Most of the incidences of adverse drug reactions may be due to:
1. Dispensing and Medication
administration errors: In many cases, physicians
overprescribe a patient. These prescriptions generally contain potent antibiotics. Similarly, self-medication by the patient
leads to overuse or misuse of the drugs leading to an adverse drug
reaction.
2. Failure to set therapeutic endpoint:
Potent medicines when abused or misused may cause adverse effects or even
death. Failure of the physician to set the therapeutic endpoint is the reason
for adverse reactions to drugs like; digitalis,
corticosteroids, diuretics, etc.
3. Bioavailability differences:
Differences in the bioavailability from different formulations or brands of the
drug may also cause adverse drug reactions.
The difference in bioavailability from various brands of digoxin,
phenytoin, and oxytetracycline has resulted in toxicity in some cases.
4. Patient factors:
Physiological and disease status of the patient affects adverse drug reactions.
Very young and old patients are more susceptible to adverse drug reactions as
compared to adults. This is due to a marked difference in the metabolism and
excretion pattern at this age. Similarly, patients with renal and hepatic
damage or dysfunction are prone to adverse reactions due to disturbed
metabolism and excretion of drugs. Adverse drug reactions may be due to the inherited
absence or deficiency of certain specific enzymes.