Pharmacokinetics and pharmacodynamics of the nitroimidazole antimicrobials.

Metronidazole, the prototype nitroimidazole antimicrobial, was originally introduced to treat Trichomonas vaginalis, but is now used for the treatment of anaerobic and protozoal infections. The nitroimidazoles are bactericidal through toxic metabolites which cause DNA strand breakage. Resistance, both clinical and microbiological, has been described only rarely. Metronidazole given orally is absorbed almost completely, with bioavailability > 90% for tablets; absorption is unaffected by infection. Rectal and intravaginal absorption are 67 to 82%, and 20 to 56%, of the dose, respectively. Metronidazole is distributed widely and has low protein binding (< 20%). The volume of distribution at steady state in adults is 0.51 to 1.1 L/kg. Metronidazole reaches 60 to 100% of plasma concentrations in most tissues studied, including the central nervous system, but does not reach high concentrations in placental tissue. Metronidazole is extensively metabolised by the liver to 5 metabolites. The hydroxy metabolite has biological activity of 30 to 65% and a longer elimination half-life than the parent compound. The majority of metronidazole and its metabolites are excreted in urine and faeces, with less than 12% excreted unchanged in urine. The pharmacokinetics of metronidazole are unaffected by acute or chronic renal failure, haemodialysis, continuous ambulatory peritoneal dialysis, age, pregnancy or enteric disease. Renal dysfunction reduces the elimination of metronidazole metabolites; however, no toxicity has been documented and dosage alterations are unnecessary. Liver disease leads to a decreased clearance of metronidazole and dosage reduction is recommended. Recent pharmacodynamic studies of metronidazole have demonstrated activity for 12 to 24 hours after administration of metronidazole 1 g. The post-antibiotic effect of metronidazole extends beyond 3 hours after the concentration falls below the minimum inhibitory concentration (MIC). The concentration-dependent bactericidal activity, prolonged half-life and sustained activity in plasma support the clinical evaluation of higher doses of metronidazole given less frequently. Metronidazole-containing regimens for Helicobacter pylori in combination with proton pump inhibitors demonstrate higher success rates than antimicrobial regimens alone. The pharmacokinetics of metronidazole in gastric fluid appear contradictory to these results, since omeprazole reduces peak drug concentration and area under the concentration-time curve for metronidazole and its hydroxy metabolite; however, concentrations remain above the MIC. Other members of this class include tinidazole, ornidazole and secnidazole. They are also well absorbed and distributed after oral administration. Their only distinguishing features are prolonged half-lives compared with metronidazole. The choice of nitroimidazole may be influenced by the longer administration intervals possible with other members of this class; however, metronidazole remains the predominant antimicrobial for anaerobic and protozoal infections.

Relative bioavailability of atovaquone suspension when administered with an enteral nutrition supplement.

OBJECTIVE: To compare the relative bioavailability of a single atovaquone 750 mg suspension oral dose when administered in the fasting state, after a normal breakfast, and after an enteral nutrition supplement. DESIGN: Ten healthy volunteers received a single dose of atovaquone suspension 750 mg/5 mL while fasting. At 2-week intervals, the subjects were then randomized in a crossover design to receive the atovaquone dose within 1 hour of consuming a normal breakfast (fat content 21 g) and 16 oz. of Sustacal Plus (fat content 28 g). Blood samples were collected at seven time points after each atovaquone dose. HPLC was used to determine the atovaquone concentrations in plasma. RESULTS: Administering atovaquone suspension with either a normal breakfast or an enteral nutrition supplement, such as Sustacal Plus, significantly increased the oral relative bioavailability. The mean AUC0-24 after the fasting dose was 43.4 micrograms.h/mL. The mean AUC0-24 values with breakfast (103.8 micrograms.h/mL) and Sustacal Plus (118.8 micrograms.h/mL) were significantly greater compared with fasting (p < 0.0001). CONCLUSIONS: This study has shown that the new atovaquone oral suspension also has significantly greater bioavailability when administered after food or a nutrition supplement that has a moderate fat content. Patients who require atovaquone therapy can use Sustacal Plus without risk of reduced absorption.

Continuous infusion of ceftazidime with an elastomeric infusion device.

