In patients unable to take oral Tacrolimus capsules, therapy may be initiated with Tacrolimus injection as a continuous IV infusion. If IV therapy is necessary, conversion from IV to oral Tacrolimus capsules is recommended as soon as oral therapy can be tolerated. This usually occurs within 2 to 3 days. In patients receiving an IV infusion, the first dose of oral therapy should be given 8 to 12 hours after discontinuing the IV infusion.

2.6 Therapeutic Drug Monitoring
Monitoring of Tacrolimus blood concentrations in conjunction with other laboratory and clinical parameters is considered an essential aid to patient management for the eva luation of rejection, toxicity, dose adjustments and compliance. Observed whole blood trough concentrations can be found in Table 1. Factors influencing frequency of monitoring include but are not limited to hepatic or renal dysfunction, the addition or discontinuation of potentially interacting drugs and the post-transplant time. Blood concentration monitoring is not a replacement for renal and liver function monitoring and tissue biopsies. Data from clinical trials show that Tacrolimus whole blood concentrations were most variable during the first week post-transplantation.

The relative risks of toxicity and efficacy failure are related to Tacrolimus whole blood trough concentrations. Therefore, monitoring of whole blood trough concentrations is recommended to assist in the clinical eva luation of toxicity and efficacy failure.

Methods commonly used for the assay of Tacrolimus include high performance liquid chromatography with tandem mass spectrometric detection (HPLC/MS/MS) and immunoassays. Immunoassays may react with metabolites as well as parent compound. Therefore assay results obtained with immunoassays may have a positive bias relative to results of HPLC/MS. The bias may depend upon the specific assay and laboratory. Comparison of the concentrations in published literature to patient concentrations using the current assays must be made with detailed knowledge of the assay methods and biological matrices employed. Whole blood is the matrix of choice and specimens should be collected into tubes containing ethylene diamine tetraacetic acid (EDTA) anti-coagulant. Heparin anti-coagulation is not recommended because of the tendency to form clots on storage. Samples which are not analyzed immediately should be stored at room temperature or in a refrigerator and assayed within 7 days; see assay instructions for specifics. If samples are to be kept longer they should be deep frozen at -20° C. One study showed drug recovery >90% for samples stored at -20° C for 6 months, with reduced recovery observed after 6 months.

Dosage Forms and Strengths
Tacrolimus Capsules USP, 0.5 mg are white to off white powder filled in hard gelatin capsule of size ‘4’, dark yellow opaque cap imprinted with ‘0.5 MG’ and dark yellow opaque body imprinted with ‘RDY 525’using red ink.

Tacrolimus Capsules USP, 1 mg are white to off white powder filled in hard gelatin capsule of size ‘4’, white opaque cap imprinted with ‘1 MG’ and white opaque body imprinted with ‘RDY 526’using red ink.

Tacrolimus Capsules USP, 5 mg are white to off white powder filled in hard gelatin capsule of size ‘4’, dark grayish red opaque cap imprinted with ‘5 MG’ and dark grayish red  opaque body imprinted wi