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Tacrolimus (FK506) and the pharmaceutical/academic/regulatory gauntlet.

ABSTRACT: The pivotal issue of transplant rejection diagnosis and management is design, conduct, and analysis of clinical trials. The historical experience with clinical trials of major immunosuppressive drugs (cyclosporine and especially tacrolimus) is examined in this article. Cyclosporine was a turning point in transplantation, providing an extraordinary improvement over previous therapies. Additionally, early investigational experience with tacrolimus was shown to be important in rescue from cyclosporine failure. Experience with tacrolimus in liver recipients for primary therapy led to understanding that the side effect profile was similar to cyclosporine and that the important side effects of tacrolimus (toxicity and diabetes) could be lessened by altering the drug dose. Early dosing regimens were determined by attempts to balance the toxicities (representing a dose ceiling) against rejection (for minimum dosing). Drug levels became understandable and trough levels could be used to guide therapy. However, when the multicenter liver trial was implemented, high starting doses were included in the protocol design, ignoring information obtained with drug level monitoring. Disregard for this information led to a distortion of the potential value of tacrolimus. Historical controls from the Pittsburgh experience suggested that tacrolimus was a critical immunosuppressant, and the randomized trial against cyclosporine confirmed the drug's ability to compete. The multicenter liver trial, however, was not balanced across treatment arms for other immunosuppressive agents (ie, higher doses of prednisone from center to center, additional induction protocols at various centers). Additionally, analysis of study results differed across continents, and the role of tacrolimus in cyclosporine rescue was not examined thoroughly. When tacrolimus was proposed for use in extrahepatic organ transplantation, again the Pittsburgh experience, as well as experience from other single centers, was determined inadequate evidence of efficacy, and randomized trials were required by the FDA. The fact that multicenter trials in transplantation have historically been poorly designed or analyzed weighed against the dramatic improvements shown from historically controlled studies or single-center trials should lead to question of the regulatory requirement for multicenter randomized trials for all organ types.

SUBMITTER: Starzl TE

PROVIDER: S-EPMC2989854 | biostudies-other | 1998 Jun

REPOSITORIES: biostudies-other

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Project description:ImportanceIn an effort to regulate physician conflicts of interest, some US academic medical centers (AMCs) enacted policies restricting pharmaceutical representative sales visits to physicians (known as detailing) between 2006 and 2012. Little is known about the effect of these policies on physician prescribing.ObjectiveTo analyze the association between detailing policies enacted at AMCs and physician prescribing of actively detailed and not detailed drugs.Design, setting, and participantsThe study used a difference-in-differences multivariable regression analysis to compare changes in prescribing by physicians before and after implementation of detailing policies at AMCs in 5 states (California, Illinois, Massachusetts, Pennsylvania, and New York) that made up the intervention group with changes in prescribing by a matched control group of similar physicians not subject to a detailing policy.ExposuresAcademic medical center implementation of policies regulating pharmaceutical salesperson visits to attending physicians.Main outcomes and measuresThe monthly within-drug class market share of prescriptions written by an individual physician for detailed and nondetailed drugs in 8 drug classes (lipid-lowering drugs, gastroesophageal reflux disease drugs, diabetes drugs, antihypertensive drugs, hypnotic drugs approved for the treatment of insomnia [sleep aids], attention-deficit/hyperactivity disorder drugs, antidepressant drugs, and antipsychotic drugs) comparing the 10- to 36-month period before implementation of the detailing policies with the 12- to 36-month period after implementation, depending on data availability.ResultsThe analysis included 16 121 483 prescriptions written between January 2006 and June 2012 by 2126 attending physicians at the 19 intervention group AMCs and by 24 593 matched control group physicians. The sample mean market share at the physician-drug-month level for detailed and nondetailed drugs prior to enactment of policies was 19.3% and 14.2%, respectively. Exposure to an AMC detailing policy was associated with a decrease in the market share of detailed drugs of 1.67 percentage points (95% CI, -2.18 to -1.18 percentage points; P < .001) and an increase in the market share of nondetailed drugs of 0.84 percentage points (95% CI, 0.54 to 1.14 percentage points; P < .001). Associations were statistically significant for 6 of 8 study drug classes for detailed drugs (lipid-lowering drugs, gastroesophageal reflux disease drugs, antihypertensive drugs, sleep aids, attention-deficit/hyperactivity disorder drugs, and antidepressant drugs) and for 9 of the 19 AMCs that implemented policies. Eleven of the 19 AMCs regulated salesperson gifts to physicians, restricted salesperson access to facilities, and incorporated explicit enforcement mechanisms. For 8 of these 11 AMCs, there was a significant change in prescribing. In contrast, there was a significant change at only 1 of 8 AMCs that did not enact policies in all 3 areas.Conclusions and relevanceImplementation of policies at AMCs that restricted pharmaceutical detailing between 2006 and 2012 was associated with modest but significant reductions in prescribing of detailed drugs across 6 of 8 major drug classes; however, changes were not seen in all of the AMCs that enacted policies.

Project description:BACKGROUND: FK506 (Tacrolimus) is an important immunosuppressant, produced by industrial biosynthetic processes using various Streptomyces species. Considering the complex structure of FK506, it is reasonable to expect complex regulatory networks controlling its biosynthesis. Regulatory elements, present in gene clusters can have a profound influence on the final yield of target product and can play an important role in development of industrial bioprocesses. RESULTS: Three putative regulatory elements, namely fkbR, belonging to the LysR-type family, fkbN, a large ATP-binding regulator of the LuxR family (LAL-type) and allN, a homologue of AsnC family regulatory proteins, were identified in the FK506 gene cluster from Streptomyces tsukubaensis NRRL 18488, a progenitor of industrial strains used for production of FK506. Inactivation of fkbN caused a complete disruption of FK506 biosynthesis, while inactivation of fkbR resulted in about 80% reduction of FK506 yield. No functional role in the regulation of the FK506 gene cluster has been observed for the allN gene. Using RT-PCR and a reporter system based on a chalcone synthase rppA, we demonstrated, that in the wild type as well as in fkbN- and fkbR-inactivated strains, fkbR is transcribed in all stages of cultivation, even before the onset of FK506 production, whereas fkbN expression is initiated approximately with the initiation of FK506 production. Surprisingly, inactivation of fkbN (or fkbR) does not abolish the transcription of the genes in the FK506 gene cluster in general, but may reduce expression of some of the tested biosynthetic genes. Finally, introduction of a second copy of the fkbR or fkbN genes under the control of the strong ermE* promoter into the wild type strain resulted in 30% and 55% of yield improvement, respectively. CONCLUSIONS: Our results clearly demonstrate the positive regulatory role of fkbR and fkbN genes in FK506 biosynthesis in S. tsukubaensis NRRL 18488. We have shown that regulatory mechanisms can differ substantially from other, even apparently closely similar FK506-producing strains, reported in literature. Finally, we have demonstrated the potential of these genetically modified strains of S. tsukubaensis for improving the yield of fermentative processes for production of FK506.

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Tacrolimus (FK506) and the pharmaceutical/academic/regulatory gauntlet.

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