Myser

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Myser

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Medically reviewed

Laura Arias

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 Myser

What is Myser? Identity and Pharmacological Class

Property Description
Active Ingredient Cycloserine (D-cycloserine)
Form Hard gelatin capsule
Pharmacological Class Antibiotic, Second-line Antitubercular Agent
General Purpose Combating drug-resistant bacterial infections
Origin Semi-synthetic (derived from Streptomyces)

Myser is the trade name for the pharmaceutical product containing the single active ingredient, Cycloserine, also known as D-cycloserine. Pharmacological studies have clinically recognized Cycloserine's unique mechanism against certain persistent bacterial strains. This medication is formally classified as a second-line Antitubercular Agent, placing it within the broader category of Antimycobacterial Agents. This designation confirms that the medicine is reserved for strategic use, primarily in adults and children who face drug-resistant infections. The chemical structure of Cycloserine is distinctive, defining it as a cyclic molecule and an isoxazolidinone derivative.


Composition, Origin, and General Purpose

Myser is a prescription-only (Rx) medication typically manufactured by a specific pharmaceutical company, distinguishing it from generic cycloserine products. It is administered via the oral route and is provided as a hard gelatin capsule, which contains the active substance along with necessary excipients. The compound is considered semi-synthetic; while manufactured through chemical processes, its core structure is derived from the natural product of the bacterium Streptomyces. The general purpose of this medication is to provide a critical therapeutic option for combating complex and resistant bacterial infections where common treatments have failed. It functions by acting as a structural analogue that disrupts essential bacterial enzymes necessary for synthesizing the protective cell wall, thereby suppressing the growth and multiplication of susceptible organisms. This specialized action establishes Myser as a crucial reserve medication against severe, hard-to-treat infections.

Regulatory References

  1. Cycloserine on WHO Essential Medicines List (eEML)

What side effects are possible with Myser?

Possible Side Effects and Safety Information

Adverse reactions associated with Myser (Cycloserine) primarily affect the Central Nervous System (CNS) and Psychiatric systems. These reactions are frequently reported and their occurrence is documented by regulatory authorities as being closely dose-related, particularly when drug blood concentrations exceed 30 mu g/ mL.


Adverse Reaction Scope

Safety Category Description
Frequency Classification Certain CNS/Psychiatric effects, such as headache, tremor, depression, and confusion, are classified as Very Common (ge 1/10) in regulatory documents. Cardiac Disorders (e.g., arrhythmias, sudden congestive heart failure) and Hypersensitivity reactions are listed as Rare (ge 1/10,000 to <1/1000).
Serious Adverse Reactions Officially documented serious reactions include Convulsions (seizures), Psychoses (with or without suicidal tendencies), Coma, and sudden congestive heart failure. These events are often correlated with higher dosages (above 500 mg daily) or inadequate renal function.
Population-Specific Safety The medication is contraindicated in severe renal insufficiency. Safety and effectiveness in the pediatric population have not been established by the US FDA. Use is restricted in patients with pre-existing conditions like epilepsy, severe anxiety, or psychosis.

Safety Restrictions

Administration is contraindicated in patients with a known hypersensitivity to the drug, active epilepsy, severe psychiatric disorders, severe renal impairment, or excessive concurrent use of alcohol, which is documented to potentiate neurotoxicity. The neurotoxic effects are also stated to be compounded by the concurrent use of drugs like ethionamide or isoniazid.

Connection to the Overall Safety Profile

The official safety information establishes that the primary risk associated with Myser is severe neurotoxicity, which is reflected in the Very Common classification of certain CNS effects and the documentation of convulsions and psychoses as serious adverse reactions. This profile is structurally constrained by safety limitations that contraindicate its use in high-risk populations, emphasizing the required stringent monitoring as defined in regulatory documents.

