Reduced Protein Binding Research Articles

Nilvadipine inhibits nuclear factor-κB-dependent transcription in hepatic cells

Background Recent findings suggest that some dihydropyridine-type calcium channel blockers, widely used as anti-hypertensive drugs, have direct anti-atherogenic action through their antioxidant properties. Methods We examined the effect of nilvadipine on the activity of a representative radical-sensitive transcription factor, nuclear factor kappa-B (NF-κB), in the human hepatocyte cell line HuH7 in vitro. Results Nilvadipine potently inhibited NF-κB-dependent transcription in a dose- and time-dependent manner, with a minimal effective concentration of 50 nmol/l. The effect was specific because no similar effects were found in the prototype dihydropyridine nifedipine. Electromobility shift assay showed reduced protein binding to the NF-κB-consensus sequence in nilvadipine-treated cells. Nilvadipine also reduced the expression of fibrinogen and plasminogen activator inhibitor-1 (PAI-1). Conclusions Since NF-κB-mediated gene products, such as fibrinogen and PAI-1, are known to facilitate hypercoagulation, thrombosis and vascular events, we suggest that nilvadipine has a direct beneficial effect separate from its anti-hypertensive properties by inhibiting NF-κB-dependent gene expression and eventually inhibiting atherosclerosis.

Discovery of 1-(3‘-Aminobenzisoxazol-5‘-yl)-3-trifluoromethyl-N-[2-fluoro-4- [(2‘-dimethylaminomethyl)imidazol-1-yl]phenyl]-1H-pyrazole-5-carboxyamide Hydrochloride (Razaxaban), a Highly Potent, Selective, and Orally Bioavailable Factor Xa Inhibitor

Modification of a series of pyrazole factor Xa inhibitors to incorporate an aminobenzisoxazole as the P(1) ligand resulted in compounds with improved selectivity for factor Xa relative to trypsin and plasma kallikrein. Further optimization of the P(4) moiety led to compounds with enhanced permeability and reduced protein binding. The SAR and pharmacokinetic profile of this series of compounds is described herein. These efforts culminated in 1-(3'-aminobenzisoxazol-5'-yl)-3-trifluoromethyl-N-[2-fluoro-4-[(2'-dimethylaminomethyl)imidazol-1-yl]phenyl]-1H-pyrazole-5-carboxyamide (11d), a potent, selective, and orally bioavailable inhibitor of factor Xa. On the basis of its excellent in vitro potency and selectivity profile, high free fraction in human plasma, good oral bioavailability, and in vivo efficacy in antithrombotic models, the HCl salt of this compound was selected for clinical development as razaxaban (DPC 906, BMS-561389).

Connective Tissue Growth Factor: Expression in Human Skin In Vivo and Inhibition by Ultraviolet Irradiation

Connective tissue growth factor, which is induced by transforming growth factor beta, has been reported to mediate the stimulatory actions of transforming growth factor beta on type I procollagen synthesis. Connective tissue growth factor is expressed in fibrotic disease such as scleroderma, where it is believed to promote abnormal deposition of collagen. Connective tissue growth factor expression has not been described in normal human skin or cultured skin cells, however. We report here that connective tissue growth factor mRNA is constitutively expressed in normal human skin. In situ hybridization demonstrated that connective tissue growth factor mRNA was expressed in keratinocytes throughout the epidermis and in dermal cells. Quantitative real-time reverse transcription polymerase chain reaction revealed that the level of connective tissue growth factor mRNA in the epidermis and dermis of normal human skin was comparable to the level of housekeeping gene 36B4. Ultraviolet irradiation (2 minimal erythema dose, UVB/A2 source) reduced connective tissue growth factor mRNA expression throughout the epidermis and dermis in normal human skin in vivo. Connective tissue growth factor mRNA was reduced (30%) within 4 h post ultraviolet irradiation, and remained reduced (50%) 8-24 h post ultraviolet. Connective tissue growth factor mRNA and protein were also constitutively highly expressed in normal cultured human skin keratinocytes and fibroblasts. Ultraviolet irradiation of cultured normal human skin fibroblasts resulted in a time-dependent inhibition of connective tissue growth factor mRNA expression. At 24 h post ultraviolet, connective tissue growth factor mRNA expression was reduced 80%. Transforming growth factor beta1 rapidly induced connective tissue growth factor mRNA levels (5-fold within 4 h) in skin fibroblasts, but not keratinocytes, and this induction was attenuated 80% by ultraviolet irradiation. Electrophoretic mobility shift assays demonstrated that ultraviolet irradiation reduced protein binding to the transforming growth factor beta/Smad responsiveness elements in the connective tissue growth factor gene promoter, in human skin in vivo and human skin fibroblasts. Constitutive expression of connective tissue growth factor in normal human skin suggests that it is a physiologic regulator of procollagen synthesis. Ultraviolet reduction of connective tissue growth factor expression may contribute to reduced procollagen synthesis observed in ultraviolet-irradiated normal human skin and human skin fibroblasts.

