Population PK modelling and simulation based on fluoxetine and norfluoxetine concentrations in milk: a milk concentration-based prediction model

AIMS: Population pharmacokinetic (pop PK) modelling can be used for PK assessment of drugs in breast milk. However, complex mechanistic modelling of a parent and an active metabolite using both blood and milk samples is challenging. We aimed to develop a simple predictive pop PK model for milk concentration-time profiles of a parent and a metabolite, using data on fluoxetine (FX) and its active metabolite, norfluoxetine (NFX), in milk

Paroxetine in human milk

Aims The primary aims of the study were to estimate the exposure of infants to paroxetine via breast milk and to determine the maternal milk:plasma ratio (M/P) of paroxetine. Secondary aims were to compare single point and area under the curve (AUC) estimates of M/P, to assess variability of M/P in fore and hind milk, and to compare the observed M/P with that predicted by a model. Methods Two studies were performed. In one study, six nursing mothers who were being treated with paroxetine were studied over a 24 h dose interval at steady-state. The total amount of paroxetine in the milk was measured, which represented the 'dose' to the infant. The M/P AUC was calculated and compared with a predicted value. In the second study, four nursing mothers who were being treated with paroxetine, were studied at steady-state, around a normal infant feeding time. A single plasma sample and a prefeed milk sample were taken approximately 3 h after the morning dose of paroxetine, and a postfeed milk sample taken around 1 h later. The dose received by the infant was estimated from the average milk concentrations of the pre and postfeed samples using standard assumptions, and M/P calculated directly. Plasma concentrations of paroxetine were measured in 8 of the 10 infants in the two studies. Results The mean dose of paroxetine received by the infants in the first study was 1.13% (range 0.5-1.7) of the weight adjusted maternal dose. The mean M/P AUC was 0.39 (range 0.32-0.51). The predicted M/P was 0.22. The mean dose of paroxetine received by the infants in the second study was 1.25% (range 0.38-2.24) of the weight adjusted maternal dose. The mean M/P was 0.96 (range 0.31-3.33) and did not differ between fore and hind milk. The drug was not detected in the plasma of seven of the infants studied and was detected but not quantifiable (<4 mg l −1 ) in one infant. No adverse effects were observed in any of the infants. Conclusions Measured M/P and estimated infant dose were similar in the two studies, although the range was wider for the single point study. Paroxetine can be considered 'safe' during breast feeding because the dose transferred to the infant is well below the recommended safety limit of 10% of the weight adjusted maternal dose, concentrations in the infants were generally undetectable, and no adverse effects were reported

Phase equilibria and glass transition in colloidal systems with short-ranged attractive interactions. Application to protein crystallization

We have studied a model of a complex fluid consisting of particles interacting through a hard core and a short range attractive potential of both Yukawa and square-well form. Using a hybrid method, including a self-consistent and quite accurate approximation for the liquid integral equation in the case of the Yukawa fluid, perturbation theory to evaluate the crystal free energies, and mode-coupling theory of the glass transition, we determine both the equilibrium phase diagram of the system and the lines of equilibrium between the supercooled fluid and the glass phases. For these potentials, we study the phase diagrams for different values of the potential range, the ratio of the range of the interaction to the diameter of the repulsive core being the main control parameter. Our arguments are relevant to a variety of systems, from dense colloidal systems with depletion forces, through particle gels, nano-particle aggregation, and globular protein crystallization.Comment: 20 pages, 10 figure

Paraquat is not accumulated in B16 tumor cells by the polyamine transport system

We have examined the effect of difluoromethylornithine on the ability of B16 melanoma cells to take up putrescine and the 4,4′-dipyridyl herbicide paraquat. Pretreatment with difluoromethylornithine for 24 hr enhanced putrescine uptake by inducing the maximum capacity of the transport system without affecting the Km for the substrate. Paraquat uptake was minor compared with that of putrescine and was not affected by difluoromethylornithine. Neither putrescine, spermidine or spermine at concentrations up to 100 μM inhibited the accumulation of paraquat. However, paraquat competitively inhibited putrescine transport (Ki = 54 ± 10 μM). Exposure of the B16 melanoma cells for 24 hr to increasing concentrations of paraquat produced a dose-dependent inhibition of DNA synthesis. Difluoromethylornithine pretreatment did not affect paraquat toxicity. These data show that paraquat is not taken up into B16 melanoma cells by the uptake system responsible for transporting putrescine. Moreover, it is likely that the difluoromethylornithine inducible polyamine transport system in B16 melanoma cells is characteristically different to that previously described in normal mammalian lung since the latter is reportedly capable of transporting both putrescine and paraquat

Measurement of organ blood flow in the rabbit

A surgical procedure to facilitate the radioactive microsphere technique for simultaneously measuring cardiac output and its regional distribution has been developed. The procedure allows the use of either anesthetized or conscious rabbits. Organ blood flows in untreated and saline-treated conscious rabbits and saline-treated anesthetized rabbits were quantified and compared. First, comparison of data from the untreated and saline-treated conscious rabbits demonstrated a significantly lower hepatic blood flow in the untreated animals. Moreover, liver blood flow in the untreated animals was markedly less than literature values. Since the untreated rabbits were not handled on a regular basis prior to the blood flow study, it is suggested that anxiety may have caused the redistribution of splanchnic circulation. Secondly, comparison of the data from the conscious and anesthetized saline-treated rabbits demonstrated that total liver blood flow was similar and in agreement with literature values. Hence, either the conscious or anesthetized animal can be used to estimate liver blood flow. By contrast, blood flow to the kidney and caecum was significantly altered by anesthesia (propanidid: nitrous oxide: halothane), indicating that blood flow to these organs is best studied in the placid conscious rabbit

