Evaluation of the effect of norfloxacin on the pharmacokinetics of theophylline

Meta-Analysis of Quinolone—Theophylline Interactions

Several fluoroquinolones currently under investigation or on the market potentially interact with theophylline. In this study, meta-analysis methodology was used to evaluate the significance of findings from quinolone-theophylline interaction studies. Two major databases were searched: Index Medicus (from 1986 to March 1990) and Current Content/Clinical Medicine (from 1985 to March 1990). A total of 32 studies were retrieved; 20 of these met the inclusion criteria. With a large effect size (ES) value of 2.26, enoxacin is the strongest inhibitor of theophylline metabolism of this family. The fail-safe N value was 135, indicating that 135 studies enrolling an average of 8 patients and showing no interaction (i.e., ES = 0) would be required to lower the ES to the threshold value of 0.1, which we considered a priori to render the results nonsignificant. Other fluoroquinolones showed a degree of interaction that can be considered significant: Ciprofloxacin (ES = 0.50, fail-safe N = 26), norfloxacin (ES = 0.31, fail-safe N = 10). Ofloxacin (ES = 0.13, fail-safe N = 4), lomefloxacin (ES = 0.12, fail-safe N = 2), and fleroxacin (ES = 0.06, fail-safe N = 2) provided the weakest evidence of interaction based on effect size and power. Among the fluoroquinolones studied, ofloxacin, lomefloxacin, and fleroxacin, when available, should be the fluoroquinolones of choice when the patient also is receiving theophylline.

Pharmacokinetic aspects of treating infections in the intensive care unit: focus on drug interactions

Pharmacokinetic interactions involving anti-infective drugs may be important in the intensive care unit (ICU). Although some interactions involve absorption or distribution, the most clinically relevant interactions during anti-infective treatment involve the elimination phase. Cytochrome P450 (CYP) 1A2, 2C9, 2C19, 2D6 and 3A4 are the major isoforms responsible for oxidative metabolism of drugs. Macrolides (especially troleandomycin and erythromycin versus CYP3A4), fluoroquinolones (especially enoxacin, ciprofloxacin and norfloxacin versus CYP1A2) and azole antifungals (especially fluconazole versus CYP2C9 and CYP2C19, and ketoconazole and itraconazole versus CYP3A4) are all inhibitors of CYP-mediated metabolism and may therefore be responsible for toxicity of other coadministered drugs by decreasing their clearance. On the other hand, rifampicin is a nonspecific inducer of CYP-mediated metabolism (especially of CYP2C9, CYP2C19 and CYP3A4) and may therefore cause therapeutic failure of other coadministered drugs by increasing their clearance. Drugs frequently used in the ICU that are at risk of clinically relevant pharrmacokinetic interactions with anti-infective agents include some benzodiazepines (especially midazolam and triazolam), immunosuppressive agents (cyclosporin, tacrolimus), antiasthmatic agents (theophylline), opioid analgesics (alfentanil), anticonvulsants (phenytoin, carbamazepine), calcium antagonists (verapamil, nifedipine, felodipine) and anticoagulants (warfarin). Some lipophilic anti-infective agents inhibit (clarithromycin, itraconazole) or induce (rifampicin) the transmembrane transporter P-glycoprotein, which promotes excretion from renal tubular and intestinal cells. This results in a decrease or increase, respectively, in the clearance of P-glycoprotein substrates at the renal level and an increase or decrease, respectively, of their oral bioavailability at the intestinal level. Hydrophilic anti-infective agents are often eliminated unchanged by renal glomerular filtration and tubular secretion, and are therefore involved in competition for excretion. Beta-lactams are known to compete with other drugs for renal tubular secretion mediated by the organic anion transport system, but this is frequently not of major concern, given their wide therapeutic index. However, there is a risk of nephrotoxicity and neurotoxicity with some cephalosporins and carbapenems. Therapeutic failure with these hydrophilic compounds may be due to haemodynamically active coadministered drugs, such as dopamine, dobutamine and furosemide, which increase their renal clearance by means of enhanced cardiac output and/or renal blood flow. Therefore, coadministration of some drugs should be avoided, or at least careful therapeutic drug monitoring should be performed when available. Monitoring may be especially helpful when there is some coexisting pathophysiological condition affecting drug disposition, for example malabsorption or marked instability of the systemic circulation or of renal or hepatic function.

