Inhibition of norfloxacin absorption by dairy products

Together or Apart? Revealing the Impact of Dietary Interventions on Bioavailability of Quinolones: A Systematic Review with Meta-analyses

BACKGROUND AND OBJECTIVE

Managing drug-food interactions is essential for optimizing the effectiveness and safety profile of quinolones. Following PRISMA guidelines, we systematically reviewed the influence of dietary interventions on the bioavailability of 22 quinolones.

METHODS

All studies describing or investigating the impact of food, beverages, antacids, and mineral supplements on pharmacokinetic parameters or pharmacokinetic/pharmacodynamic indices of orally taken quinolones were considered for inclusion. We excluded reviews, in vitro and in silico studies, studies performed on animals, and those involving alcohol. We performed the search in Medline (via PubMed), Embase, and Cochrane Library, covering reports from database inception to December 2022. We used the following tools to assess the risk of bias: version 2 of the Cochrane risk-of-bias tool for parallel trials, the Cochrane risk-of-bias tool for cross-over studies, and the NIH quality assessment tool for before-after studies. We performed quantitative analyses for each quinolone if two or more food-effect studies with specified and comparable study designs were available. If meta-analyses were not applicable, we qualitatively summarized the results.

RESULTS

We included 109 studies from 101 reports. Meta-analyses were conducted for 12 antibiotics and qualitative synthesis was employed for the remaining drugs. Of the studies, 60.5% were open-label, cross-over, as recommended by FDA. We judged 46% of studies as having a high risk of bias and only 4% of having a low risk of bias. Among 19 quinolones with available food impact data, 14 (74%) had potentially clinically important interactions. For nalidixic acid, oxolinic acid, and tosufloxacin, food exerted a high positive impact on bioavailability (AUC or Cmax increased by > 45%), whereas, for all the remaining drugs, postprandial absorption was lower. The most significant negative influence of food (AUC or Cmax decreased by > 40%) occurred for delafloxacin capsules and norfloxacin, whereas the moderate influence (AUC or Cmax decreased by 30-40%) occurred for nemonoxacin and rufloxacin. All 14 analysed quinolones showed a substantial reduction in bioavailability when co-administered with antacids and mineral supplements, except for calcium preparations. The impact of beverages was evaluated for 10 quinolones, with 50% experiencing significantly reduced absorption in the presence of milk (the highest negative impact for ciprofloxacin). Moreover, both ciprofloxacin and levofloxacin demonstrated compromised bioavailability when consumed with orange juice, particularly calcium-fortified.

DISCUSSION

Several factors may influence interactions, including the physicochemical characteristics of quinolones, the type of intervention, drug formulation, and the patient's health status. We assessed the quality of evidence as low due to the poor actuality of included studies, their methodological diversity, and uneven data availability for individual drugs.

Effects of Thylakoid-Rich Spinach Extract on the Pharmacokinetics of Drugs in Rats

Thylakoid-rich spinach extract is being used as dietary weight-loss supplements in Japan. A recent rat study has suggested that intake of thylakoid-rich spinach extract with dietary oil inhibits dietary fat absorption via binding to bile acids, which promotes excretion of bile acids in feces. While, we confirmed that a serving size of thylakoid-rich spinach extract contains a large amount of calcium (130 mg/5 g). Therefore, using rats, we evaluated whether one-time ingestion of thylakoid-rich spinach extract affects the gastrointestinal absorption of water-insoluble drugs, such as griseofulvin (GF) and indomethacin (IM), or ciprofloxacin (CPFX) that chelate with polyvalent metal cations. Pretreatment of the rats with thylakoid-rich spinach extract (100 or 300 mg/kg) for 15 min prior to oral administration of GF (50 mg/kg) or IM (10 mg/kg) did not significantly alter the pharmacokinetic properties of either drug. Meanwhile, co-administration of thylakoid-rich spinach extract (500 mg/kg) and CPFX (20 mg/kg) significantly reduced the peak plasma concentration and the area under the plasma concentration-time curve of CPFX to 25 and 40%, respectively in rats. In vitro studies demonstrated that when a mixture of thylakoid-rich spinach extract and CPFX was centrifuged, there was a significant reduction in the supernatant concentration of CPFX relative to the control. When the experiment was repeated in the presence of ethylenediaminetetraacetic acid, the concentration of CPFX was unchanged. These results suggest that the intake of thylakoid-rich spinach extract may reduce the absorption of drugs that form a chelate with polyvalent metal cations, such as CPFX.

