Is oral atropine (anticholinergic) a suitable treatment for pylorospasm in an infant?

Oral Atropine for Pylorospasm in Infants

Oral atropine is a reasonable and effective treatment option for pylorospasm in infants, with evidence supporting its use at an initial dose of 0.05 mg/kg/day divided into 8 equal doses, though it requires careful monitoring and may take several days to achieve clinical effect. 1, 2

Clinical Context and Mechanism

Pylorospasm differs from infantile hypertrophic pyloric stenosis (IHPS) but shares similar clinical presentations with nonbilious vomiting. Atropine works by competitively inhibiting acetylcholine at muscarinic receptors, leading to decreased gastrointestinal peristalsis and relief of pyloric sphincter spasm. 1 This mechanism is particularly relevant since one theory of pyloric pathology involves unopposed muscarinic stimulation causing sphincter contraction. 1

Dosing Protocol for Oral Atropine

Start with 0.05 mg/kg/day divided into 8 equal doses (each dose given in 1 mL volume), administered every 3 hours. 1 The protocol should follow this algorithm:

• Decompress the stomach via nasogastric tube before each atropine dose 1
• Position infant on right side with head elevated 20-30 degrees for 15-30 minutes after each dose 1
• Begin feeding trials 15-30 minutes after atropine administration, starting with 10 mL of 10% glucose 1
• If feeding is tolerated, gradually increase volume by 10 mL per feed until reaching full feeding (120 mL/kg/day) 1
• If vomiting occurs, repeat the same dose and volume; if still not tolerated, increase atropine by 1 mcg/kg/dose without increasing feed volume 1
• Maximum oral dose is 0.1 mg/kg/day 1

Expected Timeline and Efficacy

Clinical improvement typically occurs within 3-4 days (range 1-7 days) of starting oral atropine. 1 In the largest oral atropine series, 18 of 22 infants (82%) responded successfully to treatment. 1 A meta-analysis showed that 70% of infants treated with oral atropine alone achieved remission of IHPS, while 83.5% responded when intravenous atropine was used initially then transitioned to oral. 3

Important caveat: Pyloric muscle normalization on ultrasound lags significantly behind clinical improvement, taking 4-12 months after successful treatment. 4 Weight gain and cessation of vomiting are better clinical endpoints than sonographic changes. 4

Safety Profile and Monitoring

Oral atropine is well-tolerated in infants without significant side effects when used at recommended doses. 1, 3 This contrasts with intravenous atropine, which has higher rates of flushing and tachycardia. 1 However, critical monitoring is essential:

• Monitor heart rate continuously, as atropine-induced tachycardia can increase myocardial oxygen demand 5
• Watch for anticholinergic toxicity symptoms including fever, confusion, and excessive drying of secretions 5
• Be aware that paradoxical bradycardia can occur with very low doses (<0.5 mg total), though this is less relevant with the divided dosing protocol used for pylorospasm 5

When to Consider Surgical Intervention

If oral atropine is ineffective after 7 days at maximum dose (0.1 mg/kg/day), surgical intervention should be considered. 1 In published series, 4 of 22 patients (18%) required pyloromyotomy between days 4-6 of treatment. 1

Special Considerations for Pylorospasm vs. IHPS

The case report of successful pylorospasm management with atropine in a neonate with failure-to-thrive and hypothyroidism demonstrates that this approach can work even in complex presentations. 2 The patient in this report transitioned successfully from IV to oral atropine with resolution of emesis and weight gain. 2

Key distinction: Pylorospasm diagnosed by upper GI study (showing functional spasm without muscle hypertrophy) may respond more predictably to atropine than true IHPS, where success rates are lower. 2

Practical Algorithm

1. Confirm diagnosis with ultrasound (negative for IHPS) and/or upper GI study (showing pylorospasm) 2
2. Correct fluid and electrolyte imbalances before starting atropine 1
3. Insert nasogastric tube for gastric decompression 1
4. Begin oral atropine 0.05 mg/kg/day divided into 8 doses 1
5. Follow feeding advancement protocol as outlined above 1
6. Increase atropine dose incrementally if vomiting persists, up to maximum 0.1 mg/kg/day 1
7. Continue treatment until clinical improvement (cessation of vomiting, weight gain) is sustained 1, 2
8. Maintain therapy for average 24 days (range 11-39 days) or until ultrasound normalization if monitoring serially 1

Critical Pitfall to Avoid

Do not discontinue oral atropine prematurely based on persistent pyloric muscle thickening on ultrasound—clinical improvement (weight gain, cessation of vomiting) precedes sonographic normalization by months. 4 Conversely, do not continue ineffective atropine therapy beyond 7 days at maximum dose, as this delays definitive surgical management. 1, 6