Interaction between pefloxacin and aminophylline in genetically epilepsy-prone rats

The effects of a chronic treatment with pefloxacin on aminophylline-induced seizures in genetically epilepsy-prone rat have been investigated. Two series of experiments were performed. In the first, animals received pefloxacin orally twice a day for five days, then were administered aminophylline intraperitoneally and the occurrence of seizures was evaluated. In the second series of experiments, theophylline serum concentration was evaluated in rats subject to the same experimental protocol. Pefloxacin significantly, and in a dose-dependent manner, increased the occurrence of seizure phases induced by aminophylline, but did not influence theophylline serum levels measured at different times after the injection of aminophylline. We suggest that additive neurotoxic effects of both pefloxacin and aminophylline might contribute to the increased severity of seizure score. The possible role of GABA-benzodiazepine, excitatory amino acid and purinergic mechanism, and the role of pharmacokinetic factors are discussed.

Influence of a newly developed quinolone, T-3761, on pharmacokinetics of theophylline in rats

The effect of a new quinolone, T-3761, on the pharmacokinetics and metabolism of theophylline was investigated with rats. T-3761 at a high dose (20 mg/kg of body weight) was injected intravenously 10 min before an intravenous administration of theophylline (10 mg/kg). The presence of T-3761 slightly delayed the disappearance of theophylline from plasma. Parameters related to the pharmacokinetic interaction between theophylline and T-3761 were estimated by noncompartmental methods. A significant decrease (approximately 25%) in the systemic clearance of theophylline was observed in the presence of T-3761. However, no significant changes between the control group and the T-3761-treated groups in the volume of distribution at a steady state were observed. Pretreatment with T-3761 increased the urinary excretion of unchanged theophylline (by approximately 25%) and decreased the nonrenal clearances (by approximately 30%), indicating that T-3761 inhibits the metabolism of theophylline. These findings suggest that T-3761 at the dose used in this study affects the pharmacokinetics and metabolism of theophylline.

Effects of fluoroquinolone antimicrobials alone and in conjunction with theophylline on seizures in amygdaloid kindled rats. Mechanistic and pharmacokinetic study

The influence of three fluoroquinolone (FQ) antimicrobial drugs (ciprofloxacin (CP), norfloxacin (NF), enrofloxacin (EF)) on seizure parameters in amygdaloid kindled rats was investigated. CP and NF (100 mg/kg i.p.) did not modify seizure parameters while EF induced a decrease in seizure activity. Since clinical data indicate a seizure enhancing interaction between FQ and theophylline (THEO) we studied the influence of concurrent FQ-THEO administration in kindled rats. CP and NF, but not EF given concurrently with a non-seizure modulating dose of THEO (10 mg/kg i.p.) caused increases in seizure activity and aggressiveness in the animals. The CP-THEO induced seizure enhancement was antagonized by 2-chloroadenosine and diazepam. Pharmacokinetic studies demonstrated that THEO serum levels and elimination were not altered by concurrent CP administration. We conclude that coadministration of FQ-THEO can aggravate amygdala kindled seizures and that this aggravation may involve centrally mediated mechanisms.

Inhibitory potency of quinolone antibacterial agents against cytochrome P450IA2 activity in vivo and in vitro

Inhibition of cytochrome P450IA2 activity is an important adverse effect of quinolone antibacterial agents. It results in a prolonged half-life for some drugs that are coadministered with quinolones, such as theophylline. The objective of the study described here was to define the parameters for quantifying the inhibitory potencies of quinolones against cytochrome P450IA2 in vivo and in vitro and to investigate the relationship between the results of both approaches. Cytochrome P450IA2 activity in vitro was measured by using the 3-demethylation rate of caffeine (500 microM) in human liver microsomes. The inhibitory potency of a quinolone in vitro was determined by calculating the decrease in the activity of cytochrome P450IA2 caused by addition of the quinolone (500 microM) into the incubation medium. The mean values (percent reduction of activity without quinolone) were as follows: enoxacin, 74.9%; ciprofloxacin, 70.4%; nalidixic acid, 66.6%; pipemidic acid, 59.3%; norfloxacin, 55.7%; lomefloxacin, 23.4%; pefloxacin, 22.0%; amifloxacin, 21.4%; difloxacin, 21.3%; ofloxacin, 11.8%; temafloxacin, 10.0%; fleroxacin, no effect. The inhibitory potency of a quinolone in vivo was defined by a dose- and bioavailability-normalized parameter calculated from changes of the elimination half-life of theophylline and/or caffeine reported in previously published studies. Taking the pharmacokinetics of the quinolones into account, it was possible to differentiate between substances with and without clinically relevant inhibitory effects by using results of in vitro investigations. The in vitro test described here may help to qualitatively predict the relevant drug interactions between quinolones and methylxanthines that occur during therapy.

