What the FDA labels say about taking them together
Lopinavir/ritonavir and phenobarbital
Lopinavir/ritonavir's FDA label of July 23, 2026 names phenobarbital in its drug interactions section; the phenobarbital labels PlainMeds reads (2) do not name lopinavir/ritonavir. The lopinavir/ritonavir label: “… used with caution. KALETRA once daily in combination with carbamazepine, phenobarbital, or phenytoin is not recommended. In addition, co-administration of phenytoin and KALETRA may cause decreases in steady-state …”
Check it at the source: the lopinavir/ritonavir FDA label on DailyMed (effective July 23, 2026, AbbVie Inc.); the phenobarbital FDA label on DailyMed (effective August 27, 2026).
What does the lopinavir/ritonavir label say about phenobarbital?
Lopinavir/ritonavir label, drug interactionsConcomitant Drug Class/Drug Name: Anticonvulsants: carbamazepine, phenobarbital, phenytoin; Effect on Concentration of Lopinavir or Concomitant Drug: ↓ lopinavir ↓ phenytoin; Clinical Comments: KALETRA may be less effective due to decreased lopinavir plasma concentrations in patients taking these agents concomitantly and should be used with caution. KALETRA once daily in combination with carbamazepine, phenobarbital, or phenytoin is not recommended. In addition, co-administration of phenytoin and KALETRA may cause decreases in steady-state phenytoin concentrations. Phenytoin levels should be monitored when co-administering with KALETRA.
Source: FDA drug label (Kaletra), AbbVie Inc., effective July 23, 2026 (SPL set 8290add3-4449-4e58-6c97-8fe1eec972e3), via openFDA; the full label on DailyMed
What does the phenobarbital label say about lopinavir/ritonavir?
Phenobarbital's label (effective August 27, 2026) and its 1 other brand-application label do not name lopinavir/ritonavir in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (Phenobarbital), Chartwell RX, LLC, effective August 27, 2026 (SPL set 74428144-fb24-40a5-a670-3b876e2d116c), via openFDA; the full label on DailyMed
These are the labels' own sentences. PlainMeds does not grade interactions; a pharmacist or prescriber can say what they mean for one person's medicines.
Both medicines on the record
| Lopinavir/ritonavir | Phenobarbital | |
|---|---|---|
| Labeled for | HIV | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $4.46 per tablet 200-50 mg tablet | $0.213 per tablet 100 mg tablet |
| Shortage now | A presentation being discontinued | A presentation being discontinued |
Source: FDA NDC Directory, CMS NADAC of October 7, 2026 and the FDA Drug Shortage Database (FDA files October 8, 2026)
What next?
- Check more medicines together
- up to five at once