Nitrate salts of antihypertensive medicines

Nitrate salts of the compounds selected from the group consisting of:

• 1(2H)-phthalazinone hydrazone (Hydralazine);
• 6-(1-piperidinyl)-2,4-pyrimidinediamine 3-oxide (Minoxidil);
• 1-[[3-(4,7-dihydro-1-methyl-7-oxo-3-propyl-1H-pyrazol [4,3-d]pyrimidin-5-yl)-4-etoxyphenyl]sulphonyll-4-methyl-piperazine (Sildenafil), and 2-(2-propyloxyphenyl)-8-azapurin-6-one (Zaprinast).