Afrezza is "modestly effective" at reducing blood glucose and its long-term safety is unknown, according to a review of the inhaled insulin published this week by The Medical Letter, an independent, non-profit organization which evaluates prescription drugs.

MannKind (MNKD) developed Afrezza and secured U.S. approval last June. The rapid-acting inhaled insulin, intended for use during mealtime by Type 1 and Type 2 diabetics, was launched commercially one month ago by MannKind's marketing partner Sanofi (SNY).

The Medical Letter is influential with doctors and other healthcare professionals because the organization doesn't accept industry money and publishes drug information that aims to be an "unbiased consensus of scientific experts."

The two-page review of Afrezza in the March 2 issue of The Medical Letter, available only to subscribers, describes the efficacy and safety data from the clinical trials included in the product's FDA-approved label and places Afrezza in the context of other rapid-acting mealtime insulins, all of which require injections. The review concludes: "Afrezza, the only inhaled formulation of insulin currently available in the US, appears to be only modestly effective in reducing HBA1c. Cough is a common side effect and the long-term pulmonary safety of inhaling insulin is unknown."

The Medical Letter's review also includes a pricing chart showing Afrezza to be more expensive than the competing injectable insulins marketed by Novo Nordisk (NVO) (Novolog), Eli Lilly (LLY) (Humalog) and Sanofi (Apidra.)

Doctors have written 290 prescriptions for Afrezza during the first four weeks of the launch, according to Symphony Health.

Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.

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