PubMed Health⌕ Search

Biomedical subjects

L M Stolk

Publications and source records attributed to L M Stolk.

At least 19 recordsLinked to original sources
PubMed1999

Detection of laxative abuse by urine analysis with HPLC and diode array detection.

A simple method is proposed for analysis of stimulant laxatives and metabolites of laxatives in urine. All stimulant laxatives commercially available in Germany, Belgium and the Netherlands, the diphenylmethane derivatives and the anthraquinones, were included. Chromatography was performed with a standardized isocratic HPLC system with diode array detection ('STIP'), which is commonly used in the Netherlands for toxicological screening. The method was validated by ingestion of a normal dose of the laxatives by human volunteers. In all cases the expected laxative metabolite could be detected in urine twelve hours after intake. Also urine samples of patients, suspected of laxative abuse, were analyzed.

Adult↗
PubMed1999

The relative bioavailability of metoprolol following oral and rectal administration to volunteers and patients.

The pharmacokinetics, efficacy and safety of metoprolol tartrate 25 mg fatty suppositories were studied in 5 healthy volunteers and in 8 patients suffering from instable angina pectoris. Metoprolol 25 mg capsules were used as a control oral dosage form. Metoprolol showed a considerable rectal bioavailability (AUC, C max) and was absorbed quickly from the rectum (T max). In both groups rectal bioavailability was comparable. However, oral bioavailability was much lower in the volunteer group than in the patient group. Furthermore, ratios of metoprolol/alpha-OH-metoprolol concentrations in plasma and urine gave an indication for a partial avoidance of the first pass effect after rectal administration. Further research is necessary to define an exact rectal dosage of metoprolol. In all patients, a substantial drop in heart rate, systolic and diastolic blood pressure was seen after administration of the first suppository. Metoprolol suppositories appear to be an effective, safe and suitable alternative for patients who are in need for beta blocking medication and who are unable to take oral medication for a certain amount of time.

Administration, Oral↗
PubMed1995

A new psoralen-containing gel for topical PUVA therapy: development, and treatment results in patients with palmoplantar and plaque-type psoriasis, and hyperkeratotic eczema.

Topical photochemotherapy with psoralen and its derivatives 4,5',8-trimethylpsoralen (TMP) and 8-methoxypsoralen (8-MOP), with UVA irradiation, was evaluated with regard to minimum phototoxic dose, concentration, timing of UVA irradiation and systemic and local side-effects, in healthy volunteers. Psoralen (0.005%) in aqueous gel was found to be superior to TMP and 8-MOP in aqueous gel. No hyperpigmentation was seen after topical PUVA treatment with psoralen in aqueous gel. Patients with plaque-type psoriasis (n = 7), palmoplantar psoriasis (n = 7) and hyperkeratotic eczema (n = 2) were treated. Topical PUVA therapy was effective in most psoriasis patients, without the occurrence of local or systemic side-effects. Moreover, hyperkeratotic eczema patients who did not respond to conventional therapy showed partial remission. These results indicate that topical PUVA therapy with psoralen in aqueous gel is a useful therapeutic modality for treatment of psoriasis patients, and patients with recalcitrant dermatoses such as palmoplantar psoriasis and hyperkeratotic eczema.

Eczema↗
PubMed1995

Effects of intraperitoneal cyclooxygenase inhibition on inflammatory mediators in dialysate and peritoneal membrane characteristics during peritonitis in continuous ambulatory peritoneal dialysis.

Peritonitis complicating continuous ambulatory peritoneal dialysis (CAPD) can be used as an in vivo model to study the contribution of mediators in dialysate to the regulation of peritoneal permeability. Previously we reported that changes in the peritoneal appearance rates of the cytokines interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF alpha) were related to alterations in the effective peritoneal surface area. Changes in the intrinsic peritoneal permeability were mainly related to those in the peritoneal appearance rate of the prostanoid prostaglandin E2 (PGE2) and partly also to that of IL-6. In this intervention study the role of these mediators was further analyzed. Eleven peritonitis episodes were followed on 8 consecutive days from the start of the infection and once after recovery. Indomethacin was given intraperitoneally during the first 3 days. beta 2-Microglobulin clearance was used as indicator of the effective peritoneal surface area. The intrinsic peritoneal permeability was characterized functionally by the restriction coefficient. The 15 peritonitis episodes studied previously served as the control group. This study supports the formerly obtained relationships in two ways. First, significant reductions were observed for peritoneal PGE2, 6-keto-PGF1 alpha, and TxB2 during cyclooxygenase inhibition to 6%, 0.6%, and 9% of the values on day 1, whereas simultaneously the intrinsic permeability was less increased. This indomethacin effect on intrinsic permeability was not entirely significant, probably because of the additional role of IL-6, which was not influenced by indomethacin. Also, the appearance rate of TNF alpha in the effluent was not affected by cyclooxygenase inhibition. Accordingly, the changes in the effective surface area were similar to those in the control group. Second, in 8 of the 11 cases, new rises both in peritoneal PGE2 and in intrinsic permeability occurred after discontinuation of indomethacin. Rebounds were not seen for TNF alpha or IL-6, and, consistently, not for the effective surface area. In conclusion, local cyclooxygenase inhibition results in a less-increased intrinsic permeability during peritonitis but has no effect on the effective surface area. These data support our previous finding that IL-6 and TNF alpha contribute to alterations in surface area, whereas PGE2 is more involved in intrinsic peritoneal permeability changes.

