How to Take Antibiotics

“My GP has given me amoxicillin, but I’m not sure if I should take it with food.”

“I feel better after three days. Can I stop the course?”

“Will this antibiotic stop my contraceptive pill from working?”

“I had a reaction to penicillin years ago. Is this one safe?”

If you’ve been prescribed an antibiotic, it’s natural to have questions about how to take it, what to avoid, and what to expect. Used well, antibiotics are extraordinarily effective. Used carelessly, they lose their power, both for you and for everyone else.

In this guide, we’ll cover the antibiotics most commonly prescribed at Summerhill Health, including Amoxicillin, Flucloxacillin, Co-amoxiclav, Clarithromycin, Erythromycin, Trimethoprim, Nitrofurantoin, and Cephalexin, with practical advice on dosing, timing, food, alcohol, and what to watch for.

At Summerhill Health, Dr Natalie Summerhill prescribes antibiotics within NICE and RCGP guidance, with a strong commitment to antibiotic stewardship. Every prescription is tailored to your symptoms, your medical history, and the specific infection we’re treating.

Please note: This guide provides general information only. Always follow the specific instructions on your prescription label, and contact us if you’re unsure about anything.

Why Antibiotics, and Why Not Always?

Antibiotics treat infections caused by bacteria. They do nothing for viruses, which is why we don’t prescribe them for most coughs, colds, sore throats, or flu-like illnesses, even when symptoms feel severe.

Using antibiotics when they aren’t needed contributes to antibiotic resistance, where bacteria evolve to survive the medicines designed to kill them. This is one of the most serious threats facing modern healthcare, which is why we will only prescribe when there’s a clear clinical need.

When an antibiotic is the right choice, three principles matter:

1. Take the right dose at the right time.
2. Complete the full course unless your doctor specifically tells you to stop.
3. Tell us about any allergies, current medications, and side effects.

We’ll go through how this looks for each medication below.

How to Take Amoxicillin

Amoxicillin is a penicillin antibiotic with a broad spectrum of activity. It’s one of the most commonly prescribed antibiotics in the UK and is often used for chest infections, ear infections, sinusitis, dental infections, and some urinary tract infections.

• The usual adult dose is 500mg three times daily, typically for 5 to 7 days.
• Take it with or without food. Food doesn’t significantly affect absorption.
• Space the doses as evenly as possible across the day (for example, 8am, 2pm, and 8pm) to keep blood levels steady.
• Swallow capsules whole with water. Liquid formulations should be shaken before each dose.

Do not take amoxicillin if you have a known penicillin allergy. If you’ve ever had a rash, swelling, or breathing difficulty after a penicillin antibiotic, tell us before starting.

How to Take Flucloxacillin

Flucloxacillin is also a penicillin antibiotic, but it’s used specifically for skin and soft tissue infections such as cellulitis, infected wounds, and some bone or joint infections. It’s particularly effective against staphylococcal bacteria.

• The usual adult dose is 500mg four times daily, typically for 5 to 7 days (longer for more serious infections).
• Take flucloxacillin on an empty stomach. This means at least 1 hour before food or 2 hours after food. Food significantly reduces absorption.
• Space the doses across the day. For example, 7am, 12pm, 5pm, and 10pm works well around mealtimes.
• Swallow capsules whole with a full glass of water, and stay upright for at least 30 minutes afterwards. Flucloxacillin can cause significant oesophageal irritation or ulceration if a capsule lodges in the gullet, so plenty of fluid and an upright position are important safety steps.

As with all penicillins, do not take flucloxacillin if you have a known penicillin allergy.

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How to Take Co-amoxiclav

Co-amoxiclav (the active ingredient in Augmentin) combines amoxicillin with clavulanic acid, which extends the spectrum to cover bacteria that have developed resistance to amoxicillin alone. We typically prescribe it for more stubborn or mixed infections, such as bite wounds, sinusitis that hasn’t responded to amoxicillin, and certain respiratory or urinary infections.

• The usual adult dose is 500/125mg three times daily or 875/125mg twice daily, depending on the formulation prescribed.
• Take co-amoxiclav with food, ideally at the start of a meal. This significantly reduces the risk of stomach upset.
• Space the doses evenly across the day.
• Courses are usually 5 to 7 days.

Co-amoxiclav is a penicillin, so the same allergy rules apply. It also carries a slightly higher risk of diarrhoea and, rarely, liver inflammation, so it’s reserved for situations where the broader spectrum is genuinely needed.

How to Take Clarithromycin

Clarithromycin is a macrolide antibiotic, often used as an alternative to penicillin in people with a penicillin allergy. It’s also a first-line choice for some respiratory infections and is sometimes used as part of a regimen to treat Helicobacter pylori (a bacterium linked to stomach ulcers).

• The usual adult dose is 500mg twice daily, typically for 5 to 7 days.
• Take it with or without food, though some people find taking it with a snack reduces nausea.
• Space the doses about 12 hours apart.
• Swallow tablets whole with water.

