Drometrizole trisiloxane

Identification

Summary

Drometrizole trisiloxane is an UV ray absorbing agent used in sunscreens to protect skin from UV radiation.

Generic Name

DrugBank Accession Number

DB11585

Background

Drometrizole trisiloxane is a photostable UVA and UVB light filter ^1,3,4,5,6,9. The compound is a lipophilic benzotriazole derivative marketed as Meroxyl XL by L'Oreal, although sunscreens with drometrizole trisiloxane are currently only approved for use in the EU, Canada, Australia, and Japan, among other countries.

Despite being used elsewhere in the world with relatively few reports of adverse reactions, the FDA continues to cite that the existing scientific record is not sufficient to establish the compound as being generally recognized as safe and effective for over-the-counter sunscreen use ^8,10.

Type

Small Molecule

Groups

Approved

Structure

Similar Structures

Weight: Average: 501.849
Monoisotopic: 501.229921733
Chemical Formula: C₂₄H₃₉N₃O₃Si₃

Synonyms

Silatrizole

External IDs

OR 10154
OR-10154

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Pharmacology

Indication

Drometrizole trisiloxane is used as an active ingredient in various sunscreens for the indication of protecting the skin by absorbing the damaging UV radiation of sunlight ^{1,3,4,5,6,9,10}.

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Associated Conditions

Indication Type	Indication	Combined Product Details	Approval Level	Age Group	Patient Characteristics	Dose Form
Used in combination for prophylaxis of	Sunburn		••• •••

Contraindications & Blackbox Warnings

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Pharmacodynamics

As an active ingredient in sunscreen products, drometrizole trisiloxane is applied directly onto human skin where it acts as a chemical sunscreen layer between skin and sunlight that also directly absorbs the UV sunlight radiation ^1,3,4,5,6,9. Since drometrizole trisiloxane is also considered to have little to no absorption through the skin ^1,3,4,5,6,9, little systemic exposure and pharmacokinetics are expected and users can freely wash off and re-apply the compound as necessary.

Mechanism of action

Ultraviolet radiation is the invisible energy component to sunlight and consists of three wavelength ranges:

(a) UVA is long-range UV radiation between 320-400nm ⁷. Although not as energetic as UVB, UVA can penetrate deep into the dermis ⁷. UVA can cause immediate tanning, premature skin aging, and can also play a role in the formation of some skin cancers ⁷. Approximately 95% of UVA from the sun passes through Earth's ozone layer ⁷.

(b) UVB is short-wavelength UV radiation between 280-320nm ⁷. It is capable of penetrating the outer protective layer of the skin and is responsible for delayed tanning, sunburns, and most skin cancers ⁷. A large amount of UVB is absorbed by the ozone layer, however, as only 5% reaches the Earth's surface ⁷.

(c) UVC is comprised of wavelengths between 100-280nm and is very energetic ⁷. It is very dangerous to all forms of life, even when the exposure is short ⁷. However, UVC radiation is generally filtered out by the ozone layer and never reaches the Earth ⁷.

Ultimately, the shorter the wavelength, the more harmful the UV radiation - although shorter wavelength UV radiation is less able to penetrate the skin ⁷.

Subsequently, drometrizole trisiloxane is a broad spectrum lipophilic benzotriazole derivative chemical sunscreen that is capable of absorbing UVA and UVB radiation ^1,3,4,5,6. It is also photostable, meaning that it will not degrade in the presence of sunlight, unlike other UV filters like the widely used UVA absorber avobenzone ⁶. When combined with the UV blocker ecamsule, it has been shown that the two UV blockers elicit a synergistic effect involving an enhanced protective action for the skin against UVA and UVB radiation ^1,3,4,5,6. Additionally, drometrizole trisiloxane is usually combined with other active sunscreen agents like titanium dioxide, avobenzone, and others to ensure the combined product covers or protects against as broad a spectrum of UV radiation as possible, considering drometrizole trisiloxane does not absorb against the entire range of UV radiation ⁶.

And finally, at the molecular level, it is believed that the general structure of various UV blockers like drometrizole trisiloxane as aromatic molecules conjugated with carbonyl groups is capable of absorbing high energy ultraviolet rays and then consequently releasing that energy as less harmful, lower energy rays.

Absorption

Drometrizole trisiloxane is reported as having little to no absorption through the skin ^3,6. At this time, however, studies demonstrate that the components of most commonly used sunscreens are likely absorbed into the skin at least to some extent - although penetration to deeper tissues and the cutaneous circulation remains limited ². Despite the extensive use of sunscreen products around the world, there have been few reports of adverse effects related to their use ².

Volume of distribution