Developing core elements and checklist items for global hospital antimicrobial stewardship programmes: a consensus approach.

OBJECTIVES: With increasing global interest in hospital antimicrobial stewardship (AMS) programmes, there is a strong demand for core elements of AMS to be clearly defined on the basis of principles of effectiveness and affordability. To date, efforts to identify such core elements have been limited to Europe, Australia, and North America. The aim of this study was to develop a set of core elements and their related checklist items for AMS programmes that should be present in all hospitals worldwide, regardless of resource availability. METHODS: A literature review was performed by searching Medline and relevant websites to retrieve a list of core elements and items that could have global relevance. These core elements and items were evaluated by an international group of AMS experts using a structured modified Delphi consensus procedure, using two-phased online in-depth questionnaires. RESULTS: The literature review identified seven core elements and their related 29 checklist items from 48 references. Fifteen experts from 13 countries in six continents participated in the consensus procedure. Ultimately, all seven core elements were retained, as well as 28 of the initial checklist items plus one that was newly suggested, all with ≥80% agreement; 20 elements and items were rephrased. CONCLUSIONS: This consensus on core elements for hospital AMS programmes is relevant to both high- and low-to-middle-income countries and could facilitate the development of national AMS stewardship guidelines and adoption by healthcare settings worldwide.

Clinical outcome of fenestrated Fontan patients after closure: the first 10 years.

BACKGROUND: The late clinical status of Fontan patients after fenestration closure is unknown. Data are now available on all patients who underwent closure from 1989 to 1999. METHODS AND RESULTS: All patients who underwent catheter closure of a Fontan fenestration were enrolled in either the Clamshell (1989 to 1994) or CardioSEAL (1996 to 1999) regulatory trials. Physiological values obtained at catheterization helped assess the hemodynamic effects of fenestration occlusion. In addition to survival, outcomes assessed included O(2) saturations, medication use, significant clinical findings (eg, heart failure, protein-losing enteropathy, or new arrhythmias), and somatic growth. Of 181 patients who underwent closure, 27 had additional significant leaks. The remaining 154 patients constituted the study group. Median time from closure to latest follow-up was 3.4 years (range 0.4 to 10.3 years). Fenestration closure increased O(2) saturation 9.4% on average (P:<0. 001). The numbers of patients receiving digoxin or diuretics decreased at the most recent follow-up compared with baseline (P:<0. 001), but use of antiarrhythmic agents increased marginally (P:=0. 05). Height and weight percentiles rose (medians of 2 and 4, respectively; P:<0.001). Clinical decompensation during follow-up of 154 patients was rare (4.5%), with 2 deaths, 3 Fontan revisions, and 1 patient each with protein-losing enteropathy and ascites. No other patient developed chronic congestive symptoms; 21 patients developed new arrhythmias, and 2 had a stroke or transient ischemic attack. CONCLUSIONS: Fenestration closure in Fontan patients was followed by improved oxygenation, reduced need for anticongestive medication, and improved somatic growth at latest follow-up. Death (1.3%) or chronic decompensation (3.2%) was rare.

Pulmonary hypertension predicts mortality in infants with omphalocele.

OBJECTIVE: The objective of this study was to identify predictors of mortality in infants with omphalocele. METHODS: Medical records of infants with omphalocele born between January 1992 and June 2012, with follow-up toDecember 2012, were retrospectively reviewed. Survivors and non-survivors were compared. Evidence for pulmonary hypertension was sought between the second and seventh day after birth. All included infants had increased right ventricular pressures (RVP >40 mmhg) on echocardiogram on the second day of life with increased oxygen requirements, therefore, the finding of increased pressure was not considered a result of the transitional circulation. Logistic regression was used to evaluate the importance and independence of various factors. RESULTS: Of 51 infants whose records were reviewed, 13 died (25%) and 38 survived (75%). The median time to death was 34 days (range: 4 -408 days). The median follow-up time for those who died was 1.5 years (range: 0.01-15 years) and for survivors was 2.6 years (range: 0.08-15 years). Logistic regression revealed that respiratory insufficiency at birth (OR: 14.8; 95% CI: 2.5-85.0) and pulmonary hypertension (OR: 6.4; 95% CI: 1.1-39.0) were independently associated with mortality. CONCLUSION: Respiratory insufficiency after birth and pulmonary hypertension are independent predictors of mortality in infants with omphalocele.