The U.S. clinical experience with lomefloxacin, a new once-daily fluoroquinolone

Lomefloxacin is a new fluoroquinolone antimicrobial agent that has undergone extensive worldwide clinical evaluation. This report summarizes the safety and efficacy of lomefloxacin in the treatment of uncomplicated urinary tract infections, complicated urinary tract infections, acute exacerbations of chronic bronchitis, and for prophylaxis during urinary tract surgery. The clinical data presented are an overview of all clinical studies conducted in the United States to date. The results have been derived from multiple studies in which patients received lomefloxacin or a comparative agent in either blinded or open-label studies. During the course of the clinical program in the United States, lomefloxacin has been compared with oral norfloxacin, ciprofloxacin, and cefaclor, as well as parenteral cefotaxime. In all instances, the once-daily oral administration of lomefloxacin was either equally effective or statistically significantly superior in clinical and/or bacteriologic efficacy to these comparative agents. In addition, the comparators were administered either two or three times per day, except in the surgical prophylaxis studies, in which single doses of each antibiotic were administered preoperatively. These results attest to the value of the convenience and simplicity of the oral dosing regimen for lomefloxacin. During the course of the clinical program, lomefloxacin was well tolerated, with most adverse events of mild to moderate severity. In general, the incidence of adverse events for patients and subjects receiving lomefloxacin was comparable to that observed in patients treated with comparator drugs. The most common adverse events were related to the gastrointestinal tract (nausea and diarrhea), the skin and appendages (photosensitivity), and the central nervous system (dizziness and headache). A sub-analysis of adverse events in the respiratory studies demonstrated that concomitant administration of lomefloxacin and theophylline does not increase the incidence of adverse events when compared to lomefloxacin alone. An additional sub-analysis also showed that the incidence of adverse events in elderly patients was similar to that in younger patients. The results of the U.S. clinical program indicate that lomefloxacin administered orally once daily is effective and well tolerated in a variety of infections of bacterial origin.

The effects of quinolones on xanthine pharmacokinetics

Caffeine, theobromine, and theophylline are among the most widely consumed compounds in beverages and in pharmaceutical preparations. These methylxanthine alkaloids are metabolized by similar pathways involving demethylation and hydroxylation that are predominantly cytochrome P-450 mediated. In vivo and in vitro evidence suggests that the cytochrome P-450 isozymes involved in the demethylation pathways are distinct from the cytochrome P-450 isozymes involved in the hydroxylation pathways. Although distinctions can be made between demethylation and hydroxylation pathways, the evidence suggests that these different cytochrome P-450 isozymes are under common regulatory control. Any drug inhibiting the family of cytochrome P-450 isozymes involved in the metabolism of the methylxanthines would, therefore, be expected to have a similar effect on theophylline, theobromine, and caffeine. A number of quinolones, including enoxacin, pipemidic acid, ciprofloxacin, norfloxacin, and pefloxacin, have been shown to reduce the clearance of theophylline, while lomefloxacin has no effect on theophylline or caffeine clearance. It has been hypothesized that only fluoroquinolones that form a 4-oxo-metabolite inhibit theophylline clearance. Lomefloxacin, which does not form a 4-oxo-metabolite, would therefore not be expected to inhibit the clearance of theophylline or caffeine. In contrast, ciprofloxacin, which does form a 4-oxo-metabolite, has been shown to reduce theophylline and caffeine clearances by about one third. Another hypothesis for the differences among quinolones suggests that quinolones that have a greater impact on theophylline clearances are more stereochemically similar to theophylline. Substitutions at position 8 on the quinolone nucleus (as in lomefloxacin) would result in stearic hindrance and decrease the structural similarity to theophylline.

