Pharmacokinetics and prescribing in the elderly

[Clinical Pharmacometrics Research Aimed at Individual Optimization of Infectious Disease Treatment against Antimicrobial Resistant Bacteria]

In recent years, antimicrobial resistance bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) have become a global problem. One of the countermeasures is to optimize the use of antimicrobial drugs, specifically to optimize the dosage and administration based on the therapeutic drug monitoring (TDM) and pharmacokinetics (PK)/pharmacodynamics (PD) theory. On the other hand, in clinical practice, clinical-pharmacometrics can be used for optimized management of individual patients of pharmaceutical products. Therefore, we aimed at individual optimization of infectious disease treatment for antimicrobial resistant bacteria, and tried a series of flows from model construction to clinical application, that is, practice of clinical pharmacometrics. In the context of individual optimization and optimization management of drug therapy in the medical field, it is considered that hospital pharmacists can contribute to the improvement of infectious disease treatment of antimicrobial resistance bacteria by contributing to the optimization of administration method. In addition, clinical pharmacometrics can be applied not only to antibacterial drugs but also to all drugs, and can be said to be a useful method for quantitatively evaluating the promotion of individualized administration methods for patients.

Population Pharmacokinetic Modeling and Pharmacodynamic Target Attainment Simulation of Piperacillin/Tazobactam for Dosing Optimization in Late Elderly Patients with Pneumonia

The aim of this study was to develop a population pharmacokinetic model for piperacillin (PIPC)/tazobactam (TAZ) in late elderly patients with pneumonia and to optimize the administration planning by applying pharmacokinetic/pharmacodynamic (PK/PD) criteria. PIPC/TAZ (total dose of 2.25 or 4.5 g) was infused intravenously three times daily to Japanese patients over 75 years old. The plasma concentrations of PIPC and TAZ were determined using high-performance liquid chromatography and modeled using the NONMEM program. PK/PD analysis with a random simulation was conducted using the final population PK model to estimate the probability of target attainment (PTA) profiles for various PIPC/TAZ-regimen–minimum-inhibitory-concentration (MIC) combinations. The PTAs for PIPC and TAZ were determined as the fraction that achieved at least 50% free time > MIC and area under the free-plasma-concentration–time curve over 24 h ≥ 96 μg h/mL, respectively. A total of 18 cases, the mean age of which was 86.5 ± 6.0 (75–101) years, were investigated. The plasma-concentration–time profiles of PIPC and TAZ were characterized by a two-compartment model. The parameter estimates for the final model, namely the total clearance, central distribution volume, peripheral distribution volume, and intercompartmental clearance, were 4.58 + 0.061 × (CL_cr − 37.4) L/h, 5.39 L, 6.96 L, and 20.7 L/h for PIPC, and 5.00 + 0.059 × (CL_cr − 37.4) L/h, 6.29 L, 7.73 L, and 24.0 L/h for TAZ, respectively, where CL_cr is the creatinine clearance. PK/PD analysis using the final model showed that in drug-resistant strains with a MIC > 8 μg/mL, 4.5 g of PIPC/TAZ every 6 h was required, even for the patients with a CL_cr of 50–60 mL/min. The population PK model developed in this study, together with MIC value, can be useful for optimizing the PIPC/TAZ dosage in the over-75-year-old patients, when they are administered PIPC/TAZ. Therefore, the findings of present study may contribute to improving the efficacy and safety of the administration of PIPC/TAZ therapy in late elderly patients with pneumonia.

Population pharmacokinetic analysis of ciprofloxacin in the elderly patients with lower respiratory tract infections

The aims of the study were to develop a population pharmacokinetic model of ciprofloxacin (CPX) in the elderly patients and to examine the impact of patient-dependent variables on pharmacokinetic parameter values of this drug. The study was conducted in a group of 44 patients at the age of 44-96years, hospitalized due to pneumonia lobaris or bronchopneumonia. Patients received CPX at a dose of 200mg every 12h as a constant rate infusion over 0.5h. Concentrations of CPX in serum were measured by HPLC with UV detection. Population pharmacokinetic analysis revealed that CPX concentration versus time data were best described by a one-compartment model. The mean values of volume of distribution and clearance of CPX in the patients above 65years of age were 78.41±13.17L and 18.39±4.15L/h, respectively. The creatinine clearance influenced CPX clearance according to the equation: CLCPX (L/h)=8.0+0.21·CLCr, while the volume of distribution of CPX was dependent on the body weight of the patient as follows: VdCPX (L)=22.72+0.86·WT. In summary, the developed population model can be used to assess the pharmacokinetic parameters of CPX in the elderly patients and to select on the basis of these parameters and MIC values an optimal dosage regimen of this drug.

