Population pharmacokinetics and pharmacodynamics of oral etoposide.

AIMS: To study the population pharmacokinetics and pharmacodynamics of oral etoposide in patients with solid tumours. METHODS: A prospective, open label, cross-over, bioavailability study was performed in 50 adult patients with miscellaneous, advanced stage solid tumours, who were receiving oral (100 mg capsules) etoposide for 14 days and i.v. (50 mg) etoposide on day 1 or day 7 in randomised order during the first cycle treatment. Total and unbound etoposide concentration were assayed by h.p.l.c. Population PK parameters estimation was done by using the P-Pharm software (Simed). Haematological toxicity and tumour response were the main pharmacodynamic endpoints. RESULTS: Mean clearance was 1.14 l h(-1) (CV 25%). Creatinine clearance was the only covariable to significantly reduce clearance variability (residual CV 18%). (CL = 0.74 + 0.0057 CLCR; r(2) = 0.32). Mean bioavailability was 45% (CV 22%) and mean protein binding 91.5% (CV 5%). Exposure to free, pharmacologically active etoposide (free AUC p.o.) was highly variable (mean value 2.8 mg l(-1) h; CV 64%; range 0.4-9.5). It decreased with increased creatinine clearance and increased with age which accounted for 9% of the CV. Mean free AUC p.o. was the best predictor of neutropenia. Free AUC50 (exposure producing a 50% reduction in absolute neutrophil count) was 1.80 mg l(-1) h. In patients with lung cancer, the free AUC p.o. was higher in the two patients with responsive tumour (5.9 mg l(-1) h) than in patients with stable (2.1 mg l-1 h) or progressive disease (2.3 mg l-1 h) (P = 0.01). CONCLUSIONS: Exposure to free etoposide during prolonged oral treatment is highly variable and is the main determinant of pharmacodynamic effects. The population PK model based on creatinine clearance is poorly predictive of exposure. Therapeutic drug monitoring would be necessary for dose individualization or to study the relationship between exposure and antitumour effect.

Dose-finding and pharmacologic study of chronic oral idarubicin therapy in metastatic breast cancer patients.

Oral idarubicin (IDA) is an active drug in metastatic breast cancer, but its role in the management of this tumor is yet not established completely. To investigate a new modality of IDA administration, a dose-finding study was designed with hyperfractionated doses. The purpose was to determine the maximum tolerated dose (MTD), the dose-limiting toxicity (DLT), and the pharmacokinetics of this schedule. IDA was administered twice daily as outpatient therapy in cycles of 3 weeks followed by a 1-week rest. Thirty-one patients with progressive metastatic breast cancer and pretreated with chemotherapy (including epirubicin and doxorubicin) were enrolled. DLT was defined as G4 hematological toxicity or any other toxicity G3 or higher (Bloom and Richardson grading). Inter- and intrapatient dose increases were studied. Pharmacokinetics of IDA and its metabolite idarubicinol (IDOL) were evaluated. IDA dose was increased from 2 mg/day to 10 mg/day, by steps of 1 mg/day, with the larger dose given in the evening. MTD was reached at 10 mg/day. Overall, the therapy cycles were 69 (median/patient, 2; range, 1-6). DLTs were G4 neutropenia associated with leukopenia and thrombocytopenia in one patient and G3 diarrhea in another of the 5 patients in the 10 mg/day cohort. The two patients developing DLT at the daily dose of 10 mg received a dose normalized for body surface of 6.85 and 5.65 mg/m2/day, respectively. We considered 5.5 mg/m2/day to be the MTD. Other toxicities were nausea, vomiting, neutropenia, and diarrhea, grades G1 to G2. By univariate analysis, significant correlations were observed between absolute neutrophil count at nadir and IDA area under the curve (P = 0.022; r = -0.33), IDA Cmax (P = 0.0067; r = -0.38), IDOL area under the curve (P = 0.0009; r = -0.43), and IDOL Cmax (P = 0.0016; r = -0.41), respectively. By multivariate analysis, IDA Cmax was the strongest determinant for neutropenia (R2 = 0.14; P = 0.01). Among the 21 patients evaluable for response, 3 (14.3%) had partial response (lasting 3, 6, and 8 months, respectively), and 6 (28.6%) had a complete arrest of disease progression (lasting 2-6 months). In conclusion, the MTD of this schedule is 10 mg/day and the DLTs are neutropenia and diarrhea. Tolerance was good, and the treatment is feasible as home therapy. Some objective measurable responses were documented in this group of anthracycline-pretreated patients. IDOL could have a role for the pharmacological effect. Further evaluation of this schedule is warranted to assess the activity and toxicity of prolonged oral IDA administration.