TNFalpha decreases alphaMHC expression by a NO mediated pathway: role of E-box transcription factors for cardiomyocyte specific gene regulation.

Tumor necrosis factor alpha(TNFalpha) is thought to play a key role in the pathogenesis of cardiac failure. In the myocardium, TNFalpha enhances the expression of inducible nitric oxide synthase (iNOS). Nitric oxide (NO) has been shown to affect beta-agonist-dependent cardiac contractility and relaxation. It is not clear, however, whether TNFalpha mediated NO release has sustained cardiac effects, by altering expression of cardiomyocyte specific genes such as alpha-myosin heavy chain (alphaMHC). Neonatal rat ventricular cardiomyocytes (CM) were stimulated with TNFalpha and/or the NOS inhibitor nitro-L-arginine (L-NNA). Protein binding to the E-box enhancer element in the alphaMHC promoter was evaluated by electrophoretic mobility shift assay (EMSA) and transcriptional activity of the E-box consensus motif was determined by luciferase assay. mRNA levels of the endogenous alphaMHC gene were assessed by RT-PCR. In vivo studies were performed in transgenic mice with cardiac specific over-expression of TNFalpha. CM treated with TNFalpha exhibited decreased levels of alphaMHC transcripts (69 +/- 8% of control), the effect of TNFalpha was reversed by L-NNA (94 +/- 14% of control). As shown by EMSA, TNFalpha reduced protein binding to the alphaMHC E-box enhancer motif via NO dependent pathways. Addition of the NO-donor sodium nitroprusside (SNP) to CM nuclear extracts dose dependently disrupted protein binding to the alphaMHC E-box. Furthermore, exposure of CM to TNFalpha or SNP decreased transcription from an E-box luciferase-reporter construct (TNFalpha: 74 +/- 12%; SNP 250 microM: 72 +/- 10%; SNP 500 microM: 66 +/- 11% of control). In myocardial tissue of TNFalpha transgenic mice, increased nitrotyrosine staining, decreased protein binding to the alphaMHC E-box motif and reduced expression of alphaMHC (62 +/- 26%) were observed. The present study shows that TNFalpha reduces alphaMHC transcript levels in cardiomyocytes. Our data obtained in cultured CM and in TNFalpha transgenic mice support the notion that TNFalpha exerts these effects by NO and E-box dependent mechanisms in vitro and possibly in vivo.

European Regulatory Authorities and Pediatric Labeling

### The Need for Medicinal Product Testing in Children #### Ethical Considerations Children should not be given medicines that have not been evaluated adequately for use in that age group. There is a responsibility, shared by applicants and the appropriate authorities, to ensure that children have timely access to safe and effective medicines that have accurate, scientifically justified prescribing information. Applicants are encouraged to investigate the safety and efficacy of a product in children, if it is likely to be of therapeutic benefit in this age-group, and to develop suitable formulation, even if use is likely to be small. However important a clinical trial may be to prove or disprove the value of a treatment, individual members of one or both of the groups—subject or control—can suffer injury as a result of inclusion in the trial, even if the whole community benefits. As with adults who participate in clinical trials and who understand the issues involved in giving their informed consent, consent should be obtained from the legal guardian of children in accordance with national legislation. Children should be fully informed about the trial in language and terms they understand and, if able, should personally sign and date the written informed consent. The child should be made aware of his/her rights to decline to participate. The child's wish to be withdrawn from a study must be respected. These measures should be applied in conjunction with 1) part 4 of Directive 75/318/EEC, as amended, which requires “… details concerning patients who may be at increased risk”; the CPMP/ICH guideline for good clinical practice; and 3) the CPMP guideline on biostatistical methodology in clinical trials in applications for marketing authorizations for medicinal products. These measures are intended to assist applicants with specific problems presented by medicinal product testing in children. The child should stand to obtain some direct benefit from the clinical trial, except … Address correspondence to Elisabeth Autret, MD, Hopital Bretonneau, Pharmacologie Clinique, Boulevard Tonnele, 37044 Tours, France.

