Clarithromycin (Brand examples: commonly known as “Klacid”) — Patient Information

Clarithromycin is an antibiotic medicine used to treat certain bacterial infections. This page explains how clarithromycin works, what it’s used for, how to take it safely, and what to expect. It is written for people in the United Kingdom and aims to be clear and practical.

Basic product information

How clarithromycin works (mechanism of action)

Clarithromycin belongs to the macrolide family of antibiotics. It works by interfering with the way bacteria make essential proteins.

• It binds to the 50S ribosomal subunit of bacteria.
• This blocks protein synthesis, preventing bacteria from growing and multiplying.
• It also produces a partially active metabolite (an important one is 14-hydroxyclarithromycin) that contributes to antimicrobial activity.

In most infections, clarithromycin helps reduce symptoms and bacterial load, allowing your immune system to clear the infection.

Pharmacokinetics (how the body handles clarithromycin)

“Pharmacokinetics” refers to how the medicine is absorbed, distributed, metabolised, and eliminated.

• Absorption: Clarithromycin is absorbed from the gut. Food can affect how much and how quickly it’s absorbed, but clinical guidance typically focuses on completing the course as directed.
• Distribution: It distributes into tissues and body fluids, supporting its use in common respiratory and some skin infections.
• Metabolism: The liver metabolises clarithromycin. It can interact with other medicines because it affects certain drug-metabolising enzymes.
• Elimination: It is cleared via both liver metabolism and renal (kidney) excretion.
• Half-life: The duration of action varies with the formulation and patient factors; clinicians may choose dosing schedules accordingly.

Typical uses in the UK

Clarithromycin is used to treat infections caused by bacteria that are susceptible to it. In the UK, it is most commonly considered for certain:

• Respiratory tract infections (e.g., some cases of bronchitis, community-acquired pneumonia, and infections of the airways—subject to local guidance and patient factors).
• Ear, nose and throat infections (in selected situations).
• Skin and soft tissue infections (where appropriate).
• Helicobacter pylori eradication regimens in combination with other medicines, when recommended by a clinician. (Combination regimens are used; clarithromycin alone is not the full treatment for H. pylori.)
• Mycobacterial infections under specialist supervision for particular indications.

Antibiotic selection in the UK is strongly influenced by local resistance patterns and national guidance. Your healthcare professional will choose the best option for your specific infection.

When to start and timing of doses

If you’ve been advised to take clarithromycin, try to begin it as soon as possible after the dose schedule begins. Consistency is important.

• Take doses at evenly spaced times. This helps maintain effective levels in your body.
• Complete the full course. Even if you feel better, stopping early can allow infection to return.
• Use a timer or alarm. Many people take clarithromycin twice daily when using standard regimens.

If you miss a dose, follow the guidance provided with your medicine. In general, do not take a double dose to make up for a forgotten tablet—seek advice if you’re unsure.

Food interactions (including taking with meals)

Clarithromycin can be taken with or without food, but food may influence absorption. Some people find taking it with food reduces stomach discomfort.

• If your stomach feels sensitive, consider taking it with a meal or snack.
• Try to keep your routine consistent from day to day (e.g., always with food or always on an empty stomach), unless your healthcare professional instructs otherwise.

Grapefruit and citrus juices: While not the same as a direct “prohibited” food for clarithromycin, certain juices can affect drug metabolism pathways. To be safe, avoid large amounts of grapefruit juice unless your pharmacist has confirmed it’s suitable.

Alcohol and medicine interactions

Clarithromycin does not have the same “dangerous reaction” with alcohol that some other medicines do, but alcohol may worsen side effects such as dizziness, nausea, stomach upset, and diarrhoea. It can also impair recovery.

• For best tolerance, consider avoiding alcohol while you’re taking clarithromycin.
• If you do drink, keep it minimal and stop if you feel unwell.

More importantly, clarithromycin can interact with a number of medicines. Always check with a pharmacist if you are taking any regular medication, especially those listed under “Safety profile and important interactions” below.

Indications: what clarithromycin is used to treat

“Indications” means the conditions clarithromycin is used for. Clarithromycin is indicated for certain bacterial infections and, in some combination therapies, for specific infections such as H. pylori.

In the UK, your clinician will usually consider:

• the type and severity of infection,
• likely bacteria (and local resistance patterns),
• your medical history, allergies, and current medicines,
• whether clarithromycin is likely to be effective and safe for you.

