Cyclocin

Quick links to important sections

Cyclocin

Medically reviewed

Rosario Oropesa

Last updated on 22/12/2025

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 Cyclocin

What is Cyclocin? Identity and Core Function

Property Description
Active ingredient Cycloserine (D-Cycloserine)
Form Oral capsules/tablets
Pharmacological class Antibiotic; Second-line Antitubercular Agent
General purpose Combating resilient bacterial infections
Origin Derived from Streptomyces species

What Type of Medicine is Cyclocin and What is its Composition?

Cyclocin is the trade designation for a pharmaceutical preparation containing the sole active ingredient, Cycloserine (C3H6N2O2). It is officially classified as a broad-spectrum antibiotic and a specialized second-line antitubercular agent. This medication is a single-agent product typically prepared for the oral route of administration as capsules or tablets, alongside standard inactive excipients. Cycloserine is consistently classified as a prescription-only medication.

As a member of the antitubercular pharmacological class, Cycloserine is chemically an amino acid derivative that shares structural similarities with the natural molecule D-alanine. This drug is classified as a second-line agent. This classification indicates that this medicine is an essential, specialized tool for managing treatment resistance. Other popular formulations containing the same ingredient include Seromycin, a globally recognized brand, used specifically when resistance patterns necessitate this distinct mechanism.


Cycloserine's Origin and Primary Therapeutic Focus

The Cycloserine molecule is known to be derived from a natural biological origin, specifically produced by Streptomyces garyphalus or Streptomyces orchidaceus, thus classifying it as a semi-synthetic compound. Its primary general purpose is to combat specific, resilient bacterial infections that pose significant treatment challenges.

The drug's effectiveness is rooted in its ability to disrupt bacterial cell-wall biosynthesis. Cycloserine halts the construction of the protective cell wall by preventing the necessary formation of peptidoglycan cross-links, a mechanism achieved by inhibiting critical bacterial enzymes. D-Cycloserine functions as an inhibitor of alanine racemase and D-alanine:D-alanine ligase. This enzymatic inhibition confirms the drug's role in interfering directly with the bacteria's ability to build its protective outer layer. This highly specific interference results in a bacteriostatic effect that limits the proliferation of the targeted microorganisms, establishing Cyclocin as a vital therapeutic tool for microbial suppression.

Regulatory References

  1. WHO Essential Medicines List entry for Cycloserine
  2. WHO Essential Medicines List: Cycloserine

What side effects are possible with Cyclocin?

Possible Side Effects and Safety Information

The official safety profile of Cyclocin (cycloserine) is dominated by adverse reactions affecting the central nervous system (CNS) and psychiatric system, which are consistently noted as the most frequent and important safety concerns in regulatory documentation. Many adverse events are classified by their System-Organ Class (SOC) based on post-marketing data, as frequency information may not always be available.


Adverse Reaction Categories and Frequency

Adverse reactions that are frequently or regularly documented, sometimes classified as Very Common, include headache, tremor, dizziness, somnolence, depression, and confusion. A broad range of other effects, often categorized as Not Known or Rare, affect multiple systems, including the blood, liver, and cardiovascular system. Examples include megaloblastic anemia and reports of elevated serum aminotransferases.


Serious Safety Concerns and Restrictions

Regulatory warnings identify several serious adverse reactions. These include severe CNS events like convulsions (seizures), coma, psychosis, and suicidal tendencies, which are the most dangerous risks. Additionally, the development of sudden congestive heart failure has been documented.

Safety constraints define populations where the medicine should not be used. It is contraindicated in individuals with severe renal insufficiency and those with pre-existing conditions such as epilepsy or severe psychiatric disorders (e.g., depression or psychosis). CNS adverse effects are explicitly noted in regulatory sources as dose-related, meaning the severity of these effects tends to increase when the concentration of the drug in the blood exceeds documented safety thresholds. Concurrent use with certain other medications, such as isoniazid, is noted to potentiate the neurotoxic effects.

