Methods for Verification of Drug Levels Using Dried Blood Samples

A method of determining efficacy of treatment for a disease in a pregnant subject, the method comprising:

• (a) extracting a drug from a dried blood sample to produce an extracted DBS sample, the dried blood sample being from a pregnant subject after a treatment for the disease to the pregnant subject has been administered, wherein the DBS sample comprises blood obtained from the pregnant subject and a filter paper pretreated with a first internal standard;
• (b) performing mass spectrometry on the extracted DBS sample;
• (c) determining a peak area ratio of the drug in the extracted DBS sample to the first internal standard;
• (d) determining a peak area ratio of the drug in the extracted DBS sample to a second internal standard;
• and
• (e) identifying the administered treatment as being effective when:
• (i) the peak area ratio of the drug in the extracted DBS sample to the first internal standard is greater than 1 and
• (ii) the peak area ratio of the drug in the extracted DBS sample to the second internal standard is less than 1, wherein the peak area ratio of the drug in the extracted DBS sample to the first internal standard relates to a minimal therapeutic efficacy level and the peak area ratio of the drug in the extracted DBS sample to the second internal standard relates to a maximal therapeutic efficacy level.