Effect of Tinidazole on Norfloxacin Disposition

Co-administration of norfloxacin (NFX) and tinidazole (TNZ) has been used for the treatment of gastrointestinal and urinary tract infections. Concomitant oral administration of NFX with TNZ may affect NFX absorption and consequently its blood concentration and pharmacological effect. The present study was undertaken to investigate the effect of TNZ at the usual clinical dosage on the pharmacokinetics of NFX in healthy volunteers. This study was conducted as an open-label, randomized, two-way crossover experimental design. After an overnight fast, subjects were randomized to receive a single oral dose of NFX 400 mg alone and the fixed-dose combination (FDC) of NFX /TNZ 400 mg/600mg on two different occasions separated by 1 week washout period between treatments. Blood samples were collected up to 24 h postdose, and plasma was analyzed for NFX concentrations by using HPLC. The pharmacokinetic properties of NFX after FDC administration were compared with NFX administered alone. Twelve healthy subjects were enrolled (6 in each part), and all subjects completed the study. None of the participants showed any sign of adverse drug reactions during or after the completion of the study. The 90% confidence interval (CI) between NFX alone and when co-administered with TNZ indicated the presence of an interaction between NFX and TNZ, which would significantly increase the systemic rate and exposure of NFX absorption. The co-administration of TNZ with NFX increased the AUC and C_max of NFX significantly compared with administration of NFX alone. The AUC and C_max of NFX alone were 6.0 µg.hr/mL (2.3-9.8) and 0.87 µg/mL (0.4-1.6), respectively whereas the corresponding AUC and C_max values after administration of FDC were 7.1 µg.hr/mL (4.0-10.6) and 0.97 µg/mL (0.4-1.7), respectively. The respective geometric mean ratios of NFX for AUC and C_max with TNZ were 1.197 [90% CI, 0.941-1.522] and 1.087 (90% CI, 0.807 -1.463) compared with NFX alone. Both T_max and Ka of NFX showed a significant decrease after administration of the combination compared to administration of NFX alone. The peak plasma concentration reached at 1.3 h (0.6-2.4) and 1.9 h (0.4-4.4) after oral administration of FDC and NFX alone, respectively. Both NFX and TNZ were well tolerated. The interaction of TNZ with fluroquinolones should be investigated to determine whether this interaction is limited to NFX or if other fluroquinolones have the same pharmacokinetic interactions. Further studies are necessary to determine the role of P-gp and other transporters on NFX disposition and pharmacokinetics. Additionally, the influence of TNZ on the physiological activity of GIT should be investigated.

In vitro food-drug interaction study: Which milk component has a decreasing effect on the bioavailability of ciprofloxacin?

The purpose of the present work was developing an in vitro dissolution test to highlight the possible molecular background causing ciprofloxacin (CPFX)-milk interaction. The in vitro dissolution of CPFX from film-coated tablets (Ciprinol) 500mg) was examined at different pH values, simulating certain parts of the gastrointestinal tract, in the presence of water, low-fat milk, casein- or calcium enriched water. In order to determine the amount of dissolved CPFX, solid phase extraction sample preparation followed by high performance liquid chromatography coupled with mass spectrometry was applied. Comparing the dissolution efficiency values in various media, it can be concluded, that casein has a more pronounced effect on the absorbable amount of the antibiotic at each pH value studied, than calcium. In the case of concomitant intake of CPFX film-coated tablet and milk or other dairy products not only the complexation with calcium, but also the adsorption of CPFX on the surface of proteins decreases the absorbable amount of CPFX.

Effects of Dairy Products on the Oral Bioavailability of Moxifloxacin, a Novel 8-Methoxyfluoroquinolone, in Healthy Volunteers

OBJECTIVE

To investigate the effect of concomitant administration of dairy products on the pharmacokinetics and tolerability of moxifloxacin.

DESIGN

This was a single-centre, randomised, controlled, nonblinded, 2-way crossover study in healthy volunteers.

PARTICIPANTS

12 healthy men (aged 25 to 46 years) were enrolled in the study.