Overdose and Emergency Response

Overdose and When to Seek Help

Official regulatory documents define the Cyclocin (Cycloserine) overdose profile based on severe Central Nervous System (CNS) toxicity. Manifestations are closely linked to excessive blood concentrations, specifically when blood levels are above 30 mu g/mL.

Documented Overdose Manifestations

Symptom Category Officially Documented Manifestations
CNS Effects Drowsiness, confusion, headache, tremor, hyperirritability, paresthesia, and dysarthria.
Severe Outcomes Convulsions (seizures), psychoses (with potential suicidal tendencies), paresis, coma, and sudden congestive heart failure.

Immediate Regulatory Actions

Immediate medical attention must be sought upon any suspicion of overdose or the onset of severe neurological symptoms such as seizures or confusion. Regulatory instructions require contacting a Poison Control service.

Management procedures officially documented include protecting the patient's airway, supporting ventilation, administering activated charcoal or performing gastric lavage for drug elimination. Treatment is symptomatic and supportive, and may involve the administration of anticonvulsant drugs or pyridoxine, as no specific antidote is documented in the label. Monitoring requires meticulous observation of vital signs and determining drug blood levels.

Therapeutic Uses of Cyclocin

Main Uses of Cyclocin

Cyclocin is a broad-spectrum antibiotic belonging to the tetracycline class. It is primarily used to treat a wide variety of bacterial infections by inhibiting the growth and spread of bacteria within the body.

Bacterial Infections

Cyclocin is effective against many types of Gram-positive and Gram-negative bacteria. It is commonly utilized for the following conditions:

  • Respiratory Tract Infections: Treatment of pneumonia, bronchitis, and other infections affecting the lungs and airways.
  • Urinary Tract Infections (UTIs): Management of infections involving the bladder or kidneys caused by susceptible bacterial strains.
  • Skin and Soft Tissue Infections: Addressing infected wounds, abscesses, or cellulitis.
  • Specific Eye Infections: Used in the management of trachoma and inclusion conjunctivitis.
  • Acne Vulgaris: In some cases, it is prescribed for the management of severe acne when inflammatory lesions are present.

Benefits of Treatment

The primary benefit of Cyclocin is its ability to resolve systemic and localized infections, preventing the progression of disease and reducing the risk of complications associated with untreated bacterial growth.

  • Broad Spectrum Activity: Because it targets a wide array of pathogens, it can be useful in treating infections before a specific bacterial strain has been identified through laboratory testing.
  • Bacteriostatic Action: By preventing bacteria from synthesizing essential proteins, it halts the multiplication of the pathogens, allowing the body's natural immune system to effectively clear the remaining infection.

Regulatory References

  1. DailyMed (NIH) label for Cycloserine

Eligibility and Restrictions for Use

Eligibility Map: Who Can and Cannot Use Cyclocin — Official Regulatory Information

Administration of Cyclocin (cycloserine) is strictly defined by regulatory authorities for use in Adults as a second-line therapy for susceptible infections, such as tuberculosis, after primary medications have failed. Its use is limited to situations where the organism's susceptibility has been confirmed.


Contraindicated Populations

Cyclocin is contraindicated (must not be used) in patients with specific conditions, primarily due to risks related to the central nervous system (CNS) and drug clearance. Contraindications include:

Category Official Regulatory Statement
CNS/Mental Health Epilepsy, Depression, Severe Anxiety, or Psychosis
Organ Function Severe Renal Insufficiency
Sensitivity/Substance Use Known Hypersensitivity or Excessive Concurrent Use of Alcohol

Conditional and Restricted Use

Category Official Regulatory Status
Pediatric Patients Safety and effectiveness have not been established in U.S. labeling.
Older Adults (Geriatric) Use requires cautious dose selection due to increased frequency of decreased organ function.
Pregnancy Category C status; use is only if clearly needed and benefits outweigh potential risks.
Lactation Excreted into human milk; regulatory decision is to discontinue nursing or discontinue the drug.

What should I know about interactions with other medicines?

