Chemicals
Methadone hydrochloride was purchased from TEMAD Company (Tehran, Iran). Chloroform, acetonitrile, methanol, ammoinum acetate, sodium hydroxide were purchased from Merck company (Darmstadt, Germany). Double distilled water was used for the preparation of aqueous solutions.
Instrumentation and operating conditions
A liquid chromatographic system consisted of a 1100 series pump, a 2-channel ERC-3315 degasser, a 1200 CE detector (UV-Vis) and an interface box, all from Cecil company (Cambridge, UK); and a Nova-Pak C
18 column with dimensions of 3.9 × 150 mm from Waters Co. (Massachusetts, US). The mobile phase consisted of 25 mM ammonium acetate (pH 7.0)/acetonitrile (10/90, v/v) with the flow rate of 1 mLmin
-1 and the analyte was detected using a UV detector at 220 nm. The further details of the chromatographic method were provided in a recent paper (
17). The applicability of the reported method was extended to analysis of methadone in serum and urine samples in this work. The pH of solutions was measured with Metrohm 654 pH meter (Herisau, Switzerland). A Hettich (EBA-20) centrifuge (Tuttlingen, Germany) and a Labtron (LS-100) vortex shaker (Tehran, Iran) were used for centrifugation and shaking the solutions, respectively.
| No. | Age (yr) | Height (cm) | Weight (Kg) | Dose0 (mg) | Duration of MMT (yr) | Sampling time (hr) | Co-administered drug | EBC (mcgL-1) | Serum (mcgL-1) | Urine (mcgL-1) | Corrected dose (mg) |
|---|
| 1 | 46 | 170 | 67 | 50 | 5 | 2 | | 603 | 361 | 7411 | 48 |
| 2 | 34 | 175 | 85 | 100 | 4 | 1 | Clonidine | 615 | 253 | 1226 | 98 |
| 3 | 42 | 172 | 72 | 50 | 3 | 4 | | 513 | 1113 | 3935 | 45 |
| 4 | 32 | 174 | 67 | 15 | 2 | 1 | | 652 | 125 | 4425 | 15 |
| 5 | 28 | 190 | 88 | 50 | 0 | 3 | Propranolol, Fluoxetine,Vit B1 | 615 | 120 | 4825 | 47 |
| 6 | 41 | 183 | 87 | 20 | 2 | 4 | | 572 | 102 | 1029 | 18 |
| 7 | 45 | 175 | 83 | 100 | 3 | 4 | Propranolol, Citalopram,Vit B1 | 623 | 586 | 2890 | 92 |
| 8 | 49 | 160 | 75 | 90 | 2 | 12 | Propranolol, Alprazolam | 345 | 671 | 2275 | 67 |
| 9 | 36 | 175 | 95 | 60 | 6 | 3 | | 432 | 276 | 914 | 56 |
| 10 | 35 | 200 | 94 | 100 | 2 | 1 | | 369 | 884 | 5602 | 98 |
| 11 | 34 | 174 | 62 | 12 | 3 | 1 | | 370 | 95 | 1128 | 12 |
| 12 | 36 | 180 | 73 | 200 | 4 | 6 | | 339 | 369 | 14948 | 172 |
| 13 | 49 | 176 | 97 | 125 | 5 | 2 | Clonidine, Lorazepam | 321 | 789 | 4236 | 119 |
| 14 | 42 | 175 | 63 | 75 | 0 | 3 | | 594 | 339 | 7726 | 70 |
| 15 | 53 | 170 | 75 | 50 | 1 | 8 | | 521 | 734 | 2982 | 41 |
| 16 | 52 | 173 | 92 | 125 | 2 | 8 | | 325 | 1572 | 11982 | 103 |
| 17 | 45 | 176 | 62 | 80 | 2 | 18 | Propranolol, Citalopram | 381 | 147 | 866 | 51 |
| 18 | 47 | 160 | 61 | 90 | 2 | 20 | | 305 | 610 | 1109 | 55 |
| 19 | 48 | 170 | 65 | 20 | 2 | 20 | | 584 | 221 | 795 | 12 |
| 20 | 35 | 176 | 88 | 25 | 1 | 1 | ASA, Metoprolol | 560 | 241 | 1390 | 25 |
