A THREE-year-old boy was given out-of-date antibiotics when his mother took him to a Southampton health centre.
Mum Laura Cooper said she was "appalled" when she discovered the medication had expired by a month as she went to give it to son Beau.
Health chiefs have apologised for the mistake and vowed to review procedures.
Miss Cooper took her son to the NHS Walk-in Centre in Shirley after becoming concerned that he had developed an infection.
After checking the boy, who had recently had minor hospital treatment in connection with a circumcision, a doctor prescribed antibiotics as a precaution.
But when Miss Cooper returned to her home in Culver Close, Millbrook, she discovered the expiry date on the bottle was September, 2004.
The 23-year-old said: "The doctor checked him and said he'd give him antibiotics and he got some from the cupboard and gave them to me directly.
"I couldn't believe it when I got home and saw they were out of date. I was appalled.
"It's so lucky that I checked the label. It could have made him ill if I had given it to him."
A spokeswoman for Southampton City Primary Care Trust has blamed an "administrative error" for the mix-up.
She said: "Drug companies set expiry dates with plenty of leeway for their product not to cause any harm beyond the expiry date.
"We apologise for any distress the child and family may have been caused and we understand he is now doing well on his new medication.
"We will now be reviewing our procedures and would like to thank (Miss Cooper) for bringing this to our attention."
THE NHS WALK-IN CENTRE:
The centre in Howard's Grove was launched in October, 2001, and is open seven days a week until late in the evening.
No appointments are needed, and it offers a wide range of services, treatments and consultations.
It was one in a chain of units set up around the UK to help anyone whose busy lifestyle or practical circumstances meant they needed flexible opening hours for health checks and queries.
Staff offer treatment for minor injuries, illnesses and infections.
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