Clioquinol: 8 Hydroxyquinoline Derivative in Dermatological Therapy
Clioquinol is a halogenated 8 hydroxyquinoline derivative with antibacterial, antifungal and antiprotozoal effects. It was first synthesized in 1900 and was used for decades as a widely applied antiseptic. In Germany, clioquinol is today available almost exclusively in topical preparations for treating fungal and bacterial skin infections, often in combination with glucocorticoids (e.g. Linola Sept, Locacorten Vioform).
The history of clioquinol is marked by a dark chapter: in the 1950s and 1960s, thousands of cases of subacute myelo opticoneuropathy (SMON) were reported in Japan due to oral clioquinol consumption, a severe neurological disease with sometimes irreversible damage. Oral use of clioquinol was subsequently discontinued or severely restricted worldwide. Topical application to intact skin areas is considered safe due to minimal systemic absorption.
Mechanism of Action
Clioquinol complexes divalent metal ions such as zinc, copper and iron, which disturbs the function of numerous metal dependent bacterial and fungal enzymes. The result is inhibition of bacterial and fungal growth. The effect is broad and affects gram positive and gram negative bacteria as well as many fungi (Candida, Trichophyton, Microsporum).
In addition, clioquinol has direct cytotoxic effects on bacteria and fungi via membrane damage. At low concentrations it acts bacteriostatic, at higher concentrations bactericidal. The antiseptic effect is particularly useful in mixed infections of bacteria and fungi, as commonly occur in secondarily infected eczemas.
Pharmacokinetically, clioquinol is absorbed only minimally when applied topically to intact skin (approximately 5 percent). On damaged skin or mucous membranes, absorption increases significantly, which with long term or large area application can lead to systemic uptake.
Areas of Application
- Fungal skin infections: Tinea pedis (athlete's foot), Tinea corporis, Intertrigo
- Secondarily infected eczemas: in combination with glucocorticoids
- Skin infections with gram negative organisms: in superficial infections
- Otitis externa: in drop form for fungal and bacterial infections of the external auditory canal
- Genital infections: historically, rarely today
Dosage and Administration
Topical application: Ointment or cream with 1 to 3 percent clioquinol applied thinly to the affected skin area once or twice daily. Duration of application 1 to 2 weeks, depending on indication and course.
For otitis externa: Solution with 1 percent, 2 to 3 drops several times daily into the auditory canal.
Important: Do not apply to large open wounds, on mucous membranes or in weeping diseases. For secondarily infected eczemas with glucocorticoid combination, keep application as short as possible to reduce systemic absorption.
Side Effects
Frequent: Local irritation, burning, pruritus, skin redness, yellow brown discoloration of the treated skin area and clothing (due to complexation with iron).
Occasional: Allergic contact eczema (especially with prolonged use), photosensitivity.
Rare, but important: With absorption via damaged skin or with large area and long term application, systemic uptake can trigger clinically relevant effects. Historically, subacute myelo opticoneuropathy (SMON) was observed after oral administration in high doses, with optic nerve damage and polyneuropathy.
Important: Use in infants and small children, during pregnancy and lactation only after strict indication. If vision disturbances or paresthesias occur, discontinue use immediately and seek medical advice.
Drug Interactions
- Other topical antiseptics or antibiotics: can theoretically cause additive effects or irritation
- Topical glucocorticoids: combination possible (Locacorten Vioform), but application duration limited
- Iron preparations (oral): potential complex formation with systemic absorption
Special Information
Pregnancy and lactation: Only short term on small intact skin areas, as systemic absorption is possible. During lactation avoid application to breasts and nipples.
Discoloration: Patients should know that clioquinol can cause yellow brown discoloration of skin, clothing, bedding and jewelry. These discolorations are not harmful to health but are unpleasant. Avoid lighter clothing if possible during therapy.
Narrow angle glaucoma: Exercise caution when applying to the face or eye area, as systemic absorption can trigger eye inflammation or other effects.
More modern alternatives: For fungal infections, specific antifungal agents (Clotrimazole, Miconazole, Terbinafine) are now the treatment of choice. Clioquinol remains an option for mixed infections or when other therapies fail.
You May Also Be Interested In
- Clotrimazole, modern topical antifungal
- Miconazole, another imidazole antifungal
- Terbinafine, allylamine antifungal
- Hydrocortisone, mild glucocorticoid in combination preparations
- Polihexanide, modern wound antiseptic
Frequently Asked Questions
What is the SMON history?
SMON (subacute myelo opticoneuropathy) was a severe neurological disease with optic nerve damage and polyneuropathy that occurred in almost 10,000 cases in Japan in the 1950s and 1960s. The cause was high dose oral clioquinol consumption for traveler's diarrhea. Oral use was discontinued worldwide. Today's topical application to intact skin is considered safe because systemic absorption is minimal.
Why does clioquinol discolor my skin and clothing?
Clioquinol complexes divalent metal ions, especially iron, forming yellow brown complexes. These discolorations are not harmful to health but are cosmetically undesirable and can permanently discolor clothing, bedding and jewelry. Avoid lighter clothing if possible during therapy.
When is clioquinol still useful today?
For secondarily infected eczemas with mixed infection of bacteria and fungi, or as a backup option when other therapies fail. For pure fungal infections, modern antifungal agents such as clotrimazole or terbinafine are the first line treatment, because they are more specific and do not cause discoloration.
Can I use clioquinol on my child?
In infants and small children only on medical prescription and on small skin areas, as systemic absorption is higher and children are more sensitive to neurotoxic effects. In older children and for clearly limited skin infections, application is possible but should be kept short.
Sources
- Gelbe Liste, Clioquinol active substance profile
- AWMF Guideline Tinea and secondarily infected eczemas
- BfArM, Federal Institute for Drugs and Medical Devices
- WHO Drug Information on Clioquinol and SMON
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