Final answer:
The risk of administering cephalosporins to patients with a penicillin allergy includes the potential for cross-reactivity and an allergic reaction due to the similarity of their chemical structures, particularly the ß-lactam ring component.
Step-by-step explanation:
The risk when giving cephalosporins to patients with a reported penicillin allergy is the potential for a cross-reactivity allergic reaction. Although cephalosporins and penicillins are different, they both contain a ß-lactam ring, which is seen in allergic reactions to penicillin. The chemical structure of cephalosporins includes a six-member ring fused to the ß-lactam ring, which differs from the five-member ring in penicillins. However, this similarity in structure can still pose a risk for those with penicillin allergies, as about 5-10% of those patients may also react to cephalosporins.
When considering the use of cephalosporins in these patients, it is crucial to evaluate the severity of their penicillin allergy. Fatal reactions such as anaphylaxis can occur, although milder allergic reactions are more common. If the penicillin allergy was severe, then cephalosporins should generally be avoided. For milder reactions, cephalosporins may be used with caution or under medical supervision if deemed necessary and no alternatives are available.