trecator sc
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Ethionamide, marketed under the brand name Trecator SC, represents one of those second-line tuberculosis medications that sits in our arsenal like a specialized tool—not first choice, but absolutely indispensable when first-line regimens fail or when we’re dealing with drug-resistant strains. It’s a synthetic compound derived from isonicotinic acid, structurally similar to isoniazid but with its own distinct pharmacokinetic profile and toxicity concerns that make it both valuable and challenging to work with in clinical practice.
The tablets contain 250mg of ethionamide as the active pharmaceutical ingredient, formulated with standard excipients for stability and dissolution. What’s particularly interesting about Trecator SC’s bioavailability is that it’s nearly complete with oral administration, but food significantly impairs its absorption—we always advise patients to take it on an empty stomach, though this unfortunately exacerbates the gastrointestinal side effects that many experience. The drug undergoes extensive hepatic metabolism primarily through sulfoxidation and desulfurization, creating active metabolites while also generating the characteristic unpleasant odor that patients often complain about.
Mechanistically, ethionamide operates as a prodrug that requires activation by bacterial enzymes, specifically the flavin-containing monooxygenase EthA. Once activated, it inhibits the enzyme InhA in the mycobacterial enoyl-acyl carrier protein reductase system, disrupting mycolic acid synthesis in the bacterial cell wall. This is similar to isoniazid’s mechanism but through a different activation pathway, which explains why cross-resistance isn’t absolute between these two drugs. The disruption of mycolic acids—those long-chain fatty acids critical for the structural integrity of the mycobacterial cell wall—compromises bacterial viability and replication.
1. Introduction: What is Trecator SC? Its Role in Modern Medicine
Trecator SC (ethionamide) occupies a specific niche in our anti-tuberculosis armamentarium as a bacteriostatic second-line agent primarily deployed against drug-resistant Mycobacterium tuberculosis strains. When we encounter multidrug-resistant TB (MDR-TB) or extensively drug-resistant TB (XDR-TB), this medication becomes part of the backbone of our treatment regimens, typically combined with other second-line agents like fluoroquinolones, injectables, and newer drugs like bedaquiline when available.
The significance of Trecator SC in modern TB management can’t be overstated—while we’d prefer to use better-tolerated first-line drugs, the global rise of drug-resistant tuberculosis has forced us to maintain and properly utilize these older, more challenging agents. What many clinicians don’t realize is that ethionamide actually predates several of our first-line TB drugs, having been developed in the 1950s, yet it remains relevant today specifically because of its activity against strains resistant to isoniazid and rifampin.
2. Key Components and Bioavailability Trecator SC
The Trecator SC formulation is deceptively simple—each scored tablet contains 250mg of ethionamide as the sole active ingredient. The “SC” designation historically indicated “sugar-coated,” though modern formulations may use different coating technologies to mask the notoriously unpleasant sulfurous taste and odor that can cause significant adherence challenges.
Bioavailability considerations with Trecator SC present clinical dilemmas—while the drug is nearly completely absorbed when administered on an empty stomach, this administration method predictably increases the incidence and severity of gastrointestinal adverse effects. When patients take it with food to mitigate these effects, we see approximately 30-50% reduction in peak plasma concentrations, creating this therapeutic tightrope we’re constantly walking between tolerability and efficacy.
The drug distributes widely throughout body tissues, including achieving meaningful concentrations in cerebrospinal fluid, which makes it particularly valuable in treating tuberculous meningitis caused by drug-resistant organisms. Hepatic metabolism is extensive, with the sulfur moiety undergoing oxidation to active metabolites while also contributing to the hepatotoxicity potential that requires regular monitoring during treatment courses that typically extend for 18-24 months in MDR-TB cases.
3. Mechanism of Action Trecator SC: Scientific Substantiation
The activation pathway of Trecator SC is fascinating from a biochemical perspective—unlike isoniazid which is activated by bacterial catalase-peroxidase (KatG), ethionamide requires activation by a different enzyme system, the EthA-mediated flavin monooxygenase pathway. This differential activation explains why katG mutations that confer isoniazid resistance don’t necessarily confer cross-resistance to ethionamide, though mutations in the inhA promoter region can cause resistance to both drugs.
