Breast Cancer and Transplantation

Breast cancer is an important cancer among solid organ transplant recipients. While the incidence of breast cancer in solid organ transplant recipients is comparable to the age-matched general population, the outcomes are generally poor. Interventions such as cancer screening that preclude the development of late-stage disease through early detection are not well studied, and clinical practice guidelines for cancer screening rely solely on recommendations from the general population. Among patients with a prior breast cancer history, disease recurrence after transplantation is a rare but fearful event. Once disease recurs, the risk of death is high. The focus of this review is to present the epidemiology of breast cancer in solid organ transplant recipients, screening and preventive strategies for those who may be at risk, novel genomic profiling for determining tumor progression, and the newer targeted interventions for recipients who have developed breast cancers after solid organ transplantation.

Cntnap4 differentially contributes to GABAergic and dopaminergic synaptic transmission

Although considerable evidence suggests that the chemical synapse is a lynchpin underlying affective disorders, how molecular insults differentially affect specific synaptic connections remains poorly understood. For instance, Neurexin 1a and 2 (NRXN1 and NRXN2) and CNTNAP2 (also known as CASPR2), all members of the neurexin superfamily of transmembrane molecules, have been implicated in neuropsychiatric disorders. However, their loss leads to deficits that have been best characterized with regard to their effect on excitatory cells. Notably, other disease-associated genes such as BDNF and ERBB4 implicate specific interneuron synapses in psychiatric disorders. Consistent with this, cortical interneuron dysfunction has been linked to epilepsy, schizophrenia and autism. Using a microarray screen that focused upon synapse-associated molecules, we identified Cntnap4 (contactin associated protein-like 4, also known as Caspr4) as highly enriched in developing murine interneurons. In this study we show that Cntnap4 is localized presynaptically and its loss leads to a reduction in the output of cortical parvalbumin (PV)-positive GABAergic (γ-aminobutyric acid producing) basket cells. Paradoxically, the loss of Cntnap4 augments midbrain dopaminergic release in the nucleus accumbens. In Cntnap4 mutant mice, synaptic defects in these disease-relevant neuronal populations are mirrored by sensory-motor gating and grooming endophenotypes; these symptoms could be pharmacologically reversed, providing promise for therapeutic intervention in psychiatric disorders.

Efficacy and tolerability of irinotecan in patients with advanced colorectal cancer in Singapore

INTRODUCTION

Colorectal cancer is the commonest malignancy encountered in Singapore. The long-term outcome of patients with advanced diseases is poor. For many decades, 5-fluorouracil was the only effective cytotoxic drug against colorectal cancers. Randomised trials have documented the efficacy of irinotecan in patients with metastatic colorectal cancer. We investigated the efficacy and safety profile of irinotecan (CPT-11), as a second-line treatment for an Asian population who had failed 5-fluorouracil-based chemotherapy.

MATERIALS AND METHODS

A total of 33 patients were enrolled in the study between October 1996 and May 1999. This was an open label phase II study. All patients who had received at least one dose of CPT-11 were evaluated for toxicity. Thirty patients were evaluated for response.

RESULTS

Six patients (20%) had partial responses and 1 (3%) experienced minor response. Fourteen patients (47%) progressed. Nine patients (30%) had stable disease. The range of time to progression was 5.8 months to 21 months. The median survival was 9.5 months. There was no treatment-related death. Seven patients (23%) who received treatment had diarrhoea. Only 2 of the 7 patients had grade 3-4 diarrhoea. Eleven patients (37%) suffered from haematological toxicity, of whom 2 patients had grade 3-4 neutropenia.

CONCLUSION

We demonstrated efficacy and tolerability of CPT-11 in Singaporean patients with advanced colorectal cancer.

Adjuvant postoperative 5-fluorouracil chemotherapy combined with pelvic radiation for rectal cancer: results from an Asian population

Prospective randomized clinical trials have shown the effectiveness of combined adjuvant 5-fluorouracil-based chemotherapy and radiotherapy after surgical resection of rectal cancer. To assess toxicity of this therapy, prospective data were collected from 236 Asian rectal cancer patients treated with combined 5-fluorouracil-based chemotherapy and radiotherapy after surgery. Almost 82% of patients completed planned therapy. Grade 3 and 4 diarrhea, stomatitis, and granulocytopenia occurred in approximately 18-21% of patients. There were two treatment-related deaths from granulocytopenia and sepsis. With median follow-up of 3.5 years, median disease-free and overall survival was 75 and 88 months, respectively. In conclusion, combined adjuvant 5-fluorouracil-based chemotherapy and radiotherapy after surgical resection of rectal cancer is tolerable in Asian patients with moderate toxicity.

