Comparative pharmacokinetics and pharmacodynamics of lansoprazole oral capsules and suspension in healthy subjects.

The pharmacokinetics and pharmacodynamics of lansoprazole suspension and lansoprazole capsules were studied. Thirty-six healthy males and females were randomized in a single-dose, open-label, two-period crossover study. Lansoprazole 30 mg was administered via a nasogastric tube as simplified lansoprazole suspension (in 8.4% sodium bicarbonate) or orally as the intact capsule after a minimum 12-hour fast and 5 hours before lunch. Ambulatory 24-hour intragastric pH was monitored at baseline and on day 1 of each treatment period to assess lansoprazole's pharmacodynamics. Blood samples were collected before drug administration and at predetermined intervals up to 24 hours after each dose to assess lansoprazole's pharmacokinetics. Both formulations effectively raised the mean 24-hour intragastric pH (mean 24-hour pH of 3.75 with suspension and 3.52 with intact capsule) and maintained it above threshold values of 3 and 4 for more than 40% of the 24-hour postdose period. The suspension was associated with a significantly shorter mean time to the maximum observed concentration (tmax) compared with the intact capsule. The mean maximum observed plasma concentration (Cmax) of the suspension was significantly higher and the mean area under the concentration-time curve from time zero to infinity (AUC infinity) was significantly lower than those of the intact capsule (879 versus 810 ng/mL and 1825 versus 2229 ng.hr/mL). The 90% confidence intervals obtained by two one-sided tests for both Cmax and AUC infinity were contained within the 0.80 to 1.25 range, confirming the bioequivalence of the two regimens. Simplified lansoprazole suspension effectively controls intragastric pH, is bioequivalent to the intact capsule, and represents an effective therapeutic option for patients who have difficulty swallowing or are unable to swallow lansoprazole capsules.

Effects of ABT-761, a novel 5-lipoxygenase inhibitor, on the pharmacokinetics of a single dose of ethinyl estradiol and levonorgestrel in healthy female volunteers.

ABT-761 is a second-generation 5-lipoxygenase inhibitor in clinical development for the treatment of asthma. The effects of ABT-761 on the pharmacokinetics of an oral contraceptive were assessed in 21 female adult volunteers in a phase I, multiple-dose, open-label study. Subjects received a single dose of oral contraceptive (30 microg ethinyl estradiol and 0.15 mg of levonorgestrel) on each of days 1 and 29. Oral doses of 300 mg of ABT-761 were administered once daily beginning on day 15 continuing through day 29. Statistically significant decreases in maximum concentration (Cmax) and area under the concentration-time curve (AUC) of ethinyl estradiol were observed when oral contraceptive was administered concomitantly with ABT-761 compared with administration of oral contraceptive alone. The mean elimination rate constant of ethinyl estradiol increased by 30% (a mean decrease of 3.8 hours in half-life), and the mean apparent volume of distribution during the terminal phase (Vd(beta)/F) of ethinyl estradiol increased by 73% in the presence of ABT-761. Mean Cmax and AUC values for norgestrel decreased by 12% and 10%, respectively, when administered with ABT-761. Mean values for time to Cmax (tmax), terminal rate constant (beta), half-life (t1/2), and Vd(beta)/F of norgestrel were similar when oral contraceptive was administered alone or concomitantly with ABT-761. The mechanism responsible for the effect of ABT-761 on the clearance of ethinyl estradiol remains undefined. Because results of previous multiple-dose studies of ABT-761 do not provide any evidence of autoinduction, the effects of ABT-761 on the pharmacokinetics of ethinyl estradiol are more likely related to absorption of ethinyl estradiol.

Medication use in the breastfeeding mother.

Historically, the risks associated with drugs in breast milk were not a major clinical concern. The small percentage of infants who were breastfed and the low use of drugs in postpartum women stimulated little interest in studying medication use in the breastfeeding mother. However, explosive growth in the number of new pharmacologic agents, concerns over environmental contaminants, and a significant increase in breastfeeding, dramatically altered the interest in this clinical issue. Providers of health care to women and children often are asked to advise breastfeeding women on the choice and risks of a particular medication. However, medical professionals too often simply discourage breastfeeding when this situation arises. This short review examines factors that determine whether a drug that enters breast milk poses a risk to the breastfeeding infant. A series of questions and practical decisions are presented that should enable nurses and other health care providers to more effectively address the issue of medication use in a breastfeeding woman.

