| Research Brief|
| Fast Takes|
Ritonavir tablet formulation
Ritonavir (Norvir) tablets (100 mg) were recently approved by the U.S. Food and Drug Administration (FDA). The tablets are heat stable and do not require refrigeration.
The ritonavir tablets are not bioequivalent to the capsules. After a 100 mg ritonavir tablet, the ritonavir AUC was comparable to that of the capsule formulation, but the mean Cmax was 26% higher. Food decreases the bioavailability of the ritonavir tablets to a similar degree with both high-fat and moderate-fat meals. There are no pharmacokinetic comparisons of ritonavir tablets and capsules taken under fasting conditions.
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|Ritonavir tablets must be taken with food, though the type of food does not affect bioavailability.|
|Ritonavir tablets should be swallowed whole, and not chewed, cut in half, or crushed. |
|The tablets are stable at room temperature until the printed expiry date on the bottle (ritonavir capsules are stable at room temperature only for up to 30 days).|
|The ritonavir tablet formulation is now available in pharmacies; it is unclear how long the manufacturer intends to keep the capsule formulation on the market.|
Norvir [package insert]. North Chicago, IL: Abbott Labs; February 2010.
Maraviroc approved for initial therapy
In November 2009, the FDA approved maraviroc for use as initial therapy in the treatment of HIV infection, for persons infected with only CCR5-tropic virus. The FDA previously had approved maraviroc for treatment of patients with ARV-resistant strains of CCR5-tropic HIV. The new indication is based on a randomized double-blind noninferiority study of maraviroc vs efavirenz, each given in combination with zidovudine + lamivudine for treatment-naive adults.
At 96 weeks, similar rates of virologic suppression to <50 copies/mL were seen in the two treatment groups: 59% in maraviroc recipients and 63% in efavirenz recipients (at 48 weeks, 69% MVC, 68% EFV). These data are based on reanalysis of baseline tropism status using the enhanced sensitivity tropism assay (Trofile), and exclusion of 15% of subjects whose HIV was incorrectly identified as exclusively CCR5-tropic. CD4 increases also were somewhat higher in the maraviroc treatment group: 184 cells/µL vs 155 cells/µL.
The recommended dosage of maraviroc depends on coadministered drugs: see package label for specific information.
Treatment guidelines of the U.S. Department of Health and Human Services (most recently updated in December 2009) do not recommend maraviroc for use in initial therapy.
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Saquinavir/ritonavir and possible risk of abnormal heart rhythms
The FDA has announced that preliminary data suggest ritonavir-boosted saquinavir is associated with dose-dependent QT and PR interval prolongation in healthy adults. These conduction abnormalities may increase risk of arrhythmias, including torsade de pointes (from QT prolongation) and heart block (from PR prolongation).
Pending further investigation, the FDA recommends that saquinavir/ritonavir be avoided in patients:
|With a history of QT prolongation, cardiac conduction system disease, ischemic heart disease, cardiomyopathy|
|Who take Class 1A (eg, quinidine) or Class III (eg, amiodarone) antiarrhythmics, which prolong the QT interval|
|Who take other medications known to prolong the QT or PR interval (these are numerous, and include many antifungals, macrolides and fluoroquinolones, atazanavir, phenothiazines, and tricyclics); consult with a pharmacist before coadministering.|
Invirase (saquinavir): Ongoing safety review of clinical trial data. U.S. Food and Drug Administration MedWatch; February 23, 2010.
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