do you mean nigh-time cramp ( when you are sleeping ) or cramp after excercise? If it is nightime then I recommend stretching excercises, to stretch the calf muscles 3 times a day, make sure you drink plenty of water before you go to bed and during the night if you feel thirsty as dehydration can make it work,( you will probably be up a few times in the night but hopefully not with cramp)  don't drink too much of the old vino,as a last resort you may need to ask your Dr to check your thyroid levels as an underactive thyroid can cause cramps. Hope this works, I used to get very painful leg cramps at night but haven't suffered with them for years now! Never knew about the tonic water but worth a try if you can get hold of it. Best of luck!