Two companies focused on infectious disease successfully completed IPOs this week, ending a drought in life sciences initial public offerings since Zoetis debuted at the end of January.

Watertown, Massachusetts-based Enanta Pharmaceuticals, developing a pipeline of novel small molecule drugs targeting hepatitis C, completed a $54 million offering selling 4 million shares at $14. The offering came at the bottom of its expected $14 to $16 range.

Existing investors played a critical role in getting the company across the IPO goal line as they, along with other insiders, committed to purchase about one third of the offering. Existing stockholders, certain affiliates, and two of the company’s directors agreed to purchase an aggregate of 1,341,786 shares.

Enanta is developing multiple inhibitors to prevent replication of the HCV virus that can be used in combination with other drugs. Its lead product candidate, a NS3 protease inhibitor known as ABT-450, is in late-stage trials. The company partnered with AbbVie to develop and commercialize that drug and is partnered with Novartis to develop an early-stage candidate, EDP-239, targeting the NS5A protein.

In addition to working on additional drugs that inhibit other functions of the HCV virus, Enanta is also developing a new class of antibiotics, called bicyclolides, for the treatment of multi-drug resistant bacteria, with a current focus on developing intravenous and oral treatments for hospital and community MRSA.

JP Morgan Securities and Credit Suisse Securities are acting as joint book-running managers for the offering. Leerink Swann and JMP Securities are acting as co-managers. Enanta is trading under the symbol “ENTA.” It ended the week of March 22 at $16.81, up 20 percent.

Tetraphase Pharmaceuticals, also based in Watertown, Massachusetts and focused on infectious disease, competed a $75 million offering. The company sold a little more than 10.7 million shares at $7. The company originally planned to sell 6.8 million shares at between $10 and $12 but to complete the IPO it had to cut the price and upsize the number of shares. Existing investors and insiders committed to purchasing up to a third of the offering at the IPO price.

Tetraphase is a clinical-stage biopharmaceutical company developing novel antibiotics for serious and life-threatening multi-drug resistant infections. The company’s lead product candidate, eravacycline, recently completed a successful mid-stage clinical trial. It is a fully synthetic tetracycline derivative being developed as a broad-spectrum intravenous and oral antibiotic for use as a first-line treatment for multi-drug resistant infections, including multi-drug resistant Gram-negative infections.

The company is finalizing a late-stage clinical program for eravacycline in complicated intra-abdominal infections. It also plans to conduct a late-stage trial of eravacycline for the treatment of complicated urinary tract infections.

Tetraphase is trading under the symbol “TTPH.” It ended the week of March 22 at $7, unchanged from its initial offering price. Barclays and BMO Capital Markets acted as joint book-running managers. Stifel, JMP Securities, and Needham & Company acted as co-managers for the offering.