Effects of cefotaxime on the serum protein binding of sulfisoxazole.

The possible acylating effects of cefotaxime on sulfisoxazole binding to serum proteins were evaluated in vitro in samples of human sera incubated with 50-1000 micrograms ml-1 cefotaxime at 37 degrees for 1 h and then dialyzed against saline. This incubation resulted in concentration-related increases in the free fraction of sulfisoxazole (+25 per cent, +30 per cent, and +45 per cent, with 250, 500, and 1000 micrograms ml-1 cefotaxime, respectively). Sulfisoxazole binding was also studied in samples of sera from patients given prophylactic cefotaxime (3 g d-1, IV) following elective surgery. Sulfisoxazole free fraction increased from 7.6 +/- 0.7 per cent in samples obtained before starting treatment to 9.2 +/- 0.8 per cent 24 h thereafter, and to 10.4 +/- 1.0 per cent after 5 days of treatment, but this difference was not statistically significant. A Scatchard plot of pooled samples showed a reduction in overall affinity (from 2.38 X 10(-4) M to 1.77 X 10(-4) M) without changes in the number of binding sites. The effects of cefotaxime on sulfisoxazole binding and kinetics were also studied experimentally in the rabbit. Treatment with 30 mg kg-1 cefotaxime t.i.d. for 2 days increased the unbound fraction of sulfisoxazole in vivo, from 17.2 +/- 2.9 per cent to 27.3 +/- 3.6 per cent (p less than 0.02). Treatment with high doses of cefotaxime, and perhaps other 3-acetoxymethylcephalosporins, may result in changes in the serum protein binding of some acidic drugs.

Decrease in penbutolol central response as a cause of changes in its serum protein binding.

Penbutolol is a beta-adrenoceptor antagonist that is extensively bound to alpha 1-acid glycoprotein (alpha 1-AGP), a protein that increases in inflammatory diseases thereby binding more drug in such conditions. Changes in serum binding can lead to modifications in the pharmacokinetics and pharmacodynamics of a drug, therefore, the central effect (as the anticonvulsant response) and brain uptake of penbutolol given intravenously to mice with experimental inflammation have been measured. A significant decrease of the central effect of penbutolol and its brain uptake was seen in diseased when compared with control animals (P less than 0.01). A parallel decrease in free fraction of penbutolol in diseased vs normal animals was detected. These results suggest that there is an increase in serum binding of basic drugs related to increments in alpha 1-AGP concentration, which reduces their central pharmacological effect.

Serum protein binding of sulfisoxazole and diazepam in patients with chronic obstructive pulmonary disease.

Binding of two acidic drugs, sulfisoxazole and diazepam, to serum proteins has been investigated in patients with chronic obstructive pulmonary disease and in a control group of healthy volunteers. Marked increases in the free fraction of both drugs in serum were detected in patients (14.5 +/- 0.8% versus 6.1 +/- 0.3% in the case of sulfisoxazole, and 5.8 +/- 0.5% versus 3.2 +/- 0.0% in the case of diazepam). Decreased serum albumin concentration appeared to play a role in the defective binding of sulfisoxazole, although when this factor was corrected, some correlation between serum binding of sulfisoxazole and PaO2 values was detected. Other factors have to be considered to explain the decreased binding of diazepam in the serum of patients with chronic obstructive pulmonary disease.

Relationship between changes in seromucoid concentrations and the rate of oxidation or acetylation of several substrates.

This study was carried out to assess the relationship between turpentine-induced elevation of seromucoids and drug metabolism. Six groups of rats were used; one of them received 1 ml of turpentine sc, another received 1 ml of turpentine by gavage (po), and a third group received, ip, 80 mg/kg of phenobarbital daily for 3 days. Three control groups received saline instead of turpentine. Forty-eight hr later, the serum seromucoids were assayed and the rates of N-demethylation of aminopyrine, O-dealkylation of 7-ethoxycoumarin, and hydroxylation of aniline and total cytochrome were determined in liver microsomes. When turpentine was administered sc, seromucoids increased from 3.15 +/- 0.18 to 16.13 +/- 0.84 g/dl (mean +/- SE) (p less than 0.01), but the rates of N-demethylation (p less than 0.01), of O-dealkylation (p less than 0.01) and of hydroxylation (p less than 0.05) were all decreased. In the rats receiving turpentine po, seromucoids remained unchanged, but the rates of N-demethylation and O-dealkylation as well as the concentration of total cytochrome increased (p less than 0.01). Phenobarbital enhanced significantly the rates of N-demethylation, O-dealkylation, and hydroxylation and the total concentration of cytochrome, without modifying the concentration of seromucoids. In another set of experiments we assessed whether turpentine-induced inflammation would affect the in vivo rate of acetylation of sulfamethazine; the results show that inflammation does not affect the rate of acetylation, despite an important increase in seromucoids. It is concluded that, under the present experimental conditions, there is no direct relationship between changes in seromucoids and the rate of drug metabolism.

Differential effects of valproic acid on the serum protein binding of lorazepam and diazepam.

Valproic acid and free fatty acids have been shown to displace diazepam from its plasma binding sites both in vitro and in vivo. Since lorazepam exhibits a substantial degree of binding, but differs from other benzodiazepines in that no increase in its free fraction in serum is observed when free fatty acids are raised, the effect of valproate on the serum protein binding of diazepam and lorazepam was assessed. Sodium valproate produced a marked increase in the free fraction of diazepam, but practically no effect on the percentage of free lorazepam.

