Binding characteristics of fluoroquinolones to synthetic levodopa melanin

To define the binding characteristics of fluoroquinolones to synthetic levodopa melanin, the binding of various drugs, including levofloxacin and ofloxacin, and positive controls (timolol and chloroquine), was investigated in-vitro. The affinity and capacity of the drug binding were calculated by Langmuir's adsorption isotherm. The affinity constant (K) and the binding capacity (r(max)) of levofloxacin were similar to those of timolol and much lower than those of chloroquine. Racemic ofloxacin and its enantiomers showed similar K and r(max), suggesting that the binding lacked stereoselectivity. The binding experiment with levofloxacin derivatives indicated that the basic nitrogen atom at position 7 of the quinolone ring, but not carboxyl group at position 3, would play a critical role in the interaction of fluoroquinolones with melanin. The melanin-drug complexes of levofloxacin and chloroquine were washed with neutral phosphate buffer, ethanol and 1 M HCl solution to explain the nature of the interaction of melanin with the drugs. Electrostatic forces mainly participate in the formation of the chloroquine-melanin complex, whereas van der Waals' and hydrophobic interactions are involved in the levofloxacin-melanin complex in addition to electrostatic forces. The interactions of various fluoroquinolones such as norfloxacin, enoxacin, sparfloxacin, ciprofloxacin and lomefloxacin with melanin were also studied. The results showed that the relative K value was: chloroquine approximately ciprofloxacin, sparfloxacin >/= lomefloxacin > timolol, levofloxacin approximately enoxacin, norfloxacin, and that the relative r(max) value was: norfloxacin, enoxacin >/= chloroquine, sparfloxacin > levofloxacin, ciprofloxacin, timolol, lomefloxacin. The fluoroquinolones vary in their affinity and capacity to bind with melanin, and ciprofloxacin and sparfloxacin showed a stronger interaction with melanin than the other fluoroquinolones studied.     

Transepithelial transport of biperiden hydrochloride in Caco-2 cell monolayers

The aim of this research has been to determine the biperiden hydrochloride permeability in Caco-2 model, in order to classify it based on the Biopharmaceutics Classification System (BCS). The World Health Organization (WHO) as well as many other authors have provisionally assigned the drug as BCS class I (high solubility-high permeability) or III (high solubility-low permeability), based on different methods. We determined biperiden BCS class by comparing its permeability to 5 pre-defined compounds: atenolol and ranitidine hydrochloride (low permeability group) and metoprolol tartrate, sodium naproxen and theophylline (high permeability group). Since biperiden permeability was higher than those obtained for high permeability drugs, we classified it as a BCS class I compound. On the other hand, as no differences were obtained for permeability values when apical to basolateral and basolateral to apical fluxes were studied, this drug cannot act as a substrate of efflux transporters. As a consequence of our results, we suggest that the widely used antiparkinsonian drug, biperiden, should be candidate for a waiver of in vivo bioequivalence studies.     

Fluoroquinolones and tuberculosis

Tuberculosis (TB) remains one of the main causes of morbidity worldwide, and the emergence of multi-drug resistant (MDR) Mycobacterium tuberculosis strains in some parts of the world has become a major concern. The decrease in activity of the major anti-TB drugs, such as isoniazid and rifampicin, is an important threat and alternative therapies are urgently required. The anti-TB activity of the fluoroquinolones has been under investigation since the 1980s. Many are active in vitro but only a few, including ofloxacin, ciprofloxacin, sparfloxacin, levofloxacin and lomefloxacin, have been clinically tested. Fluoroquinolones can be used in co-therapy with the available anti-TB drugs. However, the choice of fluoroquinolone should be based not only on the in vitro activity, but also on the long-term tolerance. Fluoroquinolones are novel anti-TB drugs to be used when a patient is infected with a MDR-TB strain.     

