Pharmacokinetics of FCE 22891, a new oral penem

Effects of food on clinical pharmacokinetics

Food-drug interactions can be associated with alterations in the pharmacokinetic and pharmacodynamic profile of various drugs that may have clinical implications. The various phases in which food may interact with a coadministered drug are: (i) before and during gastrointestinal absorption; (ii) during distribution; (iii) during metabolism; and (iv) during elimination. Absorption and metabolism are the phases where food has most effect, and this review will focus on those areas. It will also review the variable and complex effects of antacids and metal ions on drug absorption. Mechanisms related to food effects on drug absorption have been described under 5 categories: those causing decreased, delayed, increased or accelerated absorption, and those in which food has no significant effect. Among the major variables that interface between differential effects of food and postprandial bioavailability are: (i) the physicochemical characteristics and enantiomorphic composition of the drug; (ii) timing of meals in relation to time of drug administration; (iii) size and composition of meals (especially fat, protein and fibre); and (iv) dose size. However, the influence of food is largely a matter of the design of the pharmaceutical formulation. In addition, the mechanism of 'food effect' may involve physiological and sensory responses to food, such as changes in gastrointestinal milieu and gastric emptying rate, reflex action, and may also involve the site and route (either portal or lymphatic) of drug absorption. Mixing drugs with fruit juice, such as grapefruit and orange juice, and acidic beverages, such as commercial soft drinks, may affect absorption because of decreases in gastric pH, which could offer a therapeutic advantage in certain clinical conditions, such as patients with HIV disease and cancer. The increased bioavailability caused by the concomitant intake of grapefruit juice results from the inhibition of intestinal cytochrome P450(CYP)3A4, but not hepatic CYP3A4 or colon CYP3A5, which probably involves the bioflavonoid naringenin and furanocoumarins. Although there is a vast amount of literature, there is still no rational scientific basis to predict the effect of food for a particular chemical entity or a chemical class of therapeutic agents. A mechanistic understanding of the effects of food may serve as a key to the pharmacokinetic optimisation of patient therapy, both in outpatients and hospitalised patients of various age groups.

Liquid chromatographic analysis of penem antibiotic FCE22101 in biological fluids with a liquid-liquid extraction procedure

A sensitive high-performance liquid chromatographic method has been developed for the determination of penem antibiotic FCE22101 in plasma and urine. FCE22101 was extracted from plasma and urine with ethyl acetate. After evaporating, the sample solutions were analyzed by a reversed-phase high-performance liquid chromatographic system using a two-sided bracketing injection technique. The determination limit of FCE22101 was 5 ng/ml in plasma. Analysis of the spiked plasma samples demonstrated the good accuracy and precision of the method. The proposed method improved from five- to ten-fold on the analytical sensitivity in comparison with the most commonly ultrafiltration method.

Clinical and bacteriological efficacy and tolerability of FCE 22891 in patients with exacerbations of chronic obstructive pulmonary disease

A beta-lactamase-stable antibiotic, the oral penem FCE 22891 (ritipenem acoxil), was investigated for use in exacerbations of chronic obstructive pulmonary disease (COPD). Thirteen of the 15 COPD patients had a proven lower respiratory tract infection. Symptom scores and forced expiratory volumes in 1 s significantly improved during therapy with FCE 22891 in combination with bronchodilators and intravenous corticosteroids. Conversion of representative sputum to nonrepresentative sputum or eradication of the original pathogen in representative sputum was effected in 12 patients. Resistance to FCE 22891 was observed in three cases with Haemophilus influenzae. Gastrointestinal disturbances, of which one was severe, were experienced by eight patients. Although FCE 22891 has some beneficial effect in exacerbations of COPD, there are reservations about its use because of adverse effects and potential inefficacy in the treatment of infection with H. influenzae.

The effect of FCE 22891, a new oral penem, on faecal flora anaerobes and their fermentation end products in patients with chronic obstructive pulmonary disease

The influence of FCE 22891 on the faecal flora was investigated in 11 patients with an acute exacerbation of chronic obstructive pulmonary disease (COPD). Colony counts of faecal (an)aerobes and concentrations of their short-chain fatty acids and organic acids were determined simultaneously in fresh faeces before, during and after administration of the drug, and compared to those of healthy human volunteers. The MIC of FCE 22891 for the 142 isolated anaerobes was determined, and compared to the biologically active concentration of the drug in faeces. The Bacteroides colony counts of the patients increased significantly by day 9 compared to day 3, but were significantly lower than those of the healthy controls before, during and after the study. Significant changes in short-chain fatty acids and organic acid concentrations occurred in faeces of the patients during and after treatment, and especially when compared to healthy controls. A strong increase in MICs during treatment was found in Clostridium species, other than Clostridium difficile. FCE 22891 had only a moderate effect on the composition of the anaerobic faecal flora, but bacterial fermentation was mainly disturbed before and early on in treatment, which could have been caused by the disease.

Pharmacokinetics of [14C]FCE 22891, a penem antibiotic, following oral administration to healthy volunteers

FCE 22891 is a prodrug of the penem antibiotic FCE 22101 and is suitable for oral administration. The pharmacokinetics of FCE 22891 were investigated in four healthy male volunteers following the oral administration of 500 mg of [14C]FCE 22891. Levels of radioactivity in plasma were always higher and persisted for longer than those of FCE 22101. The time to the maximum concentration of radioactivity in plasma generally coincided with that of FCE 22101. The respective values for the maximum concentrations of radioactivity in plasma were, on average, 8.57 +/- 2.95 micrograms equivalent/ml and 2.97 +/- 2.05 micrograms/ml. Over a 5-day period, mean urinary and fecal recovery of radioactivity accounted for 53.2 and 41.0% of the dose, respectively. The average amount of FCE 22101 excreted in urine and feces corresponded to 9.0 and 1.6% of the dose, respectively. The urinary recovery of the open-ring metabolite P1 and of its 5-S epimer P2 accounted for about 6.5 and 1.2% of the dose, respectively. Other chromatographic peaks corresponding to nonidentified compounds accounted for about 14.0% (polar metabolite fraction; peak P), 3.7% (less polar fraction; peak X), and 15.4% (least polar fraction) of the dose. Elimination of radioactivity and FCE 22101 in urine was rapid. Intersubject variability in the kinetics of total radioactivity in plasma was far less than that observed for FCE 22101. The results of the present study support suggestions that presystemic metabolism of FCE 22101 and/or transformation of the prodrug to compounds other than FCE 22101 are the main cause of intersubject variability in the kinetics of FCE 22101 produced in plasma following oral administration of its prodrug.