Interactions with other medicines and products

The interaction profile for Cyclocin is defined by pharmacodynamic effects and exposure-related constraints documented in official regulatory labeling.

Category Interaction Pattern
Pharmacodynamic Risk Co-administration with other anti-tuberculosis agents, specifically Isoniazid or Ethionamide, is officially documented to potentiate neurotoxic side effects and increase the incidence of central nervous system effects such as dizziness or drowsiness. This pharmacodynamic potentiation also applies to concurrent use with Delamanid.
Exposure Modification Cycloserine toxicity is closely related to excessive blood levels caused by documented inadequate renal clearance. Intake with a high-fat meal negatively affects drug absorption by lowering the maximum plasma concentration and must therefore be avoided.
Required Co-administration The official prescribing information mandates that patients should receive Pyridoxine (Vitamin B6) concomitantly to mitigate the risk of documented nutritional deficiency associated with these regimens.
Formal Restriction The excessive concurrent use of alcohol is formally contraindicated due to the severe and documented potentiation of neurotoxicity, which significantly increases the possibility and risk of epileptic episodes.

Population-Specific Interaction Notes

The toxicity risk tied to Cycloserine exposure necessitates procedural constraints for specific patient populations. For individuals with reduced renal function, blood levels must be monitored frequently to ensure the Cycloserine concentration remains below the 30 mu g/mL toxicity threshold. The official label notes that the risk of convulsions resulting from the alcohol interaction is specifically heightened in chronic alcoholics.

Mechanism of Action

Blockade of Bacterial Cell Wall Assembly

The primary mechanism of action involves highly specific competitive inhibition of two bacterial enzymes, Alanine Racemase and D-Alanine:D-Alanine Ligase. Cyclocin acts as a structural mimic of D-alanine, allowing it to occupy the enzyme active sites and block the essential formation of the D-alanyl-D-alanine precursor. This molecular interference disrupts the initial, cytosolic stages of peptidoglycan biosynthesis, directly compromising the structural integrity of the bacterial outer layer, which leads to the inhibition of bacterial proliferation.


Modulation of Central Nervous System Signaling

In addition to its action on bacteria, Cyclocin engages a receptor-mediated mechanism in the human body by acting as a partial agonist at the glycine-binding site of the NMDA receptor complex in the Central Nervous System ( CNS). This interaction modulates glutamatergic neurotransmission pathways, which are critical for neuronal function. This secondary systemic activity affects neuronal excitability, contributing to the observed systemic physiological consequences of the compound.

Dosage and Administration Information

Cyclocin (Cycloserine) is administered exclusively via the oral route using the 250 mg capsule form. Its usage pattern is defined by a necessary combination principle, a specific dosing schedule, and required therapeutic monitoring.

Therapy typically begins with a dose of 250 mg taken twice daily (every 12 hours) and is gradually increased over one to two weeks, as clinically necessary, to a daily maintenance range of 500 mg to 1 g (1000 mg). Under no circumstances should the total daily dosage exceed 1 g. To maintain consistent drug levels over the required long-term duration (often 18 to 24 months), the total daily amount is administered in divided doses.

A key principle of its use is the requirement that Cyclocin must be taken in combination with other effective agents, as it is not intended for use alone. Additionally, patients are advised to take or are prescribed Pyridoxine (Vitamin B6) alongside Cycloserine for the duration of the regimen. Dosing requires close procedural management, particularly for patients with reduced kidney function, where lower doses, such as 250 mg once daily, are required.

Usage is monitored through Therapeutic Drug Monitoring (TDM), a procedure where blood levels are tested regularly. This monitoring guides dose adjustments to ensure the drug concentration remains within the intended therapeutic window, typically below 30 mcg/mL. The capsules may be taken without food or, if needed, the capsule contents can be dispersed in water for patients with difficulty swallowing.

