Klacid SR

Selected form

Clarithromycin

Method of action: Antiulcer, Bactericidal, Bacteriostatic

Treatment option: Bronchitis, Community Acquired Pneumonia, Infection, Infection,Bacterial, Infection,Soft Tissue, Infection,Skin, COPD,Acute, Pneumonia, Sinus Infection, Pharyngitis

Medically reviewed

Marina Burgos

Last updated on 10/01/2026

This page provides general, reference-level information compiled from official medical sources. It is not a substitute for professional medical advice, diagnosis, or treatment. For decisions about your health, please consult a qualified healthcare professional.

Overview of Klacid SR

Quick Facts

Property	Description
Active ingredient	Clarithromycin
Form	Modified-release tablets (Sustained-Release)
Pharmacological class	Macrolide antibiotic
General purpose	Counteracting systemic bacterial growth
Origin	Semi-synthetic derivative

What Type of Medicine is Klacid SR?

Klacid SR is a specific prescription-only pharmaceutical preparation containing the active ingredient Clarithromycin, which is a Macrolide antibiotic. This systemic-use medicine belongs to the broader pharmacological class of antimicrobial agents and is used for patients requiring therapy against susceptible bacterial infections. Clarithromycin is a semi-synthetic Macrolide derivative, chemically derived from Erythromycin to provide enhanced stability and specific pharmacological characteristics. The general therapeutic purpose of Clarithromycin, as with the Macrolide class, is to inhibit the systemic spread of susceptible bacteria.

Composition and Significance of the Sustained-Release (SR) Form

Klacid SR is supplied for oral administration in the form of a modified-release tablet, also referred to as an extended-release form. The product is a single-ingredient product whose active component is solely Clarithromycin, formulated with specialized pharmaceutical excipients that determine its delivery profile. The designation SR (Sustained-Release) is a key differentiating factor, indicating that the tablet is engineered to control the rate at which Clarithromycin is released into the body. This controlled delivery is designed to provide stable plasma concentrations and support continuous therapeutic activity. This formulation facilitates once-daily dosing, a feature distinguishing it from immediate-release clarithromycin and supporting patient adherence to the treatment regimen.

How Clarithromycin Counteracts Bacterial Growth

The fundamental action of Clarithromycin involves its role as a protein synthesis inhibitor within bacterial cells. The drug exerts its antibacterial action by selectively binding to the 50S ribosomal subunit of the bacteria. By blocking this internal process, the drug prevents the bacteria from producing the proteins necessary to replicate and grow, resulting in a bacteriostatic effect. The general result of this action is the slowing or cessation of bacterial proliferation, which allows the body's natural defenses to address the microbial population and the underlying bacterial infection.

What side effects are possible with Klacid SR?

The safety profile for Klacid SR (clarithromycin) is classified by regulatory authorities based on system-organ classes and frequency, ranging from common to rare events.

Adverse Reaction Scope

Classification	Examples of Reactions	Affected Systems (SOCs)
Common	Dysgeusia (taste disturbance), Headache, Diarrhoea, Nausea, Vomiting, Abdominal pain, Insomnia	Gastrointestinal, Nervous System, Psychiatric
Serious / Clinically Significant	Fatal hepatic failure, QT prolongation, Torsades de Pointes, Severe cutaneous adverse reactions (SJS, TEN, DRESS)	Hepatobiliary, Cardiac, Immune System/Skin

Population-Specific Safety Considerations

The medicine is subject to specific regulatory constraints based on patient condition:

Severe Renal Impairment: The sustained-release (SR) tablet formulation is contraindicated in patients with creatinine clearance less than 30 mL/min because the dosage cannot be adequately reduced.
Hepatic Impairment: Caution is advised, and the medicine is contraindicated in patients with severe hepatic failure combined with renal impairment.
Cardiac Risk: Use is restricted in patients with a history of QT prolongation, ventricular arrhythmia, or uncorrected electrolyte disturbances (e.g., hypokalemia).