Guanidine derivatives as combined thromboxane A2 receptor antagonists and synthase inhibitors.

A new series of omega-disubstituted alkenoic acid derivatives derived from samixogrel 5 were designed and synthesized as combined thromboxane A2 receptor antagonists/thromboxane A2 synthase inhibitors with improved solubility and reduced protein binding compared to 5. Hexenoic acid derivatives with a 3-pyridyl group and 3-(2-cyano-3-alkyl-guanidino)phenyl substituent were found to be optimal with regard to this dual mode of action. The most potent compound, E-6-(3-(2-cyano-3-tert-butyl-guanidino)phenyl)-6-(3-pyridyl)hex-5-eno ic acid, "terbogrel" 32 inhibits the thromboxane A2 synthase in human gel-filtered platelets with an IC50 value of 4.0 +/- 0.5 nM (n = 4). Radioligand binding studies with 3H-SQ 29,548 revealed that 32 blocks the thromboxane A2/endoperoxide receptor on washed human platelets with an IC50 of 11 +/- 6 nM (n = 2) and with an IC50 of 38 +/- 1 nM (n = 15) in platelet-rich plasma. Terbogrel inhibits the collagen-induced platelet aggregation in human platelet-rich plasma and whole blood with an IC50 of 310 +/- 18 nM (n = 8) and 52 +/- 20 nM (n = 6), respectively. This was shown to translate into a potent antithrombotic effect in vivo as demonstrated in studies using a model of arterial thrombosis in rabbits (ED50 = 0.19 +/- 0.07 mg/kg; n = 20). Thus, terbogrel is the first compound with a guanidino moiety demonstrating both a potent TXA2 synthase inhibition and a potent TXA2 receptor antagonism and has been selected for further clinical development.

Interaction of DNA-binding proteins with the 5'-flanking region of a cytokinin-responsive cucumber hydroxypyruvate reductase gene.

Transcription of the cucumber hpr-A gene is responsive to cytokinin and light. To investigate the molecular basis for transcriptional regulation by cytokinin, we have identified DNA sequences and proteins that may be involved in the regulation of hpr-A gene expression. Transient expression assays in etiolated cucumber cotyledons indicate that the 315 bp fragment (-382 to -67) contains sequences necessary for cytokinin responsiveness of the luciferase reporter gene. Band shift assays detected cytokinin-enhanced and -reduced protein binding sites in a 97 bp fragment (-382 to -285) upstream of the hpr-A gene. DNase I footprinting identified two protein-protected sites, a 15 bp sequence, 5'-AAATGACGAAAATGC-3', that contains an as-1 TGACG motif found in other plant promoters, and a 13 bp sequence, 5'-AAGATTGATTGAG-3', of unknown function. Two-dimensional band shift analysis of the cytokinin-responsive DNA protein complex revealed the presence of six DNA protein interactions. Band shift assays showed that cytokinin and light have different effects on the interaction of nuclear proteins to the 97 bp fragment of the hpr-A gene. These data suggest that cytokinin and light do not share identical signal transduction pathways in regulating hpr-A gene expression.

