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Biomedical subjects

H S Tan

Publications and source records attributed to H S Tan.

At least 19 recordsLinked to original sources
PubMed2005

Development of ipsilateral adrenocortical carcinoma sixteen years after resection of an adrenal tumour causing Cushing's syndrome.

INTRODUCTION: At times, it may be difficult to differentiate early stage, low-grade adrenocortical carcinoma from benign adrenal adenoma. CLINICAL PICTURE: A 53-year-old lady underwent right adrenalectomy for a 4-cm adrenocortical tumour causing Cushing's syndrome. Histology revealed an adrenocortical adenoma. Sixteen years later, she presented with a 14-cm adrenal tumour, again on the right side. TREATMENT: She underwent surgical removal of the tumour. Histology confirmed adrenocortical carcinoma. OUTCOME: She died of metastatic disease 17 months later. CONCLUSIONS: This case highlights the importance of long-term, systematic follow-up of patients treated for benign adrenal adenomas, especially if the tumour size exceeds 4 cm.

Adrenal Cortex Neoplasms↗
PubMed2003

Pilot study using technetium-99m pertechnetate sequential radionuclide-sialography to assess salivary gland function in nasopharyngeal cancer patients on radiation therapy.

INTRODUCTION: Nasopharyngeal carcinoma (NPC) is mainly treated by radiation therapy. A common complication of radiotherapy is xerostomia. Direct measurements of the amount of saliva produced using suction cups and volumetric assessments are cumbersome and time-consuming. Sequential radionuclide sialography is a reproducible and convenient method of measuring salivary function. MATERIALS AND METHODS: Patients with newly diagnosed NPC underwent a pilot study using technetium-99m pertechnetate sequential radionuclide sialography to assess their salivary function before and at 3 months post radiation therapy. From the sialography, time activity curves were obtained for analysis of salivary function. The shape of the time activity curve with citric acid stimulation was classified into 4 types according to the degree of radiation-induced dysfunction. RESULTS: All 14 patients had worse (P < 0.005) time activity curves for both parotids and submandibular glands after radiation therapy. All patients with abnormal curves before radiation therapy presented type IV (non-functioning) curve after radiation therapy. A ratio of pre- and post-stimulation counts allowed for quantification of the degree of stimulatory response. We found a significant decrease in Rc before and after radiation therapy for all salivary glands (P < 0.001). The salivary gland to background ratio, which is a reflection of the degree of salivary gland functional uptake, also had a significant reduction after radiation. CONCLUSION: It is feasible to use technetium-99m pertechnetate in the measurement of salivary gland function in nasopharyngeal cancer patients treated with radiation therapy.

Adult↗
PubMed2001

Determination of captopril in pharmaceutical tablets by anion-exchange HPLC using indirect photometric detection; a study in systematic method development.

The development and validation of a significantly cost effective and simpler anion-exchange high performance liquid chromatorgaphic (HPLC) procedure than the compendial methods for the analysis of captopril in tablet dosage forms using indirect photometric detection is described. A low capacity anion-exchange column was used with potassium phthalate as the mobile phase marker and indirect detection at 280 nm. The chromatographic conditions were optimized using the Box and Behnken factorial experimental design. The method was precise and accurate with percent recovery (+/-%R.S.D.) of 99.8+/-0.7% (n=12) with the spiked concentrations ranging between +/-30% of the assay level. Youden and Steiner's robustness test, involving seven chosen variables, showed that the method is robust. Using the developed method, commercially available captopril tablets were assayed and the results were found to be comparable with those obtained by the compendial method.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed2001

Adenocarcinoma of the esophagus with choroidal metastasis.

In this report, a case is presented of an adenocarcinoma in a Barrett's esophagus metastatic to the choroid. A 54-year-old woman presented with a rapidly progressive decrease of vision in the right eye 8 months after intentionally curative esophagectomy for an adenocarcinoma. Fundoscopy, ultrasonography, and magnetic resonance imaging findings were suggestive of a metastasis. The patient received palliative external beam irradiation to the right eye for visual restoration, but she died before any beneficial effect was achieved.