Exposure- and Duration-Related Safety

Clarithromycin use has been associated with the potential for Clostridioides difficile-associated diarrhoea (CDAD), which has been reported to occur up to two months or more after treatment cessation. Prolonged use may be associated with the overgrowth of non-susceptible bacteria or fungi.

This structure ensures the risks are officially communicated in a medically grounded manner, outlining both the common adverse effects and the high-level constraints defined by government labeling.

Overdose and Emergency Response

Overdose and When to Seek Help

Immediate Action Mandate

If an overdose of Klacid SR (clarithromycin) is suspected or confirmed, immediate medical attention must be sought. This action is explicitly mandated by regulatory authorities due to the potential for severe, life-threatening outcomes associated with high systemic exposure to the medicine. Emergency services should be contacted without delay to ensure prompt observation and management.

Documented Clinical Manifestations and Risks

Official regulatory documentation indicates that overdose primarily presents with prominent gastrointestinal disturbance, including abdominal pain, nausea, vomiting, and diarrhea. Other documented manifestations may include headache, reports of altered mental status, or elevated liver enzymes.

The most critical documented risk is cardiac toxicity. High doses are associated with QT interval prolongation and the potential development of serious ventricular arrhythmias, such as Torsades de pointes and ventricular tachycardia. Due to this risk, continuous ECG monitoring is a mandated requirement in clinical management. It is officially stated that a specific antidote for clarithromycin overdose is not known. Furthermore, patients with pre-existing renal impairment are noted to have an increased risk of experiencing more severe effects.

Management Protocol

Official guidance describes the management as primarily symptomatic and supportive treatment to address clinical signs. Procedures such as gastric lavage may be considered for the removal of unabsorbed medicinal product. Dialysis procedures (haemodialysis or peritoneal dialysis) are stated as generally ineffective in removing clarithromycin from the system.

Therapeutic Uses of Klacid SR

What Klacid SR treats: main uses and benefits

Klacid SR (clarithromycin) is a macrolide antibiotic medication used in the management of bacterial infections. Its therapeutic action helps manage symptoms related to systemic imbalance that often accompany bacterial infection.

The active ingredient in Klacid SR is commonly used across conditions presenting with acute episodes and may assist with managing symptoms that interfere with daily functioning. This ingredient is relevant for easing symptoms associated with various infections, including upper and lower respiratory tract infections (like acute sinusitis, acute bacterial exacerbations of chronic bronchitis, and community-acquired pneumonia), uncomplicated skin and skin structure infections, and is commonly used to help with Helicobacter pylori (H. pylori) infection in combination therapy.

This application supports general well-being during symptomatic phases and is commonly used to help with infections characterized by periods of heightened symptoms. This may be part of symptomatic management in clinical settings involving acute or unstable symptom patterns. One key aspect of its use is captured by the statement:

“The medication is relevant for easing symptoms associated with several common bacterial conditions, supporting the patient during difficult episodes by easing distress.”

Quick Fact: Relief for Symptoms that interfere with daily functioning

The therapy provides support that helps ease the overall symptom burden in scenarios where symptoms escalate temporarily due to infection. It assists with maintaining functional stability when symptoms become more noticeable.

Regulatory References

NIH DailyMed official clarithromycin prescribing information

Eligibility and Restrictions for Use

Eligibility Map: Who can and cannot use Klacid SR — Official Regulatory Information

Klacid SR (Clarithromycin Sustained-Release) eligibility is defined by absolute prohibitions and specific restrictions, as documented in official regulatory labeling.

Populations for whom use is Contraindicated

Klacid SR must not be used by the following patient groups:

Patients with known hypersensitivity to clarithromycin, erythromycin, or any other macrolide antibiotic.
Individuals with a history of QT prolongation, ventricular cardiac arrhythmia, or uncorrected hypokalaemia/hypomagnesaemia.
Patients with severe hepatic failure in combination with renal impairment.
Patients taking specific concomitant medications, such as lovastatin, simvastatin, or cisapride, due to the risk of serious adverse events.

