Nirmatrelvir and ritonavir and Primidone interaction
Nirmatrelvir and ritonavir and Primidone: the Nirmatrelvir and ritonavir prescribing label flag this combination with the strongest language, such as a contraindication, a boxed warning, or an instruction to avoid it.
Do not combine without a prescriber's guidance. The label language below is the strongest FDA uses.
What the FDA labels say
From the Nirmatrelvir and ritonavir (Paxlovid) label · effective 2026-02-19
…contraindicated with drugs that are primarily metabolized by CYP3A and for which elevated concentrations are associated with serious and/or life-threatening reactions and drugs that are strong CYP3A inducers where significantly reduced nirmatrelvir or ritonavir plasma concentrations may be associated with the potential for loss of virologic response and possible resistance.
…Sedative/hypnotics: triazolam, oral midazolam • Serotonin receptor 1A agonist/serotonin receptor 2A antagonist: flibanserin • Vasopressin receptor antagonists: tolvaptan ➢ Drugs that are strong CYP3A inducers where significantly reduced nirmatrelvir or ritonavir plasma concentrations may be associated with the potential for loss of virologic response and possible resistance.
…of the following medications due to the delayed offset of the recently discontinued CYP3A inducer [see Drug Interactions (7.3) ] : • Anticancer drugs: apalutamide, enzalutamide • Anticonvulsant: carbamazepine, phenobarbital, primidone, phenytoin • Antimycobacterials: rifampin, rifapentine • Cystic fibrosis transmembrane conductance regulator potentiators: lumacaftor/ivacaftor…
• Co-administration with potent CYP3A inducers where significantly reduced nirmatrelvir or ritonavir plasma concentrations may be associated with the potential for loss of virologic response and possible resistance.
Anticonvulsants carbamazepine , phenobarbital, primidone, phenytoin ↓ nirmatrelvir/ritonavir Co-administration contraindicated due to potential loss of virologic response and possible resistance [see Contraindications (4) ] .
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