Pharmacokinetics and distribution of liposomal busulfan in the rat: a new formulation for intravenous administration.

The plasma pharmacokinetics and tissue distribution of busulfan (Bu) were investigated after intravenous injection of free Bu (D-Bu) and freshly prepared liposomal Bu (L-Bu). Liposomal Bu was prepared using L-alpha-phosphatidylcholine, 1,2-dioleolyl-sn-glycero-3-phosphate, and cholesterol. The liposomes formed were unilamellar vesicles measuring 220 +/- 14 nm in diameter and containing a Bu concentration of 0.31 +/- 0.03 mg/ml. The half-life of Bu in the present formulation was determined to be 8.7 +/- 2.7 days at 4 degrees C. The liposomes in the new formulation were stable for 20 days at 4 degrees C. After the intravenous administration of L-Bu or D-Bu (dissolved in a mixture of DMSO, ethanol, and propylene glycol) to the rats a higher bone marrow exposure to Bu as expressed in AUC marrow/AUC blood was achieved using L-Bu as compared with D-Bu (1.59 and 0.83, respectively). A higher distribution volume was observed for L-Bu as compared with D-Bu (1.39 versus 0.67 l/kg, respectively). The elimination half-lives were significantly longer in both blood and marrow after the administration of L-Bu as compared with D-Bu (2.52 and 3.08 versus 1.53 and 1.75 h, respectively). The new liposomal Bu showed linear pharmacokinetics within the range of 0.5-3.5 mg/kg, which is comparable with that obtained for D-Bu. A slight difference was observed in systemic exposure to L-Bu as compared with D-Bu as expressed in AUC (9.93 and 11.82 microg h ml(-1), respectively). The distribution study using 14C-labeled Bu showed that the radioactivity was significantly higher over 18 h in the bone marrow (3-fold) and spleen (2-fold; P < 0.01) in a comparison of L-Bu with D-Bu. However in the brain, lungs, and heart the distribution of radioactivity after the administration of L-Bu was significantly lower (P < 0.05) than that obtained using D-Bu. On the basis of the present study, the new formulation of liposomal Bu seems to be a promising preparation for clinical trials, since it appears to target bone marrow and spleen with no accumulation in the liver or other organs known for Bu toxicity.

Studies of the organ distribution in mice of teniposide liposomes designed for treatment of diseases in the mononuclear phagocytic system.

Liposomes can be used for the delivery of drugs in cancer chemotherapy. After i.v. injection liposomes are to a large extent taken up by the mononuclear phagocytic system (MPS). When treating diseases in the MPS, such as the histiocytic syndromes, this property is of potential value for drug targeting and may lead to a more efficient therapy with less systemic toxicity. Teniposide (VM-26) is a potent anti-tumor drug. Its lipophilicity makes it suitable for liposomal formulation. Teniposide liposomes were prepared by dissolving egg phosphatidylcholine and dioleoyl phosphatidic acid (19:1 molar ratio) in methylene chloride together with teniposide. After solvent evaporation, the dry lipid film was dispersed in a glucose solution (50 mg/mL), and size calibration was obtained by filtration through polycarbonate filters. The amount of teniposide incorporated was 2.5 mol%. To investigate the organ distribution, teniposide liposomes containing radiolabeled teniposide or phospholipid were given i.v. to mice. By increasing the size of the vesicles, the MPS uptake could be modulated. When vesicles of 200 nm and 1 and 3 microns were injected, the drug levels in the spleen were increased 2.6-, 6.8-, and 21-fold 40 min after injection, compared with levels after injection of the commercial teniposide formulation. It was concluded that organ distribution of teniposide in mice could be modified by administering the drug in liposomal form with the potential of improved treatment of diseases engaging the MPS.

Targeting of teniposide to the mononuclear phagocytic system (MPS) by incorporation in liposomes and submicron lipid particles; an autoradiographic study in mice.

Liposomes are concentrated in the mononuclear phagocytic system in vivo and may therefore be of value as carriers of drugs when treating diseases involving phagocytic cells. Teniposide (VM-26) is a potent and lipophilic cytotoxic drug. Teniposide was incorporated in large unilamellar liposomes (LUVs) consisting of egg phosphatidylcholine and dioleoyl phosphatidic acid and into the novel submicron lipid particles containing cholesteryl oleate, cholesteryl palmitate and soybean lecithin, in order to evaluate the drug targeting effect. Radiolabelled teniposide and lipids were used and the organ distribution in mice was studied with whole-body autoradiography 20 and 90 min post i.v. injection. When the commercial formulation of teniposide (Vumon) was administered, teniposide accumulated in the liver where the drug is metabolized. Biliary excretion was rapid and considerable already after 20 min. The liposomal formulation enhanced liver uptake of teniposide slightly. The distribution of radiolabelled phosphatidyl choline differed from that of teniposide indicating instability of the liposomes in circulation. Despite this, the splenic uptake of the drug was significantly enhanced by administration in liposomes. In the red pulp of the spleen the teniposide level was 23 times higher 90 min post injection, using the liposomal formulation as compared to free drug. The submicron lipid particles were mainly accumulated in the liver and to a lesser extent in the spleen. The study shows that liposomes and lipid particles enhance splenic and liver uptake and can be used to target teniposide to the MPS.

