Kidney issues don't look like they'll keep Gilead Sciences' (Nasdaq: GILD) Quad HIV drug off the market -- an advisory panel recommended approving the drug by a 13-1 margin -- but they might result in extra monitoring for kidney complications once the Quad is on the market.

Normally adding tests, or other hoops for doctors and patients to jump through, can decrease prescription rates. The obesity-drug battle between VIVUS' (Nasdaq: VVUS) Qnexa and Arena Pharmaceuticals' (Nasdaq: ARNA) lorcaserin might come down to what hoops (if any) the FDA potentially adds to each drug: pregnancy tests for Qnexa and heart tests for lorcaserin.

But the Quad treats HIV patients, who have a different mentality than patients with other chronic diseases do. They have to see the doctor regularly and get routine blood draws to measure their viral levels. In addition to a blood test, a urine analysis might be required to check kidney function, but that isn't much of an added burden.

The Quad's biggest competition will be Atripla, which Gilead also sells, but the biotech would rather see patients start on the Quad because it owns all four components of the drug; Gilead has to share Atripla revenues with Bristol-Myers Squibb (NYSE: BMY), which contributed one of the components of the drug.

The extra kidney test might make it harder to get doctors to prescribe the Quad over Atripla, but the Quad has other advantages, including fewer abnormal dreams, less trouble sleeping, and less dizziness compared with Atripla. Kidney issues are obviously more serious than neuropsychiatric side effects, but tolerability is a big issue with HIV drugs. My guess is that the Quad has a slow start as doctors try it on a few patients, but that the sales will accelerate once doctors gain confidence with the drug. The kidney issue is fairly rare, after all.

The Quad will also compete against cocktails of drugs, especially those that contain Abbott Labs' (NYSE: ABT) Norvir and/or Merck's Isentress, since two of the components of the Quad are in the same classes as those drugs. But having all the drugs in one convenient once-daily pill should make it easy to compete with individually prescribed cocktails. It's one of the reasons Atripla, a three-in-one combo, has been so successful, after all.

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