The shorter elimination half-life of diphenhydramine (4–8 hours) compared to doxylamine may give it an advantage over doxylamine as a sleep aid in this regard.Antihistamines like doxylamine are sedating initially but tolerance occurs with repeated use and can result in rebound insomnia upon discontinuation.Occasional case reports of coma and rhabdomyolysis have been reported with doxylamine. This is in contrast to diphenhydramine.Studies of doxylamines carcinogenicity in mice and rats have produced positive results for both liver and thyroid cancer, especially in the mouse. The carcinogenicity of the drug in humans is not well-studied, and the International Agency for Research on Cancer lists the drug as "not classifiable as to its carcinogenicity to humans". Overdose
Doxylamine is generally safe for administration to healthy adults. Doses of doxylamine of up to 1,600 mg/day for 6 months have been given to adults with schizophrenia, with little toxicity encountered. The median lethal dose (LD50) is estimated to be ~500 mg/kg in humans. Symptoms of overdose may include dry mouth, dilated pupils, insomnia, night terrors, euphoria, hallucinations, seizures, rhabdomyolysis, and death. Fatalities have been reported from doxylamine overdose. These have been characterized by coma, tonic-clonic (or grand mal) seizures and cardiorespiratory arrest. Children appear to be at a high risk for cardiorespiratory arrest. A toxic dose for children of more than 1.8 mg/kg has been reported. A 3-year-old child died 18 hours after ingesting 1,000 mg doxylamine succinate. Rarely, an overdose results in rhabdomyolysis and acute kidney injury. Pharmacology
Pharmacodynamics
Doxylamine acts primarily as an antagonist or inverse agonist of the histamine H1 receptor.
Polyonychia also known as supernumerary nails is a condition in which two or more nails grow in the same finger or toe. Signs and symptoms
The signs/symptoms of polyonychia are very easy to detect: two or more nails growing on the same finger or toe. The nails can either be separate, small nails (micronychia) or one wide, almost complete nail, the digit affected could also be wider than normal

Causes
Polyonychia is generally caused by a congenital duplication of the distal phalange of the affected digit(s), this can be caused by congenital factors (sporadic without a genetic link) or by genetic factors (sporadic or familial with genetic link). It can also be caused by polysyndactyly, which is characterized as one normal digit being connected/webbed (syndactyly) to an extra digit (polydactyly). Polyonychia can also be acquired, such as after an accident that affected the nail bed causing it to split. This type of polyonychia is just referred to as "post-traumatic split nail" Polyonychias syndromic causes include:

Isolated congenital onychodysplasiaPolyonychias non-syndromic causes include:

Polyphalangism (more specifically of the distal phalange)
Polysyndactyly

See also
Polydactyly
Syndactyly
Polysyndactyly


== References ==