Ofloxacin clinical pharmacokinetics

Ofloxacin is a new fluoroquinolone with a spectrum of activity similar to other fluoroquinolones with activity which includes Chlamydia trachomatis, Mycobacterium spp., Mycoplasma spp. and Legionella pneumophila. Through its additional mechanisms of action, ofloxacin may be less susceptible to the development of resistance from Staphylococcus aureus commonly seen with currently available fluoroquinolones. The impact of these findings cannot be evaluated without further clinical experience. The pharmacokinetics of ofloxacin are characterised by almost complete bioavailability (95 to 100%), peak serum concentrations in the range of 2 to 3 mg/L after a 400mg oral dose and an average half-life of 5 to 8h. In comparison with other available quinolones, elimination is more highly dependent on renal clearance, which may lead to more frequent dosage adjustments in patients with impaired renal function. Ofloxacin appears less likely to affect the pharmacokinetics of drugs (e.g. theophylline) which commonly interact with fluoroquinolones such as ciprofloxacin and enoxacin. The properties of ofloxacin make it a therapeutic alternative to currently available fluoroquinolones.

Overview of fluoroquinolone safety

The safety of the fluoroquinolone antimicrobial agents is reviewed, discussing documented and potential clinical and laboratory adverse effects and drug-drug interactions. In prospective, randomized, double-blind clinical trials comparing fluoroquinolones to nonquinolone drugs or placebo, the fluoroquinolones were not significantly different (22 studies) or were superior (5 studies) to comparison agents but were only rarely more toxic (2 studies). Adverse effects included mild gastrointestinal toxicities and less common but more problematic central nervous system toxicities. Clinically important interactions occurred with coadministration of antacids and all fluoroquinolones and with theophylline and enoxacin and to a lesser extent ciprofloxacin and pefloxacin but not other fluoroquinolones. Potential adverse effects such as cartilage damage, DNA damage, teratogenicity, and crystalluria, while of concern, have not as yet been shown to be of clinical importance. Therapy of bacterial infections in children and adolescents is relatively contraindicated, but growing clinical experience with treatment of these patients has not so far revealed serious bone or cartilage toxicity. The fluoroquinolones thus far have exhibited a favorable safety profile, but our clinical experience is still limited, and monitoring for as yet unappreciated toxicities is warranted.

Pharmacokinetic characteristics of N7-substituted theophylline derivatives and their interaction with quinolone in rats

Disposition of diprophylline (DPP) and proxyphylline (PXP) and the effect of enoxacin on their disposition were investigated in rats. Concentrations of the two drugs in plasma and urine were measured by HPLC. The pharmacokinetic parameters of the two drugs were estimated by model-independent methods. Although the chemical structures of the two drugs are very similar, remarkable differences in the disposition of the two drugs were observed. Total body clearance (CLT) of DPP was 1.77 L/h/kg, which was sevenfold greater than that of PXP (0.26 L/h/kg). Diprophylline was excreted in an almost completely unchanged form in the urine, but only 50% of PXP was excreted. However, no binding of either drug to proteins in rat plasma was observed. The DPP renal clearance (CLR) was 1.75 L/h/kg, approximately 13-fold the CLR for PXP (0.13 L/h/kg) and sevenfold the rat glomerular filtration rate. This study indicates that in rats, DPP is mainly excreted by active tubular secretion and that renal tubular reabsorption contributes to renal excretion of PXP with glomerular filtration. No significant changes in any pharmacokinetic parameters of the two drugs were observed when they were coadministered with enoxacin, compared with the drug administered alone, suggesting that enoxacin had no effect on the pharmacokinetics of either drug.

Effect of a new quinolone, sparfloxacin, on the pharmacokinetics of theophylline in asthmatic patients

Recently, it has become evident that some quinolones affect the processing of theophylline in the human system. The effect of a new quinolone, sparfloxacin, on the pharmacokinetics and metabolism of theophylline was investigated in six asthmatic patients receiving chronic theophylline therapy (a sustained-release theophylline tablet formulation of 200 to 300 mg twice daily at 12-h intervals). To these patients, sparfloxacin (200 mg once daily) was coadministered for 1 week. Plasma and urine samples were analyzed by high-performance liquid chromatography for theophylline and its metabolites. Plasma theophylline concentration-time curves and the urinary excretion of theophylline and its major metabolites before and after coadministration of sparfloxacin were compared. The total body clearance of theophylline after coadministration of sparfloxacin, 42.81 +/- 6.64 ml/h/kg (mean +/- standard error of the mean), was not significantly different from that after the administration of theophylline alone, 47.11 +/- 7.61 ml/h/kg. Also, no significant change in the urinary excretion of theophylline and its metabolites was observed for subjects receiving or not receiving sparfloxacin. These findings indicate that a once-daily dose of 200 mg of sparfloxacin has no significant effect on the pharmacokinetics and metabolism of theophylline and that it would be safe to coadminister this quinolone to asthmatic patients receiving chronic theophylline therapy.

