The old jokes about women using headaches as an excuse to resist the amorous intentions of partners may be revived by a recent review on cocrystals (Drug Discovery Today, 2008, 13, 440-446).

The review reports that a number of drug substances currently on the market form useful co-crystals with novel properties.  Among these is a cocrystal of sildenafil, the active ingredient of Viagra®, with acetyl salicylic acid (Aspirin) (normally sildenafil is sold in the citrate salt form).  The new cocrystal exhibits an intrinsic dissolution rate of 11.75 mg/min/cm² vs 6.64 for the citrate salt and is also stable up to 165^oC, even though it melts at 143^oC.  The new cocrystal therefore, may have advantages for oral administration, but the presence of the “aspirin” may also mean that additional testing may be necessary.