THE CHARACTERIZATION OF POTENT NOVEL WARFARIN ANALOGS

Racemic sodium warfarin, Coumadin,® is widely used in the prevention of thromboembolic disease. The present study was undertaken to characterize three novel classes of warfarin analogs, and to compare them with the warfarin enantiomers. All three classes of compounds inhibit vitamin K epoxide reductase, the enzyme inhibited by racemic warfarin. The alcohol and the ester analogs have reduced protein binding compared with R-(+)-warfarin 1 1 R-(+)-warfarin will be designated as R-warfarin; S-(−)-warfarin will be designated as S-warfarin . The ester and the fluoro-derivatives have similar in vivo anticoagulant activity in the rat to that of S-(−)-warfarin 1 . Thus, it is possible to synthesize novel warfarin analogs that differ from racemic warfarin or its enantiomers in certain selected properties. © 1997 Elsevier Science Ltd

Elevated free fatty acid concentrations in lipemic sera reduce protein binding of valproic acid significantly more than phenytoin.

Higher concentrations of free valproic acid and phenytoin have been reported in patients with uremia and liver disease. Free fatty acids also displace valproic acid and phenytoin. This is a study of the magnitude of displacement of valproic acid and phenytoin from protein binding by free fatty acid in lipemic sera. Higher concentrations of free fatty acids in lipemic sera affected protein binding of valproic acid significantly more than that of phenytoin. Supplementing normal sera with free fatty acids also increased the free concentrations of both valproic acid and phenytoin as expected, but the observed effect was several times higher in magnitude with valproic acid. There was an increased free fraction of valproic acid in patients who received valproic acid and had hypertriglyceridemia. In a patient with uremia, there was also a significant increase in free valproic acid concentration after routine hemodialysis caused by an increase in free fatty acid concentration secondary to hemodialysis. Increased protein binding of valproic acid in sera was observed after treatment with activated charcoal because charcoal can remove free fatty acid. Because higher free fatty acid concentration significantly affects protein binding of valproic acid, careful monitoring of free valproic acid in patients with lipid disorder may be beneficial.

Elevated Free Fatty Acid Concentrations in Lipemic Sera Reduce Protein Binding of Valproic Acid Significantly More Than Phenytoin

AbstractHigher concentrations of free valproic acid and phenytoin have been reported in patients with uremia and liver disease. Free fatty acids also displace valproic acid and phenytoin. This is a study of the magnitude of displacement of valproic acid and phenytoin from protein binding by free fatty acid in lipemic sera. Higher concentrations of free fatty acids in lipemic sera affected protein binding of valproic acid significantly more than that of phenytoin. Supplementing normal sera with free fatty acids also increased the free concentrations of both valproic acid and phenytoin as expected, but the observed effect was several times higher in magnitude with valproic acid. There was an increased free fraction of valproic acid in patients who received valproic acid and had hypertriglyceridemia. In a patient with uremia, there was also a significant increase in free valproic acid concentration after routine hemodialysis caused by an increase in free fatty acid concentration secondary to hemodialysis. Increased protein binding of valproic acid in sera was observed after treatment with activated charcoal because charcoal can remove free fatty acid. Because higher free fatty acid concentration significantly affects protein binding of valproic acid, careful monitoring of free valproic acid in patients with lipid disorder may be beneficial.

Transcriptional regulation of alpha(1b) adrenergic receptors (alpha(1b)AR) by nuclear factor 1 (NF1): a decline in the concentration of NF1 correlates with the downregulation of alpha(1b)AR gene expression in regenerating liver.

The 5' upstream region from --490 to --540 (footprint II) within the dominant P2 promoter of the rat alpha(1b) adrenergic receptor (alpha(1b)AR) gene is recognized by a sequence-specific DNA-binding protein (B. Gao, M. S. Spector, and G. Kunos, J. Biol. Chem. 270:5614-5619, 1995). This protein, detectable in Southwestern (DNA-protein) blots of crude nuclear extracts as 32- and 34-kDa bands, has been purified 6,000-fold from rat livers by DEAE-Sepharose, heparin-Sepharose, and DNA affinity chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and UV cross-linking of the purified protein indicated the same molecular mass as that in crude extracts. Methylation interference analysis revealed strong contact with a TTGGCT hexamer and weak contact with a TGGCGT hexamer in the 3' and 5' portions of footprint II, respectively. Nucleotide substitutions within these hexamers significantly reduced protein binding to footprint II and the promoter activity of P2 in Hep3B cells. The purified protein also bound to the nuclear factor 1 (NF1)/CTF consensus sequence, albeit with lower affinity. Gel mobility supershift and Western blotting (immunoblotting) analyses using an antibody against the NF1/CTF protein identified the purified 32- and 34-kDa polypeptides as NF1 or a related protein. Cotransfection into Hep3B cells or primary rat hepatocytes of cDNAs of the NF1-like proteins NF1/L, NF1/X, and NF1/Redl resulted in a three- to fivefold increase in transcription directed by wild-type P2 but not by the mutated P2. Partial hepatectomy markedly decreased the levels of NF1 in the remnant liver and its binding to P2, which paralleled declines in the rate of transcription of the alpha(1b)AR gene and in the steady-state levels of its mRNA. These observations indicate that NF1 activates transcription of the rat alpha(1b)AR gene via interacting with its P2 promoter and that a decline in the expression of NF1 is one of the mechanisms responsible for the reduced expression of the alpha(1b)AR gene during liver regeneration.

