N-acetylprocainamide in serum/plasma

Reference interval

• 4-10 ug/mL

Therapeutic N-acetylprocainamide concentrations vary significantly depending on the individual patient. Published information sources say that a range of 4-10 ug/mL may indicate effective serum concentration for many patients; however, some individuals are best treated at concentrations outside this range. Concentrations greater than 10 ug/mL are often associated with toxic symptoms.

In normal clinical use N-acetylprocainamide (NAPA) would be analyzed in conjunction with procainamide when evaluating patient specimens. The combined procainamide & NAPA therapeutic range is 10-30 ug/mL. Combined concentrations > 30 ug/mL are often associated with toxic symptoms. The physician must determine the appropriate therapeutic range for each patient.

Principle

The NAPA pack is used in the DuPont ACA discrete clinical analyzer to quantitatively measure N-acetylprocainamide in serum & plasma. It is an adaptation of Syva's homogeneous enzyme immunoassay technique, EMIT. The reagents used in this methodology are matched lots of anti-N-acetylprocainamide antibody and N-acetylprocainamide-glucose-6-phosphate dehydrogenase conjugate. The concentration of N-acetylprocainamide determines the amount of N-acetylprocainamide-glucose-6-phosphate dehydrogenase (NAPA-G6PD) conjugate that is bound to the anti-N- acetylprocainamide antibody. The unbound conjugate catalyzes the oxidation of glucose-6-phosphate, with the simultaneous reduction of NAD to NADH, more rapidly than does the bound conjugate. The rate of increasing absorbance at 340 nm due to the increase in NADH is related to the concentration of N-acetylprocainamide by means of a calibration curve or a mathematical function.

Clinical significance

N-acetylprocainamide is an active metabolic derivative of procainamide. Its therapeutic effects are similar to those of the parent compound, but it has a slightly longer half-life. Most patients receiving procainamide therapy have plasma levels of N- acetylprocainamide generally equivalent to their plasma procainamide levels; however, levels of NAPA may be much higher in some patients due to rate of acetylation & renal function. Levels of procainamide & NAPA must both be monitored to evaluate true therapeutic dosage as well as avoidance of toxic effect.

Specimen

Patient preparation: No special patient preparation is required.

Collect blood samples by venipuncture following established good laboratory practices. If the sample is obtained through the infusion set, flush the line thoroughly with saline before taking the blood sample. With some exceptions, any anticoagulant may be used to collect plasma for analysis. Serum, as well as plasma, may be used for most assays. If is very important that the physician be informed of the times of sample collection & dose administration; this information should be supplied to the laboratory with each sample & reported with the results of each test. Samples derived from blood should be refrigerated upon collection & stored frozen (-20 degrees Celsius or colder) if not analyzed within 24 hours. Complete mixing of each thawed sample is required before analysis.

More general terms

• therapeutic drug measurement

Additional terms

• N-acetylprocainamide (NAPA, Acecainide)
• procainamide in serum/plasma

Component of

• N-acetylprocainamide/procainamide in serum/plasma