Age-Related and Condition-Specific Eligibility Rules

Age: The sustained-release tablet form is generally used for adults and adolescents 12 years of age and older. It is not recommended for children younger than 12 years of age, who should use the pediatric suspension [Source 1.4].
Kidney Function: The sustained-release formulation is contraindicated in patients with severe renal impairment (creatinine clearance <30 mL/min), because the tablet cannot be split to achieve the necessary reduced dose [Source 1.5].
Pregnancy: Use is not recommended in pregnant women unless the clinical benefit justifies the potential risk, with particular caution advised during the first trimester [Source 1.5].

What should I know about interactions with other medicines?

Interactions with other medicines and products

Clarithromycin, the active ingredient in Klacid SR, is officially documented as a strong inhibitor of the metabolic enzyme Cytochrome P450 3A4 (CYP3A4) and the P-glycoprotein (P-gp) drug transporter. This pharmacokinetic interaction mechanism leads to significantly elevated plasma concentrations of numerous co-administered drugs.

Formal Interaction Restrictions

Co-administration with the following substances is formally restricted or contraindicated by regulatory bodies due to documented severe toxicity risks:

Interaction Type	Prohibited Substances
Cardiac Risk (QT Prolongation)	Pimozide, Astemizole, Terfenadine, Cisapride, Domperidone
Myopathy Risk	Lovastatin, Simvastatin
Vascular Risk	Ergotamine, Dihydroergotamine

Documented Exposure and Toxicity Alterations

Co-administration requires specific caution and monitoring with other CYP3A4 substrates, including certain antiarrhythmics (Quinidine, Disopyramide), oral anticoagulants (Warfarin), and Digoxin (a P-gp substrate). Strong CYP3A4 inducers such as Rifampicin or the herbal supplement St. John's Wort are documented to accelerate clarithromycin's metabolism, potentially leading to sub-therapeutic plasma levels. The combination with Colchicine is explicitly contraindicated in patients with pre-existing renal or hepatic impairment.

Mechanism of Action

Selective Inhibition of Bacterial Protein Synthesis

Clarithromycin's primary action is the selective binding to the 50S ribosomal subunit within susceptible bacteria, specifically targeting the 23S ribosomal RNA. This interaction physically blocks the ribosomal exit tunnel, functionally arresting the elongation phase of the nascent polypeptide chain. This direct interference with essential protein production results in a bacteriostatic effect, halting microbial growth and proliferation. This core action supports the physiological reduction of microbial presence by the host immune system.

️ Host Immune Pathway Modulation

Beyond its antimicrobial role, Clarithromycin also operates as a modulator of host physiology. This involves a secondary mechanism influencing the regulation of inflammatory signaling pathways by affecting the production of pro-inflammatory cytokines and the activity of immune cells. This modulation influences the host's inflammatory signaling, an effect secondary to the inhibition of microbial proliferation.

️ Constraint by Target-Based Resistance

The efficacy of the drug's mechanism is physiologically limited by microbial evolution, primarily through ribosomal methylation. This modification of the 23S rRNA target site structurally prevents Clarithromycin from binding effectively to the 50S subunit. This biological constraint results in a failure to inhibit protein synthesis, maintaining bacterial growth and negating the drug's bacteriostatic effect.

Dosage and Administration Information

How to Use Klacid SR

Klacid SR (Clarithromycin Sustained-Release) is an oral medication with specific administration guidelines designed to ensure its mechanism functions correctly over a full day. These instructions govern the dosage, frequency, and conditions of intake.

