Biomedical subjects

H Y Abdallah

Publications and source records attributed to H Y Abdallah.

8 recordsLinked to original sources

PubMed2002

Methemoglobinemia induced by topical benzocaine: a warning for the endoscopist.

Benzocaine is used routinely for topical pharyngeal anesthesia prior to upper endoscopy, to improve patient tolerance. A potentially fatal, although often unrecognized, complication of benzocaine use is methemoglobinemia. Here, we report a case of methemoglobinemia induced by benzocaine given before upper endoscopy. Rapid recognition of this complication and immediate treatment is essential to prevent complications related to significant tissue hypoxia. This case serves as an important reminder to physicians, especially endoscopists, about this serious side effect. Furthermore, we question the need for topical anesthesia for upper endoscopy in sedated patients.

Aged↗

PubMed1995

A spreadsheet program for simulation of bioequivalence and bioavailability studies.

This paper presents a spreadsheet for Excel for Windows, which simulates bioequivalence (BE) trials. The program incorporates intersubject and intrasubject variability in drug absorption and disposition as well as assay precision and the uniformity of the administered dose. The output provides confidence intervals and a pass/fail code for each study. This program is useful for simulating BE trials using widely available and simple-to-use spreadsheet programs. An example of the application of the program in assessing the influence of intrasubject variability on the outcome of BE testing of two identical formulations is also presented.

Biological Availability↗

PubMed1992

Stability and sorption of FK 506 in 5% dextrose injection and 0.9% sodium chloride injection in glass, polyvinyl chloride, and polyolefin containers.

The effects of the diluent, the storage container, light, and infusion through various types of tubing on the stability and sorption of FK 506 were studied. Solutions of FK 506 in 0.9% sodium chloride injection or 5% dextrose injection were stored at room temperature (24 +/- 2 degrees C) in glass i.v. bottles, polyvinyl chloride (PVC) minibags, and polyolefin containers. FK 506 solution in 0.9% sodium chloride injection was stored in plastic syringes at room temperature and either exposed to normal room light or stored in the dark. FK 506 solution in 5% dextrose injection was placed in plastic syringes and infused through PVC anesthesia extension tubing, PVC i.v. administration set tubing, and fat emulsion tubing over a two-hour period. The infused samples and samples collected from the containers and syringes at intervals up to 48 hours were analyzed for FK 506 concentration by high-performance liquid chromatography. FK 506 concentrations remained greater than 90% of initial concentration for admixtures in 5% dextrose injection stored in glass bottles for 48 hours and for admixtures in 5% dextrose injection or 0.9% sodium chloride injection stored in polyolefin containers for 48 hours. No change in concentration was measured for admixtures in 0.9% sodium chloride injection stored in plastic syringes, and exposure to light did not affect the stability of FK 506 solution. No substantial change in concentration occurred in FK 506 solution in 5% dextrose injection infused through PVC anesthesia extension tubing, PVC i.v. administration set tubing, or fat emulsion tubing. FK 506 admixtures prepared with 5% dextrose injection or 0.9% sodium chloride injection should be stored in polyolefin containers. If polyolefin containers are not available, solutions should be prepared with 5% dextrose injection and stored in glass bottles.

Adsorption↗

PubMed1991

The influence of age on salicylate pharmacokinetics in humans.

The pharmacokinetics of salicylate after a single oral solution dose of 600 mg of sodium salicylate were investigated in 22 male subjects. Subjects were healthy nonsmokers and were not taking any regular medication. The plasma concentration and urinary excretion of salicylic acid and its metabolite, salicyluric acid, as well as the urinary excretion of salicyl glucuronides were determined. Urinary recovery essentially accounted for the administered dose and was not influenced by age, nor was the apparent oral clearance of salicylic acid. Assuming no presystemic elimination, it could be concluded that systemic availability is unaffected by age. An increase in the apparent volume of distribution, Varea, and a decrease in the maximum plasma salicylic acid concentration with age were observed. Renal clearance of salicyluric acid decreased significantly with age and was found to correlate significantly with creatinine clearance. The authors conclude that age does not have a major influence on salicylate disposition in healthy adult men.

Administration, Oral↗

PubMed1991

Pharmacokinetics of ceftriaxone in liver-transplant recipients.

The disposition of ceftriaxone was studied after a single 2 g intravenous dose in seven patients 3 to 5 days after liver transplantation. Ceftriaxone concentrations in plasma, urine, and bile were measured by HPLC, and plasma protein binding was determined by equilibrium dialysis. Plasma protein binding was nonlinear, and the unbound fraction varied between 0.05 and 0.56. Both capacity and affinity were markedly different from reported values for normal subjects. The pharmacokinetic parameters obtained were: total body clearance (TBC), 11.2 +/- 7.8 mL/hr/kg total and 44.8 +/- 29.1 mL/hr/kg unbound; volume of distribution (V(area)), 224 +/- 76 mL/kg total and 767 +/- 432 mL/kg unbound; steady-state volume of distribution (Vss), 212 +/- 68 mL/kg total and 651 +/- 368 mL/kg unbound; terminal disposition half-life (t1/2), 21.6 +/- 14.3 hour total and 16.3 +/- 11.1 hour unbound. TBC for both total and free drug was considerably lower than literature values for normal subjects. V(area) for total drug was greater than normal, whereas the corresponding value for free drug was smaller than normal. The plasma ceftriaxone concentrations at 12 and 24 hours were above the reported minimum inhibitory concentration (MIC). The fraction of the administered dose excreted in urine over 24 hours was 38 +/- 29% and did not differ markedly from that reported for normal subjects. Less than 2% of the administered dose was excreted in 24-hour bile; however, biliary concentrations were always above MIC. Ceftriaxone can be administered once or twice daily at a dose of 2 g/day for prophylaxis in liver transplant recipients.