Interactions of antineoplastic chemotherapy with zidovudine pharmacokinetics in patients with HIV-related neoplasms.

To evaluate the perturbations in zidovudine (ZDV) pharmacokinetics as a consequence of antineoplastic chemotherapeutic treatments, we performed a prospective crossover study in 13 HIV-infected patients with cancer. The subjects received 2-day regimens of ZDV (250 mg x 2/day). On the first day ZDV was administered alone, whereas on the second day it was combined with antitumor chemotherapies specific for the histological type (ZDV + chemotherapy). Blood sample and urine collections were performed over a 12-hour period following oral administration of the antiretroviral agent. ZDV was measured with high-performance liquid chromatography. Pharmacokinetic parameters of ZDV were calculated by a noncompartmental model. The mean ZDV area under curve (AUC) was not significantly different in the patients treated with ZDV alone and ZDV + chemotherapy. Comparison of plasma elimination half-life (t((1/2))), apparent systemic clearance (CL/F), and apparent volume of distribution (Vd/F) of ZDV did not show any significant difference before and after chemotherapy. Conversely, some significant differences were observed for both mean peak concentration (C(max)) of ZDV and the corresponding time (T(max)). There was a 57% reduction in C(max) (p<0.05) and a 66% increase in T(max) (p<0.05) after chemotherapy compared with treatment with ZDV alone. No differences were observed in the urinary excretion of ZDV and ZDV glucuronide and urinary metabolic ratio, as a consequence of antineoplastic treatment. In conclusion, this study demonstrates that some minor perturbations in ZDV pharmacokinetics (i.e. C(max) and T(max)) derived from antineoplastic chemotherapy. Based on the observation that antineoplastic chemotherapy had no significant effect on plasma ZDV concentration expressed as AUC, the observed pharmacokinetic interaction would not warrant by itself a change in the ZDV dosage during chemotherapy.

Pharmacokinetics of oral etoposide in patients with hepatocellular carcinoma.

Etoposide dosage in patients with liver dysfunction remains controversial. Since etoposide has a hepatic component to its clearance (CL) and shows a high degree of protein binding, hepatic impairment could affect etoposide disposition. However, the empiric recommendation that the dose of etoposide be decreased in such patients may reduce systemic exposure and be detrimental to its antitumor activity. To address these issues we studied the pharmacokinetics (PK) of etoposide in patients with hepatocellular carcinoma (HCC) and underlying cirrhosis (n = 17) treated with daily oral etoposide. Unbound etoposide was obtained by ultrafiltration. Etoposide concentrations (total and free drug) were measured by high-performance liquid chromatography (HPLC) and analyzed by noncompartmental equations. The patients had mild or moderate liver dysfunction. Albuminemia was in the normal range for all the patients. Creatininemia was normal in all but two patients. PK results (mean and range) showed that etoposide disposition was unchanged in patients with liver dysfunction. We found slightly high etoposide bioavailability [F, 61% (17-95%)] and clearance [CL, 1.1 (0.7-2.3)l h(-1) m(-2)] resulting in a normal degree of systemic exposure (AUC(oral) 27 microg h ml(-1)). Normal protein binding [PB 93.2% (84.4-98.1%)] contributed to a normal level of exposure to free drug (AUC(f, oral) 1.9 microg h ml(-1)). The distribution volume [V(SS) 8.4 (6.1-13.2) l/m2] and the effective half-life [t1/2eff, 5.1 (3.0-9.6) h] were normal. Median CL and protein binding did not differ in the seven patients with total bilirubin value of > 1.2 mg/dl as compared with the ten patients with total bilirubin levels of < or = 1.2 mg/dl (1.3 versus 1.01 h(-1) m(-2) and 92.5% versus 93.4%, respectively). In agreement with this PK finding, we observed no clinical evidence of increased toxicity in patients with hyperbilirubinemia as compared with patients with normal bilirubinemia (mean WBC decrease 38% versus 47%). The only case of severe (grade 4) hematological toxicity was observed in one patient with reduced glomerular filtration. Since the pharmacological effects of etoposide correlate with the level of systemic exposure to the free drug, our data suggest that no dose reduction is needed in patients with HCC. It is even possible to increase the dose intensity in patients with favorable PK parameters under appropriate hematological and therapeutic drug monitoring.

