The bioavailability, dispostion kinetics and dosage of sulphadimethoxine in dogs.
The disposition kinetics of sulphadimethoxine were studied in six normal beagle dogs after intravenous injection of a single dose (55 mg/kg). The median (range) distribution and elimination half times of the drug were 2.36 (2.06-3.35) hours and 13.10 (9.71-16.50) hours, respectively. Total body clearance of the drug had a median value of 21.7 ml/kg/h and a mean value of 21.4 ml/kg/h. While the overall tissue to plasma level ratio (k12/k21) of the drug was 0.55 after distribution equilibrium had been attained, analogue computer simulated curves showed that at 24 hours the fractions (percentage) of the dose in the central and tissue compartments were 12 and 11%, respectively. The drug was shown, by equilibrium dialysis method, to be highly bound to plasma proteins (greater than 75%) within the usual therapeutic range (50 to 150 mug/ml) of plasma levels. The systemic availability of sulphadimethoxine from the oral suspension was 32.8% (22.5-80.0). Since the absorption half time, 1.87 (0.86-3.22) hours, was considerably shorter than the half-life, 13.10 (9.71-16.50) hours, of the drug, the rate of absorption would have little influence on the dosage regimen. Based on the experimental data obtained, a satisfactory dosage regimen might consist of a priming dose of 55 mg/kg by the intravenous route and maintenance doses of either 27.5 mg/kg of sulphadimethoxine injection given intravenously or 55 mg/kg of the oral suspension administered at 24 hour intervals. The adequacy and duration of therapy will depend upon the clinical response obtained. (+info)
Cocaine metabolite kinetics in the newborn.
The study goal was to determine the half-life elimination of cocaine and benzoylecgonine (BZE) in the newborn. Three 0.3-mL blood samples were collected during the first day of life. Urine was collected once daily. Cocaine and BZE concentrations were determined by gas chromatography-mass spectrometry. An extraction method was developed for measuring low concentrations of cocaine and BZE in small (0.1 mL) blood samples. Cocaine had a half-life of 11.6 h in one subject. The half-life of BZE during the first day of life, based on blood data in 13 subjects, was 16 h (95% confidence interval [CI], 12.8 to 21.4 h). The half-life of BZE during the first week of life, based on urine data in 16 subjects, was 11.2 h (95% CI, 10.1 to 11.8 h). The novel extraction method for small blood sample volumes should be applicable to other basic drugs. (+info)
Re-entering the translocon from the lumenal side of the endoplasmic reticulum. Studies on mutated carboxypeptidase yscY species.
Misfolded or unassembled secretory proteins are retained in the endoplasmic reticulum (ER) and subsequently degraded by the cytosolic ubiquitin-proteasome system. This requires their retrograde transport from the ER lumen into the cytosol, which is mediated by the Sec61 translocon. It had remained a mystery whether ER-localised soluble proteins are at all capable of re-entering the Sec61 channel de novo or whether a permanent contact of the imported protein with the translocon is a prerequisite for retrograde transport. In this study we analysed two new variants of the mutated yeast carboxypeptidase yscY, CPY*: a carboxy-terminal fusion protein of CPY* and pig liver esterase and a CPY* species carrying an additional glycosylation site at its carboxy-terminus. With these constructs it can be demonstrated that the newly synthesised CPY* chain is not retained in the translocation channel but reaches its ER lumenal side completely. Our data indicate that the Sec61 channel provides the essential pore for protein transport through the ER membrane in either direction; persistent contact with the translocon after import seems not to be required for retrograde transport. (+info)
Cardiomegaly in the juvenile visceral steatosis (JVS) mouse is reduced with acute elevation of heart short-chain acyl-carnitine level after L-carnitine injection.
The long-term administration of L-carnitine was very effective in preventing cardiomegaly in juvenile visceral steatosis (JVS) mice, which was confirmed by heart weight as well as the lipid contents in heart tissue. After i.p. injection of L-carnitine, the concentration of free carnitine in heart remained constant, although serum free carnitine level increased up to 80-fold. On the other hand, a significant increase in short-chain acyl-carnitine level in heart was observed. These results suggest that increased levels of short-chain acyl-carnitine, not free carnitine, might be a key compound in the protective effect of L-carnitine administration in JVS mice. (+info)
Protection against lymphocytic choriomeningitis virus infection induced by a reduced peptide bond analogue of the H-2Db-restricted CD8(+) T cell epitope GP33.
