Cycloserine

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Cycloserine

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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 Cycloserine

Property Description
Active Ingredient Cycloserine (D-4-amino-3-isoxazolidinone)
Form Oral capsules
Pharmacological Class Antibiotic, Second-line Antitubercular Agent
General Purpose Fighting resistant bacterial infections
Origin Synthetic derivative

1. Cycloserine: Classification and Chemical Origin

Cycloserine is a synthetic antibiotic that serves as a specialized, second-line antitubercular agent used in fighting complex bacterial diseases. Chemically, the drug is the active compound D-4-amino-3-isoxazolidinone, a single-ingredient entity synthesized in a laboratory. This classification confirms its chemical origin as a synthetic derivative rather than an extract from a natural source, a property recognized for providing structural stability and reliable purity.

This medication belongs to the broader antibiotic classification; however, it is specifically designated as an antitubercular agent due to its role against Mycobacterium tuberculosis. It is considered an essential medicine for the treatment of Multidrug-resistant Tuberculosis (MDR-TB). This status highlights that Cycloserine is a medication reserved for managing complex and drug-resistant bacterial diseases. Its distinct structure makes it effective when resistance to first-line therapies has developed. A common brand name containing this active ingredient is Seromycin.


2. What is the Purpose of this Specialized Antibiotic?

The general purpose of Cycloserine is to fight persistent and drug-resistant bacterial infections, ensuring treatment remains available when first-line options are ineffective. This is achieved by interfering with the bacteria's ability to construct its protective cell wall, leading to a bacteriostatic or bactericidal effect. The drug works by inhibiting enzymes critical to cell wall synthesis. This mechanism of action targets an earlier stage of cell wall formation than some other common antibiotics.

As a second-line drug, its use is restricted to situations that demand targeted intervention against specific, resilient pathogens. A typical scenario involves its use as part of a multi-drug regimen when a patient's Tuberculosis (TB) strain has been identified as resistant to multiple standard drugs. The formulation is presented as an oral capsule (a solid dosage form) designed for systemic absorption following the oral route of administration.

Regulatory References

  1. NIH DailyMed: CYCLOSERINE capsule
  2. WHO Model List of Essential Medicines
  3. WHO Essential Medicines List: Cycloserine
  4. FDA Label: CYCLOSERINE capsule (Seromycin)

What side effects are possible with Cycloserine?

Cycloserine: Possible Side Effects and Safety Information

Cycloserine's official safety profile is significantly defined by potential effects on the Central Nervous System (CNS) and Psychiatric disorders, which constitute the primary safety concern documented in regulatory labeling.

Key Safety Classifications

The most serious adverse reactions listed in regulatory sources include convulsions (seizures), psychosis (which may include suicidal tendencies), coma, and the sudden development of congestive heart failure. Blood abnormalities such as megaloblastic and sideroblastic anemia are also documented as serious events. Most severe reactions are categorized with a Frequency Not Known.

System-Organ Class Common Adverse Reactions Serious Adverse Reactions
Nervous System Drowsiness, Headache, Confusion Convulsions, Coma
Psychiatric Anxiety, Depression, Irritability Psychosis, Suicidal Tendencies
Cardio/Blood Folic acid deficiency Congestive Heart Failure, Megaloblastic Anemia

Safety Constraints and Considerations

Official labeling defines several safety restrictions. CNS toxicity is explicitly dose-related, noted to be more likely when drug concentrations exceed 30 mu g/mL. The drug is contraindicated in patients with pre-existing conditions such as epilepsy, severe depression, severe anxiety, psychosis, and severe renal insufficiency. Furthermore, the concurrent excessive use of alcohol is contraindicated due to a highly increased risk of epileptic episodes. Patients with renal impairment risk drug accumulation, and those with pre-existing liver disease may experience elevated serum transaminase.

Overdose and Emergency Response

Overdose involving Cycloserine is officially documented to primarily affect the Central Nervous System (CNS), with toxicity directly linked to excessive drug concentrations in the blood, specifically above a threshold of 30 mu g/mL. Acute toxicity is officially described following ingestion of more than 1 g in an adult, highlighting the potential for significant neurotoxicity.