Differences in the clinical presentation and the frequency of complications between elderly and non-elderly scrub typhus patients

Age can affect the clinical features and severity of infectious disorders, such as scrub typhus. We performed this study to examine differences between elderly and non-elderly scrub typhus patients, and to identify risk factors predictive of disease outcomes. This retrospective study included patients admitted to a tertiary hospital with scrub typhus between 2001 and 2011. A total of 615 patients were enrolled in this study, 328 of which were >65 years of age. Of the elderly patients, 46.0% (151/328) experienced at least one complication compared to only 23.0% (66/287) in younger patients. A linear trend was observed between age and complication rates (p=0.002). The most common complication in elderly patients was acute kidney injury (75, 22.9%). Treatment failure was reported in 10 elderly patients (3.0%) compared to one non-elderly patient (0.3%). Mental confusion and dyspnea of clinical manifestations at admission were common in elderly patients. Frequency of fever, rash, and eschar were similar in both groups. The following four factors were significantly associated with severe scrub typhus in elderly patients: (1) white blood cell (WBC) counts>10,000/mm(3) (OR=2.569, CI=1.298-5.086), (2) MDRD GFR<60mL/min (OR=3.525, CI=1.864-6.667), (3) albumin≤3.0g/dL (OR=4.976, CI=2.664-9.294), and (4) acute physiology and chronic health evaluation II (APACHE II) score>10 points (OR=3.304, CI=1.793-60.87). Complications and mortality were more common in elderly patients, often associated with delays in diagnosis and treatment.

Pharmacokinetic and Pharmacodynamic Aspects of Antibiotic Use in High-Risk Populations

The study of pharmacokinetics includes the absorption, distribution, metabolism, and elimination of drugs. The pharmacologic effect that a medication has on the body is known as pharmacodynamics. With antimicrobials, pharmacokinetic and pharmacodynamic parameters become especially important because of the association between host drug concentrations, microorganism eradication, and resistance. This article focuses on the pharmacokinetic changes that can occur with antimicrobials when they are used in patients at high risk of infections and how they influence pharmacodynamic effects. The populations described here include patients with obesity and diabetes mellitus, renal or hepatic failure, chronic lung disease, severe burns, and long-term prosthetic devices and the elderly.

Antibiotic agents in the elderly

Diagnosis and treatment of infections in the elderly is challenging and complicated because of age-related physiologic changes and lack of classical clinical symptoms. Elderly patients are more vulnerable to infections because of their underlying diseases. This article reviews the pharmacologic issues in treating the elderly with antibiotics, the most frequently encountered infections in this patient population, and the suggested antibiotic regimens. The discussion also includes the special challenges of treating these most frequently encountered infections in the elderly who reside in long-term care facilities.

Penetration of fosfomycin into inflammatory lesions in patients with cellulitis or diabetic foot syndrome

We investigated the distribution of the broad-spectrum antibiotic fosfomycin in infected soft tissue of patients with uncomplicated cellulitis of the lower extremities or diabetic foot infection using in vivo microdialysis. Our findings suggest that fosfomycin exhibits good and similar penetration into the fluid in the interstitial space in inflamed and noninflamed soft tissue in patients.