Quaternary salts of 2-[(hydroxyimino)methyl]imidazole. 3. Synthesis and evaluation of (alkenyloxy)-, (alkynyloxy)-, and (aralkyloxy)methyl quaternarized 2-[(hydroxyimino)methyl]-1-alkylimidazolium halides as reactivators and therapy for soman intoxication.

A series of structurally related monosubstituted 1-[(alkenyloxy)methyl]-, 1-[(alkynyloxy)methyl]-, and 1-[(aralkyloxy)methyl]-2-[(hydroxyimino)methyl]-3-methyli midazolium halides were prepared and evaluated. All new compounds were characterized with respect to (hydroxyimino)methyl acid dissociation constant, nucleophilicity, and octanol-buffer partition coefficient. The alkynyloxy-substituted compounds were also evaluated in vitro with respect to reversible inhibition of human erythrocyte (RBC) acetylcholinesterase (AChE) and kinetics of reactivation of human AChE inhibited by ethyl p-nitrophenyl methylphosphonate (EPMP). In vivo evaluation in mice revealed that coadministration of alkynyloxy-substituted imidazolium compounds with atropine sulfate provided significant protection against a 2 x LD50 challenge of GD. For the alkynyloxy-substituted imidazolium drugs there is a direct relationship between in vitro and in vivo activity: the most potent in vivo compounds against GD proved to be potent in vitro reactivators against EPMP-inhibited human AChE. These results differ from the observations made on the sterically hindered imidazolium compounds (see previous article) and suggest that several antidotal mechanisms of protective action may be applicable for the imidazolium aldoxime family of therapeutics. The ability of the alkynyloxy substituents to provide life-saving protection against GD intoxication was not transferable to the pyridinium or triazolium heteroaromatic ring systems.

Discovery of nanomolar ligands for 7-transmembrane G-protein-coupled receptors from a diverse N-(substituted)glycine peptoid library.

Screening a diverse, combinatorial library of ca. 5000 synthetic dimer and trimer N-(substituted)glycine "peptides" yielded novel, high-affinity ligands for 7-transmembrane G-protein-coupled receptors. The peptoid library was efficiently assembled using readily available chemical building blocks. The choice of side chains was biased to resemble known ligands to 7-transmembrane G-protein-coupled receptors. All peptides were screened in solution-phase, competitive radioligand-binding assays. Peptoid trimer CHIR 2279 binds to the alpha 1-adrenergic receptor with a Ki of 5 nM, and trimer CHIR 4531 binds to the mu-opiate receptor with a Ki of 6 nM. This represents the first example of the discovery of high-affinity receptor ligands from a combinatorial library of non-natural chemical entities.

Quaternary salts of 2-[(hydroxyimino)methyl]imidazole. 5. Structure-activity relationships for side-chain nitro-, sulfone-, amino-, and aminosulfonyl-substituted analogues for therapy against anticholinesterase intoxication.

Several quaternary imidazolium oxime derivatives incorporating side chains bearing nitro, sulfone, amino, and aminosulfonyl substituents were prepared and evaluated as treatment therapeutics for anti-AChE intoxication. In vivo test results in the mouse revealed that many of these compounds are highly effective in providing life-saving protection against the extremely toxic cholinesterase inhibitors soman and tabun. Several structure-activity relationships were noted that were characteristic of the side-chain substituent. In vivo test results for additional selected derivatives of some of the more therapeutically active compounds indicated that the quaternary heteroaryl nucleus is essential for activity whereas a nucleophilic moiety (i.e., oxime) is not. In support of previous suspicions, these results afforded additional evidence suggesting that reactivation is not the main mode of antidotal action by the imidazolium oximes. An alternative antidotal mechanism is postulated that is consistent with all data and that involves enzyme protection by the compounds.

Quaternary salts of 2-[(hydroxyimino)methyl]imidazole. 4. Effect of various side-chain substituents on therapeutic activity against anticholinesterase intoxication.

A series of quaternary salt derivatives of 2-[(hydroxyimino)methyl]-1-methylimidazole incorporating various side chains bearing ether, silyl, nitrile, ester, halogen, nitro, sulfone, amino, or aminosulfonyl substituents was prepared and evaluated in vivo for the treatment of anticholinesterase intoxication. Test results in the mouse revealed that the type and location of the side-chain substituent both have a significant influence on the toxicity and antidotal effectiveness of the compounds. Some of the more active examples represent the most potent therapeutics to date against intoxication by the powerful cholinesterase inhibitors soman and tabun. Significantly, the antidotal effectiveness of the compounds was not dependent on the inhibiting agent nor was there any correlation between in vivo efficacy and in vitro reactivation of ethyl (4-nitrophenyl)methylphosphonate inhibited human acetylcholinesterase. These observation suggested that the main mode of antidotal protection by the compounds is something other than enzyme reactivation.

