How the dose is calculated
Erythromycin dose is calculated in mg/kg/day, divided every 6 hours. Pertussis treatment uses a higher end of the dosing range and a longer (typically 14-day) course than most other indications.
Typical dosing by indication
| Indication | Dose | Frequency | Max |
|---|---|---|---|
| Standard infection | 40 mg/kg/day | every 6h (4×/day) | 2000 mg/day |
| Pertussis | 50 mg/kg/day | every 6h (4×/day) | 2000 mg/day |
Clinical use
- Erythromycin was the original macrolide and remains an option for pertussis treatment/prophylaxis and as a penicillin alternative, though azithromycin and clarithromycin have largely replaced it for most indications because of better tolerability and dosing convenience.
- Frequent GI side effects (nausea, cramping) relate to its prokinetic motilin-receptor effect — this limits tolerability compared to newer macrolides.
- Associated with infantile hypertrophic pyloric stenosis when used in the first 2 weeks of life — use with caution and appropriate counselling in neonates.
- Strong CYP3A4 inhibitor — review for interactions with other medications metabolised by this pathway before prescribing.
Frequently asked questions
Is erythromycin still used for pertussis (whooping cough)?
Yes — erythromycin remains an effective option for treating and preventing the spread of pertussis, though azithromycin is often preferred in infants under 1 month because of a lower risk of pyloric stenosis.
Why does erythromycin cause more stomach upset than azithromycin?
Erythromycin stimulates motilin receptors in the gut, which increases GI motility and commonly causes nausea and cramping — newer macrolides like azithromycin don't share this effect as strongly.
Is erythromycin safe for newborns?
It requires caution — erythromycin use in the first 2 weeks of life has been associated with infantile hypertrophic pyloric stenosis, so azithromycin is often preferred in this age group when pertussis treatment is needed.
Does erythromycin interact with other medications?
Yes — it's a strong inhibitor of the CYP3A4 liver enzyme, so it can raise levels of many other drugs metabolised by that pathway. Always review the full medication list before prescribing.
References
- Centers for Disease Control and Prevention. Pertussis Treatment and Prophylaxis Guidance.
- British National Formulary for Children (BNFc) — Erythromycin.
- American Academy of Pediatrics Red Book — Pertussis.