James J. Lipsky

Drug–Grapefruit Juice Interactions

Grapefruit juice, a beverage consumed in large quantities by the general population, is an inhibitor of the intestinal cytochrome P-450 3A4 system, which is responsible for the first-pass metabolism of many medications. Through the inhibition of this enzyme system, grapefruit juice interacts with a variety of medications, leading to elevation of their serum concentrations. Most notable are its effects on cyclosporine, some 1,4-dihydropyridine calcium antagonists, and some 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors. In the case of some drugs, these increased drug concentrations have been associated with an increased frequency of dose-dependent adverse effects. The P-glycoprotein pump, located in the brush border of the intestinal wall, also transports many cytochrome P-450 3A4 substrates, and this transporter also may be affected by grapefruit juice. This review discusses the proposed mechanisms of action and the medications involved in drug-grapefruit juice interactions and addresses the clinical implications of these interactions.

Methylphenidate: its pharmacology and uses.

Methylphenidate is a commonly used medication in the United States. This central nervous system stimulant has a mechanism of action distinct from that of amphetamine. The Food and Drug Administration has approved methylphenidate for the treatment of attention-deficit/hyperactivity disorder and narcolepsy. Treatment with methylphenidate has been advocated in patients with traumatic brain injury and stroke, cancer patients, and those with human immunodeficiency virus infection. Placebo-controlled trials have documented its efficacy as an adjunctive agent in the treatment of depression and pain. This article reviews the current understanding of the mechanism of action and efficacy of methylphenidate in various clinical conditions.

Lack of effect of intravenous administration on time to respond to azathioprine for steroid-treated Crohn's disease ☆ ☆☆ ★

BACKGROUND & AIMS Azathioprine is effective for Crohns disease but acts slowly. A loading dose may decrease the time to response. METHODS A placebo-controlled study was conducted in patients with active Crohns disease despite prednisone treatment. Patients were randomized to a 36-hour infusion of azathioprine, 40 mg/kg (51 patients), or placebo (45 patients) followed by oral azathioprine, 2 mg/kg, for 16 weeks. Prednisone was tapered over 5 weeks. The primary outcome measure was complete remission at week 8, defined by discontinuation of prednisone and a Crohns Disease Activity Index of </=150 points. Erythrocyte concentrations of the azathioprine active metabolite, 6-thioguanine nucleotide, were measured. RESULTS At week 8, 13 patients (25%) were in complete remission in the azathioprine-loaded group compared with 11 patients (24%) in the placebo group. The frequency of complete remission did not increase after 8 weeks in either group. Both groups achieved steady state of 6-thioguanine nucleotide by week 2, and no differences were found in mean concentrations between the groups. There were no significant differences in the frequency of adverse events between the groups. CONCLUSIONS A loading dose does not decrease the time to response in patients with steroid-treated Crohns disease beginning azathioprine therapy. Steady state of erythrocyte 6-thioguanine nucleotide and complete response occurred earlier than previously reported.

Measurement of thiopurine methyltransferase activity and azathioprine metabolites in patients with inflammatory bowel disease

BACKGROUND Measurement of 6-thioguanine nucleotide concentrations may be useful for optimising treatment with azathioprine and 6-mercaptopurine. METHODS We conducted a study of 170 patients with inflammatory bowel disease treated with azathioprine or 6-mercaptopurine to determine the relationship between 6-thioguanine nucleotide concentrations and both disease activity, as measured by the inflammatory bowel disease questionnaire (active disease <170, remission ⩾170) and leucopenia. Blood was submitted for whole blood 6-thioguanine nucleotide concentration and leucocyte count. RESULTS Mean (SD) inflammatory bowel disease questionnaire score was 176 (32). There was no correlation between inflammatory bowel disease questionnaire scores and 6-thioguanine nucleotide concentrations (r s=−0.09, p=0.24). Median 6-thioguanine nucleotide concentrations in 56 patients with active disease and 114 patients in remission were similar (139v 131 pmol/8×108 red blood cells; p=0.26). There was no correlation between 6-thioguanine nucleotide concentrations and leucocyte counts. CONCLUSIONS In patients with inflammatory bowel disease treated with azathioprine or 6-mercaptopurine, 6-thioguanine nucleotide concentrations did not correlate with disease activity, as measured by the inflammatory bowel disease questionnaire, or leucocyte count. These findings are discrepant with most previous studies, possibly due to selection of responding patients who tolerated the medications. A prospective, randomised, dose optimisation trial using 6-thioguanine nucleotide concentrations is warranted.

