New York, May 24 : The US Food and Drug Administration (FDA) issued a warning on Saturday that some popular allergy medications could cause a rare but severe itching side effect.

The FDA said in a safety warning issued in mid-May that some patients who have taken oral allergy medicines daily for long periods, at least a few months but often several years, have experienced a severe type of itching, which is known medically as pruritus, Xinhua news agency reported.

FDA warned about 'rare but severe itching after stopping long-term use of oral allergy medicines cetirizine or levocetirizine (Zyrtec, Xyzal, and other trade names)'. It can occur with both prescription and over-the-counter forms of these medicines, the agency said.

While the reported cases of severe itching side effects are rare, some have been serious and required medical intervention.

Both cetirizine and levocetirizine are available over the counter (OTC) or through a prescription. The FDA said it has revised the prescribing information for both medicines to include a warning about the possible effects.

'We will subsequently request that manufacturers add a warning about pruritus to the Drug Facts Label of the OTC versions,' the FDA said.

Cetirizine and levocetirizine are antihistamines that block a molecule called histamine that the body releases during allergic reactions. Both medicines are approved to treat seasonal allergies, called seasonal allergic rhinitis, in adults and children 2 years and older.

The medicines are also approved to treat year-round allergies, called perennial allergic rhinitis, and chronic hives, called chronic idiopathic urticaria, in patients six months and older.

Cetirizine was approved for oral use by prescription in December 1995 under the trade name Zyrtec (no longer sold as a prescription medicine) and approved for OTC use in November 2007.

Levocetirizine was approved for oral use by prescription in May 2007 under the trade name Xyzal and approved for OTC use in January 2017.

/IANS