Clinical update of gemcitabine in pancreas cancer

Pancreatic cancer constitutes less than 2% of all cancers diagnosed in Singapore, consistent with the proportion described worldwide. About 40% of patients are diagnosed when the disease is locally advanced but without metastases. Another 40% are diagnosed with distant metastases. Only 20% are diagnosed when resectable. Most are adenocarcinomas arising from the head of the pancreas. Systemic chemotherapy is used for advanced metastatic pancreatic cancer but has met with limited success. Gemcitabine is a new fluorine-substituted cytarabine compound. In a randomised study it appears to confer statistically significant, although modest, improvement in quality of life and survival of patients with metastatic pancreas cancer. Evaluation of the drug in combination chemotherapy regimens and with radiation continues.

Continuous infusion 5-fluorouracil as salvage chemotherapy in patients with advanced colorectal cancer

For almost 40 years, 5-fluorouracil (5-FU) has been the only useful drug with clinically meaningful activity in metastatic colorectal carcinoma. When the disease progresses or recurs despite bolus 5-FU treatment, the options are limited. Our study shows that 5-FU given by continuous infusion is a viable alternative. Fifty-three patients received continuous infusion 5-FU. The overall response was 9%. Median survival of the entire cohort was 5 months. Patients with partial response and stable disease had median survival duration of 8 and 9 months, respectively. A dose-response relationship was observed. The commonest toxicities were mucositis (34%) and palmar-plantar syndrome (24%). There was no central line-related complication. Continuous infusion 5-FU is an effective "second-line" treatment. Further work is needed to ascertain its role, in comparison with newer agents like irinotecan (CPT-11), and oxaliplatin.

Phase II trial of a paclitaxel and carboplatin combination in Asian patients with metastatic nasopharyngeal carcinoma

PURPOSE

An earlier phase II trial of paclitaxel in patients with metastatic nasopharyngeal carcinoma (NPC) demonstrated a response rate of 22%. Hence we proceeded to study the combination of paclitaxel and carboplatin in these patients.

PATIENTS AND METHODS

The 21-day regimen was as follows: i.v. paclitaxel 175 mg/m2 over three hours preceded by standard premedications, followed by i.v. carboplatin dosed at AUC of six infused over one hour. Only chemotherapy-naive patients with histological diagnoses of undifferentiated carcinoma of the nasopharynx, systemic metastases and radiologically measurable lesions were eligible.

RESULTS

Thirty-two patients were accrued to this study. Twenty patients (62%) had at least two sites of metastasis. The main grade 3-4 toxicity was neutropenia (31%). Nine patients (28%) developed neutropenic sepsis, which caused the demise of one of them. Twenty-four patients (75%) responded to treatment, with one (3%) attaining a complete response. The median time to progression of disease was seven months and the median survival was 12 months. At one year, 52% of the patients were alive.

CONCLUSIONS

The combination of paclitaxel and carboplatin is an active regimen in NPC. Its convenience of administration and good tolerability make it an attractive alternative regimen to consider for patients with metastatic disease.

Adjuvant chemotherapy for patients with resected Dukes' C and high-risk B2 colon cancer with fluorouracil and levamisole

Carcinoma of the large bowel is the second leading cause of cancer mortality in Singapore. Although the great majority of patients are discovered at a stage where resection with curative intent is possible, almost half of the patients afflicted will die of it. The combination of 5-fluorouracil + levamisole used in patients with curatively resected high risk Dukes B2 and all Dukes' C colon cancers has been shown to reduce cancer recurrence rate and improve overall survival. Since 1990 adjuvant chemotherapy has been recommended for this group of patients. This report describes patients treated in Singapore, their toxicities and their outcome. A total of 341 patients were treated between 1990 and 1996. Treatment compliance was 71.8%. Toxicity was moderate with mainly grade 1-2 nausea and vomiting, diarrhoea, stomatitis, alopecia, and neutropenia. There was 1 treatment-related death. Median recurrence-free interval was 81 months and median survival was not reached at 90 months. This regimen is tolerable. Until further randomised reports comparing 5-fluorouracil + levamisole to other combinations are available, this combination chemotherapy is recommended to patients after surgical resection of the high risk Dukes' B2 and Dukes' C colon cancer to reduce cancer recurrence and improve overall survival.

