Phenoxymethylpenicillin and Amoxicillin for a Sinus Infection
The UK first-line antibiotic for sinusitis, how it's dosed, why amoxicillin isn't the default here, and how to take penicillin V properly so it actually works.
Part of our Sinusitis condition guide. Not sure if you need an antibiotic at all? Start with do you need antibiotics for a sinus infection.
The headline: Phenoxymethylpenicillin (penicillin V) is the UK's first-choice antibiotic for acute sinusitis at 500mg four times daily for 5 days. Amoxicillin works too, but UK guidance prefers the narrower option for a reason—and it's not because amoxicillin is a bad drug.
Get Phenoxymethylpenicillin for Sinusitis Online
Access Doctor is a UK online doctor and GPhC-registered pharmacy supplying penicillin V for bacterial sinusitis after a regulated consultation—no GP waiting room, discreet UK delivery.
View Phenoxymethylpenicillin for Sinusitis →First, do you actually need one?
Before we get into dosing and drug names, let's be honest about the starting point: most sinus infections do not need antibiotics.
Acute sinusitis is overwhelmingly viral. NICE guideline NG79 is explicit: no antibiotic for symptoms lasting fewer than 10 days. And even beyond that, a steroid nasal spray is often the more appropriate step because the driver by then is usually inflammation, not active infection.
| Your situation | What you probably need |
|---|---|
| Under 10 days, gradually improving | No antibiotic. Self-care only. |
| 10+ days, stuck with no improvement | Steroid nasal spray usually. Back-up antibiotic sometimes. |
| Improved, then clearly worse again | Antibiotic is reasonable. This is "double sickening." |
| Systemically very unwell at any point | Get assessed now. Antibiotic is likely. |
| 12 weeks or more | Chronic sinusitis. Antibiotics have very little role here. |
Phenoxymethylpenicillin for sinusitis
Phenoxymethylpenicillin—commonly called penicillin V—is the UK first-choice antibiotic for acute sinusitis when treatment is genuinely indicated.
It works by blocking the enzymes bacteria use to build their cell walls. As the bacteria try to grow and divide, the wall fails, and the cell bursts under its own internal pressure. Human cells don't have cell walls, so penicillin can be lethal to bacteria while leaving your own tissue untouched.
The organisms behind bacterial sinusitis—most often Streptococcus pneumoniae and Haemophilus influenzae—are generally susceptible, and penicillin V remains effective against the commonest of them.
500mg
adult dose, four times daily
5 days
course length for acute sinusitis
48–72 hrs
before improvement is expected
Dosing and course length
| Age | Phenoxymethylpenicillin dose | Course |
|---|---|---|
| Adults 18 and over | 500mg four times a day | 5 days |
| 12–17 years | 500mg four times a day | 5 days |
| 6–11 years | 250mg four times a day | 5 days |
| 1–5 years | 125mg four times a day | 5 days |
Important: the course is shorter than for a sore throat. The same drug is prescribed for 5 to 10 days for a bacterial sore throat but only 5 days for acute sinusitis. Different conditions, different rules. If you've taken penicillin V before, don't assume the same course applies—follow your label.
How to take it properly
1
Empty stomach, every single dose
At least 30 minutes before food or 2 hours after. Food significantly reduces absorption. This is the single most common mistake with penicillin V—and it directly weakens the treatment.
2
Space the four doses evenly
Roughly every six hours. Build them around your meals rather than trying to fit meals around the medicine: on waking, late morning, late afternoon, and bedtime.
3
Full glass of water
Helps absorption and reduces stomach irritation, which the empty-stomach requirement can otherwise aggravate.