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.
4
Keep the saline rinsing and pain relief going
The antibiotic treats the infection; it does nothing for the pressure. Saline rinses and regular paracetamol or ibuprofen are what actually make you feel better day to day.
5
Finish the course
All 5 days, even once symptoms settle. Missed a dose? Take it when you remember unless the next is nearly due, then skip it. Never double up.
Why not amoxicillin?
This is the question people most often arrive with, often because they've been prescribed amoxicillin for sinusitis before, either in the UK or abroad.
To be clear: amoxicillin works. It's active against the organisms that cause bacterial sinusitis and is used first line in several countries including the United States. It's not a bad drug and being prescribed it isn't an error.
UK NICE guidance nonetheless puts phenoxymethylpenicillin first, and the reasoning is stewardship rather than efficacy.
| Phenoxymethylpenicillin | Amoxicillin | |
|---|---|---|
| UK position for sinusitis | First choice | Not first choice |
| Spectrum | Narrow | Broader |
| Effective against sinusitis organisms | Yes | Yes |
| Dosing frequency | Four times daily | Three times daily |
| With food? | No—empty stomach | Either |
| Effect on gut flora | Less disruption | More disruption |
| Resistance pressure | Lower | Higher |
The principle is to use the narrowest antibiotic that will do the job. A broader antibiotic kills more of your normal bacteria, causes more side effects and applies more selection pressure for resistance—without working better against the target organism. Amoxicillin is easier to take, which is a genuine advantage, but not enough to outweigh the stewardship argument in UK guidance.
A note on the glandular fever rash. Amoxicillin is strongly avoided for sore throat because sore throat is frequently caused by glandular fever, and amoxicillin triggers a widespread rash in that setting. That specific concern is much less relevant to sinusitis, since glandular fever doesn't present as sinusitis. For sinusitis the argument against amoxicillin is spectrum, not rash.
Where co-amoxiclav fits
Co-amoxiclav combines amoxicillin with clavulanic acid, which blocks the enzyme some bacteria use to destroy amoxicillin. That widens its coverage considerably.
In UK guidance it's a second-line option for acute sinusitis, reserved for people who are systemically very unwell, who show signs of a more serious condition, or who are at high risk of complications. It's also considered where a first-line antibiotic has genuinely failed.
It's not used routinely because the broader spectrum comes with a noticeably higher rate of gastrointestinal side effects, and because reserving it preserves its usefulness for infections that truly need it.
Full antibiotic comparison for sinusitis
| Antibiotic | UK position | Adult dose | Course | Key point |
|---|---|---|---|---|
| Phenoxymethylpenicillin | First choice | 500mg four times daily | 5 days | Narrow spectrum. Empty stomach required. |
| Doxycycline | Alternative first choice | 200mg day 1, then 100mg daily | 5 days total | Penicillin allergy. Not under 12s or in pregnancy. |
| Clarithromycin | Alternative first choice | 500mg twice daily | 5 days | Penicillin allergy. Many drug interactions. |
| Erythromycin | Alternative in pregnancy | 250–500mg four times daily, or 500–1000mg twice daily | 5 days | Preferred macrolide in pregnancy. |
| Co-amoxiclav | Second line | As prescribed | 5 days | Systemically very unwell or high risk. |
| Amoxicillin | Not first choice in UK | — | — | Effective, but broader than needed. |
How long it takes to work
Where the infection genuinely is bacterial, expect improvement in facial pain and fever within 48 to 72 hours.
If you're no better after three full days, contact your prescriber rather than simply finishing the course and hoping. That pattern usually means one of three things: the cause was viral all along, the doses were taken with food and poorly absorbed, or something else is driving the symptoms. Our guide on sinusitis that will not go away covers what to do next.
Antibiotics don't relieve pressure. Even when working perfectly, they treat the infection while the swelling takes days to subside. Keep saline rinsing and taking regular pain relief throughout—see how to relieve sinus pressure.
Side effects
Common, around 1 in 10
- Nausea
- Diarrhoea
- Stomach discomfort
- Oral or vaginal thrush
Usually mild and settling after the course. Taking each dose with a full glass of water and eating properly between doses helps considerably.
Less common
- Mild rash—always worth having assessed rather than assumed
- Sore or furred tongue
- Joint aches
Call 999 or go to A&E for swelling of the face, lips, mouth or tongue, difficulty breathing or swallowing, a widespread raised itchy rash, dizziness or collapse. Stop taking the medicine. Contact a clinician promptly for severe, watery or bloody diarrhoea with cramps or fever, which can indicate Clostridioides difficile infection.
If you cannot take penicillin
Doxycycline is the alternative first choice in UK guidance for adults, at 200mg on day one then 100mg once daily for four further days. It's not suitable for children under 12 or in pregnancy. Clarithromycin is the other option, with erythromycin preferred in pregnancy.
Access Doctor supplies doxycycline capsules for sinusitis and clarithromycin tablets for sinusitis. Our guide on clarithromycin and doxycycline for sinusitis covers both in detail.
Is your penicillin allergy label accurate? Around 1 in 10 people in the UK carry one, but on formal testing more than 90 per cent turn out not to be allergic. Many labels come from a childhood rash caused by the underlying viral illness. An inaccurate label pushes you towards broader antibiotics for life, so it's worth asking your GP about formal assessment—outside of an acute illness rather than during one.