Pharmacokinetic and pharmacodynamic effects of high-dose continuous intravenous verapamil infusion: clinical experience in the intensive care unit.

OBJECTIVE: Our study aimed at evaluating the pharmacokinetic, cardiovascular, and metabolic effects of high-dose verapamil continuous intravenous infusion in cancer patients. DESIGN: Prospective clinical and pharmacokinetic study. SETTING: Intensive care unit of a Cancer Research Institute. PATIENTS: Nine patients (age range 31 to 57 yrs) with progressive cancer disease and without cardiovascular, renal, or hepatic dysfunctions. INTERVENTIONS: After a loading dose (0.15 mg/kg followed by 12 hrs of continuous intravenous infusion at 0.20 mg/kg/hr), the infusion rate of verapamil was increased every 24 hrs (0.25, 0.30, 0.35, and 0.40 mg/kg/hr). The highest rate was maintained for 48 hrs. Doxorubicin was given from the 60 th to the 108 th hr. Hydrochlorothiazide (25 mg/day) and potassium (36 mmol/day) were given orally. Altogether, 17 courses were completed. MEASUREMENTS AND MAIN RESULTS: Steady state concentration (C(SS) and systemic clearance of verapamil and nor-verapamil (active metabolite) for each infusion rate were calculated. Mean arterial pressure (MAP), central venous pressure (CVP), heart rate (HR), PR, QT and QTc intervals, and left ventricular ejection fraction (LVEF) were measured, as well as daily body weight, blood glucose and potassium. C(SS) of verapamil and nor-verapamil increased more than proportionally to the infusion rate (p<.001). Systemic clearance of verapamil decreased over the range of the infusion rate (p<.005). MAP and HR decreased at the 12th hr (p<.001) and then plateaued. CVP increased (p<.01). The relationship between MAP, HR, CVP, and verapamil plasma concentrations was significant (r2 = .25, .14, and .35, respectively; p<.0001). LVEF did not change. Six patients (11 courses) developed junctional rhythm. Three patients (six courses) showed a PR interval increase (p<.05). Patients with junctional rhythm had higher Css of verapamil (p<.009). Overall, QT and QTc intervals increased (p<.01). A linear relationship was observed between verapamil plasma concentrations and QT intervals (r2 = .09, p<.01). Cardiovascular side effects did not determine treatment withdrawal in any patient. Body weight, blood glucose, and potassium did not show significant changes. CONCLUSIONS: Our data suggest a capacity-limited clearance of high-dose verapamil. In the absence of heart disease, following a step by step increase of the dosage, the high plasma verapamil concentrations (617 to 2970 ng/mL) produce frequent but well tolerated hemodynamic and electrocardiogram changes.

Effect of cyclosporin A on protein binding of teniposide in cancer patients.