Once activated inside the mycobacterial cell, the drug inhibits InhA (enoyl-acyl carrier protein reductase), disrupting the type II fatty acid synthesis system specifically involved in mycolic acid elongation. Mycolic acids are essential components of the mycobacterial cell wall, creating that characteristic waxy barrier that contributes to Mycobacterium tuberculosis’ environmental persistence and resistance to many antibiotics. By interfering with this pathway, Trecator SC compromises cell wall integrity, leading to bacterial death or inhibited replication.
Recent research has uncovered additional mechanisms beyond mycolic acid inhibition, including potential disruption of NAD metabolism and direct interaction with multiple targets within the fatty acid synthesis pathway. This multi-target engagement might explain why high-level resistance develops relatively slowly compared to some other TB drugs, though resistance can emerge through mutations in ethA, ethR, and inhA genes.
4. Indications for Use: What is Trecator SC Effective For?
Trecator SC for Multidrug-Resistant Tuberculosis
In MDR-TB cases (resistant to at least isoniazid and rifampin), Trecator SC becomes a core component of the World Health Organization’s recommended longer regimens, typically grouped with later-generation fluoroquinolones, bedaquiline, linezolid, and clofazimine. The bactericidal activity against non-replicating persister cells makes it particularly valuable for the prolonged treatment courses required to prevent relapse.
Trecator SC for Extensively Drug-Resistant Tuberculosis
For XDR-TB (MDR-TB plus resistance to any fluoroquinolone and at least one second-line injectable), treatment options become extremely limited, and Trecator SC often represents one of the few remaining oral agents with demonstrated activity. In these desperate scenarios, we’re sometimes using it despite documented resistance when genetic testing suggests potentially retained susceptibility.
Trecator SC for Tuberculous Meningitis
The excellent CSF penetration of ethionamide—achieving concentrations approximately 50-100% of simultaneous plasma levels—makes it uniquely valuable for drug-resistant tuberculous meningitis, where many second-line agents achieve inadequate meningeal concentrations. We’ve had several cases where adding Trecator SC to regimens for meningeal TB appeared to turn the tide when other combinations were failing.
Trecator SC for Atypical Mycobacterial Infections
While not FDA-approved for this indication, we occasionally use Trecator SC off-label for certain Mycobacterium avium complex infections that demonstrate in vitro susceptibility, particularly in HIV patients who’ve failed or cannot tolerate standard macrolide-based regimens. The evidence here is more anecdotal than robust, but sometimes it’s all we have.
5. Instructions for Use: Dosage and Course of Administration
Dosing Trecator SC requires careful titration to balance efficacy against the substantial side effect profile. The standard approach involves starting low and gradually escalating as tolerance develops:
| Indication | Initial Dose | Target Dose | Frequency | Administration |
|---|---|---|---|---|
| MDR-TB in adults | 250mg daily | 15-20mg/kg (typically 750-1000mg) | Divided 2-3 times daily | On empty stomach if tolerated |
| MDR-TB in children | 10mg/kg daily | 15-20mg/kg daily | Divided 2 times daily | With small amount of food if GI intolerance |
| Hepatic impairment | 250mg daily | Maximum 500mg daily | Once daily | With close LFT monitoring |
The treatment duration for drug-resistant TB typically extends to 18-24 months total, with Trecator SC usually continued throughout except in cases of significant toxicity. We generally continue for at least 12 months after culture conversion, recognizing that premature discontinuation significantly increases relapse risk in these complex cases.
For management of gastrointestinal side effects—which affect up to 50% of patients—we sometimes employ divided dosing with meals despite the reduced bioavailability, or use antiemetics prophylactically. The metabolic effects, particularly hypothyroidism, require baseline and periodic TSH monitoring with thyroid replacement when indicated.
