Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ALA-SCALP vs VOSOL HC
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 provides antibacterial and antifungal activity by acidifying the ear canal and disrupting microbial cell membranes. Hydrocortisone suppresses inflammatory mediators.
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,Treatment of seborrheic dermatitis of the ear
Topical application of a 5% solution to the scalp twice daily.
Instill 5 drops into the affected ear(s) 3-4 times daily, or as directed by physician.
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.
Terminal elimination half-life: 2–4 hours. Clinical context: Short half-life necessitates frequent dosing for sustained effect; prolonged in renal impairment.
ALA is metabolized intracellularly via the heme biosynthesis pathway to protoporphyrin IX (Pp IX).
Acetic acid is metabolized via the Krebs cycle; hydrocortisone is hepatically metabolized primarily by CYP3A4.
Primarily renal elimination of metabolites; <1% excreted unchanged in urine. Biliary/fecal excretion is negligible.
Renal: 95% as unchanged drug and metabolites; biliary/fecal: <5%.
Not characterized; systemic levels are negligible after topical administration.
90–95%, primarily to albumin.
Not applicable for topical route. If systemic exposure occurs, Vd is approximately 0.5 L/kg, consistent with distribution into total body water.
Vd: 0.3–0.5 L/kg; clinical meaning: moderate distribution into total body water, limited tissue penetration.
Topical: Systemic bioavailability is minimal (<1%) due to poor percutaneous absorption and rapid local metabolism.
Otic: 80–90% (local absorption with minimal systemic).
No dose adjustment required for renal impairment.
No dosage adjustment required for renal impairment.
No dose adjustment required for hepatic impairment.
No dosage adjustment required for hepatic impairment.
Safety and efficacy in pediatric patients have not been established.
Children: Instill 3 drops into the affected ear(s) 3-4 times daily; use as directed by physician.
No specific dose adjustment recommended; use with caution due to potential increased sensitivity.
No specific geriatric dosage adjustment; use same as adult dosing with caution for increased sensitivity.
No FDA black box warning.
None
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 external use only,Not for use in eyes,Discontinue if irritation or sensitization occurs,Prolonged use may result in overgrowth of non-susceptible organisms,Use caution in perforated tympanic membrane
Hypersensitivity to aminolevulinic acid or any component of the formulation,Cutaneous photosensitivity at wavelengths of 400-450 nm,Porphyria
Hypersensitivity to any component,Viral infections of the ear (e.g., herpes simplex, varicella),Fungal infections unless treated with concomitant antifungal therapy
No known food interactions. No dietary restrictions required.
No known food interactions. Alcohol consumption is not restricted.
No evidence of teratogenicity; topical application with minimal systemic absorption. First trimester: unlikely risk. Second/third trimester: no known fetal risks from maternal use.
VOSOL HC (acetic acid, hydrocortisone) otic solution: Pregnancy Category C. No adequate human studies; avoid use unless clearly needed. Hydrocortisone crosses placenta; prolonged systemic use may increase risk of orofacial clefts (first trimester) and fetal adrenal suppression. Acetic acid is considered low risk. Second/third trimester: minimal systemic absorption from otic use, but theoretical risk of adrenal suppression with high doses.
Minimal systemic absorption; unlikely to appear in breast milk. M/P ratio not established. Considered compatible with breastfeeding.
No data on excretion in human milk; topical otic use likely results in negligible systemic absorption. Use caution. M/P ratio unknown.
No dosage adjustment required; pharmacokinetics unlikely altered due to topical route.
No dosing adjustments required for topical otic use due to minimal systemic absorption; use standard dose (5 drops in affected ear(s) 3-4 times daily). Avoid prolonged use (>10 days) to minimize potential systemic effects.
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.
VOSOL HC contains acetic acid (2%) and hydrocortisone (1%) in a propylene glycol vehicle. It is indicated for the treatment of otitis externa (swimmer's ear), particularly when inflammation is present. The acetic acid lowers the p H to ~3-4, creating an unfavorable environment for bacteria and fungi. Hydrocortisone reduces inflammation and pruritus. Do not use in patients with a perforated tympanic membrane (risk of ototoxicity). The solution should be instilled with the patient's head tilted to the side, and the tragus massaged to facilitate penetration. Use the dropper provided; do not allow the dropper tip to contact the ear canal to avoid contamination. Duration of therapy typically 7-10 days.
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.
Instill 5 drops into the affected ear(s) 3-4 times daily for 7-10 days.,Keep the dropper tip clean; do not touch the tip to any surface, including the ear.,Tilt head sideways and stay in that position for 5 minutes after instilling drops.,Do not use if you have a punctured eardrum or ear tubes.,Notify your doctor if symptoms persist after 7 days or worsen.,This medication contains benzalkonium chloride (preservative) and propylene glycol; may cause contact dermatitis in sensitive individuals.,Avoid swimming or getting water in the ear during treatment.
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 ALA-SCALP vs VOSOL HC, 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.. VOSOL HC is a Otic Anti-infective with Corticosteroid that works by Acetic acid provides antibacterial and antifungal activity by acidifying the ear canal and disrupting microbial cell membranes. Hydrocortisone suppresses inflammatory mediators.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ALA-SCALP and VOSOL HC 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 VOSOL HC is: Instill 5 drops into the affected ear(s) 3-4 times daily, or as directed by physician.. 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 VOSOL HC 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.. VOSOL HC is classified as Category C. VOSOL HC (acetic acid, hydrocortisone) otic solution: Pregnancy Category C. No adequate human studies; avoid use unless clearly needed. Hydrocortisone crosses placenta; prolonged s. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.