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Biomedical subjects

A Forrest

Publications and source records attributed to A Forrest.

At least 91 records · Page 5Linked to original sources
PubMed1987

Steady-state pharmacokinetics of imipenem in febrile neutropenic cancer patients.

We ascertained the pharmacokinetics of imipenem in febrile granulocytopenic cancer patients. The values observed were both different from and significantly more variable than those observed in normal volunteers. Free drug concentrations exceeded the MIC for 90% of Escherichia coli, Klebsiella pneumoniae, and Staphylococcus aureus strains for greater than 6 h. The MIC for 90% of Pseudomonas aeruginosa strains was exceeded for 4 h. Because imipenem induces a 2-h postantibiotic effect in P. aeruginosa, it is promising as single-agent empiric therapy in this setting.

Adult↗
PubMed1986

Imipenem coadministered with cilastatin compared with moxalactam: integration of serum pharmacokinetics and microbiologic activity following single-dose administration to normal volunteers.

We administered 1 g of imipenem along with equal amounts of cilastatin (a dehydropeptidase I inhibitor) or 2 g of moxalactam intravenously over a period of 30 min to six volunteers in a crossover manner 1 week apart. The antibiotic concentrations and pharmacokinetics for each drug were determined and integrated with the microbiologic activity by measuring the duration of time that the free drug concentrations remained above the MICs for 90% of 581 clinical isolates and by measuring serum bactericidal activities against organisms which commonly infect granulocytopenic cancer patients. Moxalactam produced serum levels at 1 h after infusion of 99.9 micrograms/ml; these levels were four times greater than the plasma levels of imipenem (22.8 micrograms/ml). The trough (5.5-h) moxalactam serum levels were 10 times greater than those of imipenem (18.5 and 1.7 micrograms/ml, respectively). Essentially all of the imipenem was unbound to protein, whereas 36 to 42% of the moxalactam was unbound. Moxalactam produced free antibiotic concentrations that were above the MIC for 90% of the strains tested for more than 6 h against all of the species tested except Staphylococcus aureus (5.3 h), Enterobacter hafnia (1.6 h), and Pseudomonas aeruginosa (0 h). The imipenem concentrations were above the MIC for 90% of the strains tested for 5.6 h or more against all of the bacteria tested except Proteus spp. and Pseudomonas aeruginosa (4.5 h). The geometric mean peak bactericidal titers from volunteers receiving imipenem were more than 1:8 against all bacteria and were significantly higher than the titers from volunteers receiving moxalactam against S. aureus (1:7.3) and Pseudomonas aeruginosa (1:4.5). These data, in addition to information obtained from animal models, indicate that imipenem is a promising new candidate for carefully controlled clinical trials as a single agent for therapy of serious infections, including empiric therapy for fever in granulocytopenic cancer patients.

Adolescent↗
PubMed1986

Steady-state serum pharmacokinetics of novobiocin and rifampin alone and in combination.

Because of the potential of novobiocin-rifampin for oral therapy of methicillin-resistant Staphylococcus aureus infection, we evaluated the pharmacokinetics of novobiocin and rifampin, alone and in combination, in a randomized, crossover, multiple-dose evaluation (500 mg of novobiocin and 300 mg of rifampin administered orally, twice a day, for 27 doses) in 10 volunteers. The half-lives of novobiocin and rifampin when administered alone were 5.85 +/- 1.20 and 1.46 +/- 0.30 h, respectively; when administered in combination, the half-lives were 2.66 +/- 0.65 and 1.43 +/- 0.29 h, respectively. This difference was significant for novobiocin. The area under the curve also differed significantly for novobiocin when administered in combination. No significant differences were seen in the maximum concentration of drug in serum, the time to maximum concentration of drug in serum, or both for either drug when single and combination therapy groups were compared. A change in clearance of novobiocin rather than a change in absorption is the more likely explanation for these findings. The mechanism remains to be elucidated. Nevertheless, the trough serum concentrations of both novobiocin and rifampin were in excess of the MIC for 90% of strains tested of methicillin-resistant S. aureus, even when coadministered.

