Pharmacokinetics and Target Attainment of Antimicrobial Drugs Throughout Pregnancy: Part I-Penicillins

BACKGROUND AND OBJECTIVE

Pharmacokinetics (PK) are severely altered in pregnant women due to changes in volume of distribution (Vd) and/or drug clearance (CL), affecting target attainment of antibiotics in pregnant women. This review is part of a series that reviews literature on the description of PK and target attainment of antibiotics in pregnant women with specific focus on penicillins.

METHODS

A systematic literature search was carried out in PubMed. Articles were labelled as relevant when information on PK of penicillins in pregnant women was available.

RESULTS

Thirty-two relevant articles were included, 8 of which discussed amoxicillin (with and without clavulanic acid), 15 ampicillin, 4 benzylpenicillin, 1 phenoxymethylpenicillin, and 4 piperacillin (with and without tazobactam). No studies were found on pheneticillin and flucloxacillin in pregnant women. Ten out of 32 articles included information on both Vd and CL. During the second and third trimester of pregnancy, a higher CL and larger Vd was reported than in non-pregnant women and in pregnant women during first trimester. Reduced target attainment was described in second and third trimester pregnant women. Only 7 studies reported dosing advice, 4 of which were for amoxicillin.

CONCLUSION

The larger Vd and higher CL in second and third trimester pregnant women might warrant a higher dosage or shortening of the dosing interval of penicillins to increase target attainment. Studies frequently fail to provide dosing advice for pregnant women, even if the necessary PK information was available.

Pharmacokinetics and Pharmacodynamics of Temocillin

Temocillin, a 6-α-methoxy derivative of ticarcillin, is a forgotten antibiotic that has recently been rediscovered, and issues about clinical breakpoints and optimal therapeutic regimens are still ongoing. Temocillin spectrum is almost restricted to Enterobacteriaceae. The addition of the α-methoxy moiety on ticarcillin confers resistance to hydrolysis by Ambler classes A and C β-lactamases (extended spectrum β-lactamases, Klebsiella pneumoniae carbapenemase and AmpC hyperproduced enzymes). Temocillin is bactericidal, and the effect of inoculum size on its activity is relatively mild. The proportion of spontaneous resistant mutants in vitro to temocillin is low, as found in vivo. After intravenous infusion, temocillin showed a prolonged elimination half-life of approximately 5 h. The percentage of protein binding of temocillin is high (approximately 80%), and is concentration-dependent. Temocillin clearance is mainly renal, and urinary recovery is high, ranging from 72 to 82% after 24 h. Furthermore, the penetration of temocillin into bile and peritoneal fluid is high, but poor into cerebrospinal fluid. The cumulative percentage of a 24-h period during which the free drug concentration exceeds the minimum inhibitory concentration (fT > MIC) at steady-state pharmacokinetic conditions seems to be the best pharmacokinetic/pharmacodynamic (PK/PD) index correlating with temocillin efficacy. An fT > MIC of 40-50% is associated with antibacterial effect and survival in vivo. Monte Carlo simulations performed in critically ill patients showed that the 2 g every 12 h and 2 g every 8 h regimens provide a 95% probability of target attainment of 40% fT > MIC up to an MIC of 8 mg/L. In less severely ill patients or in specific foci of infection, such as urinary tract infection, a 4 g daily regimen should be adequate for strains with temocillin MIC up to 16 mg/L. Data regarding actual wild-type MIC distribution, clinical efficacy, PK profiling in volunteers or patients, and PD targets are scarce, and further studies are required to support appropriate dosing recommendations and determination of clinical breakpoints.

[Pharmacoepidemiological analysis of outpatient-based practice of antibacterial therapy of ENT organ infections]

The objective of the present study was to estimate the effectiveness of the antibacterial therapeutic regimen based at an outpatient facility. The data for statistical analysis were collected by examining 1542 patients presenting with infections of the upper pulmonary tract and ENT organs in 10 cities of the Russian Federation. It was shown that macrolides are most commonly used to treat the above infections whereas beta-lactams are prescribed significantly less frequently. The main pharmacodynamic and pharmacokinetic features of pharmaceuticals from the group of protected penicillins are described, and the rationale is provided for their application as the medicines of choice for the treatment of infections of the upper respiratory tract at the stage of outpatient-based medical care.

[Treatment of community-acquired pneumonia--treatment]

Penicillin is the drug of choice for treatment of community-acquired pneumonia (CAP) in Denmark. The primary determinant for therapeutic activity of penicillin is ''penicillin time'' (T>MIC), i.e. time with penicillin concentration above minimum inhibitory concentration. Eradication of S. pneumoniae requires T>MIC above 40-50%. The second determinant for therapeutic activity is the ratio between maximum penicillin concentration in serum and MIC (Cmax/MIC). Considering penicillin pharmacokinetics, intravenous penicillin 2 million units four times a day is recommended as empirical treatment of CAP.

Amoxicillin pharmacokinetics in pregnant women: modeling and simulations of dosage strategies

Amoxicillin is recommended for anthrax prevention in pregnancy. The objective of this study was to evaluate the pharmacokinetics of amoxicillin during pregnancy and postpartum (PP). Sixteen women received amoxicillin during gestation (18-22 weeks (T2) and 30-34 weeks (T3)) as well as 3 months postpartum (PP) to evaluate single-dose pharmacokinetics. Amoxicillin compartmental pharmacokinetic parameters were used to simulate amoxicillin concentration-time profiles following different dosage strategies. Amoxicillin CL(renal) (T2: 24.8+/-6.7 l/h, P<0.001; T3: 24.0+/-3.9 l/h, P<0.001; and PP: 15.3+/-2.6 l/h) and renal CL(secretion) (T2: 280+/-105 ml/min, P<0.002; T3: 259+/-54 ml/min, P<0.001; and PP: 167+/-47 ml/min) were higher during pregnancy than postpartum. Simulations suggest that amoxicillin concentrations adequate to prevent anthrax may be difficult to achieve during pregnancy and postpartum. Increases in amoxicillin CL(renal) and renal CL(secretion) reflect increases in filtration and secretory transport or diminished reabsorption in the kidneys. Amoxicillin may not be an appropriate antibiotic for post-anthrax exposure prophylaxis.

RP-HPLC analysis of flucloxacillin in human plasma: validation and application to a bioequivalence study

A RP-HPLC method with rapid sample processing was developed for quantitation of flucloxacillin in human plasma using dicloxacillin as the internal standard. The plasma sample (100 microL) was acidified with glacial acetic acid, and deproteinized by precipitation with acetonitrile. The supernatant was directly injected into the HPLC system. Separation was achieved on an Alltima C18 column (250 mmx4.6 mm I.D., 5 microm), with a mixture of 10 mmol x L(-1) KH2PO4-acetonitrile (64.5:35.5, v/v) as mobile phase. The assay was successfully applied to a randomized, two-period cross-over bioequivalence study in 20 healthy Chinese volunteers following a single oral dose of 250 mg flucloxacillin capsules. A non-compartmental method was used for pharmacokinetic analysis. Compared with data in the literature, flucloxacillin was eliminated more slowly in Chinese than in Caucasians. Cmax, AUC(0-t) and AUC(0-infinity) were tested for bioequivalence after log-transformation of data. No significant difference was found. Tmax was analyzed by Wilcoxon's test and no significant difference was obtained (P > 0.05). Based on these statistical inferences, the two formulations were judged to be bioequivalent and, thus, can be prescribed interchangeably.