Standard Administration Guidelines

Element	Standard Instruction
Route of administration	The medicine is intended for oral administration only.
Dosing schedule	The standard adult dose is 1 gram (1,000 mg) once daily, typically achieved with two 500 mg sustained-release tablets.
Timing in relation to meals	The tablets must be taken with food to ensure optimal absorption and systemic drug exposure.
Special handling	The tablets must be swallowed whole; they are not to be broken, crushed, or chewed, as this compromises the sustained-release mechanism.
Course duration	The length of administration is determined by the specific condition, commonly ranging from 7 days to 14 days

Procedural and Population Constraints

The extended-release formulation is specifically designed for a once-daily frequency, distinguishing it from standard immediate-release clarithromycin. It is not recommended for children younger than 12 years due to a lack of suitable dosing. Additionally, patients with severe renal impairment (creatinine clearance less than 30 mL/min) typically require a 50% dose reduction. Because the 500 mg sustained-release tablet cannot be split, a switch to an immediate-release formulation is necessary for this population to achieve the required lower dosage. These constraints define the standardized approach to using the medicine.

Recent Clinical Evidence

Research evidence / Overview of studies for Klacid SR

This overview describes the official research landscape for the active ingredient in Klacid SR (clarithromycin), summarizing what types of studies have been conducted, the outcomes they measured, and what remains uncertain, based solely on authoritative sources.

Evidence for Use in Respiratory Tract Infections (RTIs)

Research has widely examined clarithromycin in common acute bacterial conditions, including Community-Acquired Pneumonia (CAP) and acute exacerbations of chronic bronchitis. The evidence for this use primarily comes from short-term Randomized Controlled Trials (RCTs). Studies monitored patient-reported outcomes describing perceived discomfort and measurements of microbial presence compared to comparator groups included in the trials.

The findings describe patterns observed in the studies regarding measured clinical outcomes. For specific conditions like CAP, some trials reported measurements related to outcomes describing episodic or acute changes when clarithromycin was part of the regimen. Follow-up durations were limited; the reported outcomes are often based on short-term observations.

Evidence for Use in Helicobacter pylori Eradication

Research explored the inclusion of clarithromycin in multi-drug combination regimens for H. pylori infection. This area was evaluated in numerous clinical trials examining measurements of persistent microbial presence (eradication rates).

Studies report how H. pylori resistance to clarithromycin was associated with lower eradication measurements. This resistance contributes to uncertainty regarding the consistency of reported eradication measurements between older and more recent trials, as evidence quality varies across studies based on local resistance rates. Further research suggests the sustained-release tablet may be inappropriate for eradication regimens, with some studies reporting lower measured success compared to immediate-release formulations.

Long-Term Surveillance and Extended Follow-up Studies

The active ingredient was observed in specific large-scale, controlled trials examining long-term outcomes beyond the antibiotic course. The primary research of this type involved placebo-controlled, long-term RCTs studying patient groups with existing Coronary Heart Disease (CHD). Outcomes examined were major, delayed events, including all-cause mortality and cardiovascular-related mortality, with follow-up durations extending for many years.

The original RCT reported measurements of all-cause mortality observed during the extended follow-up period in the clarithromycin group and the comparator group. However, subsequent long-term observational studies designed to explore this finding have since reported findings were mixed or inconsistent (as acknowledged by the FDA). No biological mechanism has been established in the research literature to explain the long-term findings, and the certainty remains low due to the conflicting nature of the evidence.

Key Studies & References

Frequently Asked Questions (FAQ)

Common questions about Klacid SR (FAQ)

Q: What is the main difference between Klacid SR and standard Klacid tablets?

Klacid SR is a sustained-release (SR) or modified-release form of clarithromycin. Official documents describe the standard tablet as immediate-release (often taken twice a day) and Klacid SR as a specialized tablet formulated for convenient once-daily dosing.

Q: Is Klacid SR used for general flu or just bacterial infections?

Klacid SR contains an antibiotic, which is described in regulatory sources as working by stopping the growth of bacteria. Because of this mechanism, official information states that antibiotics will not work for viral infections, such as a common cold or the flu.

Q: How long does it typically take to start feeling better after taking Klacid SR?

