Att rechallenge in hepatotoxicity and skin reactions
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antituberculosis drug rechallenge hepatotoxicity skin reaction
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antituberculosis drug rechallenge hepatotoxicity
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PMID: 39497389
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ATT rechallenge protocol hepatotoxicity skin reaction WHO guidelines isoniazid rifampicin pyrazinamide
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ATT Rechallenge in Hepatotoxicity and Skin Reactions
PART 1 - ATT Rechallenge after Hepatotoxicity (AT-DILI)
When to Stop ATT
Per Harrison's (22e) and ATS guidelines, stop all hepatotoxic ATT drugs (H, R, Z) when:
- ALT > 5x ULN (asymptomatic), OR
- ALT > 3x ULN with hepatitis symptoms (nausea, vomiting, jaundice, abdominal pain), OR
- Total bilirubin reaches jaundice levels (> 2x ULN)
While awaiting liver recovery, a background/bridging regimen should be started to prevent TB progression and drug resistance, typically:
- Ethambutol (E) + Streptomycin (S) + a fluoroquinolone (levofloxacin or moxifloxacin)
- Some guidelines include linezolid or terizidone depending on availability
Rechallenge Criteria Before Starting
Wait until:
- ALT returns to < 2x ULN (ATS), or
- ALT returns to normal/near-normal (WHO / RNTCP)
- Patient is clinically well (no jaundice, nausea, vomiting)
Stop the bridging regimen at the time of rechallenge.
Sequential Rechallenge Protocol (Hepatotoxicity)
The order is: Rifampicin → Isoniazid → Pyrazinamide, introduced sequentially at 3-7 day intervals.
| Step | Day | Drug | Dose Strategy | Monitor |
|---|---|---|---|---|
| 1 | Day 1 | Rifampicin | Full dose (10 mg/kg) | Check LFTs after 3-7 days |
| 2 | Day 4-7 | Isoniazid | Add at full dose (5 mg/kg) | Check LFTs again |
| 3 | Day 7-14 | Pyrazinamide | Add if tolerated | Recheck LFTs |
- If ALT rises or symptoms recur at any step: withdraw the last drug added - that is the culprit.
- Pyrazinamide carries the highest rechallenge risk. In cases of prolonged or severe initial hepatotoxicity, pyrazinamide is often permanently omitted and treatment extended from 6 to 9 months (RHE for 9 months).
- Per ATS: "for those who have experienced prolonged or severe hepatotoxicity but tolerate reintroduction with rifampin and isoniazid, rechallenge with pyrazinamide may be hazardous" - ATS hepatotoxicity statement.
- If pyrazinamide is permanently stopped, do not rechallenge if the original episode had: total bilirubin > 34 µmol/L, coagulopathy, or encephalopathy (South African National Guidelines).
Per Harrison's (22e): "With normalization of liver enzymes, R and H may be sequentially reintroduced. With no recurrence of hepatotoxicity, Z is not resumed in many cases." - Harrison's Principles of Internal Medicine 22E, Table 186-3
Challenge Doses (Where Low-dose Start is Used)
From the Penn/ATS rechallenge protocol table:
| Drug | Day 1 (Challenge) | Day 2 (Full) |
|---|---|---|
| Isoniazid | 50 mg | 300 mg |
| Rifampicin | 75 mg | 300 mg |
| Pyrazinamide | 250 mg | 1.0 g |
| Ethambutol | 100 mg | 500 mg |
| Streptomycin | 125 mg | 500 mg |
For severe reactions, start at 1/10th of the Day 1 dose (e.g., INH 5 mg), then escalate.
Rechallenge Outcomes (Real-world Data)
From a South African high-HIV prevalence cohort (SAHIVMED study):
- Positive rechallenge (re-injury) rate: Pyrazinamide 9/46 (20%), Rifampicin 2/78 (2.6%), Isoniazid 2/74 (2.7%)
- Pyrazinamide rechallenge failure was significantly higher (p = 0.005)
- One case of fatal systemic hypersensitivity with rash + jaundice + AKI on pyrazinamide rechallenge
Monitor LFTs weekly for at least 4 weeks after rechallenge completion.