Pharmacokinetic modeling of free amoxicillin concentrations in rat muscle extracellular fluids determined by microdialysis

The aim of the present study was to investigate amoxicillin (AMX) distribution in muscle interstitial fluid by microdialysis in healthy, awake rats. Microdialysis probes were inserted into the jugular vein and hind leg muscle. Probe recoveries in each rat were determined by retrodialysis with cefadroxil. AMX was administered as a bolus dose of 50 mg.kg(-1), and microdialysis samples were collected during 180 min. Concentrations of unbound drug in blood and muscle were analyzed simultaneously by a population approach. Simulations were conducted using a hybrid, physiologically based pharmacokinetic model to investigate the potential impact of tissue blood flow on muscle AMX distribution. A two-compartment pharmacokinetic model described adequately the unbound amoxicillin concentration-time profiles in blood and muscle. Muscle AMX distribution equilibrium was rapidly achieved. Consequently, the best results were obtained by considering concentrations in muscle as part of the central compartment. The ratio of the concentration of unbound drug in muscle to that in blood (Rmodel) was estimated to 0.80 by the model, which is close to the mean value obtained by noncompartmental data analysis (Rarea= 0.86 +/- 0.29). Simulations conducted with a hybrid, physiologically based pharmacokinetic model suggest that a muscle blood flow reduction of 30% to 50%, such as could be encountered in critical care patients, has virtually no effect on muscle AMX concentration profiles. In conclusion, this study has clearly demonstrated that AMX distributes rapidly and extensively within muscle interstitial fluid, consistent with theory, and that altered muscle blood flow seems unlikely to have a major effect on these distribution characteristics.

Efficacy of beta-lactams against experimental pneumococcal endocarditis caused by strains with different susceptibilities to penicillin

OBJECTIVES

To compare the in vitro and in vivo activity of penicillin, cefotaxime and ceftriaxone, using three strains of Streptococcus pneumoniae with different susceptibilities to penicillin (MICs of 0.015, 0.25 and 2 mg/L, respectively).

METHODS

Time-kill curves and an experimental model of endocarditis in rabbits.

RESULTS

Penicillin was efficacious in clearing bacteria from vegetations and blood irrespective of whether infections were caused by penicillin-susceptible or penicillin-resistant strains (P < 0.01 with respect to control groups). The same efficacy was shown with cefotaxime and ceftriaxone. Comparing the results of the in vivo model with those obtained in time-kill curves, penicillin showed the best results.

CONCLUSIONS

These results confirm that penicillin is efficacious in the treatment of pneumococcal infections, including those produced by strains with MICs < or = 2 mg/L (with the exception of pneumococcal meningitis). These results also suggest that the breakpoints to define susceptibility and resistance of S. pneumoniae to penicillin must be reviewed, as has been done with amoxicillin and third-generation cephalosporins.

Pharmacokinetic detection of penicillin excreted in urine using a totally internally reflected resonance light scattering technique with cetyltrimethylammonium bromide

A quantitative analysis method for penicillins including ampicillin (AmP), benzyl penicillin (BP), oxacillin (OA) and amoxycillin (AmO) is proposed that makes use of the totally internally reflected resonance light scattering (TIR-RLS) signal from the penicillin at the H2O/CCl4 interface in the presence of cetyltrimethylammonium bromide (CTMAB), and enables the pharmacokinetics of penicillin taken orally and excreted through urine to be monitored. Penicillin is coadsorbed with CTMAB at the H2O/CCl4 interface in neutral solution, resulting in the formation of ion associates that display greatly enhanced TIR-RLS signals (maximum at 368-372 nm). This enhanced TIR-RLS intensity was found to be proportional to the penicillin concentration over the range 0.2 x 10(-6) to 2.2 x 10(-6) mol L(-1), with limits of determination (3sigma) of 5.0 x 10(-8) to 7.0 x 10(-8) mol L(-1). Pharmacokinetics studies performed using the present method show that the excretion of orally-taken ampicillin through urine has a half-time of 1.05 h and an excremental quantum over 8 h of 49.3%, respectively.

New dosing strategies for antibacterial agents in the neonate

Dosing of antibiotics in neonates requires finding a delicate balance between maximal efficacy and minimal toxicity. There is a lack of data on efficacy of currently used antibiotics in neonates, and rational dosing therefore needs to be based on gestational- and postnatal-age-dependent pharmacokinetics in combination with surrogate markers. These surrogate markers are: (i) the area-under-the serum concentration time curve to minimum inhibitory concentration ratio (AUC/MIC); (ii) peak concentration to MIC ratio (Cmax/MIC); and (iii) the time the concentration remains above the MIC (T>MIC). Whereas the efficacy of beta-lactam antibiotics (including carbapenems) depends on T>MIC, the efficacy of most other antimicrobials (including aminoglycosides and fluoroquinolones) is related to AUC/MIC and Cmax/MIC. Most modern dosing regimens are adequate when these concentration effect relationships are taken into account. Dosing adjustments in neonates are suggested, based on these relationships. Several antimicrobial combinations for treatment of meningitis and necrotizing enterocolitis exist. Empiric treatment should be based on efficacy, concerns about resistance as well as information from institutional microbiological surveillance.

Pharmacodynamic profiling of piperacillin in the presence of tazobactam in patients through the use of population pharmacokinetic models and Monte Carlo simulation

The primary objectives of this analysis were to determine which pharmacokinetic model most accurately describes the elimination pathways for piperacillin in the presence of tazobactam through population pharmacokinetic modeling and to characterize its pharmacodynamic profile. Once the optimal pharmacokinetic model was identified, Monte Carlo simulation of 10,000 subjects with ADAPT II was performed to estimate the probability of attaining a target free-piperacillin concentration greater than the MIC for 50% of the dosing interval for 3.375 g every 6 h or every 4 h given as a 0.5-h infusion at each MIC between 0.25 and 32 microg/ml. In the population pharmacokinetic analysis, measurements of bias and precision, observed-predicted plots, and r2 values were highly acceptable for all three models and all three models were appropriate candidates for the Monte Carlo simulation evaluation. Visual comparison of the distribution of the piperacillin concentrations at the pharmacodynamic endpoint--h 3 concentrations of a 6-h dosing interval--between the simulated populations and raw data revealed that the linear model was most reflective of the raw data at the pharmacodynamic endpoint, and the linear model was therefore selected for the target attainment analysis. In the target attainment analysis, administration of 3 g of piperacillin every 6 h resulted in a robust target attainment rate that exceeded 95% for MICs of < or =8 mg/liter. The 4-h piperacillin administration interval had a superior pharmacodynamic profile and provided target attainment rates exceeding 95% for MICs of < or =16 mg/liter. This study indicates that piperacillin-tazobactam should have utility for empirical therapy of hospital-onset infections.

[Syphilis treatment. German and international guidelines--a comparison]

Guidelines are an important instrument for improving the quality of medical care. In 2001, the German STD Society (DSTDG) published guidelines for syphilis diagnostics and treatment. For two reasons, these guidelines had to be reviewed urgently: Firstly, there is an obvious "renaissance" of syphilis among men having sex with men, which is complicated by a frequent comorbidity with HIV infection. Secondly, the standard drug for syphilis treatment in Germany, clemizole penicillin, has no longer been available since July 2003. In this article, the new German guidelines for syphilis treatment 2004, published by the DSTDG, are compared with other syphilis guidelines, which are valid for the European countries, i.e., the CDC, UK, Russian, and European guidelines 2002.