The function of protein carboxylmethyltransferase in eucaryotic cells.

Protein carboxylmethyltransferase (PCM) is an enzyme whose function in eucaryotic cells remains controversial. Early studies suggested that protein carboxylmethylation subserved a regulatory, post-translational role in such diverse processes as secretion, neuronal receptor function, chemotaxis, and cellular differentiation. Later work strongly supported a totally unrelated role for this enzyme, i.e., the repair of spontaneously altered aspartate residues in cellular proteins. More recent evidence, however, suggests that a distinct, membrane-associated PCM catalyzes the methylation of alpha-carboxyl groups of C-terminal cysteines on discrete proteins. In view of these recent investigations, the data supporting a regulatory role for PCM are critically discussed and re-evaluated. There now appears to be compelling evidence that PCM(s) subserves both repair and regulatory functions in eucaryotic cells, catalyzing post-translational modifications of proteins involved in cell division, hormonal secretion, calmodulin-associated events and the interaction of guanyl nucleotide-linked proteins with the cell membrane.

Protein carboxylmethyltransferase activity in intact, differentiated neuroblastoma cells: quantitation by S-[3H]adenosylmethionine prelabeling.

Protein carboxylmethyltransferase has been proposed to play a role in the regulation of neuroblastoma differentiation (Kloog et al., 1983). When we investigated this hypothesis further, different results for methyl ester formation were obtained when measured in acid-precipitated proteins and in proteins separated by acidic polyacrylamide gel electrophoresis, following the incubation of intact neuroblastoma cells with [3H]methionine. These unexpected findings led to the development of a modified assay using S-[3H]-adenosylmethionine as the radiolabeled precursor for quantitating carboxyl methylation in intact cells. Data obtained from either acid-precipitated proteins or those separated on an electrophoresis gel following S-[3H]adenosylmethionine incubation directly correlated with data obtained from proteins separated by electrophoresis following [3H]methionine incubation. Using each of the three methods, an approximately twofold increase in the carboxyl methylation of cellular proteins was detected in neuroblastoma cells differentiated by reducing the serum concentration from 10 to 0.5%, but not in those cells differentiated with either 5 mM hexamethylene bisacetamide or 2% dimethyl sulfoxide. The finding that all detectable methyl acceptor proteins are increasingly methylated following 0.5% serum treatment and that this modification is substoichiometric suggests that protein carboxyl methylation is not an essential component of the differentiation process in neuroblastoma cells.

Dihydropyrimidine dehydrogenase activity in human blood mononuclear cells.

Dihydropyrimidine dehydrogenase (DPD; EC 1.3.1.2) catalyzes the rate-limiting reaction in the catabolism of endogenous uracil and thymine and exogenous fluoropyrimidines. DPD activity was studied in human blood mononuclear cell supernatants utilizing a new and sensitive radiochromatographic assay. Total DPD activity showed a linear correlation with supernatant protein concentration. The affinity constants (Km) for NADPH and thymine were approximately 10 and 1 mumol/l, respectively. Maximal activity (Vmax) was observed at 0.25 mmol/l NADPH and 10 mumol/l thymine, respectively. DPD activity in normal individuals was 8.0 +/- (SD) 2.2 nmol/mg protein/h, and ranged from 4.4 to 12.3 nmol/mg/h (n = 25). This activity range was quite similar to values obtained in patients with metastatic solid tumors treated with fluorodeoxyuridine (FUdR; n = 33, p = 0.57). No correlation was found to exist between mononuclear leucocyte DPD activity and the observed toxicity of FUdR in the tested patients. A bimodal distribution of DPD activity was observed in the patients and in normal individuals. The entire study population tested could be divided into two groups with respect to DPD activity; one group with high (greater than 8 nmol/mg/h) activity and another with low (less than 8 nmol/mg/h) activity. The possibility that sex differences may have been responsible for this distribution of DPD activity could not be excluded. The findings of this study are relevant to the pharmacogenetics of fluoropyrimidines in humans.

Effects of essential fatty acid deficiency on renal papillary lipid methylation.

The relationship between lipid methylation and prostaglandin release was examined in rat renal papillae. Essential fatty acid deficiency (EFAD) was produced to deplete tissues of arachidonate precursors. The in vitro release of prostaglandin E was determined after exposure of the papillae to hypertonic sodium chloride. The EFAD animals were observed to have significantly less renal papillary lipid methylation than rats fed control diets (50%; P less than 0.05). However, stimulation of prostaglandin production in vitro was not accompanied by any detectable changes in total lipid methylation in tissues from either normal or EFAD rats.

