Table 1.
Guide to interpretation of azathioprine metabolites
| 6-TGN | 6-MMPR | Meaning | Action |
|---|---|---|---|
| Nil/negligible | Nil/negligible | Poor adherence | Patient education and pharmacist engagement |
| Low (< 235) | Low | Under-dosing | Increase dose and recheck bloods and levels in 4 weeks |
| Low (< 235) | High (6-MMPR:6-TGN ratio > 11) | Thiopurine hypermethylator (Shunter) | Switch to low dose AZA or 6-MP (25–33% weight-based dose) and introduce allopurinol 100 mg. Ongoing monitoring |
| Therapeutic (235–450) | Normal (< 5700) | Therapeutic range | Maintain if clinical indication, response and tolerated. Consider targeting a 6-TGN of 400 for endoscopic healing. Consider change of class if no response |
| High (> 450) | Elevated (> 5700) | Over-dosing | Consider reducing dose and recheck metabolites in 4 weeks |
All 6-TGN and 6-MMPR values are in pmol/8 × 108 red blood cells
6-TGN thioguanine nucleotides, 6-MMPR 6-methylmercaptopurine ribonucleotides, AZA azathioprine, 6-MP 6-mercaptopuine