Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ACTAHIST vs ALCAFTADINE
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Antihistamine; binds to histamine H1 receptors, blocking the effects of histamine; also exhibits anticholinergic and mild sedative properties.
Selective histamine H1 receptor antagonist; inhibits histamine release from mast cells and reduces ocular itch associated with allergic conjunctivitis.
Symptomatic relief of allergic rhinitis,Urticaria,Off-label: motion sickness,Off-label: insomnia
FDA: Prevention of itching associated with allergic conjunctivitis,Off-label: No established off-label uses
1.34 mg (one capsule) orally twice daily.
1 drop of 0.25% ophthalmic solution in each affected eye twice daily.
6.9 ± 1.7 hours in adults; prolonged to 12-18 hours in elderly or patients with hepatic impairment, requiring dosing interval adjustment.
Terminal elimination half-life is approximately 2 hours (range 1.5–3 h) after topical ocular administration, appropriate for twice-daily dosing.
Hepatic metabolism via CYP450 enzymes (primarily CYP3A4 and CYP2D6); major metabolite is inactive.
Not extensively metabolized; primarily excreted unchanged in urine. Cytochrome P450 metabolism is minimal.
Primarily renal (approximately 85% as unchanged drug and metabolites) and fecal (15%) via biliary elimination.
Primarily renal (approximately 50% unchanged), with the remainder as metabolites; negligible biliary/fecal elimination.
92% bound to albumin.
Approximately 40% bound to plasma proteins.
0.9 ± 0.3 L/kg, indicating extensive extravascular distribution.
Vd is approximately 1.4 L/kg, indicating distribution beyond plasma into extravascular tissues.
Oral: 68% ± 12% due to first-pass metabolism.
Systemic bioavailability after topical ocular administration is low (estimated < 0.5%) due to dilution, local metabolism, and limited corneal penetration.
No dose adjustment required for mild to moderate renal impairment. Safety not established for severe impairment (GFR <30 m L/min).
No dose adjustment required for any degree of renal impairment.
No dose adjustment required for mild to moderate hepatic impairment (Child-Pugh A or B). Not recommended for severe hepatic impairment (Child-Pugh C).
No dose adjustment required for any degree of hepatic impairment.
Not indicated for pediatric patients under 12 years of age. Safety and efficacy not established.
Children 2 years and older: same as adult dose. Safety and efficacy in children under 2 years not established.
No specific dose adjustment recommended; monitor for increased anticholinergic effects and cognitive impairment.
No specific dose adjustment needed; use same dose as for younger adults.
None.
None
May cause drowsiness; caution when driving or operating machinery. Avoid alcohol. Use with caution in patients with narrow-angle glaucoma, prostatic hyperplasia, or urinary retention. Geriatric patients more sensitive to anticholinergic effects. Pediatric patients <6 years: not recommended.
Do not inject; for topical ophthalmic use only,Avoid wearing contact lenses if eyes are red,May cause temporary blurred vision after instillation,Use with caution in patients with known hypersensitivity
Hypersensitivity to any component. Newborns or premature infants. Breastfeeding (contraindicated due to risk of adverse effects in infants). Concomitant use with MAOIs.
Hypersensitivity to alcaftadine or any component of the formulation
Avoid high-tyramine foods (aged cheese, cured meats, fermented products) if taking MAOIs. Grapefruit juice may increase phenylephrine absorption; limit intake.
No specific food interactions reported. As an ophthalmic preparation, systemic absorption is minimal and unlikely to be affected by food.
ACTAHIST (brompheniramine/phenylephrine) pregnancy category C. Inadequate human data; animal studies show no malformations at therapeutic doses. First trimester: theoretical risk from vasoconstrictive effects (phenylephrine) possibly reducing uterine blood flow; avoid if possible. Second/third trimester: phenylephrine may cause fetal hypoxia via placental vasoconstriction; use only if benefit outweighs risk. No known structural teratogenicity.
Alcaftadine is classified as Pregnancy Category B. Animal studies have not demonstrated teratogenic effects at doses up to 2400 times the human ocular dose. There are no adequate and well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, alcaftadine should be used during pregnancy only if clearly needed.