Activity of paclitaxel by three-hour infusion in Asian patients with metastatic undifferentiated nasopharyngeal cancer

BACKGROUND

Despite its moderate anti-tumour activity in head and neck cancers there have been no reports on the activity of paclitaxel in patients with nasopharyngeal cancer, a highly chemosensitive tumour. A phase II study was thus initiated to determine the objective response rate and toxicity of paclitaxel in patients with previously untreated metastatic nasopharyngeal cancer.

PATIENTS AND METHODS

Twenty-four patients with previously untreated measurable metastatic nasopharyngeal carcinoma were accrued, one of them ineligible because of concomitant beta-blocker usage. Male:female ratio was 19:5, with a median age of 46 years. All had previously received radiotherapy but were chemotherapy-naïve. The great majority (20 of 24) had undifferentiated carcinoma. Paclitaxel (Anzatax, Faulding Pharmaceuticals) 175 mg/m2 was given intravenously over three hours every 21 days after premedication with oral dexamethasone and intravenous diphenhydramine and cimetidine.

RESULTS

There were five (21.7%) partial responses while eight patients remained stable. Median response duration was 7.5 months and median survival was 12 months. The main toxicity was haematological, with grade 1-2 neutropenia in 19% and grade 3-4 neutropenia in 4.5% of cycles. Three cycles were complicated by grade 3-4 anaemia and one patient required a blood transfusion. No thrombocytopenia was seen. Peripheral neuropathy was frequent (20 of 23 patients) but mild. Alopecia was complete in 14 patients. There were no cardiac toxicity or hypersensitivity reactions.

CONCLUSIONS

Paclitaxel is well tolerated even in previously irradiated patients with metastatic nasopharyngeal cancer. Single-agent activity was 22% and its inclusion into combination chemotherapy regimens should be studied.

Gastrointestinal lymphoma--a review of 54 patients in Singapore

Primary gastrointestinal (GI) lymphoma accounts for 2% to 5% of all GI malignancies. Primary therapy in uncomplicated GI lymphoma remains controversial. Fifty-four patients (male to female ratio of 4:3, median age 56 years) with GI lymphoma were studied to evaluate complications and results of therapy. The sites involved were the stomach (31), small bowel (12), large bowel (4), gallbladder (1) and multifocal (6). Distribution by stage and grade (Working Formulation or Kiel) were: IE-30%, IIE-43%, IIIE-6%, IV-20% and unknown-1%; low grade-33%, intermediate grade-59% and high grade-8%. Majority (54%) had diffuse large cell lymphoma. Twenty-three patients (43%) underwent primary resection of the tumour followed by chemotherapy in 14 or radiotherapy in 3. Seventeen patients (31%) had primary chemotherapy and 3 (6%) had primary radiotherapy. Of the 48 patients who underwent therapy, 52% had complete response. At the last follow-up (median 21 months), 25 patients were disease-free. Overall survival was 67% at two years. Treatment strategies employing surgery, radiotherapy and chemotherapy, alone or in combination, do not appear to influence outcome. Surgical resection plus chemotherapy appear to be effective in the control of local and distant disease.

A phase II trial of etoposide, leucovorin and 5-fluorouracil (ELF) in patients with advanced gastric cancer

Etoposide, leucovorin and 5-fluorouracil (ELF) chemotherapy has been reported to be less toxic yet effective (response rates of 50%) in patients with advanced gastric cancer. A phase II study of ELF in 25 patients (11 males, 14 females, median age 53 years) with advanced adenocarcinoma of the stomach is reported. Patients received outpatient intravenous etoposide 120mg/m2 over 2 hours, folinic acid 300 mg/m2 over 2 hours, 5-fluorouracil 500 mg/m2 boluses daily for 3 days every 21 days. Of 17 measurable patients, there was one complete response (CR), 4 partial responses (PR) for a total response rate of 29.4%. Non-hematologic toxicity was modest (grade 0 vomiting 11/21, stomatitis 16/21, diarrhea 17/21). Grade 3/4 neutropenia was seen in 14/23, thrombocytopenia in 2/23, anemia in 5/23 patients. Median progression-free and overall survival was 4.1 and 7.1 months, respectively. In conclusion, ELF chemotherapy shows only modest activity in patients with advanced gastric cancer and is associated with severe hematologic toxicity.

