nurofen) to reduce fever?

Onset of Action for Ibuprofen in Fever Reduction

Ibuprofen begins reducing fever within 30 minutes to 2 hours, with peak effect typically occurring at 2-4 hours after administration. 1, 2

Timeline of Fever Reduction

Initial Response (30 minutes - 2 hours):

• Significant fever reduction begins within the first 30 minutes of intravenous administration 1
• For oral ibuprofen, measurable temperature reduction typically starts within 1.5-2 hours 3
• At 2 hours post-dose, ibuprofen (5-10 mg/kg) demonstrates superior antipyretic effect compared to paracetamol (effect size 0.19-0.34) 2

Peak Effect (2-6 hours):

• Maximum fever reduction occurs between 2-6 hours after administration 2
• At 4 hours, ibuprofen shows significantly greater temperature reduction than paracetamol (effect size 0.31-0.81) 2
• At 6 hours, the antipyretic advantage persists (effect size 0.33-0.66) 2
• In one pediatric trial, significantly more children were afebrile in the ibuprofen group compared to paracetamol at 1.5-2.5 hours (p = 0.04) 3

Comparative Effectiveness

Ibuprofen vs. Paracetamol:

• Ibuprofen provides approximately 55 additional minutes without fever in the first 4 hours compared to paracetamol alone 4
• Both drugs achieve significant fever control within 30 minutes when given intravenously, with no difference between them at this early timepoint (p = 0.980) 1
• However, ibuprofen demonstrates superior sustained antipyretic effect at 2,4, and 6 hours post-administration 2

Dual Therapy Considerations:

• Combined ibuprofen and paracetamol provides an additional 4.4 hours without fever over 24 hours compared to paracetamol alone 4
• Combined therapy clears fever approximately 23 minutes faster than paracetamol alone 4
• Network meta-analysis shows combined or alternating therapy may be superior to acetaminophen alone for achieving afebrile status at 4 and 6 hours 5

Dosing for Optimal Effect

Standard Dosing:

• Oral ibuprofen: 10 mg/kg per dose, every 6-8 hours (maximum 3 doses in 24 hours) 4
• Intravenous ibuprofen: 400 mg for adults achieves fever control within 30 minutes 1
• Higher doses (10 mg/kg vs 5 mg/kg) show greater antipyretic effect, particularly at 4 hours (effect size 0.81 vs 0.31) 2

Important Clinical Caveats

Safety Considerations:

• When using ibuprofen for fever, temperature above 38.5°C is the typical threshold for treatment 6
• Ibuprofen should be avoided in patients taking aspirin for cardiovascular protection, as it interferes with aspirin's antiplatelet effects 6
• If aspirin is necessary, ibuprofen should be taken at least 30 minutes after immediate-release aspirin or at least 8 hours before 6
• Avoid ibuprofen in chickenpox due to increased risk of severe bacterial skin infections 7
• Monitor renal function and blood pressure, especially in patients with preexisting hypertension, renal disease, or heart failure 6

When to Reconsider Treatment:

• Fever is a relatively short-lived symptom; approximately 25% of children are "back to normal" by 48 hours 4
• If fever persists despite appropriate ibuprofen dosing, evaluate for underlying serious causes rather than simply escalating antipyretic therapy 4
• The maximum recommended number of doses should not be exceeded—this occurred in 11% of children in one study, highlighting the need for careful dose tracking 4