The serum disposition, antimicrobial activity, and stability of ceftazidime continuously infused with an elastomeric infusion device (Homepump, Block Medical) were studied. Twelve healthy adult volunteers were given a 500-mg bolus dose of ceftazidime infused i.v. over two minutes, followed by a continuous i.v. infusion of 3 g over 24 hours. Blood samples were drawn five minutes before and at intervals up to 24 hours after the start of the bolus infusion. Samples were collected from the infusers immediately before and at the end of the 24-hour infusion. Infusers were insulated with ice packs. Ceftazidime concentrations were determined by high-performance liquid chromatography. Minimum inhibitory concentrations (MICs), serum inhibitory titers (SITs), and serum bactericidal titers (SBTs) were determined by the microdilution technique. Mean +/- S.D. serum ceftazidime concentrations ranged from 39.50 +/- 6.92 micrograms/ml at peak (30 minutes after the start of the bolus infusion) to 15.30 +/- 2.83 micrograms/mL at trough (24 hours after the start). The ceftazidime MIC for Pseudomonas aeruginosa was 1 microgram/mL; this MIC was exceeded 100% of the time. Serum ceftazidime concentrations achieved a median SIT and SBT of 1:32 and 1:16, respectively, at 30 minutes and 1:8 and 1:8, respectively, at 24 hours. Six infusers met or exceeded the 24-hour infusion time; ceftazidime was stable in these infusers. A 500-mg i.v. bolus of ceftazidime followed by a continuous infusion (3 g over 24 hours) delivered by an elastomeric infusion device produced serum drug concentrations that were constantly above the MIC for P. aeruginosa and maintained serum bactericidal activity against that organism. Adequate stability of ceftazidime was ensured by placing an ice pack next to the infuser.

Metronidazole. A therapeutic review and update.

The nitroimidazole antibiotic metronidazole has a limited spectrum of activity that encompasses various protozoans and most Gram-negative and Gram-positive anaerobic bacteria. Metronidazole has activity against protozoans like Entamoeba histolytica, Giardia lamblia and Trichomonas vaginalis, for which the drug was first approved as an effective treatment. Anaerobic bacteria which are typically sensitive are primarily Gram-negative anaerobes belonging to the Bacteroides and Fusobacterium spp. Gram-positive anaerobes such as peptostreptococci and Clostridia spp. are likely to test sensitive to metronidazole, but resistant isolates are probably encountered with greater frequency than with the Gram-negative anaerobes. Gardnerella vaginalis is a pleomorphic Gram-variable bacterial bacillus that is also susceptible to metronidazole. Helicobacter pylori has been strongly associated with gastritis and duodenal ulcers. Classic regimens for eradicating this pathogen have included metronidazole, usually with acid suppression medication plus bismuth and amoxicillin. The activity of metronidazole against anaerobic bowel flora has been used for prophylaxis and treatment of patients with Crohn's disease who might develop an infectious complication. Treatment of Clostridium difficile-induced pseudomembraneous colitis has usually been with oral metronidazole or vancomycin, but the lower cost and similar efficacy of metronidazole, coupled with the increased concern about imprudent use of vancomycin leading to increased resistance in enterococci, have made metronidazole the preferred agent here. Metronidazole has played an important role in anaerobic-related infections. Advantages to using metronidazole are the percentage of sensitive Gram-negative anaerobes, its availability as oral and intravenous dosage forms, its rapid bacterial killing, its good tissue penetration, its considerably lower chance of inducing C. difficile colitis, and expense. Metronidazole has notable effectiveness in treating anaerobic brain abscesses. Metronidazole is a cost-effective agent due to its low acquisition cost, its pharmacokinetics and pharmacodynamics, an acceptable adverse effect profile, and its undiminished antimicrobial activity. While its role as part of a therapeutic regimen for treating mixed aerobic/anaerobic infections has been reduced by newer, more expensive combination therapies, these new combinations have not been shown to have any therapeutic advantage over metronidazole. Although the use of metronidazole on a global scale has been curtailed by newer agents for various infections, metronidazole still has a role for these and other therapeutic uses. Many clinicians still consider metronidazole to be the 'gold standard' antibiotic against which all other antibiotics with anaerobic activity should be compared.