METHODS

The plasma and urinary pharmacokinetics of moxifloxacin were investigated after single doses of moxifloxacin 400mg administered orally either under fasting conditions or immediately after 250g of yoghurt that was to be consumed within 15 minutes. There was a 1-week interval between the study periods.

RESULTS

Administration of moxifloxacin after yoghurt had no effect on the extent of absorption, as estimated by the area under the plasma concentration-time curve from zero to infinity [AUCinfinty; geometric means 31.8 versus 33.9 mg/L x h after test and reference, respectively; estimated true treatment ratio 94%, 90% confidence interval (CI) 90 to 98%]. The rate of absorption was slightly decreased, with a slight reduction in maximum plasma concentration (Cmax; geometric means 2.44 versus 2.87 mg/L; estimated true treatment ratio 85%, 90% CI 74 to 98%) and a prolonged time to reach Cmax (tmax; median 2.75 versus 0.88 hours). The treatments were well tolerated in these healthy individuals.

CONCLUSIONS

The effects of yoghurt on the pharmacokinetics of moxitloxacin are considered not clinically relevant. Hence, no special recommendations for administration are required when moxifloxacin is given together with dairy products.

Bioequivalence evaluation of norfloxacin 400 mg tablets (Uroxin and Noroxin) in healthy human volunteers

A bioequivalence study of two oral formulations of 400 mg norfloxacin was carried out in 18 healthy volunteers according to a single dose, two-sequence, cross-over randomized design at College of Pharmacy, King Saud University, Riyadh, Saudi Arabia, jointly with King Khalid University Hospital. The two formulations were: Uroxin (Julphar, United Arab Emirates) as test and Noroxin (Merck Sharpe & Dohme, BV, Netherlands). Both test and reference formulations were administered to each subject after an overnight fasting on 2 treatment days separated by 1 week wash-out period. After dosing, serial blood samples were collected for a period of 24 h. Plasma harvested from blood, was analysed for norfloxacin by a sensitive, reproducible and accurate HPLC method. Various pharmacokinetic parameters including AUC(0-t), AUC(0-infinity), C(max), T(max), T(1/2), and K(el) were determined from plasma concentrations for both the formulations and found to be in good agreement with reported values. AUC(0-t), AUC(0-infinity), and C(max) were tested for bioequivalence after log-transformation of data. No significant difference was found based on ANOVA; 90% confidence interval for test/reference ratio of these parameters were found within a bioequivalence acceptance range of 80-125%. Based on these statistical inferences, it was concluded that Uroxin is bioequivalent to Noroxin.

Decreased in vitro fluoroquinolone concentrations after admixture with an enteral feeding formulation

BACKGROUND

The purpose of this study was to determine if mixing of fluoroquinolones with a common enteral feeding formulation, Ensure (Ross Products Division, Abbott Laboratories, Columbus, OH), would alter the measured in vitro quinolone concentrations over a 24-hour period.

METHODS

Tablets of ciprofloxacin (500 mg), levofloxacin (500 mg), and ofloxacin (300 mg) were crushed and mixed with 240 mL of Ensure, water and calcium chloride (500 mg/L), water and magnesium chloride (200 mg/L), water and calcium chloride and magnesium chloride, and water alone. Fluoroquinolone concentrations of the mixtures were measured, via high-performance liquid chromatography, at baseline and serially over 24 hours. Experiments were performed in duplicate, at three temperatures (5 degrees C, 25 degrees C, and 37 degrees C).

RESULTS

Average decreases of 82.5% +/- 1.5% for ciprofloxacin, 61.3% +/- 5.2% for levofloxacin, and 45.7% +/- 10.1% for ofloxacin (mean +/- 95% CI) were observed in vitro for Ensure over the two experimental sets at baseline. Serial analysis revealed no further significant change in any of the quinolone concentrations over the remaining 24-hour period. No significant decrease was noted with the quinolones when mixed in water and calcium, water and magnesium, water and calcium and magnesium, or water alone. This phenomenon appears to be unaffected by time and temperature.

CONCLUSIONS

These data suggest there is an immediate and significant loss of fluoroquinolone when mixed with Ensure. An explanation for the loss of fluoroquinolone remains unclear.

