Pharmacokinetic profiles for oral and subcutaneous methotrexate in patients with Crohn's disease

BACKGROUND

Methotrexate (MTX) is administered subcutaneously to Crohn's Disease (CD) patients. There are very few studies evaluating the use of oral (PO) MTX in CD. A drug and its pharmaceutical alternative are equivalent (bioequivalence) when the bioavailability of the alternative falls within 80-125% of the bioavailability of the standard (US Food and Drug Administration - FDA).

AIM

To compare the pharmacokinetic (PK) profiles of PO and subcutaneous (SC) MTX in CD patients to determine the bioequivalence of these two routes.

METHODS

Eleven patients received a PO and an SC MTX dose (25 mg) separated by one week over a two-week interval. Blood samples were collected at specified times over a 24-h period for each patient on two separate days. MTX plasma levels were obtained using sensitive mass spectrometry. Areas under the curve (AUC) were compared between the two routes.

RESULTS

The mean AUC values were 3375 ng/mL × h (PO MTX) and 3985 ng/mL × h (SC MTX). The mean AUC ratio (PO/SC) was 0.86 (0.62-1.08). This correlates with a relative PO bioavailability of 86% in comparison to SC. The 90% confidence interval for the mean AUC (PO/SC) ratio is (0.785, 0.929). There were no adverse events.

CONCLUSIONS

The mean MTX AUC (PO/SC) in these patients falls outside the 90% confidence interval for the bioequivalence limit. SC MTX is more bioavailable than PO MTX; however, the mean relative MTX bioavailability (PO/SC) nearly met the FDA bioequivalence standard and PO MTX could be proposed in responders who would prefer this route.

Lack of glutathione conjugation of melphalan in the isolated in situ liver perfusion in humans

Tumor cell resistance against melphalan (LPAM) has been associated with increased cellular reduced glutathione (GSH) levels and glutathione S-transferase activity. Therefore, GSH conjugation of LPAM has been hypothesized to be a key factor in tumor cell resistance. In the present study, we evaluated GSH conjugation of LPAM by the perfused liver in patients with colorectal cancer metastases undergoing a Phase II study of isolated liver perfusion as well as in the rat. To evaluate whether LPAM-GSH conjugates were synthesized in the rat in vivo, LPAM was infused i.v. at a rate of 2.0 micromol/kg/min. In bile samples obtained during the infusion, two major GSH conjugates were identified by mass spectrometry: mono-hydroxy-mono-GSH-LPAM and di-GSH-LPAM. The maximum biliary excretion rate of these two conjugates accounted for only 1.3% of the LPAM infusion rate. In bile or perfusate samples from patients treated for 60 min initially with 0.3 mM LPAM in the perfusion medium via isolated liver perfusion (200 mg LPAM in approximately 2 liters perfusion medium), none of the above-mentioned conjugates were detected. When comparable rat liver perfusions were performed initially with 66 microM or 0.66 mM LPAM in the perfusion medium, bile samples did contain GSH-LPAM conjugates; the cumulative biliary excretion of the two conjugates amounted to 0.4 and 0.2% of the LPAM dose, respectively. These data suggest that both in rats and humans, hepatic GSH conjugation plays a very minor (if any) role in the elimination of LPAM and, therefore, that modulation of GSH levels is unlikely to affect the rate of elimination of this drug.