BEDMINSTER, NJ ( TheStreet) -- The early verdict on Amarin's ( AMRN) Vascepa launch: Slow. Early verdicts are not final verdicts, so no one is saying Amarin is doomed just two months into the launch of its prescription-grade fish oil pill. But right now, weekly Vascepa prescription growth is decelerating at a time when it should be doing the opposite. The number of patients going back for Vascepa refills is also lower than expected. Amarin shares fell 3.5% to $7.36 in Monday trading. The stock is trading just slightly higher than its 52-week low of $7.30 -- a reflection of investor concern about the trajectory of the Vascepa launch. Let's take a look at the prescription numbers, according to IMS Health. The latest figures are for the week ended March 15.
Total Vascepa prescriptions were 1,240, up 14% from the week of March 8. Numerically, Vascepa scripts are growing but the rate of growth has dropped for four weeks straight. Week-over-week script growth was 33% for the week ended Feb. 22, down to 14% for the week of March 15. There is no "right" rate of growth for a new drug launch but this early, investors definitely want to see accelerating script growth. Deceleration at this stage of the launch is an uneasy sign. Amarin is offering incentives to doctors and patients in the form of free Vascepa samples and discounts, which is likely affecting script numbers. How much can't be quantified. Refill rates can only be estimated from weekly IMS data, but again, the numbers don't work in Amarin's favor. For the week of Feb 15 (still really early in the launch), total (560) and new (555) Vascepa scripts were essentially the same. This means just about every patient was new on Vascepa. Fast forward one month to March 15. At this point, patients prescribed Vascepa in mid-February should be going back to their pharmacy for another bottle, so ideally, the the difference between total and new prescriptions should be close to 500 for the week of March 15. The actual difference between total and new Vascepa scripts for March 15 is 141, suggesting a good number of patients didn't come back for a refill. Amarin was forced to launch Vascepa on its own in late January after a marketing partner failed to materialize. -- Reported by Adam Feuerstein in Boston. Follow @AdamFeuerstein