We investigated the effect of cyclosporin A (CSA) on protein binding of teniposide (VM26) in 16 patients with metastatic renal cell carcinoma receiving i.v. VM26 alone over 24 h (total dose, 200 mg/m2) and in association with CSA (5 mg/kg/2 h followed by 30 mg/kg/48 h i.v.). CSA was used in an attempt to overcome multidrug resistance. The unbound fraction (%fu) of VM26 was significantly (p=0.04) higher in the cycles with CSA (median 0.8; range 0.4-1.9) than in the cycles with VM26 alone (median 0.5; range 0.1-1.6). Both total VM26 area under curve concentration (AUC0-infinity) and free VM26 AUC0-infinity increased after treatment with CSA, but the median increase in free AUC0-infinity was higher (2.7-fold) than total AUC0-infinity (1.5-fold) (p = 0.04). Bilirubin was significantly (p<0.01) increased after CSA but no association was observed between bilirubin level and %fu of VM26. Albumin was in the normal range after both VM26 alone and VM26 plus CSA. The nadir of absolute neutrophil count (ANC) after VM26 plus CSA (median 700/microl, range <100-2860/microl) was lower than after VM26 alone (median 1900/microl, range 200-6000/microl) (p = 0.0007). The median percentage of ANC compared to the pretreatment value (ANC nadir/ANC pretreatment x 100) was 39.0% (range 3.1-98.8%) in the cycles with VM26 alone and 16.9% (range 1.4-97.9%) (p = 0.007) after VM26 plus CSA. Percentage change of neutrophils significantly correlated with free AUC0-infinity VM26 in the cycles with VM26 alone and VM26 plus CSA (p = 0.04, r = -0.53 and p = 0.04, r = -0.52, respectively). Only a trend which failed to reach significance was observed between total AUC0-infinity VM26 and percentage change of neutrophils in the cycles with VM26 alone and in association with CSA (p = NS, r = -0.33 and p = 0.055, r = -0.49, respectively). In conclusion, patients treated with CSA had higher systemic exposure to unbound VM26.

Pharmacology of chronic oral daily administration of idarubicin.

Idarubicin (4-demethoxydaunorubicin) (IDA) is a daunorubicin analogue with substantial activity in hematologic malignancies and solid tumors. Among several reasons, IDA is of interest because of its main metabolite derivative, the C-13 alcohol analogue, idarubicinol (IDOL). Previous studies have suggested that IDOL, unlike other anthracycline metabolic derivatives, possesses a striking growth-inhibitory activity in tumor cell lines. This suggests that IDOL, like IDA could be useful in circumventing MDR. IDA is bioavailable in an oral dosage form. After oral administration of IDA to the patients, the concentration of IDOL quickly exceeds that of IDA and is retained in the plasma for a longer period. Hence, administration of IDA to cancer patients results ina much greater overall exposure of the tumor to IDOL than to the parent compound. At the Oncology Center (CRO) in Aviano we performed a dose-finding and pharmacokinetic (PK) study of chronic daily oral IDA with intrapatient escalation in patients with metastatic breast cancer (MBC). All the patients were pretreated with anthracyclines (the cumulative dose was 530 mg and 264 mg, respectively, for epirubicin and (DOX) and had at admittance a PS < or = 2 and a left ventricular ejection fraction > 50%. IDA (1 mg capsules) was administered orally twice a day for 21 days every two weeks. Treatment was continued at escalating doses until progression or intolerance. Twenty-five patients were enrolled. MTD has not yet been reached and clinical results are reported in Table 1. Treatment was well-tolerated in all but one patient (300 ANC at day 28). Three patients had tox G3 ANC for more than three weeks after 3, 6, and 7 mg doses, respectively. Two of them stopped chemotherapy after 1 cycle and 1 patient stopped after 2 cycles (6 mg doses). Despite previous treatments with anthracyclines (the mean cumulative dose before entering the study was 530 and 264 mg, respectively, for epirubicin and DOX) no cardiotoxicity due to IDA treatment was observed. This trial demonstrates the feasibility of chronic daily IDA administration. At the dosage reported, treatment was generally well tolerated. The PK findings (high IDOL concentrations) and the unexpected G4 myelotoxicity in patients with the highest IDOL plasma concentrations suggest that IDOL is clinically relevant.

Non-linear pharmacokinetics of high-dose intravenous verapamil.

