P. Periti

Pharmacokinetic Drug Interactions of Macrolides

SummaryThe macrolide antibiotics include natural members, prodrugs and semisynthetic derivatives. These drugs are indicated in a variety of infections and are often combined with other drug therapies, thus creating the potential for pharmacokinetic interactions.Macrolides can both inhibit drug metabolism in the liver by complex formation and inactivation of microsomal drug oxidising enzymes and also interfere with microorganisms of the enteric flora through their antibiotic effects. Over the past 20 years, a number of reports have incriminated macrolides as a potential source of clinically severe drug interactions. However, differences have been found between the various macrolides in this regard and not all macrolides are responsible for drug interactions. With the recent advent of many semisynthetic macrolide antibiotics it is now evident that they may be classified into 3 different groups in causing drug interactions. The first group (e.g. troleandomycin, erythromycins) are those prone to forming nitrosoalkanes and the consequent formation of inactive cytochrome P450-metabolite complexes. The second group (e.g. josamycin, flurithromycin, roxithromycin, clarithromycin, miocamycin and midecamycin) form complexes to a lesser extent and rarely produce drug interactions. The last group (e.g. spiramycin, rokitamycin, dirithromycin and azithromycin) do not inactivate cytochrome P450 and are unable to modify the pharmacokinetics of other compounds.It appears that 2 structural factors are important for a macrolide antibiotic to lead to the induction of cytochrome P450 and the formation in vivo or in vitro of an inhibitory cytochrome P450-iron-nitrosoalkane metabolite complex: the presence in the macrolide molecules of a non-hindered readily accessible N-dimethylamino group and the hydrophobic character of the drug.Troleandomycin ranks first as a potent inhibitor of microsomal liver enzymes, causing a significant decrease of the metabolism of methylprednisolone, theophylline, carbamazepine, phenazone (antipyrine) and triazolam. Troleandomycin can cause ergotism in patients receiving ergot alkaloids and cholestatic jaundice in those taking oral contraceptives.Erythromycin and its different prodrugs appear to be less potent inhibitors of drug metabolism. Case reports and controlled studies have, however, shown that erythromycins may interact with theophylline, carbamazepine, methylprednisolone, warfarin, cyclosporin, triazolam, midazolam, alfentanil, disopyramide and bromocriptine, decreasing drug clearance. The bioavailability of digoxin appears also to be increased by erythromycin in patients excreting high amounts of reduced digoxin metabolites, probably due to destruction of enteric flora responsible for the formation of these compounds. These incriminated macrolide antibiotics should not be administered concomitantly with other drugs known to be affected metabolically by them, or at the very least, combined administration should be carried out only with careful patient monitoring.Josamycin, midecamycin and probably also the related compounds miocamycin, clarithromycin and flurithromycin, may have a clinically significant interaction with carbamazepine and cyclosporin, requiring close monitoring. Roxithromycin interaction with drugs such as theophylline or cyclosporin does not seem to justify a dosage reduction. No pharmacokinetic interactions have yet been described for spiramycin, rokitamycin, dirithromycin and azithromycin.

Adverse effects of macrolide antibacterials.