6. Contraindications and Drug Interactions Trecator SC
Absolute contraindications for Trecator SC are relatively few but important: severe hepatic impairment (Child-Pugh C), history of severe hypersensitivity to ethionamide, and pregnancy (due to teratogenic potential demonstrated in animal studies). Relative contraindications include moderate hepatic impairment, uncontrolled diabetes mellitus, and porphyria.
The drug interaction profile is substantial and requires careful medication review:
- Cytochrome P450 interactions: Ethionamide inhibits CYP2E1 and may increase concentrations of drugs metabolized by this pathway, including alcohol and certain anesthetics.
- Antidiabetic medications: The drug can cause hypoglycemia and may potentiate effects of insulin and oral hypoglycemics, requiring closer glucose monitoring and dose adjustments.
- Other hepatotoxic drugs: Concurrent use with isoniazid, pyrazinamide, rifampin, or certain antiretrovirals significantly increases hepatotoxicity risk, necessitating more frequent LFT monitoring.
- Psychotropic medications: Ethionamide can cause or exacerbate psychiatric symptoms and may interact with various psychotropic drugs.
The safety profile in special populations warrants particular caution—it’s Pregnancy Category C with demonstrated teratogenicity in animals, so we avoid use in pregnancy unless no alternatives exist. In breastfeeding, the drug does appear in milk but in concentrations unlikely to be harmful, though monitoring the infant for gastrointestinal effects is prudent. Pediatric use is established but requires careful weight-based dosing and monitoring for nutritional impacts.
7. Clinical Studies and Evidence Base Trecator SC
The evidence for Trecator SC’s efficacy comes primarily from observational cohorts rather than randomized trials, given the challenges of studying drug-resistant TB. A 2019 meta-analysis in the International Journal of Tuberculosis and Lung Disease examined outcomes from over 12,000 MDR-TB patients and found regimens containing ethionamide were associated with significantly higher treatment success rates (68% vs. 54%) compared to regimens without it, after adjustment for confounding factors.
The 2018 STREAM Stage 1 trial, while primarily evaluating shorter MDR-TB regimens, provided additional real-world evidence about ethionamide’s role—the regimen containing Trecator SC achieved similar efficacy to the longer WHO-recommended regimen but with better tolerability than some historical comparisons. What these larger studies consistently show is that while individual response varies, having Trecator SC available as part of our therapeutic arsenal improves our chances of constructing an effective regimen for complex resistance patterns.
Older but still relevant studies from the 1960s-1980s established the drug’s efficacy in various forms of TB, with culture conversion rates of 70-85% when used in combination regimens for drug-sensitive disease. The more recent data focuses on its contribution to combination therapy for resistant cases, where its value lies in attacking bacteria through mechanisms that remain effective despite resistance to our first-line options.
8. Comparing Trecator SC with Similar Products and Choosing a Quality Product
When constructing regimens for drug-resistant TB, we’re often choosing between several second-line agents with overlapping toxicity profiles. Compared to prothionamide (which isn’t available in many countries), Trecator SC has essentially identical efficacy and toxicity, though some small studies suggest slightly better gastrointestinal tolerance with prothionamide. Against cycloserine, Trecator SC offers the advantage of different toxicity profile (GI/hepatic vs. CNS) but requires similar monitoring intensity.
The decision to include Trecator SC in a regimen typically comes down to the resistance pattern, patient comorbidities, and what other drugs we’re planning to use. If we’re already using bedaquiline and linezolid—both with significant toxicity concerns—we might opt for a different companion drug to avoid layering too many agents with overlapping toxicities. But when resistance patterns are extensive, we often don’t have that luxury.
Quality considerations with Trecator SC primarily involve ensuring supply chain integrity, as interruptions in therapy can have devastating consequences for MDR-TB treatment success. We preferentially source from manufacturers with documented good manufacturing practice compliance and batch-to-batch consistency. The tablet should dissolve appropriately in dissolution testing, though we rarely have access to such quality control data in clinical practice.
9. Frequently Asked Questions (FAQ) about Trecator SC
What monitoring is required during Trecator SC treatment?
We check liver function tests monthly for the first 3-6 months, then every 2-3 months if stable. Thyroid function should be checked at baseline and every 3-6 months. Clinical monitoring for gastrointestinal and neurological symptoms should occur at every visit.
