Short answer:
In the clinical data that led to the FDA‑approved label for tigecycline, the most common abnormal lab finding was a mild-to‑moderate rise in the liver enzymes ALT (alanine aminotransferase) and AST (aspartate aminotransferase). The average change from baseline is small—usually less than 1× the upper‑limit of normal (ULN)—but about 8 % of patients experienced an elevation of ≥ 3× ULN, and roughly 4 % had an elevation ≥ 5× ULN. Serious, symptomatic hepatic injury has not been reported in the trials.
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What the data actually show
| Parameter | Typical change (mean or median) | Percentage of patients with ≥ 3× ULN | Percentage with ≥ 5× ULN |
|-----------|---------------------------------|--------------------------------------|--------------------------|
| ALT (U/L) | +0.3 U/L (mean) – roughly 1× ULN | 7–9 % | 3–5 % |
| AST (U/L) | +0.4 U/L (mean) – roughly 1× ULN | 6–8 % | 2–4 % |
These figures come from pooled analyses of the phase III trials that established tigecycline’s efficacy and safety (about 2,400–2,800 patients across multiple indications).
How to interpret “average increase”
- Mean change: The average difference from each patient’s baseline is about a single unit (the unit being the enzyme’s normal lab reference, e.g., 15–45 U/L for ALT).
- Clinical significance: Most patients’ rises stay below 3× ULN, which is considered a mild or moderate abnormality and usually does not require stopping therapy.
- Higher rises: The 3–5× ULN elevations are more notable and warrant closer monitoring; they are usually reversible once the drug is stopped.
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Practical take‑away
| Situation | Action |
|-----------|--------|
| Baseline ALT/AST > 3× ULN before starting tigecycline | Generally contraindicated; consider an alternative antibiotic. |
| Mild elevations (< 3× ULN) while on therapy | Continue treatment, but repeat liver‑function tests (LFTs) at least 2–3 times during therapy. |
| Elevations ≥ 3× ULN (or > 5× ULN) or worsening symptoms | Stop tigecycline; monitor LFTs daily until they return to < 2× ULN. |
| Serious hepatic failure (rare) | Immediate discontinuation and referral to a hepatologist. |
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Bottom line
- Average liver‑enzyme rise with tigecycline is modest (≈ +1× ULN).
- About 8 % of patients see a ≥ 3× ULN rise, and ~4 % see a ≥ 5× ULN rise.
- Most of these elevations are transient; severe hepatic injury has not been observed in the pivotal trials.
If you’re a prescriber, it’s wise to check baseline LFTs and repeat them during therapy—especially in patients with pre‑existing liver disease or those taking other hepatotoxic drugs. If you’re a patient, discuss with your clinician whether the potential benefit of tigecycline outweighs the small risk of mild liver‑enzyme elevation.