COX-2 inhibitors

Cyclo-oxygenase-2 enzyme (COX-2) inhibitors - an alternative type of NSARs

The latest weapon in the arsenal of medication against pain caused by arthritis is a new class of NSARs called COX-2 inhibitors. Compared to standard NSARs, these prescription drugs carry a lower risk of bleeding and other gastrointestinal problems.

This is good news for 30 percent of NSAR users, who are estimated to have long-term gastrointestinal problems as a consequence of taking older drugs, and for 10 percent of users who had been forced to stop using NSARs due to unpleasant side effects.

How it works

All NSAR drugs relieve pain in basically the same way - by blocking an enzyme called cyclo-oxygenase or COX. As it was mentioned, that enzyme produces prostaglandins, important chemical compounds which perform many different functions in the body. In 1991, researchers discovered that COX appears in two forms: COX-1 - which produces important prostaglandins that keeps the gastrointestinal system covered with its protective mucous membrane - and COX-2, which is responsible for the synthesis of those prostaglandins which play an important role in causing pain and inflammation in the body. Because of that, blocking COX-1 enzymes was considered bad.
A standard NSAR drug has a crude and simple approach towards COX enzymes: it relieves pain and inflammation by blocking COX-2, but it unfortunately also blocks COX-1, which makes your gastrointestinal system sensitive to irritation, which can cause ulcers and bleeding. This is where COX-2 inhibitors, NSARs developed exclusively to act only on COX-2 enzymes, come into action.

What is true, what is not

In 1996, meloxicam became the first COX-2 inhibitor given the approval for use in the UK. Celecoxib was approved in 2000. In the near future there may appear additional COX-2 inhibitors. Even though COX-2 inhibitors offer a different way of treating arthritis, it is important to keep the following in mind:

  1. Many research studies comparing COX-2 inhibitors to standard NSARs have shown that COX-2 inhibitors are not more efficient against pain and inflammation. If you are taking a standard NSAR which is working well and alongside that is not causing any problems, switching to one of the COX-2 inhibitors does not necessarily mean an improvement for you.
  2. Even though COX-2 inhibitors may cause less gastrointestinal problems than standard NSARs, it is not true that they come without risks. Clinical trials have shown that in people taking COX-2 inhibitors, ulcers, irritation and other problems still appear.
  3. COX-2 inhibitors are much more expensive than standard NSARs, which can prove to be of importance since general practitioners are being increasingly encouraged to choose drugs that are most economic.
  4. Unlike Aspirin, COX-2 inhibitors do not prevent blood clotting and in that way do not help prevent heart attacks or strokes, and may actually carry an increased risk for those people already suffering from heart conditions. Such people should not take COX-2 inhibitors.

People who should be taking COX-2 inhibitors but are allergic to sulpha drugs should avoid celecoxib, which can cause similar allergic reactions. Meloxicam does not cause such reactions.

Are COX-2 inhibitors the drug for you?

The following questions may help you in discovering whether you are eligible to be a candidate for treatment by COX-2 inhibitors:

  1. Are you suffering from a heart condition or have an increased risk of developing one? (your risk is increased in the case you are suffering from diabetes, high blood pressure or high cholesterol levels) If your answer is "YES", COX-2 inhibitors are not for you. If the answer is "NO", read on.
  2. Are you suffering, or have suffered in the past, from an ulcer?
  3. Have you previously had difficulties with standard NSARs?
  4. Are you currently taking corticosteroids? (People taking prednisolone or another corticosteroid carry an increased risk of gastrointestinal bleeding)

If you have answered "yes" to one or several questions of the three above, treatment by COX-2 inhibitors may be your solution.

According to research published in July 2000 in the Annals of Internal Medicine magazine, COX-2 inhibitors celexoxib and meloxicam are no safer than standard NSARs when it comes to jeopardizing kidney function in healthy elderly people. If you are older than 65, and are regularly taking celexoxib, meloxicam or any other NSAR for arthritis, ask your physician to refer you to blood tests with which you could monitor your kidney functions.

Different NSARs, different risks

In the UK, one to two percent of all patients taking NSARs had been admitted to a hospital due to the harmful effects of the drugs to the gastrointestinal system. It has also been estimated that between 2.500 and 3.000 cases of deaths every year can be be attibuted to taking these drugs. Despite that, the use of NSARs keeps growing so one might say that more enthusiastic consumers take risks. Research has shown that some NSAR drugs have a higher chance of causing serious problems than others.

Low risk

** celexoxib etodolac ibuprofen

** meloxicam nabumetone

Medium high risk

diclofenac

ketoprofen

naproxen

High risk

acetylsalicylic acid*

diflunisal

fenbufen

indometacin

meclofenamate

piroxicam

* More than three 325 mg tablets a day

** Should not be taken by people with a heart condition or a risk of developing one

The status od meloxicam as a COX-2 drug under doubt in the US

In the US, the Food and Drug Administration has approved meloxicam as an NSAR in 2000, but it opposed its categorization into COX-2 inhibitors, being as it is claimed to be selectively inhibitive of COX-2 in therapy doses. According to the opinion of the FDA, drugs marked as COX-2 inhibitors must work exclusively on COX-2 - even in doses twice higher than their therapy doses - and meloxicam does not fall under that standard. In the UK meloxicam was approved as a COX-2 inhibitor in 1996. Comparative research has clearly shown that it causes fewer side effects than standard NSARs.

Source: Excerpt from book "Living with Arthritis"

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