Fluoroquinolones and tuberculosis

Tuberculosis (TB) remains one of the main causes of morbidity worldwide, and the emergence of multi-drug resistant (MDR) Mycobacterium tuberculosis strains in some parts of the world has become a major concern. The decrease in activity of the major anti-TB drugs, such as isoniazid and rifampicin, is an important threat and alternative therapies are urgently required. The anti-TB activity of the fluoroquinolones has been under investigation since the 1980s. Many are active in vitro but only a few, including ofloxacin, ciprofloxacin, sparfloxacin, levofloxacin and lomefloxacin, have been clinically tested. Fluoroquinolones can be used in co-therapy with the available anti-TB drugs. However, the choice of fluoroquinolone should be based not only on the in vitro activity, but also on the long-term tolerance. Fluoroquinolones are novel anti-TB drugs to be used when a patient is infected with a MDR-TB strain.     

革兰阴性杆菌对四种氟喹诺酮药物体外耐药监测

目的了解革兰阴性杆菌(G-)对环丙沙星,左氧氟沙星,氧氟沙星,罗美沙星体外抗菌活性,为临床用药提供依据。方法采用K-B纸片法,对分离出的256株菌株进行耐药性监测,并用标准菌株进行监控,以NCCLS标准进行结果判读。结果大肠埃希菌对4种氟喹诺酮类药物有55%以上的耐药率。除铜绿假单胞菌外革兰阴性杆菌对左氧氟沙星的耐药率均低于其他3种药物,克雷伯菌、铜绿假单胞菌、不动杆菌对环丙沙星耐药率在30.76%～33.33%。结论G-杆菌对氟喹诺酮类药物有交叉耐药现象,医生应不断参考本地区细菌耐药变化,最大限度发挥氟喹诺酮药物的作用。     

国产盐酸洛美沙星体内外抗菌作用实验研究

盐酸洛美沙星对革兰阴性菌具有强的抗菌活性，其ＭＩＣ５０多数为０．２５ｍｇ·Ｌ－１；对金葡球菌ＭＩＣ５０为０．５ｍｇ·Ｌ－１；对绿脓假单胞菌ＭＩＣ５０为１ｍｇ·Ｌ－１。盐酸洛美沙星体外抗菌活性与诺氟沙星、氧氟沙星相近而略逊于环丙沙星。盐酸洛美沙星对金葡球菌、大肠杆菌和绿脓假单胞菌感染小鼠ｉｖ的ＥＤ５０分别是４．４７、１．６２和１７．１３ｍｇ·ｋｇ－１，体内抗菌作用较环丙沙星弱但强于诺氟沙星和／或氧氟沙星。     

Functional role of P-glycoprotein in limiting intestinal absorption of drugs: contribution of passive permeability to P-glycoprotein mediated efflux transport

The aim of the present study is to evaluate the quantitative contribution of passive permeability to P-glycoprotein-mediated (P-gp-mediated) efflux and the functional activity of P-gp in determining intestinal absorption of drugs, and demonstrate the relationship between efflux parameters and intestinal permeability. MDRI-MDCKII cell monolayer permeability, human intestinal absorption (HIA), and solubility data were systematically collected from the literature. Drugs were classified as a total of 63 P-gp substrates (P-gpS) and 73 nonsubstrates (NS) on the basis of efflux ratio or calcein AM inhibition and ATPase activity assays. Efflux parameters, efflux ratio (ER) and absorption quotient (AQ), were correlated to the monolayer permeability. MDRI-MDCKII cell monolayer permeability characteristics were found to be distinctly different between P-gpS and NS datasets. The ER for P-gpS was found to increase with absorptive permeability until 20 nm.s(-1), but reduced for P-gpS with high absorptive permeability. The AQ showed a linear inverse relationship with absorptive permeability. Overall, efflux parameters, ER and AQ, indicated that the transport of P-gpS with moderate passive permeability is highly attenuated by P-gp, while passive permeability overrules the P-gp-mediated efflux for high-permeability molecules. Most of the P-gpS were found towards the upper limits of molecular weight (>500) and calculated total polar surface area (>75 A(2)). This dataset indicated that unfavorable chemical features of P-gpS limit passive permeability and thus are more susceptible to P-gp-mediated efflux. In conclusion, passive permeability versus P-gp-mediated efflux determines intestinal permeability of P-gpS, where P-gp limits absorption of only moderately permeable compounds. Thus, integrating these factors with drug characteristics of the Biopharmaceutics Classification System (BCS) class better predicts the functional role of P-gp in limiting intestinal drug absorption.     