SummaryThe renewed interest in macrolide antibacterials with expanded indications for clinical use, as well as their markedly increased usage, justifies the continuous search for new compounds designed to offer the patient not only enhanced bioavailability but also a reduced incidence of adverse effects.Macrolides are an old and well established class of antimicrobial agents that account for 10 to 15% of the worldwide oral antibiotic market. Macrolides are considered to be one of the safest anti-infective groups in clinical use, with severe adverse reactions being rare. Newer products with improved features have recently been discovered and developed, maintaining or significantly expanding the role of macrolides in the management of infection. This review deals with the tolerability of the clinically available macrolide antibacterials. With the exception of drug interactions, adverse effects have been analysed during the last 40 years in many thousands of adult and paediatric patients. Recently developed derivatives have been compared with the older compounds, and the expected and well assessed adverse effects have been set apart from those which are unusual, very rare or questionable.Gastrointestinal reactions represent the most frequent disturbance, occurring in 15 to 20% of patients on erythromycins and in 5% or fewer patients treated with some recently developed macrolide derivatives that seldom or never induce endogenous release of motilin, such as roxithromycin, clarithromycin, dirithromycin, azithromycin and rikamycin (rokitamycin).Except for troleandomycin and some erythromycins administered at high dose and for long periods of time, the hepatotoxic potential of macrolides, which rarely or never form nitrosoalkanes, is low for josamycin, midecamycin, miocamycin, flurithromycin, clarithromycin and roxithromycin; it is negligible or absent for spiramycin, rikamycin, dirithromycin and azithromycin. Transient deafness and allergic reactions to macrolide antibacterials are highly unusual and have definitely been shown to be more common following treatment with the erythromycins than with the recently developed 14-, 15- and 16-membered macrolides.There have been case reports in the literature of 51 patients during the last 30 years who experienced uncommon or dubious adverse effects after treatment with older compounds and in which there appears to be strong evidence of a causal relationship with the drug. Only 3 cases had an unfavourable outcome, and these were patients administered erythromycin lactobionate intravenously too rapidly or at high dose. Targets of these occasional reactions are generally the heart, liver and central nervous system. Other unusual organ pathologies are related to immunomediated disorders more than to primary parenchymal toxicity, or to the rarely serious consequences of macrolide-induced alterations in intestinal microflora.Physicians should be alerted to the possibility of unusual toxicity that could also emerge in the future from the new and recently developed macrolide antibacterials, coinciding with their expanded clinical use worldwide.

Clinical Pharmacokinetics of Depot Leuprorelin

Leuprorelin acetate is a synthetic agonist analogue of gonadotropin-releasing hormone. Continued leuprorelin administration results in suppression of gonadal steroid synthesis, resulting in pharmacological castration.Since leuprorelin is a peptide, it is orally inactive and generally given subcutaneously or intramuscularly. Sustained release parenteral depot formulations, in which the hydrophilic leuprorelin is entrapped in biodegradable highly lipophilic synthetic polymer microspheres, have been developed to avoid daily injections. The peptide drug is released from these depot formulations at a functionally constant daily rate for 1, 3 or 4 months, depending on the polymer type [polylactic/glycolic acid (PLGA) for a 1-month depot and polylactic acid (PLA) for depot of >2 months], with doses ranging between 3.75 and 30mg.Mean peak plasma leuprorelin concentrations (Cmax) of 13.1, 20.8 to 21.8, 47.4, 54.5 and 53 µg/L occur within 1 to 3 hours of depot subcutaneous administration of 3.75, 7.5, 11.25, 15 and 30 mg, respectively, compared with 32 to 35 µg/L at 36 to 60 min after a subcutaneous injection of 1mg of a non-depot formulation. Sustained drug release from the PLGA microspheres maintains plasma concentrations between 0.4 and 1.4 µg/L over 28 days after single 3.75, 7.5 or 15mg depot injections.Mean areas under the concentration-time curve (AUCs) are similar for subcutaneous or intravenous injection of short-acting leuprorelin 1mg; a significant dose-related increase in the AUC from 0 to 35 days is noted after depot injection of leuprorelin 3.75, 7.5 and 15mg. Mean volume of distribution of leuprorelin is 37L after a single subcutaneous injection of 1mg, and 36, 33 and 27L after depot administration of 3.75, 7.5 and 15mg, respectively. Total body clearance is 9.1 L/h and elimination half-life 3.6 hours after a subcutaneous 1mg injection; corresponding values after intravenous injection are 8.3 L/h and 2.9 hours.A 3-month depot PLA formulation of leuprorelin acetate 11.25mg ensures a Cmax of around 20 µg/L at 3 hours after subcutaneous injection, and continuous drug concentrations of 0.43 to 0.19 µg/L from day 7 until before the next injection.Recently, an implant that delivers leuprorelin for 1 year has been evaluated. Serum leuprorelin concentrations remained at a steady mean of 0.93 µg/L until week 52, suggesting zero-order drug release from the implant.In general, regular or depot leuprorelin treatment is well tolerated. Local reactions are more common after application of the 3- or 4-month depot in comparison with the 1-month depot.