Social and public policy analysis: a niche for social work practice

This article provides front line social work practitioners with a mechanism for becoming more meaningfully involved in social and public policy analysis. It suggests that a new entry point for shaping policy formulation should occur earlier on in the problem identification stage of the rational policymaking process. The article offers a series of process questions to guide this approach and contends that practitioners have the necessary knowledge and skills to effect the various role expectations required of them in this regard.

Regular use of a verbal pain scale improves the understanding of oncology inpatient pain intensity

PURPOSE

This study was undertaken to determine if the daily use of a verbal pain scale could improve the correlation of pain perception between hospitalized oncology patients and their caregivers.

PATIENTS AND METHODS

Hospitalized oncology patients were asked to rate verbally their average pain over the past 24 hours on a scale ranging from 0 to 10. The patients' primary-care physicians and nurses were asked the same question on the same morning after they had evaluated their patients.

RESULTS

During a baseline study, only 64% of caregivers' pain scores were within two points of the respective patient's score. Caregivers tended to underestimate patients' pain scores. Caregivers were alerted to these poor results and then requested to ask each patient daily for the average pain score and record this score on the patient's medical record. Nonetheless, correlation between patients' and caregivers' pain scores remained poor (68% within two points of each other) during a second study. The major reason for the poor results appeared to be because caregivers did not routinely ask patients for pain scores. Subsequently, a renewed, more intensive educational effort was undertaken and a third study was conducted. During the third study, 85% of caregivers' and patients' pain scores were within two points of each other (P = .001 when compared with baseline).

CONCLUSION

The enforced use of a simple verbal pain assessment tool appears to improve caregiver's understanding of the pain status of hospitalized oncology patients.

Randomised study comparing imipenem/cilastatin to ceftriaxone plus gentamicin in cancer chemotherapy-induced neutropenic fever

Prompt initiation of empiric antibiotic therapy is the cornerstone in the therapy of chemotherapy-induced neutropenic sepsis in cancer patients. Ceftriaxone plus gentamicin (ceftriaxone/gentamicin) is the most widely used combination of empiric antibiotics in the Department of Medical Oncology, Singapore General Hospital. However, imipenem/cilastatin has been shown to be a practical alternative. To compare the efficacy and cost effectiveness of monotherapy with our usual combination antibiotic therapy, 50 evaluable neutropenic cancer patients admitted for fever were randomised to empiric imipenem/cilastatin or ceftriaxone/gentamicin. Ceftriaxone/gentamicin was started in 24 patients. The initial clinical response rate to ceftriaxone/gentamicin was 62.5% and 84.6% to imipenem/cilastatin (P = 0.075). The average cost of antibiotics per patient started on ceftriaxone/gentamicin including cost of change of antibiotics was S$63 per day of antibiotic use and for imipenem/cilastatin it was S$252 (P < 0.02). In conclusion, although more patients receiving imipenem/cilastatin had an initial clinical response than those receiving ceftriaxone/gentamicin, this difference was not statistically significant. It would appear that imipenem/cilastatin is equivalent to ceftriaxone/gentamicin for the treatment of neutropenic sepsis. However, ceftriaxone/gentamicin was more cost effective.

A phase II trial of 5-fluorouracil and cisplatinum in recurrent or metastatic nasopharyngeal carcinoma

BACKGROUND

A phase II clinical trial of the combination of 5-fluorouracil (5-FU) and cisplatinum (CDDP) was conducted in 24 patients (pts) with recurrent or metastatic nasopharyngeal carcinoma. None of the patients had prior chemotherapy and all but 4 had prior radiotherapy.

PATIENTS AND METHODS

5-FU was administered by intravenous (i.v.) infusion at a dose of 1000 mg/m2 daily on days 1 to 5 and i.v. infusion of CDDP at a dose of 100 mg/m2 in divided doses on days 1 to 3 of each 21-day cycle. Pts were examined for response after every two cycles. Of 24 pts accrued, 21 had measurable disease. Three had only bone metastases and were evaluable for toxicity and survival.