Adenocarcinoma↗
PubMed1998

Capillary gas chromatographic assay of camphor and m-cresol in dermatological creams.

Camphor and m-cresol mixtures are used in antiseptic and anti-itching creams. No compendial method exists for these preparations. This paper reports a capillary gas chromatographic method using FID detection with 2,6-di-tert-butyl-4-methylphenol as internal standard on a 30 m x 0.32 mm Supelcowax -10 column (0.25 micron film) with helium as carrier gas. Ramped temperature programming was applied. The method allows simultaneous quantitation of camphor and m-cresol in the presence of o- and p-cresols, calamine and zinc oxide. Overall percent recoveries (+/- SD, n = 9) of camphor, o-, p- and m-cresol from spiked placebo creams, at a labeled amount of 10 (w/w)% were 96.9 +/- 0.6, 98.2 +/- 0.6, 99.2 +/- 0.5 and 101.0 +/- 0.9%, respectively, and at a labeled amount of 1% were 96.7 +/- 0.6, 97.8 +/- 0.9, 97.8 +/- 0.6, and 100.3 +/- 1.0%, respectively. The recovery studies were carried out at +/- 30% of the labeled amounts. Linear peak area or height ratios were obtained (r > 0.999) for camphor, o-, p- and m-cresol covering a concentration range of 10-200% of the labeled amount. Linearity (r > 0.999) was also obtained for m-cresol when the relative concentration of o- and p-cresol was varied from 5 to 100% of the m-cresol concentration. The resolution between the 'critical pair' of p- and m-cresol was > or = 1.1. The limit of quantitation was 23 pg for m-cresol and 9.3 pg for camphor using an injection split of 1:50. The repeatability (%RSD) for all compounds were < 2% for peak area and < 1.4% for peak height ratios. System suitability and robustness of the method were established. The method was successively applied to the assay of available commercial products and allows assay of camphor and the three cresol isomers.

Antipruritics↗
PubMed1998

A review of patients with high-risk carcinoma of the cervix treated with combined surgery and postoperative radiotherapy.

From May 1992 to October 1995, 57 patients with early stage cervical carcinoma were treated with hysterectomy and postoperative pelvic radiotherapy because of the presence of adverse histopathologic features. On prospective follow-up and analysis, the clinical outcome for 50 of these patients showed a pelvic disease control rate of 90.9%, a disease-free survival of 80.6% and an overall survival of 86.3%. Of the 8 relapses, half occurred in the pelvis i.e., 2 in the vaginal vault and 2 in the pelvic side walls. No severe complications were observed, but there was a 20% long-term Radiation Therapy and Oncology Group (RTOG) grade 1 to 2 urinary bladder dysfunctional problem and 28% incidence of suprapubic and/or leg oedema.

Adenocarcinoma↗
PubMed1998

Radiotherapy as local adjuvant treatment for endometrial carcinoma--a review of 45 patients.

Forty-five patients with endometrial carcinoma were treated with local postoperative adjuvant radiotherapy during the period 1992 to 1995. Radiotherapy technique comprised both external beam irradiation as well as high-dose-rate vaginal vault brachytherapy. The 5-year overall survival and relapse-free survival rates were 74% and 73%, respectively and poorly differentiated histology grade was associated with poorer prognosis. Only 1 patient developed an isolated vaginal vault recurrence and another 9 patients relapsed mainly at the distal anatomical sites. The main radiotherapy-related complications were vaginal adhesion and stenosis. Radiotherapy is therefore effective as local adjuvant treatment in reducing risk of local-regional relapse in endometrial carcinoma.

Adenocarcinoma↗
PubMed1998

Uterine papillary serous carcinoma--the KK Hospital experience.