Adolescent↗
PubMed1986

Dose ranging study and constant infusion evaluation of ciprofloxacin.

We evaluated the pharmacokinetics of 100- and 200-mg doses of ciprofloxacin, with the 200-mg dose administered either as a 30-min infusion or as a 100-mg loading dose followed by a 4-h constant infusion of 25 mg/h in six normal volunteers. No significant differences were seen in the dose-normalized area under the curve when the 100- and 200-mg 30-min administrations were compared. Differences that approached statistical significance were seen when data from either of these trials were compared with data from the constant-infusion arm. Serum clearances averaged 23.0 +/- 9.1 liters/h per 1.73 m2 for the 100-mg dose and 23.7 +/- 5.1 liters/h per 1.73 m2 for the 200-mg dose. Renal clearance accounted for approximately two-thirds of the serum clearance in each instance. Half-lives were slightly longer than 4 h. For the constant-infusion arm, serum clearance was 28.9 +/- 2.7 liters/h per 1.73 m2, with renal clearance accounting for 58% of serum clearance. Although no nonlinearities were apparent in the 100- to 200-mg dose range, larger doses, particularly in the multiple-dosing situation, may uncover nonlinearity in the disposition of ciprofloxacin.

Adult↗
PubMed1986

Absolute oral bioavailability of ciprofloxacin.

We evaluated the absolute bioavailability of ciprofloxacin, a new quinoline carboxylic acid, in 12 healthy male volunteers. Doses of 200 mg were given to each of the volunteers in a randomized, crossover manner 1 week apart orally and as a 10-min intravenous infusion. Half-lives (mean +/- standard deviation) for the intravenous and oral administration arms were 4.2 +/- 0.77 and 4.11 +/- 0.74 h, respectively. The serum clearance rate averaged 28.5 +/- 4.7 liters/h per 1.73 m2 for the intravenous administration arm. The renal clearance rate accounted for approximately 60% of the corresponding serum clearance rate and was 16.9 +/- 3.0 liters/h per 1.73 m2 for the intravenous arm and 17.0 +/- 2.86 liters/h per 1.73 m2 for the oral administration arm. Absorption was rapid, with peak concentrations in serum occurring at 0.71 +/- 0.15 h. Bioavailability, defined as the ratio of the area under the curve from 0 h to infinity for the oral to the intravenous dose, was 69 +/- 7%. We conclude that ciprofloxacin is rapidly absorbed and reliably bioavailable in these healthy volunteers. Further studies with ciprofloxacin should be undertaken in target patient populations under actual clinical circumstances.

Adult↗
PubMed1986

Human pharmacokinetics, excretion, and metabolism of the anthracycline antibiotic menogaril (7-OMEN, NSC 269148) and their correlation with clinical toxicities.

In a Phase I study, menogaril (7-OMEN) was administered daily for 5 days/course, every 21-28 days. Dosages of 3.5, 7, 11.5, 17, and 31.5 mg/m2 were infused over 1 h, and dosages of 42, 50, and 56 mg/m2 were infused over 2 h. Pharmacokinetics was studied at all dosages. Plasma and urine samples were collected from 24 patients, and bile samples were also collected from 2 patients. 7-OMEN and metabolites were measured by high performance liquid chromatography. 7-OMEN was the major plasma fluorescent species at all times, with only trace amounts of N-demethyl menogaril observed. 7-OMEN disappeared from plasma biexponentially with t1/2 alpha 0.19 +/- 0.04 (mean +/- SE) h and t1/2 beta 13.22 +/- 1.54 h. Plasma pharmacokinetics of 7-OMEN was linear from 3.5-56 mg/m2; area under the curve increased proportionally with dosage. Total body clearance of 7-OMEN was 28.18 +/- 3.33 liter/m2/h, Vc was 224 +/- 30.8 liter/m2, and Vss was 370 +/- 25.7 liter/m2. Plasma pharmacokinetics of 7-OMEN studied on multiple days of a given course were similar. Urinary excretion of 7-OMEN and fluorescent metabolites accounted for 5.4 +/- 0.4% of the daily dose. Parent compound still represented greater than or equal to 80% of urinary drug fluorescence after 24 h. N-demethyl menogaril was the only other fluorescent drug species detected in urine. In two patients with biliary tract drains, biliary excretion of drug fluorescence accounted for 2.2-4.2% of the daily dose. Only 7-OMEN and N-demethyl menogaril were detected in bile by high performance liquid chromatography and thin layer chromatography. 7-OMEN was the major fluorescent biliary species, but, by 24 h, N-demethyl menogaril accounted for approximately 40% of biliary drug fluorescence. When considered in light of each patient's observed toxicities, excellent relationships were observed between the plasma area under the curve of 7-OMEN and the percentage of decreases in WBC and absolute neutrophil count. These latter findings should be useful in developing more precise and intelligent dosing schemes for 7-OMEN.

