Pharmacokinetics of tacrolimus after multidose oral administration and efficacy in the prevention of allograft rejection in cats with renal transplants

Preliminary study of interaction of clarithromycin with tacrolimus in cats

Tacrolimus (Tac) is a core immunosuppressive drug in human organ transplantation. In feline kidney transplantation, however, the cost of Tac therapy is a significant obstacle. Clarithromycin (CLM) increases the blood trough level of Tac, effectively reducing the Tac dosage in human transplant patients. The interaction between CLM and Tac in cats has not been reported. In this study, the effect of multiple CLM dosing on the pharmacokinetics of Tac in three healthy cats was investigated. The treatments included Tac at 0.3 mg/kg and Tac at 0.3 mg/kg + multiple-dose CLM at 10 mg/kg. Co-administration of CLM and Tac resulted in significant increases in the oral bioavailability of Tac. These preliminary findings suggest that administration of multiple doses of CLM may decrease the required Tac dosage in Tac-based immunosuppressive therapy used as an alternative to the classic cyclosporine-based protocol for feline renal transplantation.

Ascomycin and FK506: pharmacology and therapeutic potential as anticonvulsants and neuroprotectants

Ascomycin and FK506 are powerful calcium-dependent serine/threonine protein phosphatase (calcineurin [CaN], protein phosphatase 2B) inhibitors. Their mechanism of action involves the formation of a molecular complex with the intracellular FK506-binding protein-12 (FKBP12), thereby acquiring the ability to interact with CaN and to interfere with the dephosphorylation of various substrates. Pharmacological studies of ascomycin, FK506, and derivatives have mainly been focused on their action as immunosuppressants and therapeutic use in inflammatory skin diseases, both in animal studies and in humans. CaN inhibitors have been also proposed for the treatment of inflammatory and degenerative brain diseases. Preclinical studies suggest, however, that ascomycin and its derivatives exhibit additional pharmacological activities. Ascomycin has been shown to have anticonvulsant activity when perfused into the rat hippocampus via microdialysis probes, and ascomycin derivatives may be useful in preventing ischemic brain damage and neuronal death. Their pharmacological action in the brain may involve CaN-mediated regulation of gamma aminobutyric acid (GABA) and glutamate receptor channels, neuronal cytoskeleton and dendritic spine morphology, as well as of the inflammatory responses in glial cells. FK506 and ascomycin inhibit signaling pathways in astrocytes and change the pattern of cytokine and neurotrophin gene expression. However, brain-specific mechanisms of action other than CaN inhibition cannot be excluded. CaN is a likely potential target molecule in the treatment of central nervous system (CNS) diseases, so that the therapeutic potential of ascomycin, FK506, and nonimmunosuppressant ascomycin derivatives as CNS drugs should be further explored.