{HEAD ~ A useful therapeutic or prophylactic concentration} will vary from {TAIL ~ condition} to condition and in certain instances may vary with the severity of the condition being treated and the patients susceptibility to treatment 
vary from
{ HEAD ~ A useful therapeutic or prophylactic concentration } will vary from { TAIL ~ condition } to condition and in certain instances may vary with the severity of the condition being treated and the patients susceptibility to treatment
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH