The hydrogen sulphate salt of the selective phosphodiesterase type IV inhibitor (R)-4-[2-(3-Cyclopentyloxy-4-methoxyphenyl)-2-phenylethyl]- pyridine hydrogen sulphate salt is described. The salt possesses a number of advantageous chemical and physical characteristics making it particularly suitable for pharmaceutical formulation for use in inter alia the prophylaxis and treatment of asthma.
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