Decrease in penbutolol protein binding as a consequence of treatment with some alkylating agents.

The effect of in vitro treatment of serum with the alkylating agents carmustine (BCNU) and mechlorethamine on the protein binding of penbutolol, a basic agent mainly bound to alpha 1-acid glycoprotein (AAG), was investigated. The free fraction of penbutolol increased significantly (P < 0.001) after the treatment of serum with BCNU (5.27+ +/- 0.47%) and with mechlorethamine (5.23% +/- 0.17%), being 1.98% +/- 0.18% in serum not treated with BCNU or mechlorethamine. In addition, after incubation with BCNU (2 h), the free fraction of penbutolol continued increasing (10.96% +/- 0.70% vs 5.27% +/- 0.47% at time 0; P < 0.001), whereas it remained unchanged after incubation with mechlorethamine. Moreover, dialysis against saline for 24 h did not restore the free fraction of penbutolol, which increased after treatment with carmustine (9.05% +/- 1.24% vs. 11.04% +/- 1.55%, nondialyzed). We concluded that the treatment of cancer patients with alkylating agents could alter the serum proteins and modify their binding capacity, and this should be taken into account in the simultaneous treatment of these patients with other basic drugs like penbutolol, e.g., methadone.

Effect of sodium valproate on midazolam distribution.

The displacement of midazolam, a new water-soluble, short acting benzodiazepine, from its plasma binding sites by sodium valproate, has been studied in man. An increase of its free fraction (ranging from 2.71 to 5.35%) in plasma from epileptic patients receiving sodium valproate was observed. A similar situation was created in rabbits by pretreatment with sodium valproate (600 mg kg-1 day-1) and posterior hypnosis with midazolam. Due to the interaction, sodium valproate-pretreated rabbits showed an increase in midazolam brain levels (130.91 micrograms g-1 in cortex vs 84.55 micrograms g-1 in control animals). Therefore, it seems likely that displacement of midazolam by sodium valproate in epileptic patients could lead to an increase of the midazolam response.

Influence of changes in protein binding on the central activity of antidepressants.

The central effect (expressed as analgesic response), protein binding and brain uptake of mianserin were measured in mice receiving drug intraperitoneally. A significant decrease of the central effect of mianserin (30 mg kg-1) was seen in mice with experimental inflammation when compared with control animals (reaction time (s) = 12.12 +/- 1.22 vs 25.56 +/- 2.92; P less than 0.001) and the dose-analgesia response curve (10-60 mg kg-1) was significantly shifted to the right in mice with inflammation. In serum of mice with inflammation, unbound concentration of mianserin was decreased from 19.37 +/- 0.73 to 17.83 +/- 0.30% (P less than 0.05) and seromucoid levels were significantly increased (P less than 0.001). Following the intraperitoneal administration of 30 mg kg-1 of mianserin, brain uptake decreased in diseased mice when compared with control animals (P less than 0.02), suggesting that the decrease in analgesia was secondary to a decrease in drug delivery to the brain because of increased protein binding.

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 binding of ketoconazole in health and disease.

The plasma protein binding of ketoconazole, an oral antifungal agent of a weak basic nature, was measured after the addition of the drug (10 micrograms.ml-1) to serum from 35 healthy individuals, ten patients with chronic renal disease and seven patients with hepatic cirrhosis. The percentage of free ketoconazole was markedly increased in patients with chronic renal disease and in patients with hepatic cirrhosis, when it was compared with the group of healthy volunteers (7.33 +/- 0.11 in renal patients; 6.12 +/- 1.43 in hepatic patients compared with 2.93 +/- 0.12 in healthy individuals). The binding ratio of ketoconazole in health and disease was significantly related to plasma albumin concentration, but not to plasma alpha 1-acid glycoprotein (AAG) concentration. Moreover, ketoconazole binds to isolated human serum albumin in a greater proportion but does not bind to isolated AAG indicating that human serum albumin is the major binding protein for this drug in plasma.