Antineoplastic Agents↗
PubMed1985

Safety and tolerability of multiple doses of imipenem/cilastatin.

The safety and tolerability of 1 gm imipenem and cilastatin given together every 6 hours for 10 days was evaluated in a randomized, double-blind, placebo-controlled trial in normal subjects. Nausea was more common in the drug-treated group (five of six subjects) than in the control group (two of six subjects). No consistent changes in hepatic function indices were noted. Although beta 2-microglobulin excretion showed a significant trend of rising over time in the drug group, there were no differences between groups with regard to 24-hour urinary excretion of either N-acetyl-beta-glucosaminidase or beta 2-microglobulin. Urinalysis did not reveal any casts and serial creatinine clearance determinations showed no change in renal function in either the drug- or placebo-treated groups. Pure tone audiograms were performed before and after dosing in 11 of 12 subjects; no changes were noted. We conclude that the combination of imipenem and cilastatin was well tolerated and safe.

Acetylglucosaminidase↗
PubMed1985

Pharmacokinetics of ceftazidime, alone or in combination with piperacillin or tobramycin, in the sera of cancer patients.

We administered 2 g of ceftazidime intravenously every 8 h to cancer patients for the empiric therapy of febrile episodes. Ceftazidime was administered as monotherapy for patients with granulocyte counts in excess of 1,000/microliter. Febrile, neutropenic patients were randomized to also receive either piperacillin or tobramycin. The pharmacokinetic profile of ceftazidime during a steady-state dosing interval was ascertained in 21 patients. No differences were seen between groups for any of the pharmacokinetic parameters examined. As expected, the observed half-life was longer, the serum clearance was smaller, and the volumes of distribution were larger than in previously reported studies of volunteers. Serum concentrations remained above the MIC for inhibition of 90% of strains of the most common bacteremic pathogens seen in our cancer center for the entire 8-h dosing interval.

Adolescent↗
PubMed1985

Multiple-dose pharmacokinetics of ciprofloxacin administered intravenously to normal volunteers.

We administered multiple doses of ciprofloxacin intravenously over 30 min every 12 h for 1 week to nine healthy volunteers. Three volunteers received a placebo (vehicle) intravenously. Doses of 100, 150, and 200 mg were evaluated with a 1-week wash-out period intervening between each dose level. Terminal excretion half-lives averaged 3.67 +/- 0.65, 3.60 +/- 0.26, and 4.00 +/- 0.69 h for the 100-, 150-, and 200-mg doses, respectively. Serum clearances were 30.1 +/- 3.4, 29.8 +/- 4.0, and 26.9 +/- 4.1 liters/h per 1.73 m2 for these doses. Urine concentrations remained in excess of the MIC for 90% of the relevant urinary tract pathogens for the full 12-h dosing interval at each dose. Renal clearance accounted for 56 to 71% of the serum clearance. However, because a microbiologic assay was used and biologically active, renally excreted metabolites were identified, the renal clearance determinations are likely to be in excess of the true values. The doses of ciprofloxacin administered intravenously were well tolerated, and the drug concentrations appeared adequate for the treatment of the vast majority of cases of nosocomially acquired sepsis and urinary tract infections. For patients with serious Pseudomonas infections and perhaps staphylococcal infections, either an 8-h dosing schedule or larger doses on a 12-h schedule should be considered.