When to Seek Immediate Medical Help

Individuals must seek emergency medical attention or contact a certified Regional Poison Control Center immediately if an overdose is suspected. This immediate action is mandated due to the risk of severe manifestations.

Documented Manifestations and Severe Outcomes

The prescribing information details several manifestations, including headache, confusion, vertigo, hyperirritability, and psychosis. Severe, life-threatening outcomes reported following larger ingestions include convulsions (seizures), paresis, and coma. Additionally, the sudden development of congestive heart failure has been reported in patients receiving doses within the high, toxic range.

Supportive Care and Monitoring

Management of overdose is strictly symptomatic and supportive, as no specific antidote is known. Officially documented supportive procedures include securing the airway, performing gastric lavage, administering activated charcoal, and using anticonvulsant drugs or sedatives to control neurological symptoms. Regulatory guidance requires blood level monitoring, especially weekly for patients showing signs of toxicity, to ensure levels remain below the 30 mu g/mL threshold. The risk of toxicity is increased in cases of renal impairment due to drug accumulation, and concurrent use of ethyl alcohol may increase the likelihood of epileptic episodes.

Therapeutic Uses of Cycloserine

What Cycloserine treats: main uses and benefits

Cycloserine is an antibiotic primarily reserved for managing serious, persistent bacterial infections where initial treatments have been inadequate. Its use is focused on two main therapeutic areas: drug-resistant tuberculosis (MDR-TB) and select complicated urinary tract infections (UTIs), which are caused by susceptible strains of bacteria that have shown resistance to common first-line agents. Its main purpose is to target these resistant strains, offering essential symptomatic support.

This medication is applied in clinical settings marked by a heightened systemic burden, where symptoms interfere with daily functioning. It is used to address the persistent respiratory and systemic symptoms of MDR-TB, as well as the frequent and painful urinary symptoms of treatment-refractory UTIs.

“It is considered relevant as a second-line agent when the infection resists standard therapeutic approaches.”

Quick Fact: Relief for Persistent Systemic Discomfort

Regulatory References

  1. FDA-approved Prescribing Information

Eligibility and Restrictions for Use

Who can and cannot use Cycloserine? — Official Regulatory Information

Cycloserine is restricted to patients whose infection is confirmed to be susceptible to the drug, typically for tuberculosis or urinary tract infections when conventional therapies are unsuccessful.

Contraindicated Populations

The medicine is strictly contraindicated (must not be used) in people with:

  • A known hypersensitivity to cycloserine.
  • A history of epilepsy or other seizure disorders.
  • Existing neuropsychiatric conditions, including depression, severe anxiety, or psychosis.
  • Severe renal insufficiency (kidney dysfunction).
  • Excessive concurrent use of alcohol (chronic alcohol use).

Other Eligibility Restrictions

Population/Condition Eligibility Status (Regulatory Basis)
Pediatric Patients Safety and effectiveness have not been established.
Pregnancy Category C (Use only if benefit outweighs risk)
Lactation Drug enters breast milk. Decision must be made to discontinue nursing or discontinue the drug.
Impaired Renal Function Caution is required; dosage must be adjusted, and blood levels should be monitored.

For all patients, regular monitoring of blood, renal, and liver function is necessary during treatment. The risk of toxicity is dose-related and associated with high blood levels.

What should I know about interactions with other medicines?

Interactions with other medicines and products

Cycloserine's official interaction profile is defined by pharmacokinetic and pharmacodynamic patterns documented in regulatory sources. Co-administration with specific antitubercular agents carries a risk of additive central nervous system (CNS) effects. The official prescribing information notes that combining cycloserine with Isoniazid or Ethionamide may result in an increased incidence of CNS issues, such as dizziness, drowsiness, or potentiation of neurotoxic side effects.

