I Am 60 Years Of Age And Have Been Prescibed

I am 60 years of age and have been prescibed neurobion injections which I get from the local nursing sister at the chemist once a week . However after a few days it feels as if the optimum results are diminishing - how often us still safe to repeat these injections- we are in the midst of an extreme heatwave in South Africa.
Thank you in anticipation for your reply