Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ACTAHIST vs ADALAT
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.
Dihydropyridine calcium channel blocker; inhibits calcium ion influx across cardiac and vascular smooth muscle cells, reducing peripheral vascular resistance and blood pressure.
Symptomatic relief of allergic rhinitis,Urticaria,Off-label: motion sickness,Off-label: insomnia
Hypertension,Chronic stable angina,Vasospastic angina (Prinzmetal's angina)
1.34 mg (one capsule) orally twice daily.
10-20 mg orally three times daily; extended-release: 30-60 mg orally once daily; maximum 120 mg/day.
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: 2-5 hours (immediate-release); 8-14 hours (extended-release). Context: shorter half-life necessitates multiple daily dosing for immediate-release; extended-release allows once-daily dosing.
Hepatic metabolism via CYP450 enzymes (primarily CYP3A4 and CYP2D6); major metabolite is inactive.
Hepatic via CYP3A4; extensive first-pass metabolism; metabolites are inactive.
Primarily renal (approximately 85% as unchanged drug and metabolites) and fecal (15%) via biliary elimination.
Renal: 70-80% as metabolites; Fecal: 15-20% as metabolites; <1% unchanged in urine
92% bound to albumin.
92-98% bound to plasma proteins (albumin and alpha-1-acid glycoprotein)
0.9 ± 0.3 L/kg, indicating extensive extravascular distribution.
0.8-1.2 L/kg. Clinical meaning: indicates extensive tissue distribution, consistent with high lipophilicity.
Oral: 68% ± 12% due to first-pass metabolism.
Oral immediate-release: 45-60% (due to first-pass metabolism); extended-release: 60-85% (due to slower release and reduced first-pass effect).
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 GFR ≥30 m L/min; for GFR <30 m L/min, use with caution and reduce initial dose by 50%.
No dose adjustment required for mild to moderate hepatic impairment (Child-Pugh A or B). Not recommended for severe hepatic impairment (Child-Pugh C).
Child-Pugh Class A: no adjustment; Class B: reduce dose by 50%; Class C: avoid use or reduce by 75%.
Not indicated for pediatric patients under 12 years of age. Safety and efficacy not established.
0.25-0.5 mg/kg/dose orally every 6-8 hours; maximum 3 mg/kg/day. Extended-release not recommended.
No specific dose adjustment recommended; monitor for increased anticholinergic effects and cognitive impairment.
Start at 10 mg orally twice daily; titrate slowly due to increased sensitivity and risk of hypotension.
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.
May cause hypotension, especially in patients on beta-blockers or with poor cardiac reserve,Risk of increased angina and/or myocardial infarction upon initiation or dose increase,Peripheral edema,Stevens-Johnson syndrome and toxic epidermal necrolysis (rare),Hepatic impairment,Exacerbation of angina on withdrawal
Hypersensitivity to any component. Newborns or premature infants. Breastfeeding (contraindicated due to risk of adverse effects in infants). Concomitant use with MAOIs.
Hypersensitivity to nifedipine,Cardiogenic shock,Significant aortic stenosis,Concurrent use with rifampin,Pregnancy (category C)
Avoid high-tyramine foods (aged cheese, cured meats, fermented products) if taking MAOIs. Grapefruit juice may increase phenylephrine absorption; limit intake.
Avoid grapefruit and grapefruit juice; they inhibit CYP3A4 and increase nifedipine serum concentrations, leading to enhanced hypotensive effects and risk of toxicity. Grapefruit interaction persists for 24 hours; separate consumption by at least 4 hours if unavoidable, but preferable to avoid entirely. Avoid alcohol which can increase hypotension. High-fat meals may reduce absorption of extended-release formulations; take consistently with or without 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.
First trimester: Limited human data; animal studies show embryotoxicity. Second/third trimester: May cause fetal hypoxia due to maternal hypotension; risk of preterm labor inhibition. Category C.
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.
Excreted in breast milk; M/P ratio ~0.85. Consider risks versus benefits; monitor infant for hypotension.
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 standard dose adjustment; monitor clinical response and blood pressure; may require lower doses due to vasodilation effects.
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.
Adalat (nifedipine) is a dihydropyridine calcium channel blocker. Use immediate-release capsules only for hypertensive emergencies, not chronic treatment due to risk of reflex tachycardia and unpredictable hypotension. Extended-release formulations are preferred for stable angina and hypertension. Avoid grapefruit juice as it increases nifedipine levels via CYP3A4 inhibition. Monitor for peripheral edema, gingival hyperplasia, and constipation. Contraindicated in cardiogenic shock, severe aortic stenosis, and within 4 weeks of myocardial infarction.
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.
Swallow extended-release tablets whole; do not crush, chew, or split.,Avoid grapefruit and grapefruit juice while taking this medication.,Report persistent swelling of ankles/feet, gum tenderness or bleeding, or severe dizziness.,Do not stop abruptly; taper under medical supervision to avoid rebound hypertension.,Take at the same time each day; if a dose is missed, skip it if near next dose.,May cause dizziness; avoid driving until you know how it affects you.,Increase fluid and fiber intake to prevent constipation.,Store at room temperature away from light and moisture.
No interactions on record
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ACTAHIST vs ADALAT, 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.. ADALAT is a Calcium Channel Blocker that works by Dihydropyridine calcium channel blocker; inhibits calcium ion influx across cardiac and vascular smooth muscle cells, reducing peripheral vascular resistance and blood pressure.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ACTAHIST and ADALAT 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 ADALAT is: 10-20 mg orally three times daily; extended-release: 30-60 mg orally once daily; maximum 120 mg/day.. 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 ADALAT 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. ADALAT is classified as Category C. First trimester: Limited human data; animal studies show embryotoxicity. Second/third trimester: May cause fetal hypoxia due to maternal hypotension; risk of preterm labor inhibiti. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.