Adult↗

PubMed1991

The preparation and evaluation of a tablet dosage form of cyclosporine in dogs.

Cyclosporine (CsA) is commercially available for oral administration as a solution in olive oil with alcohol and an emulsifier. To improve its variable absorption and low patient acceptability, several oral formulations were prepared and tested in vitro and in vivo in dogs. A tablet formulation prepared by direct compression was then selected for comparison with the commercial oil solution placed into soft gelatin capsules. The study involved a randomized crossover design in six dogs. In order to determine absolute bioavailability and to compensate for any time-dependent changes in clearance, an intravenous tracer dose of 3H-CsA was administered along with each oral test product on each of two occasions. Absolute bioavailability (mean +/- SD) was 46.0 +/- 11.1 and 45.4 +/- 9.9% for the capsules and tablets, respectively. Cmax, tmax, and mean absorption time were not significantly different between the two products. No differences were observed in the pharmacokinetics of the intravenously administered CsA in the two experiments, which were separated by 8-13 days. We conclude that the proposed tablet formulation for CsA is equivalent in dogs to the commercial dosage form placed into soft gelatin capsules.

Administration, Oral↗

PubMed1991

In-vitro interaction of a novel immunosuppressant, FK 506, and antacids.

The effect of selected antacids on the amount of FK 506 in solution in simulated gastric juice has been studied. FK 506 (2.5 mg) was incubated in 100 mL simulated gastric fluid (SGF) with the equivalent of 500 mg of various antacids. The addition of Mylanta and Tums resulted in 14 and 30% loss of FK 506, respectively, in 24 h; 98% loss was observed in 12 h in the presence of Mag-Ox; 100% loss was observed in the presence of magnesium oxide powder in 2 h. The loss of FK 506 from these solutions appears to be due to a pH mediated degradation of FK 506. The addition of aluminium hydroxide gel USP (Roxane) to the FK 506 solution resulted in a 35% loss within 2 min but no further loss was noted for 24 h, indicative of adsorption of FK 506. These results suggest that until additional in-vivo studies are carried out, it is prudent not to dose FK 506 and antacids at the same time to avoid potential interactions.

Antacids↗

PubMedDate not supplied

An area correction method to reduce intrasubject variability in bioequivalence studies.

PURPOSE: This paper investigates the use of a corrected area (AUC*K) to compensate for intrasubject variability in bioequivalence studies. METHODS: Using computer simulation, this technique was applied to bioequivalence studies for two drugs. Both drugs exhibit first-order absorption and linear one-compartment disposition kinetics and total elimination by the liver. Drug I has a low intrinsic clearance (Cl(int)) and is not bound to blood components, while Drug II has a high Cl(int) and is highly bound. Two-way crossover trials, each including 24 subjects, were simulated using a spreadsheet program, which also performs ANOVA and provides 90% confidence intervals for C(max), AUC and AUC*K. The intrasubject CV for the parameter of interest was 30%. For all other pharmacokinetic parameters, the intrasubject CVs were 10%. RESULTS: Drug I: With high variability in Cl(int), AUC's were concluded to be bioequivalent in 335, 303, 222, 102 and 32 of 500 trials for mean difference in % absorbed (DeltaA = [A(test) -A(ref)]x100/A(ref)), -5%, -10%, -15% and -20% respectively. The corresponding numbers of trials that passed for AUC*K were 500, 500, 500, 382 and 23. Drug II: With high variability in Cl(int), 273, 281, 190, 106 and 29 of 500 trials passed for AUC at DeltaA of 0%, -5%, -10%, -15% and -20% respectively. The corresponding numbers that passed for AUC*K were 378, 351, 239, 113 and 38 trials. For both drugs, when high variability was assigned to V, area correction reduced the number of trials passing for AUC. When the same intrasubject %CV was assigned to both Cl and V, area correction resulted in no change (Drug I) or a decrease (Drug II) in the number of passing trials. Assigning high intrasubject %CV to DeltaA did not appear to alter the outcome of the simulation. CONCLUSION: Area correction appears to be helpful only when high intrasubject variability exists in clearance and not in the other parameters. It may be more helpful for drugs with low, compared to high Cl(int) since in the latter case variability in Cl(int) is reflected in both systemic clearance and bioavailability. It is recommended that area correction be attempted in bioequivalence studies of drugs where high intrasubject variability in clearance is known or suspected. It should be avoided where there appears to be a difference in K between treatments. The value of this approach in regulatory decision making remains to be determined.

Humans↗