Pyrimidine base degradation in cultured murine C-1300 neuroblastoma cells and in situ tumors.

Dihydropyrimidine dehydrogenase (DPD), the initial, rate-limiting step in pyrimidine degradation, was studied in two cell lines of murine neuroblastoma (MNB-T1 and MNB-T2) that were derived from C-1300 MNB tumor carried in A/J mice. The MNB-T2 (low malignancy) cell line was originally derived from the in situ tumor and carried in tissue culture for more than 100 passages; the MNB-T1 (high malignancy) line consisted of a new sub-culture that was also established from the in situ MNB tumor. DPD activity was determined in cytosolic preparations of MNB utilizing high performance liquid chromatography to separate the radiolabeled substrate ([2-14C]thymine) from [2-14C]dihydrothymine. The apparent affinity of DPD for NADPH in MNB cells (Km approximately 0.08 mM) was identical to that of A/J mouse brain and liver. The DPD activity of the high malignancy (MNB-T1) cell line was 14.3% of that observed in the low malignancy (MNB-T2) line. In situ tumors formed after implantation of high malignancy (MNB-T1) cells into A/J mice had only 25.2% of the DPD activity observed in tumors derived from low malignancy (MNB-T2) cells. When MNB-T2 cells were injected into naive A/J mice, tumors developed in only 68% of animals, the tumor growth rate was slow and a mortality of 20% was observed. In contrast, tumors derived from injected MNB-T1 cells showed a faster growth rate and 100% mortality. Most MNB-T2 derived tumors were not lethal and ultimately resolved while the MNB-T1 derived tumors were invariably lethal. These studies support the concept that the levels of DPD activity in neoplastic cells are inversely related to their malignant expression and also provide a model to study differences between neuroblastoma cell lines derived from the same in situ tumor but which manifest different neoplastic behavior.

Cytotoxic action of adenosine nucleoside and dialdehyde analogues on murine neuroblastoma in tissue culture: structure-activity relationships.

A series of purine nucleoside and dialdehyde analogues was studied to determine their potency as inhibitors of C-1300 murine neuroblastoma cell growth in tissue culture. Tumor cells were incubated with each analogue for 72 h, and the number of viable cells was determined at 24, 48, and 72 h. Dose-response curves were generated (concentration range, 10(-8) to 10(-3) M), and the drug concentration producing 50% inhibition of cell growth was calculated for each analogue. The 50% inhibitory concentrations, in ascending order of potency, were as follows: adenosine (inactive); S-adenosylhomocysteine (inactive); methylfuryladenine (5.6 X 10(-1)M); adenosine 5'-carboxylic acid (2.0 X 10(-1)M); 5'-chloro, 5'-deoxy-ara-adenosine (3.0 X 10(-2)M); sinefungin (1.7 X 10(-3) M); 5'-deoxyadenosine (2.2 X 10(-4)M); 5'-chloro, 5'-deoxyadenosine (2.1 X 10(-4)M); 3',5'-dichloro, 2',3',5'-trideoxyadenosine (1.3 X 10(-4)M); 3-deazaadenosine (5.6 X 10(-5)M); and adenosine dialdehyde (1.5 X 10(-6)M). Oxidation of the pentose to a dialdehyde increased, whereas reduction of the dialdehyde or substitution of adenine with either hypoxanthine, guanine, uracil, or cytosine decreased the inhibitory potency. The analogues 4',5'-anhydroadenosine dialdehyde and 5'-deoxyadenosine dialdehyde, which cannot be phosphorylated at the 5' position, had 50% inhibitory concentrations of 9.1 X 10(-6) and 7.6 X 10(-6)M, respectively. These data suggest that the inhibitory action and potency of nucleoside dialdehydes on neuroblastoma growth are independent of their capacity to undergo a kinase-mediated phosphorylation at the 5' position.

Effect of adenosine analogues on protein carboxylmethyltransferase, S-adenosylhomocysteine hydrolase, and ribonucleotide reductase activity in murine neuroblastoma cells.