Overdose and Emergency Response

Overdose and when to seek help

Overdose of Myser (Cycloserine) primarily involves Central Nervous System (CNS) toxicity, a severe risk directly related to excessive blood concentrations, typically above 30 mug/mL. Acute toxicity is formally documented following the ingestion of more than 1 gram in an adult. Chronic toxicity is dose-related, occurring if higher-than-usual doses are administered daily for extended periods.

Documented manifestations of this toxicity include severe neurological signs such as convulsions (seizures), coma, psychosis (potentially with suicidal tendencies), confusion, tremor, vertigo, paresis, and dysarthria (slurred speech). Sudden congestive heart failure has also been reported with documented high chronic dosing.

Immediate medical help is required for any suspected or confirmed overdose event. Regulators mandate that individuals seek emergency medical attention or contact a Poison Control Center for guidance. If severe symptoms of CNS toxicity occur, the official guidance is to discontinue the drug or promptly reduce the dosage.

Management is focused on symptomatic and supportive therapy, as no specific antidote is known. Measures include administering Pyridoxine (Vitamin B6) to help treat and prevent neurotoxic effects and potentially using anticonvulsant drugs for seizure control. Haemodialysis is documented as a procedure reserved for managing life-threatening toxicity. Individuals with renal impairment are known to be at increased risk for drug accumulation and toxicity.

Therapeutic Uses of Myser

Myser (Cycloserine) is commonly used in situations involving certain distressing symptoms and conditions marked by increased physiological stress. The medication is applied across domains where additional symptomatic support is needed, particularly when conditions involve resistant bacterial strains. The drug is indicated for specific, resistant clinical situations.


Primary Therapeutic Scope

This medication is commonly used as an essential component within multi-drug regimens for Tuberculosis (TB) strains that show confirmed resistance, including Multidrug-Resistant Tuberculosis (MDR-TB) and Extensively Drug-Resistant TB (XDR-TB). Additionally, it is applied in addressing specific acute and complicated bacterial infections that have not cleared following adequate courses of standard antibiotics, such as severe, refractory Urinary Tract Infections (UTIs) caused by susceptible organisms. Its inclusion in a regimen supports the patient during difficult episodes by easing distress, which contributes to easing the overall symptom load.

“The strategic inclusion of Cycloserine is applied in clinical settings that involve acute or unstable symptom patterns where resistance is confirmed.”

This may assist with managing symptoms related to systemic imbalance, which may be part of symptomatic management in situations where patients experience fevers and night sweats associated with persistent infection.


Quick Fact: Relief for Persistent Symptoms
Myser is considered relevant in conditions presenting with systemic or localized discomfort when symptoms, like fever or persistent cough, appear due to drug-resistant bacterial activity.

Regulatory References

  1. FDA's DailyMed drug label information

Eligibility and Restrictions for Use

Eligibility Profile for Myser

Myser (Cycloserine) eligibility is strictly defined by regulatory authorities based on a patient's pre-existing conditions and physiological status.


Absolute Contraindications

Patients must not use Myser if they have a known hypersensitivity to the drug, a history of epilepsy or seizure disorder, or a history of depression, severe anxiety, or psychosis. The medication is also prohibited for individuals with severe renal insufficiency or those with excessive concurrent use of alcohol.


Conditional Use and Restrictions

Use in non-severe renal impairment requires careful monitoring. For pediatric patients, safety and effectiveness have not been established according to U.S. labeling. In older adults, eligibility is maintained but requires caution related to renal function.


Pregnancy and Lactation

Myser is categorized as Pregnancy Category C; its use is only justified if the potential benefit clearly outweighs the risk to the fetus. Since the drug is distributed into breast milk, a decision must be made to discontinue nursing or discontinue the drug during lactation.

The official regulatory documents establish these clear exclusion and restriction criteria, which are independent of the drug's intended therapeutic use.

What should I know about interactions with other medicines?

Myser (Cycloserine) has a documented interaction profile primarily involving Central Nervous System (CNS) toxicity and metabolic effects, as outlined in official regulatory documents.