Selecting antibiotics based on pharmacokinetic and pharmacodynamic principles.

Key pharmacokinetic and pharmacodynamic parameters influencing antimicrobial selection include the area under the curve (AUC) and minimum inhibitory concentration (MIC). These concepts can be integrated to describe the unique triangular relationship between the antibiotic, infecting organism, and patient. Antibiotic pharmacodynamics have been described as the ratio of AUC/MIC, maximum concentration to MIC, and time above MIC. These relationships can help define whether an antibiotic class kills by concentration-dependent or concentration-independent mechanisms. For example, aminoglycosides and fluoroquinolones have concentration-dependent killing while beta-lactams are concentration-dependent. This killing is also reflected in the post-antibiotic effect (PAE) that describes the prolonged activity even when the antibiotic levels are undetectable. These principles allow antibiotic classes to be selected and dosed via new strategies such as once daily aminoglycosides and continuous infusion beta-lactams.

Calcium-channel antagonists for prevention of atherosclerosis.

OBJECTIVE: To critically evaluate the current literature regarding the role of calcium-channel antagonists in preventing atherosclerosis. DATA SOURCES: English language clinical studies, abstracts, conference proceedings, and review articles pertaining to calcium-channel antagonists and atherosclerosis. STUDY SELECTION: Relevant animal and human studies examining the role of calcium-channel antagonists in atherosclerosis prevention and treatment. DATA EXTRACTION: Potential mechanisms for the development of atherosclerosis and the use of calcium antagonists for preventing and treating coronary artery disease are discussed. Animal studies are summarized; next, significant data from human clinical studies are presented. DATA SYNTHESIS: Available studies are described and discussed. CONCLUSIONS: Results from animal and clinical trials in humans suggest that calcium antagonists may retard the development and progression of atherosclerosis. However, most clinical trials to date have been conducted in patients with proven atherosclerotic plaques. Further studies examining the role of calcium-channel antagonists in preventing and treating atherosclerosis are needed, but may be difficult to conduct because of the large numbers of patients required, long trial duration, and associated costs.

Erythromycin therapy for gastroparesis.

Gastroparesis from numerous causes has been treated with a number of prokinetic agents. We report the successful use of erythromycin as a prokinetic agent in the treatment of two cases of idiopathic gastroparesis in which treatment with metoclopramide or domperidone or both had failed. We also review information about erythromycin's mechanism of action, previous therapeutic uses, administration (doses, duration, and route), and role as an alternative to other prokinetic agents. When treatment with other agents is unsuccessful, erythromycin is a viable alternative therapy for gastroparesis.

Irreversibility of procainamide-dextrose complex in plasma in vitro.

The extent to which the procainamide-dextrose complex reverts to free procainamide hydrochloride in plasma was studied in vitro. The procainamide-dextrose species was formed, isolated using preparative liquid chromatography, and then added to six different lots of pooled plasma that were maintained at physiological temperature (37 +/- 0.1 degrees C). At zero, four, and eight hours after preparation of the samples, 1-mL portions were removed from each sample, extracted, and assayed for procainamide hydrochloride using high-performance liquid chromatography. The mean procainamide hydrochloride concentrations at zero, four, and eight hours after preparation were 2.67, 4.81, and 1.38 g/mL, respectively. Each lot of pooled plasma was statistically analyzed to determine if a significant amount of procainamide hydrochloride reappeared. Analysis of variance showed significant difference between the concentrations of free procainamide hydrochloride in the samples at zero, four, and eight hours (p less than 0.02). Follow-up with Duncan's multiple comparisons test determined that the mean procainamide hydrochloride concentrations immediately after preparation were not significantly different from those at eight hours, but the mean procainamide hydrochloride concentrations at four hours were significantly different from those at eight hours (p less than 0.01). A paired Student's t test comparing the data from zero and eight hours showed a significant reduction in mean procainamide hydrochloride concentrations with time (p less than 0.05). The procainamide-dextrose complex in vitro does not revert to free procainamide hydrochloride in plasma at physiological temperature during the first eight hours.

Determination of sedative and amnestic doses of lorazepam in children.

