Well absorbed macrocrystalline is absorbed more slowly due to slower dissolution (causes less GI distress) Distributionīody tissues (except plasma) metabolize 60% of drug to inactive metabolites Excretion Pharmacokinetics/Pharmacodynamics Absorption The broad-based nature of this mode of action may explain the lack of acquired bacterial resistance to nitrofurantoin, as the necessary multiple and simultaneous mutations of the target macromolecules would likely be lethal to the bacteria. Nitrofurantoin is bactericidal in urine at therapeutic doses. Nitrofurantoin is reduced by bacterial flavoproteins to reactive intermediates that inactivate or alter bacterial ribosomal proteins leading to inhibition of protein synthesis, aerobic energy metabolism, DNA, RNA, and cell wall synthesis.