A review of 355 cases of endometrial cancer treated at the KK Gynaecological Cancer Centre from June 1987 to June 1997 revealed 19 cases (5.3%) of uterine papillary serous carcinoma (UPSC), a clinically aggressive and pathologically distinct variant of adenocarcinoma which closely resembles ovarian papillary serous carcinoma. The majority of UPSC presented as late stage disease with 79% showing extrauterine disease. Twelve of 15 patients also had lymphovascular space invasion. Of the 19 cases, 15 had total hysterectomy and bilateral salpingo-oophorectomy with or without omentectomy and lymphadenectomy. Two had omental biopsy only and another 2 had dilatation and curettage only. The overall median survival in the series was 15 months. Twelve patients had died of disease (67%). Early stage disease seemed to confer a better prognosis. The poor prognosis is frequently ascribed to its tendency to present at a late stage.

Combined Modality Therapy↗
PubMed1996

Indirect photometric detection for determination of citrate in pharmaceutical matrices by ion chromatography.

The development of a simple ion chromatographic method for the analysis of citrate in pharmaceutical matrices is described utilizing the technique of indirect photometric detection. A polymeric anion exchange column was used with a mobile phase consisting of an aqueous solution of trimesic acid (pH 10) and indirect detection at 280 nm. The developed method was precise and accurate with percent recoveries (+/-%RSD) of 99.3 +/- 0.97% and 98.2 +/- 0.25% at 6 and 12 micrograms of citrate injected. Linear detector response was found over the range 1-12 micrograms of citrate injected with a limit of quantitation of 0.26 microgram of citrate injected. The method is specific for tricarboxylic acids as most other ions were not retained by the column. Youden's robustness test, involving seven selected operating variables, showed that the method is fairly robust. A system suitability test was also performed. Many commercial USP and non-USP liquid and tablet formulations were assayed for citrate by the developed method and the results were found to be comparable with those obtained by the compendial method.

Chromatography, High Pressure Liquid↗
PubMed1996

High performance liquid chromatographic assay of amprolium and ethopabate in chicken feed using solid-phase extraction.

A method for the assay of mixtures of amprolium and ethopabate in chicken feed was developed utilizing reversed-phase high-performance liquid chromatography (HPLC) after sample clean-up of a methanolic extract by solid-phase extraction using CN cartridges. HPLC was done with benzocaine as internal standard on a C-8 column with methanol-water 40:60, containing octanesulfonic acid, triethylamine and acetic acid, as mobile phase. Eluate was monitored at 274 nm. Baseline separation was achieved with retention times of approximately 7.5, 9.4, and 10.4 min, for amprolium, benzocaine, and ethopabate respectively. Feed constituents did not give peaks after 6.5 min. Peak area ratios were linear over 10-180 ng of amprolium, and 2-18 ng of ethopabate injected. Limits of quantitation at AUFS 0.05 were 0.5 and 0.3 ng respectively. Recovery studies from spiked feed (n = 9), covering +/- 30% of usual doses in feed, gave percent recoveries (+/- SD) of 99.4 +/- 1.4% for amprolium and 100.5 +/- 2.6% for ethopabate. Applying the method to two different batches of commercial feed gave results which were comparable to those obtained by the AOAC spectrofluorometric methods.

Amprolium↗
PubMed1995

Recurrent hepatic pre-coma resulting from a spontaneous porto-spleno-renal shunt (PSRS).

A 64-year-old Turkish male is described with recurrent hepatitic (pre-)coma resulting from a spontaneous porto-spleno-renal shunt, portal hypertension and hepatic insufficiency. In cases of chronic encephalopathy resulting from hepatic insufficiency that may be due to liver cirrhosis, the presence of a spontaneous porto-spleno-renal shunt should be considered as a distinct possibility, not only in the absence of apparent oesophageal varices and splenomegaly, but also when there is hepatopetal flow in the portal vein.

Fistula↗
PubMed1994

Use of high dose rate gammamed brachytherapy in the palliative treatment of gynaecological cancer.

