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Biomedical subjects

N Brock

Publications and source records attributed to N Brock.

At least 37 records · Page 2Linked to original sources
PubMed1989

Clinical use of the neuromuscular blocking agents atracurium and pancuronium for equine anesthesia.

Neuromuscular blocking agents (muscle relaxants) are useful and common adjuncts to general anesthesia for human beings, but have not been used extensively during anesthesia of large animal species. Over a 3-year period, atracurium or pancuronium were used as adjuncts to general anesthesia for 89 anesthetic procedures in 88 equids (of 18 breeds and age ranging in age from 5 weeks to 25 years) at the teaching hospital. Forty-one of the anesthetic procedures were for abdominal surgery, and orthopedic (n = 19), ophthalmologic (n = 17), thoracotomy (n = 1), and soft tissue (n = 14) procedures composed the rest. Most equids were given atracurium because it was less expensive than pancuronium. Initial dosage of either relaxant ranged from 0.12 to 0.2 mg/kg of body weight IV, and repeat doses ranged from 10 to 30 mg. Relaxants were used for as long as 205 minutes. Muscles of the face or hind limb digital extensor muscles were used to monitor relaxation. Muscles of the hind limb were more sensitive to the effects of relaxants than were muscles of the face. At the end of a surgical procedure, just prior to being taken to the recovery stall, a relaxant antagonist, edrophonium (0.5 to 1 mg/kg), was administered IV to each equid. Edrophonium caused blood pressure to increase in most of the equids. Heart rate change was variable, with approximately half the equids having no change or increased heart rate and the remainder having decreased heart rate. Recovery to standing after anesthesia was rated excellent or good for 72 equids, fair for 11, and poor for 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, General↗
PubMed1989

Oxazaphosphorine cytostatics: past-present-future. Seventh Cain Memorial Award lecture.

The development of the oxazaphosphorine cytostatics cyclophosphamide, ifosfamide, and trofosfamide was based on the idea of applying the transport form/active form principle to the highly reactive nitrogen mustard group. A critical analysis and synopsis of the available results and knowledge will include examination of the extent to which the hypotheses on which this concept is based have been confirmed by experimental and clinical findings: 1. Chemical synthesis succeeded in converting the reactive nitrogen mustard into an inactive transport form (latentiation). 2. The requirement that the transport form be enzymatically activated to the active form in the target organ (the cancer cell) has been achieved by a sequence of metabolic reactions. 3. The aim of considerably increasing the therapeutic index of alkylating agents has been achieved by the oxazaphosphorine cytostatics. The greater cancerotoxic selectivity is closely correlated with the cytotoxic specificity of their activated primary metabolites. 4. The cancerotoxic selectivity of oxazaphosphorines was further increased when mesna was introduced as a regional uroprotector. Mesna eliminates the risk of therapy-limiting urotoxic side effects of oxazaphosphorines. With mesna protection, these cytostatics can be given in higher doses with increased safety, and their therapeutic efficacy can be enhanced. 5. Stabilization of the primary oxazaphosphorines, e.g., by attaching 2-mercaptoethanesulfonic acid (mafosfamide), opens up new possibilities in preclinical investigations and in therapy, e.g., for the clonogenic stem cell assay, for in vitro purging in autologous bone marrow transplantation, for regional perfusion of tumors, and, in small doses, for immunomodulation, where appropriate, in conjunction with "biological response modifiers."

Cyclophosphamide↗
PubMed1989

Experimental investigations into the carcinogenic effect of antitumor and immunosuppressive agents.