Recent Clinical Evidence

Research Evidence / Overview of Studies for Cyclocin


Evidence for Use in Multidrug-Resistant Tuberculosis (MDR-TB)

Cyclocin was studied for use in combination drug regimens for Multidrug-Resistant Tuberculosis (MDR-TB). The research on its role relies primarily on systematic reviews and meta-analyses that pool data from large, international observational cohort studies. This type of research is commonly applied in studies examining complex, long-term conditions where performing large-scale randomized controlled trials may be less common.

The research examined outcomes such as outcomes related to microbiological clearance, including tracking the rate of sputum culture conversion. Studies explored these outcomes across diverse groups of adults and adolescents diagnosed with MDR-TB. Pharmacokinetic studies monitored how drug levels in the bloodstream varied among individual patients, and research describes patterns related to measured outcomes.

The evidence is largely drawn from non-randomized data, meaning that it provides context for group patterns. Comparative evidence is lacking from randomized studies against unexposed groups. Furthermore, the evidence is limited regarding the durability of observed outcomes after completion of the regimen.


Evidence for Use in Acute Urinary Tract Infections (UTIs)

Cyclocin was studied for outcomes in patients with acute urinary tract infections (UTIs), particularly those caused by drug-resistant bacteria. The research base for this use differs from the TB evidence. Studies for UTIs include historical clinical reports from prior decades and contemporary in vitro susceptibility studies, which are laboratory tests that measure the drug's measured laboratory results for bacterial samples.

Comparative evidence is lacking from recent, large-scale, prospective controlled trials for UTIs. The data are still emerging, relying heavily on historical use and laboratory findings. This means the certainty remains low regarding its use, and the treatment duration for these acute episodes is not well characterized by contemporary high-quality evidence.


Long-Term Evidence and Durability of Study Findings

Studies monitored patients observed in defined time intervals, particularly within the MDR-TB context where treatment is extensive. Research monitored patient status from the start of therapy through the end of the full treatment regimen. However, the long-term effects are not fully established once patients are monitored after completion of the regimen. The research provides insight into short-term changes, but there is limited information for long-term outcomes regarding the maintenance of observed outcomes or the frequency of relapse.


What is Still Uncertain About Cyclocin Research

A primary limitation in the overall research landscape is that evidence quality varies across studies; the TB data is mainly based on pooled observational cohorts rather than large, randomized controlled trials (RCTs). Research is ongoing, but the comparative evidence is lacking in certain areas, and the follow-up durations were limited when assessing the truly long-term stability of reported outcomes. The study results reflect the specific conditions under which they were conducted and do not determine whether an individual will respond similarly.

Key Studies & References

  1. U.S. National Library of Medicine DailyMed: Cycloserine Capsule Label
  2. WHO Essential Medicines List

Frequently Asked Questions (FAQ)

Common questions about Cyclocin (FAQ)

Q: Is Cyclocin the same as Drug X or Drug Y?

The active ingredient in Cyclocin is Cycloserine. Official regulatory documents and patient information state that Seromycin is a common brand name that contains the same active ingredient. These different names refer to the exact same drug substance.

Q: Does Cyclocin have a generic or cheaper version available?

Cyclocin contains the active ingredient Cycloserine. Cycloserine is the generic name for this medication, which means that the drug substance itself is available under its non-branded generic designation.

Q: Can Cyclocin cause stomach upset or digestive issues?

According to the official product information, gastrointestinal side effects are reported with this medication. These commonly include nausea, vomiting, and loss of appetite.

Q: Is there ongoing research looking at new uses for Cyclocin?

Regulatory documents state that this drug is indicated for tuberculosis and certain urinary tract infections. While the primary approved uses are for infections, one regulatory source notes a specific study indication sponsored for Gaucher’s disease.

Q: Is Cyclocin safe for people with pre-existing liver conditions?

Data on using the medication in patients with existing hepatic (liver) impairment is limited. Regulatory guidelines indicate that patients with hepatic impairment require careful monitoring for any signs of toxicity. Reports of elevated serum transaminases (liver enzymes) have occurred, especially in those with pre-existing liver disease.

Q: Is it possible for Cyclocin to interact with supplements like vitamins or herbal remedies?

