a) Is it common for international airlines to issue their staff antimalarial prophylaxis? (Malaria tablets in particular).
Yes. (I think health and safety rules, plus liability, require this, although I suggest you verify the legal side).
b) How do airlines work out which drug for which patient?
Usual guidelines as used by medical profession or advisors to the travel industry, with some modifications (see below).
c) How do they monitor and record side effects and adverse reactions?
They can't. Crew are advised to take medication under medical guidance and this includes the reporting of side FX. Health wise, crew belong to their GP, not their the company or even their AME. Standard medical ethics/protocol I think.
d) How do they link in with AME/GP? (Record keeping/PMH etc.)
As above, ie they don't, unless specialist advice is required (eg adverse reactions or drug sensitivities to recommended prophylaxis).
e) Do pilots take MEFLOQUINE (Larium), and if not, how are they informed about the risks of (?) less effective medication.As far as I know, mefloquine is contra-indicated in those performing precision activities.
They don't take mefloquine (or at least they are not supposed to). AICs (UK) are issued to cover medical topics like these, and they are usually repeated in company standard procedures and aircrew notices, which are usually mandatory. (By that I mean the banning of larium is mandated, not the taking of the prophylaxis. You can only take the horses to the water . . )
Some companies have supplies of the recommended drugs at their bases that can be picked up by crews flying to areas of risk, and specify which prophylactic regime is recommended for the various geographical areas.
I am well aware of the indications/cautions/contra-indications/side effects of each drug, I am more interested in the systems that are in place to ensure efficacy and safety.
Hope this helps.