Microanalysis of amoxicillin, flucloxacillin, and rifampicin in neonatal plasma.

Simple and rapid reversed-phase high-performance liquid chromatographic assays with ultraviolet detection have been developed and validated for the determination of amoxicillin, flucloxacillin and rifampicin in neonatal plasma. Plasma samples were either precipitated with perchloric acid (amoxicillin) or methanol (rifampicin) or extracted with methylene chloride (flucloxacillin). Precision coefficients of variation and inaccuracy were less than 15% for all three assays. Only small sample volumes (20-40 microL) were required, making the assays suitable for therapeutic drug monitoring and pharmacokinetic studies in preterm and term neonates. The assays have successfully been applied to analysis of amoxicillin, flucloxacillin and rifampicin in previously published pharmacokinetic studies in neonates.

Amoxicillin pharmacokinetics in (preterm) infants aged 10 to 52 days: effect of postnatal age.

The pharmacokinetic parameters of amoxicillin were determined in 32 newborn infants aged 10 to 52 days (mean postnatal age, 24.7 +/- 12.4 days) to improve amoxicillin dosing in this age group. Amoxicillin plasma concentrations were determined using reversed-phase high-performance liquid chromatography in surplus plasma samples from routine gentamicin assays. Amoxicillin pharmacokinetic parameters (mean +/- SD) were as follows: first-order elimination constant (K(el)) = 0.27 +/- 0.10 h(-1), volume of distribution corrected for body weight (V/W) = 0.66 +/- 0.27 L/kg, total body clearance corrected for body weight (CL/W) = 0.18 +/- 0.10 Lkg(-1)h(-1), and elimination half-life (t(1/2)) = 3.0 +/- 1.3 hours. Amoxicillin body clearance was approximately twofold greater in our patients compared with published values in younger neonates (mean postnatal age, 0.76 +/- 1.57 days). Simulation studies using the observed amoxicillin pharmacokinetic data suggest an amoxicillin dose of 40 mg/kg administered every 8 hours in infants older than 9 days postnatal age, independent of gestational age and postconceptional age, to achieve satisfactory target plasma amoxicillin concentrations less than 140 mg/L and time above minimum inhibitory concentration of at least 40%. Prospective evaluation of this suggested new dosage regimen is necessary before implementation in the care of ill neonates.

Therapeutic drug monitoring of tacrolimus with the dried blood spot method.

In a preliminary investigation an assay for tacrolimus based on fingerprick sampling and consecutive application as a blood spot on sampling paper has been developed. The dried blood spot was analysed by HPLC-tandem mass spectrometry. The validated range was 1-30 microg/l. Intra- and inter-assay variability for precision and accuracy was <7.5% and 15%, respectively. Tacrolimus concentrations of 24 stable out patients were compared after both blood spot sampling and conventional venous sampling. Method agreement was investigated with the methods of Passing and Bablok and Bland Altman and proved suitable for clinical use. The dried blood spot method for tacrolimus seems promising for patient monitoring.

Toxic rise of clozapine plasma concentrations in relation to inflammation.

Recently a small number of patients were observed in two psychiatric hospitals in the Netherlands with clozapine intoxications that complicate or mimic infections. These patients were on chronic medication and normally had stable clozapine blood plasma levels. This article presents four of these cases. Medline was searched for reports of similar cases. A hypothesis was formulated and tested by literature study. Immune modulatory and toxic effects of clozapine protein reactive metabolites or haptens, may play a role in the development of inflammation. Clozapine has a direct influence on different cytokines resembling an inflammatory reaction. Infection or inflammation could induce bioactivation of clozapine into its nitrenium ion that can exert a toxic reaction that induces apoptosis and gives rise to elevated cytokine levels. Clozapine can function as a hapten and induce an IgG, IgM or IgE mediated hypersensitivity reaction. The cytokines released during infection or inflammation downregulate the clozapine metabolism in the P450 system through CYP 1A2. Clozapine plasma levels should be monitored closely if an inflammatory or infectious process is suspected.

Comparison between human pharmacokinetics and imaging properties of two conjugation methods for 99mTc-annexin A5.

Annexin A5 (AnxA5) is a protein with high affinity for phosphatidyl serine, a phospholipid exposed on the cell surface during apoptosis. This phenomenon has been used for determination of cell death after myocardial infarction. To evaluate the potential of (99m)Tc-AnxA5 for in vivo scintigraphy of apoptotic cells, the pharmacokinetics and imaging properties of two radiopharmaceuticals, (99m)Tc-(n-1-imino-4-mercaptobutyl)-AnxA5 (I-AnxA5) and (99m)Tc-(4,5-bis(thioacetamido)pentanoyl)-AnxA5 (B-AnxA5), were studied. I-AnxA5 was administered intravenously to seven patients and one healthy volunteer, and B-AnxA5 was administered to 12 patients. All patients in the pharmacokinetic study had myocardial disease. Additionally, imaging was performed in a patient with acute myocardial infarction, as well as in three patients with different malignancies. The plasma concentration, excretion and biodistribution of (99m)Tc-AnxA5 were measured, as well as levels of AnxA5 antigen. The kinetic data of both radiopharmaceuticals in plasma fitted a two-compartment model. Both preparations had similar half-lives, but a different distribution over the two compartments. Plasma levels of AnxA5 antigen showed a broad variation. Both radiopharmaceuticals accumulated in the kidney, liver and gut. B-AnxA5 was excreted significantly faster than I-AnxA5. Both compounds can be used for imaging of the head/neck region, the thorax and the extremities. B-AnxA5 has a faster clearance and a lower radiation dose. Imaging of apoptosis in the abdomen will be difficult with both radiopharmaceuticals, and especially with B-AnxA5 because of its faster appearance in the gut.

Population pharmacokinetics and relationship between demographic and clinical variables and pharmacokinetics of gentamicin in neonates.

Population pharmacokinetic parameter estimates were calculated from 725 routine plasma gentamicin concentrations obtained in 177 neonates of 24 to 42 weeks' gestational age in their first week of life. Kel increases and V/W decreases with increasing gestational age. Almost identical results were obtained with iterative two-stage Bayesian fitting (MW\PHARM 3.30) as with a non-parametric maximization algorithm (NPEM2). The effect of various covariates on drug disposition was investigated retrospectively using multiple regression analysis. Predictive power for Kel increases with rising gestational age. For neonates 28.5 weeks and 30.9 weeks (r2 = 0.482), with gestational age, postnatal age, and Apgar score at 5 minutes being predictors. A very strong correlation existed between volume of distribution and weight (r2 = 0.83). Volume as a function of weight could be described with low predictivity by gestational age and to a lesser degree by Apgar score at 5 minutes (r2 = 0.298). The developed models need appropriate prospective clinical validation.

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.

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.

Analysis of methadone and its primary metabolite in meconium.

Methods for analysis of methadone and its principal metabolite, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) in meconium, based on fluorescence polarization immunoassay (FPIA) and high-performance liquid chromatography (HPLC) and diode array detection were developed. Meconium and urine samples of 16 neonates from 15 methadone-using mothers were analyzed. Because of the lower detection limit and the possibility of coanalyzing EDDP, meconium analysis with HPLC for detecting methadone use is very much preferable to FPIA. Identical results were obtained with HPLC analysis for both matrices: methadone or EDDP or both could be detected in the urine and meconium samples from 15 children. The amount of EDDP in meconium was much higher than the amount of methadone (ratio, 9.6). EDDP only was detected in eight of the meconium samples. A positive correlation was found between the methadone dose of the mothers and the methadone concentration in meconium, but not with the EDDP concentration in meconium.

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.

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.

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.