AIMS: In an attempt to reverse multidrug resistance, in a recent trial of verapamil in association with doxorubicin, we used escalating doses of continuous intravenous (i.v.) verapamil under close haemodynamic monitoring. We report the pharmacokinetics of escalating doses of verapamil. METHODS: We studied nine patients [seven males, two females; median age 46 years (range, 31-57)] with advanced adenocarcinoma of the colon and normal renal, hepatic, and cardiac functions. After a loading dose (0.15 mg kg-1 followed by 12 h continuous i.v. infusion at 0.20 mg kg-1 h-1), the infusion rate (ko) of verapamil was increased every 24 h (0.25, 0.30, 0.35, and 0.40 mg kg-1 h-1). The highest rate was maintained for 48 h. Doxorubicin was given as a continuous i.v. infusion from 12 to 108 h (n = 4) or 60 to 108 h (n = 5). Blood samples and urine collections were taken every 12 h. Verapamil and nor-verapamil were assayed by high performance liquid chromatography. We calculated systemic clearance of verapamil (CL = ko/Css) and renal clearance (CLr) of verapamil and nor-verapamil. The Css vs rate relationship was fitted to a Michaelis-Menten equation: Css = ko. (K(m)+Css)/(V.Vm). RESULTS: CL was dose-dependent and in all nine patients a significant reduction in CL was observed over the dose range (mean CL +/- s.d. were 0.51 +/- 0.31, 0.38 +/- 0.16, 0.32 +/- 0.18, and 0.27 +/- 0.11 l h-1 kg-1, respectively, at 0.25, 0.30, 0.35, and 0.40 mg kg-1 h-1; P = 0.0001). Css increased more than proportionally to the dose rate and the Css vs rate relationship was best defined by a Michaelis-Menten equation (K(m) = 730 micrograms l-1; V.Vm = 0.55 mg kg-1 h-1), (r = 0.994; P = 0.006). CLr of verapamil and nor-verapamil was not saturable but the contribution to the elimination was only 2 to 4% of the dose. CONCLUSIONS: These findings suggest a non-linear, capacity-limited metabolic clearance of high-dose verapamil. Using escalating infusion rates, high verapamil concentrations (1500-2500 ng ml-1) were achieved without major toxicity. Saturable clearance may cause higher bioavailability and slower elimination of verapamil after acute oral overdoses.

Paclitaxel as a radiosensitiser: a proposed schedule of administration based on in vitro data and pharmacokinetic calculations.

Paclitaxel is efficacious against many human cancers. Because it blocks cells at the radiosensitive G2-M interface, paclitaxel has been investigated as a radiosensitiser. The results have been equivocal and somewhat contradictory. It is impossible to obtain proper pharmacokinetic calculations, aimed at obtaining maximum cytotoxicity and/or radiosensitisation, without knowing (i) how long the drug must be in contact with the cells, (ii) how long the effect lasts after the drug is removed from the cellular environment, (iii) whether the drug acts as a radiosensitiser even when, like cis-platinum, it is added after the radiation and (iv) what the minimum quantity of drug in the cellular environment is required for both chemotoxicity and radiosensitisation. The present work addresses the above questions. Two radioresistant cell lines of human origin were used, A375 melanoma and S549 lung carcinoma, in a clonogenic assay where only colonies with 50 or more cells were counted. For the irradiation, 6 MV X-rays were used. Any G2-M block was quantified by cell cycle kinetics analysis. From the results, a simulation of pharmacokinetics was conducted to calculate the schedule of administration of paclitaxel most likely to achieve and maintain significant chemotoxocity and radiosensitisation. The minimum concentration of paclitaxel for measurable cytotoxicity was 3 nM for both cell lines, but the drug was more toxic to the A549 cells. The minimum concentration for measurable radiosensitisation was 3 nM for A375 and approximately 0.1 nM for A549, but whereas above 3 nM the radiosensitivity increased in A375, it decreased above 1 nM for A549. A minimum of 18 h incubation with the drug was necessary for measurable effects and the radiosensitising effects were lost soon after its removal. There was no radiosensitisation if paclitaxel was added after the radiation, and, at the minimum effective concentrations, it caused only a minor and transient G2-M block. The pharmacokinetic calculations predict that 15 mg/m2 paclitaxel given as a 1 h infusion 5 days/week for 3 weeks during the radiotherapy should achieve both cytotoxicity and radiosensitisation. The mechanism of radiosensitisation by paclitaxel at the concentrations suggested by our results does not appear to be via a G2-M block and is probably concentration dependent. The results imply that low-dose, daily infusions of paclitaxel for as long as possible during a course of radiotherapy are more likely to result in radiosensitisation and prolonged cytotoxicity than high-dose infusions given once a week.