Official patient information indicates that individuals typically begin to feel better during the first few days of treatment with clarithromycin. The total length of the course is defined by your prescription based on the specific medical condition.

Q: Does Klacid SR interact with alcohol?

Official safety information indicates that the concomitant use of alcohol may increase the chances of dizziness while taking Klacid SR. Additionally, alcohol can contribute to potential side effects related to the liver in combination with this medicine.

Q: What should be avoided while taking Klacid SR due to drug interactions?

Regulatory documents formally restrict the use of Klacid SR with several medications due to the risk of serious side effects. These include certain heart rhythm drugs (like cisapride and pimozide), ergot alkaloids, and the statins lovastatin and simvastatin.

Q: What are the most common reasons why Klacid SR is prescribed?

Klacid SR is indicated for treating mild to moderate infections caused by susceptible bacteria. These commonly include infections of the lungs (pneumonia, bronchitis), sinuses, ears, throat (pharyngitis/tonsillitis), and certain skin/skin structure infections.

Q: What is the research evidence for Klacid SR in treating skin infections?

Official regulatory documents indicate that the drug is formally indicated for the treatment of mild to moderate uncomplicated skin and skin structure infections. This use is directed at conditions caused by specific susceptible bacteria, such as Staphylococcus aureus or Streptococcus pyogenes.

Q: Is Klacid SR known to cause metallic taste, and is that normal?

Dysgeusia is the medical term for a disturbance in the sense of taste, and it includes the symptom of a metallic taste. Official documents list dysgeusia as one of the most frequent adverse reactions reported in clinical trials, suggesting it is a common observation.

Q: Are there any specific foods or drinks that interact with Klacid SR?

Regulatory guidance primarily focuses on the requirement to take the SR tablet with food to ensure optimal absorption. Specific prohibitions for other common foods or drinks are generally not highlighted in formal labeling, with the exception of alcohol.

Q: Does Klacid SR affect birth control pills?

Official patient information, based on regulatory data, indicates that clarithromycin does not stop the action of hormonal contraception, including the combined pill or emergency contraception.

Q: What is the risk of a severe allergic reaction to Klacid SR?

The medicine is formally contraindicated in patients with a known hypersensitivity to the drug or any macrolide antibiotic. Regulatory documents classify severe skin reactions (such as SJS, TEN, and DRESS) as Serious/Clinically Significant events reported in association with the drug.

Q: Does Klacid SR have a risk of causing diarrhea or C. diff infection?

Diarrhoea is listed as a common adverse reaction. Official safety information also notes that Klacid SR use has been associated with the potential for Clostridioides difficile-associated diarrhoea (CDAD), which can occur even after treatment is stopped.

Q: Why do official sources sometimes mention heart rhythm issues with this type of drug?

The concern is related to the drug's mechanism of strongly inhibiting a liver enzyme called CYP3A4. This action can lead to elevated concentrations of other medicines, which may cause a condition known as QT prolongation (a change in the heart’s electrical activity) and potentially life-threatening abnormal heart rhythms.

Q: Is it normal to feel dizzy or lightheaded while taking Klacid SR?

Dizziness is listed in the official safety information as a reported adverse reaction associated with the medicine. This information is provided to patients for awareness of potential effects.

Q: What should I know about Klacid SR and statin medicines?

The use of Klacid SR is contraindicated (must not be used) with the statins lovastatin and simvastatin. For other statins, regulatory guidance states that caution is advised, and consideration may be given to using the lowest registered dose or switching to an alternative statin not metabolized by the CYP3A4 enzyme.

Q: Is it possible to become resistant to Klacid SR after repeated use?

Regulatory documents mention the biological constraint of bacterial resistance developing, specifically through changes to the bacteria's internal structure (ribosomal methylation). This factor can affect the consistency of treatment success measurements observed in clinical trials.

Q: Is Klacid SR used for H. pylori infections?