An open-label, dose-escalation study was conducted to determine doses of lorazepam required to induce anterograde amnesia and sedation in children without producing excessive toxicity. Oncology patients 4 to 17 years of age undergoing lumbar puncture or bone marrow aspiration were eligible; a patient could be entered in the study for a second procedure at a different lorazepam dose. A single oral dose of lorazepam was administered 45-60 minutes before the procedure. Starting with 0.02 mg/kg, the same dose was given to three patients; if no dose-limiting effects occurred, dose was increased by 0.01 mg/kg. Before the procedure the patient was shown a toy that he or she was later asked to identify. Immediately after the procedure (usually 60-75 minutes after the lorazepam dose), sedation was assessed on a scale of 0 (alert) to 4 (coma), and the clinician performing the procedure was asked to subjectively evaluate sedation. Patients were rated for amnesia 24 hours after the procedure; a scale of 0 (recalls procedure and toy without prompting) to 4 (recalls nothing since procedure) was used. Twenty patients received 28 doses of lorazepam. The study was terminated when two patients who received 0.10 mg/kg had excessive ataxia. Sedation was subjectively considered adequate for 24 of the procedures. Sedation and amnesia scores were not well correlated with increased dose. Amnesia occurred in some patients with doses as low as 0.03 mg/kg. In children undergoing lumbar puncture or bone marrow aspiration, premedication with oral lorazepam 0.02-0.09 mg/kg generally produced adequate sedation for the procedure.(ABSTRACT TRUNCATED AT 250 WORDS)

Chromatographic methods for the bioanalysis of antiviral agents.

The present review has concentrated on chromatographic techniques for the quantitative determination of antiviral drugs in biological samples. Special attention has been paid to the elements of chromatographic assays that are essential to ensure selectivity, sensitivity, accuracy and precision of the various methods. Wherever possible, attempts have been made to determine the suitability of the methods for application to investigations in pharmacokinetics in man and experimental animals, biopharmaceutics, therapeutic drug monitoring, metabolism and pharmacology. Because of the serious consequences of infection from material contaminated with viruses, special consideration has been given to the handling of contaminated samples. It was convenient to divide the antiviral drugs for the purpose of this review into two groups, the nucleoside and the non-nucleoside antiviral drugs. The nucleosides discussed are vidarabine, cytarabine, ribavirin, riboxamide, acyclovir, ganciclovir, desciclovir, carbovir, 2',3'-dideoxyadenosine, 2',3'-dideoxycytidine, zidovudine, 2',3'-dideoxyinosine, 2',3'-didehydro-3'-deoxythymidine, idoxuridine, 5-(2-bromovinyl)-2'-deoxyuridine, 2'-fluoro-5-iodoaracytidine and 5-iodo-2'-deoxycytidine. The non-nucleoside antiviral drugs discussed are arildone, amantidine, rimantidine, moroxydine, enviroxime, foscarnet and ampligen.

A comparison of computer-assisted instruction and printed information as methods of pharmacy continuing education.

A continuing education (CE) program was developed to teach hospital pharmacists parameters for monitoring adult total parenteral nutrition (TPN) patients. The effectiveness of a computer-assisted instruction (CAI) module as a method of CE was compared with that of printed information (PI). The computer program was developed using an Apple IIe personal computer and Apple Pilot. Forty-nine hospital pharmacists were given a pretest, the CAI or PI program, a posttest immediately after the instruction, and a retention test 2 weeks later. The CAI group (n = 23) had mean test scores of 53.3% for the pretest, 87.7% for the posttest, and 81.9% for the retention test. The PI group (n = 26) had mean test scores of 54.2% for the pretest, 84.7% for the posttest, and 78.2% for the retention test. Both methods were effective CE programs based on increases in mean test scores from pretest to posttest. Retention-test scores showed a statistically significant drop from posttest scores for each group. A comparison of mean retention-test scores with mean pretest scores for each group demonstrated that participants in each group had retained a statistically significant amount of material from baseline knowledge. When differences in mean pretest, posttest, and retention-test scores were compared between the two groups, no statistically significant differences were found. CAI and PI were equally effective methods of continuing education.