Mirum Pharmaceuticals enters the post-earnings window with a sharply upgraded growth story — Q1 sales of $159.9M beat estimates by 7%, and management lifted full-year guidance to $660M–$680M, well above the consensus of $644.9M at the time of release.
The revenue beat is the headline. Adjusted EPS came in at -$0.50, short of the -$0.35 estimate, but the Street's reaction to biotech misses on the bottom line is almost always governed by the top line when a company is still investing through profitability. GAAP EPS was a wide miss at -$13.43, though this appears to reflect non-cash charges rather than cash burn worsening — the Q4 2025 report showed the net loss narrowing sharply year-over-year, to just $5.7M versus $23.8M a year prior. Revenue grew 55% year-over-year in 2025, and the Q1 2026 result keeps that trajectory very much alive. The stock gained 12.6% on the week heading into the print, having already reflected considerable optimism — and the guidance raise suggests that optimism was well-founded.
Short positioning tells an interesting supplementary story here. Shorts represent a meaningful 15.5% of the free float — elevated for a biotech with a clear commercial product — but the direction of travel has recently shifted. Short interest has climbed about 6.6% over the past month, even as the stock rallied hard, suggesting some bears were building into the print rather than cutting exposure. Over the past week, however, shorts pulled back slightly, trimming 0.07% of the float ahead of the result. Borrow conditions remain conspicuously easy: availability is wide, cost to borrow is just 0.51% annualised, and that rate has eased roughly 8% over the past month. With borrow this cheap, the elevated short interest reflects a genuine fundamental disagreement rather than a technically stressed position. The ORTEX short score of 67.6 is moderate-to-elevated, but it has actually edged lower over the past week as the rally unfolded, consistent with incremental short covering.
The options market reflected a meaningful pivot over the week. The put/call ratio finished at 0.98 — near parity — down from above 1.16 for most of late April. Earlier in April, the ratio was running as low as 0.07–0.08, an extreme call-skewed reading that preceded the run-up in price. The current reading is now above its 20-day average of 0.77, though the z-score is a modest 0.49, so this does not yet signal outright defensive positioning. The shift from aggressive call-buying toward something closer to balance likely reflects a natural reset after a 12%-plus weekly gain, with traders switching from directional longs into more measured hedges around an earnings release.
Analyst activity has been uniformly constructive. Every firm that updated in the past two weeks raised its price target. Morgan Stanley, a bellwether, lifted its target from $130 to $140 on May 5 while maintaining Overweight. HC Wainwright went further, raising to $175 from $150 on May 4, the most aggressive target on the Street. Baird, Stifel and TD Cowen all moved targets higher in the preceding days. The consensus mean price target of $138 already sat above the stock price going into the print; with the stock at $105.81 and guidance now raised, the gap between current price and Street targets has closed considerably on the upside. The bull case rests on Livmarli and brelovitug addressing rare liver diseases with no approved alternatives — a structurally attractive unmet-need story. The bear case centres on whether pipeline readouts beyond those two products, including the BLOOM study for MRM-3379 and Volixbat VISTAS, can actually move the needle on a stock that already carries significant premium.
Insider activity from March was entirely sells — the CEO sold roughly $3.8M worth of stock at ~$92 on March 16, alongside the President, CFO and CMO. These look like planned-sale dispositions executed near a former high, and all were accompanied by equity award grants to the CEO a few days earlier. The net 90-day insider figure is positive at $19.3M in value terms, driven by the awards, but the open-market sales by senior management are worth noting for those tracking sentiment at the top. The EASL Congress in Barcelona at the end of May is the next meaningful clinical forum for the company, where liver-disease data could draw further investor attention.
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