Systems and methods to determine body drug concentration from an oral fluid
Oral fluid for drug testing has several advantages over other specimens: (1) It may be collected noninvasively and under direct supervision; (2) its drug concentration reflects blood-drug concentrations; and (3) it can be processed by conventional drug screening and confirmation methods. This technology provides a system that measures the quantity of a drug (without needing a priori knowledge of the drug) in an oral fluid specimen and translates this level to a blood plasma drug concentration. The method first measures the concentration of a drug in an oral fluid sample. Next, a processor calculates the blood plasma concentration from the measured oral fluid drug concentration. Finally, this blood plasma drug level is utilized to calculate a total body drug concentration.
1. A method for determining a donor's adherence to a dosing regimen, the method comprising the steps of:
collecting a sample of oral fluid from the donor;
determining the pH of the oral fluid sample;
readying the sample for transport and analysis by placing the sample in an appropriate buffer, and sealing and packing the sample;
determining a concentration of the drug in the in the oral fluid sample;
calculating an expected plasma steady state minimum drug concentration (C ss min) and an expected plasma steady state maximum drug concentration (C ss max);
calculating an equivalent expected oral fluid steady state minimum drug concentration (Smin) and an expected oral fluid steady state maximum drug concentration (Smax) using C ss min and according to the following steps:
if the drug is an acidic drug, determine Smin and Smax using Eq. 5 by inputting C ss min and C ss max for P and solving for Smin and Smax (S):
S/P=[ 1+10 (pHs-pKa) ×fp]/[1+10 (pHp-pKa) ×fs]; and Eq. 5:
if the drug is a basic drug, determine Smin and Smax using Eq. 6 by inputting C ss min and C ss max for P and solving for Smin and Smax (S):
S/P=[ 1+10 (pKa-pHs) ×fp]/[1+10 (pKa-pHp) ×fs]; Eq. 6:
wherein:
pH s is a pH of saliva to be determined at the time of collection;
pH p is a pH of plasma;
pKa is a dissociation constant of the drug;
fp is a free fraction of the drug in plasma; and
fs is free fraction of the drug in saliva; and
determining whether measured oral fluid drug concentration of the donor complies with the dosing regimen of the drug, at steady state, if the measured oral fluid drug concentration is within the range between Smax and Smin, wherein the step of determining the oral fluid drug concentration comprises preparing the sample for toxicological measurement of drug content and extracting the drug from the sample using mixed-mode cationic exchange columns.
2. The method of claim 1 wherein the dosing regimen comprises a plurality of drugs.
3. The method of claim 1 further comprising the step of collecting a predefined volume of oral fluid from the donor.
4. The method of claim 1 wherein the pH is determined by providing visual indicia of the pH.
5. The method of claim 1 wherein the predefined volume of the sample is collected with a simultaneous measurement of the sample pH.
6. The method of claim 1 wherein the step of determining the drug comprises using Liquid Chromatography Tandem Mass Spectrometry.
7. The method of claim 1 further comprising evaluating steady state drug levels via oral fluid drug measurements.
8. The method of claim 1 further comprising comparing measured oral fluid concentration with an expected oral fluid steady state range based on the prescribed dosing regimen.