Stability of gentamicin sulfate and tobramycin sulfate in extemporaneously prepared ophthalmic solutions at 8 degrees C.

The stability of gentamicin sulfate and tobramycin sulfate in fortified ophthalmic solutions stored under refrigeration was studied. Fortified gentamicin ophthalmic solution and fortified tobramycin ophthalmic solution were prepared to a final theoretical concentration of 13.6 mg/mL by using commercially available ophthalmic and injectable solutions. Volumes of each solution were packaged in plastic bottles and refrigerated at 4-8 degrees C. Samples of each solution were analyzed by fluorescence polarization immunoassay on days 0 (before refrigeration), 1, 2, 3, 4, 7, 14, 28, 63, and 91. To validate the method, identical solutions were prepared, stored under refrigeration at 4-8 degrees C, and analyzed by a stability-indicating high-performance liquid chromatographic assay on days 0 (before refrigeration), 9, 28, 56, and 91. Fluorescence polarization immunoassay showed the mean concentrations of gentamicin and tobramycin on day 91 to be 104.4% and 97.4%, respectively, of the time 0 concentrations; the difference was not significant in either case. HPLC validated these results; the mean concentration of gentamicin and tobramycin on day 91 was 103.3% and 101.2%, respectively, of the mean day 0 concentrations. Gentamicin and tobramycin in ophthalmic solutions prepared by mixing ophthalmic and injectable products and stored in plastic bottles at 4-8 degrees C were stable for three months.

Pharmacokinetic comparison of 5 g of azlocillin every 8 h and 4 g every 6 h in healthy volunteers.

To compare the multiple-dose pharmacokinetics of two dosage regimens of azlocillin, we studied 12 healthy volunteers via a randomized, crossover design with a 2-week washout phase between regimens. Serum and urine samples were collected for 8 h following the fifth dose of a regimen of 4 g every 6 h and the fourth dose of a regimen of 5 g every 8 h. Data for concentrations in serum were fitted to a two-compartment open model by nonlinear regression. Statistically significant differences (P less than 0.05) were observed in the following parameters (mean +/- standard deviation) for the 4- and 5-g regimens, respectively: area under the serum concentration-time curve during the dosing interval, 592 +/- 140 versus 772 +/- 151 micrograms.h/ml; terminal elimination rate constant, 0.5364 +/- 0.0912 versus 0.4758 +/- 0.0486 h-1; renal clearance, 87.6 +/- 16.1 versus 76.1 +/- 13.5 ml/min; maximum drug concentration in serum, 381 +/- 89 versus 473 +/- 90 micrograms/ml; and minimum drug concentration in serum, 19 +/- 10 versus 8 +/- 4 micrograms/ml. No significant differences were seen in the following parameters: V1, V beta, k10, k12, k21, total systemic clearance, and nonrenal clearance. These data support the presence of saturable renal elimination of azlocillin, as well as the feasibility of an 8-h dosing interval.

Phenytoin-induced hypersensitivity reactions.

A case of phenytoin-induced hepatitis with mononucleosis is reported, and syndromes associated with phenytoin hypersensitivity reactions are discussed. A 23-year-old black woman with a two-month history of seizure disorder was admitted to a hospital with nausea, vomiting, fever, lymphadenopathy, diffuse maculopapular rash, left-upper-quadrant tenderness, and hepatomegaly. She was receiving phenytoin sodium 300 mg/day; carbamazepine 200 mg four times daily had been discontinued four days before admission because of leukopenia. Phenytoin was discontinued after admission; however, phenytoin 1 g i.v. was given for a tonic-clonic seizure two days after admission, after which swelling of the face and legs and pruritus developed. Over the next few days, signs and symptoms of hepatotoxicity progressed, and she became comatose. Seizures were treated with diazepam. She began to recover after 10 days of supportive therapy and was discharged several weeks later on primidone therapy. Serious phenytoin hypersensitivity reactions may appear as dermatologic, lymphoid, or hepatic syndromes. Fever, rash, and lymphadenopathy often accompany hepatic injury. Encephalopathy and death may occur. Proposed mechanisms for phenytoin hypersensitivity include antigen-antibody reactions, alteration of lymphocyte function, and an enzyme abnormality causing the production of toxic metabolites. Treatment is supportive; phenobarbital and carbamazepine may be used with caution as alternate anticonvulsant therapy. The possibility of phenytoin hypersensitivity reactions should be considered when patients receiving phenytoin have unusual symptoms, particularly fever, rash, and lymphadenopathy.

The effect of in-line filtration on tobramycin delivery.

The purpose of this study was to determine if the presence of an in-line 0.22 mu cellulose ester membrane filter would hamper the delivery of a common adult dose of tobramycin sulfate. Solutions of tobramycin sulfate 80 mg in 100 ml D5W were assayed after 30 minute infusions through unfiltered and filtered administration sets; solutions post-flush of filtered sets were also assayed. Assay was done by Emit-QST. The results indicated that there was no significant difference in the delivery of tobramycin sulfate, regardless of the presence of an in-line filter. Solutions post-flush contained about ten percent of the drug, reflecting the amount in solution that remained in the tubing. Since ten percent can alter pharmacokinetic monitoring for patient dosing, a consistent procedure for flushing filtered administration sets should be adopted to enhance accuracy of such determinations.