Pharmacokinetics and pharmacodynamics of fluoroquinolones

The fluoroquinolones have moderate to excellent bioavailability, moderate to long elimination half-lives (50 to 98%) and volumes of distribution >1.5 L/kg. There is considerable variation in elimination pattern between fluoroquinolone agents, ranging from predominant renal excretion to extensive hepatic metabolism. Protein binding also varies between agents. Tissue concentrations often exceed plasma concentrations, while concentrations in CSF are modest in the presence of inflammation. Fluoroquinolones show concentration-dependent killing in vitro, and animal models have demonstrated the 24-hour AUC/MIC (area under the concentration-time curve/minimum inhibitory concentration) ratio to be the best predictor of bacterial killing in vivo, with the peak plasma concentration (Cmax)/MIC ratio being important for some bacteria, to prevent the emergence of resistance during treatment. Animal models and human studies with ciprofloxacin, grepafloxacin and levofloxacin show that a 24-hour AUC/MIC ratio of about 100, or a Cmax/MIC ratio of about 10 gives maximum clinical and bacteriological efficacy. These values can be used to predict the efficacy of different agents against different pathogens, and to define pharmacodynamic 'breakpoints'.

Effects of food on the pharmacokinetics of sparfloxacin

Sparfloxacin, a fluoroquinolone with a broad antimicrobial spectrum and long elimination half-life, is indicated for the treatment of community-acquired pneumonia and acute bacterial exacerbations of chronic bronchitis in adult patients. The present study was undertaken to determine the effects of skim milk and a high-fat breakfast without milk on the single-dose pharmacokinetic characteristics of this antibiotic. The pharmacokinetics of a single 200-mg dose of sparfloxacin were assessed in a 3-way crossover study that included 23 healthy male volunteers who had fasted, had ingested 240 mL of skim milk, or had consumed a standard high-fat breakfast. The subjects' mean age and weight were 26.5 years and 73.2 kg, respectively; 17 were white, 5 Hispanic, and 1 black. Neither skim milk nor the high-fat breakfast had a statistically significant effect on sparfloxacin absorption, as reflected in the maximum plasma concentration (Cmax) and area under the plasma concentration-time curve (AUC). Ninety percent confidence limits for logarithmically transformed AUC from time zero to infinity and Cmax were within the 80% to 125% range, demonstrating that the rate and extent of sparfloxacin absorption with skim milk or a high-fat breakfast were not different from those under fasted conditions. As indicated by an increase in the time to Cmax from 3.6 to 5.4 hours, the high-fat breakfast slightly delayed the onset of sparfloxacin absorption. Skim milk and the high-fat breakfast did not significantly affect the elimination kinetics of sparfloxacin. Sparfloxacin was well tolerated in all 3 treatment groups. Despite the apparent delay in the onset of absorption, the bioavailability of sparfloxacin in the healthy male subjects in this study population was not affected by concomitant administration with skim milk or a high-fat meal. Accordingly, the results suggest that sparfloxacin can be administered without regard to the ingestion of milk or meals.

Modification of fluorescent properties of norfloxacin in the presence of certain antacids

Modification of the fluorescent properties of norfloxacin samples in the presence of different antacids in terms of dissolution rates has been reported in a previous paper. The formation of chelates with Al3+ and Mg2+ ions has been previously suggested as a mechanism of interaction. In the present paper, the chelation was studied with different types and amounts of antacids and the stability of the non-absorbable chelates with each antacid was studied. Six dose fractions of each antacid were used in samples with the same norfloxacin concentration (9 microg ml(-1)). All samples were measured using both UV/Vis-spectrophotometry and spectrofluorimetry, and compared to a standard solution of norfloxacin (10 microg ml(-1)) without antacids, used as a reference in the calibration of the spectrofluorimeter. The results showed that the fluorescence signal features remarkable differences depending on the kind and the concentration of antacid, as well as on the time of contact. It was found that increasing amounts of antacids increased the fluorescence signal of norfloxacin samples. The evolution of the fluorescence signal in function of the antacid concentration showed a maximum and a posterior decrease. It was observed that, for a higher concentration of antacid in the medium, a higher signal was obtained and lower stability of the compound norfloxacin-antacid was observed. The data obtained strongly indicated that the binding of Al3+ and Mg2+ ions to the carboxylic groups of norfloxacin produced non-absorbable chelates. This effect might reduce the drug bioavailability.