Effect of heparin administration on flunitrazepam protein binding.

Non-esterified fatty acids have been shown to displace diazepam from its plasma binding sites both in vitro and in vivo. However, the binding of other benzodiazepines such as lorazepam is not affected in similar situations. Flunitrazepam exhibits a substantial degree of binding to plasma proteins, therefore it was deemed interesting to investigate the role of free fatty acids on flunitrazepam binding to human plasma proteins. Incubation of plasma with sodium oleate (1.5 and 3.0 microEq per ml) produced a decrease in the binding of flunitrazepam. The free fraction increased from 4.20 +/- 0.34 to 6.30 +/- 0.53 and to 22.18 +/- 1.28% respectively). Sodium heparin administration (10IU/kg, intravenously) increased free fatty acids levels and produced similar changes in the binding of flunitrazepam. After ten minutes of heparin administration free fatty acids increased from 0.16 +/- 0.03 mEq/l to 0.34 +/- 0.01 mEq/l and the free fraction of flunitrazepam in plasma increased from 3.70 +/- 0.22% to 6.20 +/- 1.24%. These binding data further support a relationship between increases in the concentrations of free fatty acids and decreases in the fraction of flunitrazepam bound to plasma proteins.

Effect of halothane anesthesia and trifluoroacetic acid on protein binding of benzodiazepines.

The in vitro effect of the halothane metabolite, trifluoroacetic acid, on the protein binding of three different benzodiazepines (diazepam, lorazepam and midazolam) has been investigated. Furthermore, protein binding of these drugs was studied in serum from patients under the effect of halothane anesthesia (1-2.5%; 2.5 h). Trifluoroacetic acid, 4 mmol/l, displaced diazepam and midazolam from serum and produced a marked increase in the free percentage, but did not influence lorazepam binding. Moreover, 48 h after the end of halothane anesthesia, there were changes in protein binding of diazepam (3.9 +/- 0.3% at 48 h vs. 3.3 +/- 0.3% before halothane anesthesia; p less than 0.05). It can be concluded that halothane anesthesia (1-2.5%; 2.5 h) may temporarily potentiate the pharmacological effect of diazepam in the postoperative period following anesthetic procedures.

[Adverse drug reaction surveillance in pediatric and adult patients in an emergency room]. / Monitorización en un servicio de urgencias de reacciones adversas causadas por medicamentos en niños y adultos.

BACKGROUND: Adverse drug reactions (ADR) in the pediatric emergency room of a tertiary care hospital in Spain are described and compared with the adult ward. METHODS: Identification of cases was carried out through review of admission diagnoses and selection of those included in a previous list of diagnoses considered as possible ADR, that were thereafter verified. RESULTS: During 25 months, in 47.107 pediatric consultations were detected 451 cases as suspicious of ADR (0.96%). The ADR was moderate in 29 and serious in 1, being hospitalized 4. In adults, there were 68,431 consultations, and 704 cases detected (1.03%); moderate 218, serious 34 and mortal 1, being hospitalized 101. The most common reactions were dermatological (43.9% in children, 19.5% in adults) and of digestive nature (28.5 and 36.6%, respectively). The drugs most frequently involved in children were antimicrobials (49.5%), drugs used in respiratory illnesses (19.9%), non-steroid anti-inflammatory drugs (NSAID) (10.4%) and vaccines (9.2%); only two recently marketed products were involved. In adults, drugs involved were NSAID (28.2%), cardiovascular drugs (15.9%), antimicrobials (14.5%) and drugs active in digestive system (11.1%). There were 10 cases of hypoglycemia in diabetic adults, probably by interaction of hypoglycemic agents with angiotensin-converting enzyme inhibitors, and 7 cases of gastrointestinal hemorrhage associated with ketorolac, that generated an alert; 12 recently marketed products were involved. CONCLUSIONS: Intensive monitoring in emergency ward measures ADR problem, estimates underreporting, but it has a moderate value to generate alert or to survey new products.