Brompheniramine is excreted in breast milk in small amounts; M/P ratio not established. Phenylephrine has minimal excretion. Due to anticholinergic effects, may reduce milk production or cause sedation in infants. Use caution; prefer non-sedating alternatives if possible.
It is not known whether alcaftadine is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when alcaftadine is administered to a nursing woman. The M/P ratio has not been established.
No specific pharmacokinetic studies. Increased plasma volume and renal clearance in pregnancy may reduce drug levels, but efficacy threshold remains. No dose adjustment recommended; use the lowest effective dose for shortest duration due to potential risks.
No pharmacokinetic studies have been performed in pregnant women. Based on the available animal data and the low systemic exposure after ocular administration, no dosing adjustment is recommended during pregnancy.
Actahist is a combination antihistamine-decongestant (chlorpheniramine/phenylephrine). Avoid in patients with hypertension, severe coronary artery disease, or MAOI use. Monitor for sedation and urinary retention, especially in elderly males with BPH.
ALCAFTADINE is a topical ophthalmic antihistamine and mast cell stabilizer used for allergic conjunctivitis. Administer one drop twice daily in each affected eye. Onset of action is within minutes. Contraindicated in patients with hypersensitivity to any component. Use with caution in contact lens wearers; remove lenses before instillation and wait 10 minutes before reinserting. Do not touch dropper tip to any surface to avoid contamination.
Take with food or milk to reduce stomach upset.,Avoid alcohol and CNS depressants as they can increase drowsiness.,Do not drive or operate machinery until you know how this medication affects you.,Contact your doctor if you experience chest pain, rapid heartbeat, or difficulty urinating.
Do not wear contact lenses if your eyes are red; after the redness subsides, wait at least 10 minutes after instilling the drop before reinserting lenses.,Do not touch the dropper tip to your eye or any surface to avoid contamination.,Wait at least 5 minutes between using this drug and other eye drops.,If you miss a dose, use it as soon as you remember; if it is almost time for the next dose, skip the missed dose and resume your regular schedule.,Do not use more than prescribed; overuse may cause eye irritation.,Tell your doctor if you are pregnant, planning to become pregnant, or breastfeeding.,Wash hands before and after use.
No interactions on record
"Dextroamphetamine, a central nervous system stimulant, may reduce the sedative effects of Alcaftadine, an antihistamine used for allergic conjunctivitis, by opposing its central histamine H1 receptor blockade. This pharmacodynamic antagonism can lead to diminished sedation and potentially decreased therapeutic efficacy of Alcaftadine for its intended ocular antiallergic effects. Patients may experience reduced symptom relief and increased ocular discomfort."
"Hydroxyamphetamine may decrease the sedative activities of Alcaftadine."
"Phentermine may decrease the sedative activities of Alcaftadine."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ACTAHIST vs ALCAFTADINE, answered by our medical review team.
ACTAHIST is a Antihistamine that works by Antihistamine; binds to histamine H1 receptors, blocking the effects of histamine; also exhibits anticholinergic and mild sedative properties.. ALCAFTADINE is a Ophthalmic Antihistamine that works by Selective histamine H1 receptor antagonist; inhibits histamine release from mast cells and reduces ocular itch associated with allergic conjunctivitis.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ACTAHIST and ALCAFTADINE depend on the specific clinical indication. These are agents from distinct pharmacological classes and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of ACTAHIST is: 1.34 mg (one capsule) orally twice daily.. The standard adult dose of ALCAFTADINE is: 1 drop of 0.25% ophthalmic solution in each affected eye twice daily.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between ACTAHIST and ALCAFTADINE in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. ACTAHIST is classified as Category C. ACTAHIST (brompheniramine/phenylephrine) pregnancy category C. Inadequate human data; animal studies show no malformations at therapeutic doses. First trimester: theoretical risk f. ALCAFTADINE is classified as Category C. Alcaftadine is classified as Pregnancy Category B. Animal studies have not demonstrated teratogenic effects at doses up to 2400 times the human ocular dose. There are no adequate a. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.