Antiarrhythmic potency of procainamide and N-acetylprocainamide in rabbits

The antiarrhythmic potency of procainamide (PA) and N-acetylprocainamide (NAPA) has been investigated in rabbits using isolated atrial preparations and ouabain-induced ventricular fibrillation in vivo. At concentrations in the range 3 × 10 to 1 × 10 M, both PA and NAPA decreased the maximum following frequency (MFF) of isolated atria. The dose-response curves were not parallel but at a concentration of 10M, NAPA had only one tenth of the potency of PA. Threshold level voltage of the atria was increased by PA but NAPA had no significant effect on this parameter. When atria were preincubated with NAPA (1.6 × 10 or 8.0 × 10 M), the dose-response curve for PA on MFF was displaced to the right. Pretreatment of anaesthetised rabbits with either PA (25 mg/kg i.v.) or NAPA (75 mg/kg i.v.) prolonged the time to onset of ouabain-induced ventricular fibrillation. NAPA (25 mg/kg) did not affect the response to PA (25 mg/kg). The data support the view that NAPA is less potent than PA and suggest that, under certain circumstances, NAPA may antagonise the actions of PA

Characterisation of putrescine uptake by cultured adult mouse hepatocytes

Uptake of polyamines by cultured cells has been shown to be influenced by growth rate and/or differentiation. In this study, we have investigated whether the fully differentiated, non-proliferating adult mouse hepatocyte is capable of accumulating extracellular putrescine. When hepatocytes were cultured from 4 to 48 h, uptake of putrescine was found to increase substantially with time spent in culture. The V for putrescine uptake increased 22-fold during this period with no change in apparent K. Treatment of the cells with cycloheximide or actinomycin D at concentrations that did not affect cell viability inhibited the induction of putrescine uptake. Endogenous putrescine levels increased from 19.7 nmol/mg DNA after 4 h in culture to over 500 nmol/mg DNA after 48 h in culture. This increase was accompanied by a loss of over 90% of ornithine decarboxylase activity. Spermidine levels did not change over this time period, whereas spermine levels decreased by 35%. Difluoromethylornithine prevented the observed increase in intracellular putrescine but did not affect putrescine uptake. The increase in putrescine transport was not inhibited by culturing the hepatocytes in a high concentration of putrescine, spermidine or spermine. Moreover, the induction process was not stimulated by foetal calf serum but was selectively inhibited by the differentiating agents dimethylsulfoxide and retinoic acid. The results from those studies show that cultured mouse hepatocytes express a putrescine transport system that is poorly regulated by extracellular polyamines. The expression of the transporter requires the synthesis of mRNA and protein, and appears to be related to a time-dependent change in hepatocyte phenotype

Cell cycle–dependent uptake of putrescine and its importance in regulating cell cycle phase transition in cultured adult mouse hepatocytes

Previous studies in which investigators have induced the rate of polyamine uptake in vitro have used either inhibitors of polyamine biosynthesis or growth factors that induce cell proliferation. Recently, however, we have described the induction of putrescine uptake in cultured adult mouse hepatocytes and have shown that uptake is independent of both intracellular polyamine levels and proliferation. Although proliferation was not apparent in those studies, data suggested that, after isolation, the cells entered G of the cell cycle. In this study, we have examined whether the induction of putrescine uptake is a function of entry into the cell cycle and whether uptake activity is essential for optimal progression into the S phase. Using ribonuclease reductase subunit M1 as a marker of entry into the cell cycle, we have shown that hepatocytes enter G during the first 4 hr of culture. Both putrescine uptake and ornithine decarboxylase activity increased as the cells entered G. Treatment of the cells with retinoic acid (10 to 33 μmol/L) prevented them from entering G and also inhibited the induction of the putrescine transporter by up to 90%. In contrast, initiation of G to S phase transition markedly down‐regulated the activity of the transporter. Thus induction of the putrescine transporter in isolated hepatocytes appears to be a G‐specific event. Culturing the hepatocytes in the presence of 1,1′‐bis[3‐(1′‐methyl‐[4,4′‐bipyridinium]‐1‐yl)‐propyl]‐4,4′‐bipyridinium, a potent competitive inhibitor of putrescine uptake, resulted in a 47% decrease in intracellular putrescine. Measurement of the distribution of tracer H polyamines showed a loss of intracellular polyamines and an accumulation of extracellular polyamines when cells were treated with 1,1′‐bis[3‐(1′‐methyl‐[4,4′‐bipyridinium]‐1‐yl)‐propyl]‐4,4′‐bipyridinium, indicating that the re‐uptake of effluxed polyamines contributes to intracellular polyamine homeostasis in cultured hepatocytes. DNA synthesis was significantly inhibited in 1,1′‐bis[3‐(1′‐methyl‐[4,4′‐bipyridinium]‐1‐yl)‐propyl]‐4,4′‐bipyridinium–treated cells, and this effect was completely reversed by the addition of 200 μmol/L extracellular putrescine. We concluded that putrescine uptake is important for maintaining high intracellular putrescine levels required for optimal G to S phase transition in isolated mouse hepatocytes. (HEPATOLOGY 1991;14:1243–1250.