Even apparently insignificant chemical deviations among bioequivalent generic antibiotics can lead to therapeutic nonequivalence: the case of meropenem.

Several studies with animal models have demonstrated that bioequivalence of generic products of antibiotics like vancomycin, as currently defined, do not guarantee therapeutic equivalence. However, the amounts and characteristics of impurities and degradation products in these formulations do not violate the requirements of the U.S. Pharmacopeia (USP). Here, we provide experimental data with three generic products of meropenem that help in understanding how these apparently insignificant chemical differences affect the in vivo efficacy. Meropenem generics were compared with the innovator in vitro by microbiological assay, susceptibility testing, and liquid chromatography/mass spectrometry (LC/MS) analysis and in vivo with the neutropenic guinea pig soleus infection model (Pseudomonas aeruginosa) and the neutropenic mouse thigh (P. aeruginosa), brain (P. aeruginosa), and lung (Klebisella pneumoniae) infection models, adding the dihydropeptidase I (DHP-I) inhibitor cilastatin in different proportions to the carbapenem. We found that the concentration and potency of the active pharmaceutical ingredient, in vitro susceptibility testing, and mouse pharmacokinetics were identical for all products; however, two generics differed significantly from the innovator in the guinea pig and mouse models, while the third generic was therapeutically equivalent under all conditions. Trisodium adducts in a bioequivalent generic made it more susceptible to DHP-I hydrolysis and less stable at room temperature, explaining its therapeutic nonequivalence. We conclude that the therapeutic nonequivalence of generic products of meropenem is due to greater susceptibility to DHP-I hydrolysis. These failing generics are compliant with USP requirements and would remain undetectable under current regulations.

Dipeptidyl peptidase inhibitors, an emerging drug class for inflammatory disease?

Dipeptidyl peptidase (DPP)-4 is a member of the S9b serine protease family, which also includes DPP8 and DPP9. DPP4 cleaves a number of regulatory factors, including chemokines and growth factors. DPP4 inhibitors have recently emerged as an effective treatment option for type 2 diabetes. Early in vitro studies demonstrated that DPP4 inhibitors inhibit T-cell proliferation and cytokine production, leading to their investigation in numerous pre-clinical models of inflammatory diseases, including arthritis, multiple sclerosis and inflammatory bowel disease. Recent data suggest that the early DPP4-specific inhibitors might also bind DPP8 and DPP9, thus exerting their effects through non-specific binding. This review highlights recent insights into the applicability of DPP inhibitors as novel pharmacological agents for inflammatory disease.

Docking-based 3D-QSAR study for selectivity of DPP4, DPP8, and DPP9 inhibitors.

In order to obtain information regarding the design of selective DPP4 inhibitors, a 3D-QSAR study was conducted using DPP4, DPP8, and DPP9 inhibitors including newly synthesized six- and seven-membered cyclic hydrazine derivatives (KR64300, KR64301), which were evaluated in vitro for their inhibition of DPP4, DPP8, and DPP9. In this study, a highly predictive CoMFA model based on the fast-docking for DPP4, DPP8, and DPP9 inhibitors was obtained. This reliable model showed leave-one-out cross-validation q(2) and conventional r(2) values of 0.68 and 0.96 for the DPP4 inhibitors, 0.58 and 0.98 for the DPP8 inhibitors, and 0.68 and 0.97 for the DPP9 inhibitors, respectively. The validation of the CoMFA model was confirmed by the compounds in the test set, including the synthesized six- and seven-membered cyclic hydrazines. According to this study, to obtain selective DPP4 inhibitors compared to their isozymes, the interaction of the inhibitors with the S3 site and S1' site in DPP4 must be considered. The proposed newly synthesized compounds, KR64300 and KR64301, interact well with the sites mentioned above, showing excellent selectivity.

2-[3-[2-[(2S)-2-Cyano-1-pyrrolidinyl]-2-oxoethylamino]-3-methyl-1-oxobutyl]- 1,2,3,4-tetrahydroisoquinoline: a potent, selective, and orally bioavailable dipeptide-derived inhibitor of dipeptidyl peptidase IV.

Dipeptidyl peptidase IV (DPP-IV) inhibitors are expected to become a new type of antidiabetic drugs. Most known DPP-IV inhibitors often resemble the dipeptide cleavage products, with a proline mimic at the P1 site. As off-target inhibitions of DPP8 and/or DPP9 have shown profound toxicities in the in vivo studies, it is important to develop selective DPP-IV inhibitors for clinical usage. To achieve this, a new class of 2-[3-[[2-[(2S)-2-cyano-1-pyrrolidinyl]-2-oxoethyl]amino]-1-oxopropyl]-based DPP-IV inhibitors was synthesized. SAR studies resulted in a number of DPP-IV inhibitors, having IC(50) values of <50 nM with excellent selectivity over both DPP8 (IC(50) > 100 microM) and DPP-II (IC(50) > 30 microM). Compound 21a suppressed the blood glucose elevation after an oral glucose challenge in Wistar rats and also inhibited plasma DPP-IV activity for up to 4 h in BALB/c mice. The results show that compound 21a possesses in vitro and in vivo activities comparable to those of NVP-LAF237 (4), which is in clinical development.