Serum protein binding of model acidic drugs in smokers and non-smokers.

The serum protein binding of sulfisoxazole (sulfafurazole, INN) and diazepam, drugs that bind to the two main binding sites for acidic drugs on albumin, has been studied in young smokers and non-smokers. No differences between the two groups could be detected with regard to the serum protein binding of either drug. Thiocyanate, present in relatively large amounts in the serum of smokers, does not seem to affect the drug-binding properties of serum proteins.

Morphine-induced skin wheals: a possible model for the study of histamine release.

We evaluated the ability of morphine to release histamine when injected intradermally in man. Mathematic analysis of the dose-response (wheal) relationship suggested that two different effects were involved. The effect of low doses of morphine (0.05 to 1 microgram) was clearly antagonized by naloxone (0.4 or 1.2 mg im 30 minutes before), whereas the effect of higher doses (5 to 50 micrograms) was not modified. The median effective doses of morphine (ED50) for the low dose range effect were 0.07 +/- 0.01 and 0.08 +/- 0.01 microgram before naloxone and 0.14 +/- 0.02 and 0.15 +/- 0.03 microgram after 0.4 and 1.2 mg doses, respectively. Astemizole (45 mg po 30 minutes before) and oxatomide (60 mg po 120 minutes before) produced similar inhibition of histamine-induced wheals, but there were clear differences in their effects on wheals elicited by morphine. Morphine ED50 values for the low dose range effect rose from 0.09 +/- 0.01 to 0.20 +/- 0.01 microgram after astemizole and from 0.08 +/- 0.01 to 0.46 +/- 0.04 microgram after oxatomide. Opiate receptors may be involved in some of the effects produced by morphine injection in the human skin, but morphine-induced wheals seem to offer a suitable model for the evaluation of agents capable of inhibiting histamine release in man.

Carbamylation of proteins and sulfacetamide free fraction in serum in experimentally-induced high blood urea states.

The aims of this study were to investigate the time course of carbamylation of serum proteins in animals with experimental renal failure (RF) or with high blood urea levels without RF and finally, to document the effect of these states on the binding of sulfacetamide. RF (mean serum creatinine of 24.5 mg/dL and BUN 190 mg/dL) was originated by administrating i.v. uranyl nitrate. Uremia (mean BUN of 94 mg/dL and serum creatinine of 1.3 mg/dL) was induced by giving multiple doses of urea by gavage. RF was associated with a marked increase in the carbamylation of serum proteins and in the free fraction of sulfacetamide (Sff), but the degree of carbamylation did not correlate with Sff. Uremia without RF increased the carbamylation of serum proteins and in this case, the degree of carbamylation correlated with Sff. It is concluded that in vivo, carbamylation of serum proteins modifies, in a limited manner, drug binding to serum protein.

Serum protein binding of tolbutamide in patients treated with antiepileptic drugs.

The possible development of a displacement interaction involving tolbutamide, in epileptic patients, has been explored by studying the serum protein binding of this drug in vitro in 199 samples of sera from patients treated with antiepileptic agents included in a programme of therapeutic drug monitoring. 82 of the samples were from patients receiving a single drug, 86 from patients treated with 2 drugs, and 31 from patients treated with 3 drugs. The free fraction of tolbutamide was higher in serum from patients treated with antiepileptic drugs than in serum from untreated 'normal' volunteers. The increase was more marked the greater the number of antiepileptic drugs administered. Valproate appeared to be the most powerful displacing agent.

Underestimation of albumin content by bromocresol green, induced by drug displacers and uremia.

Phenylbutazone and clofibric acid, two drugs strongly bound to human albumin, produce low readings of albumin content in serum when the bromocresol green immediate reaction is used. This abnormality is observed at drug concentrations within the range obtained during therapeutic use, and tends to be more marked in diluted samples of serum. Abnormally low values of albumin content are also obtained when the bromocresol green method is used in uremic sera, and the disparity seems related to the degree of carbamylation of these samples. The reported interferences are great enough in some cases as to suggest that the use of the immediate reaction between bromocresol green and serum should not be considered a valid measure of albumin content when these factors cannot be totally excluded.

Abnormal serum protein binding of acidic drugs in diabetes mellitus.

Nonenzymatic glycosylation of proteins is common in diabetes mellitus and glycosylation of serum albumin in this condition has been described. To evaluate whether glycosylation of albumin affects acidic drug binding, sulfisoxazole and diazepam binding was examined in samples of normal serum incubated with glucose and in samples of serum from 42 patients with diabetes mellitus. Incubation of normal serum with 20mM glucose for several days resulted in progressive glycosylation of proteins, with decreased binding of sulfisoxazole (100 micrograms/ml) but not of diazepam (3 micrograms/ml). Free fractions of sulfisoxazole and diazepam were higher in serum from patients with diabetes. The percentage of free sulfisoxazole in serum from 10 normal subjects was 5.1% +/- 0.2%, whereas it was 16.0% +/- 1.3% in serum from 42 patients with diabetes with varying degrees of carbohydrate control. The percentage of free diazepam in plasma was 2.6% +/- 0.1% in the normal group and 3.6% +/- 0.4% in patients with diabetes. Decreased serum albumin levels, increased levels of free fatty acids, and glycosylation of plasma proteins seem to play a role in the defective acidic drug binding in diabetes. Elevated free fatty acid levels explain the abnormal binding of diazepam and the increased free fraction of sulfisoxazole is directly related to glycosylation of plasma proteins.