Plasma protein binding of penbutolol in pregnancy.

Penbutolol is a not cardioselective beta-adrenergic blocking drug; it is lipid soluble and differs in its protein binding from the other members of its group because shows linkage to alpha 1-glycoprotein, with no detectable binding to albumin. AAG levels change during pregnancy and so the binding of [3H]-penbutolol was compared in 11 pregnant patients and in 10 healthy women. Binding was obtained by ultrafiltration and measurement of the free fraction by scintillation spectrometry. The free penbutolol fraction was significantly higher in the pregnant women than in the controls (6.06 +/- 0.34 compared with 3.55 +/- 0.29, P less than 0.001). The AAG levels in the pregnant women were significantly lower (0.40 +/- 0.03 g/l) than in the controls (0.77 +/- 0.06 g/l) (P less than 0.001) which showed a significant correlation with the bound/free penbutolol ratio (r = 0.61, P less than 0.005). On the other hand there was no significant correlation with the extent of penbutolol's protein binding even though the albumin levels were lower in the pregnant women (2.83 +/- 0.17 compared with 4.86 +/- 0.17; P less than 0.001). Penbutolol's nK1a for AAG was lower in pregnant women, and this suggests that the fall in AAG levels is not the only factor involved in the reduced binding of penbutolol in pregnancy.

Differential effect of cancer on the serum protein binding to mianserin and imipramine.

Protein binding of mianserin and imipramine in vitro was determined in sera from 10 patients with cancer and from 28 drug-free normal subjects. alpha 1-acid glycoprotein (AAG) concentrations ranged from 0.91 +/- 0.04 g/l in control subjects to 2.17 +/- 0.18 g/l in cancer patients. Albumin concentrations ranged from 55.80 +/- 1.68 g/l in control subjects to 39.71 +/- 4.40 g/l, respectively. Serum samples containing concentrations of 100 ng/ml for mianserin and 500 ng/ml for imipramine were ultrafiltered and the free concentration were measured with scintillation spectrophotometer. The mean free percentage of mianserin was significantly less in patients with cancer (8.70 +/- 0.29% in patients vs 14.30 +/- 0.50% in control subjects P < 0.001). A multiple regression analysis revealed a significant contribution of plasma AAG (r2 = 0.56, P < 0.01), but not of albumin to the overall variability in mianserin binding. No correlation was observed between protein binding of imipramine and AAG concentrations in serum of cancer patients. No significant changes were observed for protein binding of imipramine in cancer patients as compared with control subjects. Our results suggest that for antidepressant (AD) drugs, of which the binding depends on AAG, variability in protein binding could be expected in cancer patients. Thus, in cancer therapy, changes in analgesic doses could be necessary with this kind of antidepressant drug.

[Characterization of propofol binding to plasma proteins and possible interactions]. / Caracterización de la fijación de propofol a las proteínas plasmáticas y posibles interacciones.

OBJECTIVES: a) To study the binding of propofol to proteins in plasma samples from healthy volunteers and in solutions of albumin and alpha 1-acid glycoprotein (AGA); b) to describe the nature of the bond and possible interactions with other substances that are potential displacers: salicylate, phenylbutazone, sulfisoxazole, tolbutamide, sodium valproate, sodium oleate and penbutolol; c) to assess the effect of propofol on the binding of specific markers and possible binding sites in the following proteins: 14C-warfarin, 3H-diazepam, 3H-midazolam, 3H-imidazole, 3H-penbutolol and 3H-morphine. MATERIAL AND METHODS: The free fraction was obtained in all samples by ultrafiltration and measurement of the free concentration of propofol by liquid chromatography and of the markers by scintillation spectrometry. RESULTS: The free fraction of propofol in plasma was 0.98 +/- 0.12% and binding was not saturable. Albumin seems to play an important role (95% bound), whereas the participation of AGA was low (54% bound). Propofol did not affect the binding of any of the markers studied. Nor did the presence of other drugs at therapeutic plasma concentrations affect the binding of propofol. CONCLUSIONS: The binding of propofol to plasma proteins seems unlikely to cause drug interactions in clinical practice.

