Clarithromycin and Doxycycline for Sinusitis (Penicillin Allergy)
The two penicillin-allergy options for a bacterial sinus infection, how they differ, and which suits which situation.
Part of our Sinusitis condition guide. For the first-line option, see penicillin for a sinus infection.
Key fact: Doxycycline is the alternative first choice for adults in UK sinusitis guidance, with clarithromycin as the other option. The practical split is straightforward—doxycycline has almost no drug interactions but marked sun sensitivity and cannot be used in pregnancy or under-12s; clarithromycin has neither of those restrictions but interacts with a great deal.
Get a Penicillin-Allergy Antibiotic for Sinusitis Online
Access Doctor is a UK online doctor and GPhC-registered pharmacy supplying doxycycline and clarithromycin for bacterial sinusitis after a regulated online consultation, with no GP appointment needed.
View Sinusitis Treatments →First: do you need an antibiotic at all?
Being penicillin-allergic does not change the underlying calculation. Acute sinusitis is overwhelmingly viral, and NICE advises against antibiotics for symptoms lasting fewer than 10 days regardless of what you can or cannot take.
Beyond 10 days, a steroid nasal spray is frequently the more appropriate step for anyone, because by that stage the driver is usually inflammation blocking drainage rather than active infection. Our guide on antibiotics for a sinus infection covers the decision in full.
1 in 10
UK adults carry a penicillin allergy label
90%+
of those are not allergic on testing
5 days
course length for both alternatives
Is your penicillin allergy label accurate?
This is worth pausing on before accepting a lifetime of alternatives.
Around one in ten people in the UK carry a penicillin allergy label. On formal testing, more than 90 per cent turn out not to be allergic. Most labels originate in childhood, when a child given penicillin for a viral illness developed a rash caused by the virus, and the rash was attributed to the drug.
What a genuine allergy looks like
- Symptoms within an hour of a dose—hives, swelling of the face or throat, wheeze, collapse
- A severe blistering or peeling skin reaction
- A reaction that needed emergency treatment or hospital admission
What usually is not
- Nausea, diarrhoea or stomach upset—side effects, not allergy
- A flat, non-itchy rash several days into a course during a viral illness
- A family history with no personal reaction
- A vague childhood episode with no detail
An inaccurate label is not harmless caution. It pushes you towards antibiotics with more interactions and more restrictions for the rest of your life. If yours is vague or inherited, ask your GP about formal allergy assessment—but do that when you are well, not in the middle of an acute infection.
Doxycycline vs clarithromycin
| Doxycycline | Clarithromycin | |
|---|---|---|
| UK position for sinusitis | Alternative first choice (adults) | Alternative first choice |
| Drug class | Tetracycline | Macrolide |
| Adult dose | 200mg day 1, then 100mg once daily | 500mg twice daily |
| Course | 5 days total | 5 days |
| Doses per day | One, after day 1 | Two |
| Drug interactions | Few | Many—a major consideration |
| Sun sensitivity | Marked | No |
| Under 12s | Not suitable | Suitable, dosed by weight |
| Pregnancy | Avoided | Erythromycin usually preferred |
| Must stay upright after dosing | Yes, 30 minutes | No |
| Distinctive side effect | Photosensitivity | Metallic or altered taste |
Doxycycline for sinusitis
Doxycycline is a tetracycline antibiotic. It works by binding to the bacterial ribosome and blocking protein synthesis, so bacteria cannot grow or reproduce and the immune system clears the rest.
Dosing for sinusitis
| Day | Dose |
|---|---|
| Day 1 | 200mg (loading dose) |
| Days 2–5 | 100mg once daily |
The higher first dose builds blood levels quickly; the once-daily maintenance dose is considerably easier to sustain than the four-times-daily schedule penicillin V requires.
How to take it
- With a full glass of water, sitting or standing upright
- Stay upright for at least 30 minutes afterwards—doxycycline can irritate and even ulcerate the oesophagus if a capsule lodges there. Never take it lying down or immediately before bed.
- Can be taken with food, which reduces nausea
- Separate from dairy, antacids, iron and calcium supplements by a couple of hours, since these bind it and reduce absorption
- Complete the full 5 days
Side effects
- Nausea and stomach upset—less if taken with food
- Diarrhoea
- Photosensitivity—covered below
- Oesophageal irritation if taken incorrectly
- Thrush
- Headache
Doxycycline is not suitable for children under 12 or in pregnancy, because tetracyclines can affect developing bones and teeth. It is also avoided while breastfeeding in most circumstances.
The sun sensitivity problem
This deserves emphasis because it genuinely catches people out, and a bad burn lasts far longer than the infection did.
