Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ALA-SCALP vs ACETIC ACID W/ HYDROCORTISONE
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
ALA-SCALP (aminolevulinic acid) is a photosensitizer precursor that is converted intracellularly to protoporphyrin IX (Pp IX), which accumulates in cells with increased heme synthesis, such as rapidly dividing cells. Upon exposure to blue light (BLU-U®), Pp IX produces reactive oxygen species, leading to cellular damage and apoptosis of targeted cells.
Acetic acid exerts antibacterial and antifungal activity by lowering p H and disrupting microbial cell membranes. Hydrocortisone is a corticosteroid with anti-inflammatory, antipruritic, and vasoconstrictive properties.
Treatment of minimally to moderately thick actinic keratoses of the scalp (Grade 1 or 2) in immunocompetent patients,Off-label: other photosensitivity disorders
Treatment of superficial bacterial infections of the external auditory canal (otitis externa) and associated inflammation.
Topical application of a 5% solution to the scalp twice daily.
1 applicatorful (approximately 5 g) of the cream or ointment (containing 2% acetic acid and 1% hydrocortisone) inserted intravaginally once or twice daily for 7 days.
Not applicable; topical ALA-SCALP is not significantly absorbed systemically. After systemic absorption from photodynamic therapy, terminal half-life is approximately 1 hour due to rapid metabolism.
Acetic acid: not applicable; hydrocortisone: plasma half-life ~1.5 hours (biologic half-life 8–12 hours). Due to low systemic absorption from topical application, systemic half-life is clinically irrelevant.
ALA is metabolized intracellularly via the heme biosynthesis pathway to protoporphyrin IX (Pp IX).
Acetic acid is metabolized via the Krebs cycle to carbon dioxide and water. Hydrocortisone is primarily metabolized in the liver.
Primarily renal elimination of metabolites; <1% excreted unchanged in urine. Biliary/fecal excretion is negligible.
Acetic acid: minimal systemic absorption; hydrocortisone: hepatic metabolism, renal excretion of metabolites (<5% unchanged). Less than 10% of applied dose excreted in urine as metabolites; biliary/fecal excretion negligible.
Not characterized; systemic levels are negligible after topical administration.
Hydrocortisone: ~90% bound to corticosteroid-binding globulin (CBG) and albumin. Acetic acid: negligible binding.
Not applicable for topical route. If systemic exposure occurs, Vd is approximately 0.5 L/kg, consistent with distribution into total body water.
Hydrocortisone: Vd ~0.3–0.5 L/kg (systemic); topical application results in negligible systemic distribution.
Topical: Systemic bioavailability is minimal (<1%) due to poor percutaneous absorption and rapid local metabolism.
Topical: ~1–5% of hydrocortisone absorbed through intact skin; higher with inflamed skin or occlusion. Acetic acid: negligible systemic absorption.
No dose adjustment required for renal impairment.
No dose adjustment required for acetic acid. Hydrocortisone is minimally affected by renal impairment; no specific adjustment recommended.
No dose adjustment required for hepatic impairment.
No dose adjustment required for acetic acid. For hydrocortisone, use with caution in severe hepatic impairment (Child-Pugh C) due to reduced metabolism; consider reducing frequency or dose, though no specific guidelines exist.
Safety and efficacy in pediatric patients have not been established.
Safety and efficacy not established in pediatric patients; use not recommended.
No specific dose adjustment recommended; use with caution due to potential increased sensitivity.
No specific dose adjustment required. Use caution due to potential skin atrophy and systemic absorption; limit duration to minimum effective course.
No FDA black box warning.
Not applicable.
Photosensitivity: avoid exposure to sunlight or bright indoor light (e.g., examination lamps, operating room lamps) for at least 40 hours post-application.,Application site reactions: severe stinging, burning, erythema, and edema may occur.,Use sun-protective measures (e.g., wide-brimmed hat, sunscreen) after treatment.,Do not apply to eyes or mucous membranes.
For otic use only; not for ophthalmic or systemic use.,Prolonged use may lead to fungal or bacterial superinfection.,Discontinue if irritation or sensitization develops.
Hypersensitivity to aminolevulinic acid or any component of the formulation,Cutaneous photosensitivity at wavelengths of 400-450 nm,Porphyria
Hypersensitivity to any component.,Viral or fungal infections of the external ear (e.g., herpes simplex, varicella).,Perforated tympanic membrane (risk of ototoxicity).
No known food interactions. No dietary restrictions required.
No clinically relevant food interactions. No specific dietary restrictions.
No evidence of teratogenicity; topical application with minimal systemic absorption. First trimester: unlikely risk. Second/third trimester: no known fetal risks from maternal use.
Topical corticosteroids are generally considered low risk in pregnancy. Hydrocortisone is a weak corticosteroid. No increased risk of congenital malformations has been observed with topical use. Systemic absorption is minimal with small-area application. Avoid prolonged use on large areas, occlusive dressings, or high-potency steroids. Acetic acid has no known teratogenic risk.
Minimal systemic absorption; unlikely to appear in breast milk. M/P ratio not established. Considered compatible with breastfeeding.