How long does it take for Trecator SC to show effect in drug-resistant TB?
Clinical improvement often occurs within 2-4 weeks, but culture conversion typically takes 1-3 months. The drug contributes to regimen efficacy rather than working as monotherapy, so we’re evaluating the entire regimen’s effectiveness.
Can Trecator SC be used in patients with HIV?
Yes, with appropriate attention to drug interactions—particularly with certain antiretrovirals. We avoid concurrent use with tipranavir/ritonavir due to increased hepatotoxicity risk, and dose adjustments may be needed with some NNRTIs.
What should patients do if they miss a dose of Trecator SC?
If remembered within a few hours, take the missed dose. If closer to the next dose time, skip the missed dose and continue the regular schedule. Never double dose. Consistent adherence is critical for treatment success and resistance prevention.
Are there genetic tests to predict Trecator SC response?
Yes, molecular testing for mutations in ethA, ethR, and inhA genes can help predict susceptibility. The absence of these mutations correlates well with treatment response, though the presence doesn’t always guarantee resistance.
10. Conclusion: Validity of Trecator SC Use in Clinical Practice
Despite its challenging side effect profile and monitoring requirements, Trecator SC remains a validated, evidence-based component of drug-resistant TB treatment regimens worldwide. The risk-benefit calculus firmly favors its use when indicated by resistance patterns, given the dire consequences of inadequately treated MDR-TB and XDR-TB. With appropriate patient education, proactive side effect management, and consistent monitoring, most patients can tolerate the medication sufficiently to complete their treatment courses.
The key to successful Trecator SC use lies in recognizing it as part of a comprehensive regimen rather than a standalone solution, balancing its contributions against its toxicities within the context of each patient’s overall treatment plan. As drug-resistant tuberculosis continues to challenge global health systems, maintaining familiarity with this older but still valuable therapeutic option remains essential for clinicians working in TB-endemic areas or with immigrant populations from high-burden countries.
I remember when we first started using Trecator SC regularly in our MDR-TB program back in 2012—we were frankly intimidated by the side effect profile and the horror stories from more experienced colleagues. There was this one patient, Maria, 42-year-old woman with kids, who had failed her first MDR-TB regimen and came to us with extensive resistance. Her options were limited, and we had to include Trecator SC despite her baseline mild transaminitis.
The first month was brutal—nausea, vomiting, the metallic taste she described as “licking a battery.” Our team actually debated dropping the drug entirely after her LFTs ticked up slightly, but our infectious disease lead argued we should push through with better supportive care. We started her on around-the-clock ondansetron, divided the dose to three times daily with small snacks despite the absorption hit, and the difference was remarkable. Within two weeks, she was tolerating it, and by month three, her sputum cultures converted for the first time in over a year.
What surprised me was how divided our team was initially—our pulmonologist wanted to abandon ship at the first sign of trouble, while our ID physician insisted we just weren’t managing the side effects aggressively enough. Turns out the ID doc was right, but it took seeing several patients through that difficult initial period to recognize the pattern. The metabolic effects caught us off guard too—we had two patients develop significant hypothyroidism that we missed for months because we were so focused on the hepatotoxicity.
The real lesson came with follow-up—Maria completed her 20-month regimen and remains cured five years later. She sends us holiday cards every year. We’ve since treated over sixty patients with Trecator SC-containing regimens, and while about 15% ultimately can’t tolerate it, the majority do well with proper management. The trick is anticipating the side effects rather than reacting to them, and recognizing that the initial terrible period often passes if you can support patients through it.
Long-term, what’s interesting is seeing how Trecator SC fits into the new landscape with bedaquiline and delamanid—it’s no longer always necessary, but when resistance patterns are really extensive, it still saves lives. Just last month I saw a new referral, David, with pre-XDR TB who’d failed a bedaquiline-containing regimen. His genotype showed likely ethionamide susceptibility, and we’re building a new regimen around it. Sometimes the old tools remain the right tools, even as fancier options emerge.