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Diseases are a major cause of variation in drug response. Although many different diseases are known that have an effect on the pharmacokinetics or sometimes the pharmacodynamics of a drug, disorders associated with a so-called acute phase response (APR) are the most important in this respect. During APR, for example caused by tissue damage or invasion of a pathogen, a group of symptoms can be observed that often include fever, lassitude, inhibition of gastric function and synthesis of acute phase proteins. All phases that together determine the pharmacokinetic profile of a drug, absorption, distribution, metabolism and excretion, can be affected during APR. From a clinical point of view however, the effects on absorption and metabolism are the most relevant. For drugs that are given orally, a slower absorption rate is often observed during APR due to a delayed gastric emptying. Even more important from a clinical point of view is the depression of biotransformation capacity in the liver during APR, especially affecting the enzymes of the cytochrome P450 (CYP450) complex. Although much has become known about the mechanism of this effect, a number of questions remain. Cytokines, nitric oxide and possibly the enzyme heme oxygenase are playing a role in a complex process that depends on a mutual interaction between Kupffer cells (macrophages) and hepatocytes in the liver. The clinician should be aware of unexpected changes in drug effects or residue levels due to cumulation of the compound during disease or after vaccination. In these situations, drugs that are excreted unchanged may be better alternatives.

During infection and inflammation drug disposition and hepatic metabolism are markedly affected in mammals. Pro-inflammatory mediators play an important role in the suppression of (cytochrome-P450-mediated) drug metabolism. Inflammatory mediators like cytokines, nitric oxide (NO), reactive oxygen species (ROS) and eicosanoids are released by activated macrophages from various sources, including liver and lung. It was the aim of this study to investigate ways to suppress the activation of macrophages during the onset of the inflammatory cascade. Therefore porcine lung and liver macrophages were isolated, and incubated with lipopolysaccharide (LPS) to initiate an acute inflammatory response, represented by the release of high amounts of tumour necrosis factor-alpha (TNF-alpha) into the culture medium. Additionally the primary macrophages were coincubated with phosphodiesterase-IV-(PDE-IV)-inhibitors or beta-adrenoceptor agonists that in previous studies demonstrated strong suppressive effects on TNF-alpha release. Especially the beta-adrenoceptor agonists showed to be very potent TNF-alpha suppressants, which indicates that the beta-adrenoceptor might be an interesting target for suppression of activation of macrophages. This was strengthened by the observation that the beta-adrenoceptor expression was not altered during the onset of the inflammatory cascade.

The selective control of inflammatory reactions will continue to be a major issue in the development of new drugs. Many new molecular targets are coming up. This paper highlights a few key mediators that are nowadays considered as interesting therapeutic intervention points. Cytokines play an important regulatory role in the initiation, maintenance and termination of inflammatory reactions. More than 50 cytokines have been identified, and more and more has become known about their receptors and signal transduction pathways. Tumour necrosis factor-alpha (TNF-alpha) is still regarded as one of the initial cytokines of the cascade, and different approaches are followed to control its synthesis, release or effects. Lipopolysaccharide (LPS) is a one of the triggers that is able to induce a strong TNF-response. Inhibitors of cyclic nucleotide phosphodiesterases (PDEs), including rolipram and pentoxifylline suppress the LPS-induced TNF-alpha production in monocytes/macrophages. In our laboratory it has been shown that the alternative way to increase cAMP levels, via stimulation of beta-adrenergic receptors, also provides an effective way, both in vitro and in vivo, to inhibit TNF-alpha release. Other therapeutic ways include the use of antibodies directed to cytokines, TNF receptor fused to IgG, antibody therapy against TNF, the use of MAP kinase inhibitors. The different signal transduction pathways, including the NF-kappa B activation route may provide alternative pharmacological tools. We may surely expect anti-inflammatory drugs of much greater specificity to be developed in the next decade. Despite the relative limited investments in veterinary drug development this will also have consequences for veterinary therapy.

1. The pharmacokinetic interactions between paracetamol (PA) and antipyrine (AP) were studied in pigs in order to investigate the usefulness of this combination for the simultaneous assessment of oxidative and conjugative metabolism. 2. When both drugs were given at a dose of 5 mg/kg, AP plasma clearance was reduced from 2.22 to 0.96 lh-1 kg-1. PA clearance was not changed in comparison with control values. 3. At a dose of 2 mg/kg no pharmacokinetic interaction between the two drugs was observed. 4. The only oxidative AP metabolite found in urine was 4-hydroxyantipyrine (4-OHA). It accounted for 80% of the dose and, like PA, it was completely glucuronidated. 5. The glucuronidation of PA has been studied in vitro in pig liver microsomes. The apparent Km value for PA glucuronidation was 40 mM with a Vmax = 54 nmol min-1 mg protein-1. To determine if 4-OHA and PA competed for the same UDP-glucuronosyl-transferase, the effect of 4-OHA and AP on PA glucuronidation was studied. It appeared that 4-OHA was a competitive inhibitor with a Ki app = 0.07 microM, whereas AP had no effect. 5. Results suggest a dose-dependent interaction between AP and PA, which may be due to competition at the level of glucuronidation. Therefore, the usefulness of AP and PA in vivo in a cocktail for metabolism studies is limited.

1. In the rat, scoparone (6,7-dimethoxycoumarin) is regioselectively O-demethylated in vitro by the hepatic cytochrome P450 (P450) system, yielding isoscopoletin and scopoletin. 2. Scoparone has been proposed as an indicator substrate for the assessment of P450 differentiation in vitro in rat. It has been suggested that isoscopoletin formation mainly reflects activity of enzymes of the P4501A subfamily, whereas scopoletin formation has been associated with P4502B activity. 3. In the present study, rate of formation of scopoletin and isoscopoletin were measured in hepatic microsomes from male, female and castrated male rats, in castrates treated with testosterone, in males treated with oestradiol, and in females treated with testosterone. Furthermore, effects of induction by phenobarbital (PB), beta-naphthoflavone (BNF), isoniazid, triacetyloleandomycin, and dexamethasone were studied in both sexes. 4. Scoparone metabolism was partly sex- and steroid-dependent. Variation of isoscopoletin formation with sex or hormonal status correlated well with ethylmorphine demethylation. 5. Scoparone-O-demethylation was regioselectively induced by PB and BNF. Induction effects were not very large and showed no sex differences. 6. Microsomal metabolism of scoparone was partly inhibited by a monoclonal antibody against P4502C11. Scopoletin and isoscopoletin formation were inhibited when ethylmorphine was added to the incubation mixture. Scoparone competitively inhibited testosterone 6 beta-hydroxylation. 7. It is concluded that a number of P450 enzymes, including those which are constitutively expressed, contribute to the biotransformation of scoparone. This lack of selectivity limits the usefulness of scoparone as a general indicator substrate for P450 differentiation in rats.