I keep on reading that amoxicillian can cause a false positive for
cocaine.  If this is true what will be the ppm level range
concentration,on a 500mg capsule taken twice daily for three days.

If you are asking for information on the pharmacokinetics of amoxicillin:

according to the Prescription Products Guide 1992. Aust.
Pharmaceutical Publishing Co Ltd (print)

"The half life of Amoxil is 61.3 minutes with normal renal function
and in the absence of renal function 16-20 hours.

Amoxil is excreted in the urine both unchanged and as penicilloic
acid. About 75% of a 1 g dose is excreted in the urine in 6 hours in
the presence of normal renal function (60% is biolog ically active and
15% is penicilloic acid). However about 32% of a 3 g dose is excreted
via the urine as the biologically active component in 8 hours (by
which time most of the urinary excretion is complete). This
proportional difference in the amount excreted from the different
doses reflects a lack of linearity between doses and extent of
absorption with a levelling off at higher doses of oral amoxycillin.

Excretion of Amoxil can be delayed by concurrent administration of
probenecid thus prolonging its therapeutic effect.

Arnoxil is not highly protein bound, being only 17% proteinbound in
serum as measured by ultrafiltration or equilibrium dialysis.

Orally administered doses of 250 mg and 500 mg amoxycillin result in
average peak serum levels one to two hours after administration of 5.0
mcg/mL and
6.6-10.8 mcg/mL respectively. Delectable serum levels of amoxycillin
are present 8 hours after ingestion of a single dose."

according to http://www.rxlist.com/cgi/generic/amox_cp.htm

"Orally administered doses of 250-mg and 500-mg amoxicillin capsules
result in average peak blood levels 1 to 2 hours after administration
in the range of 3.5 mcg/mL to 5.0 mcg/mL and 5.5 mcg/mL to 7.5 mcg/mL,
respectively."

Hi again,
Just to correct a couple of unproofed OCR errors in my previous post
'Arnoxil' should of course read 'Amoxil',
and while serum levels may indeed be 'delectable', the word should
have been 'detectable'.
Thanks.