As a semi-frequent visitor to Egypt, and having observed what is advised LOCALLY by medical professionals (and locals who deal with the general public - pharmacists, dive center operators, hotel "doctors", etc), their drug of choice is called ANTINAL. It is produced by a french company and is available over the counter for about 5LE (0.5GBP) for a pack of 12 capsules.
Antinal is described as an "Intestinal antiseptic", it is not an antibiotic and as such will not contribute to the generation of antibiotic resistant strains of bacteria (eg MRSA, VRSA etc). From experience, a single capsule if taken immediately on the onset of symptoms, can (not will) stop the trots dead.
Do a search for "Antinal" on
www.tripadvisor.com and make your own mind up.
As an aside, upset stomachs in hot countries can also be caused by rapidly drinking large volumes of very cold liquid, the temperature shock to the stomach can trigger upsets. So when I now visit hot climates, I drink lots of fluid but "little and often - i.e. continually sip from a small bottle, not at fridge temperature".
Ingestion of local bacillus via yoghurt type foods is a sensible option, but I must confess, I do not do this.
If you do experience "delhi-belhi" or the like, rehydration powders should be started immediately, as you will rapidly lose electrolytes and have further problems.
Similarly, if you take over the counter medication, and it has not cleared up in 24/36 hours, do not hesitate to see a local medical professional.