What are the potential side effects of Tamiflu (oseltamivir) in a relatively healthy child with no significant past medical history?

Side Effects of Tamiflu (Oseltamivir) in Children

In relatively healthy children, Tamiflu's most common side effect is vomiting (occurring in 16% of treated children versus 8% on placebo), followed by nausea and diarrhea, with these gastrointestinal effects being mild, transient, and rarely leading to treatment discontinuation. 1, 2

Common Gastrointestinal Side Effects

Vomiting is the predominant adverse effect in pediatric patients:

• Occurs in 16% of children aged 1-12 years treated with oseltamivir compared to 8% receiving placebo 1, 2
• In children under 1 year, vomiting occurs in approximately 9% of treated infants 2
• This represents an increased risk of 5.34% (NNTH = 19), meaning approximately 1 in 19 children will experience vomiting due to the medication 3

Nausea affects approximately 10% of treated pediatric patients 1

Diarrhea is particularly notable in infants under 1 year of age, occurring in 7% of treated infants 1, 2

Important mitigation strategy: Taking oseltamivir with food significantly reduces the severity of nausea and vomiting 4, 5. This is a simple intervention that can improve tolerability without compromising efficacy.

Other Common Side Effects

• Headache: Occurs in approximately 2% of treated pediatric patients 1
• Skin reactions: Including rash and diaper rash (7% in infants) 1, 2

Neuropsychiatric Events: Addressing Parental Concerns

This is often the most concerning issue for parents, but the evidence is reassuring:

• No established causal link: Comprehensive reviews of controlled clinical trial data have failed to establish a causal relationship between oseltamivir and neurologic or psychiatric events 1, 2
• Influenza itself causes these symptoms: The influenza infection is strongly associated with neuropsychiatric symptoms (delirium, confusion, abnormal behavior), which may occur before oseltamivir is even initiated 1, 2
• Risk is not increased: The FDA advises monitoring children closely for abnormal behavior during treatment, but the risk in patients taking oseltamivir is no higher than in those not receiving antivirals 1, 2
• Postmarketing reports: While abnormal behavior, delirium, hallucinations, and agitation have been reported during postmarketing surveillance (primarily in Japanese adolescents and adults), several analyses found oseltamivir is not associated with increased risk for neuropsychiatric events 4, 2

Clinical recommendation: Monitor for abnormal behavior as you would with any child with influenza, but do not withhold treatment based on neuropsychiatric concerns in children who would otherwise benefit 4, 1

Rare but Serious Adverse Effects

While uncommon, parents should be aware of these serious reactions that require immediate medical attention:

• Serious skin reactions: Including Stevens-Johnson Syndrome, toxic epidermal necrolysis, and erythema multiforme 2
• Anaphylactic/anaphylactoid reactions: Though rare, can occur 1, 2
• Symptoms requiring immediate discontinuation: Skin rash or hives, blistering/peeling skin, blisters or sores in mouth, swelling of face/eyes/lips/tongue/throat, trouble breathing, or chest pain 2

Age-Specific Considerations

Infants under 1 year: The safety profile is similar across all pediatric age ranges, with vomiting (9%), diarrhea (7%), and diaper rash (7%) being most frequently reported 2. Limited safety data in this age group have not demonstrated age-related safety concerns, but careful attention to dosing is essential 4

Children 1-12 years: Vomiting is the predominant side effect at 16% versus 8% in placebo 1, 2

Adolescents ≥13 years: The adverse effect profile is similar to adults, with nausea (10%), vomiting (8%), and headache (2%) being most common 1

Important Clinical Context: Benefits vs. Risks

The side effects must be weighed against the benefits:

• Oseltamivir reduces illness duration by approximately 17.6-29.9 hours in otherwise healthy children 4, 5
• It reduces the risk of otitis media by 34% in children 4
• Only approximately 1% of patients discontinued oseltamivir due to side effects in clinical trials 4
• The gastrointestinal effects are mild, transient, and resolve spontaneously within 1-2 days 2

Special Population: Hereditary Fructose Intolerance

Critical warning: One 75 mg dose of oseltamivir oral suspension delivers 2 grams of sorbitol, which is above the daily maximum limit for patients with hereditary fructose intolerance and may cause dyspepsia and diarrhea 2. Screen for this condition before prescribing.

Practical Counseling Points for Parents

1. Expect vomiting in about 1 in 6 children (16%), but it's typically mild and doesn't require stopping the medication 1, 2
2. Give with food to reduce nausea and vomiting 4, 5
3. Monitor for abnormal behavior as you would with any child with influenza, but understand this is more likely due to the flu itself than the medication 1, 2
4. Stop medication and seek immediate care if serious skin reactions or allergic symptoms develop 2
5. Complete the full 5-day course unless serious adverse effects occur—only 1% of children discontinue due to side effects 4