Nov 19 (Reuters) - The European Union"s drug regulator has issued advice on using Merck"s (MRK.N) COVID-19 pill for adults and began a review of a rival tablet from Pfizer (PFE.N) to help member states decide on quick adoption ahead of any formal EU-wide approval. In two separate statements on Friday, the European Medicines Agency (EMA) detailed efforts to advance use of the experimental but promising options, as infections and COVID-related deaths are rapidly rising in the region and forcing renewed lockdowns. read moreEMA said Merck"s COVID-19 tablet, Lagevrio, developed with Ridgeback Biotherapeutics, should be given early and within five days of first symptoms to treat adults who do not need oxygen support and are at risk of their disease worsening. It advised against treatment during pregnancy and for women who plan to or could get pregnant, while adding that breastfeeding must also be stopped around the time of using the pill, which is to be taken twice a day for five days. Drugs in the same class as Merck"s Lagevrio have been linked to birth defects in animal studies. The drugmaker, known as MSD outside the United States and Canada, has said animal testing shows its pill is safe, but the data have not been made public. EMA said it was studying available data on the Pfizer pill Paxlovid, days after the drugmaker sought U.S. approval, adding that a more comprehensive rolling review was expected to start ahead of any approval. It did not specify when that review would be. The EMA last month began a rolling review of the Merck pill and expects to conclude that evaluation by the end of the year. EMERGENCY USE Pfizer this week applied for U.S. emergency use authorisation of its tablet following data that showed the pill cut the chance of hospitalisation or death by 89% in adults who are at risk of their illness worsening. read more Merck"s pill, which was approved by Britain earlier this month, has been shown halve those chances when given early in the illness. While vaccines are central to the fight against the pandemic, regulators are looking at therapies, including the Pfizer and Merck pills, and EMA last week backed drugs from Regeneron-Roche (REGN.O), (ROG.S) and Celltrion (091990.KQ). Unlike the regulators in the United States, the world"s biggest pharmaceuticals market, the European Union"s EMA does not have emergency use procedures for treatments or vaccines, and often relies on a lengthier process for authorisation. But faced with rising COVID-19 cases, the EMA has offered its scientific expertise to nations that may need advice on early-use before any wider recommendations by the regulator. It has done that for the antibody-based treatment sotrovimab from GSK-Vir (GSK.L), (VIR.O), the generic steroid dexamethasone and Gilead"s (GILD.O)remdesivir antiviral. While reviews on COVID-19 pills are ongoing, the EU is also negotiating with Merck and Pfizer over possible contracts to supply their tablets, an official told Reuters last week, adding that talks with Merck were more advanced. Reporting by Pushkala Aripaka in Bengaluru; Editing by Arun Koyyur, Giles Elgood and Barbara