Top 20 PTCB Drug Interactions to Know!

Drug Interactions for the PTCB Exam

Questions on drug interactions are common on the PTCB exam. Of course, given the tens of thousands of potential drug interactions, students are not expected to know every single one.

That said, students are expected to know the most common drug interactions for the PTCB exam.

There are different kinds of drug interaction:

• Drug-drug interaction – where two medicines collide to produce either a desirable or adverse effect. For example – taking aspirin with NSAIDs increases the risk of bleeding.
• Drug-food interaction – where a medicine interacts with food or drink, again, that produces either a wanted or unwanted effect. For example – taking grapefruit juice with statins increases the risk of adverse effect such as muscle pain and rhabdomyolysis.
• Drug-disease interaction – where a medicine has a harmful effect on the progress of a disease. For example – beta-blockers can assist patients with heart disease, but they may worsen asthma in the same patient.

In the table below, we review all three kinds of drug interactions for the PTCB exam.

Drug interactions are not random. There is always a mechanistic or clinical reason for the interaction to take place. And as we alluded to earlier, not all drug interactions are clinically negative outcomes.

For example – ritonavir is a drug used in the treatment of HIV/AIDS. However, ritonavir not used to directly treat the condition, but instead it is used to inhibit liver enzymes that metabolize other HIV drugs, such as protease inhibitors. This means that – when protease inhibitors are taken with ritonavir – a lower dose of protease inhibitors can be used to achieve the same clinical effect, whilst also reducing the risk of side effects. Ritonavir is used to “boost” the effects of other protease inhibitors.

A second example is antihistamines. First-generation antihistamines are likely to cause sedation. For many patients, this is a desirable effect as they may have trouble sleeping due to their allergy symptoms. Second-generation antihistamines, such as fexofenadine, do not cross the blood-brain barrier and so do not cause this sedative effect.

These are the kinds of drug interactions that get examined on the PTCB test.

Must-Know Drug Interactions!

Below, we have put together a neat table on the most common drug interactions for the PTCB exam to know.

Of course, this is not a complete list – there are many other drug interactions that students should learn. But this is a convenient starting point if you are struggling to get to grips with drug interactions.

As always, the more you understand the pharmacology of medicines, the greater appreciation you have for why specific drug interactions take place. It demystifies the subject – making interactions appear less random and offering a structure that you can easily remember.

If you would like access to our complete study of drug interactions, take a few moments to become a registered member of PTCB Test Prep. There, you also have access to PTCB practice test questions to help you review your knowledge of must-know drug interactions.