 Pyrazolones are amongst the oldest synthetic pharmaceuticals, starting with the introduction of antipyrine (phenazone) in 1880s.The compounds generally act as analgesics and include dipyrone (Metamizole), aminopyrine, ampyrone, famprofazone, morazone, nifenazone, piperylon and propyphenazone, aminophenazone.Of these dipyrone is perhaps the most widely used.