What the FDA labels say about taking them together
Fosphenytoin and lopinavir/ritonavir
Fosphenytoin's FDA label of May 18, 2025 names lopinavir/ritonavir in its drug interactions section; the lopinavir/ritonavir label PlainMeds reads does not name fosphenytoin. The fosphenytoin label: “… fluvastatin, simvastatin Antiplatelets Ticagrelor Antiviral agents Efavirenz, lopinavir/ritonavir, indinavir, nelfinavir, ritonavir, saquinavir Fosamprenavir: phenytoin when given with fosamprenavir alone may decrease …”
Check it at the source: the fosphenytoin FDA label on DailyMed (effective May 18, 2025, Pfizer Laboratories Div Pfizer Inc); the lopinavir/ritonavir FDA label on DailyMed (effective July 23, 2026, AbbVie Inc.).
What does the fosphenytoin label say about lopinavir/ritonavir?
Fosphenytoin label, drug interactionsCarbamazepine, felbamate, lamotrigine, topiramate, oxcarbazepine, lacosamide Antilipidemic agents Atorvastatin, fluvastatin, simvastatin Antiplatelets Ticagrelor Antiviral agents Efavirenz, lopinavir/ritonavir, indinavir, nelfinavir, ritonavir, saquinavir Fosamprenavir: phenytoin when given with fosamprenavir alone may decrease the concentration of amprenavir, the active metabolite.
Source: FDA drug label (CEREBYX), NDA020450 (Parke Davis), as published by Pfizer Laboratories Div Pfizer Inc, effective May 18, 2025 (SPL set de5a6711-4abb-4c3d-a18b-266b094ace11), via openFDA; the full label on DailyMed
What does the lopinavir/ritonavir label say about fosphenytoin?
Lopinavir/ritonavir's label (effective July 23, 2026) does not name fosphenytoin in these sections. A label lists what its studies and reports found; it is not a complete list.
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
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
| Fosphenytoin | Lopinavir/ritonavir | |
|---|---|---|
| Labeled for | Seizures and epilepsy | HIV |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | n/a | $4.46 per tablet 200-50 mg tablet |
| Shortage now | No current entry | 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