The noncompetitive S-adenosylhomocysteine (AdoHcy) hydrolase antagonist adenosine dialdehyde (AD) has been shown to suppress the growth of cultured C-1300 murine neuroblastoma (MNB) cells. The enzymatic sites at which AD and other nucleoside analogues exert their cytotoxic effects have been postulated to include protein carboxylmethyltransferase (PCM), AdoHcy hydrolase, and ribonucleotide reductase. AD (10(-5) M) increased PCM activity 350% in suspensions prepared from disrupted cells after 72 h of drug exposure; in contrast, 3-deazaadenosine (10(-4) M) increased PCM activity 57%, whereas AdoHcy and sinefungin had no effect. When intact MNB cells were incubated with AD for varying time periods up to 72 h and then pulse labeled with the S-adenosylmethionine precursor L-[3H]-methionine, AD (10(-8) to 5 X 10(-6) M) produced a concentration-dependent inhibition of protein carboxylmethylation which persisted for up to 6 h. Following extended periods of AD treatment (48 to 72 h), AD (10(-6) to 10(-5) M) produced a 250% increment in protein carboxylmethylation, similar in magnitude to that observed in disrupted cell preparations. This increase in carboxylmethylation was observed at timepoints when AdoHcy hydrolase activity remained suppressed. The inhibitory effect of AD on AdoHcy hydrolase activity was maximal within 4 h and still apparent after 72 h of incubation. In contrast, AD treatment had no effect on the ribonucleotide reductase activity of MNB cells. These data suggest that the cytotoxic effect of AD on MNB cells results directly from its inhibition of AdoHcy hydrolase activity and indirectly through its suppression of methyltransferase enzyme systems. The potential linkage between the observed long-term elevations in PCM activity and AD-induced cytotoxicity remains to be defined.

Effects of uridine and thymidine on the degradation of 5-fluorouracil, uracil, and thymine by rat liver dihydropyrimidine dehydrogenase.

The kinetic properties and control mechanisms of 5-fluorouracil (5-FU), uracil, and thymine degradation by rat liver dihydropyrimidine dehydrogenase were studied in vitro. The calculated Michaelis constant (Km) for 5-FU was 3.49 +/- 0.41 (SE) microM, similar to those for uracil (2.26 +/- 0.28 microM) and for thymine (2.23 +/- 0.34 microM). However, the reduction of 5-FU appears to be most sensitive to the inhibitory effects of increased substrate concentration. The specific activities of dihydropyrimidine dehydrogenase (nmol/min/mg of protein) for 5-FU, uracil, and thymine were 0.82, 0.68, and 0.56, respectively. Uridine was found to be a potent noncompetitive inhibitor of pyrimidine base degradation in vitro, displaying an inhibition constant (Ki) for 5-FU of 0.71 microM. Total inhibition of 5-FU degradation occurred at a uridine concentration of 10 microM, whereas thymidine was found to be a much less potent noncompetitive inhibitor of pyrimidine base degradation (Ki 24 microM). This paper provides the first documentation of in vitro inhibition of dihydropyrimidine dehydrogenase activity by nucleosides. The concomitant utilization of uridine and 5-FU in clinical situations might prove useful by decreasing 5-FU catabolism to toxic metabolites as well as enhancing 5-FU cytotoxicity.

Effect of calcium, sodium and isoproterenol on renin secretion from disaggregated rat renal cortical cells.

A disaggregated cell system prepared from rat renal cortices has been developed to study the regulation of renin release in vitro. Cell suspensions were prepared by incubating minced renal cortical tissue in collagenase. The digested tissue was filtered sequentially through graded Teflon meshes of 125 and 44 mu, respectively. This preparation contained less than 2% intact glomeruli or tubules. Incubation of cell suspensions with the beta-adrenergic agonist L-isoproterenol (ISO) significantly increased the activity of renin released into the incubation media. Peak levels of renin activity were detected 10 to 15 min after the addition of ISO. The apparent ED50 for stimulation of renin release by ISO was 6 X 10(-8)M and the response was antagonized by the beta-adrenergic antagonist dl-propranolol. The spontaneous release of renin was also suppressed by increasing the concentration of extracellular calcium, whereas sodium ions had no effect on this process. These data have demonstrated that disaggregated renal cortical cell models are useful for studying the in vitro effects of pharmacologic agents and ions on renin secretion.

Tobramycin serum level monitoring in young patients with normal renal function.