Quaternary salts of 2-[(hydroxyimino)methyl]imidazole. 2. Preparation and in vitro and in vivo evaluation of 1-(alkoxymethyl)-2-[(hydroxyimino)methyl]-3-methylimida zolium halides for reactivation of organophosphorus-inhibited acetylcholinesterases.

A series of structurally related mono- and bis-1,3-disubstituted 2-[(hydroxyimino)methyl]imidazolium halides were evaluated in vitro for their ability to reactivate electric eel, bovine, and human erythrocyte (RBC) acetylcholinesterases (AChE) inhibited by ethyl p-nitrophenyl methylphosphonate (EPMP) and 3,3-dimethyl-2-butyl methyl-phosphonofluoridate (soman, GD). All new compounds were characterized for (hydroxyimino)methyl acid dissociation constant, nucleophilicity, octanol-buffer partition coefficient, reversible AChE inhibition, and kinetics of reactivation of EPMP-inhibited AChEs. For GD-inhibited AChEs, maximal reactivation was used to compare compounds since rapid phosphonyl enzyme dealkylation "aging" complicated interpretation of kinetic constants. For comparison, we also evaluated three known pyridinium therapeutics, 2-PAM, HI-6, and toxogonin. In vivo evaluation in mice revealed that when selected imidazolium compounds were coadministered with atropine sulfate, they were effective in providing lifesaving protection against both GD and EPMP challenges. This was a major accomplishment in the search for effective anticholinesterase therapeutics--the synthesis and preliminary evaluation of the first new monoquaternary soman antidotes with potencies superior to 2-PAM. Significantly, there was an apparent inverse relationship between in vitro and in vivo results; the most potent in vivo compounds proved to be the poorest in vitro reactivators. These results suggested that an alternative and possibly novel antidotal mechanism of protective action may be applicable for the imidazolium aldoximes. Selected compounds were also evaluated for their inhibition of AChE phosphorylation by GD and antimuscarinic and antinicotinic receptor blocking effects.

Temporal assessment of Candida risk factors in the surgical intensive care unit.

HYPOTHESIS: Risk factors for Candida infection in surgical intensive care units (SICUs) change over time. Risk factor progression may influence Candida colonization and infection. DESIGN: Multicenter cohort survey. SETTING: Three urban teaching institutions. PATIENTS: A total of 301 consecutively admitted patients in SICUs for 5 or more days. MAIN OUTCOME MEASURES: Assessment of patients on SICU days 1, 3, 4, 6, and 8 and SICU discharge for risk factors, Candida colonization, and antifungal use. Candida colonization status was categorized as noncolonized (NC), locally colonized (LC) if 1 site was involved, and disseminated infection (DI) if 2 or more sites or candidemia were involved. RESULTS: The most frequent risk factors in the 301 patients enrolled were presence of peripheral and central intravenous catheters, bladder catheters, mechanical ventilation, and lack of enteral or intravenous nutrition. Early risk factors included total parenteral nutrition or central catheter at SICU day 1 and previous SICU admissions or surgical procedures. Peak number of risk factors (mean +/- SD) were as follows: 7.2 +/- 2.6 in NC (n = 229), 9.2 +/- 2.3 in LC (n = 45), and 9.2 +/- 2.6 in DI (n = 27). These numbers were reached at day 8 in the NC and LC groups and day 4 in the DI group. The LC and DI groups had more risk factors on each SICU day than the NC group and longer median SICU length of stay (28 days in the DI group vs 11 and 19 days in the NC and LC groups, respectively). Antifungal therapy, while used most frequently in the DI group, was initiated later for this group than in NC and LC groups. CONCLUSIONS: Risk factors for Candida infection in SICU patients change over time. Patients with DI demonstrate a greater number of and more rapid increase in risk factors than patients in the LC and NC groups. Presence of early risk factors at the time of SICU admission, a high incidence of risk factors, or a rapid increase in risk factors should prompt clinicians to obtain surveillance fungal cultures and consider empirical antifungal therapy.

Antitumor efficacy and pharmacokinetic analysis of 4-hydroperoxycyclophosphamide in comparison with cyclophosphamide +/- hepatic enzyme effectors.