Negative interference of metal (II) ions with nucleotide excision repair in human cell-free extracts.

Inhibition of the nucleotide excision repair (NER) process is believed to cause the potentiation of the genotoxic and mutagenic effects of DNA damaging agents like UV-light or cisplatin by metal ions. However, the precise underlying molecular mechanism of this phenomenon is still unknown. Using in vitro assays, we have determined the potential interference of several metal (II) ions with the lesion recognition and strand incision/displacement steps of the NER mechanism, independently from the DNA polymerization step. When combinations of an optimal Mg2+ concentration and concentrations of various metal ions in a range from 0.1 to 1 mM were tested, all combinations, with Mn2+ and Ni2+ excepted, inhibited specifically the incision repair activity by human protein extracts. There was a good correlation for Cd2+, Co2+, Fe2+, Cu2+, Hg2+, Pb2+ and Zn2+ between an inhibiting effect on the incision activity and a reduced protein binding activity to a damaged DNA probe as assessed by gel mobility shift assay.

AraC protein contacts asymmetric sites in the Escherichia coli araFGH promoter.

AraC protein regulates the transcription of arabinose transport and catabolic operons in Escherichia coli through interaction with specific DNA sequences in the promoter regions of the operons. The interaction of AraC protein with two binding sites in the araFGH promoter was determined and compared to previously studied AraC binding sites in the araBAD promoter. Methylation and ethylation interference assays show that AraC protein binds along one side of the DNA to four adjacent major groove regions at each of the araFG1 and araFG2 sites. Mutations within any of the four regions of araFG1 greatly reduce protein binding in vitro. The promoter function in vivo is also greatly reduced, indicating that all four regions of the binding site are required. The chemical interference and genetic data, combined with the consensus sequence for AraC protein binding to ara promoters, support a binding motif in which two directly repeated units each span two adjacent turns of the DNA helix. The function of the two AraC binding sites was also examined. The proximal araFG1 site is required for promoter activation, whereas the distal araFG2 site has only a slight effect on the promoter activity.

Plasma protein binding of catecholamines, prazosin and propranolol in diabetes mellitus.

In the present study equilibrium dialysis has been used to determine the degree of protein binding of the catecholamines adrenaline and noradrenaline and the adrenergic receptor blockers, prazosin and propranolol in diabetics. The binding of the catecholamines in plasma from Type I and II diabetic patients was not significantly different from that of healthy subjects. The ratio of the bound and free catecholamine concentrations was correlated with the level of albumin (HSA). Significantly reduced protein binding of prazosin was observed in Type I and II diabetic subjects compared to healthy volunteers. The binding of propranolol was significantly reduced in Type I patients. The ratios between the bound and unbound concentrations of prazosin and propranolol were significantly correlated with the levels of alpha 1-acid glycoprotein (AAG). The results suggest that non-enzymatic glycosylation of plasma proteins may increase the unbound fraction of the adrenergic blockers prazosin and propranolol.

