AMANTADINE drug test results

Our 37 year old son has been taking 2 capsules per day of amantadine 100 mg each daily and was given a drug test (urine) and it was positive for drugs, he has had an addiction to cocaine in the past and claims the drug test should have been clean. Is it possible that amantadine would give a "dirty" test result?

He also takes zoloft 100 mg per day

Thank you