Minimal systemic absorption of topical hydrocortisone and acetic acid; unlikely to affect the breastfed infant. Use on limited areas, avoid application to breast or nipple area. M/P ratio not established.
No dosage adjustment required; pharmacokinetics unlikely altered due to topical route.
No dosing adjustments required for pregnancy. Use lowest effective dose for shortest duration to minimize systemic absorption.
ALA-SCALP is a topical aminolevulinic acid preparation used for photodynamic therapy of actinic keratoses on the scalp. Must be applied by a healthcare professional. Avoid sun exposure to treated area for 48 hours post-application due to photosensitivity. Do not apply to eyes or mucous membranes. Lesions should be prepped by gentle removal of scales and crusts. Use with a compatible light source (blue light). Burning and stinging during light exposure is common; consider pain management strategies.
Combination otic suspension for external otitis. Ensure tympanic membrane is intact before use; perforation risks ototoxicity. Shake well before instillation. Use for no longer than 10 days to avoid fungal overgrowth or adrenal suppression. Warm bottle in hands to avoid caloric vertigo. Contraindicated in viral or fungal infections of the ear canal.
This medication is applied by your doctor to treat precancerous spots on your scalp.,After application, you will need a special light treatment (photodynamic therapy).,Avoid sunlight and bright indoor light on the treated area for 48 hours after the procedure.,You may experience temporary redness, swelling, scaling, or discomfort at the treatment site.,Use sunscreen and protective clothing when going outdoors during the photosensitivity period.,Do not wash the treated area for at least 4 hours after the solution is applied.,Contact your doctor if you experience severe pain, blistering, or signs of infection.
For ear use only. Do not swallow or put in eyes.,Lie on side with affected ear upward for 5 minutes after instillation.,Keep ear clean and dry while using the medication.,Complete full course even if symptoms improve.,Do not use if you have a perforated eardrum; seek medical evaluation first.,Shake the bottle well before each use.
No interactions on record
"Hydrocortisone, a corticosteroid, may inhibit the hepatic metabolism of doxycycline, a tetracycline antibiotic, leading to increased doxycycline plasma concentrations. This elevation can potentiate doxycycline's adverse effects, such as gastrointestinal disturbance, photosensitivity, and hepatotoxicity. Clinically, this interaction may reduce the therapeutic window of doxycycline, requiring dose adjustment or alternative therapy selection."
"Fluconazole, a potent inhibitor of cytochrome P450 3A4 (CYP3A4), can significantly reduce the hepatic clearance of hydrocortisone, a corticosteroid metabolized primarily by CYP3A4. This interaction leads to increased systemic exposure to hydrocortisone, potentially resulting in exaggerated corticosteroid effects such as hyperglycemia, immunosuppression, and adrenal suppression. Clinically, patients may experience symptoms of Cushing's syndrome or require dose adjustments to avoid toxicity."
"Rifaximin, a non-systemic antibiotic primarily acting in the gastrointestinal tract, may inhibit intestinal P-glycoprotein (P-gp), reducing the efflux of corticosteroids like hydrocortisone. This can lead to increased systemic absorption and elevated serum concentrations of hydrocortisone, potentially enhancing both therapeutic and adverse effects such as hyperglycemia, immunosuppression, and adrenal suppression."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ALA-SCALP vs ACETIC ACID W/ HYDROCORTISONE, answered by our medical review team.
ALA-SCALP is a Topical Corticosteroid that works by ALA-SCALP (aminolevulinic acid) is a photosensitizer precursor that is converted intracellularly to protoporphyrin IX (Pp IX), which accumulates in cells with increased heme synthesis, such as rapidly dividing cells. Upon exposure to blue light (BLU-U®), Pp IX produces reactive oxygen species, leading to cellular damage and apoptosis of targeted cells.. ACETIC ACID W/ HYDROCORTISONE is a Corticosteroid that works by Acetic acid exerts antibacterial and antifungal activity by lowering p H and disrupting microbial cell membranes. Hydrocortisone is a corticosteroid with anti-inflammatory, antipruritic, and vasoconstrictive properties.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ALA-SCALP and ACETIC ACID W/ HYDROCORTISONE 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 ALA-SCALP is: Topical application of a 5% solution to the scalp twice daily.. The standard adult dose of ACETIC ACID W/ HYDROCORTISONE is: 1 applicatorful (approximately 5 g) of the cream or ointment (containing 2% acetic acid and 1% hydrocortisone) inserted intravaginally once or twice daily for 7 days.. 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 ALA-SCALP and ACETIC ACID W/ HYDROCORTISONE 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. ALA-SCALP is classified as Category C. No evidence of teratogenicity; topical application with minimal systemic absorption. First trimester: unlikely risk. Second/third trimester: no known fetal risks from maternal use.. ACETIC ACID W/ HYDROCORTISONE is classified as Category D/X. Topical corticosteroids are generally considered low risk in pregnancy. Hydrocortisone is a weak corticosteroid. No increased risk of congenital malformations has been observed wit. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.