PART 2 - ATT Rechallenge after Skin Reactions
Classification of Skin Reactions - Guides Rechallenge Decision
Before rechallenging, classify the reaction severity:
| Reaction Type | Severity | Rechallenge? |
|---|---|---|
| Maculopapular rash (mild, non-blistering) | Mild-moderate | YES, can rechallenge |
| Urticaria (without systemic features) | Mild-moderate | YES, with caution |
| Drug Rash with Eosinophilia and Systemic Symptoms (DRESS) | Severe | Extreme caution; specialist only |
| Stevens-Johnson Syndrome (SJS) | Severe/SCAR | CONTRAINDICATED |
| Toxic Epidermal Necrolysis (TEN) | Life-threatening/SCAR | ABSOLUTELY CONTRAINDICATED |
| Exfoliative dermatitis | Severe | CONTRAINDICATED |
| Fixed drug eruption | Variable | Generally avoid rechallenge |
Per the Dermatology 5e textbook (Griffiths et al.): "Rechallenge carries the risk of inducing a more severe reaction, thus it is contraindicated after SCARs [severe cutaneous adverse reactions]." - Dermatology 2-Volume Set 5e
Rechallenge Protocol for Mild-Moderate Skin Reactions
ATS/IDSA recommends rechallenge 2-3 days after symptoms improve.
Sequence: One drug is added every 4 days (every ~96 hours), monitoring closely for recurrence. This sequential reintroduction identifies the culprit drug.
Recommended order of rechallenge (lowest to highest risk of skin reaction):
- Isoniazid (lowest risk)
- Rifampicin
- Pyrazinamide
- Ethionamide
- Cycloserine
- Ethambutol
- PAS
- Streptomycin (highest risk)
Key points:
- More than 90% of rechallenge reactions occur within 72 hours, hence 96-hour intervals between each drug.
- If the patient tolerates individual drugs but does not tolerate the fixed-dose combination (FDC RHZE), suspect an excipient/inactive ingredient as the cause.
- If rechallenge is positive (rash recurs), that drug is the culprit - withdraw it and modify the final regimen.
When ATT Rechallenge After Skin Reaction is Especially Justified
Per Dermatology 5e: "In critical situations, rechallenge may be useful, e.g. a patient with active tuberculosis who develops a rash while receiving a cocktail of antituberculous drugs; a step-by-step reintroduction may be performed in specialized centers. However, the recurrence rate is not 100% with rechallenge and a negative result may give an erroneous sense of security."
This is because:
- Second-line ATT is less effective, longer, more toxic, and more expensive
- Discontinuing ATT increases risk of disseminated disease and drug resistance
- Therefore, rechallenge is strongly preferred over switching to second-line drugs, when safely possible
Summary - Key Differences: Hepatotoxicity vs Skin Reaction Rechallenge
| Feature | Hepatotoxicity | Skin Reaction |
|---|---|---|
| Wait period before rechallenge | ALT < 2x ULN | Rash resolved for 2-3 days |
| Preferred starting drug | Rifampicin first | Isoniazid first (least skin risk) |
| Interval between drugs | 3-7 days | 4 days (96 hours) |
| Contraindication | Severe/fulminant hepatitis with jaundice + coagulopathy | SCARs (SJS, TEN, exfoliative dermatitis) |
| Pyrazinamide risk | High - often permanently omitted | Moderate - added last |
| Monitoring | LFTs (weekly x4 post-rechallenge) | Clinical skin exam daily during rechallenge |
| Bridging regimen needed | Yes (E + FQ ± S) | Yes (continue effective drugs while rechallenging) |
References:
- Harrison's Principles of Internal Medicine 22E (2025), Table 186-3 - Monitoring and Clinical Management of TB Treatment
- Dermatology 2-Volume Set 5e (Griffiths), Chapter 21 - Drug Responsibility Assessment
- ATS Official Statement: Hepatotoxicity of Antituberculosis Therapy
- Moosa et al. - Rechallenge after AT-DILI in HIV cohort, SAHIVMED
- Chinese Medical Association TB Branch - Guidelines for ATB-DILI 2024 (PMID: 39497389)
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