Beta-lactamase-producing nontypeable Haemophilus influenzae fails to protect Streptococcus pneumoniae from amoxicillin during experimental acute otitis media

Acute otitis media (AOM) is the most common reason for outpatient antimicrobial therapy. Mixed infections pose a potential problem, since the first-line drug used for the treatment of AOM, amoxicillin, can be neutralized by beta-lactamase-producing pathogens of the upper respiratory tract. To study the effects of a 5-day course of amoxicillin on a mixed middle ear infection, rats were challenged with Streptococcus pneumoniae alone or in combination with beta-lactamase-producing nontypeable Haemophilus influenzae. Amoxicillin was introduced at the clinical peak of the infection. Local and systemic changes were monitored by otomicroscopy, bacterial culture, and analysis of histological changes and the expression of the transforming growth factor beta (TGF-beta) gene. beta-Lactamase-producing H. influenzae did not demonstrate an ability to protect S. pneumoniae. Amoxicillin eradicated the pneumococci in all treated animals but increased to some degree the ability of H. influenzae to persist at the site of infection. Thus, only an insignificant acceleration of the resolution of the AOM caused by a mixture of pathogens was observed during treatment. Moderate to major morphological changes could not be avoided by treatment of the mixed infections, but a slight downregulation of TGF-beta expression was observed. In contrast to infections caused by a single pathogen, the mixed infections induced white plaques in the tympanic membrane at a remarkably high frequency independent of treatment. These experimental findings constitute support for further studies of antimicrobial drugs and AOM caused by bacteria with and without mechanisms of antibiotic resistance.

Effect of sodium diclofenac on serum and tissue concentration of amoxicillin and on staphylococcal infection

The effect of sodium diclofenac on serum and tissue amoxicillin concentration as well as their effect against staphylococcal infection was observed. Four polyurethane sponges were placed in the back of thirty rats. After 14 d, two granulomatous tissues received 0.5 ml of 10(8) cfu/ml (Staphylococcus aureus). Two days later, the rats were divided into five groups: group 1 received amoxicillin 50 mg/kg/p.o., group 2 received amoxicillin 25 mg/kg/p.o., group 3 received sodium diclofenac 2.5 mg/kg/i.m. and amoxicillin 50 mg/kg/p.o., group 4 received sodium diclofenac 2.5 mg/kg/i.m., and group 5 (control group) received NaCl 1 ml/p.o. After six hours of drug administration, blood serum (10 microl) and noninfected granulomatous tissues were placed on Mueller-Hinton agar inoculated with 10(8) cfu/ml (S. aureus). Infected tissues were dispersed in a sonic system and were spread (10 microl) on salt mannitol agar. Microorganisms were counted and the inhibition zones were measured after 18 h of incubation at 37 degrees C. Amoxicillin tissue concentration was 6.27 microg/g for group 1, 2.18 microg/g for group 2, and 0.72 microg/g for group 3. The serum concentrations were 11.56 microg/ml for group 1, 5.36 microg/ml for group 2, and 1.34 microg/ml for group 3. No differences were observed among group 1, 2, and 3 regarding staphylococci counts (Kruskall-Wallis test p>0.05). Group 4 reduced (p<0.05) staphylococci counts comparing to group 5. It was concluded that sodium diclofenac reduced serum and tissue amoxicillin concentration and, even in large doses, amoxicillin was not effective in eradicating the staphylococcal infection after 6 h of administration.

Ampicillin and penicillin concentration in serum and pleural fluid of hospitalized children with community-acquired pneumonia

BACKGROUND

Optimal therapeutic efficacy of beta-lactam antibiotics for treatment of pneumococcal pneumonia is thought to be associated with the serum concentration greater than the minimum inhibitory concentration for 40-50% of the interdose interval at site of infection.

OBJECTIVE

Establish whether intravenous administration of ampicillin 400 mg/kg/day or penicillin 200,000 IU/kg/day in 6 divided doses reaches serum and or pleural concentrations above 4 microg/ml for at least 40% of the interdose interval.

MATERIALS AND METHODS

Hospitalized healthy children 1 month-14 years old with community-acquired bacterial pneumonia and empyema were eligible. Blood samples were obtained 30 min (C1) and 3 h (C2) after an antibiotic dose. Pleural fluid samples were obtained 1 and 4 h after the same dose in which blood samples were obtained. The concentrations were measured by high performance liquid chromatography.

RESULTS

The study included 17 patients treated with ampicillin and 13 treated with penicillin. For ampicillin, mean serum concentrations were C1 37.3 +/- 19 microg/ml and C2 11 +/- 10.2 microg/ml and mean pleural fluid concentrations were C1 25.8 +/- 9.9 microg/ml and C2 16.2 +/- 7.9 microg/ml. For penicillin, mean serum concentrations were C1 21.8 +/- 16.4 microg/ml and C2 23.9 +/- 3.4 microg/ml. Mean pleural fluid concentrations were C1 10.9 +/- 2.2 microg/ml and C2 7.7 +/- 3.4 microg/ml. In 8 of 30 patients, serum C2 was <4 microg/ml; in all of them serum concentrations were >4 microg/ml for >40% of the interdose interval.

CONCLUSIONS

This study of the pharmacokinetics of beta-lactam antibiotics in children with bacterial pneumonia may help in the development of therapeutic guidelines for the treatment of pneumococcal pneumonia.

QSAR modeling of beta-lactam binding to human serum proteins

The binding of beta-lactams to human serum proteins was modeled with topological descriptors of molecular structure. Experimental data was the concentration of protein-bound drug expressed as a percent of the total plasma concentration (percent fraction bound, PFB) for 87 penicillins and for 115 beta-lactams. The electrotopological state indices (E-State) and the molecular connectivity chi indices were found to be the basis of two satisfactory models. A data set of 74 penicillins from a drug design series was successfully modeled with statistics: r2 = 0.80, s = 12.1, q2 = 0.76, spress = 13.4. This model was then used to predict protein binding (PFB) for 13 commercial penicillins, resulting in a very good mean absolute error, MAE = 12.7 and correlation coefficient, q2 = 0.84. A group of 28 cephalosporins were combined with the penicillin data to create a dataset of 115 beta-lactams that was successfully modeled: r2 = 0.82, s = 12.7, q2 = 0.78, spress = 13.7. A ten-fold 10% leave-group-out (LGO) cross-validation procedure was implemented, leading to very good statistics: MAE = 10.9, spress = 14.0, q2 (or r2press) = 0.78. The models indicate a combination of general and specific structure features that are important for estimating protein binding in this class of antibiotics. For the beta-lactams, significant factors that increase binding are presence and electron accessibility of aromatic rings, halogens, methylene groups, and =N- atoms. Significant negative influence on binding comes from amine groups and carbonyl oxygen atoms.

[Antimicrobial prophylaxis in surgery]

Antimicrobial prophylaxis is widely performed in any surgical procedures to prevent postoperative infections. However, we have neither double-blind placebo-controlled studies nor sufficient surveillance of postoperative infections that are common in Europe and the United States, and therefore there is little convincing scientific basis accounting for the validity of this therapy. In addition, prophylactic agent is still uncovered by medical insurance despite the persistent arguments as to its necessity. To establish the guidelines in our own country, a greater deal of evidence needs to be accumulated. Strategies for antimicrobial prophylaxis should be determined based on the types of possible postoperative infections and the classifications of operations according to contamination levels in individual operative fields. This process may involve the precise selection of prophylactic agents for suspected contaminating bacterial species in each operative organ and their administration regimens suitable for the individual surgery. Upon selection of prophylactic agents for postoperative infections, various conditions should be considered: e.g., susceptibility, resistance, blood concentrations, urinary excretion, transition into body fluid and tissues, and adverse reactions. The first and second generations of cephem and cephamycin derivatives can be the first choice, but the use of various other antibacterial agents may be necessary for resistant bacterial strains such as methicillin-resistant Staphylococcus aureus (MRSA) and penicillin-resistant Streptococcus pneumoniae (PRSP). Cyclic therapy based on penicillins (including mixtures), cephems (including cephamycins) and phosphomycins also seems useful for such resistant strains. At present, there is only limited evidence supporting the importance of prophylactic agents. Controlled trials employing well-designed protocols that endure scientific criticism must be done with due consideration for medical economics.