Doxycycline makes skin markedly more sensitive to ultraviolet light. People have been badly burnt on unremarkable British days, on overcast days, and through car and office windows—circumstances where they would never normally think about sun protection.
- Use high-factor sun protection on exposed skin, even in weather you would usually ignore
- Cover up where practical—long sleeves, a hat
- Avoid sunbeds entirely for the duration
- Be careful through glass, including while driving
- Take extra care on holiday—if you are travelling somewhere sunny, mention it, as clarithromycin may be the more sensible choice
The sensitivity resolves once the course ends. The burn does not.
Clarithromycin for sinusitis
Clarithromycin is a macrolide antibiotic. It binds to the bacterial ribosome and blocks protein synthesis, halting bacterial growth so the immune system can clear the infection.
For adults with acute sinusitis the dose is 500mg twice daily for 5 days. Young people aged 12 to 17 are dosed at 250mg or 500mg twice daily. It can be taken with or without food, and unlike doxycycline there is no requirement to stay upright afterwards.
Side effects
- Nausea, vomiting and diarrhoea
- Indigestion and abdominal pain
- An altered, bitter or metallic taste—distinctive to this drug, harmless, and resolving when the course ends
- Headache
- Difficulty sleeping, and occasionally vivid dreams
Less commonly, clarithromycin can prolong the QT interval, an effect on the heart's electrical recovery that can rarely cause dangerous rhythm disturbances. Risk is higher if you already have a heart rhythm problem, low potassium or magnesium, or take other QT-prolonging medicines. This is part of why your full medicine list matters.
Clarithromycin interactions
This is the single biggest practical difference between the two options.
Clarithromycin inhibits CYP3A4, a liver enzyme responsible for metabolising a large share of common medicines. Block the enzyme and those medicines accumulate to higher levels than intended.
| Medicine group | Examples | Concern |
|---|---|---|
| Statins | Simvastatin, atorvastatin | Raised levels increase muscle damage risk. Statin often paused. |
| Anticoagulants | Warfarin, apixaban, rivaroxaban | Increased bleeding risk. Warfarin needs INR monitoring. |
| Heart rhythm drugs | Amiodarone, sotalol, digoxin | Additive QT effects, or raised digoxin levels. |
| Sedatives | Midazolam, some benzodiazepines | Prolonged and deepened sedation. |
| Immunosuppressants | Ciclosporin, tacrolimus | Raised levels and toxicity. |
| Gout treatment | Colchicine | Serious, potentially fatal toxicity. |
| Antipsychotics and antidepressants | Quetiapine, citalopram | Raised levels or additive QT effects. |
| Herbal products | St John's wort | Reduces clarithromycin levels. |
List everything you take, including things you would not think of as medicines—over-the-counter products, supplements and herbal remedies. This is not box-ticking; the table above contains combinations that are genuinely dangerous.
Pregnancy and breastfeeding
Doxycycline is avoided in pregnancy because tetracyclines can affect developing bones and teeth.
Where a penicillin cannot be used in pregnancy, erythromycin is generally preferred, having a longer and more reassuring safety record in pregnancy than clarithromycin. Clarithromycin is not absolutely ruled out and may still be chosen in some circumstances.
This is a decision for a clinician who knows your pregnancy. Access Doctor's online sinusitis service is for adults aged 18 and over. If you are pregnant, might be pregnant or are breastfeeding, tell us at consultation—where treatment needs direct clinical oversight, our prescribers will advise you to see your GP or midwife instead, and that is the right outcome.
How the choice is made
1
Is an antibiotic genuinely indicated?
Under 10 days and improving means no. This question comes before any choice between drugs.
2
Is the penicillin allergy real?
If the label is vague, first-line penicillin V may still be appropriate. Your prescriber will ask what actually happened.
3
Pregnant, breastfeeding or under 12?
Doxycycline is out. Erythromycin is usually preferred in pregnancy.
4
What else do you take?
A long medicine list, particularly statins or anticoagulants, pushes towards doxycycline.
5
Any sun exposure coming up?
An outdoor job or a sunny holiday pushes towards clarithromycin.
Access Doctor supplies doxycycline capsules for sinusitis and clarithromycin tablets for sinusitis, with phenoxymethylpenicillin remaining first choice for anyone who can take penicillin.
If it does not work
Expect improvement in facial pain and fever within 48 to 72 hours where the infection is genuinely bacterial. If you are no better after three full days, contact your prescriber rather than finishing and hoping.
The usual explanations are that the cause was viral all along, that doses were taken incorrectly—doxycycline alongside dairy or antacids, for instance—or that the driver is inflammation rather than infection and a steroid nasal spray would serve better. Our guide on sinusitis that will not go away covers what to do next.
