One of the most common forms of arthritis is gout.

The most recent drug approved for use in gout is Krystexxa.

The chemical name for Krystexxa is pegloticase. It is a drug that should be used only after other therapies have failed. Kyrstexxa is an enzyme that converts urate into allantoin. By doing this, Krystexxa converts the ingredient that accumulates in gout and causes organ damage, into an inert ingredient that is removed by the kidneys fairly easily.

Krystexxa is given intravenously at a dose of 8 mg every two weeks and rapidly reduces blood uric acid levels.

In clinical trials, pegloticase was given to patients with severe gout who had not responded to other conventional therapies. Seventy-one per cent of patients had tophi (large deposits of uric acid crystals under the skin.)

The average blood urate level was 10 mg/dL. The participants were mostly men (82%), with longstanding gout, who also had other medical conditions such as high blood pressure, heart disease, elevated lipids, and diabetes.

Several precautions regarding the use of this drug were apparent from the clinical trials.

First, patients with glucose-6-phosphate dehydrogenase deficiency (G6PD) should not receive this drug. That's because they can develop a life-threatening condition called methemaglobinemia.

Second, patients treated with this drug can expect an increased incidence of gout flares just as is seen with other anti-gout therapies.

Third, infusion reactions (reactions due to receiving an intravenous drug) were seen in a high percentage of patients. Forty-one per cent of patients receiving the drug every four weeks had an infusion reaction. A lower percentage was seen in patients getting the drug every two weeks.

Five per cent of patient had severe allergic reactions.

Worsening of congestive heart failure was also noted in a number of treated patients.

Antibodies to pegloticase were seen in about 92% of patients receiving the drug. This was significant since patients with high levels of antibody to the drug had less of a response to the drug and were also the ones who developed allergic reactions more readily.

The drug is given over a two hour period and patients need to be pre-treated with steroids and antihistamines. Patients need to be observed for at least an hour after infusion. Pegloticase is given every two weeks. The duration of treatment has not been determined yet.

Pegloticase should be reserved for patients with severe, refractory gout who are unable to get to a normal serum uric acid level with conventional therapy such as allopurinol or febuxostat (Uloric).

Measurement of a routine serum uric acid a few days before each infusion may be helpful in identifying patients who have lost a therapeutic response to pegloticase and may be at increased risk of infusion reactions and allergic reactions.

Personally, I'm not sure if I would use this drug because of the high incidence of potential side effects. Fortunately, nowadays, we identify gout patients earlier and most of the times, conventional therapies are effective.

The rheumatologist who has written the most about gout recently is John Sundy at Duke University. He is the author of the update on Krystexxa for the American College of Rheumatology. He is a proponent of the use of Krystexxa... but he probably sees many more severe cases than I do.