Lack of interaction between lomefloxacin and caffeine in normal volunteers

Sixteen healthy, nonsmoking adult males participated in a randomized, double-blind, placebo-controlled, two-way crossover study to evaluate the influence of chronic lomefloxacin administration on the disposition of caffeine and its major metabolite, paraxanthine, at steady-state conditions. Lomefloxacin (400 mg) or placebo was administered orally once daily for 5 days to xanthine-free volunteers after an overnight fast. Caffeine (200 mg orally) was administered simultaneously with lomefloxacin on days 3 through 5. After a 2-day washout period, subjects were crossed over to the alternate 5-day regimen with caffeine, which was again given on the final 3 days. Blood samples for caffeine, paraxanthine, and lomefloxacin concentration determinations were serially collected for 48 h following the last dose of each regimen. All compounds were analyzed by high-performance liquid chromatography. For the placebo versus lomefloxacin-containing treatments, maximum caffeine concentrations in plasma (4.35 +/- 0.63 versus 4.07 +/- 0.56 micrograms/ml), areas under the concentration-time curve from time zero to 24 h at steady state (30.3 +/- 6.9 versus 29.7 +/- 6.6 micrograms.h/ml), and elimination half-lives of caffeine (4.8 +/- 1.1 versus 4.8 +/- 1.2 h) were not significantly different. In addition, there were no significant changes in the disposition parameters of paraxanthine as a result of lomefloxacin administration. The frequencies of central nervous system-related effects for the two treatments were not statistically different. We conclude that lomefloxacin has no significant effect on the disposition of caffeine in young healthy volunteers.

Pharmacokinetic interactions between theophylline and other medication (Part II)

Part I of this article, which appeared in the previous issue of the Journal, covered the effects or lack of effects on theophylline clearance of sympathomimetics, corticosteroids, antihistamines and other antiallergy drugs, antimicrobial agents, phenytoin, carbamazepine, barbiturates, antacids and activated charcoal. In Part II, this discussion is extended to the effects of other agents. Overall summaries, both textual and tabular, appear in Part I.

The possible mechanism of interaction between xanthines and quinolone

To clarify the mechanism of interaction between theophylline and enoxacin, the effects of enoxacin and its metabolite, 4-oxo-enoxacin, on the disposition of new xanthine derivatives, 1-methyl-3-propylxanthine (MPX) and 3-propylxanthine (enprofylline), as models of theophylline have been investigated in rats. Pretreatment with enoxacin significantly delayed the elimination of MPX from plasma. No significant change in the volume of distribution of MPX was observed in the presence of enoxacin, but the total body clearance of MPX was significantly decreased by approximately 60 and 80% after pretreatment with 25 and 100 mg kg-1 of enoxacin, respectively. The amount of the decrease in total body clearance depended on the dose of enoxacin. 4-Oxo-enoxacin had little or no effect on MPX disposition. A newly developed quinolone, NY-198, which does not affect the disposition of theophylline, also did not affect the disposition of MPX. Enoxacin also had no effect on the disposition of enprofylline. These results indicate that the mechanism for decrease in theophylline clearance induced by enoxacin may not be due to its metabolite, 4-oxo-enoxacin, but to enoxacin itself, and that enoxacin does not inhibit solely the elimination process depending on cytochrome P450 isoenzyme for N-demethylation. It is likely that enoxacin has no influence on the renal excretion of xanthines.

The effect of ciprofloxacin on the pharmacokinetic and ECG parameters of quinidine

Ciprofloxacin decreases the clearance of antipyrine and other drugs which, in part, undergo oxidative metabolism. Based on these findings, the authors hypothesized that ciprofloxacin may decrease the clearance of quinidine, a drug which also undergoes oxidative metabolism. The purpose of this study was to evaluate the effect of ciprofloxacin on the pharmacokinetic and ECG parameters of quinidine in seven healthy men. Oral quinidine sulfate 400 mg was administered alone (Phase A) and after oral ciprofloxacin pretreatment (Phase B) in a randomized crossover fashion with a 2-week washout period between each phase. During Phase B, ciprofloxacin pretreatment (750 mg every 12 hours) was administered for 5 days before and 24 hours after quinidine administration. Quinidine serum samples were obtained over a 24-hour period. QRS and QTc intervals were measured over a 12-hour period. There were no significant differences in clearance (20.3 +/- 3.3 L/hr vs 20.1 +/- 2.3 L/hr, P = .836), half-life (7.9 +/- 1 hr vs 7.8 +/- 0.8 hr, P = 0.8), maximum concentration (1.4 +/- 0.6 mg/L vs 1.5 +/- 0.6 mg/L, P = 0.613), or time to maximum concentration (1.5 +/- 0.2 hr vs 1.5 +/- 0.1 hr, P = 0.571) for quinidine between Phase A and Phase B, respectively. The largest decrease in clearance observed for Phase B compared to Phase A was 10%. There was also no significant difference in the degree of QRS and QTc prolongation between Phase A and Phase B. From these results, it appears that ciprofloxacin in the dose given does not alter the pharmacokinetic or ECG parameters of quinidine. Therefore, no adjustment in the dose of quinidine is needed when coadministered with ciprofloxacin.