Inhibition of Interleukin-1-stimulated NF-κB RelA/p65 Phosphorylation by Mesalamine Is Accompanied by Decreased Transcriptional Activity

Nuclear factor κB (NF-κB) is an inducible transcription factor that regulates genes important in immunity and inflammation. The activity of NF-κB is highly regulated: transcriptionally active NF-κB proteins are sequestered in the cytoplasm by inhibitory proteins, IκB. A variety of extracellular signals, including interleukin-1 (IL-1), activate NF-κB by inducing phosphorylation and degradation of IκB, allowing nuclear translocation and DNA binding of NF-κB. Many of the stimuli that activate NF-κB by inducing IκB degradation also cause phosphorylation of the NF-κB RelA (p65) polypeptide. The transactivating capacity of RelA is positively regulated by phosphorylation, suggesting that in addition to cytosolic sequestration by IκB, phosphorylation represents another mechanism for control of NF-κB activity. In this report, we demonstrate that mesalamine, an anti-inflammatory aminosalicylate, dose-dependently inhibits IL-1-stimulated NF-κB-dependent transcription without preventing IκB degradation or nuclear translocation and DNA binding of the transcriptionally active NF-κB proteins, RelA, c-Rel, or RelB. Mesalamine was found to inhibit IL-1-stimulated RelA phosphorylation. These data suggest that pharmacologic modulation of the phosphorylation status of RelA regulates the transcriptional activity of NF-κB, independent of nuclear translocation and DNA binding. These findings highlight the importance of inducible phosphorylation of RelA in the control of NF-κB activity.

Leucopenia resulting from a drug interaction between azathioprine or 6-mercaptopurine and mesalamine, sulphasalazine, or balsalazide

AIM We evaluated the effect of coadministration of sulphasalazine, mesalamine, and balsalazide on the pharmacokinetics and pharmacodynamics of azathioprine and 6-mercaptopurine. METHODS Thirty four patients with Crohns disease receiving azathioprine or 6-mercaptopurine were enrolled in an eight week non-randomised parallel group drug interaction study and treated with mesalamine 4 g/day, sulphasalazine 4 g/day, or balsalazide 6.75 g/day. The primary outcome measure was the occurrence of clinically important leucopenia during the study, defined separately as total leucocyte counts <3.0 x 109/l and ⩽3.5×109/l. Whole blood 6-thioguanine nucleotide concentrations were determined. RESULTS Three patients could not be evaluated for the primary outcome measure. In the remaining 31 patients, the frequency of total leucocyte counts <3.0 and ⩽3.5 were: 1/10 and 5/10 in the mesalamine group; 1/11 and 6/11 in the sulphasalazine group; and 0/10 and 2/10 in the balsalazide group. There were significant increases in mean whole blood 6-thioguanine nucleotide concentrations from baseline at most time points in the mesalamine and sulphasalazine groups but not in the balsalazide group. CONCLUSIONS In patients with Crohns disease receiving azathioprine or 6-mercaptopurine, coadministration of mesalamine, sulphasalazine, and possibly balsalazide results in an increase in whole blood 6-thioguanine nucleotide concentrations and a high frequency of leucopenia.

An intravenous loading dose of azathioprine decreases the time to response in patients with Crohn's disease☆☆☆

BACKGROUND & AIMS Azathioprine, an effective therapy for Crohns disease, is limited by a prolonged time to response. The aim of this study was to determine the safety and utility of a loading dose of azathioprine to decrease the time to response in patients with Crohns disease. METHODS Twelve patients were studied: 6 with 13 fistulae and 6 with inflammatory disease. All patients received an intravenous infusion of azathioprine (50 mg/h for 36 hours). Response was determined by physical and radiographic examination for fistulae and by the Crohns Disease Activity Index for inflammatory disease. Erythrocyte concentrations of azathioprine metabolites were measured by chromatography. RESULTS Seven of 13 fistulae closed by week 4, and three had a temporary decrease in drainage. One fistula improved at week 16. Two fistulae failed to improve. Four of 6 patients with inflammatory disease achieved remission, and 1 improved temporarily. Improvement was rapid (< or = 4 weeks). Peak concentrations of azathioprine metabolites occurred within 3 days. Clinical response did not correlate with azathioprine metabolite concentrations at the azathioprine dose studied. No adverse events occurred. CONCLUSIONS An 1800-mg intravenous loading dose of azathioprine is safe and may decrease the time to response to < or = 4 weeks in patients with Crohns disease. Correlation between clinical response and azathioprine metabolite concentrations at larger azathioprine doses should be determined.