Biochemical properties of new synthetic carnosine analogues containing the residue of 2,3-diaminopropionic acid: the effect of N-acetylation.

Three novel carnosine analogues 7-9 containing the residue of L(+)2,3-diaminopropionic acid with different degree of N-acetylation instead of beta-alanine have been synthesized and characterized. Comparative analysis of hydrolysis by carnosinase revealed that the mono- and bis-acetylated compounds 8 and 9 are resistant to enzymatic hydrolysis and act as competitive inhibitors of this enzyme. The hydroxyl radical scavenging potential of the three analogues was evaluated by their ability to inhibit iron/H(2)O(2)-induced degradation of deoxyribose. The second-order rate constants of the reaction of compounds 7-9 with hydroxyl radical were almost identical to that of carnosine. These compounds were also found to act as protective agents against peroxynitrite-dependent damage as assessed by their ability to prevent nitration of free tyrosine induced by this species.

Membrane dipeptidase is the receptor for a lung-targeting peptide identified by in vivo phage display.

In vivo phage display is a powerful method to study organ- and tissue-specific vascular addresses. Using this approach, peptides capable of tissue-specific homing can be identified by performing a selection for that trait in vivo. We recently showed that the CGFECVRQCPERC (termed GFE-1) peptide can selectively bind to mouse lung vasculature after an intravenous injection. Our aim in the present study was to identify the receptor for this lung-homing peptide. By using affinity chromatography, we isolated a 55-kDa lung cell-surface protein that selectively binds to the GFE-1 peptide. Protein sequencing established the identity of the receptor as membrane dipeptidase (MDP), a cell-surface zinc metalloprotease involved in the metabolism of glutathione, leukotriene D4, and certain beta-lactam antibiotics. Phage particles displaying the GFE-1 peptide selectively bind to COS-1 cells transfected with the murine MDP cDNA. Moreover, the synthetic GFE-1 peptide could inhibit MDP activity. By establishing MDP as the receptor for the GFE-1 peptide, our results suggest potential applications for both MDP and the GFE-1 peptide in delivery of compounds to the lungs. This work also demonstrates that cell-surface proteases can be involved in tissue-specific homing.

Imipenem/cilastatin as initial therapy for febrile neutropenic patients.

Imipenem 2 g daily was administered intravenously to 40 evaluable patients with neutropenia and fever. Twenty-three patients had acute leukaemia and 17 malignant lymphoma. The overall response rate was 70.0%. Of the 14 patients with documented infection, 9 (64.3%) responded. Poorer responses were observed in patients with pneumonia (40%) or pseudomonal infection (50%). The response rate was significantly higher among patients with increasing neutrophil counts during therapy (P less than 0.02). Fungal infection was a common cause of treatment failure. Gastrointestinal side effects and skin rashes were occasionally seen. No patient developed central nervous system toxicity. Imipenem is a practical alternative to antibiotic combinations for management of neutropenic infection. However, careful monitoring is essential in the subgroups of patients with pneumonia or pseudomonal infections, who may require modifications of therapy.

Imipenem/cilastatin in the treatment of severe nosocomial pneumonia.

Imipenem/cilastatin (Tienam 500; Logos) 1 g, administered intravenously every 8 hours, was evaluated in an open clinical trial in 35 patients with severe nosocomial pneumonia. In 84.4% of cases there was a favourable clinical response; microbiological success was achieved in 63.3% and partial success in 20% of patients. The majority of Gram-negative and Gram positive organisms were sensitive to imipenem, including those resistant to the aminoglycosides. Although colonisation was frequent, superinfection was uncommon. Imipenem was well tolerated in these critically ill patients, many of whom had renal and other organ failure. The wide spectrum of antimicrobial activity and minimal side-effects made it a useful agent in patients with severe nosocomial pneumonia.

An overview of the pharmacology of imipenem/cilastatin.

