Adds sector context, analyst comment in paragraphs 2 and 4

By Kashish Tandon

May 22 (Reuters) - Sun Pharmaceutical Industries' SUN.NS fourth-quarter profit edged past estimates, helped by robust demand for its specialty drugs, although increasing cost pressures squeezed margins and sent shares lower on Friday.

The drugmaker's shares fell as much as 3.1% after results before closing 2.5% lower for the day.

Growing costs, especially in the research and development category, as per analysts, pushed up overall expenses 16% to 115.19 billion rupees.

This ate into core margins, which contracted to 27.1% from 28.7% last year. Shrikant Akolkar, a pharma analyst with Nuvama Institutional Equities, called the cost pressure and margins "disappointing".

Consolidated net profit for the March quarter rose 26.2% to 27.14 billion rupees ($283 million), edging past analysts' estimate of 27.12 billion rupees, according to LSEG data.

The drugmaker's push towards boosting its specialty therapies such as dermatology, oncology and obesity helped its bottomline and also allowed it to outperform rivals Dr Reddy's REDY.NS and Cipla CIPL.NS, which missed March-quarter estimates.

Revenue in the specialty drugs segment rose 20% to $354 million - accounting for nearly a quarter of total sales - helped by 14.8% growth in India, its biggest market. U.S. sales fell 1.1%.

The earnings come weeks after Sun Pharma struck its most ambitious deal yet: an $11.75 billion all-cash offer for U.S.-based Organon & Co OGN.N, the largest acquisition ever by an Indian pharmaceutical company.

($1 = 95.9125 Indian rupees)