In a comprehensive experimental study on rats, the carcinogenicity of various therapeutically important antitumor drugs was investigated. The influences of strain, sex, dose and time of administration were systematically varied. The tested compounds showed remarkable differences in their carcinogenic potential. These differences were particularly obvious, not only when the total tumor rate was analyzed, but also when the distribution of tumor rates to the various localizations was considered (tumor spectrum). Three classes of carcinogenic substances were identified: (1) Substances showing a specific carcinogenicity: they lead to tumorogenesis primarily in organs or organ systems that, in the untreated control animals, remain virtually tumor-free for life. One example of such a substance is chlormethine. (2) Substances with non-specific carcinogenicity: they lead to an increase in tumors in organs that are also stricken in the control animals, however, to a clearly reduced extent. Oxazaphosphorine carcinogenicity is typical for this class. (3) Substances of mixed-type carcinogenicity: this group shows non-specific carcinogenicity, as well as a carcinogenic action with marked organ specificity. One example of this class is procarbazine. The antimetabolites tested were shown to be practically non-carcinogenic. Characteristic differences occurred between the two rat strains used in the investigation, Sprague-Dawley and BD II, with regard to the spontaneous tumor spectrum and the organ-related extent of carcinogenicity under the influence of the substances tested. In an experiment involving short-term application (up to 17% LD50, five times i.v. at 14-day intervals), the carcinogenic effects were substantially lower than in an experiment involving long-term application (up to 7% LD50, once a week for 52 weeks, i.v.), although the strain- and substance-specific characteristics in both experiments were rather similar.

Animals↗
PubMed1988

Basis and new developments in the field of oxazaphosphorines.

All the research results summarized herein were gained in the attempt to improve selectivity in cancer chemotherapy: "Chemotherapeutic agents are not only ends in themselves, they are also beginnings,. . . Selectivity must be our goal and understanding its basis our guide to the future" (138). The development of the OAP cytostatics CP, IFO, TRO, and SUFO derives from the idea of applying the principle of transport form/active form to the highly reactive nitrogen mustard compounds. The desired conversion of the reactive nitrogen mustard into an inactive transport form (latentiation) was performed by chemical synthesis. The requirement for an enzymatic activation of the transport form to give the active form in the target organ cancer cell was met and has been shown to occur in a sequence of various metabolic reactions. The goal of a substantial increase in the therapeutic range of alkylating agents has been achieved with the development of the OAP cytostatics. The higher cancerotoxic selectivity is closely correlated with the cytotoxic specificity of their activated primary metabolites. A further increase in the cancerotoxic selectivity in OAPs was achieved by the development of mesna as a regional uroprotector. Mesna eliminates the danger of therapy-limiting urotoxic side effects of OAPs, allowing administration of higher dosages and more safely optimizing their therapeutic efficacy and partly overcoming resistance phenomena. The stabilization of the primary OAP metabolites (MAFO), opens up new possibilities in clinical therapy and in preclinical tests, for examination in the clonogenic stem cell test, for in vitro purging in ABMT, and for the regional therapy of tumors. A completely new type of therapy is emerging for OAP, specifically for low-dosage MAFO, as an immunomodulator, under certain circumstances, in combination with further substances, from the biological response modifier group.

Animals↗
PubMed1988

Treatment of advanced malignancies with ifosfamide under protection with mesna.

Fifty-seven patients with advanced malignant tumours were treated with ifosfamide (Holoxan) and mesna (Uromitexan) in our department from November 1979 to December 1984. This series comprised eight cases of soft tissue sarcoma, nine cases of ovarian carcinoma, five cases of non-seminomatous testicular tumour, 11 cases of bronchogenic carcinoma, three cases of renal carcinoma, seven cases of non-Hodgkin's lymphoma, two cases of skeletal fibrosarcoma, two cases of breast carcinoma, one case each of Ewing's tumour, prostatic carcinoma, seminoma, plasma cell tumour, multiple myeloma, malignant teratoma, nasopharyngeal carcinoma, Wilms's tumour, neuroblastoma and mycosis fungoides. Out of these 57 cases, 53 were evaluable. There were five complete remissions and 20 partial remissions, corresponding to a total response rate of 47%. The overall median survival time (MST) of the 53 evaluable patients was 7.5 months. The responders had a longer survival time (MST 10 months) than the non-responders (MST 4.75 months) (p greater than 0.05). Analysis of the results according to sex, age, dosage of ifosfamide and degree of histological differentiation of the tumour cells failed to show any influence of these factors on the therapeutic results. The response rate to ifosfamide found in this study might be related to the histological origin of the tumours and to whether the primary tumours had been resected. The non-seminomatous testicular tumours, non-Hodgkin's lymphomas and ovarian carcinomas showed a high response rate. The response rate was higher in the group in which the primary tumour had been resected (61%) than in the non-resected group (12%) (except the non-Hodgkin's lymphoma). The side-effects of this regimen were moderate. Dyspepsia, nausea, vomiting, myelodepression, dizziness, and alopecia were common. Cystitis could be prevented nearly completely by concomitant administration of mesna, when given correctly, for preventing side-effects of ifosfamide on the urinary system (haemorrhagic cystitis, etc.).