Interaction of norfloxacin with divalent and trivalent pharmaceutical cations. In vitro complexation and in vivo pharmacokinetic studies in the dog

The formation constants of the fluoroquinolones norfloxacin and ciprofloxacin with Mg2+ (log beta 1 = 2.97(4), log beta 2 = 5.6(2)), Zn2+ (log beta 1 = 3.77(2), log beta 2 = 7.59(3)), and Fe2+ (log beta 1 = 3.99(5), log beta 2 = 7.2(5)) were determined by potentiometric titration. The pH at which precipitation occurred in the titration solutions was compared for the metal ions Ca2+, Mg2+, Zn2+, Fe2+, Cu2+, and Al3+. The formation constants were used to predict a rank order of metals that may be expected to hinder the gastrointestinal absorption of the fluoroquinolones, in vivo. The effects of metal ions on the pharmacokinetics of orally-administered norfloxacin in the dog were investigated. Norfloxacin (12 mg/kg) was administered alone or with equimolar doses of each of the chloride salts of Ca2+, Mg2+, Zn2+, Fe2+, and Al3+. Statistically significant reductions in serum norfloxacin concentrations were observed after analysis by HPLC. The Cmax was reduced 29-85%, while the area under the norfloxacin serum concentration-time curve (AUC0-infinity) was reduced by 29-79%. The extent of the reduction in AUC0-infinity was correlated with the magnitude of the formation constant of the 1:1 norfloxacin:metal chelate complex for the divalent metal ions. On coadministration of 12 mg/kg norfloxacin with various doses of Mg2+ (chloride) the AUC0-infinity and Cmax decreased with increasing Mg2+ dose. The interaction peaked at a Mg2+:norfloxacin ratio of 1:2 suggesting the formation of a 1:2 Mg:norfloxacin complex. Formation constant data were used to simulate the percentage of norfloxacin complexed at pH 6.5. Combinations of metal ion and norfloxacin which result in only a small extent (< 20%) of norfloxacin complex formation can result in relatively large decreases in oral bioavailability of this antimicrobial agent.

Enoxacin: a reappraisal of its clinical efficacy in the treatment of genitourinary tract infections

Enoxacin is a 6-fluoronaphthyridinone antibacterial agent with good in vitro activity against Neisseria gonorrhoeae and most Gram-negative urinary tract pathogens. It is less active in vitro against Acinetobacter spp., Pseudomonas aeruginosa, and most Gram-positive bacteria, than against Gram-negative organisms. Enoxacin is rapidly absorbed, with a high oral bioavailability (87 to 91%). Of the absorbed dose, 44 to 56% is excreted unchanged in the urine, with peak urinary concentrations (>500 mg/L within 4 hours) remaining high (>100 mg/L) for up to 24 hours, sufficient to inhibit most urinary tract pathogens. Single (400 mg) and multiple oral dose regimens (100 to 600 mg twice or 3 times daily for 5 to 14 days) of enoxacin are as effective for the treatment of patients with complicated or uncomplicated urinary tract infections as other antibacterial agents such as amoxicillin, cefuroxime axetil, cotrimoxazole (trimethoprim-sulfamethoxazole) or trimethoprim. Noncomparative data suggest that enoxacin is also an effective agent for the treatment of prostatitis. Single 400 mgoral doses of enoxacin produce >/- 95% bacteriological cure rates in gonococcal infections, comparable to those produced by single intramuscular doses of ceftriaxone 250 mg. Perioperative doses of oral enoxacin 200 mg provide effective prophylaxis against postoperative bacteriuria after transurethral resection of the prostate. Concomitant administration of enoxacin with a number of commonly used therapeutic agents (e.g. antacids, methylxanthines, warfarin) affects the pharmacokinetic properties of either enoxacin or the coadministered agents. Enoxacin is reasonably well tolerated, with the incidence of adverse experiences ranging from 0 to 24%. Adverse events are mainly gastrointestinal, neurological or dermatological and resolve with minimal intervention. Overall, although enoxacin exhibits a number of clinical characteristics that are similar to those of other agents for the treatment of genitourinary tract infections, the advantages offered by this agent generally do not outweigh those of alternative fluoroquinolone agents. Thus, it is likely to prove to be yet another addition to the list of agents available for the management of these infections.