How to calculate clearance of highly protein-bound drugs during continuous venovenous hemofiltration demonstrated with flucloxacillin

BACKGROUND

Flucloxacillin is an important antimicrobial drug in the treatment of infections with Staphylococcus aureus and therefore is often used in staphylococcal infections. Furthermore, flucloxacillin has a high protein binding rate as for example ceftriaxone or teicoplanin--drugs which have formerly been characterized as not being dialyzable.

METHODS

The pharmacokinetic parameters of 4.0 g flucloxacillin every 8 h were examined in 10 intensive care patients during continuous venovenous hemofiltration (CVVH) using a polyamide capillary hemofilter. In addition, the difficulty of calculating the hemofiltration clearance of a highly protein-bound drug is described.

RESULTS

Flucloxacillin serum levels were significantly lowered (56.9 +/- 24.0%) even though only 15% of the drug was detected in the ultrafiltrate. Elimination half-life, total body clearance and sieving coefficient were 4.9 +/- 0.7 h, 117.2 +/- 79.1 ml/min and 0.21 +/- 0.09, respectively. These discrepancies can be explained by the high protein binding of flucloxacillin, the adsorbing property of polyamide and the equation in order to calculate hemofiltration clearance. The unbound fraction of a 4.0 g flucloxacillin dosage facilitates time above the minimum inhibitory concentration (T > MIC) of 60% only for strains up to a minimum inhibitory concentration (MIC) of 0.5 mg/l.

CONCLUSION

Based on the data of this study, we conclude that intensive care patients with staphylococcal infections on CVVH should be treated with 4.0 g flucloxacillin every 8 h which was safe and well tolerated. Moreover, further studies with highly protein-bound drugs are recommended to check the classical 'hemodialysis' equation as the standard equation in calculating the CVVH clearance of highly protein-bound drugs.

Orally administered targeted recombinant Beta-lactamase prevents ampicillin-induced selective pressure on the gut microbiota: a novel approach to reducing antimicrobial resistance

Antibiotics that are excreted into the intestinal tract promote antibiotic resistance by exerting selective pressure on the gut microbiota. Using a beagle dog model, we show that an orally administered targeted recombinant beta-lactamase enzyme eliminates the portion of parenteral ampicillin that is excreted into the small intestine, preventing ampicillin-induced changes to the fecal microbiota without affecting ampicillin levels in serum. In dogs receiving ampicillin, significant disruption of the fecal microbiota and the emergence of ampicillin-resistant Escherichia coli and TEM genes were observed, whereas in dogs treated with ampicillin in combination with an oral beta-lactamase, these did not occur. These results suggest a new strategy for reducing antimicrobial resistance in humans.

A tissue cage model in calves for studies on pharmacokinetic/pharmacodynamic interactions of antimicrobials

An in vivo model for studies of pharmacokinetic/pharmacodynamic (PK/PD) interactions of antimicrobials was developed. Tissue cages with a constant surface area but with different volumes were implanted in calves and infected with Mannheimia haemolytica. Penicillin was injected directly into the cages. With this procedure, different concentration-time profiles could be simulated so that the effect of a range of PK/PD indices on the infection could be monitored. The area under the curve to minimum inhibitory concentration (MIC) and time above MIC were equally predictive for effect, but Cmax to MIC was not. If drug dosages in relation to the MIC of strains used for infection are optimised, the model offers an interesting alternative to explore relevant factors for drug dosage optimisation.

Performances of antibiotic screening tests in determining the persistence of penicillin residues in ewe's milk

Milk collected at 12-h intervals throughout 6 days from three groups of Manchega ewes (n = 12 per group), treated intramuscularly with beta-lactams (benzyl penicillin procaine, ampicillin, and amoxicillin, respectively), was evaluated for antibiotic residue persistence with four microbial inhibitor tests (BRT MRL, CH ATK P&S, Delvotest SP, and Eclipse 100ov) and one enzymatic test (Penzym 100). Antibiotic depletion time was established using a logistic regression model. A clear effect (P < 0.0001) of milking order on the response of all tests was observed with the three antibiotics, but no significant effects were found for milk yield. Except with Eclipse 100ov, positive tests were observed after the recommended withdrawal period of benzyl penicillin procaine (five milkings) from 2% (Delvotest SP) to 11% (CH ATK P&S). There were almost no positive responses beyond the withdrawal period (six milkings) of ampicillin, except for the Penzym 100 test (7%). Residues of amoxicillin were found to persist beyond the six milkings established as the withdrawal period, from 2.8% (Eclipse 100ov) to 72.4% (CH ATK P&S) of positive cases. Higher frequencies of doubtful cases were found with BRT MRL and Delvotest SP assays with the three beta-lactams. Positive and doubtful results could be obtained when milk samples from individual ewes were analyzed using BRT MRL, CH ATK P&S, Delvotest SP, and Penzym 100 tests, even if farmers follow the antibiotic withdrawal periods.

Efficacy of ampicillin combined with ceftriaxone and gentamicin in the treatment of experimental endocarditis due to Enterococcus faecalis with no high-level resistance to aminoglycosides

OBJECTIVE

This study tests the usefulness of ceftriaxone combined with ampicillin as an alternative to ampicillin plus gentamicin for the treatment of experimental endocarditis due to Enterococcus faecalis without high-level resistance to aminoglycosides. It also determines whether adding ceftriaxone to ampicillin and gentamicin increases the effectiveness against experimental enterococcal endocarditis resulting from E. faecalis.

METHODS

Animals with catheter-induced endocarditis were infected intravenously with 108 cfu of the EF91 strain of E. faecalis and were treated for 3 days with ampicillin 2 g every 4 h administered as 'human-like' (H-L) pharmacokinetics, plus gentamicin 1 mg/kg every 8 h H-L, or ceftriaxone 2 g every 12 h H-L alone or combined with gentamicin 6 mg/kg every 24 h administered subcutaneously.

RESULTS

The results of therapy for experimental endocarditis resulting from EF91 showed that the combination of ampicillin plus ceftriaxone was as effective as ampicillin plus gentamicin. The triple combination did not improve on the overall efficacies of the two-drug combinations.

CONCLUSIONS

Because of its lower nephrotoxicity, ampicillin plus ceftriaxone may be a useful alternative therapy for E. faecalis endocarditis in selected patients.

Selection of resistant Streptococcus pneumoniae during penicillin treatment in vitro and in three animal models

Pharmacokinetic (PK) and pharmacodynamic (PD) properties for the selection of resistant pneumococci were studied by using three strains of the same serotype (6B) for mixed-culture infection in time-kill experiments in vitro and in three different animal models, the mouse peritonitis, the mouse thigh, and the rabbit tissue cage models. Treatment regimens with penicillin were designed to give a wide range of T(>MIC)s, the amounts of time for which the drug concentrations in serum were above the MIC. The mixed culture of the three pneumococcal strains, 10(7) CFU of strain A (MIC of penicillin, 0.016 micro g/ml; erythromycin resistant)/ml, 10(6) CFU of strain B (MIC of penicillin, 0.25 micro g/ml)/ml, and 10(5) CFU of strain C (MIC of penicillin, 4 micro g/ml)/ml, was used in the two mouse models, and a mixture of 10(5) CFU of strain A/ml, 10(4) CFU of strain B/ml, and 10(3) CFU of strain C/ml was used in the rabbit tissue cage model. During the different treatment regimens, the differences in numbers of CFU between treated and control animals were calculated to measure the efficacies of the regimens. Selective media with erythromycin or different penicillin concentrations were used to quantify the strains separately. The efficacies of penicillin in vitro were similar when individual strains or mixed cultures were studied. The eradication of the bacteria, independent of the susceptibility of the strain or strains or the presence of the strains in a mixture or on their own, followed the well-known PK and PD rules for treatment with beta-lactams: a maximum efficacy was seen when the T(>MIC) was >40 to 50% of the observation time and the ratio of the maximum concentration of the drug in serum to the MIC was >10. It was possible in all three models to select for the less-susceptible strains by using insufficient treatments. In the rabbit tissue cage model, a regrowth of pneumococci was observed; in the mouse thigh model, the ratio between the different strains changed in favor of the less-susceptible strains; and in the mouse peritonitis model, the susceptible strain disappeared and was overgrown by the less-susceptible strains. These findings with the experimental infection models confirm the importance of eradicating all the bacteria taking part in the infectious process in order to avoid selection of resistant clones.

