Can I mix ibuprofen and acetaminophen for a child with post‑vaccine fever at night?

Short answer

Why people ask this

Nighttime fevers after vaccines can disrupt a child’s sleep and worry caregivers, especially when comfort is the goal until morning. Parents also hear mixed advice about alternating medicines overnight and don’t want to affect the vaccine’s benefits. After-vaccine fever is common and usually mild; giving pain/fever medicine after symptoms start is acceptable. The decision to mix depends on age (ibuprofen is for 6+ months), hydration, and correct weight-based dosing.

When it might be safe

• Child is 6 months or older (ibuprofen age cutoff) and taking fluids well; acetaminophen is dosed 10–15 mg/kg every 4–6 hours, ibuprofen 10 mg/kg every 6–8 hours, within daily maximums.
• You try one medicine first at bedtime, and only add the other if fever or discomfort returns and is disrupting sleep.
• Short-term use (often just one night after vaccines like DTaP or MMR) with a written or app-based schedule to avoid dosing errors.
• No contraindications to NSAIDs (e.g., kidney issues, prior NSAID reactions) and no liver disease or acetaminophen-containing combo products on board.
• Clear post-vaccine symptoms (fever, soreness) without red flags like breathing issues, hives, or swelling of face/tongue.

When it is not safe

• Infants under 6 months: avoid ibuprofen; under 3 months: any fever needs medical guidance before treating at home.
• Poor hydration, persistent vomiting, or diarrhea at night (ibuprofen can stress kidneys when dehydrated).
• Using combination cold/flu products or multiple acetaminophen/ibuprofen formulations that risk double-dosing.
• History of asthma worsened by NSAIDs, stomach ulcers, kidney or liver disease, or prior severe vaccine reaction.
• High fever >104°F (40°C), inconsolable crying >3 hours, stiff neck, rash with bruising, or breathing/swallowing trouble—seek care instead of layering meds.

Possible risks

• Dosing mistakes overnight (too close together or above daily maximums), leading to liver toxicity (acetaminophen) or kidney/stomach issues (ibuprofen).
• Masking signs of a serious reaction that needs prompt care, especially if new symptoms escalate after the vaccine.
• Dehydration plus ibuprofen increasing kidney strain, particularly when the child isn’t drinking well at night.
• Unnecessary dual therapy when one agent would control a typical post-vaccine fever or soreness.

Safer alternatives

• Use a single agent first: acetaminophen or ibuprofen (age-appropriate), then reassess before adding the other.
• Non-drug measures at night: light clothing, comfortable room temperature, gentle fluids or breastfeeding, and soothing routines.
• Use a dosing chart/app and measure by weight with an oral syringe; set phone alarms if a repeat dose is needed.
• Call your pediatrician or an after-hours nurse line if the child is very young, has medical conditions, or symptoms are atypical.
• If vomiting prevents oral dosing, ask about rectal acetaminophen suppositories as a temporary option.

Bottom line

For a child with post-vaccine fever at night, mixing acetaminophen and ibuprofen can be acceptable short-term if the child is 6+ months, hydrated, and you use careful weight-based dosing—often one night and only if a single medicine doesn’t maintain comfort. Avoid mixing in infants under 6 months, in dehydration, or when red flags are present. When in doubt, start with one medicine, prioritize safe dosing, and contact a clinician if symptoms are severe or unusual.

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