Drug interactions
Fosphenytoin + Loratadine
Severity: Minor
Fosphenytoin and Loratadine: minor interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Phenytoin, the active metabolite of fosphenytoin, induces CYP3A4 and may lower loratadine concentrations, potentially reducing antihistamine effect.
What this interaction means in plain words
Fosphenytoin and Loratadine have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised.
Fosphenytoin belongs to Central Nervous System; Loratadine belongs to Respiratory.
Why it happens
Enzyme induction by phenytoin increases CYP3A4-mediated loratadine metabolism.
What to do
No empiric dose change is needed; if allergy symptoms are poorly controlled, consider an alternative antihistamine less dependent on CYP metabolism.
What to ask your pharmacist
- Is there anything I should notice while taking both?
- Do I need to tell my doctor at the next visit?
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Other interactions of Loratadine
- Acrivastine + Loratadine Moderate
- Amobarbital + Loratadine Moderate
- Fentanyl + Loratadine Moderate
- Isocarboxazid + Loratadine Moderate
- Levoketoconazole + Loratadine Moderate
- Loratadine + Mavacamten Moderate
Other interactions of Fosphenytoin
- Dronedarone + Fosphenytoin Contraindicated
- Fosphenytoin + Ledipasvir-sofosbuvir Contraindicated
- Fosphenytoin + Lorlatinib Contraindicated
- Fosphenytoin + Lurasidone Contraindicated
- Fosphenytoin + Ranolazine Contraindicated
- Fosphenytoin + Sofosbuvir-velpatasvir-voxilaprevir Contraindicated
Frequently asked questions
Can I take Fosphenytoin with Loratadine?
MediHelp rates the interaction as minor. Fosphenytoin and Loratadine have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised. Phenytoin, the active metabolite of fosphenytoin, induces CYP3A4 and may lower loratadine concentrations, potentially reducing antihistamine effect.
How serious is the interaction between Fosphenytoin and Loratadine?
MediHelp rates it minor, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: No empiric dose change is needed; if allergy symptoms are poorly controlled, consider an alternative antihistamine less dependent on CYP metabolism.
What other medicines interact with Loratadine?
MediHelp also lists interactions of Loratadine with, for example, Acrivastine, Amobarbital, Fentanyl. The full list is on the Loratadine page.
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