氟喹诺酮类药对人肝药酶活性的影响

目的 :观察氟喹诺酮类 (FQs)药物对人肝微粒体药物代谢酶 (细胞色素P 4 5 0 )活性影响的差异。方法 :反应体系中微粒体蛋白终浓度为 0 .33～2 .0 g·L- 1,药物终浓度为 4 0 0mg·L- 1,测定药物代谢酶的活性。对照不加药。并测定不同底物浓度和不同环丙沙星浓度时乙基吗啡N 脱甲基酶的Vm和Km 值 ,求抑制常数Ki。结果 :FQs对酶活性的抑制强度为 :培氟沙星 (PFLX) >环丙沙星 (CPLX)>氧氟沙星 (OFLX) >左氧氟沙星 (LVLX)。FQs对戊巴比妥侧链羟化酶 (PSCH )、苯并芘羟化酶(BPH)、氨基比林N 脱甲基酶 (ADM )、乙基吗啡N 脱甲基酶 (EDM )和NADPH 细胞色素C还原酶的平均被抑制率分别为 :2 9% ,2 6 % ,19% ,17%和2 .3%。CPLX对EDM的抑制为竞争性抑制为主的混合性抑制 ,抑制常数Ki=2 5 0mg·L- 1。结论 :4种FQs对多种肝药酶活性均有不同程度的抑制 ,LVLX的抑制作用相对较弱。 5种肝药酶对药物的敏感性也各不相同。CPLX对EDM的抑制是竞争性抑制为主的混合性抑制。     

Interplay of biopharmaceutics,biopharmaceutics drug disposition and salivary excretion classification systems

The aim of this commentary is to investigate the interplay of Biopharmaceutics Classification System (BCS), Biopharmaceutics Drug Disposition Classification System (BDDCS) and Salivary Excretion Classification System (SECS). BCS first classified drugs based on permeability and solubility for the purpose of predicting oral drug absorption. Then BDDCS linked permeability with hepatic metabolism and classified drugs based on metabolism and solubility for the purpose of predicting oral drug disposition. On the other hand, SECS classified drugs based on permeability and protein binding for the purpose of predicting the salivary excretion of drugs. The role of metabolism, rather than permeability, on salivary excretion is investigated and the results are not in agreement with BDDCS.

Conclusion

The proposed Salivary Excretion Classification System (SECS) can be used as a guide for drug salivary excretion based on permeability (not metabolism) and protein binding.     

3种喹诺酮类药物治疗老年性肺炎的药物经济学评价

目的 :评价3种喹诺酮类药物治疗老年性肺炎的疗效及经济效果。方法 :选择186例老年性肺炎患者 ,随机分为3组 ,分别给予氧氟沙星、左氧氟沙星、洛美沙星治疗 ,观察各组疗效并运用药物经济学方法进行分析。结果 :3组治疗有效率分别为80 65 %、87 1 %、72 58 % ;不良反应发生率分别为7 65 %、6 35 %、13 81 %。平均成本 -效果比分别为2176、3464、3732。结论 :药物经济学分析结果为氧氟沙星优于左氧氟沙星 ,优于洛美沙星。     

In vitro activity of levofloxacin against coagulase-positive and -negative staphylococci.