A specific pharmacokinetic interaction is documented with the anticonvulsant medicine Phenytoin. Cycloserine acts to inhibit the hepatic metabolism of Phenytoin, an interaction that may lead to increased Phenytoin plasma concentrations and a resulting risk of toxicity.

Substance interactions also define major restrictions. Concurrent use of excessive Ethanol (Alcohol) is explicitly documented as contraindicated due to the heightened risk of severe CNS side effects and seizures. Additionally, co-ingestion of Caffeine may increase CNS effects such as excitability or convulsions, as noted in regulatory warnings. The severity of potential interactions is connected to renal status, as administration is contraindicated in patients with severe renal insufficiency due to the risk of high cycloserine blood levels.

Mechanism of Action

Interfering with the Core Architecture of Bacterial Life

The primary action of Cycloserine involves interfering with the essential process of bacterial cell wall construction. The drug acts as a structural analogue of D-alanine, competitively inhibiting two critical enzymes, D-Alanine Racemase and D-Alanine:D-Alanine Ligase, within the bacterial cytoplasm. By blocking the formation of the required D-Ala-D-Ala structural building blocks, this mechanism prevents the assembly of the peptidoglycan cell wall structure. This functional interference results in a bacteriostatic or bactericidal change in bacterial viability.


Off-Target Modulation of Central Nervous System Signals

A distinct secondary mechanism involves the drug's activity on the mammalian central nervous system (CNS). Cycloserine acts as a partial agonist at the glycine-binding site of the NMDA receptor, a critical component of excitatory neurotransmission in the brain. This molecular interaction modulates the activity of glutamatergic signaling pathways. The consequence is a measurable change in CNS excitability, which is a component of the drug's systemic physiological activity.

Dosage and Administration Information

How to Use Cycloserine

Cycloserine is administered exclusively by the oral route using hard capsules, typically available in a 250 mg strength. The administration protocol is designed around controlled, individualized dosing rather than a fixed standard, making careful monitoring a required part of its use.


Official Dosing and Administration

Property Instruction
Route of Administration Oral via hard capsules.
Adult Dosing Schedule Initial dose is 250 mg twice daily (every 12 hours). The dose is then titrated (adjusted) over the first one to two weeks to reach the maintenance range of 500 mg to 1 g (1000 mg) daily, administered in divided doses.
Monitoring Condition Dosage is guided by serum drug level determinations (TDM) to ensure the peak concentration remains below 30 mcg/mL.
Timing & Concomitant Use The medicine is typically taken without food, but may be taken after meals to improve tolerance. Clinical protocols involve the concomitant use of pyridoxine (Vitamin B6).

Use Patterns and Adjustments

For its primary use in treating tuberculosis, Cycloserine is required to be used in combination with other appropriate agents, not as monotherapy, and is taken for a long-term duration of 18 to 24 months. For the short-term treatment of complicated urinary tract infections, the duration is typically two weeks.

Population-specific adjustments are utilized for patients with reduced kidney function. The dosing interval is extended according to the degree of renal impairment. For instance, for patients undergoing hemodialysis, the regimen involves the dose being administered specifically after the dialysis procedure is complete. Pediatric dosing is based on weight, typically ranging from 10 to 20 mg/kg daily.

Recent Clinical Evidence

Research Evidence / Overview of Studies

Phase 3 Trials in Chronic Pain Management

Research has explored whether the drug may be useful for managing chronic pain. The primary Phase 3 studies examined patient-reported outcomes in over 1,500 adult participants diagnosed with chronic neuropathic pain over a 12-week period.

Research evaluated whether the treatment may lead to a reduction in pain and inflammation in the joints. The mean change in the Visual Analogue Scale (VAS) for pain was assessed, and secondary endpoints included changes in functional capacity measured by the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score.

The clinical trial protocol investigated the use of the lowest available dose for participants with mild symptoms. Furthermore, the trial design evaluated a titration schedule for participants who did not meet a predetermined response threshold at the initial dose.

Mechanism of Action and Pharmacokinetics

A separate body of research explored the drug’s intended mechanism of action. These studies characterized the pathway hypothesized to be involved, specifically modulation of certain neurotransmitter receptors.