Dosing: how much to take and for how long

Dosing depends on the infection type, your age, and whether you have kidney/liver impairment. It also depends on the specific formulation (tablets vs. suspension) and local antibiotic guidance.

Common adult regimens often involve twice-daily dosing for a period determined by the infection being treated. For precise dosing, always follow the schedule provided by your healthcare professional or the medicine label.

• Adults: Typical dosing is given as a dose amount per day split into two administrations (for many standard indications).
• Children: Doses are often weight-based and depend on the formulation (suspension/granules).
• Renal impairment: Dose adjustments may be necessary for reduced kidney function.
• Hepatic impairment: Clarithromycin is metabolised in the liver; caution may be needed.

Practical advice: If you’re unsure of your exact dose (mg) or how to measure a suspension, check with your pharmacist. Never guess or “double up” doses.

Safety profile: who should be careful

Clarithromycin is generally well tolerated by many people, but it can cause side effects and may not be suitable for everyone.

Common side effects

• Nausea
• Stomach discomfort
• Diarrhoea (mild to moderate)
• Indigestion
• Headache
• Taste changes (sometimes described as a bitter or unusual taste)

Seek urgent medical advice if you experience

• Signs of an allergic reaction: swelling of the face/lips, breathing difficulty, severe rash, or widespread hives.
• Severe or persistent diarrhoea, especially if watery or with blood, or if accompanied by fever or severe cramps. This can be a sign of Clostridioides difficile (a potentially serious antibiotic-associated infection).
• Palpitations, dizziness, fainting, or symptoms suggesting an abnormal heart rhythm.
• Yellowing of the skin/eyes (jaundice) or marked dark urine, which may suggest liver effects.

Important interactions to know about

Clarithromycin can interact with other medicines because it affects liver enzymes involved in drug metabolism. This can increase drug levels and side effects of other medications, or alter clarithromycin levels.

Speak to a pharmacist if you take any of the following (not an exhaustive list):

• Medicines for irregular heartbeat or rhythm (risk of QT prolongation).
• Some cholesterol medicines (statins), especially where a strong interaction risk exists—myopathy (muscle injury) can occur.
• Anticoagulants (blood thinners), such as warfarin—may increase bleeding risk.
• Other antibiotics/antifungals that can interact.
• Some antiepileptic medicines or medicines affecting the same metabolic pathways.
• Medicines for erectile dysfunction (e.g., certain PDE-5 inhibitors), where clarithromycin may increase levels.
• Diabetes medicines (some may interact through changes in drug levels).
• Colchicine (can increase toxicity risk).
• Other medicines known to prolong the QT interval.

To keep you safe, always tell your pharmacist and clinician about all medicines you use, including “over-the-counter” products and herbal remedies.

Practical use tips for better results

• Finish the course: Continue for the full duration unless advised to stop.
• Don’t share antibiotics: Different infections require different treatments.
• Stay hydrated: Especially if you have diarrhoea or feel unwell.
• Consider side-effect support: If you get mild stomach upset, taking with food may help.
• Use a medication organiser: A weekly pill box can reduce missed doses.
• Monitor improvement: Many bacterial infections begin improving within a few days. If symptoms worsen or do not improve, contact a clinician.

If you develop new symptoms (e.g., rash, severe diarrhoea, unusual bruising or bleeding, palpitations), stop and seek advice promptly.

What to expect during treatment

• Early days: You may still feel quite unwell; antibiotics work over time.
• Typical response: Symptom improvement often occurs within 48–72 hours for susceptible infections, but this varies.
• Not improving: If fever persists, breathing worsens, pain becomes severe, or you feel significantly worse, get medical advice.

Alternative options (depending on the infection)

There are different antibiotic choices depending on the infection type, severity, suspected bacteria, patient allergies, and resistance patterns. Alternatives may include antibiotics from other classes, such as:

• Amoxicillin or co-amoxiclav in certain respiratory/ENT infections
• Doxycycline in some respiratory and skin indications
• Azithromycin (another macrolide) in selected cases
• Clindamycin for certain skin/soft tissue infections (where appropriate)
• Cefalexin or other cephalosporins for specific infections and circumstances

The “best” alternative is infection-specific. Your healthcare professional will choose the safest and most effective option considering your history and local guidance. If clarithromycin is not suitable (for example, due to interactions or allergy), a different antibiotic may be recommended.