The in vitro activity of levofloxacin compared with that of ciprofloxacin, ofloxacin and norfloxacin were examined by conventional in vitro tests against 150 clinical isolates of staphylococci, subdivided according to species and susceptibility to methicillin. Although the minimum inhibitory concentrations (MICs) of all quinolones were highest in methicillin-resistant Staphylococcus aureus strains, the activity of levofloxacin was almost complete in methicillin-resistant S. epidermidis and methicillin-resistant S. haemolyticus when compared with ciprofloxacin and ofloxacin, which showed more than 30% resistance. Methicillin-susceptible S. aureus and S. epidermidis strains were susceptible to all quinolones with few differences between the antibiotics tested. The minimal bactericidal activity of levofloxacin was within the double dilution range of MIC values for all strains tested, demonstrating its potent role against staphylococci. In time-kill studies, levofloxacin exerted bactericidal activity within 3 h against all staphylococci. These in vitro results suggest that levofloxacin is a potent fluoroquinolone against coagulase-negative staphylococci and that it is both methicillin-susceptible and resistant. Further studies are necessary to determine the role of this drug in the treatment of infections sustained by these microorganisms.     

Using Physiologically Based Pharmacokinetic (PBPK) Modeling to Evaluate the Impact of Pharmaceutical Excipients on Oral Drug Absorption: Sensitivity Analyses

Drug solubility, effective permeability, and intestinal metabolism and transport are parameters that govern intestinal bioavailability and oral absorption. However, excipients may affect the systemic bioavailability of a drug by altering these parameters. Thus, parameter sensitivity analyses using physiologically based pharmacokinetic (PBPK) models were performed to examine the potential impact of excipients on oral drug absorption of different Biopharmaceutics Classification System (BCS) class drugs. The simulation results showed that changes in solubility had minimal impact on C_max and AUC_0-t of investigated BCS class 1 and 3 drugs. Changes in passive permeability altered C_max more than AUC_0-t for BCS class 1 drugs but were variable and drug-specific across different BCS class 2 and 3 drugs. Depending on the drug compounds for BCS class 1 and 2 drugs, changes in intestinal metabolic activity altered C_max and AUC_0-t. Reducing or increasing influx and efflux transporter activity might likely affect C_max and AUC_0-t of BCS class 2 and 3 drugs, but the magnitude may be drug dependent. Changes in passive permeability and/or transporter activity for BCS class 2 and 3 drugs might also have a significant impact on fraction absorbed and systemic bioavailability while changes in intestinal metabolic activity may have an impact on gut and systemic bioavailability. Overall, we demonstrate that PBPK modeling can be used routinely to examine sensitivity of bioavailability based on physiochemical and physiological factors and subsequently assess whether biowaiver requirements need consideration of excipient effects for immediate release oral solid dosage forms.     

Molecular properties of WHO essential drugs and provisional biopharmaceutical classification

The purpose of this study is to provisionally classify, based on the Biopharmaceutics Classification System (BCS), drugs in immediate-release dosage forms that appear on the World Health Organization (WHO) Essential Drug List. The classification in this report is based on the aqueous solubility of the drugs reported in commonly available reference literature and a correlation of human intestinal membrane permeability for a set of 29 reference drugs with their calculated partition coefficients. The WHO Essential Drug List consists of a total of 325 medicines and 260 drugs, of which 123 are oral drugs in immediate-release (IR) products. Drugs with dose numbers less than or equal to unity [Do = (maximum dose strength/250 mL)/solubility < or = 1] are defined as high-solubility drugs. Drug solubility for the uncharged, lowest-solubility form reported in the Merck Index or USP was used. Of the 123 WHO oral drugs in immediate-release dosage forms, 67% (82) were determined to be high-solubility drugs. The classification of permeability is based on correlations of human intestinal permeability of 29 reference drugs with the estimated log P or CLogP lipophilicity values. Metoprolol was chosen as the reference compound for permeability and log P or CLogP. Log P and CLogP were linearly correlated (r2 = 0.78) for 104 drugs. A total of 53 (43.1%) and 62 (50.4%) drugs on the WHO list exhibited log P and CLogP estimates, respectively, that were greater than or equal to the corresponding metoprolol value and are classified as high-permeability drugs. The percentages of the drugs in immediate-release dosage forms that were classified as BCS Class 1, Class 2, Class 3, and Class 4 drugs using dose number and log Pwere as follows: 23.6% in Class 1, 17.1% in Class 2, 31.7% in Class 3, and 10.6% in Class 4. The remaining 17.1% of the drugs could not be classified because of the inability to calculate log P values because of missing fragments. The corresponding percentages in the various BCS classes with dose number and CLogP criteria were similar: 28.5% in Class 1, 19.5% in Class 2, 35.0% in Class 3, and 9.8% in Class 4. The remaining 7.3% of the drugs could not be classified since CLogP could not be calculated. These results suggest that a satisfactory bioequivalence (BE) test for more than 55% of the high-solubility Class 1 and Class 3 drug products on the WHO Essential Drug List may be based on an in vitro dissolution test. The use of more easily implemented, routinely monitored, and reliable in vitro dissolution tests can ensure the clinical performance of drug products that appear on the WHO Essential Medicines List.     

