How the dose is calculated
Azithromycin's long tissue half-life allows once-daily dosing over a short course. This calculator uses the standard once-daily mg/kg dose for the selected indication; azithromycin's classic 5-day course (a higher day-1 loading dose followed by a lower maintenance dose) is noted separately since it doesn't fit a single flat mg/kg/day figure.
Typical dosing by indication
| Indication | Dose | Frequency | Max |
|---|---|---|---|
| Standard 3-day course | 10 mg/kg once daily | once daily | 500 mg/day |
| Typhoid fever | 20 mg/kg once daily | once daily | 1000 mg/day |
Clinical use
- Azithromycin's long half-life and tissue penetration allow short courses (typically 3 days) or a 5-day regimen (higher loading dose on day 1, lower maintenance dose days 2–5) — check the specific product regimen being prescribed.
- Useful first-line option for atypical respiratory pathogens (Mycoplasma, Chlamydophila) and as a macrolide alternative in true penicillin allergy.
- Higher-dose, longer-course regimens are used for typhoid fever and some other specific indications — confirm the indication-specific course length, not just the daily dose.
- Can prolong the QT interval — use caution with other QT-prolonging drugs or known arrhythmia risk.
Frequently asked questions
Why is azithromycin often a 3-day course?
Its long tissue half-life means drug concentrations stay therapeutic for several days after the last dose, so a short 3-day course is often as effective as a longer course of drugs with a shorter half-life.
What is the 5-day azithromycin regimen?
Some products use a higher loading dose on day 1 (about 10 mg/kg) followed by a lower maintenance dose (about 5 mg/kg) on days 2–5 — check which regimen your product/guideline specifies rather than assuming a flat daily dose throughout.
Is azithromycin safe in penicillin allergy?
Yes — azithromycin is a macrolide, structurally unrelated to penicillins, and is commonly used as an alternative in patients with true penicillin allergy for suitable indications.
Does azithromycin interact with other medications?
Yes — notably other QT-prolonging drugs, and it can increase levels of some drugs metabolised by the same pathways. Review the patient's full medication list before prescribing.
References
- World Health Organization. Guidelines for the Management of Typhoid Fever.
- Bradley JS, et al. PIDS/IDSA Community-Acquired Pneumonia Guideline. Clin Infect Dis. 2011.
- British National Formulary for Children (BNFc) — Azithromycin.