When
drugs are administered to some patients, a severe adverse reaction, such
as collapse, may occur. This may be caused by an allergy to the drug
administered, e.g. penicillin, or interaction with another drug which the
patient is already taking for medical reasons. To prevent these
undesirable effects, careful study of a case history must always be
made before any drugs are used. If it is found that a drug allergy
exists, or the patient is taking drugs prescribed by the doctor, or taking
nonprescription drugs for self-medication, this information must be
recorded on the patient’s chart, regularly updated and appropriate
precautions taken.