Monograph: |
Hydroquinone
FOR EXTERNAL USE ONLY
DESCRIPTION
Hydroquinone is 1,4-benzenediol. Hydroquinone is structurally related to monobenzone. Hydroquinone occurs as fine, white needles. The drug is freely soluble in water and in alcohol and has a pK a of 9.96. Chemically, hydroquinone is designated as p-dihydroxybenzene; the empirical formula is C 6 H 6 O 2 ; molecular weight 110.0.
CLINICAL PHARMACOLOGY
Topical application of hydroquinone produces a reversible depigmentation of the skin by inhibition of the enzymatic oxidation of tyrosine to 3,4-dihydroxyphenylalanine (dopa) (Denton, C. et al., 1952) 1 and suppression of other melanocyte metabolic processes (Jimbow, K. et al., 1974). 2 Exposure to sunlight or ultraviolet light will cause repigmentation of bleached areas which may be prevented by the sunblocking agents.
INDICATIONS AND USAGE
For the gradual bleaching of hyperpigmented skin conditions such as chloasma, melasma, freckles, senile lentigines and other unwanted areas of melanin hyperpigmentation.
CONTRAINDICATIONS
Prior history of sensitivity or allergic reaction to these products or any of the ingredients. The safety of topical hydroquinone use during pregnancy or in children (12 years and under) has not been established.
WARNINGS
Caution: Hydroquinone is a skin bleaching agent which may produce unwanted cosmetic effects if not used as directed. The physician should be familiar with the contents of the package insert before prescribing or dispensing these medications.
Test for skin sensitivity before using by applying a small amount to an unbroken patch of skin and check in 24 hours. Minor redness is not a contraindication, but where there is itching or vesicle formation or excessive inflammatory response, further treatment is not advised. Close patient supervision is recommended. Contact with the eyes should be avoided. If no bleaching or lightening effect is noted after 2 months of treatment use, the medication should be discontinued.
After clearing and during maintenance therapy, sun exposure should be avoided on bleached skin by application of a sunscreen or sunblock agent or protective clothing to prevent repigmentation
Keep this and all medication out of the reach of children. In case of accidental ingestion, call a physician or a poison control center immediately.
Warning: Contains sodium metabisulfite, a sulfite that may cause serious allergic type reactions (e.g., hives, itching, wheezing, anaphylaxis, severe asthma attack) in certain susceptible persons.
PRECAUTIONS (SEE WARNINGS )
General. Treatment should be limited to relatively small areas of the body at one time since some patients experience a transient skin reddening and a mild burning sensation which does not preclude treatment.
Pregnancy Category C. Animal reproduction studies have not been conducted with topical hydroquinone. It is also not known whether hydroquinone can cause fetal harm when used topically on a pregnant woman or affect reproductive capacity. It is not known to what degree, if any, topical hydroquinone is absorbed systemically. Topical hydroquinone should be used in pregnant women only when clearly indicated.
Nursing mothers. It is not known whether topical hydroquinone is absorbed or excreted in human milk. Caution is advised when topical hydroquinone is used by a nursing mother.
Pediatric usage. Safety and effectiveness in pediatric patients below the age of 12 years have not been established.
ADVERSE REACTIONS
No systemic adverse reactions have been reported. Occasional hypersensitivity (localized contact dermatitis) may occur, in which case the medication should be discontinued and the physician notified immediately.
DOSAGE AND ADMINISTRATION
Should be applied twice daily and rubbed gently before going in the sun.
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