Imipenem is the first clinically available carbapenem antibiotic. Since it is hydrolysed by dehydropeptidase-I, a zinc metallo-enzyme resident in the brush border of the renal tubule, it is co-administered with cilastatin, a reversible inhibitor of this enzyme. This provides clinically relevant concentrations of imipenem in the urine for 8-10 h after a 500 mg dose. The half-life of both drugs is 1 h in normal volunteers. Plasma clearances are reproducible between volunteers and studies and average 220 ml/min for imipenem. Renal clearance of unchanged imipenem accounts for 60-70% of plasma clearance when the imipenem is given with cilastatin. Administration of radiolabelled drugs results in recovery of over 99% of the radiolabel in the urine for both imipenem and cilastatin. With increasing renal dysfunction, the half-life of imipenem is controlled by a metabolic clearance pathway which is unaffected by cilastatin. Renal clearance is by glomerular filtration and active tubular secretion for both imipenem and cilastatin. Renal dysfunction results in terminal half-lives of slightly greater than 4 h for imipenem and 16 h for cilastatin in the functionally anephric. Both drugs are well cleared by haemodialysis and supplemental 500 mg doses are recommended after a dialysis. In the case of severe renal failure, dose and schedule alterations serve to prevent accumulation of cilastatin and circulating metabolites of imipenem, while still providing therapeutic concentrations of imipenem.

Experience with imipenem/cilastatin in the intensive care unit.

Twenty-two patients admitted to the ICU with a severe nosocomial infection caused by multi-resistant Gram-negative bacilli were treated with imipenem combined with cilastatin. We treated nine cases of meningo-ventriculitis, eight cases of septicaemia, four cases of mediastinitis, and one case of pneumonia. The bacteria responsible were Acinetobacter spp. (10), Pseudomonas aeruginosa (5), Enterobacter cloacae (5), Klebsiella pneumoniae (3), Proteus spp. (2), Streptococcus spp. (2), Serratia marcescens (1). More than one pathogen was isolated in five cases. The dosages ranged between 1.5 g to 4 g per day by intravenous infusion; the highest doses were used for the treatment of meningitis. The mean duration of treatment was 17 days. An aminoglycoside was combined with imipenem in 18 cases. Cure was obtained in 17 out of the 22 cases. Very rapid sterilization of the CSF in the cases of meningitis and ventriculitis was noted. Two patients died rapidly despite eradication of the bacteria. One case of meningitis relapsed but cure was subsequently obtained with continuation of the same treatment. In three cases of Ps. aeruginosa infection, resistant mutants were isolated from the sites of infection and were responsible for two failures and one colonization. Imipenem appears to be an antibiotic of choice in severe nosocomial infections including meningo-ventriculitis, especially those caused by Acinetobacter spp. and Ps. aeruginosa. It is also one of the few antibiotics active against both streptococci and multi-resistant Gram-negative bacilli. Careful bacteriological monitoring is recommended during treatment.

Safety and efficacy of high-dose treatment with imipenem-cilastatin in seriously ill patients.

Imipenem-cilastatin was given in doses of 1 g intravenously every 6 h to 31 patients. Twenty-five patients, with 27 infections, were clinically evaluable and received 20 to 210 g of imipenem for a duration of 5 to 56 days (average 16.3 days). Infections included seven cases of osteomyelitis, seven of bacteremia, five of cellulitis, two of pneumonia, three of pelvic cellulitis, two of intraabdominal abscess, and one each of empyema, mediastinitis, and endometritis. Fifty-five percent of the infections were caused by gram-negative bacilli, 33% were due to gram-positive organisms, and 10% were caused by anaerobes. Twenty-two patients (81%) were cured, three improved, one relapsed, and one became superinfected with a resistant organism. In 5 of 11 cases with Pseudomonas aeruginosa, the imipenem MIC for organisms isolated by the end of treatment was higher than it was initially, raising concern that imipenem should not be used alone to treat Pseudomonas aeruginosa infections. Twenty-one patients had no adverse reaction; of the remaining 10 patients, 4 had nausea, 1 had urticaria, and 6 had mild abnormalities in hepatic function; three episodes of diarrhea included two with Clostridium difficile toxin in stool and one with pseudomembranous colitis, as determined by sigmoidoscopy. Levels of creatinine, hemoglobin, leukocytes, platelets, prothrombin, and urine components were unchanged. Imipenem-cilastatin is a clinically effective antibiotic with freedom from nephrotoxicity and hematological abnormalities in the large doses used in this study.

Primaxin in the treatment of acute bacterial pneumonia in adults.

Imipenem (N-Formimidoyl thienamycin) (MK-0787) is a new beta-lactam carbapenem antibiotic. When it is combined with the renal dipeptidase inhibitor cilastatin (MK-0791) the combination is known as primaxin. In this study 28 adult patients (24 males and 4 females) with acute bacterial pneumonia were treated with primaxin. Twenty-one patients were evaluable and 20 (95%) were clinically cured of their pneumonia. Bacteriological cures were demonstrated in 84% of the cases. One patient with a susceptible Pseudomonas aeruginosa failed. Major complications or toxic reactions included antibiotic associated diarrhoea in one patient; hypotension in one patient; increased grand mal seizures in one patient and elevated liver function studies in one patient. Results of this study suggest that primaxin will be useful in the treatment of a variety of serious Gram-positive and Gram-negative pneumonias. The true incidence of possible toxic reactions with this drug is not known at this time and awaits further experience.