Evidence of an interaction between nifedipine and nafcillin in humans

AIMS

Nafcillin (Wyeth Laboratories, Philadelphia, PA, USA) has been reported to induce the metabolism of cyclosporin and warfarin, which are known substrates of cytochrome P-450 (CYP). However, there has not been any report to date on its possible interaction with nifedipine, an index substrate of the enzyme, CYP3A4.

METHODS

Nine healthy normotensive subjects participated in this randomized placebo-controlled two-way crossover study examining the effects of 5 days' pretreatment of nafcillin 500 mg or placebo four times daily on the pharmacokinetics of an oral dose of nifedipine 10 mg. Plasma nifedipine concentrations were measured by gas chromatography-mass spectro.

RESULTS

The area under the plasma nifedipine concentration-time curve (AUC0-alpha) in nafcillin-pretreated subjects (80.9 +/- 32.9 micro g l-1 h-1) was significantly decreased compared with subjects who received only nifedipine (216.4 +/- 93.2 micro g l-1 h-1) (P < 0.001). Total plasma clearance of nifedipine (CL/F) was significantly increased with nafcillin pretreatment (138.5 +/- 42.0 l h-1 vs 56.5 +/- 32.0 l h-1) (P < 0.002).

CONCLUSIONS

The results show that nafcillin pretreatment markedly increased the clearance of nifedipine and suggest that nafcillin is a potent inducer of CYP enzyme.

Penetration of piperacillin and tazobactam into pneumonic human lung tissue measured by in vivo microdialysis

OBJECTIVES

The pharmacokinetic profile of antibiotics at the site of anti-infective action is one of the most important determinants of drug response, since it correlates with antimicrobial effect. Up to now, only limited information on the lung tissue pharmacokinetics of antibiotic agents has been available. The aim of this study was to measure, using a new microdialysis-based approach, antibiotic penetration into the extracellular space fluid of pneumonic human lung parenchyma.

PATIENTS AND METHODS

The lung penetration of a combination of piperacillin and tazobactam, substances with low protein binding, was determined in five patients suffering from pneumonia and metapneumonic pleural empyema. The condition was treated by decortication after lateral thoracotomy. Intra-, or post-operatively, respectively, two microdialysis probes were inserted into pneumonic lung tissue, and into healthy skeletal muscle to obtain reference values. Serum and microdialysis samples were collected at 20-min intervals for at last 8 h following i.v. administration of a single dose of 4 g piperacillin and 500 mg tazobactam.

RESULTS

The mean free interstitial concentration profiles of piperacillin in infected lung tissue and serum showed a maximal tissue concentration (Cmax) of 176.0 +/- 105.0 mg l-1 and 326.0 +/- 60.6 mg l-1, respectively. The mean AUC (area under the curve) for infected lung tissue was 288.0 +/- 167.0 mg.h l-1 and for serum 470.0 +/- 142.0 mg.h l-1. There was a statistically significant difference between AUC (lung) and AUC (serum) (P = 0.018) as well as between AUC (lung) and AUC (muscle) (P = 0.043). The intrapulmonary concentrations of piperacillin and tazobactam exceeded the minimum inhibitory concentrations (MIC) for most relevant bacteria for 4-6 h. The procedure was well tolerated by all patients and no adverse events or microdialysis-associated side-effects were observed.

CONCLUSION

This microdialysis technique enabled continuous tissue pharmacokinetic measurement of free, unbound anti-infective agents in the lung tissue of patients with pneumonia. The present data corroborate the use of piperacillin and tazobactam in the treatment of lung infections caused by extracellular bacteria and demonstrate the distribution of piperacillin and tazobactam in the interstitial space of pneumonic lung tissue.

Benzathine penicillin G and procaine penicillin G in piglets: comparison of intramuscular and subcutaneous injection

The disposition of penicillin G in piglets is described after intramuscular or subcutaneous injection of depot preparations. The piglets were injected with 33,000 IU/kg or 100,000 IU/kg benzathine + procaine penicillin G intramuscularly or subcutaneously, or 100,000 IU/kg procaine penicillin G intramuscularly or subcutaneously. Intramuscular injection of benzathine + procaine penicillin resulted in higher maximum concentrations in plasma (Cmax) than did subcutaneous injection. The mean residence time (MRT) of penicillin G was longer when the drugs were injected subcutaneously rather than intramuscularly. The plasma concentration versus time profiles of the subcutaneous injections of benzathine + procaine penicillin revealed secondary peaks, possibly reflecting a certain degree of inflammation at the injection site.

HPLC determination of amoxicillin comparative bioavailability in healthy volunteers after a single dose administration

PURPOSE

An accurate, precise and sensitive HPLC assay was developed for the determination of amoxicillin in human plasma samples, to compare the bioavailability of two amoxicillin capsule (500mg) formulations (Amoxicilina from Brazil, as a test formulation and Amoxil from SmithKline Beecham Laboratories Ltda., Brazil, as a reference formulations) in 24 volunteers of both sexes.

METHODS

Amoxicillin concentrations were analyzed by combined reversed phase liquid chromatography and UV detection (lambda=229 nm). Amoxicillin and cefadroxil (internal standard) were extracted from the plasma by addition of cold methanol. The separation was achieved using the Lichrosorb 10 microm, C18 reversed phase column at room temperature. The mobile phase consisted of a 95% phosphate buffer (0.01 mol/L), pH=4.8 and 5% acetonitrile mixture. The study was conducted using an open randomized 2-period crossover balanced design with a 1-week washout period between the doses. Plasma samples were obtained over an 8-hour period. The bioequivalence between the two formulations was assessed by calculating individual peak plasma concentrations (C(max) ) and area under the curve (AUC(0-8h) ) ratios (test/reference). The statistical interval proposed was 80-125%, as established by the US Food and drug administration Agency.

RESULTS

The internal standard and amoxicillin eluted about 4.2 and 5.2 min, respectively at a flow rate of 1.3ml/min. The mean absolute recovery of AMO in plasma was 90.0% at 3 microg/ml, 98.6% at 25 microg/ml and 95.3 at 50 microg/ml. The assay showed excellent relationships between peak height ratios and plasma concentrations (r(2)>or= 0.999). The limit of quantification was 1g/ml, based on 200l of plasma. The geometric mean of Amoxicilina/Amoxil 500 mg capsules individual percentage ratio was 101.4% for AUC(0-8h), and 99.9% for C(max). The 90% confidence intervals were 98.3-104.4% and 95.7-103.9%, respectively.

CONCLUSION

This simple, rapid and selective method is suitable for pharmacokinetic, bioavailability and bioequivalence studies. Since the 90% CI for both C(max )and AUC(0-8h) lies within the 80-125% interval proposed by the Food and Drug Administration, it was concluded that Amoxicilina 500 mg capsules was bioequivalent to Amoxil capsules 500 mg, in terms of both the rate and extent of absorption.