Anticonvulsants in pregnancy

To review the potential problems and their management associated with the use of anticonvulsant drugs during pregnancy. Studies published between 1968 and 1990 assessing the effect of pregnancy on the pharmacokinetics of anticonvulsant drugs, the teratogenicity of anticonvulsants, breast feeding and anticonvulsants and use of the oral contraceptive pill in patients taking anticonvulsant medication, were reviewed. In general, plasma levels fall during pregnancy and rise during the puerperium. A number of factors including possible reduced absorption, increased volume of distribution, reduced protein binding, increased clearance and noncompliance, contribute to this fall in plasma concentration. All anticonvulsants are potentially teratogenic. The incidence of fetal malformations is higher in patients treated with multiple anticonvulsant drugs and on higher dosages with higher plasma levels. Anticonvulsants are excreted in low concentrations in breast milk. All anticonvulsants except valproic acid have been associated with failure of the oral contraceptive pill. This is due to liver enzyme induction of these drugs. As plasma levels of anticonvulsants fall during pregnancy, concentrations should be monitored regularly. Due to the fall in protein binding, marginally low total plasma levels of highly protein bound drugs may not reflect reduced unbound levels, and hence an increase in dosage may not be required. In order to reduce teratogenicity, one should aim to use a single anticonvulsant drug and the lowest dosage able to achieve seizure control. In general, breast feeding is not contraindicated.

Pharmacokinetics of antibiotics in critically ill patients

Differences in pharmacokinetic data of aminoglycosides, ceftazidime and ceftriaxone between intensive care patients and volunteers or patients who are less severely ill, are described. Similar differences are observed for midazolam. In severely ill patients with normal renal function a wide interpatient variability of aminoglycoside half-life (t1/2) and increased distribution volume (Vd) are observed. This results in inadequate serum levels. A pharmacokinetic approach of drug dosing, based on serum concentrations in individual patients, is advised. For ceftazidime and ceftriaxone similar changes of t1/2 and Vd are observed. Since protein binding is frequently reduced in severely ill patients, the influence of altered binding of highly bound drugs on Vd and drug clearance is discussed. As both may be increased by reduced protein binding, the change of t1/2 to be expected is unpredictable. Dosing regimens should be based on pharmacokinetic data derived from patients whose severity of disease is comparable to that of the patients to be treated.

Drug-protein binding in elderly subjects

It is important to know the magnitude of serum-protein binding of drug dynamics in vivo. The authors investigated the effects of a variety of serum free fatty acids in elderly subjects. Serum albumin levels and ceftezole (CTZ)-protein binding in elderly subjects were lower than in younger subjects. No significant difference was noted between the two groups in regard to total free fatty acid (T-FFA) level. However, compared with younger subjects, palmitolic and oleic acid were higher and myristic and linoleic acid were lower in elderly subjects, suggesting that free fatty acid (FFA) undergoes qualitative changes due to ageing. In elderly subjects CTZ-binding correlated negatively with T-FFA, oleic acid and linoleic acid, but positively with stearic acid. Oleic acid decreased CTZ-protein binding. This decrease was higher than that due to decreased albumin levels in elderly subjects with albumin levels less than 4.0 g/dl. These findings indicated that reduced protein binding in elderly subjects is due to decreased serum albumin and changes in FFA constitution with ageing. Therefore it was suggested that drug-albumin binding may change due to the competitive action of albumin sites, and albumin-drug binding capacity. Since drug-protein binding capacity seriously affect metabolism, excretion, efficacy and side effects due to the presence of free drugs, these aspects require further investigation in elderly subjects.

Drug metabolism and pharmacokinetics in malnourished children.

