PTCB Guide to Bisphosphonates!

Introduction to Bisphosphonates

With over 15 million prescriptions each year, bisphosphonates are among the most widely prescribed drug classes in the United States. Here, we review the fundamental facts you need to know about these essential medicines.

Bisphosphonates are routinely tested on the PTCB exam. To pass PTCB questions on this topic, students should know:

• Indications of bisphosphonates – what they are used to treat
• How to identify a bisphosphonate
• Mechanism of action
• Prominent side effects and drug interactions
• Common brand names

In this PTCB guide to bisphosphonates, we attempt to cover all five of these topics.

First, we begin with indications.

Bisphosphonates are first-line drugs used to treat a wide range of bone disorders, including:

• Osteoporotic fragility fractures
• Paget’s disease of bone
• Certain cancers – where they are used to prevent pathological fractures

Bisphosphonates are easily identifiable drugs, too. They all contain either of the following two suffixes – –dronate or –dronic acid.

Bisphosphonate	Brand Names
Alendronate	Fosamax Binosto
Pamidronate	Aredia
Zoledronic acid	Reclast Zometa
Risedronate	Actonel Atelvia

With these medicines in mind, let’s take a few seconds to learn more about how these drugs work – namely, their mechanism of action.

Mechanism of Action

Bisphosphonates act on bone – where they inhibit cells called osteoclasts.

The function of osteoclasts is to break down bone, an essential function for the bone maintenance and repair. However, in diseases such as osteoporosis, osteoclasts can play a pathological role and so, by intervening in how osteoclasts work, it can reduce bone loss and improve bone mass.

Bisphosphonates have a similar structure to naturally occurring pyrophosphate and so are readily absorbed into bone. There, bisphosphonates accumulate in osteoclast cells – triggering cell death. Fewer osteoclast cells lead to reduced bone turnover and an increase in bone mass and reduction in bone loss.

Side Effects

One of the most common side effects of orally administered bisphosphonates is esophagitis – or inflammation of the esophagus. To reduce the risk of esophagitis, patients are counseled to take bisphosphonates in a more cautionary manner compared to other drug classes.

Patients are counselled to take these drugs whilst remaining upright, first thing in the morning and 30 minutes before food/medicines and taken with a full glass of water. Patients should remain upright for 30-minutes post-administration. By taking these steps, the risk of esophagitis or irritation to the esophagus, is substantially reduced.

Other side effects of bisphosphonates include:

• Hypophosphatemia – low blood phosphorus levels
• Osteonecrosis of the jaw – a rare effect associated with high-dose IV therapy
• Atypical femoral fracture
• Headache
• Constipation
• Nausea

Bisphosphonates may also be associated with other side effects not listed in this guide.

Food and Drug Interactions

One of the most important food-drug interactions is how bisphosphonates interact with calcium. Put simply, these drugs bind calcium.

By binding calcium, absorption is reduced. Given that calcium is rich in foods such as milk and other dairy products or supplements, these should be avoided whilst taking bisphosphonates.

Similarly, antacids and iron also reduce bisphosphonate efficacy.

That concludes our PTCB guide to bisphosphonates – an important drug class that routinely gets tested on the PTCB exam. Here we have reviewed indications, drug and common brand names, mechanism of action, side effects, and notable food and drug interactions.

By committing these pharmacy facts to memory, you will ace this topic should it appear on the day of your exam.