Antibacterial therapy of neurosyphilis: lack of impact of new therapies

Neurosyphilis is caused by the spirochete Treponema pallidum. These organisms divide slowly, requiring long exposure to antibacterials for treatment success. In order for an antibacterial to be effective in the therapy of neurosyphilis, it must achieve treponemicidal concentrations in the CSF, have a long half-life and be given in a treatment regimen that favours compliance. Penicillin was first introduced for the treatment of syphilis in 1943, and despite interest in the use of amoxicillin, erythromycin, tetracycline, doxycycline, ceftriaxone and azithromycin, penicillin remains the only recommended antibacterial agent for neurosyphilis.

Interpolymer complexes of poly(acrylic acid) and chitosan: influence of the ionic hydrogel-forming medium

Non-covalent polyionic complexes were developed for localized antibiotic delivery in the stomach. Freeze-dried interpolymer complexes based on polyacrylic acid (PAA) and chitosan (CS) were prepared in a wide range of copolymer compositions by dissolving both polymers in acidic conditions. The influence of hydrogel-forming medium on the swelling and drug release was evaluated. The properties of these complexes were investigated by using scanning electron microscopy, dynamic swelling/eroding and release experiments in enzyme-free simulated gastric fluid (SGF). The electrostatic polymer/polymer interactions generate polyionic complexes with different porous structures. In a low pH environment, the separation of both polymer chains augmented as the amount of cationic and carboxilic groups increased within the network. However, the presence of higher amount of ions in the hydrogel-forming medium produced a network collapse, decreasing the maximum swelling ratio in SGF. PAA:CS:A (1:2.5:2)-1.75 M complexes released around 54% and 71% of the amoxicillin in 1 and 2 h, respectively, in acidic conditions. A faster drug release from this interpolymer complex was observed when the ionic strength of the hydrogel-forming medium increased. Complexes with a high amount of both polymer chains within the network, PAA:CS:A(2.5:5:2), showed a suitable amoxicillin release without being affected by an increased amount of ions in the hydrogel-forming medium. These freeze-dried interpolymer complexes could serve as potential candidates for amoxicillin delivery in an acidic enviroment.

Release of amoxicillin from polyionic complexes of chitosan and poly(acrylic acid). Study of polymer/polymer and polymer/drug interactions within the network structure

Polyionic complexes of chitosan (CS) and poly(acrylic acid) (PAA) were prepared in a wide range of copolymer composition and with two kind of drugs. Release of amoxicillin trihydrate and amoxicillin sodium from these different complexes were studied. The swelling behavior of and solute transport in swellable hydrogels were investigated to check the effect of polymer/polymer and polymer/drugs interactions. The electrostatic polymer/polymer interactions take place between the cationic groups from CS and the anionic ones from PAA. The diffusion of amoxicillin trihydrate was controlled only by the swelling/eroding ratio of the polyionic complexes. The swelling degree of amoxicillin sodium hydrogels was more extensive when compared to the swelling degree of amoxicillin trihydrate formulations. It was concluded that the water uptake was mainly governed by the degree of ionization. Restriction of amoxicillin sodium diffusion could be achieved by polymer/ionized-drug interaction that retards the drug release. Freeze-dried polyionic complexes could serve as suitable candidates for amoxicillin site-specific delivery in the stomach.

Comparing pharmacokinetics of amoxicillin given twice or three times per day to children older than 3 months with pneumonia

For children with ambulatory pneumonia, the World Health Organization (WHO) recommends oral amoxicillin (15 mg/kg of body weight/dose) thrice daily (t.i.d.) or oral cotrimoxazole (4 mg of trimethoprim/kg/dose) twice daily (b.i.d.). The more frequent amoxicillin dosing may lead to compliance problems. To compare the pharmacokinetics and levels of amoxicillin in plasma in the current WHO acute respiratory infection recommendations with the 25-mg/kg/dose b.i.d. regimen, we performed a two-group parallel study of 66 children ages 3 to 59 months with pneumonia. Amoxicillin was given orally at 25 mg/kg/dose b.i.d. or 15 mg/kg/dose t.i.d. Amoxicillin concentrations were determined by high-performance liquid chromatography after the first dose on days 1 and 3. After the first dose on day 1, the mean area under the concentration-time curve (AUC) for amoxicillin after the 25-mg/kg dose was 54.7 versus 24.9 micro g. h/ml after the 15-mg/kg dose. After the first dose on day 3, the mean AUC was 44.1 versus 28.5 micro g. h/ml. All but two children had plasma amoxicillin concentrations above 0.5 micro g/ml for >50% of the dose interval on both days. Six children on day 1 and five children on day 3 had concentrations above 1.0 micro g/ml for <50% of the dose interval. On day 1, 16 of 27 children in the b.i.d. group and 11 of 26 children in the t.i.d. group had concentrations that were above 2.0 micro g/ml for <50% of the dose interval, and on day 3, 18 of 31 children in the b.i.d. group and 8 of 31 children in the t.i.d. group had concentrations that were above 2.0 micro g/ml for <50% of the dose interval. Amoxicillin b.i.d. is a feasible alternative for t.i.d. dosing. To lengthen the time above the MIC at higher concentration levels, a 30- to 40-mg/kg/dose b.i.d. should be considered instead of the 25 mg/kg/dose used in this study.

Suboptimal antibiotic dosage as a risk factor for selection of penicillin-resistant Streptococcus pneumoniae: in vitro kinetic model

Optimizing pharmacokinetic/pharmacodynamic indices of antibiotics to obtain clinical and microbiological efficacy is essential, but dosing regimens must also be tailored to minimize the risk for emergence of resistance. The aim of the present study was to investigate whether certain concentrations of benzylpenicillin are critical for the selection of resistant subpopulations. A mixed culture of Streptococcus pneumoniae containing ca. 90% susceptible (MIC = 0.031 mg/liter), 9% intermediate (MIC = 0.25 mg/liter), and 1% resistant (MIC = 8 mg/liter) was studied in an in vitro kinetic model. The time that concentrations exceeded the MIC (T>MIC) for the three strains in the culture was varied by different initial concentrations of benzylpenicillin. Samples for viable counts were withdrawn at different times during 24 h and seeded on blood agar plates and on selective antibiotic-containing plates. The T>MIC varied from 46 to 100% for the susceptible strain, from 6 to 100% for the intermediate strain, and from 0 to 48% for the resistant strain. Our study, which may mimic the clinical situation with carriage of a mixed population of S. pneumoniae with different antibiotic susceptibilities, has shown that selection of resistant bacteria may easily occur if dosing regimens are only targeted toward fully susceptible strains.

Population pharmacokinetic analysis of nonlinear behavior of piperacillin during intermittent or continuous infusion in patients with cystic fibrosis

The purpose of this study was to describe the nonlinear pharmacokinetics of piperacillin observed during intermittent infusion and continuous infusion by using a nonparametric population modeling approach. Data were 120 serum piperacillin concentration measurements from eight adult cystic fibrosis (CF) patients. Individual pharmacokinetic parameter estimates during intermittent infusion or continuous infusion were calculated by noncompartmental analysis and with a maximum iterative two-stage Bayesian estimator. To simultaneously describe concentration-time data during intermittent infusion and continuous infusion, nonlinear models were parameterized as two-compartment Michaelis-Menten models. Models were fit to the data with the nonparametric expectation maximization algorithm. The calculations were executed on a remote supercomputer. Nonlinear models were evaluated by log-likelihood estimates, residual plots, and R(2) values, and predictive performance was based on bias (mean weighted error [MWE]) and precision (mean weighted square error [MWSE]). A linear pharmacokinetic model could not describe combined intermittent infusion and continuous infusion data well. A good population model fit to the intermittent infusion and continuous infusion data was obtained with the constructed nonlinear models. Maximum a posteriori probability (MAP) Bayesian R(2) values for the nonlinear models were 0.96 to 0.97. Median parameter estimates for the best nonlinear model were as follows: K(m), 58 +/- 75 mg/liter (mean and standard deviation); V(max), 1,904 +/- 1,009 mg/h; volume of distribution of the central compartment, 14.1 +/- 3.0 liters; k(12), 0.63 +/- 0.41 h(-1); and k(21), 0.37 +/- 0.19 h(-1). The median bias (MWE) and precision (MWSE) values for MAP Bayesian estimation with the Michaelis-Menten model were 0.05 and 4.6 mg/liters, respectively. The developed nonlinear pharmacokinetic models can be used to optimize piperacillin therapy administered via continuous infusion in patients with CF and have distinct advantages over conventional linear models.