Pharmacokinetic determination of relative potency of quinolone inhibition of caffeine disposition

Quinolone is reported to interact with caffeine, often resulting in an increase both in the plasma half-life and AUC, a decrease in total plasma clearance, and little change in the absorption rate constant and maximum plasma level. These complex changes in the pharmacokinetics of caffeine were analyzed experimentally and from published reports in order to determine the nature of the interaction, which is thought to be due to inhibition of caffeine metabolism by quinolones. A simple pharmacokinetic model for the caffeine-quinolone interaction was developed, which provides a unified method for evaluation and comparison of the effect of quinolones on the disposition of caffeine. The model is applicable to other methylxanthines, such as theophylline. The relative potency of the interactions of quinolones with caffeine in humans has been established as enoxacin (100), pipemidic acid (29), ciprofloxacin (11), norfloxacin (9) and ofloxacin (0).

Effects of enoxacin on renal and metabolic clearance of theophylline in rats

The effects of enoxacin and its metabolite 4-oxoenoxacin on the disposition of theophylline were investigated in rats. Systemic clearance of theophylline was significantly decreased by approximately 40, 46, and 50% after oral coadministration of 25, 100, and 200 mg of enoxacin per kg, respectively. No significant changes in the volume of distribution of theophylline were observed. 4-Oxoenoxacin had no direct effect on theophylline disposition. Significant changes in urinary excretion of theophylline and its metabolites were observed. (i) Urinary excretion of unchanged theophylline was significantly increased in proportion to increases in enoxacin dosage. (ii) Decreases in renal clearance of theophylline and metabolic clearance of 1-methyluric acid and 1,3-dimethyluric acid were observed. (iii) The percent decreases in the metabolic clearance of 1-methyluric acid were dependent on enoxacin dosage. It is likely that enoxacin inhibits the elimination process, which depends on cytochrome P-450-mediated isozymes for N demethylation and oxidation, and that the capacity of the inhibitory effect of enoxacin is greater in the N-demethylation pathway than it is in oxidation.

Update on quinolone drug interactions

Concurrent administration of both ciprofloxacin and norfloxacin with sucralfate leads to a decrease in quinolone bioavailability. It is unknown whether this decrease is clinically significant because studies have focused primarily on pharmacokinetics and not therapeutic outcomes. A reasonable recommendation may be to avoid using sucralfate and norfloxacin concurrently, or avoid administration of norfloxacin and ciprofloxacin within two hours of sucralfate administration. Magnesium- and aluminum-containing antacids may also interfere with quinolone absorption. Calcium carbonate and H2 receptor antagonists do not appear to interact with quinolones and may be considered as an alternative to sucralfate or magnesium- and aluminum-containing antacids when quinolones are administered. Concurrent administration of ciprofloxacin and theophylline may precipitate theophylline toxicity if not monitored carefully. Some clinicians recommend a 30% empiric reduction in theophylline dosage when ciprofloxacin therapy is initiated. Because the drug interaction is not completely predictable, the patient's theophylline levels should be monitored and signs and symptoms of toxicity noted, adjusting the dose as needed. Decreased theophylline clearance may persist for as long as five days following discontinuation of ciprofloxacin. Some potential for slight increases in serum theophylline concentrations secondary to norfloxacin administration may exist. However, it is unlikely to be clinically significant, based on currently available information.

