Imiquimod

Mechanism of action

◎Toll-like receptor 7 (TLR7) on immune cells of the skinImiquimod

ⓘ The figure shows rhesus monkey TLR7 (very close to the human receptor) with imiquimod bound; no human TLR7-imiquimod structure is used here.

Imiquimod is an imidazoquinoline that acts as a ligand at toll-like receptor 7. Stimulated mononuclear cells release interferon-α, and macrophages produce interleukins (IL-1, IL-6, IL-8) and TNF-α. These cytokines drive an innate and cell-mediated immune response against HPV-infected cells and atypical or malignant keratinocytes. Local inflammation at the treated site (redness, crusting, erosion) is common and expected.

1. Imiquimod activates TLR7 on immune cells in the skin
2. Cells release interferon-α, TNF-α and interleukins
3. An immune response attacks HPV-infected or atypical cells
4. Warts, actinic keratoses or superficial BCC clear

Indications

• External genital and perianal warts in immunocompetent people Viral warts (verruca) →
• Actinic keratoses on the face or scalp in immunocompetent adults Actinic keratosis →
• Biopsy-confirmed superficial basal cell carcinoma when surgery is less appropriate Basal cell carcinoma →

Adverse effects

Common

• Redness, flaking, scabbing, swelling and erosion at the site (expected)
• Itching and burning
• Fatigue, fever and headache
• Increased sunburn

Contraindications

• None absolute in the label; not used inside the vagina, anus, mouth or eyes

Key interactions

Condoms and vaginal diaphragms

The cream can weaken them, so they may fail as contraception or protection.

Sunlight, sunlamps and UV therapy

Heightened sunburn; treatment waits until the skin has recovered from any sunburn.

What is monitored

• Severity of local skin reactions; treatment can pause for a few days if they are severe
• Flu-like symptoms
• Clearance of the lesion at the end of the course; lesions that persist are reassessed

Administration and safety

• Applied as a thin layer at bedtime on the scheduled days, left on for several hours, then washed off with soap and water.
• Topical use only; not inside the vagina, anus, mouth or eyes.
• Hands are washed before and after; only non-occlusive dressings (cotton gauze) are used.
• Sexual contact is avoided while the cream is on genital skin.

Pregnancy and breastfeeding

Case reports have not shown a clear risk, but human data are limited.

Nursing care

• Explain that redness and crusting are common and expected, and how to recognise a reaction severe enough to pause treatment.
• Teach sun protection and to avoid tanning beds during treatment.
• Warn that condoms and diaphragms can be weakened.
• Ask women with genital warts to report swelling that makes urination difficult.

Pharmacokinetics

Absorption

Minimal absorption through the skin.

Onset and duration

Lesions clear over weeks of treatment.

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Connections

← Back to the class: Other dermatological medicines

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: Imiquimod Topical: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); DailyMed - IMIQUIMOD cream (DailyMed (U.S. National Library of Medicine), 2025); Crystal structure of monkey TLR7 in complex with imiquimod (RCSB Protein Data Bank, 2026).

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Representative model, for educational purposes only.