4-Hydroperoxycyclophosphamide is an oxazaphosphorine which is readily converted without enzymatic involvement to 4-hydroxycyclophosphamide-a key intermediate in the antitumor activity of this class of drugs. The efficacy of 4-hydroperoxycyclophosphamide as a systemically administered antitumor drug was examined in mice bearing EMT-6 mammary carcinoma and in rats bearing 13762 mammary carcinoma in comparison with other oxazaphosphorines. 4-Hydroperoxycyclophosphamide was a more potent tumor cell killing agent than cyclophosphamide or ifosfamide in animals bearing the EMT-6 tumor. There were no significant differences in the toxicity to bone marrow amongst the three oxazaphosphorines. 4-Hydroperoxycyclophosphamide (90 mg/kg) on days 7, 9 and 11 produced 11.5 days of tumor growth delay compared with 10.4 days and 7.1 days for cyclophosphamide (150 mg/kg) and ifosfamide (150 mg/kg) administered on the same schedule, respectively. 4-Hydroperoxycyclophosphamide was tolerated at 90 mg/kg daily for 5 days and at 75 mg/kg twice daily for 4 days producing tumor growth delays of 14.4 days and 16.6 days, respectively. In rats bearing 13762 tumors, 4-hydroperoxycyclophosphamide (90 mg/kg) on days 8, 10 and 12 produced a tumor growth delay of 14.5 days compared with 8.9 days for cyclophosphamide (100 mg/kg) administered on the same schedule. Treatment of 13762 tumor-bearing rats with phenobarbital, pentobarbital or etanidazole increased the tumor growth delay produced by cyclophosphamide while treatment with cimetidine decreased the tumor growth delay produced by cyclophosphamide but not significantly. Administration of 4-hydroperoxycyclophosphamide (90 mg/kg) produced blood concentrations of 4-hydroxycyclophosphamide three-fold higher than those produced by administration of cyclophosphamide (100 mg/kg) at 15 min after drug injection. Treatment with phenobarbital or pentobarbital increased 4-hydroxycyclophosphamide blood concentration while pretreatment with cimetidine decreased 4-hydroxycyclophosphamide blood concentration from cyclophosphamide. 4-Hydroperoxycyclophosphamide is an effective antitumor agent worthy of further investigation.

Antiangiogenic treatment (TNP-470/minocycline) increases tissue levels of anticancer drugs in mice bearing Lewis lung carcinoma.

Although the antiangiogenic agent TNP-470 does not, in general, increase the cytotoxicity of anti-cancer therapies in cell culture, the antiangiogenic agents TNP-470 and minocycline individually and especially in combination have been shown to increase the tumor growth delay produced by several standard cytotoxic therapies in the Lewis lung carcinoma. In an effort to understand the mechanism by which the antiangiogenic agent combination TNP-470/minocycline potentiates the antitumor activity of cytotoxic therapeutic agents in vivo, the biodistribution of [14C]-cyclophosphamide and cis-diamminedichloroplatinum(II) was determined 6 h after cytotoxic drug administration in animals bearing Lewis lung carcinoma pretreated with TNP-470/minocycline and in animals without pretreatment. Higher levels of 14C and platinum were found in 9 tissues (including tumor) except blood in animals pretreated with TNP-470/minocycline. The increased drug levels in the tumors may be sufficient to account for the increased tumor growth delays observed previously. DNA alkaline elution of tumors from animals pretreated with TNP-470/minocycline showed increased DNA cross-linking by both cyclophosphamide and cis-diamminedichloroplatinum(II). The possible implications of these results are discussed.

Impact of a clinical pharmacist on antibiotic prescribing. A multicenter trial.

Within the past two decades, hospital pharmacists have become increasingly involved in providing consultation to physicians for drug management. Antibiotic use has become a complex and rapidly expanding discipline, complicated by the introduction of multiple new antimicrobial agents, each with unique features, and the pressures of prospective payment schemes. This study demonstrated that a team including a pharmacist had a positive impact on medical residents' utilization of antibiotics.

Amebic prostatitis.

A man with persistent prostatitis despite antibiotic therapy was found to have amebas compatible with Entamoeba histolytica in his urine after prostatic massage. Two indirect hemagglutination titers for E histolytica were negative. The patient had a prompt response to metronidazole therapy. Prostatitis due to amebic infection should be considered in patients who do not respond symptomatically to standard antibiotic therapy.

Substituted 2-iminothiolanes: reagents for the preparation of disulfide cross-linked conjugates with increased stability.