Selective Inhibition of Inflammatory Gene Expression in Activated T Lymphocytes: A Mechanism of Immune Suppression by Thiopurines

Azathioprine and 6-mercaptopurine are antimetabolite thiopurine drugs that play important roles in the treatment of leukemia and in the management of conditions requiring immunosuppression, such as inflammatory bowel disease. The biochemical pharmacology of these drugs suggests that inhibition of purine nucleotide formation through the 6-thioguanine nucleotide metabolites is their key molecular mechanism. However, it is unclear how these metabolites suppress immunity. We hypothesized that azathioprine produces a selective inhibitory effect on activated but not quiescent T lymphocytes. We first established a model system of T lymphocyte culture with azathioprine that produced pharmacologically relevant concentrations of 6-thioguanine nucleotides. Using genome-wide expression profiling, we identified a group of azathioprine-regulated genes in quiescent and activated T lymphocytes. Several genes involved in immunity and inflammation were selectively down-regulated by azathioprine in stimulated but not quiescent cells. Quantitative reverse transcription-polymerase chain reaction for three of these genes, tumor necrosis factor-related apoptosis-inducing ligand, tumor necrosis factor receptor superfamily member 7, and α4-integrin, confirmed down-regulated expression of transcript levels. Tumor necrosis factor-related apoptosis-inducing ligand protein expression was further studied and found to be inhibited by azathioprine, 6-mercaptopurine, and 6-thioguanine, implying that the inhibitory effects of azathioprine on expression are mediated by 6-thioguanine nucleotides. These results therefore provide a previously unrecognized molecular mechanism for the immunosuppressive properties of thiopurine antimetabolite drugs.

Antiretroviral drugs for AIDS

Treatment of HIV disease with antiretroviral agents has changed considerably. We now know that monotherapy is not the best strategy in most cases to combat rapid turnover of virus and development of resistance (the exception being mother-to-child transmission) and various combination drug regimens are being explored. Apart from the main drug groups, consisting of nucleoside analogues, proteinase inhibitors, and reverse-transcriptase inhibitors, many new compounds are under development. The timing of therapy may likewise be important, and the indications of benefit from early initiation of treatment need to be confirmed in randomised trials. Overall, there is far more optimism about the use of drugs in HIV infection than there was several years ago.

Azathioprine pharmacokinetics after intravenous, oral, delayed release oral and rectal foam administration.

BACKGROUND: 6-Mercaptopurine and its prodrug azathioprine are effective medications for refractory inflammatory bowel disease. However, use of these drugs has been limited by concerns about their toxicity. Colonic delivery of azathioprine may reduce its systemic bioavailability and limit toxicity. AIM: To determine the bioavailability of 6-mercaptopurine after administration of azathioprine via three colonic delivery formulations. METHODS: Twenty four healthy human subjects each received 50 mg of azathioprine by one of four delivery formulations (each n = 6): oral; delayed release oral; hydrophobic rectal foam; and hydrophilic rectal foam. All subjects also received a 50 mg dose of intravenous azathioprine during a separate study period. Plasma concentrations of 6-mercaptopurine were determined by high pressure liquid chromatography. RESULTS: The bioavailabilities of 6-mercaptopurine after colonic azathioprine administration via delayed release oral, hydrophobic rectal foam, and hydrophilic rectal foam (7%, 5%, 1%; respectively) were significantly lower than the bioavailability of 6-mercaptopurine after oral azathioprine administration (47%) by Wilcoxon rank sum pairwise comparison. CONCLUSIONS: Azathioprine delivered to the colon by delayed release oral and rectal foam formulations considerably reduced systemic 6-mercaptopurine bioavailability. The therapeutic potential of these colonic delivery methods, which can potentially limit toxicity by local delivery of high doses of azathioprine, should be investigated in patients with inflammatory bowel disease.