A woman from Spain suffered a potentially life-threatening allergic reaction after performing oral sex on her partner, who was taking penicillin — a first reported case of its kind.

The unidentified 31-year-old woman from Alicante began vomiting and was rushed to a hospital with suspected anaphylactic shock, according to the British Medical Journal Case Reports.

She told doctors at the Hospital General Universitari d’Alacant that she was allergic to the antibiotic but that she had not taken the medication before having oral sex.

It was later discovered that her partner had been on amoxicillin-clavulanic acid — a form of penicillin – because of an ear infection, and that the drug had entered his semen.

The woman began breathing normally after being treated with adrenalin and steroids – and recovered completely in a week.

“To our knowledge, this is the first case reported of a suspicion of amoxicillin-induced anaphylaxis in a woman after a sexual contact with a man who was taking the drug, we hypothesised an oral drug transfer through semen,” according to the British Medical Journal Case Reports.

Report lead author Susana Almenara urges anyone with known drug allergies to be aware of the potential risk and make sure they use condoms.

“We think that as clinicians, it is important to be aware of this phenomenon so as to inform and prevent potentially serious reactions in sensitized patients,” Almenara said.

“We also recommend condom use during treatment with drugs that can induce hypersensitivity responses in partners.”

There have been reports of people suffering allergic reactions to a drug transferred through sexual intercourse and kissing, but this was the first reported case through oral sex.

Although it is possible to be allergic to the proteins contained in semen, health providers thought it unlikely in this woman’s case since she had previously performed oral sex without problems.

Almenara said that one in 250 penicillin treatments resulted in an anaphylactic shock.