Much attention has been focused recently on the stability of immunotoxin (antibody-toxin) conjugates linked by a disulfide bridge. Conflicting reports have appeared regarding the in vivo stability of such conjugates prepared with the two most commonly used cross-linking reagents, SPDP and 2-iminothiolane. We have developed (i) a series of reagents based on 2-iminothiolane substituted at the 4- and/or 5-positions (X2ITs) which, based on model studies with simple amines, should show enhanced disulfide stability when conjugated with antibodies or other proteins and (ii) a real-time method for monitoring the rate and extent of conjugation of these reagents with amino groups. Depending upon the substituent, the stability of model-activated disulfides relative to unsubstituted 2-iminothiolane was increased from 5- to 4000-fold as measured by glutathione-induced release of thionitrobenzoic acid. This family of cross-linking reagents should allow the construction of disulfide cross-linked toxin, drug, or enzyme conjugates with enhanced stability in vivo.

Nasopharyngeal carriage of antibiotic-resistant pneumococci by children in group day care.

We compared rates of antibiotic resistance in strains of Streptococcus pneumoniae recovered from nasopharyngeal secretions of a group of children studied longitudinally in a research day care center between 1978 and 1985 and recovered from usually sterile body fluids of patients at a tertiary care hospital between 1981 and 1985. The prevalence of trimethoprim-sulfamethoxazole (TMP-SMZ) resistance was 11.5% in isolates from the hospital, whereas 30.0% of episodes of nasopharyngeal carriage of S. pneumoniae studied in day care children included TMP-SMZ-resistant isolates. The proportion of episodes of colonization with TMP-SMZ-resistant isolates in the day care study increased from 5.4% before 1981 to 39% between 1981 and 1985. Isolates of S. pneumoniae relatively resistant (MIC greater than or equal to 0.125 micrograms/mL) to penicillin G, amoxicillin, or cefuroxime accounted for 8% of isolates from the hospital and 11.9% of episodes of nasopharyngeal colonization in children in day care. Pneumococci with reduced susceptibility to either TMP-SMZ or a beta-lactam antibiotic were recovered from 68% of 72 children in the day care study.

Isolation of fluconazole-resistant Candida albicans from human immunodeficiency virus-negative patients never treated with azoles.

Isolation of fluconazole-resistant strains of Candida species from human immunodeficiency virus (HIV)-infected patients after repeated or continuous courses of treatment has been reported with increasing frequency. During 1991-1992, MICs of fluconazole for 139 Candida albicans isolates from our institution were bimodally distributed: 102 strains were susceptible (MICs, < or = 4 micrograms/mL) and 37 were resistant (MICs, > or = 8 micrograms/mL). There was incomplete cross-resistance between fluconazole and ketoconazole or miconazole, and there was no cross-resistance between azoles and amphotericin B or flucytosine. Twenty of the 37 fluconazole-resistant strains were isolated from 17 HIV-negative patients, some with systemic infections, who had never been treated with azoles. There were no differences in characteristics or risk factors for those patients as compared with those for an equal number of HIV-negative patients from whom fluconazole-susceptible strains were isolated. Among patients with systemic infection, 6 (50%) of 12 with infection caused by fluconazole-resistant strains survived and 11 (69%) of 16 with infection caused by fluconazole-susceptible strains survived (P = .54). Survival was not found to be related to treatment regimen, but the number of patients was small. The emergence of fluconazole-resistant C. albicans among HIV-negative patients never exposed to azoles is of concern.

Absorption characteristics of three phenytoin sodium products after administration of oral loading doses.

The absorption characteristics of three phenytoin sodium products given orally as loading doses in five healthy men were studied. Extended phenytoin sodium capsules, prompt phenytoin sodium capsules, and phenytoin sodium injection were administered in a randomized, crossover trial as single 18-mg/kg doses and as divided doses of 6 mg/kg every three hours for three doses. Each dose was given with 200 ml of water, and a two-week washout period followed each treatment. The maximum plasma concentration (Cmax), time to reach maximum plasma concentration, time to reach the lower end (10 mg/liter) of the therapeutic range, time to reach a plasma concentration greater than 15 mg/liter, and time within the therapeutic range were determined for each loading-dose regimen. Prompt phenytoin sodium capsules (prompt PHT) given in divided doses produced a mean Cmax of 22.0 mg/liter, which was significantly higher than that observed with any of the other loading-dose regimens. In addition, all subjects receiving prompt PHT in divided doses had plasma phenytoin concentrations of 10 mg/liter within six hours; only this treatment produced plasma concentrations greater than 15 mg/liter at nine hours in all subjects. Plasma concentrations remained within the therapeutic range (10-20 mg/liter) for 81 and 78% of the first 24-hour period for prompt PHT in divided and single doses, respectively. Adverse effects were minimal in all regimens. The prompt-release phenytoin sodium capsules used in this study may provide an alternative means for rapidly achieving therapeutic phenytoin concentrations in situations where i.v. administration is not indicated or practical.(ABSTRACT TRUNCATED AT 250 WORDS)

Development and validation of an instrument to measure physicians' attitudes toward the clinical pharmacist's role.