Norfloxacin does not alter warfarin's disposition or anticoagulant effect

Drug interactions related to inhibition of hepatic drug metabolism have been identified for some fluoroquinolone antibiotics. This study was designed to investigate whether the fluoroquinolone norfloxacin at the usual clinical dosage interacts with the anticoagulant agent warfarin. Ten healthy male subjects were administered a single oral dose of 30 mg warfarin sodium alone or during multiple-dose treatment with norfloxacin, 400 mg bid, in a randomized, crossover fashion. Plasma warfarin concentrations and prothrombin times were measured for 6 days after each of the two warfarin doses. The pharmacokinetic parameters of warfarin were comparable in the absence and presence of norfloxacin, including no significant differences in warfarin's elimination half-life, apparent total clearance, apparent volume of distribution, or peak plasma concentration. Norfloxacin also had no significant effect on the anticoagulant effect of warfarin, as assessed by the area under the prothrombin time versus time curve and the maximum response for prothrombin time. The lack of pharmacokinetic or pharmacodynamic interaction observed in this study suggests that a clinically important interaction of norfloxacin and warfarin is unlikely to occur in patients requiring both drugs.

Management of asthma and chronic airflow limitation. Are methylxanthines obsolete?

After almost 50 years as first-line drugs in the management of asthma and COPD, methylxanthines have been largely superceded by inhaled adrenoceptor agonist and anticholinergic bronchodilators which are more potent and far less toxic. Accumulating evidence indicates that intravenous theophylline contributes side effects, but is rarely of benefit in acute exacerbations of asthma or COPD. In the maintenance therapy of asthma, first-line therapy is dose-optimized inhaled steroids, reducing the need for bronchodilators. Inhaled adrenoceptor agonists are second line medications, anticholinergic aerosols third line, and theophylline, if needed at all, may fulfill a minor systemic steroid-sparing function in severe asthmatics on maximum doses of the inhaled medications. In the maintenance therapy of some patients with COPD, theophylline sometimes may be useful but these responders should be identified by objectively establishing therapeutic benefit. Since many patients have side effects from the methylxanthines, while their therapeutic benefit over and above dose-optimized inhaled therapy is marginal, their continued almost routine use in the management of reversible airflow obstruction is hard to justify, although this class of drugs may be useful in selected patients in whom both subjective and objective benefit can be demonstrated. In COPD, theophylline may improve exercise capacity in some patients by still incompletely understood mechanisms probably unrelated to bronchodilation.

Safety of fleroxacin coadministered with theophylline to young and elderly volunteers

The influence of multiple doses of fleroxacin on the plasma clearance and the urinary excretion of theophylline was studied in 19 young and 18 elderly male volunteers. A theophylline dosage individualized to obtain a mean theophylline concentration in plasma of 10 +/- 3 micrograms/ml was administered for 1 week to each subject. At week 2, oral fleroxacin (400 mg once daily) was added. Theophylline concentrations in plasma were measured with TDx (Abbott Diagnostics, Mississauga, Ontario, Canada), and urinary excretion of theophylline and its three major metabolites was measured by high-performance liquid chromatography. Total theophylline clearance remained essentially unchanged throughout the study period (3.5 and 2.9 liters/h in the young and the elderly, respectively) both after a single fleroxacin dose and after multiple doses. Although significant changes occurred in the urinary excretion of unchanged theophylline and its metabolites after a single fleroxacin dose, no changes were observed after multiple doses. Side effects consisted mainly of gastrointestinal and sleep disturbances, more related to theophylline; photosensitivity was observed in six subjects and was attributed to fleroxacin. We conclude that fleroxacin may be administered concomitantly with theophylline in either young or elderly patients. Close monitoring of theophylline concentrations in serum should be performed, particularly in patients with chronic obstructive pulmonary disease, for whom data are currently lacking.

Ofloxacin: a review

Ofloxacin is a new fluorinated quinolone antibiotic with a broad spectrum of activity against a variety of gram-positive and -negative bacteria including Enterobacteriaceae, Pseudomonas aeruginosa, and methicillin-resistant Staphylococcus aureus. In addition, ofloxacin has significant activity against Neisseria gonorrhoeae, Chlamydia trachomatis, and Mycobacterium tuberculosis and this may give rise to new indications for the class of quinolone antibiotics. Clinical trials to date have demonstrated the efficacy of ofloxacin in the treatment of lower respiratory tract infections, urinary tract infections, and sexually transmitted diseases. Adverse effects to ofloxacin are usually mild and include gastrointestinal, central nervous system, and hypersensitivity reactions. Significant drug interactions with ofloxacin have not been reported.

