The principal side-effects of the penicillins are;
- hypersensitivity resulting in urticaria, fever, joint pains and occasionally anaphylaxis. The hypersensitivity is related to the basic penicillin structure and therefore a patient hypersensitive to one penicillin will be hypersensitive to all. Note that it is important to clarify the history in penicillin hypersensitivity - the patient may have a different understanding of the word allergy to the physician.
- encephalopathy which occurs with high doses or normal doses in people with renal failure. For this reason the penicillins cannot be given intrathecally.
- diarrhoea with oral therapy especially with ampicillin and its derivatives which may also cause pseudomembranous colitis.