Piper Jaffray analyst Joshua Schimmer downgraded MannKind to Underweight from Neutral and cut his price target for shares to $1.50 from $4. Underweight is Piper's equivalent of a sell rating. Shares of MannKind closed yesterday up 19c to $4.07. Prescription trends for the company's inhaled insulin Afrezza "have been lackluster to say the least," Schimmer tells investors in a research note. Afrezza is being viewed as a "very niche product," the analyst writes after speaking to five primary care and endocrinology specialists with high volumes of diabetes patients. Schimmer believes MannKind has "vastly over-estimated" the commercial potential for Afrezza. He notes his new price target assumes 60% downside from current share levels.