Pharmacokinetics and tolerance of vinorelbine in elderly patients with metastatic breast cancer.

25 patients older than 65 years with metastatic breast cancer were treated with vinorelbine 30 mg/m2 i.v. days 1 and 8 every 3 weeks; the pharmacokinetics were studied in 10 of them. Vinorelbine showed a large apparent volume of distribution (mean 23.4 l/kg), a long terminal half-life (mean 26.2 h) and a large systemic clearance rate (mean 1.2 l/kg). These results are similar to those reported in younger patients. No correlation has been found between toxicity, age and drug exposure. We observed 6 partial responses out of 20 evaluable patients despite a relatively low mean dose intensity (67%). Severe neutropenia occurred in 37% of the patients; other side-effects were acceptable. This study does not provide a pharmacokinetic rationale for reducing the dosage of vinorelbine in selected elderly patients.

Determination of unbound etoposide concentration in ultrafiltered plasma by high-performance liquid chromatography with fluorimetric detection.

Etoposide is a highly protein bound drug, and monitoring the concentration of free drug could help individualize dosage in oncological patients. The cost and difficulty of the standard techniques (equilibration dialysis) has hampered the monitoring of free drugs. We describe a simple HPLC method for the measurement of free etoposide concentration in plasma. Sample preparation involves the ultrafiltration of plasma by a Centrifree device for 30 min at 2000 g and extraction with chloroform. The isocratic separation is performed with a mu Bondapak phenyl analytical column. Fluorimetric detection is used (288-328 nm excitation and emission wavelengths). Linearity of the calibration curve is excellent between 0.05 and 1 microgram/ml. Accuracy and precision are reported at the concentrations 0.06 and 0.4 microgram/ml: within-run accuracy is 10% and 6.2%, respectively; between-run accuracy is < or = 1%; within-run coefficients of variation (C.V.) are 10.6 and 5.0%; between-run C.V. are 11.6 and 6.8% respectively. The range of the assay is 0.05 to 1 microgram/ml. The feasibility of the technique has been tested in 7 patients treated with oral etoposide for hepatocarcinoma (mean protein binding 91%). We found no interference from endogenous substances, co-administered drugs (alizapride, furosemide, ranitidine) and other antineoplastic agents (doxorubicine, idarubicine, vinblastine, vinorelbine).

Sensitive high-performance liquid chromatographic method with fluorescence detection for measurement of vinorelbine plasma concentrations.

A high-performance liquid chromatographic (HPLC) method with fluorescence detection for the determination of vinorelbine in plasma is described. The technique was derived from that published by Debal for an assay of vinorelbine in cell culture medium. The modifications concern the preparation procedure for plasma samples (a two-step liquid-liquid extraction from plasma is described), optimization of the mobile phase composition, and use of a single C18 column. These changes resulted in an improved sensitivity and reproducibility of the assay and led to its feasibility for clinical pharmacokinetic studies. The range of the assay is 2 to 1000 ng/ml.

Pharmacokinetics of vinorelbine in patients with liver metastases.

BACKGROUND: The main elimination pathway of vinorelbine is hepatic metabolism, and the clearance of vinorelbine could be reduced in patients with liver metastases. OBJECTIVES: To study the pharmacokinetics of vinorelbine in patients who have advanced breast cancer with or without liver metastases and to study the relationship between hepatic function and vinorelbine clearance. PATIENTS AND METHODS: We studied 29 patients with advanced breast cancer: 19 with liver metastases and 10 control patients with extrahepatic metastases (mean age, 61 years; age range, 38 to 81 years). The vinorelbine dose was 30 mg/m2 as a short intravenous infusion; the dose was reduced by 50% in patients with bilirubin > 2 mg/dl. Patients were classified by ultrasonographic estimation of the liver volume replaced by tumor (%LVRT). Standard liver function tests and a monoethylglycinexylidide test (a quantitative liver function test based on lidocaine metabolite formation) were performed. Vinorelbine was assayed in plasma by HPLC with fluorescence detection. Vinorelbine determination was impossible in two patients with more than 75% LVRT because of interferences. Pharmacokinetic parameters were calculated with a noncompartimental method and compared by means of the Kruskal-Wallis test. RESULTS: A lower vinorelbine clearance rate was observed in the five patients with more than 75% LVRT (22.9 L/hr/m2) compared with the 10 patients with no liver metastases (48.0 L/hr/m2) and the 12 patients with 25% to 75% LVRT (45.3 L/hr/m2). Terminal elimination half-life and apparent volume of distribution were not significantly different among groups. The monoethylglycinexylidide test had a significant correlation with vinorelbine clearance. (r2 = 0.70; p = 10(-4). CONCLUSIONS: These results support vinorelbine dose reduction in patients with severe liver failure but not in patients with moderate secondary liver involvement. The monoethylglycinexylidide test may prove to be useful for vinorelbine dose individualization.