Clinical pharmacokinetic properties of the macrolide antibiotics. Effects of age and various pathophysiological states (Part II).

SummaryThe pharmacokinetic aspects in humans of macrolide antibiotics that are currently or soon to be on the market (i.e. erythromycin, oleandomycin, spiramycin, josamycin, midecamycin, miocamycin, rosaramycin, roxithromycin and azithromycin) are reviewed.Macrolide antibiotics are basic compounds, poorly soluble in water, which are mostly absorbed in the alkaline intestinal environment. They are acid unstable, but the newer semisynthetic derivatives (i.e. roxithromycin and azithromycin) are characterised by increased stability under acidic conditions. Macrolides are highly liposoluble and consequently penetrate well into tissue, especially bronchial secretions, prostatic tissue, middle ear exudates and bone tissues, as evidenced by tissue/serum concentration ratios greater than 1. They do not penetrate well into the CSF. Macrolides undergo extensive biotransformation in the liver. With a few exceptions (e.g. miocamycin), the metabolites of these drugs are characterised by little or no antimicrobial activity.Plasma protein binding is variable from one compound to another. At therapeutic concentrations, protein-bound erythromycin accounts for 80 to 90% of the total drug present in the blood, and the fraction is 95% for roxithromycin. The lowest values of protein-bound fraction are observed for midecamycin and josamycin (about 15%), and intermediate values are reported for spiramycin and miocamycin. However, the clinical relevance of this parameter is not clearly established.Plasma half-life (t½) values vary for the macrolides described: erythromycin, oleandomycin, josamycin and miocamycin have a t½ ranging from 1 to 2 hours; spiramycin, erythromycin stearate, the mercaptosuccinate salt of propionyl erythromycin and rosaramicin have an intermediate t½ (about 7, 6.5, 5 and 4.5 hours, respectively); the newer semisynthetic compounds roxithromycin and azithromycin are characterised by high t½ values (i.e. 11 and 41 hours, respectively).Under normal conditions, the major route of elimination is the liver. Renal elimination also takes place but it contributes to total clearance only to a small degree, as evidenced by low renal clearance values. The degree of modification of macrolide pharmacokinetics by renal insufficiency or hepatic disease is usually not considered clinically relevant, and no recommendation for dose modification is necessary in these patients.The pharmacokinetics of macrolides are modified in elderly patients. Accordingly, their use must be accompanied by a closer than usual clinical monitoring of the older patient.Clinically the newer semisynthetic macrolides, such as roxithromycin, possess an antibacterial spectrum at least equivalent to that of erythromycin, and superior pharmacokinetic properties (i.e. longer elimination half-life, higher tissue penetration) over erythromycin and other macrolides, allowing longer intervals between doses.

Clinical Pharmacokinetic Properties of the Macrolide Antibiotics

The pharmacokinetic aspects in humans of macrolide antibiotics that are currently or soon to be on the market (i.e. erythromycin, oleandomycin, spiramycin, josamycin, midecamycin, miocamycin, rosaramycin, roxithromycin and azithromycin) are reviewed. Macrolide antibiotics are basic compounds, poorly soluble in water, which are mostly absorbed in the alkaline intestinal environment. They are acid unstable, but the newer semisynthetic derivatives (i.e. roxithromycin and azithromycin) are characterised by increased stability under acidic conditions. Macrolides are highly liposoluble and consequently penetrate well into tissue, especially bronchial secretions, prostatic tissue, middle ear exudates and bone tissues, as evidenced by tissue/serum concentration ratios greater than 1. They do not penetrate well into the CSF. Macrolides undergo extensive biotransformation in the liver. With a few exceptions (e.g. miocamycin), the metabolites of these drugs are characterised by little or no antimicrobial activity. Plasma protein binding is variable from one compound to another. At therapeutic concentrations, protein-bound erythromycin accounts for 80 to 90% of the total drug present in the blood, and the fraction is 95% for roxithromycin. The lowest values of protein-bound fraction are observed for midecamycin and josamycin (about 15%), and intermediate values are reported for spiramycin and miocamycin. However, the clinical relevance of this parameter is not clearly established. Plasma half-life (t½) values vary for the macrolides described: erythromycin, oleandomycin, josamycin and miocamycin have a t½ ranging from 1 to 2 hours; spiramycin, erythromycin stearate, the mercaptosuccinate salt of propionyl erythromycin and rosaramicin have an intermediate t½ (about 7, 6.5, 5 and 4.5 hours, respectively); the newer semisynthetic compounds roxithromycin and azithromycin are characterised by high t½ values (i.e. 11 and 41 hours, respectively). Under normal conditions, the major route of elimination is the liver. Renal elimination also takes place but it contributes to total clearance only to a small degree, as evidenced by low renal clearance values. The degree of modification of macrolide pharmacokinetics by renal insufficiency or hepatic disease is usually not considered clinically relevant, and no recommendation for dose modification is necessary in these patients. The pharmacokinetics of macrolides are modified in elderly patients. Accordingly, their use must be accompanied by a closer than usual clinical monitoring of the older patient. Clinically the newer semisynthetic macrolides, such as roxithromycin, possess an antibacterial spectrum at least equivalent to that of erythromycin, and superior pharmacokinetic properties (i.e. longer elimination half-life, higher tissue penetration) over erythromycin and other macrolides, allowing longer intervals between doses.