3种喹诺酮类药物治疗呼吸道感染的成本-效果比较

目的比较氧氟沙星、左氧氟沙星及洛美沙星治疗呼吸道感染的成本-效果,促进临床合理用药。方法回顾性分析医院2011年6月至12月收治的134例呼吸道感染患者的临床资料,根据不同治疗方法分为氧氟沙星组、左氧氟沙星组和洛美沙星组,采用药物经济学方法进行分析。结果氧氟沙星、左氧氟沙星及洛美沙星的有效率分别为80.43%,88.64%,77.27%,成本-效果比值分别为6.27,6.16,6.88。结论左氧氟沙星注射液是治疗呼吸道感染最安全有效、经济合理的药物。     

Enhanced oral paclitaxel absorption with vitamin E-TPGS: Effect on solubility and permeability in vitro, in situ and in vivo

Solubility and permeability being important determinants of oral drug absorption, this study was aimed to investigate the effect of d--tocopheryl polyethylene glycol 1000 succinate (TPGS) on the solubility and intestinal permeability of paclitaxel in vitro, in situ and in vivo, in order to estimate the absorption enhancement ability of TPGS. Aqueous solubility of paclitaxel is significantly enhanced by TPGS, where a linear increase was demonstrated above a TPGS concentration of 0.1 mg/ml. Paclitaxel demonstrated asymmetric transport across rat ileum with significantly greater (26-fold) basolateral-to-apical (B–A) permeability than that in apical-to-basolateral (A–B) direction. Presence of P-glycoprotein (P-gp) inhibitor, verapamil (200 μM), diminished asymmetric transport of paclitaxel suggesting the role of P-gp-mediated efflux. TPGS showed a concentration-dependent increase in A–B permeability and decreased B–A permeability. The maximum efflux inhibition activity was found at a minimum TPGS concentration of 0.1 mg/ml, however, further increase in TPGS concentration resulted in decreased A–B permeability with no change in B–A permeability. Thus, the maximum paclitaxel permeability attained with 0.1 mg/ml TPGS was attributed to the interplay between TPGS concentration dependent P-gp inhibition activity and miceller formation. In situ permeability studies in rats also demonstrated the role of efflux in limiting permeability of paclitaxel and inhibitory efficiency of TPGS. The plasma concentration of [¹⁴C]paclitaxel following oral administration (25 mg/kg) was significantly increased by coadministration of TPGS at a dose of 50 mg/kg in rats. Bioavailability is enhanced about 4.2- and 6.3-fold when [¹⁴C]paclitaxel was administrated with verapamil (25 mg/kg) and TPGS, respectively, as compared to [¹⁴C]paclitaxel administered alone. The effect of verapamil on oral bioavailability of [¹⁴C]paclitaxel was limited relative to the TPGS, consistent with the in vitro solubility and permeability enhancement ability of TPGS. In conclusion, the current data suggests that the coadministration of TPGS may improve the bioavailability of BCS class II–IV drugs with low solubility and/or less permeable as a result of significant P-gp-mediated efflux.     

