Fosphenytoin and Lopinavir and ritonavir interaction
Fosphenytoin and Lopinavir and ritonavir: both prescribing labels 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 Lopinavir and ritonavir (Kaletra) label · effective 2026-07-23
…Non-opioid Analgesic (selective blocker of Nav1.8 sodium channels): suzetrigine PDE5 Inhibitor: sildenafil (Revatio ® ) when used for the treatment of pulmonary arterial hypertension Sedative/Hypnotics: triazolam, orally administered midazolam KALETRA is contraindicated with drugs that are potent CYP3A inducers where significantly reduced lopinavir plasma concentrations…
Postmarketing life-threatening cases of cardiac toxicity (including complete AV block, bradycardia, and cardiomyopathy), lactic acidosis, acute renal failure, CNS depression and respiratory complications leading to death have been reported, predominantly in preterm neonates receiving KALETRA oral solution.
Sedative/Hypnotics: triazolam, orally administered midazolam ↑ triazolam ↑ midazolam Contraindicated due to potential for prolonged or increased sedation or respiratory depression [see Contraindications ( 4 )] .
…potential risks, infants should be monitored closely for increases in serum osmolality and serum creatinine, and for toxicity related to KALETRA oral solution including: hyperosmolality, with or without lactic acidosis, renal toxicity, CNS depression (including stupor, coma, and apnea), seizures, hypotonia, cardiac arrhythmias and ECG changes, and hemolysis.
Anticonvulsants: carbamazepine, phenobarbital, phenytoin ↓ lopinavir ↓ phenytoin KALETRA may be less effective due to decreased lopinavir plasma concentrations in patients taking these agents concomitantly and should be used with caution.
From the Fosphenytoin (CEREBYX) label · effective 2025-08-28
…trazodone, warfarin Drugs that may decrease phenytoin serum levels Antineoplastic agents usually in combination Bleomycin, carboplatin, cisplatin, doxorubicin, methotrexate Antiviral agents Fosamprenavir, nelfinavir, ritonavir Antiepileptic drugs Carbamazepine, vigabatrin Other Chronic alcohol abuse, diazepam, diazoxide, folic acid, reserpine, rifampin, St.
Carbamazepine, felbamate, lamotrigine, topiramate, oxcarbazepine, lacosamide Antiplatelets Ticagrelor Antilipidemic agents Atorvastatin, fluvastatin, simvastatin Antiviral agents Efavirenz, lopinavir/ritonavir, indinavir, nelfinavir, ritonavir, saquinavir Fosamprenavir: phenytoin when given with fosamprenavir alone may decrease the concentration of amprenavir, the active…
Phenytoin when given with the combination of fosamprenavir and ritonavir may increase the concentration of amprenavir Calcium channel blockers Nifedipine, nimodipine, nisoldipine, verapamil Other Albendazole (decreases active metabolite), chlorpropamide, clozapine, cyclosporine, digoxin, disopyramide, folic acid, methadone, mexiletine, praziquantel, quetiapine…
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Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.