**14.16. Adverse drug reactions**

Pharmacological formulations are potentially harmful to the individuals taking the drugs. There is need to ascertain the safety of new drugs before allowing them to be marketed. The following figures highlight the magnitude of the problem: ~ 10 – 20% of hospital‐ ized patients suffer adverse drug reactions, while 0.3 – 5.0% inpatients admissions and ~ 0.3% deaths in hospital are due to adverse drug reactions. Adverse drug reactions can be classified into two main categories: They may be dose related or non dose related with each being short-term or long-term.

#### **14.17. Dose related adverse reactions**

Adverse drug reactions can occur because of the changes in the systemic availability of a formulation. For instance, the change of excipients in phenytoin capsules from CaSO4 to lactose leads to high availability and hence adverse drug reactions. Sometimes, adverse drug reactions can occur due to the presence of contaminants like bacteria if quality con‐ trol breaks down. Out-of-date formulations may also cause adverse drug reactions be‐ cause of degradation products arising from the drug e.g. outdated tetracycline may cause Faconis Syndrome (a type of rickets) because of the transformation product,epiandrote‐ tracycline. Dose related adverse reactions may also arise from pharmacokinetic variations in the individuals taking the drug. Pharmacokinetic variations may also arise due to hep‐ atic disease like advanced cirrhosis which lowers the clearance of drugs such as pheny‐ toin and morphine. The pharmacological variations could be environmental such as diet or smoking, while others are genetic.