Important: Clarithromycin interacts with several common medications, including some statins, warfarin, and certain heart rhythm drugs. Always tell us about all your current medicines, including over-the-counter products and supplements, before starting.

How to Take Erythromycin

Erythromycin is an older macrolide antibiotic. It’s used for similar infections to clarithromycin and is sometimes preferred in pregnancy, where its safety profile is better established.

• The usual adult dose is 250mg to 500mg four times daily, depending on the infection.
• Take it with or just after food to reduce the risk of nausea, which is the most common side effect.
• Space the doses evenly across the day.
• Courses are usually 5 to 14 days, depending on what’s being treated.

Like clarithromycin, erythromycin has multiple drug interactions, including some statins, warfarin, and certain heart rhythm drugs. Combining erythromycin or clarithromycin with statins significantly increases the risk of muscle problems (statin-induced myopathy), so we’ll always review your full medicines list first. Always check with us or your pharmacist before combining it with other medications.

How to Take Doxycycline

Doxycycline is a tetracycline antibiotic with a broad spectrum of activity. It’s used for chest infections (including atypical pneumonia), acne and rosacea, certain sexually transmitted infections such as chlamydia, and some dental and travel-related infections. Because it isn’t a penicillin, it’s a useful option for people with a penicillin allergy.

• The usual adult dose is 200mg on the first day, then 100mg once daily, or 100mg twice daily for some infections, with the course length depending on what’s being treated.
• Take it with a full glass of water while sitting or standing, and stay upright for at least 30 minutes afterwards. Like flucloxacillin, doxycycline can irritate or ulcerate the gullet if a capsule lodges on the way down.
• For the same reason, don’t take it immediately before lying down or going to bed.
• You can take doxycycline with food to reduce stomach upset. However, avoid taking it at the same time as milk or dairy, antacids, or supplements containing iron, calcium, magnesium or zinc, as these bind to it and stop it being absorbed. Separate them by at least 2 hours.
• Doxycycline can make your skin more sensitive to sunlight. Use a high-factor sun cream and avoid strong sun or sunbeds during the course.

Doxycycline isn’t suitable in pregnancy or while breastfeeding, or for children under 12, as it can affect developing bones and teeth. Always let us know if you’re pregnant, trying to conceive, or breastfeeding before starting.

How to Take Trimethoprim

Trimethoprim is most commonly prescribed for uncomplicated urinary tract infections (UTIs) in women. It’s a folate antagonist, which is why it isn’t suitable in the first trimester of pregnancy or for people taking methotrexate.

• The usual adult dose for a UTI is 200mg twice daily for 3 days in women, and 7 days in men or in more complicated infections.
• Take it with or without food, with a full glass of water.
• Space the doses about 12 hours apart.
• Drink plenty of fluids throughout the day to support recovery.

Let us know if you’re pregnant, trying to conceive, or have any kidney concerns before starting trimethoprim.

How to Take Nitrofurantoin

Nitrofurantoin is another first-line option for uncomplicated UTIs. It concentrates in the urine, so it works locally in the bladder rather than throughout the body.

• The usual adult dose is 50mg to 100mg four times daily (immediate-release) or 100mg twice daily (modified-release, often labelled MR or Macrobid), typically for 3 to 7 days.
• Take nitrofurantoin with food or a glass of milk. This improves absorption and reduces nausea.
• Space the doses evenly across the day.
• Nitrofurantoin can turn your urine a dark yellow or brown colour, which is harmless and expected.

Nitrofurantoin isn’t suitable if you have significantly reduced kidney function or are in the last trimester of pregnancy. We’ll always check before prescribing.

How to Take Cephalexin

Cephalexin is a cephalosporin antibiotic, used for skin and soft tissue infections, some UTIs, and certain respiratory infections. It’s often a useful alternative when penicillins aren’t suitable.

• The usual adult dose is 500mg two to three times daily, typically for 5 to 7 days.
• Take it with or without food, with a full glass of water.
• Space the doses evenly across the day.

There is a small risk of cross-reactivity in people with a severe penicillin allergy, so we’ll always take a thorough allergy history before prescribing cephalexin.

Comparing Commonly Prescribed Antibiotics

What to Expect When Taking Antibiotics

Most people start to feel better within 48 to 72 hours of starting the right antibiotic. If you don’t notice any improvement after 3 days, or you feel significantly worse, please get in touch. It may be that we need to switch to a different antibiotic or reconsider the diagnosis.

Common side effects across most antibiotics include:

• Nausea or mild stomach upset
• Loose stools or short-lived diarrhoea
• Changes in taste (particularly with clarithromycin)
• Thrush (oral or vaginal), as antibiotics can disturb the natural balance of bacteria

These effects are usually mild and settle once the course finishes. Eating well, staying hydrated, and (if appropriate) taking a probiotic supplement a few hours apart from your antibiotic dose can help.