Malnutrition is a complex condition in which many deficiencies occur simultaneously. Protein-energy malnutrition is a major public health and clinical problem in paediatric practice that accounts for high child mortality and morbidity. It includes many different clinical syndromes with protean manifestations. The malnourished often have several concomitant diseases; drugs are therefore as widely used as in the well-nourished. The pathophysiological profile in malnutrition can alter pharmacokinetic processes, drug responses and toxicity. This review summarizes the available knowledge on nutrient-drug interactions in malnourished children. Although there is much evidence in the literature that diet and nutritional status are 2 important environmental variables determining the pharmacotoxicological properties of chemicals, there are few data on humans. Recently, intense effort has been initially directed at studying drug kinetics in grade III malnutrition, namely kwashiorkor and marasmus. Studies on drugs and nutrients indicate delayed or decreased absorption, reduced protein binding of several drugs, fluctuations in volume of distribution, altered hepatic oxidative drug biotransformations and conjugations, reduced elimination of conjugates and reduced elimination of renally excreted drugs. The estimated steady-state levels of a few drugs suggest accumulation. Bioavailability problems with certain drugs are due to divergent effects of pharmacokinetic processes. Clinical risk of toxicity appears to be higher in malnourished children. Rehabilitation studies suggest that a number of these pharmacological abnormalities can be reversed. The majority of studies have concentrated on single-dose pharmacokinetics in severely malnourished children. A number of abnormalities seen in drug disposition during the acute phase of malnutrition need to be confirmed for other grades of malnutrition. For practical purposes, it is important to consider steady-state levels and data in mild and moderate forms of growth-retarded children; drug-induced nutritional deficiencies can occur more easily in these populations. Although some of the drugs described in this review have been in use for many years, knowledge on drug response and toxicity is still only approximate. There is at present enough evidence to support monitoring plasma drug concentrations in malnourished children, particularly for those drugs which have dose-dependent kinetics and narrow margins of safety. The metabolism and disposition of xenobiotics seem to vary widely in children with protein-energy malnutrition. Therapeutic inadequacies and toxicities need careful evaluation in malnourished children.

Pharmacokinetics in liver disease.

Some general pharmacokinetic principles, relevant to understand and predict altered disposition of drugs in liver disease, are reviewed. It is appropriate to differentiate between high- and low-clearance drugs as to the influence of hepatic dysfunction. On intravenous administration high-clearance drugs generally show reduced systemic clearance predominantly caused by decreased liver blood flow, whereas on oral administration a considerable increase in systemic availability may occur caused by reduced enzyme activity and (in cirrhosis) bij portacaval shunting. Low-clearance drugs are sensitive to reduced enzyme activity and reduced protein binding. It seems that oxidative reactions are far more affected than conjugation reactions in liver disease. Large inter-patient variability exists in the kinetics of a drug in any type of hepatic disease. The conventional liver-function tests are of no value in predicting altered drug disposition.

Nifedipine. Relationship between pharmacokinetics and pharmacodynamics.

The availability of specific chemical assays and the development of appropriate biological models have made it feasible to study the relationship between the pharmacokinetics and the pharmacodynamics of nifedipine, a relationship that is presumed to be sigmoidal for most effects. In healthy volunteers the haemodynamic effects of a single dose of nifedipine are markedly influenced by the pharmaceutical preparation and the rate of drug input. When the plasma concentration of nifedipine increases rapidly, such as after an intravenous bolus injection or rapidly disintegrating capsules, there is a marked increase in heart rate and little or even no effect on blood pressure. On the other hand, when the drug is given as a slow intravenous infusion or as a sustained release tablet and when the capsules are taken together with food, the decrease in blood pressure is accompanied by few or no changes in heart rate. Furthermore, it has been shown that not only haemodynamic effects of nifedipine, but also oesophageal motor function may be used as a quantifiable pharmacological effect. For patients with angina pectoris, a plasma concentration range that is associated with optimal treatment has not been defined, since large inter-individual variations in the nifedipine plasma concentration were observed in effectively treated patients. For patients with hypertension, significant sigmoidally shaped correlations between blood pressure reduction and nifedipine plasma concentrations following single or multiple doses have been demonstrated. The concentration-effect parameters were very similar to those found for normotensive subjects. After 6 weeks of treatment the potency of the drug had decreased, which might indicate the development of some tolerance. In patients with severe renal impairment, the maximal effect of nifedipine on diastolic blood pressure was more than doubled, which cannot be explained by differences in pharmacokinetics; therefore these patients appear to be more sensitive at the pharmacodynamic level. In patients with liver cirrhosis, the pharmacokinetics of nifedipine were quite different due to reduced protein binding and reduced enzyme activity; in patients with a portacaval shunt, considerable increased bypassing of the liver during the first pass after oral administration was observed. When corrected for free drug concentrations, the concentration-effect relationship for these patients is essentially the same as that found for healthy subjects.(ABSTRACT TRUNCATED AT 400 WORDS)