Adult↗
PubMed1987

Electron microscopic investigations of the cyclophosphamide-induced lesions of the urinary bladder of the rat and their prevention by mesna.

Fully developed cyclophosphamide-induced cystitis is characterized by nearly complete detachment of the urothelium, severe submucosal edema owing to damage to the microvascular bed and focal muscle necroses. The initial response to the primary attack by the cyclophosphamide metabolites seems to be fragmentation of the luminal membrane. This damages the cellular barrier against the hypertonic urine. Subsequent breaks in the lateral cell membranes of the superficial cells and in all the plasma membranes of the intermediate and basal cells, intercellular and intracellular edema and disintegration of the desmosomes and hemidesmosomes lead to progressive degeneration and detachment of the epithelial cells with exposure and splitting of the basal membrane. The morphological changes of the endothelial cells, which become more pronounced in the later stages of the experiment, the involvement of blood vessels regardless of their diameter and the location-dependent extent of the damage indicate a direct type of damage which is preceded by a mediator-induced increase in permeability, the morphological correlate of which is the formation of gaps in the interendothelial cell connections on the venules. These changes can be effectively prevented by mesna. The only sign of a possible involvement is the increase in the number of specific granules with a presumed lysosomal function in the superficial cells.

Animals↗
PubMed1986

Ideas and reality in the development of cancer chemotherapeutic agents, with particular reference to oxazaphosphorine cytostatics.

The development of the oxazaphosphorine cytostatics, cyclophosphamide, ifosfamide and trofosfamide was based on the idea of extending the transport from/active from principle to the highly reactive nitrogen mustard group. In a critical analysis and synopsis of the available findings and knowledge, the question of the extent to which the hypotheses on which this concept is based have been confirmed in experiments and in clinical practice is investigated. From the chemical and synthetic viewpoint, the intended conversion of the reactive nitrogen mustard into an inactive transport from (latentiation) has been achieved. The requirement of enzymatic activation of the transport form in the target organ (the cancer cell) has been achieved by a sequential series of various metabolic reactions and has been proven. The objective of a substantial increase in the therapeutic range of alkylating agents has been achieved with the development of the oxazaphosphorine cytostatics. The high cancerotoxic selectivity of these compounds is closely linked with the cytostatic specificity of their activated primary metabolites. A further increase in the cancerotoxic selectivity of oxazaphosphorines has been achieved by the development of mesna as a regional uroprotector. Mesna eliminates the danger of therapy-limiting urotoxic side effects of oxazaphosphorines. Under mesna protection oxazaphosphorines can be used at higher dosages and with greater safety and their therapeutic efficacy can be increased.

Alkylating Agents↗
PubMed1986

Prevention of urotoxic side effects by regional detoxification with increased selectivity of oxazaphosphorine cytostatics.