Parenteral antibiotic therapy in the treatment of lower respiratory tract infections. Strategies to minimize the development of antibiotic resistance

Antibiotic use is often imputed for increases in the prevalence of infections due to antibiotic-resistant bacteria. Resistance depends on the variety of genotypes in the large bacterial population and also on the selective pressures that are produced along the antibiotic concentration gradients in the body. In effect, at certain selective concentrations the antibiotic eliminates the susceptible majority, leaving a selected remainder intact. Therefore, the choice of antibiotics for the treatment of lower respiratory tract infections should take into consideration not only their effectiveness but also the pharmacokinetics of each agent and its delivery schedule. In fact, the potential therapeutic efficacy of an antibiotic depends not only on its spectrum of action, but also on the concentration it reaches at the site of infection. Most infections occur in the tissues of the body rather than in the blood and that it is accepted that appropriate antibiotic therapy requires the maintenance of significant concentrations of antibiotics at the site of infection in the lung long enough to eliminate the invading pathogen. Thus, the development of dosing schedules for most antimicrobials has been based on the postulate that drug levels need to be above the minimal inhibitory concentration (MIC) at this site for most or all the dosing interval. The selection of antimicrobial resistance appears to be strongly associated with suboptimal antimicrobial exposure, defined as an AUIC(0-24)/MIC ratio of less than 100O125. Antimicrobial regimens that do not achieve these values cannot prevent the selective pressure that leads to overgrowth of resistant bacterial subpopulations. It has been suggested that resistance can be avoided with attention to dosing, since dosing which provides an AUIC(0-24)/MIC ratio of at least 100 appears to reduce the rate of the development of bacterial resistance. Unfortunately, very different serum or lung concentration profiles can result in the same AUIC(0-24)/MIC. High doses administered sufficiently may often completely prevent any possibility of attaining a selective concentration. Alternatively, an antibiotic which has good bactericidal potency and maintains tissue and/or serum concentrations greater than the MIC or, better, minimal bactericidal concentration (MBC) throughout the dosing interval is equally effective in minimizing the development of antibiotic resistance.

Antibiotic agents in the elderly

Changes that occur in the pharmacology of drugs in the elderly must be considered in the use of antimicrobial agents. Although absorption of orally administered drugs is not affected in a significant way, renal function decreases, drug-drug interactions increase, compliance with regimens may be decreased, and drug toxicity is increased. The most frequent infections occurring in the elderly are pneumonia, urinary tract infection, and soft-tissue infection. CDAD is usually a complication of antibiotic therapy. Pneumonia can be categorized as community-acquired, LTCF, and hospital-acquired. Therapeutic approaches vary according to which of these sites is involved. Urinary tract infection is divided into upper tract infection, lower tract infection, and asymptomatic bacteriuria. Upper tract infection is treated for a longer period than lower tract infection; with few exceptions, asymptomatic bacteriuria is usually not treated. Soft-tissue infection is usually caused by an infected pressure ulcer or cellulitis (which may be a complication of a diabetic foot ulcer or an ulcer due to peripheral vascular disease). These infections have different microbial causes and require different therapeutic approaches.

Malaria Prophylaxis in Different Age Groups

Background: There is a perceived increased health risk in senior visitors to malaria endemic countries. Methods: The authors sought to compare effectiveness and tolerability of malaria chemoprophylaxis in senior travelers (>=60 years) with those in younger travelers (20-59 years). The "Malpro 2" database consists of more than 100,000 questionnaires completed by travelers on charter planes returning from East Africa to Europe during July 1988-December 1991. Among them, 9106 (9.1%) of the travelers were 60 years or older, and 84,562 (84.6%) of the travelers reported to be 20-59 years. Variables of demography, travel data, and the effectiveness and tolerability of chemoprophylaxis were compared in the two subgroups. Results: Malaria in Africa was reported by 8 (1/1000) elderly travelers and by 189 (2.2/1000) travelers aged 20-59 years. Adjusting for age, sex, prophylaxis, and duration of stay in Africa in a logistic regression model, malaria was significantly more frequent in younger than in senior travelers (p<.05). Any travel-associated illness was reported by 7.0% in the senior age group and by 13.6% in the younger age group (p<.05). The rates of travelers who indicated they had "side effects" attributable to malaria prophylaxis varied between 9.7% in the elderly and 15.5% in the younger travelers (p<.05). Conclusion: Senior travelers tolerate malaria chemoprophylaxis and visits to the tropics at least as well as younger travelers.