Chapter 23

Pharmaceutical Analysis

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Fluorescence Polarization Immunoassay (FPIA)

FPIA Procedure

• Fluorescein-labelled drug competes with unlabelled drug for antibody
• Sample excited with plane polarized light (490 nm)
• Fluorescein emits plane polarized light (520 nm)
• Small, free drug-fluorescein, rotates faster leading to less emission
• Larger, antibody-drug-fluorescein, rotates slower and produces more emission
• Drug in sample competes for antibody with fluorescein bound drug
• More drug in the sample; less fluorescein labelled drug bound to antibody; lower emission of plane polarized light
• Higher drug concentration results in lower light emission values

• Available for a variety of drugs
• Advantages
  • Rapid turnaround times, sensitivity, ease of operation
• Disadvantages
  • Background interference in serum sample (requires blank measurement)

Fig 23.9.1 FPIA Equipment Set-up
See Pieper and Rutledge, Laboratory Techniques for Pharmacists, Upjohn 1989, page 43, figure 14 for a more detailed image

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