Recent investigations have suggested that pseudopeptides containing modified peptide bonds might advantageously replace natural peptides in therapeutic strategies. We have generated eight reduced peptide bond Psi(CH2-NH) analogues corresponding to the H-2Db-restricted CD8(+) T cell epitope (called GP33) of the glycoprotein of the lymphocytic choriomeningitis virus. One of these pseudopeptides, containing a reduced peptide bond between residues 6 and 7 (Psi(6-7)), displayed very similar properties of binding to major histocompatibility complex (MHC) and recognition by T cell receptor transgenic T cells specific for GP33 when compared with the parent peptide. We assessed in vitro and in vivo the proteolytic resistance of GP33 and Psi(6-7) and analyzed its contribution to the priming properties of these peptides. The Psi(6-7) analogue exhibited a dramatically increased proteolytic resistance when compared with GP33, and we show for the first time that MHC-peptide complexes formed in vivo with a pseudopeptide display a sustained half-life compared with the complexes formed with the natural peptide. Furthermore, in contrast to immunizations with GP33, three injections of Psi(6-7) in saline induced significant antiviral protection in mice. The enhanced ability of Psi(6-7) to induce antiviral protection may result from the higher stability of the analogue and/or of the MHC-analogue complexes. (+info)
In vivo modulation of alternative pathways of P-450-catalyzed cyclophosphamide metabolism: impact on pharmacokinetics and antitumor activity.
The widely used anticancer prodrug cyclophosphamide (CPA) is activated in liver by a 4-hydroxylation reaction primarily catalyzed by cytochrome P-4502B and P-4502C enzymes. An alternative metabolic pathway involves CPA N-dechloroethylation to yield chloroacetaldehyde (CA), a P-4503A-catalyzed deactivation/neurotoxication reaction. The in vivo modulation of these alternative, competing pathways of P-450 metabolism was investigated in pharmacokinetic studies carried out in the rat model. Peak plasma concentrations (Cmax) for 4-OH-CPA and CA were increased by 3- to 4-fold, and apparent plasma half-lives of both metabolites were correspondingly shortened in rats pretreated with phenobarbital (PB), an inducer of P-4502B and P-4503A enzymes. However, PB had no net impact on the extent of drug activation or its partitioning between these alternative metabolic pathways, as judged from AUC values (area-under-the-plasma concentration x time curve) for 4-OH-CPA and CA. The P-4503A inhibitor troleandomycin (TAO) decreased plasma Cmax and AUC of CA (80-85% decrease) without changing the Cmax or AUC of 4-OH-CPA in uninduced rats. In PB-induced rats, TAO decreased AUCCA by 73%, whereas it increased AUC4-OH-CPA by 93%. TAO thus selectively suppresses CPA N-dechloroethylation, thereby increasing the availability of drug for P-450 activation via 4-hydroxylation. By contrast, dexamethasone, a P-4503A inducer and antiemetic widely used in patients with cancer, stimulated large, undesirable increases in the Cmax and AUC of CA (8- and 4-fold, respectively) while reducing the AUC of the 4-hydroxylation pathway by approximately 60%. Tumor excision/in vitro colony formation and tumor growth delay assays using an in vivo 9L gliosarcoma solid tumor model revealed that TAO suppression of CPA N-dechloroethylation could be achieved without compromising the antitumor effect of CPA. The combination of PB with TAO did not, however, enhance the antitumor activity of CPA, despite the approximately 2-fold increase in AUC4-OH-CPA, suggesting that other PB-inducible activities, such as aldehyde dehydrogenase, may counter this increase through enhanced deactivation of the 4-hydroxy metabolite. Together, these studies demonstrate that the P-4503A inhibitor TAO can be used to effectively modulate CPA metabolism and pharmacokinetics in vivo in a manner that decreases the formation of toxic metabolites that do not contribute to antitumor activity. (+info)
Prediction of the effects of inoculum size on the antimicrobial action of trovafloxacin and ciprofloxacin against Staphylococcus aureus and Escherichia coli in an in vitro dynamic model.
