Pharmacokinetics of three sulphonamides in ruminant and preruminant kids.
The pharmacokinetic properties of three sulphonamides were determined in ruminant and preruminant kids after oral and intravenous administration. First, sulphisomidine (SIM, 50 mg kg-1) and sulphadoxine (SDX, 30 mg kg-1) were given to seven kids, 10 to 12 weeks old, while on a milk replacer diet and again at 15 to 18 weeks when fed roughage. Secondly, SIM (100 mg kg-1) and sulphadimidine (SDD, 100 mg kg-1) were given at six to nine, 12 to 15 and 18 to 21 weeks old to eight kids, of which four were fed milk replacer and four were with their mothers (with access to roughage) until 15 weeks, after which all were fed roughage only. SDX and SDD exhibited non-linear (or capacity limited) absorption after oral dosage, suggesting possible active absorption mechanisms, and both drugs also showed non-linear elimination. Intravenous curves for SDD and SIM indicated that recycling occurred. With SDX, ruminant kids showed poorer systemic availability after oral dosage, shorter t1/2(el) and higher B than did preruminants. For SDD, ruminant kids had lower Vd and higher B than preruminants. SIM's t1/2(el) tended to shorten and beta to increase in both groups throughout the experiment. Not all differences between ruminants and preruminants in sulphonamide pharmacokinetics could be explained by the accumulation of acidic forestomach contents and the change of urine pH from acid to alkaline in the maturing ruminant. Other potential contributing factors require investigation, including possible alterations in hepatic drug metabolism. Of the three drugs tested, SDX might be the most satisfactory for therapeutic use in preruminant animals, because it has good bioavailability after oral administration and long t1/2(el).
Veterinary drugs: disposition, biotransformation and risk evaluation.
Veterinary drugs may only be produced, distributed and administered after being licensed. This implies that, prior to marketing, a critical evaluation of the pharmaceutical quality, the clinical efficacy and the over-all pharmacological and toxicological properties of the active substances will be performed by national and/or supranational authorities. However, despite a sophisticated legal (harmonized) framework, a number of factors involved in residue formation and safety assessment remain unpredictable or dependant on the current 'state of the art' in the understanding of molecular pharmacology and toxicology. For example, drug disposition and residue formation in the target animal species may be influenced by a broad variety of physiological parameters including age, sex and diet, as well as by pathological conditions especially the acute phase response to infection. These factors affect both drug disposition and metabolite formation. Furthermore, current thinking in toxicological risk assessment is influenced by recent developments in molecular toxicology and thus by an increased but still incomplete understanding of the interaction of a toxic compound with the living organism. General recognized principles in the evaluation of potential toxicants are applied in the recommendation of withdrawal times and the establishment of maximum residue limits (MRL values). Apart from toxicological-based assessment, increasing awareness is directed to other than toxicological responses, especially the potential risk of effects of antimicrobial residues on human gastrointestinal microflora. Thus, the methodology of risk assessment is discussed in the context of the recently established legal framework within the European Union.
Economics of General-Purpose Assembly Robots
Summary A study of the comparative economics of various automatic assembly systems using general-purpose assembly robots is described. In the study, use is made of a “typical” candidate assembly whose profile is obtained from statistical analysis of actual products submitted by interested companies. It is shown that the choice of assembly system and the various parts presentation methods depends on three main factors, namely: the annual production volume per shift, the number of parts in the product and the equipment payback period.