Adolescent↗
PubMed1985

Prospective validation of a pharmacologically based dosing scheme for the cis-diamminedichloroplatinum(II) analogue diamminecyclobutanedicarboxylatoplatinum.

We previously correlated both renal function and thrombocytopenia, the dose limiting toxicity of carboplatin, with the plasma pharmacokinetics of carboplatin. From these correlations, we developed equations to calculate carboplatin dosage for any patient based on that patient's creatinine clearance, body surface area, pretreatment platelet count, desired platelet nadir, and status of prior chemotherapy. We prospectively applied these equations in 44 courses of carboplatin given to 24 patients. There were 13 males and 11 females with median age 53 (range, 33-77), median Karnofsky performance status 80 (range, 50-100), and creatinine clearance 32 to 118 ml/min. Ten patients had creatinine clearances less than 60 ml/min. Precision of the equations used for dose calculation was evaluable in 38 courses administered to 23 patients. In 23 courses of carboplatin administered to 12 patients without extensive prior chemotherapy, the observed change in platelets = 1.04 X predicted change -48,000 (r = 0.96). In the 15 courses of carboplatin administered to 11 heavily pretreated patients, the observed change in platelets = 1.13 X predicted change +6,600 (r = 0.97). For the overall combined population, the observed change in platelets = 0.96 X predicted change -7,000 (r = 0.94). These relationships which nearly define the line of identity (observed = expected) validate our initial observations. Only 2 patients developed WBC less than 2,000, but 12 patients developed hematocrit less than or equal to 29% and 8 required RBC transfusions. Fifteen patients had nausea and vomiting greater than or equal to grade 2. There were no other nonhematological toxicities observed. In view of continuing documentation of the antitumor activity of carboplatin, these equations allow safe and rational drug dosing of patients with potentially platinum-responsive tumors but with renal function too poor to receive cisplatin. Among the 9 patients in this study evaluable for response, there was 1 partial response in a patient with malignant melanoma and 1 objective response (less than partial response) in a patient with adenocarcinoma of the cervix.

Blood Cell Count↗
PubMed1984

The plasma pharmacokinetics of high dose (1 g) imipenem coadministered with 1 g cilastatin in six normal volunteers.

The plasma pharmacokinetics of imipenem, a beta-lactam antibiotic of the new class of carbapenems, was evaluated by administering 1 g imipenem plus 1 g of the dehydropeptidase inhibitor cilastatin to six healthy male volunteers over 30 min. Subsequently intensive plasma sampling was done for 5.5 h. The volume of distribution of the central compartment was 0.16 +/- 0.04 1/kg; the volume of distribution (area) was 0.28 +/- 0.07 1/kg; the volume of distribution (steady state) was 0.23 +/- 0.03 1/kg. The mean plasma clearance was 10.1 +/- 1.0 1/h/1.73 m2. Model-independent analysis showed excellent agreement with these values. The terminal excretion half-life was short (1.3 +/- 0.4 h). For approximately 6 h after administration, the observed plasma levels were above those required to inhibit most nosocomial pathogens in vitro.

Adolescent↗
PubMed1984

Effect of saturable clearance during high-dose mezlocillin therapy.

As mezlocillin has been shown to display nonlinear pharmacokinetics in single-dose evaluations, we evaluated a crossover trial in patients with renal dysfunction the impact on serum clearance of fixed-dose versus fixed-interval administration of identical daily doses of the drug. In four patients with creatinine clearances of 0.00 to 1.78 liters/h per 1.73 m2, equal serum clearances were observed when the calculated daily total dose of mezlocillin was given either as a fixed dose of 5,000 mg at various intervals or every 4 h at various doses. We found that repetitive large daily doses that are equivalent to 30 g/day in patients with normal renal function can be administered to patients with impaired renal function as a reduced dose every 4 h instead of prolonging the dosing interval, as suggested by Mangione et al. (Antimicrob. Agents Chemother. 21:428-435, 1982). The observed serum clearances were equal for the two schedules, probably owing to the degree of continuing saturation of the nonlinear clearance mechanisms of mezlocillin.

Adult↗
PubMed1984

Multiple-dose pharmacokinetics of imipenem-cilastatin.

