[4] Some side effects require treatment to correct potentially serious and sometimes fatal reactions to penicillin.
Research has suggested that having penicillin allergy incorrectly noted in the medical records can have negative consequences.
[8] A small proportion of people who are allergic to penicillins also have similar cross sensitivities to other antibiotics such as cephalosporins.
Those medications that may cause a cross sensitivity reaction are: carbapenems, ampicillin, cefazolin, cephalosporins and cloxacillin.
For this purpose, clinical risk assessment tools have been developed such as "PEN-FAST": Patients scoring 4 or greater have a high (50%) probability of testing positive for penicillin allergy.
[14][needs update] When penicillin is used at high doses hypokalemia, metabolic acidosis, and hyperkalemia can occur.
[20] Destruction of the normal protective flora of beneficial bacteria can occur in dogs and horses.
[21][22] Dogs may have side effects that include: joint pain, loss of appetite, vomiting, flatulence (intestinal gas), fungal infections and digestive problems.
[citation needed] Cats and dogs have had adverse reactions to intravenous penicillin that include: hypothermia, pruritus, hypotension, tremors, seizures, blindness, vocalization, agitation, cardiac arrest and transient loss of vision.