| 21 | 42 | 175 | 104 | 20 | 2 | 3 | | 521 | 219 | 1796 | 19 |
| 22 | 52 | 175 | 60 | 60 | 4 | 1 | | 539 | 203 | 2704 | 59 |
| 23 | 39 | 170 | 73 | 55 | 5 | 4 | | 545 | 401 | 979 | 50 |
| 24 | 34 | 170 | 70 | 75 | 2 | 4 | | 550 | 528 | 2712 | 68 |
| 25 | 40 | 180 | 78 | 70 | 4 | 14 | | 569 | 394 | 2648 | 50 |
| 26 | 35 | 179 | 70 | 100 | 8 | 16 | | 574 | 355 | 3521 | 67 |
| 27 | 31 | 178 | 90 | 60 | 0 | 3 | | 421 | 246 | 3990 | 56 |
| 28 | 50 | 185 | 110 | 55 | 3 | 3 | | 307 | 812 | 4567 | 51 |
| 29 | 35 | 170 | 65 | 80 | 1 | 4 | | 409 | 381 | 2838 | 72 |
| 30 | 33 | 173 | 63 | 45 | 2 | 1 | | 261 | 201 | 998 | 44 |
| 31 | 44 | 176 | 78 | 60 | 2 | 11 | | 416 | 164 | 2920 | 46 |
| 32 | 26 | 183 | 85 | 90 | 2 | 3 | Amitriptyline, Chlordiazepoxide | 449 | 1346 | 1162 | 85 |
| 33 | 29 | 173 | 72 | 30 | 3 | 1 | Clonazepam | 330 | 253 | 1993 | 29 |
| 34 | 25 | 185 | 65 | 75 | 2 | 15 | | 364 | 154 | 4323 | 52 |
| 35 | 38 | 170 | 80 | 100 | 1 | 2 | Propranolol, Alprazolam,Vit B1, Fluoxetine | 839 | 659 | 2723 | 95 |
| 36 | 30 | 178 | 83 | 100 | 4 | 8 | Alprazolam, Citalopram | 245 | 769 | 3955 | 82 |
| 37 | 29 | 183 | 90 | 85 | 2 | 12 | Propranolol | 308 | 831 | 2643 | 63 |
| 38 | 32 | 180 | 95 | 75 | 2 | 2 | | 330 | 378 | 3065 | 71 |
| 39 | 31 | 165 | 81 | 75 | 12 | 3 | Clonazepam, Nortriptyline | 321 | 784 | 3011 | 70 |
| 40 | 54 | 170 | 84 | 15 | 3 | 18 | Clonazpam | 285 | 94 | 860 | 10 |
| 41 | 56 | 170 | 78 | 12 | 0 | 1 | Atenolol | 360 | 210 | 742 | 12 |
| 42 | 44 | 175 | 59 | 25 | 10 | 1 | | 284 | 459 | 1378 | 25 |
| 43 | 49 | 168 | 68 | 25 | 3 | 7 | | 318 | 291 | 1165 | 21 |
| 44 | 36 | 175 | 68 | 7 | 1 | 20 | | 282 | 155 | 5541 | 4 |
| 45 | 36 | 174 | 68 | 75 | 1 | 5 | | 324 | 782 | 1374 | 66 |
| 46 | 36 | 168 | 82 | 150 | 7 | 1 | | 300 | 775 | 4330 | 148 |
| 47 | 37 | 175 | 69 | 25 | 0 | 2 | | 322 | 316 | 1993 | 24 |
| 48 | 47 | 168 | 70 | 100 | 2 | 9 | | 412 | 784 | 2431 | 80 |
| 49 | 32 | 180 | 78 | 50 | 2 | 5 | | 811 | 286 | 3176 | 44 |
| 50 | 33 | 175 | 95 | 75 | 3 | 3 | | 369 | 542 | 951 | 70 |
| 51 | 34 | 170 | 60 | 30 | 4 | 5 | | 271 | 102 | 822 | 27 |
| 52 | 28 | 178 | 75 | 40 | 1 | 1 | | 285 | 86 | 757 | 40 |
| 53 | 56 | 185 | 83 | 75 | 5 | 6 | | 229 | 85 | 880 | 65 |
| Case # | EBC (pgmin-1) | Plasma (mcgL-1) | Urine (mcgL-1) |
|---|
| 2 | 4.9 | - | 1190 |
| 6 | - | 131 | - |
| 8 | 330 | - | >2000 |
| 9 | 39 | 1100 | >2000 |
| 11 | 40 | - | - |
| 16 | 5600 | 550 | >2000 |
| 21 | 29800 | - | >2000 |
| 34 | - | 55 | - |
| 35 | 200 | 6500 | >2000 |
| 41 | 35 | - | >2000 |
| 49 | - | 1930 | >2000 |
| 51 | 300 | 640 | - |
| 52 | 60 | 3550 | >2000 |
Serum concentrations of methadone versus its daily dose
Comparison of mean standard deviations of plasma/serum methadone concentrations against daily dose (dose0) from our work and the literature data
Methadone concentrations in EBC versus administered daily dose of methadone (dose0).