Are current pediatric dose recommendations for intravenous theophylline appropriate?

Theophylline, a first-line antiasthma drug, is often associated with severe toxicity even when taken in the recommended schedule. Theophylline toxicity has been associated with upper respiratory tract infections (URTI) due to reduced total-body clearance of theophylline. Some researchers believe this inhibition stems from a direct effect of viruses, but others postulate it is a result of the fever. We examined whether current theophylline dose recommendations are appropriate for children with acute asthma with a concurrent URTI. We also wished to elucidate whether the viral infection or the fever inhibits theophylline clearance. A total of 2254 medical records of asthmatic children admitted to The Hospital for Sick Children in Toronto were reviewed between 1987 and 1990. Clearance rate was calculated as the ratio between the infused dose rate and measured steady-state concentrations. Subsequently, these clearance rates were used to calculate steady-state concentrations that would be achieved by the recommended dose rates of theophylline. Reduced theophylline clearance was associated with the presence of URTI (p = 0.029) but not fever. Age correlated significantly with theophylline clearance (p = 0.027). If these children were to receive the recommended intravenous dose rate of theophylline, two-thirds of them would achieve steady-state serum concentrations above 15 mg/L, and one-third would achieve concentrations above 20 mg/L. Reevaluation of the present recommended theophylline dose rate is needed, as the majority of children requiring intravenous theophylline have a concurrent URTI with compromised total-body clearance. A correction factor of 60% is recommended to adjust the dose rate during an URTI. If utilized by prescribing physicians, it may reduce theophylline toxicity during an URTI episode.

The perception of teratogenic risk of cocaine.

While there has been a substantial increase in recreational use of cocaine by young adults, conclusive evidence for cocaine teratogenicity in humans is lacking, and even those believing the drug is teratogenic agree that the rates are quite small. While counseling pregnant women on their teratogenic risk, it was our impression that there is an unrealistically high perception of reproductive risk of cocaine. We wished to quantify the perception of teratogenic risk of cocaine by the public, physicians, and by pregnant women who were counseled following gestational exposure to the drug. Women taking cocaine during the first trimester of pregnancy (n = 54), controls with post secondary education (n = 30), and physicians (n = 30) were asked, using a visual analogue scale, to quantify the teratogenic risk of cocaine and the tendency to terminate/continue the pregnancy after first trimester exposure; in the case of the "public" and physicians this was a hypothetical question. Both physicians and the controls perceived cocaine to be teratogenic (13.4 +/- 11% risk of major malformations by physicians, and 56.5 +/- 22.8% by the "public"). The controls believed cocaine to be as hazardous as thalidomide (57.2 +/- 25.6% risk for thalidomide). Asked whether they would wish to terminate such pregnancy in their family, most physicians (56%) and the controls (70%) had a greater than 50% tendency to terminate.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronopharmacology of methotrexate pharmacokinetics in childhood leukemia.