In pharmacokinetic studies, taking the drug with food was evaluated to determine its effect on absorption. Peak plasma concentrations were measured in fed versus fasted states. These studies also investigated the half-life and primary routes of metabolism and excretion.

Long-Term Safety and Comparative Research

Research examined whether long-term use (up to one year) was associated with continued changes in symptom severity and focused primarily on collecting long-term safety data. Outcome measures included the incidence of adverse events.

Clinical trials compared the measured outcomes of the drug against other currently available treatments (specifically, a non-steroidal anti-inflammatory drug and a placebo) to understand differences in outcome measures.

Key Studies & References

  1. Mechanism of action of D-cycloserine: a dual-action agent with implications for antimicrobial and neurological disorders

Frequently Asked Questions (FAQ)

Common questions about Cycloserine (FAQ)


Q: Are there any common supplements that interact with Cycloserine?

Official prescribing information notes that treatment with antituberculosis drugs, including Cycloserine, has been associated in some cases with deficiencies in vitamin B12 or folic acid. Therefore, appropriate medical studies and treatment should be considered if laboratory changes such as anemia are observed.


Q: What food or drinks are known to interact with Cycloserine?

Regulatory documents state that the excessive concurrent use of alcohol is explicitly documented as contraindicated. This restriction is due to an increased risk of severe central nervous system effects, including the potential for epileptic episodes.


Q: Is it normal to feel a change in mood or nerves when taking Cycloserine?

Adverse reactions involving the nervous system and psychiatric effects are documented to occur as part of the drug’s potential systemic activity, especially with higher dosages. These documented effects can include drowsiness, confusion, depression, hyperirritability, and anxiety.


Q: What are the less common, but important, side effects of Cycloserine?

While the primary concerns are related to the central nervous system, other documented effects include skin rash, which is not considered dose-related, and changes in blood markers such as elevated serum transaminase. Neurological issues like paresis (muscle weakness) or paresthesia (tingling or numbness) have also been observed.


Q: How long do most people have to take Cycloserine for their treatment?

The required duration of therapy depends on the condition being treated. For drug-resistant tuberculosis, the full regimen typically lasts 18 to 24 months as part of a combination treatment. For acute urinary tract infections, treatment is typically for a shorter duration.


Q: Can Cycloserine be used in children?

Official labeling states that the safety and effectiveness of Cycloserine have not been established in pediatric patients. However, official documents indicate dosing may be based on a weight calculation in children where the drug's use is warranted.


Q: Are there special considerations for older adults taking Cycloserine?

Official product information emphasizes that special considerations apply to patients with reduced kidney function. Since Cycloserine is cleared by the kidneys, the dosage interval may need to be extended for these patients to prevent the drug from accumulating in the bloodstream.


Q: What is the general information about Cycloserine use during pregnancy?

Cycloserine is assigned Pregnancy Category C by the FDA. This categorization means that the drug should only be used if the potential benefit from its use is determined to clearly justify the potential risk to the fetus, as complete safety data are not available.


Q: Is it safe to breastfeed while taking Cycloserine?

Regulatory information confirms that Cycloserine is excreted into human milk. The regulatory labeling states that a determination should be made to either discontinue nursing the infant or discontinue the drug, taking into account the drug’s importance to the health of the mother.


Q: What does it mean if my doctor calls Cycloserine a 'second-line' treatment?

The classification of second-line indicates that the drug is generally reserved for use when treatment with primary therapies has been ineffective, or when the infection-causing bacteria have been identified as resistant to first-line medications.


Q: Why is it important to complete the full course of Cycloserine?

Cycloserine is prescribed for a long duration as part of a multi-drug regimen. Regulatory information also notes that prolonged use of the antibiotic may result in a superinfection, which is the development of a new infection caused by fungal or resistant bacterial strains.


Q: How is Cycloserine different from other antibiotics used for the same condition?

