Yes, you can prescribe both NovoLog (insulin lispro) and Novolin 70/30 together, but this is generally not the optimal approach for most patients.
The combination is technically feasible but represents redundant prandial coverage that complicates dosing and increases hypoglycemia risk without clear benefit. Novolin 70/30 already contains 30% regular insulin for prandial coverage plus 70% NPH for basal needs, so adding a rapid-acting analog like NovoLog creates overlapping short-acting insulin action 1.
Why This Combination Is Problematic
The core issue is pharmacologic redundancy:
- Novolin 70/30 provides both basal (NPH) and prandial (regular insulin) coverage in a fixed 70/30 ratio 1
- NovoLog is a rapid-acting prandial insulin designed to cover meals
- Using both means you're essentially "double-dosing" prandial insulin at meals where both are given
This creates several clinical problems:
- Increased hypoglycemia risk from overlapping insulin action
- Dosing complexity that makes titration difficult
- Loss of the flexibility advantage that rapid-acting analogs normally provide
When This Combination Might Be Considered
There are limited scenarios where prescribing both could be justified:
1. Transitioning Between Regimens
During a short transition period when converting from premixed to basal-bolus therapy, you might temporarily overlap insulins for 1-2 days while establishing new doses.
2. Supplemental Correction Doses
If a patient on twice-daily Novolin 70/30 has persistent hyperglycemia at specific meals not adequately covered by the premixed insulin, you could theoretically add small supplemental NovoLog doses. However, this is a suboptimal solution - the better approach would be to either:
- Switch to three-times-daily Novolin 70/30 2
- Convert to a proper basal-bolus regimen with NPH plus NovoLog at each meal 3
Better Alternatives
Current guidelines support more rational approaches 3:
If premixed insulin is preferred:
- Use Novolin 70/30 twice daily (breakfast and dinner)
- Consider three-times-daily dosing if glycemic control inadequate 2
- Accept the trade-off of less flexibility for simpler dosing
If flexible prandial coverage is needed:
- Convert to basal-bolus therapy: NPH (or long-acting analog) for basal coverage + NovoLog before each meal 3
- This provides true flexibility and allows independent titration of basal vs. prandial insulin
- Research demonstrates that rapid-acting analogs like lispro (similar to NovoLog) can be safely mixed with NPH immediately before injection if needed 4, 5, 6
If cost is a concern:
- Human insulins (regular + NPH) are less expensive alternatives 3
- Novolin 70/30 alone is simpler and more cost-effective than adding NovoLog
Practical Guidance
If a patient presents already on both insulins:
- Assess the rationale - was this intentional or prescribing error?
- Review glucose patterns to identify if there's actual benefit
- Strongly consider simplifying to one regimen:
- For simple regimens: Optimize Novolin 70/30 dosing alone
- For flexibility needs: Switch to NPH + NovoLog basal-bolus 3
Common pitfall to avoid: Don't reflexively add rapid-acting insulin to "fix" inadequate premixed insulin coverage. Instead, address the root problem through proper regimen selection and dose optimization.
The 2025 ADA Standards recommend that when basal insulin alone is insufficient and prandial coverage is needed, clinicians should either add a GLP-1 receptor agonist or advance to proper prandial insulin dosing - not create hybrid regimens that lack clear evidence 3.