Survival has been shown to improve when maintenance therapy for acute lymphocytic leukemia in children is given at night rather during the day. We examined the possibility that diurnal variation in methotrexate pharmacokinetics may contribute to this improvement. In a crossover study, we determined the pharmacokinetics of intravenous methotrexate at 10:00 and 21:00 h in six children with standard or high-risk leukemia. During the study, children refrained from concomitant drugs (6-mercaptopurine and trimethoprim sulfamethoxazole). There was a significant fall in methotrexate plasma clearance at night (from 5.6 +/- 3 ml/min/kg to 4.7 +/- 2.3 ml/min/kg p < 0.05). Renal clearance of methotrexate tended to decrease at night and unbound renal clearance decreased significantly (from 17.5 +/- 1.7 ml/min/kg to 8.5 +/- 3.6 ml/min/kg p < 0.05). Creatinine clearance did not exhibit diurnal variation, when comparing two 12-h collections, but there was a significant decrease in the nonglomerular clearance of methotrexate (from 14.8 +/- 5.2 to 6 +/- 4 ml/min/kg). Because it is a weak organic acid, the tubular secretion of methotrexate depends on urinary pH. At night urinary pH is more acidic. This may result in more reabsorption and hence reduced renal clearance.

Pain perception and effectiveness of the eutectic mixture of local anesthetics in children undergoing venipuncture.

The emulsion of lidocaine and prilocaine (EMLA) is effective in preventing the pain of venipuncture in children. It is therefore important to identify children who could benefit the most from EMLA. We studied the safety and feasibility of two methods of application of EMLA (patch and cream) in a randomized, open-label trial of EMLA patch versus EMLA cream in 160 children with chronic diseases undergoing venipuncture. EMLA patch or cream was applied 60 to 120 min before puncture. Pain was assessed by the children using a visual analogue score. Children also scored the pain of their last puncture and the pain of removing the tape. EMLA patch and cream had similar efficacy (visual analogue scores for the venipuncture were 8.5 +/- 16 and 9.5 +/- 17 out of 100, respectively). Side effects occurred in similar frequencies in the two groups. Adhesiveness of the patch was less effective than that of the cream with Tegaderm. Age was a major determinant of pain perception; younger children recalled more severe pain in their previous puncture. Children recently diagnosed had higher visual analogue scores than those with a long history of chronic disease. We concluded that EMLA patch and cream have a similar efficacy in children undergoing venipuncture. Young children recently diagnosed with chronic disease are most likely to benefit from EMLA.

Analgesia in children with sickle cell crisis: comparison of intermittent opioids vs. continuous intravenous infusion of morphine and placebo-controlled study of oxygen inhalation.

The objectives of the study were to compare the efficacy and safety of a continuous infusion (CIV) of morphine and intermittent parenteral opioids (IPO) in children with sickle cell vaso-occlusive crises (VOCs); to determine whether 50% oxygen administration through a face mask can reduce the duration of severe pain in patients receiving CIV morphine; and to measure morphine concentration at steady state for pharmacokinetic and pharmacodynamic analysis in patients receiving CIV morphine. The study was designed as a prospective, controlled, "before-and-after" evaluation of two different analgesic regimens. For patients receiving CIV morphine, there was a randomized, double-blind, placebo-controlled study of O2 vs. air. The patients were 66 children with sickle cell disease, 3-18 years old, requiring opioid therapy for severe VOC (32 patients in phase A, 34 in phase B). The analgesic regimens were as follows: phase A: meperidine, morphine, or codeine IM or IV bolus every 3 or 4 hours; phase B: morphine sulfate, loading dose 0.15 mg followed by CIV 0.04 mg/kg/hr. The infusion rate was adjusted every 8 hours according to pain and/or symptoms of opioid toxicity. Pain assessment was by behavioral observation (BPS). In terms of results, the mean opioid dose (morphine equivalent) was similar in both groups (0.032 +/- 0.020 mg/kg/hr in phase A and 0.035 +/- 0.011 in phase B). However, the duration of severe pain was significantly shorter in phase B (0.9 +/- 1.0 days) than in phase A (2.0 +/- 1.8 days). No severe opioid toxicity was observed in either group. Oxygen did not shorten the duration of severe pain compared to the placebo group (0.94 +/- 1.08 and 0.95 +/- 1.19 days, respectively) nor did it prevent the appearance of new pain sites. Pharmacokinetic analysis was performed in 24 patients of phase B. Total body clearance (TBC) of morphine was greater in children before puberty than after (40.4 +/- 10 vs. 28 +/- 11 mL/kg/min; p < 0.05). In conclusion, in children with severe VOCs, continuous infusion of morphine provides better analgesia than intermittent opioid therapy. Fifty percent oxygen inhalation had no effect on the duration of pain.