The effect of inoculum size (N0) on antimicrobial action has not been extensively studied in in vitro dynamic models. To investigate this effect and its predictability, killing and regrowth kinetics of Staphylococcus aureus and Escherichia coli exposed to monoexponentially decreasing concentrations of trovafloxacin (as a single dose) and ciprofloxacin (two doses at a 12-h interval) were compared at N0 = 10(6) and 10(9) CFU/ml (S. aureus) and at N0 = 10(6), 10(7), and 10(9) CFU/ml (E. coli). A series of pharmacokinetic profiles of trovafloxacin and ciprofloxacin with respective half-lives of 9.2 and 4 h were simulated at different ratios of area under the concentration-time curve (AUC) to MIC (in [micrograms x hours/milliliter]/[micrograms/milliliter]): 58 to 466 with trovafloxacin and 116 to 932 with ciprofloxacin for S. aureus and 58 to 233 and 116 to 466 for E. coli, respectively. Although the effect of N0 was more pronounced for E. coli than for S. aureus, only a minor increase in minimum numbers of surviving bacteria and an almost negligible delay in their regrowth were associated with an increase of the N0 for both organisms. The N0-induced reductions of the intensity of the antimicrobial effect (IE, area between control growth and the killing-regrowth curves) were also relatively small. However, the N0 effect could not be eliminated either by simple shifting of the time-kill curves obtained at higher N0s by the difference between the higher and lowest N0 or by operating with IEs determined within the N0-adopted upper limits of bacterial numbers (IE's). By using multivariate correlation and regression analyses, linear relationships between IE and log AUC/MIC and log N0 related to the respective mean values [(log AUC/MIC)average and (log N0)average] were established for both trovafloxacin and ciprofloxacin against each of the strains (r2 = 0.97 to 0.99). The antimicrobial effect may be accurately predicted at a given AUC/MIC of trovafloxacin or ciprofloxacin and at a given N0 based on the relationship IE = a + b [(log AUC/MIC)/(log AUC/MIC)average] - c [(log N0)/(log N0)average]. Moreover, the relative impacts of AUC/MIC and N0 on IE may be evaluated. Since the c/b ratios for trovafloxacin and ciprofloxacin against E. coli were much lower (0.3 to 0.4) than that for ampicillin-sulbactam as examined previously (1.9), the inoculum effect with the quinolones may be much less pronounced than with the beta-lactams. The described approach to the analysis of the inoculum effect in in vitro dynamic models might be useful in studies with other antibiotic classes. (+info)
Pharmacokinetics and urinary excretion of amikacin in low-clearance unilamellar liposomes after a single or repeated intravenous administration in the rhesus monkey.
Liposomal aminoglycosides have been shown to have activity against intracellular infections, such as those caused by Mycobacterium avium. Amikacin in small, low-clearance liposomes (MiKasome) also has curative and prophylactic efficacies against Pseudomonas aeruginosa and Klebsiella pneumoniae. To develop appropriate dosing regimens for low-clearance liposomal amikacin, we studied the pharmacokinetics of liposomal amikacin in plasma, the level of exposure of plasma to free amikacin, and urinary excretion of amikacin after the administration of single-dose (20 mg/kg of body weight) and repeated-dose (20 mg/kg eight times at 48-h intervals) regimens in rhesus monkeys. The clearance of liposomal amikacin (single-dose regimen, 0.023 +/- 0.003 ml min-1 kg-1; repeated-dose regimen, 0.014 +/- 0.001 ml min-1 kg-1) was over 100-fold lower than the creatinine clearance (an estimate of conventional amikacin clearance). Half-lives in plasma were longer than those reported for other amikacin formulations and declined during the elimination phase following administration of the last dose (from 81.7 +/- 27 to 30.5 +/- 5 h). Peak and trough (48 h) levels after repeated dosing reached 728 +/- 72 and 418 +/- 60 micrograms/ml, respectively. The levels in plasma remained > 180 micrograms/ml for 6 days after the administration of the last dose. The free amikacin concentration in plasma never exceeded 17.4 +/- 1 micrograms/ml and fell rapidly (half-life, 1.47 to 1.85 h) after the administration of each dose of liposomal amikacin. This and the low volume of distribution (45 ml/kg) indicate that the amikacin in plasma largely remained sequestered in long-circulating liposomes. Less than half the amikacin was recovered in the urine, suggesting that the level of renal exposure to filtered free amikacin was reduced, possibly as a result of intracellular uptake or the metabolism of liposomal amikacin. Thus, low-clearance liposomal amikacin could be administered at prolonged (2- to 7-day) intervals to achieve high levels of exposure to liposomal amikacin with minimal exposure to free amikacin. (+info)