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Antibiotics, Alcohol, and the Contraceptive Pill

Alcohol

For most antibiotics, a small amount of alcohol won’t stop the medication from working. However, alcohol can intensify side effects such as nausea, dizziness, and stomach upset, and it slows your recovery. We generally suggest avoiding alcohol until you’ve finished the course.

One important exception: metronidazole and tinidazole (not in the list above, but commonly prescribed for dental or gynaecological infections) cause a severe reaction with alcohol and must be avoided completely during the course and for 48 hours afterwards.

The contraceptive pill

Most modern antibiotics, including those listed in this guide, do not reduce the effectiveness of the combined pill or progestogen-only pill. The older guidance to use extra contraception during short antibiotic courses has been updated.

However, if your antibiotic causes vomiting or significant diarrhoea, your pill may not be absorbed properly. In that case, follow the missed-pill rules in your pill leaflet and consider using condoms as a backup. If you’re unsure, contact us for tailored advice.

How to Store Antibiotics

• Tablets and capsules: Store at room temperature, in a dry place, away from direct sunlight. Keep in the original packaging.
• Liquid antibiotics: Many liquid antibiotics, including amoxicillin and co-amoxiclav suspensions, need to be kept in the fridge once made up by the pharmacist. Check the label.
• Always use the measuring device provided with liquid antibiotics. Household teaspoons are inaccurate.
• Keep all antibiotics out of reach of children and do not use beyond the expiry date.

Do not save leftover antibiotics for future use, and do not share antibiotics with anyone else. Return unused medication to your pharmacy for safe disposal.

Frequently Asked Questions

Do I really need to finish the whole course if I feel better?

In most cases, yes. Stopping early can leave residual bacteria, which may regrow and cause the infection to return, sometimes in a more resistant form. The exception is if your doctor has specifically advised a shorter course, which is increasingly common for uncomplicated infections. If in doubt, check with us before stopping.

What should I do if I miss a dose?

Take it as soon as you remember, unless your next dose is nearly due. Do not double up. Then carry on with the rest of the course at the usual intervals.

Can I take painkillers alongside my antibiotic?

Paracetamol and ibuprofen are generally safe to take with all the antibiotics listed here, provided you have no other reason to avoid them. If you’re on any prescription painkillers or anticoagulants, please check with us first.

What if I develop a rash?

Not all rashes that appear during a course of antibiotics are allergic reactions. A mild, flat, heat-style rash without other symptoms is sometimes a viral exanthem from the underlying infection rather than a true drug allergy. Stopping the antibiotic unnecessarily can allow the infection to flare back up, so it’s worth getting advice before pausing treatment.

• Mild, flat rash with no other symptoms: Contact us or your pharmacist before stopping the antibiotic so we can review and advise.
• Any hint of an allergic reaction, including hives (raised, itchy welts), intense itching, lip, tongue or facial swelling, or wheezing: Stop the antibiotic immediately and contact us.

Seek urgent medical advice if you develop a rash alongside facial or throat swelling, breathing difficulty, or blistering, as this can indicate a serious allergic reaction.

Should I take a probiotic alongside my antibiotic?

There’s reasonable evidence that probiotics can reduce the risk of antibiotic-associated diarrhoea, particularly in older adults and those on broader-spectrum antibiotics. If you’d like to try one, take it at least 2 hours apart from your antibiotic dose, and continue for a week or two after finishing the course.

Can I drink coffee or tea while on antibiotics?

Generally, yes. Caffeine doesn’t interact significantly with the antibiotics listed in this guide, and staying well-hydrated with water alongside is sensible. Worth noting for future reference: some other antibiotics, particularly ciprofloxacin (a fluoroquinolone sometimes prescribed for complex UTIs), can slow caffeine metabolism and cause jitteriness or palpitations. Always check the leaflet for any antibiotic you haven’t taken before.

When to Contact the Clinic

Get in touch if:

• You’re not feeling better after 3 days on the antibiotic.
• You develop a new rash, swelling, or breathing difficulty.
• You experience severe or persistent diarrhoea (especially watery or with blood).
• You’re vomiting and can’t keep doses down.
• You’re pregnant, breastfeeding, or planning a pregnancy and want to double-check the medicine is suitable.
• You have any questions or concerns.

Seek urgent medical advice if you develop facial or throat swelling, severe breathing difficulty, widespread blistering, or signs of sepsis such as confusion, high fever with shivering, very rapid breathing, or skin that is mottled or unusually pale. These are rare but require immediate assessment.

Need to Discuss Your Prescription?

If you have questions about your antibiotic, or you’re concerned that an infection isn’t settling, our team at Summerhill Health is here to help. Our same-day and evening appointments mean you don’t have to wait.
Contact us on 0161 552 2382 or book an appointment online.

Related Information

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