Absorption interactions with fluoroquinolones. 1995 update

The utility of the fluoroquinolone class of antibiotics is rapidly expanding due to their favourable pharmacokinetic profile and the continuing development of new compounds. These agents are often used for indications not successfully treated with other orally available antimicrobials in the past, or for 'step-down' therapy in patients originally treated with intravenous agents. As the usage of these agents expands for serious systemic infections, knowledge of absorptive interactions with fluoroquinolones becomes paramount. Fluoroquinolones are often utilised in dosages and against modestly susceptible pathogens which allow a narrow margin for acceptable decreases in bioavailability. Chelation interactions with multivalent cations can result in inactivation of the fluoroquinolone with ramifications in vitro and in vivo. Chelation interactions have been reported to occur in between 22 and 76% of patients prescribed fluoroquinolones. Concurrent administration of magnesium-aluminum antacids and sucralfate has the greatest effect on the bioavailability of quinolones followed by iron, calcium and zinc. Spacing doses of fluoroquinolones and interactants has been suggested as a method of ensuring adequate quinolone absorption, but this can make optimal administration of the cation interactant difficult, if not impossible.

Effects of milk and food on the absorption of enoxacin

The effects of milk and a standard breakfast on the oral absorption of enoxacin were evaluated in eight healthy volunteers in a randomized, balanced, four-way crossover study. After an overnight fast, 400 mg enoxacin was given with water, milk, a breakfast or with a breakfast and milk. The extent of enoxacin absorption was not affected by any of the three treatments, and no statistically significant changes were found with respect to peak plasma enoxacin concentration or time to peak. We conclude that enoxacin can be taken together with food and dairy products.

Effect of enteral feeding with ensure on oral bioavailabilities of ofloxacin and ciprofloxacin

The relative oral bioavailabilities of ciprofloxacin and ofloxacin when they were coadministered with water or an enteral feeding product (Ensure) were assessed in 13 healthy volunteers. The area under the concentration time curve from time zero to infinity and the maximum concentration of drug in serum for both drugs were reduced by Ensure in comparison with those by water (P < 0.01). However, Ensure reduced the percent relative bioavailability of ciprofloxacin (72% +/- 14%; range, 52 to 96%) significantly more than ofloxacin (90% +/- 8.3%; range, 74 to 105%) (P < 0.005). Coadministration of Ensure significantly diminished ciprofloxacin and ofloxacin absorption, but ciprofloxacin absorption was reduced significantly more than ofloxacin absorption.

Effect of a fat- and calcium-rich breakfast on pharmacokinetics of fleroxacin administered in single and multiple doses

The effect of a fat- and liquid-calcium-rich meal on the pharmacokinetics of single and multiple doses of fleroxacin in 20 healthy men and women was investigated in a randomized crossover fashion. Fleroxacin was administered as 400 mg daily for 3 days and as a single 400 mg dose. Concurrent administration of fleroxacin with food resulted in a statistically significant (P < or = 0.05) decrease in the area under the curve (13.9% for multiple-dose administration, 10% for single-dose administration) and in the peak concentration (25.9% for multiple-dose administration, 27% for single-dose administration) and a lengthening of the time to peak (more than doubled for single- and multiple-dose phases). In addition, by using an equivalence criteria of 80 to 125%, the two one-sided tests procedure indicated that the mean areas under the curves for fleroxacin administered in a fed and a fasted state were statistically bioequivalent (P < or = 0.05) for both the single- and multiple-dose regimens. Although a meal high in fat and containing liquid calcium reduces the peak concentration by approximately 25%, a minimal effect on bioavailability is seen with concomitant food administration. In addition, multiple-dose bioavailability studies appear to give similar information to single-dose studies while representing the clinical setting more closely.

Effect of sucralfate on absorption of norfloxacin and ofloxacin

The effect of sucralfate on the pharmacokinetics of norfloxacin and ofloxacin was assessed in two separate crossover studies with healthy volunteers. In both studies, eight subjects were randomized to one of the following three regimens: a 400-mg dose of norfloxacin or ofloxacin alone, norfloxacin or ofloxacin given simultaneously with sucralfate (1 g), or norfloxacin or ofloxacin given 2 h before sucralfate. Coadministration of sucralfate reduced the bioavailability of norfloxacin and ofloxacin by 91% (P < 0.001) and 61% (P < 0.001), respectively. However, when norfloxacin and ofloxacin were given 2 h before sucralfate, there were no significant alterations in the pharmacokinetics of either fluoroquinolone. Similar results were obtained when the cumulative amount of each fluoroquinolone recovered in the urine was used to calculate bioavailability. To avoid these interactions and potential therapeutic failures, norfloxacin and ofloxacin should not be used concurrently with sucralfate. The interaction can be minimized by maximizing the time between the fluoroquinolone dose and the previous sucralfate dose and giving the fluoroquinolone at least 2 h before another sucralfate dose.