Comparative Multicenter Trial of Teicoplanin versus Cefazolin for Antimicrobial Prophylaxis in Prosthetic Joint Implant Surgery

Abstract A randomized multicenter study was carried out in 12 centers in Italy to compare administration of a single dose of teicoplanin (400 mg i.v. bolus at time of anesthesia) versus that of five doses of cefazolin over a 24-h period (2 g at induction of anesthesia and 1 g every 6 h postoperatively, i.v. bolus) as antimicrobial prophylaxis in patients undergoing hip or knee arthroplasty. Of 860 patients enrolled, 427 received teicoplanin and 433 cefazolin. A total of 846 patients (422 teicoplanin and 424 cefazolin) were evaluable for safety and 826 patients for efficacy. Six patients (1.5%) in the teicoplanin group and seven patients (1.7%) in the cefazolin group developed a surgical wound infection during their postoperative hospital stay: this difference was not significant. Proven or suspected infections involving other body systems occurred in 114 patients (57 in each group). Seven hundred ninety-two patients completed a 3-month evaluation and 738 patients a 12-month evaluation; the success rates in evaluable patients at these observation times were 99.2% and 99.7% for teicoplanin and 99.2% and 99.7% for cefazolin, respectively. Adverse events occurred in three (0.7%) teicoplanin patients and nine (2.1%) cefazolin patients (P=0.083). A single preoperative dose of teicoplanin ensures adequate surgical antisepsis, with results comparable to a standard multiple-dose regimen of cefazolin.

Regional and systemic prophylaxis with teicoplanin in monolateral and bilateral total knee replacement procedures: study of pharmacokinetics and tissue penetration.

Twenty-four patients undergoing monolateral or bilateral total knee replacement (TKR) procedures were randomized to receive teicoplanin (T) either systemically or regionally. Subjects scheduled for systemic prophylaxis and undergoing monolateral (six patients) or bilateral (five patients) TKR received a single 800-mg dose of T in 100 ml of saline as a 5-min infusion into a forearm vein 2.5 h before surgery. For regional prophylaxis, patients undergoing monolateral surgery (eight subjects) received 400 mg of T in 100 ml of saline as a 5-min infusion into a foot vein of the leg to be operated on immediately after the tourniquet was inflated. For the five patients scheduled for bilateral operation and regional prophylaxis, the administration of T was also repeated for the second knee operation. The tourniquet, as the standard TKR surgical technique, was inflated to 400 mm Hg (c. 50 kPa) in all 24 patients immediately before the beginning of surgery and kept in place for the duration of the operation. Samples of serum, bone, skin, synovia, and subcutaneous tissue were collected at timed intervals during surgery. They were microbiologically assayed for T by using Bacillus subtilis as the test organism. Overall, the mean T concentrations obtained with regional route prophylaxis were found to be 2 to 10 times higher than those achieved following systemic prophylaxis. Moreover, peak levels in different tissues after regional prophylaxis were significantly higher (P < 0.05). None of the patients experienced adverse effects due to regional or systemic T administration; no prosthetic or wound infections were observed in the follow-up period (from 12 to 26 months).

