http://www.medschat.com/Discuss/pink-and-white-pill-with-2131-on-one-side-192478_s2.htm I found a pink and white capsule marked zenith 100mg with he numbers 2131 on the bottom. I think it may have been from my dog. - Filed in Nitrofurantoin en-us Copyright 2013 MedsChat.com. All Rights Reserved. Thu, 6 Aug 2009 17:02:18 GMT 60 http://www.medschat.com/images/mc_logo.png http://www.medschat.com/Discuss/pink-and-white-pill-with-2131-on-one-side-192478_s2.htm http://www.medschat.com/Discuss/pink-and-white-pill-with-2131-on-one-side-192478_s2.htm#r_136991 http://www.medschat.com/Discuss/pink-and-white-pill-with-2131-on-one-side-192478_s2.htm#r_136991 The pill you described is <a href="http://www.medschat.com/Drugs/Nitrofurantoin/" target="_blank">Nitrofurantoin</a> macrocrystals (100 mg). <br/> <br/> <a href="http://www.medschat.com/Drugs/Nitrofurantoin/" target="_blank">Nitrofurantoin</a> is an antibiotic that is only clinically proven for use against E. coli or Staph. saprophyticus; but is often used in treating urinary track infection. <br/> <br/> You can learn more information about this drug, by visiting the link below... <br/> <a href="http://www.medschat.com/wiki/Nitrofurantoin/" target="_blank">http:/&#173;/&#173;www.medschat.com/&#173;wiki/&#173;Nitrofurantoin/&#173;</a> <br/> <br/> If you have any more questions or concerns, please post back and I will be happy to help you. Thu, 6 Aug 2009 17:02:18 GMT