The pharmacokinetic profile of liposomal amphotericin B, based upon total plasma concentrations of amphotericin B, was determined in cancer patients with febrile neutropenia and bone marrow transplant patients who received 1 hour infusions of 1.0 to 7.5 mg/kg/day liposomal amphotericin B for 3 to 20 days. Liposomal amphotericin B has a significantly different pharmacokinetic profile from that reported in the literature for conventional presentations of amphotericin B, with higher amphotericin B plasma concentrations (Cmax) and increased exposure (AUC0-24) compared to conventional amphotericin B. After the first dose and last dose, the pharmacokinetic parameters of amphotericin B (mean ± standard deviation) ranged from:
Cmax 7.3µg/ml (±3.8) to 83.7µg/ml (±43.0)
T1/2 6.3 hr (±2.0) to 10.7 hr (±6.4)
AUC0-24 27 µg.hr/ml (±14) to 555 µg.hr/ml (±311)
Clearance (Cl) 11 ml/hr/kg (±6) to 51 ml/hr/kg (±44)
Volume of distribution (Vss) 0.10 L/kg (±0.07) to 0.44 L/kg (±0.27)
Minimum and maximum pharmacokinetic values do not necessarily relate to the lowest and highest doses, respectively. Following administration of liposomal amphotericin B, steady state was reached quickly (generally within 4 days of dosing).
Absorption
Liposomal amphotericin B pharmacokinetics following the first dose of L-AmB appear nonlinear such that amphotericin B concentrations are greater than proportional with increasing dose. This non-proportional dose response is believed to be due to saturation of reticuloendothelial liposomal amphotericin B clearance. There was no significant drug accumulation in the plasma following repeated administration of 1 to 7.5 mg/kg/day.
Distribution
Volume of distribution on day 1 and at steady state suggests that there is extensive tissue distribution of liposomal amphotericin B.
Elimination
After repeated administration of liposomal amphotericin B, the terminal elimination half-life (t½β) of amphotericin B was approximately 7 hours. The excretion of liposomal amphotericin B has not been studied.
Metabolism
The metabolic pathways of amphotericin B and liposomal amphotericin B are not known. Due to the size of the liposomes, there is no glomerular filtration and renal elimination of liposomal amphotericin B, thus avoiding interaction of amphotericin B with the cells of the distal tubuli and reducing the potential for nephrotoxicity seen with conventional amphotericin B presentations.
Special populations
Renal Impairment
The effect of renal impairment on the pharmacokinetics of liposomal amphotericin B has not been formally studied. Data suggest that no dose adjustment is required in patients undergoing haemodialysis or filtration procedures, however, Amphotericin B Tillomed liposomal administration should be avoided during the procedure.
Pharmacokinetic/pharmacodynamics relationship
Mechanism of resistance
Intrinsic resistance, though rare, may be primarily due to decrease in ergosterol or a change in the target lipid, leading to reduced binding of amphotericin B to the cell membrane.
Breakpoints
EUCAST breakpoints for liposomal amphotericin B have not yet been established, however, susceptibility to L-AmB may differ to that of amphotericin B deoxycholate.
Amphotericin B, the antifungal component of L-AmB, is active in vitro against many species of fungi, most strains of Histoplasma capsulatum, Coccidioides immitis, Candida spp, Blastomyces dermatidis, Rhodotorula, Cryptococcus neoformans, Sporothrix schenkii and Aspergillus fumigatus, Penicillium marneffi, and members of the mucormycetes group of moulds including Mucor mucedo, Rhizomucor and Rhizopus oryzae.
The majority of clinically important fungal species seem to be susceptible to amphotericin B, although intrinsic resistance has rarely been reported, for example, for some strains of S. schenckii, C. glabrata, C.krusei, C. tropicalis, C. lusitaniae, C. parapsilosis and Aspergillus terreus.
L-AmB has been shown to be effective in animal models of visceral leishmaniasis (caused by Leishmania infantum and Leishmania donovani).