Fluoroquinolone antimicrobial agents

The fluoroquinolones, a new class of potent orally absorbed antimicrobial agents, are reviewed, considering structure, mechanisms of action and resistance, spectrum, variables affecting activity in vitro, pharmacokinetic properties, clinical efficacy, emergence of resistance, and tolerability. The primary bacterial target is the enzyme deoxyribonucleic acid gyrase. Bacterial resistance occurs by chromosomal mutations altering deoxyribonucleic acid gyrase and decreasing drug permeation. The drugs are bactericidal and potent in vitro against members of the family Enterobacteriaceae, Haemophilus spp., and Neisseria spp., have good activity against Pseudomonas aeruginosa and staphylococci, and (with several exceptions) are less potent against streptococci and have fair to poor activity against anaerobic species. Potency in vitro decreases in the presence of low pH, magnesium ions, or urine but is little affected by different media, increased inoculum, or serum. The effects of the drugs in combination with a beta-lactam or aminoglycoside are often additive, occasionally synergistic, and rarely antagonistic. The agents are orally absorbed, require at most twice-daily dosing, and achieve high concentrations in urine, feces, and kidney and good concentrations in lung, bone, prostate, and other tissues. The drugs are efficacious in treatment of a variety of bacterial infections, including uncomplicated and complicated urinary tract infections, bacterial gastroenteritis, and gonorrhea, and show promise for therapy of prostatitis, respiratory tract infections, osteomyelitis, and cutaneous infections, particularly when caused by aerobic gram-negative bacilli. Fluoroquinolones have also proved to be efficacious for prophylaxis against travelers' diarrhea and infection with gram-negative bacilli in neutropenic patients. The drugs are effective in eliminating carriage of Neisseria meningitidis. Patient tolerability appears acceptable, with gastrointestinal or central nervous system toxicities occurring most commonly, but only rarely necessitating discontinuance of therapy. In 17 of 18 prospective, randomized, double-blind comparisons with another agent or placebo, fluoroquinolones were tolerated as well as or better than the comparison regimen. Bacterial resistance has been uncommonly documented but occurs, most notably with P. aeruginosa and Staphylococcus aureus and occasionally other species for which the therapeutic ratio is less favorable. Fluoroquinolones offer an efficacious, well-tolerated, and cost-effective alternative to parenteral therapies of selected infections.

Effect of quinolone antimicrobials on theophylline pharmacokinetics

The purpose of the research was to ascertain the comparative differences of quinolone antibiotics on theophylline pharmacokinetics. Eight healthy male volunteers were randomly assigned to four treatments. Each was administered norfloxacin (NOR) 800 mg/d, ciprofloxacin (C) 1 g/d, nalidixic acid (NAL) 2 g/d and placebo (P) for 7 days. On the seventh day of each treatment, theophylline (5 mg/kg) iv was administered. The elimination half-life (T 1/2), total body clearance (CL) and volume of distribution at steady state (Vss) of theophylline were calculated using model-independent methods. ANOVA for repeated measures was used for data comparisons. The mean (SD) theophylline results were: CL l/kg/h--NOR .038 (.006), C .033 (.006), NAL .045 (.008), P .044 (.007); T 1/2 h--NOR 9.2 (1.8), C 10.6 (1.8), NAL 8.3 (1.8), P 7.5 (1.4). Theophylline Vss differences by treatment were not significant. NOR and C significantly decreased theophylline's clearance and the clearance change can be of clinical significance.

Effect of lomefloxacin on theophylline pharmacokinetics

A study involving 25 health male volunteers was conducted to evaluate the effect of lomefloxacin on the pharmacokinetics of theophylline. The mean age was 22.4 +/- 3.0 years, and the mean weight was 77.3 +/- 7.7 kg. A single 6-mg/kg aminophylline dose was given intravenously on study days 1 and 15. The subjects received a 400-mg lomefloxacin dose (four 100-mg capsules) on study days 9 through 15. No treatment was given on study days 2 through 8. Thirteen blood samples were collected within 24 h after each aminophylline dose. Theophylline concentrations in serum were measured by enzyme immunoassay (EMIT). The mean aminophylline dose was 437 +/- 36 mg, equivalent to 344 mg of theophylline. Multiple doses of lomefloxacin had no effect on the area under the concentration-time curve from 0 h to infinity, maximal concentration, or clearance of theophylline from serum. There was a slight increase in the theophylline half-life from 6.72 +/- 1.63 to 7.02 +/- 1.37 h after lomefloxacin dosing (P = 0.04); however, the change was clinically insignificant. No change in theophylline dose is required when lomefloxacin therapy is instituted in a patient receiving theophylline.