Five clinical strategies for monitoring serum tobramycin concentrations were compared in a population of children and young adults with normal renal function receiving tobramycin for suspected sepsis. The drug monitoring strategies were evaluated on the basis of the ability of each to predict subsequent drug levels. The strategies included 3 methods requiring assessment of individual drug disposition: (a) measurement of peak drug concentrations after 2 separate doses; (b) a 3-point kinetic study to define distribution volume and elimination rate; (c) a 3-point kinetic study with adjustment of the value for elimination rate to account for deep compartment drug accumulation; and 2 strategies using a fixed-dose approach in which prediction of individual levels was made on the basis of mean population kinetic parameters. Although all methods were of similar accuracy, the fixed-dose strategy was the most precise in predicting subsequent serum tobramycin levels (95% tolerance limits = 84-135% of predicted). Poor performance of the other strategies was accounted for by interpatient variability of tobramycin disposition that was small relative to the intrapatient variability in these measurements. We conclude that these strategies for aminoglycoside serum level monitoring, which have proven beneficial in patients with impaired renal function, afford little benefit to children and young adults with normal renal function. Administration of these drugs on a fixed-dose schedule without serum concentration monitoring appears to be warranted in this select population. Alternatively, specific strategies for this population must be developed that consider the small interindividual differences in drug disposition and low incidence of toxicity.

Antihypertensive effect and elimination kinetics of captopril in hypertensive children with renal disease.

The efficacy and safety of captopril were studied in 10 patients with secondary hypertension (renal parenchymal disease, four patients; renal artery stenosis, two; and renal transplant rejection, four). Captopril was administered according to a dose titration protocol that randomized the initial three doses (0.5, 1.0, and 2.0 mg/kg) of drug to one of six possible sequences. All patients received diuretics prior to and during captopril therapy. A significant reduction in mean blood pressure was observed in all 10 patients during the initial dose titration. No correlation was observed between captopril dose and magnitude of the blood pressure reduction. The onset of antihypertensive action began approximately 15 minutes after each orally administered dose and reached the nadir approximately 1 1/2 hours later. Blood pressure returned to predrug levels between 6 and 10 hours after the dose. A significant reduction in systolic and diastolic blood pressure was noted in all subjects after 1 week of captopril treatment and was maintained during the course of continuous therapy in nine of 10 patients. Captopril combined with hydrochlorothiazide produced a satisfactory therapeutic response in five patients; in four others, additional antihypertensive drugs were required. No significant adverse effects were observed. Plasma renin activity determined prior to initiation of captopril was not predictive of blood pressure response to the drug. The clearance of captopril from patients with kidney failure ranged from 14.1 to 18.8 ml/min/kg in five subjects with creatine clearance between 10 and 21 ml/min/1.73 m2.

Protein carboxyl-O-methyltransferase activity in cultured C-1300 neuroblastoma cells.

Protein carboxylmethyltransferase (PCM) has been identified in a variety of tissues derived from neural crest anlage, including in vivo C-1300 murine neuroblastoma (MNB). These observations have stimulated interest in further defining the role of PCM as a potential modulator of neoplastic cell behavior. The subcellular distribution and kinetic behavior of PCM have been characterized in a tissue culture line derived from the C-1300 murine neuroblastoma (clone NB41A3). The specific and total activities of PCM in the presence and absence of exogenous substrate were determined in subcellular fractions of MNB cells prepared by differential centrifugation. In the presence of exogenous substrate (+ gelatin), 40% of the total PCM activity was present in the 100,000 g supernatant fraction and 41% in the 800 g particulate fraction, whereas the higher specific activity of PCM was present in the 100,000 g supernatant fraction. Enzyme activity measured in the absence of gelatin, which reflects the concentration of endogenous methyl acceptor proteins in a cell fraction, was negligible. This activity represented less than 1.6 and 0.4% of the total PCM activity present in the 800 g particulate and 100,000 g soluble fractions respectively. Cytosolic PCM had an apparent Km of 13.9 x 10(-6) M for AdoMet and a Vmax of 33 pmoles per min per mg protein. Cytoplasmic PCM was inhibited competitively by S-adenosylhomocysteine (Ki equal 0.2 microM). These data demonstrate that the specific activity of PCM was greatest in the soluble component of subcellular fractions prepared from cultured MNB cells. This distribution pattern of PCM is similar to that observed in the C-1300 MNB tumor grown in situ and in non-malignant tissues. In contrast to the latter tissues, cultured MNB cells exhibited low PCM activity when assayed in the absence of exogenous substrate.