Mechanical characteristics of antibiotic-laden bone cement

We studied the mechanical characteristics of cement-antibiotic combinations in vitro. Palacos R was tested without antibiotics, with gentamicin alone and with gentamicin plus vancomycin or flucloxacillin. Palacos LV was studied only with gentamicin added. CMW 1 was studied with gentamicin added, with gentamicin plus vancomycin, and with gentamicin plus flucloxacillin. We performed four-point bending tests on beams of cement to establish bending strength and modulus, and compared the values to ISO standards. Density was also assessed. Palacos R was the strongest of the cements (bending strength 80 MPa). Palacos formulations (apart from Palacos LV) had a higher density and bending modulus than CMW 1. Statistical comparison of various cements with plain Palacos R showed lower density in 4 of the mixtures, and lower bending strength and modulus in 6 of the mixtures. Palacos R/gentamicin plus vancomycin and CMW 1/gentamicin plus vancomycin had bending strength slightly above minimum ISO standards, suggesting that the addition of vancomycin during cement mixing may compromise the outcome in revision surgery for sepsis.

Clinical significance of inhibition kinetics for Streptococcus pyogenes in response to penicillin

OBJECTIVES

The antibiotic mode of action against clinical isolates of Streptococcus pyogenes and physiological factors involved in modifying the inhibitory response to the antibiotic were investigated.

METHODS

We developed high-resolution respirometry for continuous monitoring of bacterial growth and inhibition kinetics. One hundred and ten clinical isolates from 90 paediatric patients were tested, including 48 isolates obtained from 28 patients with eradication failure. Respirometric inhibition curves were monitored at 4 mg/L penicillin G over a short 30 min period, corresponding to the drug's serum half-life.

RESULTS

None of the clinical isolates exhibited penicillin tolerance. Latency in the respirometric response of S. pyogenes to penicillin increased significantly with decreasing strain-specific respirometric growth rate. No difference in inhibition kinetics was found in vitro for isolates from patients with or without bacteriological treatment failure.

CONCLUSIONS

In streptococcal pharyngotonsillitis, tolerance is not a relevant concept to explain bacteriological treatment failure. Definitions of tolerance should be reconsidered in the framework of growth-dependent antibiotic susceptibility.

Relative oral bioavailability of microgranulated amoxicillin in pigs

A new microgranulated formulation of amoxicillin trihydrate for in-feed medication was developed using a lipogelled matrix. Its relative bioavailability was compared with powdered drug in pigs and an assessment was made to determine whether therapeutic concentrations were achieved. Microgranules containing 10% (MICR10) and 30% (MICR30) amoxicillin and free amoxicillin trihydrate powder (reference, AMX) were administered at dosages of 50 mg of amoxicillin/kg b.w. using a three-way-crossover design. Amoxicillin analysis in serum was performed by a sensitive high performance liquid chromatography (HPLC) method with fluorometric detection, using an extraction procedure already described for edible tissues of fish and adapted and validated for pig serum. The oral bioavailability of both microgranulated formulations was higher than that of the reference formulation [relative bioavailability (F): 153.9 +/- 58.2% for MICR10; 126.2 +/- 70.5% for MICR30] and the area under the concentration-time curve (AUC) values of MICR10 and AMX formulations were significantly different (P < 0.05). Differences between the mean maximum concentration (Cmax), time of Cmax (tmax) and mean residence time (MRT) of the drug formulations were not significant. Microgranulated amoxicillin is suitable for in-feed administration to pigs and, because of its higher oral bioavailability compared with the powdered compound, it may be more effective for the treatment of susceptible infections.

Twenty-six week carcinogenicity study of ampicillin in CB6F1-TgrasH2 mice

As a part of the ILSI-HESI Alternative to Carcinogenicity Testing (ACT) program, we performed a 26-week carcinogenetic study of nonmutagenic drug, ampicillin (ABPC) in Tg-rasH2 mice. ABPC was given to Tg-rasH2 mice (0, 350, 1000, 3000 mg/kg, p.o.) and Non-Tg mice (0, 3000 mg/kg, p.o.) daily for 26 weeks. As a positive control, a single dose of MNU was administered once to Tg-rasH2 mice (75 mg/kg, i.p.). In this study, Tg-rasH2 mice did not demonstrate any increases in tumor development in response to ABPC. Thus, ABPC had no carcinogenicity in the 26-week carcinogenesis study in Tg-rasH2 mice or in a 2-year carcinogenesis study in B6C3F1 mice.

Measurement of amoxicillin in plasma and gastric samples using high-performance liquid chromatography with fluorimetric detection

A rapid, selective and sensitive HPLC assay has been developed for the routine analysis of amoxicillin in rat plasma, gastric juice aspirate and gastric tissue which is applicable to low concentrations of amoxicillin (<1 microg mL(-1)) or small sample volumes. Amoxicillin was converted, via an internal rearrangement, to form a fluorescent product which was subsequently recovered using liquid-liquid extraction. A Kromasil ODS 3 microm (150 x 3.2 mm I.D.) column was maintained at 40 degrees C and used with a mobile phase consisting of methanol-water (55:45, v/v). Fluorimetric detection was at an lambda(ex) of 365 nm and an lambda(em) of 445 nm. The limits of quantitation for amoxicillin were 0.1 microg mL(-1) for gastric juice aspirate (500 microL), 0.5 microg mL(-1) for plasma (50 microL) and 0.075 microg g(-1) for gastric tissue (250 mg). The method was linear up to at least 15 microg mL(-1) in gastric juice aspirate, up to 200 microg mL(-1) in plasma and up to 100 microg g(-1) in gastric tissue, with inter- and intra-day RSDs being less than 19%. The assay has been applied to the measurement of amoxicillin in rat plasma, gastric juice aspirate and gastric tissue for pharmacokinetic studies in individual rats.

Pharmacokinetics and pharmacodynamics of piperacillin/tazobactam when administered by continuous infusion and intermittent dosing

BACKGROUND

Although intermittent bolus dosing is currently the standard of practice for many antimicrobial agents, beta-lactams exhibit time-dependent bacterial killing. Maximizing the time above the minimum inhibitory concentration (MIC) for a pathogen is the best pharmacodynamic predictor of efficacy. Use of a continuous infusion has been advocated for maximizing the time above the MIC compared with intermittent bolus dosing.

OBJECTIVE

This study compared the pharmacokinetics and pharmacodynamics of piperacillin/tazobactam when administered as an intermittent bolus versus a continuous infusion against clinical isolates of Pseudomonas aeruginosa and Klebsiella pneumoniae.

METHODS

Healthy volunteers were randomly assigned to receive piperacillin 3 g/ tazobactam 0.375 g q6h for 24 hours, piperacillin 6 g/tazobactam 0.75 g continuous infusion over 24 hours, and piperacillin 12 g/tazobactam 1.5 g continuous infusion over 24 hours. Five clinical isolates each of P aeruginosa and K pneumoniae were used for pharmacodynamic analyses.