Urotoxic side effects, particularly haemorrhagic cystitis, have been a limiting factor for the therapeutic use of the oxazaphosphorine cytostatics cyclophosphamide, ifosfamide and trofosfamide. The development of mesna (Uromitexan) has made it possible to carry out regional detoxification in the kidneys and the efferent urinary tract and thus to achieve clinically prophylaxis against the urotoxic side effects of oxazaphosphorines. In the body, mesna is rapidly converted to the biologically inactive disulfide form (dimesna). After glomerular filtration, dimesna is reduced by interaction with the glutathione system of the renal tubular cells and is excreted in the urine as mesna, the free thiol compound. This compound is then capable of definitively detoxifying the oxazaphosphorine metabolites in the urine. In extensive experiments on rats, it has been demonstrated that the cyclophosphamide-induced occurrence of urinary bladder tumours could be reduced or even eliminated by simultaneous administration of mesna. Detoxification by mesna enables the clinical use of higher doses and, consequently, a possible increase in therapeutic efficiency.

Animals↗
PubMed1985

Identification and quantification of metabolite conjugates of activated cyclophosphamide and ifosfamide with mesna in urine by ion-pair extraction and fast atom bombardment mass spectrometry.

The high bladder toxicity of the alkylating oxazaphosphorine anticancer drugs, cyclophosphamide and ifosfamide is effectively reduced by the concomitant administration of mesna (sodium 2-mercaptoethane sulphonate). The formation and rapid urinary excretion of conjugates of the activated (4-hydroxylated) oxazaphosphorine metabolites with mesna has been suggested as the pharmacological basis for the selective detoxification, but separation and identification of such metabolites in vivo have been extremely difficult due to their high polarity and chemical lability. In this study an ion-pair extraction procedure in combination with positive and negative ion fast atom bombardment mass spectrometry has been developed which enabled the identification and quantification of the conjugation products of activated oxazaphosphorine metabolites with mesna in urine. The conjugates extracted as the tetra-n-butylammonium salts are directly identified by their characteristic positive molecular ion adducts and fragment ions, and the corresponding abundant molecular anions. The pattern of molecular and fragment ion formation was established by comparison of the fast atom bombardment mass spectra of synthetic cyclophosphamide-mesna conjugates with various organic and inorganic counter ions. The ifosfamide-4-(2-thioethylsulphonate) (ifosfamide-mesna) conjugate was identified as a metabolite in the urine of rats, and in patients after administration of the combination, ifosfamide + mesna. By means of a two-step extraction and with the use of suitable analogues as internal standards, procedures for the quantification of parent oxazaphosphorine and of oxazaphosphorine-mesna conjugates by negative ion fast atom bombardment mass spectrometry have been developed, and first examples for the determination of excretion kinetics are described.

Acrolein↗
PubMed1984

Models in cytostatic chemotherapy.

Models play a fundamental role in all sciences. Scientific theories can be understood as "intellectual models" of the relations and interrelations between the elements of the science. Such relational models consider the scientific topics as "systems," and may therefore be called "system models." The basic elements of chemotherapy are the processes of kinetics (absorption, distribution, metabolizing, and elimination of drugs in organisms), interaction of drug molecules or their metabolites with specific receptors, and the effect-formation. The basic system models for these processes with special reference to cancer chemotherapy are discussed. For the evaluation of these system models appropriate experimental models are necessary. For cancer chemotherapy the experiment with living tumor-bearing animals is the basis as well for evaluation of scientific theories (models) as well as for inference in clinical situations. Such inferences are "inductive" inferences, i.e., inferences made under uncertain conditions. To assess probabilities for the degree of uncertainty the theorem of Bayes is a valuable tool. Experimental models, as models for clinical situations, are used for screening, pharmacologic characterization, and preclinical pharmacology of drugs. In each of these phases of preclinical drug development the experimental models must be appropriate for the relevant clinical situation. So, for the screening of anticancer drugs appropriate experimental tumor systems must be used to reveal the clinical relevant toxic and therapeutic potency of the drug. In our laboratory, test systems with relatively chemosensible experimental tumors on rats and mice have proved as efficient for primary screening. In this system a total cure could be achieved with cyclophosphamide as standard. For the pharmacologic characterization, test systems must be used which are able to reveal the clinically relevant safety margins, time-effect relations, and organotoxic effects of the drug. For the preclinical pharmacology, the experimental models should give some information about the relevant pharmacokinetics, pharmacodynamics, and possible (toxic or therapeutic) interactions with other drugs. The most important aspects of these models for cancer chemotherapy are discussed. Special attention is given to the clinical aspects.

