Generic and biosimilar substitution is safe and cost-saving for most drugs, but a few situations warrant caution and closer monitoring.
Narrow-therapeutic-index drugs, where small changes in level matter, deserve attention around any switch: examples include warfarin, levothyroxine, some antiepileptics, lithium, ciclosporin and tacrolimus. Keep the patient on a consistent product where possible, and recheck the relevant level or clinical marker after a switch. For biologics, remember that biosimilars are highly similar but not identical; a single, documented switch from reference to biosimilar is well supported, whereas repeated switching between multiple products is less well studied. Always maintain traceability of the exact product given for pharmacovigilance.
The habit worth keeping is to treat most substitutions as routine, but to flag narrow-therapeutic-index drugs and biologics for consistency, monitoring and clear documentation.
- Most generic and biosimilar substitutions are safe and reduce cost.
- Take care with narrow-therapeutic-index drugs such as warfarin, levothyroxine, antiepileptics, lithium and tacrolimus.
- Recheck the relevant level or clinical marker after switching such drugs.
- A single documented reference-to-biosimilar switch is well supported; repeated multi-switching less so.
- Record the exact product dispensed to support pharmacovigilance.
Why it matters
The small number of drugs where levels are critical is where an unmonitored switch can cause harm.
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