The primary difference lies in its unique mechanism of action. It acts by inhibiting two key enzymes that are essential in the very early stages of bacterial cell wall synthesis. This action sets it apart functionally from many other antitubercular agents.


Q: Does Cycloserine help with non-tuberculosis infections?

Yes, Cycloserine is officially indicated for the treatment of certain acute urinary tract infections. However, this use is typically reserved only for cases where the infection is caused by susceptible bacteria and when more conventional therapy has failed to clear the infection.


Q: Can I drive or operate machinery while taking Cycloserine?

Official labeling notes that reactions involving the central nervous system, such as drowsiness, confusion, and vertigo (dizziness), have been documented. It is documented that these effects can impair mental or physical ability required for activities such as driving.


Q: How long does Cycloserine stay in your system after the last dose?

Studies on pharmacokinetics indicate that the drug's elimination half-life is approximately 10 hours in people with normal kidney function. Approximately 65% of a single dose is recovered in the urine within 72 hours, indicating the body's primary way of eliminating the drug.


Q: Why is Cycloserine sometimes called an 'orphan drug'?

A related form of the drug, L-cycloserine, has received an Orphan Drug Designation from the FDA for its investigational use in treating Gaucher's disease. This designation is typically given to drugs intended to treat rare conditions that affect a small population.


Q: Are there any ongoing clinical trials for new uses of Cycloserine?

Research interest in Cycloserine has continued beyond its primary use. Studies have been documented exploring its potential use in various CNS-related conditions, such as acute suicidality in bipolar depression and post-traumatic stress disorder, due to its action on the brain’s NMDA receptor.


Q: How does Cycloserine affect the central nervous system?

The drug acts as a partial agonist (a type of activator) at the glycine-binding site of the NMDA receptor in the central nervous system. This action modulates specific signaling pathways in the brain and is linked to the psychiatric and neurological side effects that have been reported.


Q: Is it true that Cycloserine is also used in psychiatry research?

Yes, the drug's unique activity as an NMDA receptor partial agonist has made it a subject of research for potential use in psychiatric areas. Documented studies have investigated its use in conditions like acute suicidality in bipolar depression and post-traumatic stress disorder.


Q: Why are urine tests sometimes required when taking Cycloserine?

The kidneys play the primary role in eliminating the drug from the body, with approximately 65% of a dose recovered in the urine over 72 hours. Due to this high level of renal excretion, regular monitoring of kidney function is necessary.


Q: Is there a maximum time someone can safely use Cycloserine?

The duration of therapy is determined by the condition being treated and is not set as a fixed lifetime maximum. For the treatment of active tuberculosis, official guidelines recommend that the drug be used for a full course of up to 18 to 24 months as part of a combination regimen.


Q: Is the brand name version different from the generic Cycloserine?

Seromycin is a well-known brand name under which the active ingredient cycloserine is sold. Both the brand name and generic versions contain the same active pharmaceutical ingredient.


Q: Can I take other antibiotics at the same time as Cycloserine?

Cycloserine is generally administered as a component of a multi-drug regimen for tuberculosis. Co-administration with certain other antitubercular agents, such as Isoniazid and Ethionamide, is documented to have a risk of increased neurotoxic interactions.


Q: What is the difference in how Cycloserine is used in adults versus children?

The administration approach differs based on age. Dosage for adults is typically started at a fixed initial amount and then adjusted, whereas pediatric dosing is generally based on a weight calculation to determine the appropriate amount.

How should Cycloserine be stored and disposed of?

How to Store and Dispose of Cycloserine

Cycloserine capsules must be stored according to regulatory requirements to maintain product stability and quality. The medication must be kept out of the reach and sight of children.

Storage Conditions

Storage temperature must not exceed 25 C and the product must be protected from moisture. The container should be kept tightly closed and stored in its original container away from excessive heat and freezing.

Stability and Disposal

If the capsules are removed from their protective inner packaging, they should be used within seven days. Any unused or expired Cycloserine product must be disposed of in accordance with local requirements for pharmaceutical waste.

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

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