RESULTS

Thirteen pts had partial response and three achieved complete response, for an overall response rate of 66% (95% confidence interval 59% to 93%). Median time to progression for all patients was 8 months (range 4 to 28+ months) and median survival for all patients was 11 months. Grades 3 to 4 toxicities included granulocytopenia (10 pts). There was no treatment-related mortality. Average relative dose intensity was 0.8.

CONCLUSION

This combination is highly effective with acceptable toxicity. The duration of response tended to be brief. Its role in the neoadjuvant and adjuvant setting in patients with poor prognostic features should be further studied.

Use of oral and intravenous ondansetron in patients treated with cisplatin

Ondansetron, a selective 5-HT3 antagonist, has been shown to be effective in preventing chemotherapy-induced nausea and vomiting. From July and August 1991, 25 patients were accrued in a phase II study to assess the efficacy of ondansetron in patients receiving cisplatin-containing chemotherapy. Patients received intravenous cisplatin 100 mg/m2, given either as a 24-hour infusion on day 1 or in divided doses as eight-hour infusions daily on days 1 to 3. Each patient received 24 mg of ondansetron per day for six days. Intravenous dexamethasone 24 mg was given daily on the days of cisplatin infusion. The emetic episodes and degree of nausea were evaluated daily. "Good" control of emesis (0-2 episodes of vomiting) and nausea (mild or no nausea) ranged from 64-100% and 88-100% respectively. Failure in emesis control occurred most frequently on days 3 and 4. Ondansetron was generally well tolerated with only minimal side-effects. One patient developed unexplained encephalopathy which resolved completely. Our results suggest that ondansetron is an effective anti-emetic agent with minimal toxicities. Randomised studies comparing ondansetron against "standard" anti-emetics should be conducted.

Management of chemotherapy-induced neutropenic sepsis--combination of cephalosporin and aminoglycoside

In cancer patients undergoing combination chemotherapy, neutropenic febrile episode (NFE) is a life-threatening condition. Prompt initiation of empirical antibiotics is essential to limit morbidity and mortality. To understand the effectiveness of combination antibiotics consisting of a third-generation cephalosporin and an aminoglycoside, a retrospective review of all patients admitted for NFEs was conducted. Between August 1990 and December 1991, there were 34 NFEs in 26 cancer patients which were treated with a combination of aminoglycoside (gentamicin or amikacin) and a cephalosporin (ceftriaxone or ceftazidime). Initial antibiotic therapy included aminoglycoside plus ceftriaxone in 23 NFEs and ceftazidime in 11 NFEs. A change of antibiotics was required in 11 NFEs because of deteriorating clinical status or culture-proven drug resistance. Bacteria were isolated in 12 (35%) NFEs (blood 7, respiratory tract 2, skin 2, urine 1). Of these, eight (62%) were gram-negative bacteria and five were gram-positive bacteria. One blood specimen grew both gram-positive and gram-negative organisms. Broad spectrum antibiotics were effective in almost all NFEs. Thirty-one (91%) NFEs resolved with antibiotics. Three patients succumbed to their infection despite combination antibiotics. Aminoglycoside and cephalosporin is an effective antibiotic combination in the management of fever in neutropenic hosts. Randomised trials comparing this combination with newer antibiotics like monobactams and quinolones are needed in the search for more effective therapy.

Combined chemotherapy using cisplatin, ifosfamide and bleomycin (PIB) in the treatment of advanced and recurrent cervical carcinoma

Combined cisplatin, ifosfamide and bleomycin (PIB) chemotherapy was given to 14 (11 recurrent and 3 advanced and metastatic) cervical carcinoma patients. At least 2 cycles of chemotherapy were given before assessment of tumour response. The overall response rate was 28.6%; the complete response rate was 14.3%. Sites of response included cervical lymph nodes and the lung. Toxicity was common. Alopecia was universal. Other toxicity included suppression of haematopoiesis (73%), leucopenia (71%) and nausea and vomiting. Two patients died from sepsis during the myelosuppressive phase. The role of PIB in the management of advanced and recurrent carcinoma of the cervix should be evaluated in a randomized-controlled trial.

