A gel is a nongreasy, semisolid, aqueous solution. The semisolid properties are due to a polymer imparting a continuous structure to the hydrophilic liquid. The polymers used include natural gums such as tragacanth, pectin, and agar; semisynthetic materials such as methylcellulose, hydroxymethylcellulose, and carboxymethylcellulose; and synthetic polymers such as carbopol. Medicaments are generally well released from gels, which are easily washed off on account of their water miscibility.
A solution for topical use is a mixture of two or more components that form a single phase down to the molecular level. Topical solutions include eye drops, ear drops, and lotions.
Eye drops are sterile liquids that contain a range of drugs, including local anesthetics, antibiotics, anti-inflammatory agents, and drugs acting on the autonomic nervous system of the eye.
They are instilled onto the eyeball or within the conjunctival sac. Ear drops are solutions of drugs such as antibiotics, insecticides, or anti-inflammatory agents. They are applied to the external auditory canal. A lotion is usually an aqueous solution or suspension for application to inflamed, ulcerated skin.
Lotions cool the skin by evaporation of solvents, leaving a film of dry powder. Lotions are suitable for use on hairy areas and for lesions with minor exudation and ulceration. A suspension concentrate for topical use is a mixture of insoluble, solid active ingredients, which are typically at high concentrations, in water or oil.
Suspension concentrate formulations are generally water-based; the water-insoluble active ingredients and inert ingredients are of very small particle size 0. Other formulation additives include suspending agents, surfactants, and other excipients to ensure the production of a shelf-stable, pourable product.
Surfactants wet, disperse, and stabilize the solid particles in the continuous phase, prevent flocculation, and prevent changes in particle size. Thickening agents are included to increase the viscosity of the formulation, thereby overcoming sedimentation of the suspended particles and affording good longterm stability. Suspension concentrates are used topically as pour-ons, plunge and shower dip concentrates, and jetting fluids.
A suspoemulsion combines the elements of an emulsion and a suspension, allowing active ingredients with widely varying physical properties to be formulated in a single product. Typically, a suspoemulsion contains one or more solvent-soluble active ingredients in an emulsion phase, combined with one or more low solubility active ingredients in a continuous aqueous suspension phase. After dilution, an emulsifiable concentrate for topical use produces a two-phase system involving two immiscible liquids, a dispersed phase, consisting of fine oil droplets ranging in size from 0.
Active ingredients that are soluble in water-immiscible organic solvents are frequently formulated as emulsifiable concentrates. Zinc sulfate, used as a dip additive to minimize the spread of dermatophilosis in sheep, also adversely affects emulsions. A flank paint comprises an antifoaming agent such as a detergent or mineral oil and is used to prevent pasture bloating in cattle.
A flank paint is applied to the flanks of animals, from where it is licked off and ingested. Bloat, or ruminal tympany, refers to excessive accumulation of gas in the rumen. Frothy bloat commonly develops in cattle on pasture, particularly those grazing lush, leguminous pastures. Frothing of rumen ingesta occurs when the viscosity of the fluid is increased. Froth obstructs the cardia of the stomach, preventing the eructation of excessive gas produced in the rumen. Antifoaming agents reduce the stability of the froth by lowering the viscosity of the fluid ingesta.
In addition to alcohol, tinctures may contain cosolvents, stabilizers, and solubilizers. The reddish brown color of iodine tincture produces skin staining that delineates treated skin.
Friar's balsam is compound benzoin tincture and is used to protect and toughen ulcerated or fissured skin. A transdermal delivery gel consists of a vehicle, most commonly pluronic lecithin organogel PLO gel , which delivers drug via the transdermal route to the bloodstream. The micellar composition of PLO gel enhances skin penetration of the pharmaceutical agent present in the formulation.