Animals↗
PubMed1984

The key role of hydroxylation for the cytostatic activity and selectivity of cyclophosphamide.

The "pro-drug" cyclophosphamide (CP) is activated by liver "mixed function" hydroxylases to 4-hydroxy-cyclophosphamide (4-OH-CP), which represents the cytostatically active principle. Since the primary metabolite 4-OH-CP retains all the specific pharmacological properties of the parent compound without the need of metabolic activation, it constituted the basic principle and rationale for further drug development. Due to its chemical instability, 4-OH-CP had to be stabilized through appropriate substitutions at the 4-position of the oxazaphosphorine ring. ASTA Z 7557, in which the side chain is a 2-mercapto-ethanesulfonate, represents the prototype of this new class of oxazaphosphorines.

Biotransformation↗
PubMed1984

Pharmacokinetics and mechanism of action of detoxifying low-molecular-weight thiols.

A number of thiol compounds have been studied with reference to their selective protective action against urotoxic side-effects of oxazaphosphorine cytostatics. The uroprotective capacity is determined exclusively by the pharmacokinetic behavior of the compound. When given PO, all compounds tested were absorbable from the gut. Both thiols and disulfides are rapidly eliminated from the blood, but during their short half-life a number of unknown chemical reactions probably take place to maintain a physiological redox equilibrium. Elimination from the blood plasma occurs via two fundamentally different mechanisms: by distribution throughout the tissues and intracellular uptake or, alternatively, by rapid renal excretion. Most of the compounds tested belong to the first group: N-acetylcysteine, carboxycysteine, disulfiram and its metabolite DDTC, glutathione, WR 2721, etc. Few compounds are quantitatively excreted through the urine: mesna, dimesna, and DA 12. Only these compounds were suitable for selective regional detoxification and for the prevention of oxazaphosphorine-induced urotoxic lesions.

Animals↗
PubMed1984

Effect of the uroprotector sodium 2-mercaptoethane sulfonate (Mesna) on the proliferation of the bladder urothelium in the rat after administration of cyclophosphamide.

The chemotherapy of malignant tumors with oxazaphosphorine cytostatics, e.g., cyclophosphamide (CP) and ifosfamide, is limited by their severe urotoxic side effects. As a result of cytotoxic damage, the proliferation of the urinary bladder urothelium is considerably stimulated during an intensive reparative regeneration. The recently developed uroprotector sodium 2-mercaptoethane sulfonate (Mesna) allows regional detoxification limited to the kidneys and lower urinary tract and thus protects against damage by aggressive oxazaphosphorine metabolites. The object of the present quantitative autoradiographic investigation was to study urothelial proliferation in the bladder of rats after administration of CP alone and in combination with Mesna. 20 h after intraperitoneal injection of a single dose of CP alone (100 mg/kg), the urothelium showed a steep rise of the 3H-thymidine (3H-TdR) labeling index which reached a peak of 17.6% at 30 h. Thereafter, the 3H-TdR index rapidly dropped. A second peak of 4.4% was observed after 7 days. With supplementary intravenous administration of a single dose of Mesna (100 mg/kg) 15 min before treatment with CP, the labeling index was substantially lower than after administration of CP alone. Thus, maximal values of only 1.6 and 1.9% were observed at 35 h and 7 days, respectively. Histopathological examination of the bladders showed severe necrotizing and ulcerative cystitis, 10, 20 and 25 h after administration of CP alone whereas with additional treatment with Mesna only slight edema of the lamina propria developed. The results obtained clearly demonstrate the protective action of Mesna on the urothelium of the lower urinary tract against the urotoxic effects of CP.

Animals↗