Busulfan bioavailability.

Busulfan is widely used as a component of the myeloablative therapy in bone marrow transplantation. Recent studies have shown that the drug disposition is altered in children and is associated with less therapeutic effectiveness, lower toxicities, and higher rates of engraftment failure. We have evaluated the bioavailability of the drug in two groups of patients: eight children between 1.5 and 6 years of age and eight older children and adults between 13 and 60 years. Oral bioavailability showed a large interindividual variation. In children, the bioavailability ranged from 0.22 to 1.20, and for adults, it was within the range 0.47 to 1.03. The elimination half-life after intravenous administration in children (2.46 +/- 0.27 hours; mean +/- SD) did not differ from that obtained for adults (2.61 +/- 0.62 hours). However, busulfan clearance normalized to body weight was significantly higher in children (3.62 +/- 0.78 mL.min-1.kg-1) than that in adults (2.49 +/- 0.52 mL.min-1.kg-1). Also, the distribution volume normalized for body weight was significantly higher in children (0.74 +/- 0.10 L.kg-1) compared with 0.56 +/- 0.10 L. kg-1 in adults. The difference in clearance between children and adults was not statistically significant when normalized to body surface area, which most probably shows that busulfan dosage should be calculated on the basis of surface area rather than body weight. However, to avoid drug-related toxicities, drug monitoring and an individual dose adjustment should be considered because of the variability in busulfan bioavailability.

Successful treatment of hepatosplenic candidiasis with a liposomal amphotericin B preparation.

The case of a granulocytopenic patient with acute undifferentiated leukaemia and hepatosplenic candidiasis who was refractory to conventional deoxycholate amphotericin B (AmpB) and 5-flucytosine therapy is reported. He experienced severe AmpB-related side-effects, and was subsequently successfully treated with a pharmaceutical preparation of AmpB (5.7 g) entrapped in sonicated liposomes, composed of lecithin, cholesterol and stearylamine in a molar ratio of 4:3:1. Three months later, during maintenance chemotherapy, liposomal AmpB (5.1 g) was reinstituted due to the finding of biopsies positive for Candida albicans at bronchoscopy. After healing of the patient's fungal infection a left upper lobe resection was performed, which showed advanced fibrosis with signs of inflammation, but no evidence of fungal disease. Since no acute side-effects and only moderate hypokalaemia were observed, it appears that liposomal AmpB is superior to conventional AmpB treatment in granulocytopenic patients with hepatosplenic candidiasis and unbearable therapy-related side-effects.

Phenobarbital metabolism in adults and in newborn infants.

Two adult volunteers and four newborn infants were given a single dose of phenobarbital. The output in the urine o f unchanged phenobartital and of the two main metabolites p-hydroxy phenobarbital and conjugated p-hydroxy phenobarbital was followed during 8 days in the newborns and during 2 or 4 weeks in the adults. The plasma levels were also determined and some pharmacokinetic constants calculated. It was found that the newborn patients excreted unchanged phenobartibal and p-hydroxy phenobarbital in the same proportions relative to dose as did the adult volunteers, 2.e. 16--17% unchanged drug and 9--10% of the metabolite during the first 8 days after administration. On the other hand, there was a clear-cut age difference in output of conjugated metabolite where the newborns excreted only 5% of the given dose during the 8-day observation period. The corresponding value for the adults was 15%. It is concluded that a poor conjugating capacity in the newborn may not have any serious consequences with a drug like phenobarbital where major alternative routes of excretion exist (unchanged drug and unconjugated metabolite). The clinical significance of immature drug metabolites and of unchanged drug is taken into consideration.

Determination of 8-methoxypsoralen in plasma by electron capture gas chromatography.

A method is given for the determination of 8-methoxypsoralen in human plasma at the low ng/ml level using gas chromatography with electron capture detection. 8-Methoxypsoralen was extracted from plasma with methylene chloride at pH 7.0. After addition of the internal standard, 8-butoxypsoralen, the psoralens were hydrolysed in sodium hydroxide and the aqueous phase was purified by extraction with methylene chloride and toluene. The aqueous phase was acidified and the re-lactonized psoralens were extracted with toluene and analysed. Some determinations of plasma levels of 8-methoxypsoralen after oral administration are presented.

Quantitation of phenobarbital and its main metabolites in human urine.

A method for the quantitative determination of phenobarbital and free and conjugated p-hydroxyphenobarbital in urine samples is described. The method includes initial extraction, purification on a small chromatographic column and finally determination by gas chromatography. The barbituric acids are methylated by trimethylanilinium hydroxide which serves as a "flash heater" methylating agent. The conjugate of p-hydroxyphenobarbital, which appears to be a glucuronide, is hydrolysed with hydrochloric acid.