Foals neonatal

The pharmacokinetics of ketoprofen has also been studied in neonatal foals. Neonatal foals clear ketoprofen more slowly and have a larger than adult horses (VVilcke et al 1998). It is important to note that these studies were carried out in healthy normal foals and that pharmacokinetic parameters could be altered in sick or compromised foals. Nevertheless, the results of these studies suggest that the initial dose of ketoprofen may need to be increased in neonatal foals and the subsequent dosing interval increased in order to produce plasma concentrations comparable to adults (Wilcke et al 1998). 

Intraosseous administration is a feasible alternative to intravenous injection of some antimicrobial agents (sodium ampicillin or amoxicillin, cefotaxime, gentamicin or amikacin sulfate) in neonatal foals (less than 7 days of age). This particularly applies in the treatment of septicemia in neonatal foals that are in a state of septic shock or dehydration or both. The plasma concentration profiles for amikacin administered intraosseously and intravenously to neonatal foals are similar (Fig. 4). ... 

Aminoglycosides are almost exclusively eliminated by glomerular filtration. Elimination is dependent on cardiovascular and renal function, age, fever, other physiological factors and the V. The half-lives are usuaUy 1-2 h in normal adult horses but are increased in horses with renal dysfunction and in neonates. Increased dosage intervals must be used in these patients to prevent nephrotoxicity. The renal elimination of the aminoglycosides increases with age. The half-life of gentamicin is approximately 50% longer in 1-day-old than in 30-day-old foals. 

In horses, 75-100% of a gentamicin dose is excreted unchanged in the urine in the first 8-24 h after administration. The half-life is 1-2 h and is longer in neonatal foals than in older foals and adult horses. Any gentamicin that accumulates in the renal cortical tissue is eliminated slowly however, these levels are often below the limits of quantification of the assays used and are, therefore, not demonstrated in pharmacokinetic studies. 

The elimination of amikacin is similar to gentamicin. The half-life of amikacin ranges from 1 to 3 h in adult horses but may be as long as 5 h in neonatal foals. 

Chloramphenicol is not administered i.v. to horses because of its short half-life, which precludes achieving therapeutic plasma concentrations. Injections of chloramphenicol i.m. are associated with severe pain in horses and are not recommended. Chloramphenicol and florfenicol are absorbed rapidly and extensively after p.o. administration to horses. The bioavailability was 83% after p.o. administration of chloramphenicol to neonatal foals and of florfenicol in an organic solvent. 

Amikacin 0.14-0.22 (adult), 0.4-0.6 (foal) 1-3 (adult), 5 (foal) Base RE Infections with bacteria resistant to gentamicin 6mg/kg i.v, i.m., s,c. once daily 20 mg/kg i,v once daily in neonatal foals... 

In neonatal foals, enteritis is associated with the accumulation of fluid in the bowel lumen and either poor propulsive motility or excessive contractions of the bowel. Also, neonatal foals with septicemia often have poor intestinal motility. In these cases, neither enteral feeding nor pharmacological stimulation of intestinal motility is indicated. In older foals, duodenitis is associated with... 

Impaction of the small colon with meconium occurs in neonatal foals. T) ically, these impactions result from an excessive amount of meconium. Small-colon impactions are unusual in older foals and occur infrequently in adult horses. Apparently there is a posihve associahon between small-colon impaction and fecal culture of Salmonella spp. (Rhoads et al 1999). Small-colon impactions in adult horses may represent a primary motility disorder secondary to inflammation. Small-colon impactions are often treated conservatively using enemas, although in some cases surgery is required. Drugs that alter motility are typically not used in these cases. 

Sanchez L C, Lester G D, Merritt A M 1998 Effect of ranitidine on intragastric pH in clinically normal neonatal foals. Journal of the American Veterinary Medical Association 212 1407-1412... 

Seizures occur more infrequently in horses than in dogs and cats. Seizures are seen in adult horses from brain trauma, bacterial meningitis, viral encephalitis and, rarely, hepatic encephalopathy or vascular accidents. Convulsions are seen in young neonatal foals with NMS as a result of brain hypoxia and in Arabian foals aged 3-9 months (idiopathic Arabian epilepsy). Anticonvulsant therapy is used to prevent the spread of the seizure focus, increase (raise) the seizure threshold and decrease the electrical excitement of abnormal... 

In horses, diazepam is distributed widely to the tissues and metabolized extensively the values quoted for elimination half-life range from 3 to 22 h (Muir et al 1982). High doses of benzodiazepines cause muscle weakness, facial and neck muscle fasciculations, ataxia and recumbency. In neonatal foals, the i.v. administration of benzodiazepines can cause respiratory depression or arrest, through accumulation (Norman et al 1997), so resuscitation equipment should be available and repeated doses should be administered with extreme care. 

Spear A M, Hill M R, Mayhew I G et al 1984 Preliminary study on the pharmacokinetics of phenobarbital In the neonatal foal. Equine Veterinary Journal 16 368-371... 

Mannitol, the most commonly employed osmotic diuretic, is a large polysaccharide molecule. It is often selected for use in the prophylaxis or treatment of oliguric ARF. It is not absorbed from the gastrointestinal tract and, therefore, is only administered i.v. with its elimination dependent on the GFR (within 30 to 60 min with normal renal function). Mannitol is distributed within the plasma and extracellular fluid spaces and produces an increase in the serum osmolality and expansion of the circulating volume. It is not generally used for the treatment of edema because any mannitol retained in the extracellular fluid can promote further edema formation. Furthermore, acute plasma volume expansion may challenge individuals with poor cardiac contractility and can precipitate pulmonary edema. Mannitol is commonly administered for the treatment of cerebral edema consequent to head trauma or to hypoxic-ischemic encephalopathy in neonatal foals. Because mannitol promotes water excretion, hypernatremia is a potential complication in patients that do not have free access to water (Martinez-Maldonado Cordova 1990, Wilcox 1991). 