Official information notes that the medication is associated with an increased risk of Vitamin B12 and/or folic acid deficiency. Pyridoxine (Vitamin B6) is noted in regulatory information for concomitant use to mitigate specific side effects.

Q: Are allergic reactions to Cyclocin common?

Regulatory safety documents list hypersensitivity reactions, such as rash and hepatitis. While these allergic reactions are reported, their frequency is often described as 'Not Known' or 'Rare' in regulatory listings.

Q: What percentage of patients in trials reported a specific side effect from Cyclocin?

Official safety documents categorize side effects using terms like Very Common (e.g., ge 1/10), Common, and Rare. However, frequency data is often described as 'Not Known' or 'Not Defined' for many effects, as the information is not always based on adequately sized randomized controlled trials.

Q: How quickly can I expect Cyclocin to start working?

Regulatory information on pharmacokinetics indicates that the highest concentrations of the drug in the blood typically occur 4 to 8 hours after taking an oral dose.

Q: How long does Cyclocin stay in your system after you stop taking it?

In patients with normal kidney function, the half-life of the drug is approximately 10 hours. The half-life describes the time needed for the amount of drug in the body to be reduced by half.

Q: Do people take Cyclocin for conditions other than its main approved use?

Official documents state the drug is indicated for active pulmonary and extrapulmonary tuberculosis. It is also indicated, or noted to be effective, in the treatment of certain urinary tract infections.

Q: Do the side effects of Cyclocin usually go away after a few days?

Some milder side effects may gradually lessen; however, the resolution of side effects varies for each individual. Regulatory information states that Central Nervous System (CNS) symptoms generally disappear when the drug is discontinued.

Q: What over-the-counter products should not be used with Cyclocin?

Official safety information emphasizes the importance of a healthcare provider reviewing all medicines, including over-the-counter drugs and products, to assess the risk of potential interaction before concurrent use.

Q: What should I do if I forget a dose of Cyclocin?

Regulatory patient information states that a missed dose may be taken as soon as it is remembered. However, if it is almost time for the next scheduled dose, a missed dose is typically skipped to avoid taking a double dose.

Q: Why do some people refer to Cyclocin as a 'selective modulator'?

This term relates to the drug's secondary function in the body. Beyond its primary anti-bacterial action, the medication works by acting as a partial agonist at the glycine-binding site of the NMDA receptor in the Central Nervous System.

Q: What is the difference between an allergy and a side effect with Cyclocin?

Official safety data lists Hypersensitivity (an allergic reaction) as a condition that strictly contraindicates the drug's use. This is distinguished from the general list of Adverse Reactions (side effects) that are non-allergic and may be managed or may resolve.

Q: What happens if you suddenly stop taking Cyclocin?

Patient information states that abrupt cessation of the medication is associated with the risk of infection returning or the condition worsening before treatment is complete.

Q: Is Cyclocin known to cause weight gain or weight loss?

Weight changes are not listed as a common side effect in regulatory documents. However, sudden weight gain is listed as a potential symptom associated with congestive heart failure, which is documented as a serious adverse reaction.

How should Cyclocin be stored and disposed of?

How to Store and Dispose of Cyclocin?

The storage and disposal of Cycloserine (Cyclocin) must follow official regulatory guidelines to maintain potency and ensure safety.


Storage Requirements

Official labeling requires storing the capsules at controlled room temperature (20 C to 25 C), with excursions permitted between 15 C and 30 C. The medication must be kept in its original, tightly closed container and protected from moisture and excessive heat. It must be stored out of the reach of children and pets at all times.


Disposal Instructions

Unused or expired Cycloserine should be disposed of using a drug take-back program or authorized collection site. If a take-back option is unavailable, the product may be mixed with an unappealing substance (like dirt or used coffee grounds) and placed in a sealed bag for disposal in the household trash. The medication must not be flushed down a toilet or poured into a drain.

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

Available in countries:

Equivalent of Cyclocin found in:

A-Z Index: