quinidine in serum/plasma

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Indications

Reference interval

  • Therapeutic Range: 1.3-5.0 ug/mL
  • Toxic Range: > 6.0 ug/mL

Principle

The unique reagents in this methodology are the matched lots of anti-quinidine antibody & quinidine - glucose-6-phosphate dehydrogenase conjugate. The reaction sequence, in two steps, is as shown:

           Quin                   Ab-Quin
  • Ab + + ---------> + + Quin-G6PD
         Quin-G6PD                Ab-Quin-G6PD      (active)
                                  (inhibited)
  Glucose-6-phosphate
                        Quin-G6PD
  • + ------------> NADH (absorbs at 340 nm)
                        (active)
       NAD+
   Where:        Ab = Antiquinidine antibody
               Quin = Quinidine
          Quin-G6PD = Quinidine -  glucose-6-phosphate dehydrogenase conjugate

The concentration of quinidine determines the amount of quinidine- glucose-6-phosphate dehydrogenase conjugate (Quin-G6PD) that is bound to the antiquinidine 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 quinidine concentration by means of a mathematical function.

Clinical significance

Quinidine, available as either quinidine sulfate or quinidine gluconate, is used in the treatment of certain types of irregular and rapid heart rates. Peak serum concentrations are reached in 1.5-2 hours of oral intake, unless the slow release preparation is used. Peak plasma concentrations are reached 4-5 hours after quinidine gluconate administration, & the trough concentration occurs 1-2 hours after the next administration. Clearance of quinidine is dependent on adequate hepatic & renal function.

Routine monitoring of quinidine is most commonly an effort to document adequate dosage. In this case the trough specimen is appropriate. When symptoms of intoxication are observed, then a peak specimen may be more useful. Clearance of quinidine is dependent upon an active mixed-function oxidase system in the liver. Induction of this system by barbiturates will lead to enhanced clearance of quinidine.

Specimen

Patient Preparation: No special patient preparation is required.

  • Serum is the specimen of choice. Serum is collected in a red top vacutainer by venipuncture. Serum samples are stable when stored in the dark or frozen at -20 C. If frozen samples are stable for at least one year.
  • Plasma samples are also acceptable. These samples are collected in green top vacutainer by venipuncture. Plasma samples should be stored in the dark or frozen if analysis cannot be performed several hours after collection.

Minimum sample size 0.6 milliliters: With an optimum size of 1.5 milliliters or larger.

More general terms

More specific terms

References

  1. Kaplan, L., & Pesce, A., Clinical Chemistry:theory, analysis, & correlation, C. V. Mosby Co., St. Louis, MO., 1984, pp. 1381.
  2. Tietz, N., Fundamentals of Clinical Chemistry, 3rd edition W. B. Saunders Co., Philadelphia, 1987, pp. 857.
  3. Tietz, N., Textbook of Clinical Chemistry, W. B. Saunders Co., Philadelphia, 1986, pp. 1642.
  4. ACA IV Discrete Clinical Analyzer Instrument Manual, Volume 1:Operation, DuPont Company, Wilmington, Delaware, 1984.
  5. ACA IV Discrete Clinical Analyzer Instrument Manual, Volume 3:Chemistry, DuPont Company, Wilmington, Delaware, 1984.
  6. Quinidine Laboratory Test Directory ARUP: http://www.aruplab.com/guides/ug/tests/0090245.jsp