We characterized the pharmacokinetic profile of imipenem-cilastatin administered intravenously to six normal volunteers in a dose of 1,000 mg of each drug every 6 h for 40 doses. The plasma concentrations of imipenem and cilastatin 1 h after the end of a 30-min infusion were 18.7 (+/- 2.1) and 19.1 (+/- 4.6), 20.0 (+/- 3.2) and 17.8 (+/- 4.8), and 23.4 (+/- 2.3) and 19.1 (+/- 3.5) micrograms/ml in the 1st, 17th, and 37th dosing intervals, respectively. The central compartment volumes of distribution for imipenem and cilastatin were 0.16 (+/- 0.05) and 0.14 (+/- 0.03) liter/kg, respectively. Elimination half-lives were short: 0.93 (+/- 0.09) h for imipenem and 0.84 (+/- 0.11) h for cilastatin. Plasma clearances were 12.1 (+/- 0.06) liters/h per 1.73 m2 for imipenem and 12.4 (+/- 1.1) liters/h per 1.73 m2 for cilastatin. Renal clearance accounted for 54% of the plasma clearance of imipenem and 69% of the plasma clearance of cilastatin. The concentrations of imipenem in plasma and urine remained above the MICs of the vast majority of pathogens throughout the dosing interval.

Adult↗
PubMed1980

Influence of surgery on plasma propranolol levels and protein binding.

The influence of surgery and anesthesia on perioperative plasma propranolol levels was studied in 25 hyperthyroid and five euthyroid patients undergoing thyroidectomy. Propranolol levels fell markedly after surgery as a consequence of poor drug administration in the immediate postoperative period due largely to patients' nausea and inability to swallow. Propranolol was not detectable in the plasma of three hyperthyroid patients 8 hr after surgery. When propranolol was given through a nasogastric tube, propranolol levels were satisfactory throughout. Compared with preoperative levels, in all patients there was a two- to threefold rise in total and free propranolol levels 24 hr after surgery, suggesting decreased hepatic clearance of propranolol. The degree of plasma protein binding of propranolol had also increased on the day after surgery, leading to a 30% reduction in propranolol free fraction. Surgery and anesthesia greatly influence the handling of propranolol in the perioperative period.

Absorption↗
PubMed1980

Propranolol dosage in thyrotoxicosis.

Eighteen thyrotoxic patients receiving chronic treatment with propranolol (160 mg/day) were studied to determine the relationship between plasma propranolol concentration and drug effect. There was a considerable interindividual variability in both the plasma propranolol steady state concentration and the degree of beta-adrenergic blockade. The plasma propranolol steady state concentration correlated significantly with both beta-adrenergic blockage and weight change but not with the degree of subjective improvement. In a group of 40 patients, including 10 severely thyrotoxic patients, who had the dosage of propranolol titrated objectively preoperatively to bring about a greater than 25% reduction in exercise heart rate at the end of a dosage interval, no case of thyroid storm was encountered. Many patients, the younger and severely thyrotoxic in particular, require doses in excess of 160 mg/day to achieve this degree of beta-adrenergic blockade.

Adolescent↗
PubMed1977

Controlled randomized group comparison of nomifensine and imipramine in depressive illness.

1. Nomifensine, an isoquinoline dopaminergic agonist, was investigated in a randomized double-blind group comparison with imipramine, in 40 out-patients with depression. 2. Assessments were made at weekly intervals for 4 weeks using the Hamilton Depression Scale and the Beck Depression Inventory. Blood, kidney and liver function were also monitored weekly. 3. Nomifensine was shown to be at least as effective as imipramine in relieving depression and to relieve tha anxiety component of the disease significantly more rapidly. Neither drug produced serious unwanted effects.

Adult↗
PubMed1975

Subcultural mental handicap.

Some conceptual problems in relation to the interaction of genetic influence and social disadvantagement are discussed, and some of the results of a study of 144 families with mentally handicapped children reported. The work of Heber and his associates in Milwaukee is briefly reviewed, and the Edinburgh data discussed in relation to the study in Aberdeen by Birch et al. (1970). Possible strategies for intervention are considered.

Adaptation, Psychological↗