Interaction Type Interacting Substance Official Outcome Described
Contraindicated Combination Alcohol (Ethanol) Concurrent use is formally prohibited due to the potential for increased seizures and heightened CNS toxicity.
Pharmacodynamic Ethionamide, Delamanid Co-administration risks potentiation of neurotoxic side effects.
Pharmacokinetic Isoniazid Reported to cause increased Myser toxicity by decreasing its metabolism.
Pharmacokinetic Phenytoin Myser inhibits the hepatic metabolism of this anticonvulsant, potentially leading to elevated blood levels.

The drug's regulatory profile highlights clinically significant interactions with other antitubercular agents. For instance, the combination with Isoniazid increases the systemic exposure of Myser due to an officially stated decrease in metabolism. Conversely, Myser is documented to inhibit the metabolism of Phenytoin. Beyond drug-drug interactions, a key administration restriction states that intake with a high-fat meal must be avoided due to a negative effect on absorption. Furthermore, the risk of neurotoxicity is specifically noted for patients with renal impairment, requiring close attention to serum concentrations when receiving daily doses above 500 mg. The prohibition of alcohol is explicitly tied to the higher seizure risk noted in chronic alcoholics.

Mechanism of Action

Dual Inhibition of Bacterial Cell Wall Precursors

The primary action of Myser (Cycloserine) involves the precise competitive inhibition of two bacterial enzymes: Alanine Racemase and D-alanine:D-alanine Ligase. By structurally mimicking the essential cell-wall precursor D-alanine, the drug binds to the active sites of these enzymes, blocking the early formation of building blocks necessary for the peptidoglycan synthesis pathway. This mechanistic cascade leads directly to the creation of a structurally compromised bacterial cell wall, resulting in cell lysis and the arrest of cellular multiplication.

Off-Target Modulation of NMDA Receptors

A second, distinct mechanistic domain involves the drug's activity within the human Central Nervous System (CNS), specifically due to its ability to cross the blood-brain barrier. Here, the molecule acts as a partial agonist at the glycine-binding site of the NMDA receptor, a critical mediator of excitatory glutamatergic neurotransmission. This modulation of neuronal signaling is the direct biological basis for the dose-dependent functional consequences observed in systems governing neuronal communication and efferent signaling.

Dosage and Administration Information

How to Use Myser: Official Administration Guidelines

Administration Scope

Myser (cycloserine) is an oral medication provided in a hard gelatin capsule form. The administration of this drug is governed by specific regulatory guidelines that define its dosing, frequency, and use conditions, particularly due to its role as a second-line treatment for resistant infections. Myser is never administered as the sole treatment; official protocols mandate its use exclusively as part of a multi-drug therapeutic regimen.

Field Instruction Statement
Route of Administration Oral (by mouth)
Adult Dosing Schedule Therapy begins with a 250 mg dose two times a day (q12hr), which is then gradually increased, or titrated, to reach a maintenance range of 500 mg to 1 g daily. The maximum daily dose must not exceed 1 g.
Timing in Relation to Meals Best taken without food, but may be taken after meals if needed to avoid gastrointestinal upset.
Pediatric Dosing Rules The dose is calculated based on body weight, typically 10 to 20 mg/kg per day in divided doses, remaining below the adult maximum.

Procedural Context and Monitoring

Therapeutic use of Myser requires rigorous oversight. The standard course of treatment for the primary indication is long-term, often extending for 18 to 24 months. A critical requirement is Therapeutic Drug Monitoring (TDM); blood levels must be determined regularly, especially when the daily dose exceeds 500 mg or in patients with reduced kidney function, to ensure the concentration remains below 30 mcg/mL. Furthermore, specific dose adjustments are mandated for patients with renal impairment, which may involve increasing the time interval between doses to prevent accumulation. These procedural requirements structure the precise and controlled use of the medicine.