From January 1992 to December 1993, 24 patients with advanced and incurable malignancies of the female genital tract were treated at the Department of Therapeutic Radiology, Singapore General Hospital, with high dose rate (HDR) brachytherapy. Results from the evaluation of these patients showed an overall complete palliation of symptoms in 16 of 23 (69.5%) patients. Total cessation of bleeding was observed in 14 of 20 (70%) and pain relief in two of three (66.6%). Of the 16 patients who exhibited full symptomatic response, almost half (43.7%) had clinical complete resolution of their local disease at last follow-up. Acute complications following treatment were minimal and only in one was intervention required to stop radiation haemorrhagic cystitis. We conclude that the use of HDR brachytherapy either alone or in combination with external beam radiotherapy can provide effective palliation for malignant tumours involving the female genital tract with minimal acute toxicity.

Adenocarcinoma↗
PubMed1994

[Determination of psoralens by gas chromatography].

A gas chromatography capillary column determination of a mixture of psoralens is proposed. The validation of quantitative analysis is detailed and used for the evaluation of psoralens extraction from pharmaceuticals. Moreover stability in acidic or basic media is studied by LC/MS as well as the proposed gas chromatographic methods. A gas chromatography capillary column determination of a mixture of psoralens is proposed.

Chromatography, High Pressure Liquid↗
PubMed1993

Unilateral cholinergic stimulation of the rabbit's cerebellar flocculus: asymmetric effects on optokinetic responses.

In previous work, we have demonstrated an acceleration of the buildup of slow-phase velocity of optokinetic nystagmus (OKN) after bilateral floccular injection of the aselective cholinergic agonist carbachol (Tan and Collewijn 1991; Tan et al. 1992a). In the present study we investigated the effects of unilateral floccular injections of carbachol. Such unilateral injections specifically enhanced the buildup of OKN slow-phase velocity in the direction toward the injected flocculus (ipsiversive). During binocular optokinetic stimulation, this enhancement was expressed in the motion of both eyes. Acceleration of the eye contralateral to the injected flocculus increased from 1 to about 2 degrees/s2, while the acceleration of the ipsilateral eye increased from 1 to about 1.5 degrees/s2. In contrast, buildup of contraversive OKN was unchanged. No changes were found in the steady-state OKN and optokinetic afternystagmus (OKAN). Monocular optokinetic stimulation was only effective in the nasal direction, and the effects of unilateral injection of carbachol were disconjugate. Ipsiversive OKN was enhanced only in the contralateral, seeing eye, while the response of the ipsilateral, covered eye was unchanged. We hypothesize that the directionally specific effect of unilateral cholinergic floccular stimulation on OKN is due to enhancement of predominantly the excitatory phase of modulation of the Purkinje cell's simple-spike activity by carbachol, without a marked effect of carbachol on the inhibitory phase of simple-spike modulation.

Acetylcholine↗
PubMed1993

Shortening of vestibular nystagmus in response to velocity steps by microinjection of carbachol in the rabbit's cerebellar flocculus.

It has been proposed that a common velocity-storage mechanism is responsible for the prolongation of vestibular nystagmus beyond the duration of the change in firing frequency of primary vestibular fibers in response to a step in velocity, and for the production of optokinetic afternystagmus (OKAN). In a previous study, bilateral injection of the aselective cholinergic agonist carbachol in the flocculus shortened the duration of buildup of optokinetic nystagmus (OKN) and the duration of OKAN, suggesting floccular involvement in velocity storage (Tan et al. 1992). In extension to that study of OKN, the present study assesses the effects of floccular carbachol on vestibular nystagmus in response to velocity steps. Our results show that injection of carbachol shortens the duration of vestibular nystagmus from about 13 to about 8 s; a finding which supports a common velocity-storage mechanism for optokinetic and vestibular signals. We propose that the indistinguishable effects of carbachol on OKAN and vestibular nystagmus are due to modification of the transmission of an oculomotor corollary signal, which has been identified electrophysiologically in the flocculus.

Animals↗