Drug regulatory authorities in the United States have updated the product labelling of the protease inhibitor Kaletra (lopinavir/ritonavir), warning that it should not be prescribed to individuals with either heart rhythm problem or any underlying heart problems.
The update was issued by the Food and Drug Administration (FDA) on 6 April 2009, after reports that treatment with Kaletra could cause some types of irregularities in the rhythm of the heart.
The first of these is prolonged PR interval. This involves lengthened electrical impulses in the atria, two of the four chambers of the heart. This can lead to a serious cardiac problem called atrioventricular block.
Atazanavir (Reyataz) can also cause this abnormality in heart rate, as can a number of other drugs including calcium channel blockers, beta-adrenergic blockers, and digoxin. The FDA warns that caution is required if any of these drugs are used with Kaletra. Caution is especially important if any of the drugs are, like Kaletra, processed by the body using the CYP3A pathway in the liver.
Treatment with Kaletra has also been associated with another irregularity in heart rhythm called QT interval prolongation. However, it has not been established that Kaletra is the cause. Nevertheless, the FDA is advising that the use of Kaletra should be avoided in patients with congenital long QT syndrome, as well as by individuals with low levels of potassium in the blood (hypokalemia) and by those taking other drugs that prolong QT interval.
Dr Mark Nelson of the Chelsea and Westminster Hospital told aidsmap.com that these revisions were "not too big a deal” and noted that similar heart rate problems had been associated with “atazanavir and possibly other protease inhibitors.” Should irregularities in the rhythm of the heart develop, however, he recommended that these should be taken very seriously.