Factors contributing to the occurrence of drug interactions

1. Multiple pharmacological effects

- Combined therapy: phenothiazines antipsychotic, tricyclic antidepressant and
antiparkinson employed in some patients. Despite the common Anticholinergic
activity but primary action is different.

2. Multiple prescribers

- Seeing many prescribers causes consequences while different drug group can
involve drawbacks. E.g. Antihistamines and opioid analgesic / antianxiety agent.

3. Use OTC products

- Many patients hide the use of OTC while possible for a multiple drug used in short
period may have the same active ingredient but work differently then provoke side
effects. Usually when using prescribe drug with OTC (aspirin, antacids and
decongestant) and herbal.....etc assessed having incompliance to patients.

4. Patient noncompliance

- Patient used to discontinue the mediation rule due to forgetting or confusion. In
same case of forgetting patients used to double the dosage. The worse is when patients
thought to relieve their pain using two tablets instead of one prescribed by the doctor.

5. Drug abuse

- The specificity of drug played a great role to the quantification level. E.g.
Anticoagulant, anti diabetic agent and antihypertensive are specific to prothrombin.
Whilst antipsychotic and analgesics are difficult to quantify the level.