RESULTS

Eleven healthy subjects (7 men, 4 women; mean +/- SD age, 28 +/- 4.7 years) were enrolled. Mean steady-state serum concentrations of piperacillin were 16.0 +/- 5.0 and 37.2 +/- 6.8 microg/mL with piperacillin 6 and 12 g, respectively. Piperacillin/tazobactam 13.5 g continuous infusion (piperacillin 12 g/tazobactam 1.5 g) was significantly more likely to produce a serum inhibitory titer > or = 1:2 against P aeruginosa at 24 hours than either the 6.75 g continuous infusion (piperacillin 6 g/tazobactam 0.75 g) or 3.375 g q6h (piperacillin 3 g/ tazobactam 0.375 g). There were no statistical differences against K pneumoniae between regimens. The median area under the inhibitory activity-time curve (AUIC) for the 13.5 g continuous infusion was higher than that for 3.375 g q6h and the 6.75 g continuous infusion against both P aeruginosa and Kpneumoniae (P < or = 0.007, 13.5 g continuous infusion and 3.375 g q6h vs 6.75 g continuous infusion against K pneumoniae). The percentage of subjects with an AUIC > or = 125 was higher with both 3.375 g q6h and the 13.5 g continuous infusion than with the 6.75 g continuous infusion against P aeruginosa and K pneumoniae (both, P < 0.001 vs 6.75 g continuous infusion against K pneumoniae).

CONCLUSIONS

Piperacillin 12 g/tazobactam 1.5 g continuous infusion consistently resulted in serum concentrations above the breakpoint for Enterobacteriaceae and many of the susceptible strains of P aeruginosa in this study in 11 healthy subjects. Randomized controlled clinical trials are warranted to determine the appropriate dose of piperacillin/tazobactam.

Antibiotics in the treatment of acute exacerbations of chronic bronchitis

The benefit of antimicrobial therapy for patients with an acute exacerbation of chronic bronchitis (AECB) remains controversial for two main reasons. First, the distal airways of patients with chronic bronchitis are persistently colonised, even during clinically stable periods, with the same bacteria that have been associated with AECB. Second, bacterial infection is only one of several causes of AECB. These factors have led to conflicting analyses on the role of bacterial agents and the response to antimicrobial therapy of patients with AECB. An episode of AECB is said to be present when a patient with chronic obstructive pulmonary disease (COPD) experiences some combination of increased dyspnoea, increased sputum volume, increased sputum purulence and worsening lung function. While the average COPD patient experiences 2 - 4 episodes of AECB per year, some patients, particularly those with more severe airway obstruction, are more susceptible to these attacks than others. Bacterial agents appear to be particularly associated with AECB in patients with low lung function and those with frequent episodes accompanied by purulent sputum. Non-typeable Haemophilus influenzae, Streptococcus pneumoniae and Moraxella catarrhalis account for up to 50% of episodes of AECB. Gram-negative bacilli are more likely to occur in patients with more severe lung disease. Antibiotics have been used to ameliorate AECB, to prevent AECB and to prevent the long-term loss of lung function that characterises COPD. Numerous prevention trials have been conducted with fairly consistent results; antibiotics do not lessen the number of episodes of AECB but do reduce the number of days lost from work. Most antibiotic trials have studied the impact of treatment on episodes of AECB and results have been inconsistent, largely due to patient selection and end point definition. In patients with severe airway obstruction, especially in the presence of purulent sputum, antibiotic therapy significantly shortens the duration of symptoms and can be cost-effective. Over the past 50 years, virtually all classes of antimicrobial agents have been studied in AECB. Important considerations include penetration into respiratory secretions, spectrum of activity and antimicrobial resistance. These factors limit the usefulness of drugs such as amoxicillin, erythromycin and trimethoprim-sulfamethoxazole. Extended-spectrum oral cephalosporins, newer macrolides and doxycycline have demonstrated efficacy in clinical trials. Amoxicillin-clavulanate and flouoroquinolones should generally be reserved for patients with more severe disease. A number of investigational agents, including ketolides and newer quinolones, hold promise for treatment of AECB.

Amoxicillin and ampicillin are not transferred to gastric juice irrespective of Helicobacter pylori status or acid blockade by omeprazole

BACKGROUND

The effects of proton pump inhibitors and Helicobacter pylori infection on the distribution of drugs used for the eradication of the bacteria are poorly understood.

AIM

The aim of this study was to investigate the effects of a 7-day administration of 20 mg of omeprazole on the pharmacokinetics of amoxicillin and ampicillin in the plasma, saliva and gastric juice of individuals with and without H. pylori infection.

METHODS

Fifty-four healthy volunteers without endoscopic lesions were enrolled. Twenty-six volunteers were included in the amoxicillin study and 28 individuals in the ampicillin study. Each study had an open randomized two-period crossover design and a 21-day washout period between phases. Plasma, saliva and gastric juice concentrations of amoxicillin and ampicillin in subjects with and without omeprazole pre-treatment were measured by reversed-phase HPLC using UV detection.

RESULTS

Neither pre-treatment with omeprazole nor H. pylori infection interfered with the plasma bioavailability of amoxicillin or ampicillin, as assessed by the AUC0-2 h. Neither ampicillin nor amoxicillin were detected in saliva or gastric juice in any study phase.

CONCLUSION

Short-term treatment with omeprazole does not interfere with the pharmacokinetics of amoxicillin or ampicillin. Our results also exclude the presence of a transfer mechanism for amoxicillin or ampicillin from the plasma to the gastric lumen.

Pharmacokinetic and pharmacodynamic evaluation of two dosing regimens for piperacillin-tazobactam

STUDY OBJECTIVE

To compare the pharmacokinetic and pharmacodynamic profiles of two dosing regimens for piperacillin-tazobactam against commonly encountered pathogens. The regimens compared were piperacillin 4.0 g-tazobactam 0.5 g administered every 8 hours, and piperacillin 3.0 g-tazobactam 0.375 g administered every 6 hours.

DESIGN

Multiple-dose, open-label, randomized, crossover study.

SETTING

Clinical research center at Hartford Hospital.

SUBJECTS

Twelve healthy volunteers.

INTERVENTION

The two dosing regimens for piperacillin-tazobactam were administered intravenously in crossover design. Blood was sampled after the third dose.

MEASUREMENTS AND MAIN RESULTS

Drug concentrations were determined by a validated high-performance liquid chromatography assay. The percentage of time above minimum inhibitory concentration (%T>MIC) for piperacillin was calculated for a range of MIC values. The maximum concentration (Cmax), area under the concentration-time curve (AUC0-tau), and total clearance of piperacillin differed significantly between the two study regimens, as did the Cmax, AUC0-tau, volume of distribution, and total clearance of tazobactam (p<0.05). The piperacillin 4.0 g-tazobactam 0.5 g regimen provided 40-50% T>MIC for MIC values 8-16 microg/ml; a similar value for the piperacillin 3.0 g-tazobactam 0.375 g regimen was 16-32 microg/ml.

CONCLUSION

Although statistically significant differences in the pharmacodynamic profile were noted for the regimens, both provide adequate T>MIC against commonly encountered pathogens considered susceptible to piperacillin-tazobactam. However, for treatment of Pseudomonas aeruginosa infection, combination therapy or higher-dosage regimens (e.g., piperacillin 3.0 g-tazobactam 0.375 g every 4 hours, piperacillin 4.0 g-tazobactam 0.5 g every 6 hours, or continuous-infusion piperacillin 12 g-tazobactam 1.5 g/day) may be a prudent option when full MIC data are unavailable.