A scale to measure physicians' attitudes toward clinical pharmacy was developed and validated. Based on physician-clinical pharmacist interactions, statements were written and edited into tentative subscales. A preliminary test resulted in a reduction in the number of items and subscales. The final field test, based on responses from 166 physicians, after factor analysis, yielded 23 items in 5 subscales, with a scale reliability of 0.94. As additional measures of validity, physicians' responses showed significant differences in attitudes between subscales and differences by specialty. Differences also were demonstrated by physician status and age. No differences were shown by amount of exposure to clinical pharmacists. Reliability and validity of the scale have been supported and additional research into the concurrent validity of the scale is suggested.

Intermediates in the formation of the chlorophyll isocyclic ring.

Cell-free, organelle-free synthesis of Mg-2,4-divinylpheoporphyrin a(5) (MgDVP) from Mg-protoporphyrin IX monomethyl ester (Mg-Proto Me) has been described (Wong and Castelfranco 1984 Plant Physiol 75: 658-661). This system consists of plastid membrane and stromal fractions and requires O(2), NAD(P)H and S-adenosylmethionine (SAM). The synthetic 6-methyl-beta-ketopropionate analog of Mg-Proto Me was converted to MgDVP by the same catalytic system in the presence of O(2) and NADPH. SAM was not required. A compound (X) displaying the kinetic behavior of an intermediate was isolated from reaction mixtures with Mg-Proto Me as the substrate, but not with the 6-methyl-beta-ketopropionate analog as the substrate. X was identified as the 6-methyl-beta-hydroxypropionate analog of Mg-Proto Me by conversion to the dimethyl ester with CH(2)N(2) and comparison with authentic 6-beta-hydroxydimethyl ester. X was converted to MgDVP by the same catalytic system in the presence of O(2) and NADPH. We conclude that the conversion of Mg-Proto Me to MgDVP proceeds through the 6-beta-hydroxy and the 6-beta-ketopropionate esters in agreement with earlier suggestions.

Enhanced stability in vitro and in vivo of immunoconjugates prepared with 5-methyl-2-iminothiolane.

Substituted 2-iminothiolanes (X2ITs) are new heterobifunctional crosslinking agents designed for the preparation of disulfide-linked conjugates with enhanced resistance to reduction. Based upon 2-IT substituted at the 4 and/or 5 position, these reagents appear to function by sterically protecting the conjugate disulfide bond from attack by thiolate nucleophiles. Here, we have used the X2ITs to prepare and evaluate a series of immunoconjugates (antibody-cytotoxin conjugates) between the murine monoclonal antibody 791/T36, which recognizes a 72-kDa surface antigen present on many human tumor cells, and RTA30, the naturally occurring 30-kDa glycoform of ricin A chain. The X2IT-linked conjugates were also compared to immunoconjugates prepared with N-succinimidyl 3-(2-pyridyldithio)-propionate (SPDP) and 4-[(succinimidyloxy)carbonyl]-alpha-methyl-alpha-(2- pyridyldithio)toluene (SMPT), as well as with methyl- and dimethyl-substituted structural analogs of SPDP. In vitro, 791-(X2IT)-TNB model compounds exhibited a 6000-fold range of stabilities. In contrast, the corresponding 791-(X2IT)-RTA30 immunoconjugates were up to 20-fold more stable than conjugates made with unhindered linkages. These improvements resulted in immunoconjugates with prolonged serum half-lives in animals. Our data indicate that one of the crosslinking agents, 5-methyl-2-iminothiolane (M2IT), has optimal properties for the preparation of disulfide crosslinked immunoconjugates intended for therapeutic use in that (i) it is highly water soluble and reacts rapidly with protein amino groups at neutral pH, preserving the positive charge, (ii) it forms conjugates with RTA30 efficiently, and (iii) its conjugates exhibited enhanced disulfide bond stability in vitro and in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)