Recent Clinical Evidence

Research Evidence / Overview of Studies for Myser

Evidence for Use in Drug-Resistant Tuberculosis (MDR-TB and XDR-TB)

The research exploring the use of Myser (Cycloserine) for drug-resistant tuberculosis (TB), including Multidrug-Resistant (MDR-TB) and Extensively Drug-Resistant (XDR-TB) strains, includes large-scale observational studies and systematic reviews that combine data from many different clinics around the world. Since this medicine is part of complex, multi-drug regimens, the research often focuses on patients who received the entire combination of medicines over long periods, typically 18 to 24 months.

Studies in this area research examined key endpoints such as treatment outcome status (including classifications of successful completion, failure, or death) and the time it took for a microbiological cure to be observed. The study populations included both adults and children who were diagnosed with these hard-to-treat forms of TB.

Official regulatory reviews of the existing data indicate patterns related to how symptoms evolved in the observed populations that are influenced by many factors, including the specific profile of drug resistance. However, because the drug is always used alongside many other antibiotics, it is challenging for research to isolate the specific influence of Myser within the combination regimen.


Evidence for Use in Refractory Urinary Tract Infections (UTIs)

The research base for using Myser for acute and complicated Urinary Tract Infections (UTIs) where standard antibiotics have failed relies on a different body of evidence than the TB research. This data mainly comes from early clinical reports and case series conducted historically when the medicine was first introduced.

These historical reports research examined how frequently patients experienced changes in clinical status reported during the course of their infection and monitored the microbiological cure. However, the evidence level is assessed as low for this indication in the context of current treatment options. Comparative evidence is lacking against modern treatments.

Key Studies & References Cycloserine Capsules, USP: FDA Label Information

Frequently Asked Questions (FAQ)

Common questions about Myser (FAQ)


Q: Are there any common over-the-counter medicines that interact with Myser?

A: Official safety information includes warnings regarding concurrent use with other medications that cause central nervous system (CNS) effects, such as certain sedatives. Official warnings exist regarding concurrent use with substances that increase the risk of central nervous system (CNS) side effects. While not every over-the-counter product is individually named, the caution applies to any non-prescription medicine known to affect the nervous system.

Q: Is it normal to feel a bit tired when starting Myser?

A: Official product information indicates that central nervous system side effects are common with this medicine. Symptoms like drowsiness (somnolence) and headache are frequently reported adverse reactions. These effects can contribute to a general feeling of tiredness, particularly when first starting the medication.

Q: Do I need to change my diet while taking Myser?

A: Regulatory documents note a specific caution regarding food intake. According to official product labeling, the absorption of the medicine may be reduced if taken along with a high-fat meal. No other general dietary restrictions or requirements are typically specified in the regulatory information.

Q: How does Myser generally make a person feel?

A: The most frequently reported adverse reactions relate to the nervous system. Official information indicates that patients commonly experience symptoms such as a headache, tremor, dizziness, or confusion. These effects are often closely related to the dose being taken and reflect the drug's activity in the nervous system.

Q: Can I drive or operate machinery after taking Myser?

A: Due to the known potential for central nervous system side effects, including confusion, drowsiness, and vertigo, official product information suggests caution regarding activities that require full mental alertness. This includes operating heavy machinery or driving motor vehicles.

Q: How long does the effect of one dose of Myser typically last?

A: Official pharmacological data describes the elimination half-life of the drug. In people with typical kidney function, the half-life—the time it takes for half the drug to be cleared from the bloodstream—is approximately 10 hours. This duration provides context for the typical administration schedule for the medicine.

Q: Why do some people say Myser isn't effective for them?

A: Studies and official information indicate that Myser is a second-line agent and must be used as a component of a multi-drug regimen. Because it is always used alongside other antibiotics, researchers find it challenging to isolate the specific impact of Myser on patient outcomes. Additionally, the evidence level for some secondary indications is described as low.

Q: What happens if I miss a dose of Myser?