Ultrastructural characterization of murine limb buds after in vitro exposure to grepafloxacin and other fluoroquinolones

The effects of selected quinolones (levofloxacin, lomefloxacin, temafloxacin and grepafloxacin) on growth and differentiation of murine limb buds were studied in vitro. Ciprofloxacin and ofloxacin served as controls. We used limb buds from 12-day-old mouse embryos that were grown for 6 days in a serum-free, standard or magnesium-deficient medium. Besides evaluation under a dissecting microscope, we used electron microscopy to characterize the effects in detail. The following results are noteworthy. (1) Comparing the effects of standard and magnesium-deficient medium after 3 and 6 days in culture, we found ultrastructural changes after 6 days only. (2) Direct comparison of ofloxacin (racemate) and levofloxacin (L-enantiomer) showed that they had a similar, rather low, potential for affecting cartilage development. (3) The effects of temafloxacin and ciprofloxacin were more pronounced in magnesium-deficient medium, but those of the other drugs were not. (4) Grepafloxacin was the most active quinolone in this assay. It impaired growth and differentiation of limb buds at 30 mg/l; at higher concentrations the explants did not grow. With lower concentrations of 10 mg grepafloxacin/l, no effects were detectable under a dissecting microscope but characteristic changes were seen by electron microscopy. We observed electron-dense aggregates on and within chondrocytes, detachment of the cell membrane from the matrix with matrix-free pericellular areas around chondrocytes, and swelling of cell organelles such as mitochondria and rough endoplasmic reticulum. (5) The affinity of grepafloxacin for divalent cations (Mg2+, Ca2+) was studied by measuring the fluorescence of grepafloxacin solution at various concentrations of Mg2+ and Ca2+. Grepafloxacin showed a relatively high affinity for Ca2+ in the fluorescence assay, which was more pronounced than the affinities of six other fluoroquinolones tested before.     

Activity of eight fluoroquinolones against methicillin-resistant Staphylococcus aureus isolated from cutaneous infections

The in vitro susceptibility of methicillin-resistant Staphylococcus aureus to eight fluoroquinolones, norfloxacin, ofloxacin, enoxacin, ciprofloxacin, lomefloxacin, sparfloxacin and nadifloxacin, was evaluated. Methicillin-resistant S. aureus strains were isolated from 64 cutaneous infections from 1991 to 1993. Nadifloxacin exhibited the lowest MIC among all of the fluoroquinolones. In addition, there was no resistance to nadifloxacin. The MIC(50) of these drugs has been increasing in the past 3 years.     

In vitro activity of four fluoroquinolones against Mycobacterium tuberculosis

The in vitro activity of ciprofloxacin, ofloxacin, levofloxacin and moxifloxacin against strains of Mycobacterium tuberculosis was studied. Moxifloxacin and levofloxacin showed the greatest activity having an MIC(90) of 1 mg/l. The MIC(90) for ofloxacin was 2 mg/l and for ciprofloxacin 4 mg/l. Further studies should be made to determine the role played by these compounds in the treatment of tuberculosis.     

Biopharmaceutics classification of selected beta-blockers: solubility and permeability class membership

The purpose of this study was to determine the permeability and solubility of seven beta-blockers (acebutolol, atenolol, labetalol, metoprolol, nadolol, sotalol, and timolol) and to classify them according to the Biopharmaceutics Classification System (BCS). Apparent permeability coefficients (Papp) were measured using the Caco-2 cell line, and the solubility was determined at 37 degrees C over a pH range of 1.0-7.5. The permeability coefficients ranged from 1.0x10(-7) to 4.8x10(-5) cm/s. On the basis of the in vitro permeability and solubility data observed in the study, labetolol, metoprolol, and timolol can be categorized as BCS Class I drugs, whereas acebutolol, atenolol, and nadolol belong to BCS Class III. The permeability coefficients in Caco-2 cells were consistent with the reported extent of intestinal absorption in humans for all drugs except sotalol. Sotalol displayed low permeability in the Caco-2 cell line, but the extent of intestinal absorption in humans is over 90%. The low permeability through the Caco-2 monolayers might be largely related to its low lipophilicity. In addition, the difference between the tightness of the intercellular junction in vivo and in vitro may partially contribute to this disparity in the sotalol permeability of in vivo and in vitro.