Order Doxycycline or Clarithromycin for Sinusitis
Complete a short online consultation and a GPhC-registered pharmacist independent prescriber will review your allergy history and full medicine list before deciding which suits you. Dispensed from our UK pharmacy and delivered discreetly, with no GP appointment needed.
View Doxycycline 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. Also for swelling of the face, lips or tongue, difficulty breathing, a widespread raised itchy rash, or palpitations with dizziness or fainting after starting an antibiotic.
Contact your GP or NHS 111 the same day if you are no better after three days of treatment, if you develop severe or bloody diarrhoea, or if you develop yellowing of the skin or eyes.
Frequently Asked Questions
What antibiotic can I take for sinusitis if I am allergic to penicillin?
Doxycycline is the alternative first choice in UK guidance for adults, taken as 200mg on the first day then 100mg once daily for four further days. It is not suitable for children under 12 or during pregnancy. Clarithromycin is the other alternative, at 500mg twice daily for 5 days in adults, and it is the option used where doxycycline cannot be given. In pregnancy, erythromycin is generally preferred over both.
What is the dose of doxycycline for a sinus infection?
For adults, UK guidance for acute sinusitis recommends 200mg on day one as a loading dose, then 100mg once daily for the following four days, making a 5-day course in total. The higher first dose builds levels quickly. Take each capsule with a full glass of water while sitting or standing upright, and stay upright for at least 30 minutes afterwards to avoid irritating the oesophagus.
Does doxycycline make you sensitive to sunlight?
Yes, and this is the side effect most likely to catch people out. Doxycycline makes skin burn far more readily than usual, and people have been badly burnt on mildly sunny UK days or through car windows. Use high-factor sun protection, cover up, avoid sunbeds entirely and be cautious even in weather you would normally ignore. The sensitivity resolves after the course finishes, but a burn acquired during it will not.
Doxycycline or clarithromycin: which is better for sinusitis?
Doxycycline is the alternative first choice in UK guidance and has the advantage of once-daily dosing after the first day and very few drug interactions. Clarithromycin is taken twice daily and interacts with a long list of common medicines including statins and anticoagulants. Doxycycline's disadvantages are marked sun sensitivity and that it cannot be used in pregnancy or in children under 12. The right choice depends on your age, pregnancy status and what else you take.
Can I take doxycycline in pregnancy?
No. Doxycycline is avoided in pregnancy because tetracyclines can affect developing bones and teeth, and it is also not used in children under 12 for the same reason. Where a penicillin cannot be used for sinusitis in pregnancy, erythromycin is generally preferred. Always tell your prescriber if you are pregnant, might be pregnant or are breastfeeding, so the antibiotic choice can be made appropriately.
What should I tell my prescriber before taking clarithromycin?
Every medicine you take, including over-the-counter products, supplements and herbal remedies. Clarithromycin interacts considerably more than most antibiotics because it inhibits the liver enzyme CYP3A4, which raises blood levels of many other drugs. Important interactions include statins such as simvastatin and atorvastatin, where muscle damage risk rises, warfarin and other anticoagulants, some heart rhythm medicines, certain antipsychotics, ciclosporin, colchicine and midazolam. Give your prescriber a complete list of everything you take, including over-the-counter products and supplements.
Am I definitely allergic to penicillin?
Possibly not. Around 1 in 10 people in the UK carry a penicillin allergy label, but on formal testing more than 90 per cent are found not to be allergic. Many labels date from a childhood rash that was actually caused by the viral illness being treated. This matters because the label pushes you towards alternatives with more interactions and more restrictions. If your allergy history is vague or inherited, ask your GP about formal assessment, ideally when you are well rather than during an acute illness.
Completing the treatment
An antibiotic addresses the infection but does nothing for the pressure, so saline rinsing and regular pain relief remain what make the days bearable. Access Doctor supplies both antibiotic options 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
Doxycycline Capsules for Sinusitis
Alternative first choice for adults with penicillin allergy.
View product →Antibiotic · Rx
Clarithromycin Tablets for Sinusitis
The option where doxycycline cannot be used.
View product →Antibiotic · Rx
Phenoxymethylpenicillin for Sinusitis
First choice if your allergy label turns out to be inaccurate.
View product →Steroid spray · Rx
Mometasone Nasal Spray for Sinusitis
Often the better option than any 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: doxycycline. bnf.nice.org.uk
- Joint Formulary Committee. British National Formulary: clarithromycin. bnf.nice.org.uk
- NICE. Drug allergy: diagnosis and management (CG183). nice.org.uk
- NICE Clinical Knowledge Summaries. Sinusitis. cks.nice.org.uk
- Medicines and Healthcare products Regulatory Agency. Drug Safety Update: macrolides. gov.uk
- Electronic Medicines Compendium. Doxycycline 100mg capsules SmPC. medicines.org.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.