[Influence of verapamil and diltiazem on the muscle-relaxing effect of atracurium in vivo]. / Influencia de verapamilo y diltiazem sobre el efecto relajante muscular del atracurio in vivo.

The interaction between atracurium and the two calcium antagonists verapamil and diltiazem were studied in rabbits. It was observed that intravenous verapamil (0.2 mg/kg) reduced by 25% and 30% respectively, the dose of atracurium required to produce a 50% or 95% of neuromuscular blockade. In contrast, intravenous diltiazem (1 mg/kg) failed to produce significant changes.

A study of package inserts of potentially toxic drugs.

Information contained in the package inserts of drugs chosen as potential causes of blood dyscrasia, renal toxicity, hepatotoxicity, and cardiac toxicity has been studied. Chloramphenicol and pyrazolones were chosen as representatives of drugs that could produce blood dyscrasia, aminoglycosides and cephaloridine as potential nephrotoxic agents, isoniazid and monoamine oxidase inhibitors as possible hepatotoxic drugs, and tricyclic antidepressants and digitalis as drugs of recognized cardiac toxicity. Adverse effects were clearly described in only 27.8% of the package inserts, whereas 40.3% did not mention them, and 15.7% specifically stated that the product was devoid of adverse effects. Information about the type of toxicity that led to the selection of drugs included in this study was uncommon in most cases.

Unchanged protein binding of penbutolol in renal insufficiency: a possible role of carbamylation.

The effect of in vitro carbamylation of serum protein with potassium cyanate on protein binding of penbutolol, a basic agent exclusively bound to alpha 1 acid glycoprotein (AAG), was investigated. Carbamylation of serum resulted in a weak increase on free fraction of penbutolol (4.45 +/- 0.54% before carbamylation vs 5.66 +/- 0.40% after; p < 0.025). Parallelly, potassium cyanate added to pure AAG and incubated for 90 min induced carbamylation of this protein (38 mumoles of 14C cyanate incorporated per gram of protein). A study in serum from patients with chronic renal disease (pre and postdialysis) showed no changes in protein binding of penbutolol, although AAG levels were significantly higher. However, Scatchard [1949] plot for penbutolol binding to serum from renal patients (both pre and postdialysis) showed a decrease in affinity constant (nKa = 11.13 x 10(5) M-1 in healthy volunteers, vs 5.56 x 10(5) M-1 in patients before dialysis and 4.57 x 10(5) M-1 after dialysis). We concluded that carbamylation of serum AAG in uremic patients could explain, in part, the absence of changes in protein binding of any basic drugs in this pathological condition. It appears that a decreased affinity constant could balance the effect of increased AAG levels.

Intravesical BCG therapy of superficial bladder cancer: study of adverse effects.

Immunotherapy with intravesical bacillus Calmette-Guérin (BCG) has proved to be more effective than most chemotherapeutic agents in the prophylaxis and treatment of superficial bladder tumours. Side-effects, both local and systemic, are the main limitations against its use. With the aim of lowering the incidence and severity of side-effects, we started to use two vials of BCG, Connaught type, per instillation, instead of three vials, as recommended by the manufacturer. We prospectively reviewed adverse effects of BCG treatment at the lower dosage in 92 patients. Compared with other series, we found a similar incidence of adverse effects except for some local effects as haematuria which showed a higher incidence, but we also found a lower rate of tumour relapse. Four primary tumours were recorded during the study period. In our open study, a lower BCG intravesical dosage is not followed by a reduction in side-effects.