A: Official administration instructions advise that if a dose is missed, it should be taken as soon as possible. However, if it is nearly time for the next scheduled dose, the regulatory text advises that the missed dose should be skipped.

Q: Does Myser cause weight gain?

A: Official documents list the known and frequently reported side effects. Weight gain or significant clinically relevant changes in weight are typically not listed as a common or very common adverse reaction in the regulatory product information.

Q: Is Myser a controlled substance?

A: Official government classification agencies, such as the Drug Enforcement Administration (DEA) in the U.S., provide a control status for medications. According to this official classification, this medicine is not scheduled as a controlled substance.

Q: Can Myser affect birth control pills?

A: Regulatory documents list known drug interactions, including those with hormonal contraceptives. No specific interaction is typically described in the regulatory text regarding oral birth control pills.

Q: Is Myser safe for people with liver problems?

A: Regulatory documents focus the primary safety warnings on the kidneys, requiring dose adjustments for renal impairment. While the documents do note the potential for elevated liver enzymes, liver dysfunction is generally not listed as a primary contraindication.

Q: Are there any specific supplements I should avoid while taking Myser?

A: Regulatory documents contain warnings about combining Myser with substances that interfere with Vitamin B6 (pyridoxine) or those that increase the risk of neurotoxic side effects. This warning may apply to certain dietary supplements.

Q: Is there any evidence that Myser works differently in men versus women?

A: Official product labeling addresses the use of the drug in specific populations. The regulatory text generally states that no clinically significant differences in the safety profile or efficacy were observed when comparing men and women in the studied populations.

Q: What is the risk of dependence or addiction with Myser?

A: Official regulatory documents contain a dedicated section on abuse and dependence potential. The regulatory text explicitly states there is no known evidence of physical or psychological dependence associated with the use of this medicine.

Q: Does Myser interact with common pain relievers like ibuprofen?

A: Official labeling lists known drug-to-drug interactions. No specific interaction is typically described between this medicine and common non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen.

Q: What happens when you stop taking Myser?

A: Due to the nature of the serious infection it treats, the regulatory text indicates that prematurely stopping the drug carries a risk of relapse of the underlying infection. Official documents do not describe a specific withdrawal syndrome.

Q: Does Myser affect sleep patterns?

A: Official documents list side effects related to sleep. Both insomnia (difficulty falling or staying asleep) and somnolence (drowsiness) are listed as potential adverse reactions.

Q: Can people with high blood pressure safely take Myser?

A: The drug is not generally contraindicated for high blood pressure, but the official documents do list congestive heart failure as a documented, serious, though rare, adverse reaction.

Q: Are there any known interactions between Myser and herbal remedies?

A: Regulatory documents list interactions with specific drug classes. The primary safety warning is against concurrent use of any substances that may increase neurotoxicity (harm to the nervous system), which is a key safety risk associated with the medicine.

Q: Does Myser affect blood sugar levels?

A: Official documents list known metabolic side effects. While various enzyme changes are noted, the regulatory text generally reports no clinically significant or common effect on blood glucose levels (blood sugar).

How should Myser be stored and disposed of?

Storage and Disposal Requirements for Myser (Cycloserine)

Myser capsules must be stored according to official regulatory specifications to maintain stability and effectiveness.


Storage and Handling

Condition Requirement (Official Labeling)
Temperature Store at Controlled Room Temperature, typically 20 C to 25 C (68 F to 77 F).
Container Keep in the original container and maintain the lid tightly closed to protect from moisture.
Restrictions Do not refrigerate and do not freeze the capsules. Do not use past the expiration date.
Safety Store all medication out of the reach and sight of children.

Disposal Instructions

Disposal of unused or expired Myser must follow local pharmaceutical waste regulations. The medication should be taken to an authorized drug take-back program or collection site. Regulatory documents advise not to flush the capsules down the toilet or pour them down a drain to prevent environmental contamination.

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

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