What diseases is cycloserine used to treat? What are its side effects?

Cycloserine (Cycloserine, CYS) is an antibiotic mainly used to treat tuberculosis, especially multi-drug-resistant tuberculosis (MDR-TB). It is a second-line anti-tuberculosis drug and is often used in combination with other anti-tuberculosis drugs to improve treatment effectiveness and reduce the development of drug resistance. Additionally, cycloserine may be used to treat infections caused by atypical mycobacteria such as Mycobacterium avium and in some cases for urinary tract infections that are resistant to other antibiotics.

The mechanism of action of cycloserine is to inhibit bacterial cell wall synthesis. It works by competitively inhibiting D-alanine synthase (D-alanine racemase) and D-alanyl-D-alanine synthase (D-Ala-D-Ala ligase), preventing the synthesis of peptidoglycan precursors, thereby destroying the bacterial cell wall, ultimately leading to bacterial death. Because its target is different from most first-line anti-tuberculosis drugs (such as isoniazid, rifampicin), cycloserine is still effective against drug-resistant Mycobacterium tuberculosis and therefore plays an important role in the treatment of multi-drug-resistant tuberculosis.

Cycloserine side effects

Although cycloserine plays an important role in the treatment of multidrug-resistant tuberculosis, it has relatively many side effects, especially on the nervous system. Side effects mainly include neurotoxicity, psychiatric symptoms, allergic reactions, and gastrointestinal discomfort.

1. Nervous system side effects: The most common and serious side effect of cycloserine is its effect on the central nervous system. This may manifest as headaches, dizziness, insomnia, drowsiness, ataxia (impaired body coordination), tremors, and seizures. Some patients may experience cognitive impairment or sensory abnormalities, such as numbness or tingling in the hands and feet. In severe cases, cycloserine can trigger epilepsy, so use caution or adjust the dose in patients with a history of epilepsy or other neurological disorders.

2. Psychiatric symptoms: Cycloserine can cause mood and behavioral changes, such as anxiety, depression, irritability, hallucinations, confusion and even psychotic symptoms. Some patients may suffer from severe depression and suicidal tendencies. Therefore, while taking cycloserine, patients and their families need to pay close attention to their mood changes and seek medical treatment in a timely manner if necessary. For patients with a history of mental illness, doctors often weigh the benefits and risks when using cycloserine and may combine it with antipsychotic drugs to mitigate adverse effects.

3. Allergic reaction: Some patients may have allergic reactions to cycloserine, manifesting as rash, urticaria, itching, and even rare anaphylactic shock. If patients develop severe allergy symptoms, such as difficulty breathing, swelling of the face or throat, they should stop taking the drug immediately and seek emergency medical attention.

4. Gastrointestinal discomfort: Cycloserine may cause gastrointestinal reactions such as nausea, vomiting, diarrhea, and stomach pain. These symptoms are usually mild and can be relieved by taking the drug with a meal or adjusting the dose. If a patient develops severe gastrointestinal distress, their doctor may need to evaluate whether to continue using this medication.

5. Liver and kidney toxicity: Although cycloserine is less toxic to the liver, liver function still needs to be monitored during long-term use. For patients with renal insufficiency, since cycloserine is mainly excreted by the kidneys, the dose may need to be adjusted to prevent accumulation of the drug in the body and worsening neurotoxicity.

How to reduce the adverse effects of cycloserine

Monitor the nervous system and mental status: Since cycloserine has a great impact on the nervous system, patients should be closely observed for mood abnormalities, anxiety, depression or other neurological symptoms while taking the drug. If severe psychiatric symptoms or seizures occur, discontinue medication and seek medical attention immediately.

Combined use with vitaminsB6 (pyridoxine): Studies have shown that supplementation with vitaminsB6 (pyridoxine) can reduce neurotoxicity caused by cycloserine. Therefore, while using cycloserine, it is usually recommended to supplement 50-100 mg of vitamin B6 daily to reduce the risk of peripheral neuritis.

Adjust dosage and administration: In older patients, those with compromised kidney function, or individuals with a susceptible nervous system, doctors may adjust the dosage to reduce the risk of side effects. In addition, patients are advised to take the medication at a fixed time and avoid taking it on an empty stomach to reduce gastrointestinal irritation.

Avoid alcohol and other nervous system depressants: Alcohol and other drugs that may affect the central nervous system (such as sedatives, antidepressants, etc.) may worsen the side effects of cycloserine. Therefore, patients should avoid drinking alcohol while taking this drug and consult their doctor before using other medications.

Cycloserine is an important second-line anti-tuberculosis drug, mainly used to treat multi-drug-resistant tuberculosis, and can also be used to treat other drug-resistant bacterial infections. However, the drug has many side effects, especially its effects on the nervous system and mental state, including epilepsy, depression, anxiety, psychosis, etc. In order to reduce these risks, patients need to closely monitor neurological and psychological symptoms during treatment, reasonably adjust the dosage under the guidance of a doctor, and supplement vitamin B6 at the same time. Despite the serious side effects, cycloserine still plays an irreplaceable role in the treatment of drug-resistant tuberculosis.

Reference materials:https://en.wikipedia.org/wiki/Cycloserine