The quinolone antibiotic enrofloxacin has been found to cause articular cartilage damage in neonatal foals similar to that found in immature animals of other species (Vivrette 2001). Safety studies investigating the effects of enrofloxacin therapy in pregnant mares on the articular cartilage of fetal foals have not been performed therefore, caution should be exercised in the use of this antibiotic (see Ch. 2). 

Vivrette S L 1997 Parturition and postpartum complications. In Robinson N E (ed) Current therapy in equine medicine, 4th edn. Saunders, Philadelphia, PA, pp. 547-551 Vivrette S L 2001 Fluorquinolone arthropathy in neonatal foals. In Proceedings of the 47th American Association of Equine Practitioners Annual Convention, San Diego, CA, pp. 376-377... 

The pharmacokinetics of flunixin meglumine has also been studied in foals. In neonatal foals. 

The influence of the active metabolites becomes more significant with repeated administration of the parent drug, as might occur for the control of seizures (see Ch. 9), or chronic oral administration for continued sedation of a neonatal foal. Foals less than 21 days of age have a lower total body clearance of diazepam than older foals and adult horses and, therefore, a greater tendency to develop effects caused by drug accumulation (Norman et al 1997). 

Chaffin M K, Walker M A, McArthur N H et al 1997 Magnetic resonance imaging of the brain of normal neonatal foals. Veterinary Radiology and Ultrasound 38 102-111... 

Hug C G (eds) Pharmacokinetics of anaesthesia. Blackwell, Boston, MA, p. 157 Riedesel D H, Hildebrand S V 1985 Unusual response following use of succinylcholine in a horse anesthetized with halothane. Journal of the American Veterinary Medical Association 187 507-508 Robertson S A, Carter S W, Donovan M et al 1990 Effects of intravenous xylazine hydrochloride on blood glucose, plasma insulin and rectal temperature In neonatal foals. Equine Veterinary Journai 22 43-47 Roger T, Bardon T, Ruckebush Y 1994 Comparative effects of mu and kappa opiate agonists on the cecocolic motility In the pony. Canadian Journal of Veterinary Research 58 163-166... 

Conditions that result in the loss of large volumes of body fluids, such as high-volume diarrhea and gastric reflux, obviously require aggressive fluid therapy. However, many other horses may require fluid therapy because of prolonged mild-to-moderate fluid losses or prolonged reduced fluid intake. In neonatal foals, reduced fluid intake can rapidly result in hypovolemia and severe dehydration. This section addresses the identification of these horses and foals. 

Because of the risks associated with rapid changes in plasma osmolality (Adrogue Madias 2000a), 7% saline should probably not be administered to neonatal foals. The author has used 1.8% saline in foals with ruptured bladders (which are hyponatremic and hypochloremic) with apparently good clinical results. 

New research in human patients suggests a role for moderately hypertonic saline solutions (1.6-3%) in children with head injuries (Khanna et al 2000, Peterson et al 2000, Simma et al 1998). Whether this might also be useful in head injury or hypoxic ischemic encephalopathy in neonatal foals remains to be evaluated. 

Dextrose (5% dextrose (170kcal/l) (D5W) is used to replace a deficit of pure water (without accompanying electrolyte deficits) and is effectively hypotonic because the dextrose is rapidly metabolized to carbon dioxide and water. It is indicated where fluid loss exceeds electrolyte loss, which can occur in horses with strangulating intestinal lesions (Table 17.6) (Brownlow Hutchins 1982). Hypernatremia and hyperchloremia are also relatively common in neonatal foals, where... 

Plasma has been used extensively in horses with colitis and in neonatal foals for the passive transfer of immunity (Table 17.12). Plasma may either be purchased commercially or collected from donors and can be used fresh or stored frozen. Commercial plasma may be from donors who are hyperimmunized with certain equine pathogens and thus will contain antibodies to these pathogens. Hyperimmunized plasma may be preferable for the passive transfer of immunity... 

It is thought that both of these requirements are increased in disease (e.g. by an estimated 25-50% in sepsis Ralston 1990). Therefore, the daUy energy requirement of a hospitalized adult horse is approximately 30kcal/kg and normal neonatal foals require 55-65 kcal/kg daily for maintenance and up to 150 kcal/kg daily for growth and normal... 

A variety of fluid administration sets are available commercially. Sets that include large-bore tubing and a coil are suitable for most situations in adult horses and are recommended. Coils can also be helpful in neonatal foals, but wide-bore tubing is unnecessary. The flow rate can be estimated by counting the number of drops per 10 s in the drip chamber (Table 17.17) or can be set by using an electronic infusion pump. In all situations, a record should be kept of the time the infusion was started and the infusion rate to ensure that the desired volume is being delivered in the appropriate time. 

The "shock dose" concept is borrowed from small animal medicine. The shock dose for adult horses and neonatal foals is 50-80ml/kg crystalloid fluids. Depending on the perceived degree of hypovolemia, one-quarter to one-half of the shock dose is given as rapidly as possible (in less than 20 min) and the horse is reassessed. If the horse requires further fluid, another quarter of the shock dose is given and again the horse is reassessed. The final quarter of the shock dose is only given to severely hypovolemic horses. 

It is important to include all fluids being administered in the calculation of fluid rates and volumes. This is especially true in neonatal foals, which often receive dextrose solutions, plasma and... 

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