Adult parameningeal rhabdomyosarcoma--a case report and literature review

Although rhabdomyosarcoma is predominantly a malignant disease of children, it is also seen in adults. Since adults account for only 15% of rhabdomyosarcomas, the experience gathered for the treatment of the malignancy has been derived from treating children. The treatment of a case of adult extensive parameningeal rhabdomyosarcoma with CyVADlC chemotherapy and radiotherapy is described, together with a review of the literature.

Ophthalmia neonatorum--the Middle Road Hospital perspective

In a retrospective study of ophthalmia neonatorum seen in Middle Road Hospital between 1983 and 1986, 68% were caused by Neisseria gonorrhoeae. 40% of the Neisseria gonorrhoeae isolates were PPNG strains. For therapy of gonococcal ophthalmia neonatorum, 1% kanamycin eyedrops combined with a single intramuscular injection of kanamycin or a third generation Cephalosporin (Ceftriaxone or Cefotaxime) were all effective regimens. The use of intramuscular kanamycin was stopped because of concern for ototoxicity. Chlamydia trachomatis remains an uncommon cause of ophthalmia neonatorum in Singapore, in only 2 cases was this agent identified.

Neuromuscular blocking effects of tobramycin, gentamicin, and cefazolin

Forty patients (A.S.A. class I or II), 18 to 75 years of age, who were undergoing elective surgery were studied to determine the clinical and subclinical neuromuscular blocking effects of two antibiotics, tobramycin and gentamicin and to compare these effects with those produced by cefazolin, an aminoglycoside not known to produce paralysis. Patients were prospectively and randomly assigned in approximately equal numbers to one of four groups: group A received 1 mg/kg of tobramycin; group B, 1 mg/kg of gentamicin; group C, 500 mg of cefazolin; or group D, control (no antibiotic). Antibiotics were administered intravenously 45 minutes immediately preceding the study. The ulnar nerve was stimulated supramaximally and neuromuscular function was measured electromyographically. Anesthesia was induced with thiopental, 4 mg/kg IV, and maintained with endotracheal enflurane 1.0% to 1.5% (inspired) and N2O-O2 (2 L:1 L) after intubation. Succinylcholine (1 mg/kg) was administered after induction of anesthesia and the magnitude and duration of neuromuscular block monitored. d-Tubocurarine (0.1 mg/kg) was given 5 to 10 minutes after full recovery from succinylcholine and repeated as required. At the end of the operation, atropine, 0.02 mg/kg, and neostigmine, 0.4 mg/kg, were used to reverse the block. Base line neuromuscular data, duration of block of succinylcholine, and potency, duration of block, recovery rate, train-of-four fade, tetanic trend, response to double stimuli, post-tetanic effect, and reversibility of the subsequent d--tubocurarine-induced neuromuscular block were not significantly different (p less than 0.01) between any two groups. Tobramycin, gentamicin, and cefazolin, in recommended single doses, lack clinical neuromuscular blocking and subclinical relaxant-potentiating effects.

Reversal of dantrolene sodium-induced depression of skeletal muscle in the cat

Dantrolene sodium, a muscle relaxant, does not have a clinically useful antagonist. The present study was undertaken to test the efficacies of germine monoacetate, 4-aminopyridine, neostigmine, and calcium chloride as possible agents for the reversal of the direct skeletal muscle depression produced by dantrolene sodium in the cat anesthetized with alpha-chloralose. Depression of the indirectly elicited twitch responses (0.1 Hz) of the tibialis anterior muscle by 25, 50, 75 and 84 per cent was produced by dantrolene, 0.16, 0.36, 0.88 and 1.13 mg/kg respectively; spontaneous recovery of twitch tension during the subsequent 30 min was negligible. After the 30-min observation period had elapsed, one of the reversal agents under study was given (iv) in divided doses at intervals of 10 min (five cats for each agent). Germine monoacetate (2 X 0.5 mg/kg) immediately reversed the dantrolene-induced twitch depression, with an over-shoot that persisted for an hour. 4-Aminopyridine (4 X 0.5 mg/kg) caused a steady but incomplete reversal to 17 per cent depression, 30 min after the last dose. Neostigmine (4 X 0.04 mg/kg) caused an immediate, but transient, reversal of the twitch depression, with overshoot. Calcium chloride (4 X 10 mg/kg) was without effect. It is concluded that germine monoacetate is the drug of choice for reversal of the muscle depression produced by dantrolene sodium in the cat.