Preparation
Sodium nitroprusside can be synthesized by digesting a solution of potassium ferrocyanide in water with nitric acid, followed by neutralization with sodium carbonate:

  
    
      
        
          
            K
            
              4
            
            
              
            
          
          
            [
            Fe
            
              
                (
                CN
                )
              
              
                6
              
              
                
              
            
            ]
          
          +
          6
          
          
            HNO
            
              3
            
            
              
            
          
          ⟶
          
            H
            
              2
            
            
              
            
          
          
            [
            Fe
            
              
                (
                CN
                )
              
              
                5
              
              
                
              
            
            
              (
              NO
              )
            
            ]
          
          +
          
            CO
            
              2
            
            
              
            
          
          +
          
            NH
            
              4
            
            
              
            
          
          
            NO
            
              3
            
            
              
            
          
          +
          4
          
          
            KNO
            
              3
            
            
              
            
          
        
      
    
    {\textstyle {\ce {K4[Fe(CN)6] + 6 HNO3 -> H2[Fe(CN)5(NO)] + CO2 + NH4NO3 + 4 KNO3}}}
  

  
    
      
        
          
            H
            
              2
            
            
              
            
          
          
            [
            Fe
            
              
                (
                CN
                )
              
              
                5
              
              
                
              
            
            NO
            ]
          
          +
          
            Na
            
              2
            
            
              
            
          
          
            CO
            
              3
            
            
              
            
          
          ⟶
          
            Na
            
              2
            
            
              
            
          
          
            [
            Fe
            
              
                (
                CN
                )
              
              
                5
              
              
                
              
            
            
              (
              NO
              )
            
            ]
          
          +
          
            CO
            
              2
            
            
              
            
          
          +
          
            H
            
              2
            
            
              
            
          
          O
        
      
    
    {\textstyle {\ce {H2[Fe(CN)5NO] + Na2CO3 -> Na2[Fe(CN)5(NO)] + CO2 + H2O}}}
  Alternatively, the nitrosyl ligand can be introduced using nitrite:

  
    
      
        
          
            
              [
              Fe
              
                
                  (
                  CN
                  )
                
                
                  6
                
                
                  
                
              
              ]
            
            
              4
              −
            
          
          +
          
            H
            
              2
            
            
              
            
          
          O
          +
          
            NO
            
              2
            
            
              −
            
          
          ⟶
          
            
              [
              Fe
              
                
                  (
                  CN
                  )
                
                
                  5
                
                
                  
                
              
              
                (
                NO
                )
              
              ]
            
            
              2
              −
            
          
          +
          
            CN
            
              −
            
          
          +
          2
          
          
            OH
            
              −
            
          
        
      
    
    {\textstyle {\ce {[Fe(CN)6]^4- + H2O + NO_2^- -> [Fe(CN)5(NO)]^2- + CN- + 2OH-}}}

Other uses
Sodium nitroprusside is often used as a reference compound for the calibration of Mössbauer spectrometers.
Since PGI2 is primarily produced in a nucleated endothelial cell, the COX inhibition by NSAID can be overcome with time by increased COX gene activation and subsequent production of more COX enzymes to catalyze the formation of PGI2. In contrast, TXA2 is released primarily by anucleated platelets, which are unable to respond to NSAID COX inhibition with additional transcription of the COX gene because they lack DNA material necessary to perform such a task. This allows NSAIDs to result in PGI2 dominance that promotes circulation and retards thrombosis. In patients with pulmonary hypertension, inhaled epoprostenol reduces pulmonary pressure, and improves right ventricular stroke volume in patients undergoing cardiac surgery. A dose of 60 μg is hemodynamically safe, and its effect is completely reversed after 25 minutes. No evidence of platelet dysfunction or an increase in surgical bleeding after administration of inhaled epoprostenol has been found. The drug has been known to cause flushing, headaches and hypotension. Synthesis
Biosynthesis
Prostacyclin is produced in endothelial cells, which line the walls of arteries and veins, from prostaglandin H2 (PGH2) by the action of the enzyme prostacyclin synthase. Although prostacyclin is considered an independent mediator, it is called PGI2 (prostaglandin I2) in eicosanoid nomenclature, and is a member of the prostanoids (together with the prostaglandins and thromboxane). PGI2, derived primarily from COX-2 in humans, is the major arachidonate metabolite released from the vascular endothelium.