Mean and standard deviations of EBC concentrations of methadone against its daily dose (dose0
Mean and standard deviations of urine concentrations of methadone against its daily dose (dose0
Sample preparations
Standard stock solution of methadone (1000 mgL
−1) was prepared in methanol and stored at 4 ºC. Working solutions were prepared by diluting with methanol. Sampling of EBC was done using a lab-made setup based on a cooling trap system patented in the national patent office (18). EBC samples were collected for 10 min and then transferred to a micro tube and stored at -80 °C until analysis. Serum and urine samples at different times after drug intake (see
Table 1, column 7) were collected and centrifuged at 13000 rpm for 10 min, then stored at -80 °C until analysis.
pH of EBC sample was adjusted (at 10.0) with sodium hydroxide (0.1 M), 1 mL of EBC was mixed with 200 µL of chloroform (as an extracting solvent), sonicated for 2 min, centrifuged for 10 min at 13000 rpm, organic phase was transferred to another micro tube, evaporated to dryness overnight, the residue was dissolved in 100 µL of the mobile phase and injected to the LC system.
1 mL of serum was mixed with 1 mL of acetonitrile (as protein precipitant and disperser solvent) in a test tube with conic bottom, centrifuged for 15 min, the supernatant transferred to another micro tube, repeatedly centrifuged for 5 min and 1 mL of the supernatant carried over to another test tube and mixed with 100 µL chloroform (as an extracting solvent), sonicated for 2 min in an ultrasonic bath, centrifuged for 10 min at 13000 rpm, and the organic phase settled to the bottom of tube transferred to a micro tube after discarding the supernatant. Finally the organic phase was evaporated to dryness overnight, the residue was dissolved in 100 µL of the mobile phase and injected to the LC system.
1 mL of urine sample was diluted (1 to 5 times) with water, pH was adjusted (to 10.0) with sodium hydroxide (0.1 M), centrifuged for 10 min at 6000 rpm, 1 mL of this sample mixed with 1 mL acetonitrile, vortexed, centrifuged for 10 min at 6000 rpm, the supernatant mixed with 200 µL of chloroform and continued with the same method as done for serum samples.
To calculate the calibration graphs in EBC, serum and urine samples, the blank samples collected from healthy volunteers were thawed at room temperature and calibration standards were prepared by spiking 1000 µL of drug-free EBC, serum and urine samples with known amounts of the drug to achieve the concentrations ranging from 0.5 to 500 µgmL−1 and were kept at room temperature for 20 min before use. Then the samples were treated as mentioned above and the peak heights of the samples were plotted against the added concentrations of methadone.
All sample donors have been informed on details of this study and signed a consent form approved by the Ethics Committee of Tabriz University of Medical Sciences.
Dosage correction according to sampling time
According to the half life definition, the dose correction after a given period of time could be done as:
where dose0 is the administered dose, doset is the normalized dose of methadone according to the sampling time (t), and t½ is the half life of methadone (t½=28 h (1)).