Order Penicillin V for a Bacterial Sinus Infection
Complete a short online consultation and a GPhC-registered pharmacist independent prescriber will assess whether an antibiotic is genuinely indicated and which suits your allergy history. Dispensed from our UK pharmacy and delivered discreetly.
View Phenoxymethylpenicillin for Sinusitis →Red flags needing emergency care
Call 999 or go to A&E for swelling or redness around an eye, a bulging eye, double or reduced vision, a severe headache unlike your usual headaches, neck stiffness, drowsiness or confusion. These suggest infection spreading beyond the sinuses and aren't a prescription decision.
Contact your GP or NHS 111 the same day if you're no better after three days of antibiotics, deteriorate at any point, or develop severe diarrhoea.
Frequently Asked Questions
Is penicillin used for a sinus infection?
Yes. Phenoxymethylpenicillin, also called penicillin V, is the first-choice antibiotic in UK guidance for acute sinusitis where an antibiotic is genuinely indicated. The usual adult dose is 500mg four times a day for 5 days. It is worth stressing that most sinus infections do not need any antibiotic, since acute sinusitis is overwhelmingly viral and UK guidance advises against antibiotics for symptoms lasting fewer than 10 days.
What is the dose of phenoxymethylpenicillin for sinusitis?
For adults aged 18 and over, UK guidance recommends 500mg four times a day for 5 days for acute sinusitis. Note that this is a shorter course than the 5 to 10 days used for a bacterial sore throat, because the conditions are treated differently. Doses for children are calculated by age. Always take the dose and duration your prescriber has specified rather than a general figure.
Can you take amoxicillin for sinusitis?
Amoxicillin is effective against the bacteria that cause sinusitis and is used first line in some countries, but it is not the first choice in UK NICE guidance, which recommends phenoxymethylpenicillin. The reasoning is antimicrobial stewardship rather than any failure of amoxicillin: it has a broader spectrum than necessary, so it disturbs more of the body's normal bacteria and adds more resistance pressure without producing better results for this infection.
How do I take penicillin V correctly for a sinus infection?
Take it on an empty stomach, at least 30 minutes before food or 2 hours after eating, with a full glass of water. Food significantly reduces how much of the drug is absorbed, so taking it with meals makes the treatment less effective. Space the four daily doses reasonably evenly, and complete the whole course even once you feel better. This empty-stomach requirement is a genuine difference from amoxicillin, which can be taken with or without food.
How long does penicillin take to work for a sinus infection?
Where the infection is genuinely bacterial, most people notice an improvement in facial pain and fever within 48 to 72 hours. If you are no better after three full days of treatment, contact your prescriber, because that pattern often means the cause was not bacterial after all and a steroid nasal spray would serve you better. Continue regular pain relief and saline rinsing alongside the antibiotic throughout.
Which sinusitis antibiotic is used instead of penicillin?
Doxycycline is the alternative first choice in UK guidance for adults with penicillin allergy, at 200mg on the first day then 100mg once daily for four further days. It is not suitable for children under 12 or in pregnancy. Clarithromycin is the other alternative. Your prescriber will ask what happened when you reacted to penicillin, because more than 90 per cent of people carrying a penicillin allergy label are not actually allergic when formally tested.
Is co-amoxiclav used for sinusitis?
Co-amoxiclav is reserved as a second-line option, generally for people who are systemically very unwell, who have signs of a more serious condition, or who are at high risk of complications. It combines amoxicillin with clavulanic acid to cover bacteria that would otherwise break down amoxicillin. Because it is considerably broader spectrum and carries a higher rate of gastrointestinal side effects, it is not used routinely for straightforward acute sinusitis.
Completing the treatment
An antibiotic treats the infection but does nothing for the pressure, so pairing it with saline rinsing and regular pain relief is what actually makes the days bearable. Access Doctor supplies antibiotics and steroid nasal sprays after a short online consultation reviewed by a GPhC-registered pharmacist independent prescriber. See the full range on the sinusitis treatment page.
Antibiotic · Rx
Phenoxymethylpenicillin for Sinusitis
UK first-choice antibiotic for bacterial acute sinusitis.
View product →Antibiotic · Rx
Doxycycline Capsules for Sinusitis
Alternative first choice for adults with penicillin allergy.
View product →Antibiotic · Rx
Clarithromycin Tablets for Sinusitis
The other penicillin-allergy option.
View product →Steroid spray · Rx
Mometasone Nasal Spray for Sinusitis
Often the better option than an antibiotic past day 10.
View product →References
- National Institute for Health and Care Excellence. Sinusitis (acute): antimicrobial prescribing (NG79). nice.org.uk
- Joint Formulary Committee. British National Formulary: phenoxymethylpenicillin. bnf.nice.org.uk
- Joint Formulary Committee. British National Formulary: amoxicillin. bnf.nice.org.uk
- Joint Formulary Committee. British National Formulary: co-amoxiclav. bnf.nice.org.uk
- NICE Clinical Knowledge Summaries. Sinusitis. cks.nice.org.uk
- NICE. Drug allergy: diagnosis and management (CG183). nice.org.uk
- UK Health Security Agency. Managing common infections: guidance for primary care. gov.uk
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for diagnosis and treatment. In a medical emergency, call 999.