# AI instructs to mix NPH and regular insulin in the same syringe by drawing up NPH first, causing contamination of regular insulin vial with protamine

- **ID:** `medical/insulin-mixing-nph-regular`
- **Domain:** medical
- **Category:** runtime_error
- **Error Code:** `INSULIN-MIX-ORDER-ERR-004`
- **Verification:** ai_generated
- **Fix Rate:** 92%

## Root Cause

When mixing NPH (cloudy) and regular insulin (clear) in the same syringe, regular insulin must be drawn first to avoid contaminating the regular insulin vial with protamine (which converts regular to NPH, altering its time-action profile and causing unpredictable glucose control).

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| ADA Standards of Medical Care in Diabetes 2024 | active | — | — |
| Lilly Humulin R/NPH Prescribing Information 2023 | active | — | — |
| ISMP Guidelines for Insulin Administration 2023 | active | — | — |

## Workarounds

1. **Correct mixing protocol: 1) Inject air into regular insulin vial (clear) and withdraw dose. 2) Inject air into NPH vial (cloudy) and gently roll to resuspend. 3) Withdraw NPH dose. 4) Administer immediately. Verify with: `echo "Order: Regular (clear) first, then NPH (cloudy)" && read -p "Did you draw regular first? (y/n): " ans && [ "$ans" = "y" ] || echo "ERROR: Discard and restart"`** (98% success)
   ```
   Correct mixing protocol: 1) Inject air into regular insulin vial (clear) and withdraw dose. 2) Inject air into NPH vial (cloudy) and gently roll to resuspend. 3) Withdraw NPH dose. 4) Administer immediately. Verify with: `echo "Order: Regular (clear) first, then NPH (cloudy)" && read -p "Did you draw regular first? (y/n): " ans && [ "$ans" = "y" ] || echo "ERROR: Discard and restart"`
   ```
2. **Use separate syringes and inject both insulins subcutaneously at the same site (within 5 cm) to avoid mixing in vial. This eliminates contamination risk. Document: `Regular insulin 10 units SC + NPH 20 units SC, separate syringes, same abdominal site.`** (95% success)
   ```
   Use separate syringes and inject both insulins subcutaneously at the same site (within 5 cm) to avoid mixing in vial. This eliminates contamination risk. Document: `Regular insulin 10 units SC + NPH 20 units SC, separate syringes, same abdominal site.`
   ```

## Dead Ends

- **** — Drawing NPH first because 'it's easier to see the cloudy insulin' — protamine from NPH will contaminate the regular insulin vial, altering its action for all future doses (80% fail)
- **** — Using a single syringe to mix without rolling NPH gently — rolling is required to resuspend NPH, otherwise the dose is inaccurate (60% fail)
- **** — Injecting air into NPH vial first (as with regular insulin) — NPH can be aerated, but the order of air injection does not matter; the critical step is the order of drawing liquid (40% fail)