The effect of ferrous sulphate on the absorption of norfloxacin, ciprofloxacin and ofloxacin

The effect of ferrous sulphate on the absorption of norfloxacin, ciprofloxacin and ofloxacin was studied in three separate, two-period crossover trials, each involving eight healthy volunteers. After an overnight fast, a single dose of norfloxacin (400 mg), ciprofloxacin (500 mg) or ofloxacin (400 mg) was administered with and without ferrous sulphate (corresponding to 100 mg elemental iron). The absorption of all the fluoroquinolones studied was significantly reduced when they were co-administered with ferrous sulphate. The reduction in the area under the plasma drug concentration-time curve from 0 to 24 h was most marked in the case of norfloxacin, while ofloxacin was least affected by ferrous sulphate. The AUC of norfloxacin was reduced by 73% (P < 0.001) and its peak plasma concentration by 75% (P < 0.01) by concomitant ingestion of ferrous sulphate. The AUC and peak plasma concentration of ciprofloxacin were reduced by 57% (P < 0.001) and 54% (P < 0.01), respectively, by ferrous sulphate. Concomitant ingestion of ferrous sulphate reduced the AUC and peak plasma concentration of ofloxacin by 25% (P < 0.01) and 36% (P < 0.01), respectively. Similar results were obtained with respect to the urinary recoveries of each fluoroquinolone. We recommend that norfloxacin and ciprofloxacin should not be taken together with ferrous sulphate. It would also be advisable not to take ofloxacin with ferrous sulphate, especially if the organism causing infection is only moderately susceptible.

Effect of multiple staggered doses of calcium on the bioavailability of ciprofloxacin

OBJECTIVE

To determine the effect on the relative bioavailability (Fr) of a staggered single dose of ciprofloxacin given two hours after a morning dose of calcium carbonate given three times daily over the three previous days.

DESIGN

Thirteen male volunteers participated in this randomized, nonblinded, crossover investigation; 12 subjects were included in the final analysis.

SETTING

Data collection and ciprofloxacin administration occurred at Albany Medical Center, a tertiary-care teaching institution. Calcium carbonate administration was on an outpatient basis.

RESULTS

For 12 volunteers, the mean +/- SD Fr of ciprofloxacin staggered with calcium was 0.87 +/- 0.23 (noncompartmental model) and 0.98 +/- 0.27 (compartmental model). Other statistically significant findings were a decrease in the time to maximum concentration of ciprofloxacin staggered with calcium in serum compared with ciprofloxacin alone (from 1.76 +/- 0.54 to 1.23 +/- 0.52 h in the noncompartmental model; p < 0.05), and a decrease in the same parameter (from 1.92 +/- 0.96 to 0.77 +/- 0.53 in the compartmental model; p < 0.005). Maximum concentration of ciprofloxacin staggered with calcium was decreased in the noncompartmental model compared with ciprofloxacin alone (from 2.11 +/- 0.72 to 1.60 +/- 0.33, respectively; p < 0.05). The elimination half-life and area under the concentration-time curve of ciprofloxacin were not significantly altered.

CONCLUSIONS

Repeated doses of calcium carbonate, administered two hours before ciprofloxacin, did not significantly alter the Fr of this fluoroquinolone.

Milk and yoghurt do not impair the absorption of ofloxacin

The effects of milk and yoghurt on the oral absorption of ofloxacin were studied in seven healthy volunteers in a randomized cross-over trial. After an overnight fast, 200 mg ofloxacin was given with 300 ml water, milk or yoghurt. Plasma concentrations and urinary excretion of ofloxacin were determined up to 24 h. Values of total plasma AUC and 24 h urinary excretion of ofloxacin were not affected by milk or yoghurt. Plasma ofloxacin concentrations from 0.5 to 1.5 h and the peak concentration were lower (P less than 0.05) after yoghurt than without and the time to peak was prolonged by 1 h (P less than 0.05).