Second-generation H1 antihistamine (tricyclic)
Loratadine is a non-sedating antihistamine, used to relieve the symptoms of allergic rhinitis (sneezing, runny nose, itchy eyes and nose). It is taken once a day and causes little drowsiness. In patients with liver or kidney disease, a dose adjustment may be needed.
Also known as: Clarityn, loratadina, loratadine
Loratadine + erythromycin: possible increased loratadine concentrations.
Loratadine is metabolised in the liver by CYP3A4 (and CYP2D6) and erythromycin is a known CYP3A4 inhibitor — the combination raises loratadine and its active metabolite desloratadine concentrations, potentially potentiating somnolence (especially in the elderly and with high loratadine doses). The erythromycin label states that "erythromycin has been associated with prolongation of the QT interval and infrequent cases of arrhythmia", with class IA/III antiarrhythmics contraindicated and caution in hypokalaemia/hypomagnesaemia — although loratadine at therapeutic doses does not significantly prolong the QT, the arrhythmogenic risk of erythromycin itself must be respected. In practice, watch for sedation and cardiovascular symptoms, use the lowest effective loratadine dose and monitor the QT interval in at-risk patients (long QT, hypokalaemia, elderly).
Erythromycin + loratadine: erythromycin (CYP3A4 inhibitor) reduces loratadine metabolism, raising its levels. Watch for somnolence and erythromycin QT risk.
Erythromycin (CYP3A4 inhibitor) reduces loratadine metabolism.
Symptoms of antihistamine excess.
Drowsiness, headache, palpitations.
Watch for sedation and adverse effects; most tolerate without dose adjustment.
DailyMed (FDA) — approved Loratadine label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=569a35be-d653-181c-e063-6294a90a6eb9 ; approved Erythromycin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=0c05e1f7-a3d4-8e69-e063-6394a90aecc3 — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Loratadine + ketoconazole: possible increased loratadine concentrations.
Loratadine is metabolised by CYP3A4, and ketoconazole can raise its concentrations. Unlike first-generation antihistamines, loratadine is not associated with significant QT prolongation, even at high levels; the interaction manifests mainly as drowsiness or mild sedation in susceptible patients. Monitor symptoms, use the lowest effective dose and consider an alternative antihistamine if sedation is troublesome.
Ketoconazole + loratadine: the azole raises loratadine levels (CYP3A4), without relevant QT prolongation. Monitor drowsiness.
Ketoconazole (CYP3A4 and P-gp inhibitor) reduces loratadine clearance.
Sedative effects and ECG if risk factors present.
Syncope, palpitations, marked drowsiness.
Watch for drowsiness; trials showed no relevant QTc prolongation.
DailyMed (FDA) — approved Loratadine label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=569a35be-d653-181c-e063-6294a90a6eb9 ; approved Ketoconazole label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=f162e616-21b4-49b1-b437-15e21001a6f0 — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Grapefruit (juice) inhibits CYP3A4 and may raise loratadine concentrations.
Avoid grapefruit juice during treatment.
EMC-UK (MHRA) — approved Loratadine SmPC: https://www.medicines.org.uk/emc/product/10942/smpc
Alcohol may potentiate drowsiness (rare with loratadine).
Limit alcohol in susceptible patients.
EMC-UK (MHRA) — approved Loratadine SmPC: https://www.medicines.org.uk/emc/product/10942/smpc
Reduced hepatic metabolism may increase loratadine exposure.
Use with caution; alternative initial dose in severe hepatic impairment.
EMC-UK (MHRA) — approved Loratadine SmPC: https://www.medicines.org.uk/emc/product/10942/smpc
Loratadine is considered compatible in pregnancy (extensive use experience).
Can be used when indicated, at the lowest effective dose.
Excreted into milk in small amounts; compatible.
No specific additional contraception.
EMC-UK (MHRA) — approved Loratadine SmPC: https://www.medicines.org.uk/emc/product/10942/smpc
Clinical and educational support tool. The information does not replace a medical prescription or the opinion of a qualified healthcare professional.
Non-sedating H1 antihistamine available over-the-counter, indicated for the temporary relief of symptoms of hay fever and other upper respiratory allergies (runny nose, sneezing, itchy nose/throat, itchy and watery eyes). Fast onset of action (1-3 hours), peak effect at 8-12 hours and 24-hour duration. The active metabolite, desloratadine, has a half-life of ~27 hours.
Selective peripheral H1 histamine receptor antagonist, without relevant sedation at recommended doses (does not significantly penetrate the CNS). The peripheral antihistaminic effect relieves the nasal and ocular symptoms of allergy.
Rapidly absorbed after oral administration, with peak plasma concentrations in about 1-2 hours; taking with food slightly increases bioavailability (AUC and Cmax) without clinical relevance. Onset of action within 1-3 hours, with peak effect at 8-12 hours. Plasma protein binding of 97-99%.
Extensively metabolised in the liver to the active metabolite desloratadine (via CYP3A4 and CYP2D6) and other metabolites. About 40% of the dose is excreted in urine and 40% in faeces, mainly as conjugated metabolites; only ~1% appears unchanged. Hepatic or renal impairment reduces clearance — consider alternate-day or reduced dosing.
Mean elimination half-life of approximately 8-14 hours (mean ~11 h; range 3-20 h) for loratadine, with a longer half-life (~28 h) for the active metabolite desloratadine — allowing once-daily dosing. In chronic hepatic impairment the half-life is prolonged (adjust the dose).
Medicines from the same therapeutic group (ATC classification) or the same pharmacological class.