Yes. Official regulatory labeling indicates that Klacid SR is used in combination with other medicines (such as a proton pump inhibitor and another antibiotic) for the specific treatment of H. pylori infection, which is associated with duodenal ulcer disease.

Q: Does Klacid SR affect the nervous system, like causing strange dreams?

Yes. Official safety documentation lists several reported psychiatric and nervous system side effects, including insomnia, anxiety, confusion, abnormal dreams, psychotic disorders, and depression.

Q: How is Klacid SR described for use in children?

The sustained-release tablet form is generally used for adults and adolescents 12 years of age and older. It is not recommended for children younger than 12 years of age, for whom the pediatric suspension formulation is typically prescribed.

Q: Are there any common supplements or vitamins that interact with Klacid SR?

The Interaction section formally lists the herbal supplement St. John's Wort as a strong CYP3A4 inducer that may accelerate the metabolism of Klacid SR. Other common supplements or vitamins are not specifically listed in the formal restrictions.

Q: Why is it important to finish the full course of Klacid SR even if I feel better?

Official patient information notes the importance of completing the medicine until the full prescription is finished, even if symptoms improve. This approach is generally described as helping to ensure all illness-causing bacteria are eliminated, which supports the goal of preventing resistance.

Q: Is Klacid SR considered a broad-spectrum antibiotic?

Studies and official information indicate that Klacid SR (clarithromycin) is described as a broad-spectrum macrolide antibiotic. This means it is effective against and prescribed for a wide range of common bacterial pathogens.

Q: Does Klacid SR treat infections in the chest or lungs?

Yes. Klacid SR is officially indicated for the treatment of certain bacterial infections of the lungs and respiratory tract. Examples listed in regulatory documents include Community-Acquired Pneumonia and Acute Bacterial Exacerbation of Chronic Bronchitis.

Q: How does the sustained-release (SR) technology work for Klacid SR?

Regulatory documents describe that the sustained-release formulation is engineered to control the rate at which the active ingredient is absorbed into the body. This controlled delivery ensures stable drug concentrations over a longer period, which facilitates the once-daily dosing.

Q: What is the primary way Klacid SR is removed from the body?

The drug is eliminated from the body through a combination of metabolism and excretion. Official data indicates that a significant portion of the medicine and its active metabolite are excreted in the urine via the kidneys.

Q: Is Klacid SR used to prevent infections in certain situations?

Yes. Official regulatory labeling indicates that the drug is used for the prevention (prophylaxis) of disseminated Mycobacterium avium complex (MAC) infection in specific, at-risk patient populations, such as those with advanced HIV infection.

Q: Does Klacid SR interact with blood thinners like warfarin?

Yes. Due to the drug's strong inhibition of the CYP3A4 enzyme, it can lead to elevated concentrations of blood thinners like warfarin, which may increase the risk of bleeding. Regulatory documents state that specific caution and monitoring are necessary when these drugs are used together.

Q: Are there official warnings about mental health changes while using Klacid SR?

Official safety information lists several reported psychiatric and nervous system side effects. These include conditions such as insomnia, anxiety, confusion, abnormal dreams, psychotic disorders, and depression.

How should Klacid SR be stored and disposed of?

How to Store and Dispose of Klacid SR?

Klacid SR (clarithromycin extended-release) must be stored under specific conditions to maintain product stability and safety, as defined by regulatory documents.

Storage Requirements

Klacid SR tablets require storage at controlled room temperature, specifically between 20 C and 25 C (68 F and 77 F). The medication must be kept in the original container and maintained tightly closed to provide protection from both light and moisture. Always ensure Klacid SR is kept out of the reach of children.

Disposal Instructions

Unused or expired Klacid SR must be thrown away. When a local drug take-back program is not available, the tablets should be mixed (uncrushed) with an undesirable substance, sealed in a container, and discarded in the household trash. Remember to scratch out personal information on the prescription label before disposal.

Attention! Always consult to a doctor or pharmacist before using pills or medicines.