Los Angeles (CNN) -- The illness that derailed Miley Cyrus' U.S. tour in April has returned like a wrecking ball at the start of her European tour.
Cyrus' Friday and Saturday shows in Amsterdam and Antwerp have been rescheduled for June 20 and 22 because she suffered a setback in her battle against a "severe allergic reaction" to an antibiotic, her rep said.
The 21-year-old singer fell ill on April 15 and was kept in a Kansas City hospital for several days. The remaining North American shows in her "Bangerz" tour were postponed until August.
"After a period of improvement, Cyrus' symptoms have returned and doctors will not permit her to travel," her representative told CNN Wednesday. "This type of extreme reaction can last up to 27 days and Cyrus must remain under doctors' care at this time."
Cyrus is still hoping to perform her "Bangerz" show at London's O2 Arena on May 6, the rep said.
She initially became ill in early April with a flu-like illness, which caused her to pull out of her Charlotte show. After being prescribed the antibiotic Cephalexin, her health woes grew when an allergic reaction to the drug left Cyrus hospitalized for more than a week, according to a statement from her representative earlier this month.
Cyrus used Twitter to express her sadness, posting a tweet of 132 crying emoticons Tuesday.
CNN's Breeanna Hare and Carolyn Sung contributed to this report.