Adult↗
PubMed1994

L-phenylalanine and UVA irradiation in the treatment of vitiligo.

In order to evaluate the efficacy of L-phenylalanine (L-Phe) in combination with UVA therapy for vitiligo an open trial (149 patients, 18 months) and a small double-blind trial (32 patients, 6 months) were conducted. Oral L-Phe loading resulted in peak plasma levels of L-Phe after 30-60 min and a slight increase in the plasma tyrosine level. Response to L-Phe plus UVA irradiation was positive, and various grades of repigmentation not exceeding 77% in the open and 60% in the blind trial were observed. An increased L-Phe dose resulted in increased L-Phe plasma levels but not in improved clinical results. The optimal L-Phe dose appears to be lower than 50 mg/kg/day. Although it is difficult to draw firm conclusions from the present investigation, we think that L-Phe may have a place in the treatment of vitiligo and its role merits further investigation.

Administration, Oral↗
PubMed1990

Dissolution profiles of mesalazine formulations in vitro.

In vitro dissolution profiles of three controlled-release mesalazine formulations were determined at pH 1.0, 6.0 and 7.5. A closed-column type dissolution apparatus was used. A reproducible gradual dissolution profile was seen for Pentasa at all pH values. Dissolution starts immediately and is complete after 20 h. Dissolution profiles at pH 1 and pH 7.5 are much alike and dissolution is faster than at pH 6. The behaviour of Asacol at different pH values corresponds with the expectations: no release at pH 6 and pH 1, fast release at pH 7.5. Dissolution starts after 1 h and is complete after 3 h. Mesalazine release from Salofalk tablets at pH 7.5 and pH 6.0 starts after 2 and 3 h, respectively, and is complete after 5 and 10 h. However, after a long lag-time (10 h) mesalazine is also released from Salofalk tablets at pH 1 and dissolution is complete after 23 h.

Aminosalicylic Acids↗
PubMed1990

Absorption of oral mesalazine-containing preparations and the influence of famotidine on the absorption.

The mesalazine-containing preparations Asacol, Pentasa, and Salofalk (=Claversal) are frequently used in the treatment of inflammatory bowel disease. The release patterns of these formulations are time- and/or pH-dependent. The aim of this study was to investigate the patterns of absorption of these preparations and the influence of raised intragastric pH on absorption. Gastric pH was raised by simultaneous administration of famotidine. Absorption was determined by assaying with a high-performance liquid chromatography method the urinary excretion of acetylmesalazine, the major metabolite of mesalazine. A large intra- and inter-individual variability in absorption was found for all three formulations, both with and without concomitant famotidine administration. Asacol and Pentasa were significantly less absorbed than Salofalk. A significant lower absorption of mesalazine was seen when Asacol was combined with famotidine. Variations in gastric pH have negligible effect on the bioavailability of mesalazine in vivo.

Administration, Oral↗
PubMed1989

Formulation and stability of a beclomethasone dipropionate enema.

A beclomethasone dipropionate (BDP) enema and a BDP/mesalazine combination enema (containing 2 mg BDP and 1 g mesalazine and 2 mg BDP, respectively per 40 ml) were formulated. BDP and mesalazine were suspended in a carbomer-water gel. No degradation of BDP was measured during the storage period of the BDP enema (4 weeks at 20 degrees C) and of the BDP/mesalazine enema (44 days at 4 degrees C, 20 degrees C and 37 degrees C, respectively). Progressive darkening of colour occurred for the BDP/mesalazine enema during storage at 20 degrees C and at 37 degrees C, probably induced by mesalazine degradation products. Only very slight colouring was observed at 4 degrees C. Hardly any precipitation of BDP and mesalazine was seen during the storage period and the enemas could easily be resuspended.

Beclomethasone↗
PubMed1988

Biopharmaceutics, pharmacokinetics and pharmacology of psoralens.

The psoralen derivative 8-methoxypsoralen (8-MOP) and to a lesser extent some other psoralens, including 5-methoxypsoralen (5-MOP) and 4,5',8-trimethylpsoralen (TMP) have acquired a place in the treatment of psoriasis and other dermatoses. They are only active when combined with long-wave ultraviolet light: PUVA therapy (Psoralen plus UVA). Successful PUVA therapy depends on sufficiently high psoralen concentrations coinciding with the time of irradiation. The use of oral or rectal pharmaceutical formulations with 8-MOP dissolved in liquid is preferable to conventional tablets or capsules. Since no formulation of 5-MOP with fast and predictable absorption is available 8-MOP should be preferred in PUVA therapy. The effectiveness of oral TMP is doubtful, because of low serum concentrations, probably due to malabsorption.

Animals↗
PubMed1987

In vitro dissolution rates of six 8-methoxypsoralen formulations.

Dissolution rates in water of six oral 8-methoxypsoralen formulations were determined with both the rotating basket method and a column type flow-through method. Comparable and reproducible results were obtained with both methods. In view of the necessity in psoralen-UVA (PUVA) therapy that effective tissue concentrations of the drug be present in the skin during the irradiation period, we propose a requirement for a dissolution rate of 8-MOP tablets or capsules of at least 80% within 25 min. None of the three preparations registered in The Netherlands met this requirement. However, two preparations from abroad and a new capsule formulated in our pharmacy department with solid 8-MOP dispersed in polyethylene glycol 6000 showed satisfactory dissolution profiles.

Capsules↗