New criteria for selecting the proper antimicrobial chemotherapy for severe sepsis and septic shock

The mortality rate resulting from severe bacterial sepsis, particularly that associated with shock, still approaches 50% in spite of appropriate antimicrobial therapy and optimum supportive care. Bacterial endotoxins that are part of the cell wall are one of the cofactors in the pathogenesis of sepsis and septic shock and are often induced by antimicrobial chemotherapy even if it is administered rationally. Not all antimicrobial agents are equally capable of inducing septic shock; this is dependant on their mechanism of action rather than on the causative pathogen species. The quantity of endotoxin released depends on the drug dose and whether filaments or spheroplast formation predominates. Some antibiotics such as carbapenems, ceftriaxone, cefepime, glycopeptides, aminoglycosides and quinolones do not have the propensity to provoke septic shock because their rapid bactericidal activity induces mainly spheroplast or fragile spheroplast-like bacterial forms.

Methicillin-resistant staphylococci in clean surgery : Is there a role for prophylaxis?

SummaryThe incidence of infection in clean surgery (i.e. surgery with no major contamination of the operative site) should be less than 2%, although the incidence of postoperative infections can be higher in patients with various risk factors (namely insertion of foreign bodies, a compromised immune status or prolonged duration of surgery). Although antibiotic prophylaxis has been shown to reduce the incidence of postoperative infections in clean surgery, there is still no consensus regarding its use in this area. However, for clean surgical procedures that involve implantation of foreign material, grafts or prosthetic devices, prophylaxis is well accepted and justifiable, since this practice is indicated when the benefits exceed the expected risks. Staphylococcus aureus and coagulase-negative staphylococci are responsible for 70 to 90% of wound infections in this type of surgery.First and second generation cephalosporins are considered the drugs of choice for surgical prophylaxis. Cefazolin and other cephalosporins have good tissue penetration but poor coverage against methicillin-resistant staphylococci. The frequency with which methicillin-resistant staphylococci have been recovered in nosocomial infections has increased steadily during recent years. This provides a rationale for the use of alternative antibiotics, such as the glycopeptides (van-comycin and teicoplanin), for prophylaxis in clean surgery in hospitals where the prevalence of methicillin-resistant staphylococci is high.The effectiveness and tolerability of teicoplanin as prophylaxis for orthopaedic surgery involving joint replacement were analysed in 4 randomised controlled trials. Two compared teicoplanin with cefamandole, while the others compared teicoplanin with either cefuroxime or cefazolin. The overall early wound infection rates (within 3 months) in these studies were 1.1% for teicoplanin and 1.7% for the comparator cephalosporin. The overall late infection rate was 0.2% for both treatment groups. Adverse events were attributed to the drug in 1% of patients in both treatment groups. Therefore, on the basis of these trials, single dose teicoplanin is as efficacious and as well tolerated as multiple dose cephalosporin regimens for prophylaxis in prosthetic joint surgery.

Antimicrobial chemoimmunoprophylaxis in colorectal surgery with cefotetan and thymostimulin : prospective, controlled multicenter study

Surgical antimicrobial prophylaxis was performed with a controlled study on 859 evaluable patients randomized into two groups treated with chemoprophylaxis only or chemo- and immunoprophylaxis in colorectal surgery. Immuno and chemoprophylactic treatment (425 patients) consisted of 70 mg i.m. thymostimulin per day for 7 days beginning 48 h before surgery plus 2 g cefotetan at the moment of induction of anesthesia; the other group (434 patients) received only the single dose of antibiotic. Results in the two different groups were significantly different regarding abdominal abscess and the total infectious episodes in the surgical site with lower frequency in patients receiving both thymostimulin and the antibiotic (cefotetan). Moreover the respiratory tract infections were more than double in those patients not treated with perioperative immunotherapy. Stratifying patients on the basis of grade of skin test reaction, we observed a significantly lower percentage of surgical site infection in hypoergic patients receiving chemo- and immunoprophylaxis.