For years the immediate precursor in the synthesis of methamphetamine was tightly controlled until a clandestine chemist devised a synthesis of methamphetamine from the easily available precursor; ephedrine, a sympathomimetic amine widely used in over-the-counter drugs for colds. A stereoisomer, pseudoephedrine (Pseudofed) is a popular cold tablet, also used in the manufacture of amphetamine. This new synthesis has flooded the illicit market with cheap “crystal” or “speed” methamphetamine. Some Labratories have found a greatly increased number of specimens positive for methamphetamine. Amphetamines have been added to the California Health and Safety Code 11550(b) sections (including PCP, heroin, and methamphetamine) providing a mandatory 30 day sentence for being under the influence. Possession of amphetamines is a felony.
Amphetamine and methamphetamine are the prototypical stimulant amphetamines and are widely abused. Small chiral or structural changes in the molecule can have substantial differences in effects. A large number of compounds resemble the neurotransmitters epinephrine, norepinephrine, and dopamine (dihydroxyphenylethylamine) and are chemically of the phenylethylamine class of drugs. These are generally referred to as sympathomimetic amines including the common over-the-counter drugs ephedrine and phenylpropanolamine. They are stimulant drugs, some with central nervous stimulation and some with smooth muscle actions (antiasthmatics). The mechanism of action is probably to release the natural neurotransmitters from their storage sites along with some direct action on the neurotransmitter receptor. L-methamphetamine is also found in the Vicks inhaler and as a urinary metabolite from selegeline, an anti-Parkinson medication.
Urinary detection of methamphetamine and its minor metabolite amphetamine is initially performed by immunoassay. Specimens screened positive are retested by gas chromatography/mass spectrometry (GC/MS) for confirmation.
Cutoff and Detection Post Dose
The screening immunoassay uses a cutoff of 1000 ng/ml. The cutoff for GC/MS is 500 ng/ml for both metabolites – amphetamine and methamphetamine. Amphetamine has a 7-32 hour half life, depending on the urinary pH. The assay is capable of detecting the use of methamphetamine or amphetamine for 24-48 hours post dose or as long as 72 hours depending on factors such as amount used, fluid intake, excretion, and urinary pH.