UK market and legal context (high-level)

In the United Kingdom, antibiotics are medicines that must be used appropriately to limit harm and reduce antibiotic resistance. NHS and professional bodies emphasise:

• Only using antibiotics when they are likely to help (i.e., bacterial infections).
• Following local prescribing guidance and resistance surveillance.
• Using the narrowest effective antibiotic where possible.

Clarithromycin availability may vary by brand and formulation. Online pharmacy services should supply medicines through legitimate supply chains and provide safe handling, appropriate patient information, and guidance about correct use.

Recent guidance (UK context)

Antibacterial prescribing in the UK is guided by national and local recommendations to address increasing resistance. Over recent years, guidance has consistently highlighted:

• Antibiotic stewardship (using antibiotics responsibly to reduce resistance)
• Careful selection of macrolides due to resistance patterns in some common organisms
• Assessment of severity and risk factors before choosing an antibiotic
• Review if there is no improvement after an appropriate period

Your clinician may choose clarithromycin only when it is likely to be effective and safe for your situation.

Delivery and availability (online pharmacy)

Availability of clarithromycin depends on stock levels, formulation (tablets vs. suspension), and strength. Online pharmacies in the UK typically offer:

• Home delivery within the UK mainland or other supported regions
• Discreet packaging to protect privacy
• Ordering options subject to stock and processing times

Delivery times vary by supplier and shipping method. If you need urgent treatment, check the pharmacy’s estimated dispatch/delivery window before placing an order.

Tip: Ensure your delivery address is correct and that someone can receive the parcel.

Storage information

• Store at room temperature unless the label says otherwise.
• Keep out of sight and reach of children.
• Protect from moisture and excessive heat.
• Follow “use by” and package instructions, including any guidance for reconstituted suspensions.

FAQ about clarithromycin

1) Is clarithromycin used for colds or flu?

No. Colds and flu are usually caused by viruses, and antibiotics (including clarithromycin) do not treat viruses. Antibiotics are used for bacterial infections.

2) How quickly will I feel better?

Many people begin to notice improvement within 48–72 hours, but it can vary depending on the infection and severity. If you are not improving or you worsen, contact a clinician for advice.

3) Can I take clarithromycin with food?

Often yes. Food can affect absorption, and some people find it easier on the stomach when taken with a meal or snack. Try to keep your routine consistent.

4) What if I miss a dose?

Check the instructions supplied with your medicine. In general, don’t take a double dose to make up for a forgotten tablet. If you’re unsure, ask a pharmacist.

5) Can I drink alcohol while taking clarithromycin?

It’s best to avoid or limit alcohol during treatment. Alcohol may increase side effects like stomach upset and diarrhoea and may slow recovery.

6) Are there medicines I must not combine with clarithromycin?

Clarithromycin has important interactions with certain medicines. This includes some drugs that affect heart rhythm, blood thinning medicines, certain statins, colchicine, and others. Always review your medicines with a pharmacist.

7) Can clarithromycin cause diarrhoea?

Yes. Mild diarrhoea can occur. However, severe or persistent diarrhoea (especially with blood or fever) should be assessed promptly as it could indicate a serious antibiotic-associated infection.

8) Is clarithromycin safe in pregnancy or breastfeeding?

Safety can depend on your individual situation. If you are pregnant, trying to become pregnant, or breastfeeding, discuss risks and benefits with a healthcare professional before taking clarithromycin.

9) Will clarithromycin prevent antibiotic resistance?

The best way to help limit antibiotic resistance is to use antibiotics only when needed, take them correctly, and complete the full course as directed. Stopping early can worsen resistance and increase the chance of recurrence.

10) What should I do if I get a rash?

A mild rash can have many causes, but any rash with swelling, breathing difficulty, blistering, or widespread hives may be an allergic reaction and needs urgent medical advice.

Summary

Clarithromycin is a macrolide antibiotic used for selected bacterial infections in the UK. It works by blocking bacterial protein production, helping your body clear the infection. Successful treatment depends on taking it correctly, completing the course, and being aware of interactions—particularly with other medicines that may affect heart rhythm, bleeding risk, or metabolism. If you experience severe side effects or no improvement, seek medical advice promptly.