My 18‑month‑old child vomited after taking a medication—should I repeat the dose and how should I assess for dehydration?

Management of Vomiting After Medication in an 18-Month-Old Child

Should You Repeat the Dose?

Do not automatically repeat the dose—the decision depends primarily on the time interval between medication administration and vomiting, with redosing generally recommended only if vomiting occurred within 15-30 minutes of ingestion. 1

Decision Algorithm for Medication Redosing

Time-Based Approach:

• If vomiting occurred <15 minutes after dose: Redose the full amount, as minimal absorption has likely occurred 1
• If vomiting occurred 15-30 minutes after dose: Consider redosing based on medication type and visibility of medication in vomitus 1
• If vomiting occurred >30 minutes after dose: Do not redose, as significant absorption has likely occurred 1

Critical Factors to Consider Beyond Timing

Medication-Specific Considerations:

• For critical medications (antibiotics, anticonvulsants, immunosuppressants), err toward redosing if vomiting occurred within 30 minutes 1
• For less critical medications (vitamins, symptomatic treatments), observation without redosing may be appropriate 1

Visibility of Medication in Vomitus:

• If intact tablets/capsules or large amounts of liquid medication are clearly visible in the vomitus, redosing is more strongly indicated regardless of timing 1
• If vomitus contains no visible medication, absorption may have already occurred 1

Assessment for Dehydration

Assess dehydration severity using specific clinical signs rather than waiting for laboratory confirmation, as prompt recognition and treatment directly impact morbidity and mortality. 2, 3

Clinical Signs by Dehydration Severity

Mild Dehydration (3-5% body weight loss):

• Slightly dry mucous membranes 2, 3
• Normal mental status and vital signs 2
• Decreased urine output but still producing some urine 2

Moderate Dehydration (6-9% body weight loss):

• Sunken eyes 2, 3
• Loss of skin turgor with tenting when skin is pinched 4, 2
• Dry mucous membranes 4, 2
• Decreased capillary refill (>2 seconds) 2, 3
• Irritability or lethargy 2
• Significantly decreased urine output 2

Severe Dehydration (≥10% body weight loss):

• Severe lethargy or altered consciousness 2, 3
• Prolonged skin tenting (>2 seconds when pinched) 2
• Cool and poorly perfused extremities 2
• Markedly decreased capillary refill 2
• Rapid, deep breathing indicating metabolic acidosis 2
• Minimal or absent urine output 2

Most Reliable Clinical Predictors

Prioritize these findings as they correlate best with actual fluid deficit:

• Prolonged skin retraction time (>2 seconds) is more reliably predictive than sunken fontanelle or absence of tears 2
• Capillary refill time correlates well with fluid deficit, though fever and ambient temperature can affect this 2
• Rapid, deep breathing is a critical sign of severe dehydration with metabolic acidosis 2
• Acute weight change is the most accurate assessment if you know the child's pre-illness weight 2

Immediate Management Based on Dehydration Status

For Mild to Moderate Dehydration:

• Begin oral rehydration solution (ORS) immediately using small, frequent volumes of 5-10 mL every 1-2 minutes via spoon or syringe 2, 5
• Administer 50-100 mL/kg ORS over 2-4 hours 2, 5
• Replace ongoing losses: give 60-120 mL ORS for each diarrheal stool or vomiting episode 2, 5
• Gradually increase volume as tolerated without triggering more vomiting 2

For Severe Dehydration:

• This is a medical emergency requiring immediate intravenous rehydration 2, 3
• Administer isotonic crystalloid (lactated Ringer's or normal saline) at 20 mL/kg over 30 minutes 5, 3
• Continue IV fluids until pulse, perfusion, and mental status normalize 5, 3

Red Flags Requiring Immediate Medical Attention

Seek emergency care immediately if any of these are present:

• Altered mental status (severe lethargy, decreased consciousness, or extreme irritability) 2
• Signs of severe dehydration as listed above 2
• Bloody stools with fever 2
• Bilious (green) vomiting, which suggests intestinal obstruction 4, 6
• Persistent vomiting despite small-volume ORS administration 2
• Absent bowel sounds on examination 2
• Rapid, deep breathing indicating acidosis 2

Common Pitfalls to Avoid

Critical Errors in Medication Redosing:

• Do not automatically redose every time a child vomits—this can lead to overdosing if significant absorption already occurred 1
• Do not rely solely on parental report of "immediate" vomiting without clarifying the actual time interval 1

Critical Errors in Rehydration:

• Do not allow the child to drink large volumes of ORS rapidly from a cup, as this triggers more vomiting and falsely suggests oral rehydration has failed 2
• Do not use sports drinks, apple juice, or soft drinks as primary rehydration fluids—they lack appropriate electrolyte balance and contain excess sugars 2, 5
• Do not withhold food or enforce fasting once rehydration begins—early feeding reduces illness severity and duration 2, 5
• Do not underestimate dehydration severity in young infants, who are at highest risk for rapid deterioration 2

Antiemetic Considerations

Ondansetron may facilitate oral rehydration in children with persistent vomiting:

• Appropriate for children >4 years with significant vomiting that impedes oral intake 5, 3, 6
• Dose: 0.15 mg/kg (maximum 4 mg) 6, 7
• Has been shown to reduce recurrent vomiting, need for IV fluids, and hospital admissions 7
• However, at 18 months, your child is below the typical age recommendation, so this should only be considered under direct medical supervision 5, 3