PLO gel is generally well tolerated and is nontoxic if ingested. However, not all drugs are suitable for transdermal application, and there are relatively few studies of the bioavailability of drugs from compounded transdermal gels. Transdermal gels are used to deliver drugs to treat several diseases in dogs and cats, including undesirable behavior, cardiac disease, and hyperthyroidism. The dose is applied to the inner surface of the pinnae, thereby offering ease of administration, especially in cats.
A transdermal delivery patch typically consists of a drug incorporated into a reservoir, a protective backing layer, a rate-limiting release membrane, and an adhesive layer to secure the patch to the skin. The physicochemical properties of a drug suitable for transdermal delivery ideally include low molecular weight The control of internal and external parasites of companion and food-producing animals has led to development of specialized dosage forms, delivery systems, and application methods unique to veterinary medicine.
A spot-on formulation is a solution of active ingredient s that typically contains a cosolvent and a spreading agent. The active ingredients in spot-on products for flea, GI parasite, or heartworm control in dogs and cats include fipronil, imidacloprid, selamectin, pyriproxyfen, ivermectin, and moxidectin. Spot-on formulations are also available to control lice in cattle. The physicochemical properties of the active ingredient s are important determinants of topical or transdermal behavior.
Topical activity against ectoparasites depends to some extent on the active ingredient spreading, mixing with the sebum coating the skin and hair, and forming depots in the pilosebaceous units. The mechanism of percutaneous drug absorption varies between species and is not completely understood.
Backliner products for sheep consist of pour-on and spray-on formulations for the control of lice and sheep blowflies. Sheep lousicides include synthetic pyrethroids, organophosphates, and insect growth regulators. These products are formulated for pour-on application within 24 hr after shearing ie, off-shears or spray-on application in short-wool sheep with wool growth 6 wk. Their efficacy against lice depends on topical activity and not on percutaneous absorption of the active ingredient into the bloodstream.
Translocation of the pesticide from the application site to remote sites at concentrations lethal to lice is critical to the efficacy of these products and, in the case of pour-on applications, is facilitated by the increased secretion of wool grease that occurs at shearing. The active ingredients in sheep blowfly products include insect growth regulators, synthetic pyrethroids, and organophosphates. After their topical application, sheep blowfly larvicides form follicular depots and subsequently translocate as a coating on new wool growing out of the follicles.
The pesticides used include rotenone, synthetic pyrethroids, organophosphates, insect growth regulators, and macrocyclic lactones. The solution is applied under pressure and penetrates to the skin. Some pour-on products on the market are formulated to deliver an active ingredient percutaneously. The macrocyclic lactones ivermectin, moxidectin, doramectin, and eprinomectin are formulated as pour-on preparations for application to cattle. These formulations are usually solutions or emulsifiable concentrates for dilution with water before use.
The principal route of percutaneous absorption for most drugs in people is the intercellular pathway, making the intercellular lipid matrix the primary barrier to absorption.
However, this may not be the case in species in which the emulsifying properties of skin secretions and the large numbers of follicles and glands per unit surface area must be considered eg, cattle and sheep. Ionized solutes, for example, are reported to cross the skin of animals via shunt pathways sweat ducts, follicles. Pour-on products are formulated to spread without run-off when applied to the skin and to be resistant to rain. The formulation also facilitates the partitioning of the drug out of the vehicle and into the skin and transport of the drug across the skin.
The control of these processes is critical, because some drug is required to remain at the skin if the drug is to be active against external parasites that are not blood sucking. In addition, too rapid passage of drug through the skin may result in unacceptable chemical residues in tissues or milk. The plunge dipping of sheep and cattle for external parasites requires a dipping vat, which may be a portable unit or a permanent in-ground structure shielded from direct sunlight by roofing.
A draining pen located at the exit of the vat allows dip wash that drains off treated animals to return to the vat. Dip chemicals are usually formulated as aqueous solutions, emulsifiable concentrates, or suspension concentrates, all of which are diluted with water before use. The high costs associated with plunge dipping relate principally to the costs of chemicals for charging large vats, labor, and the disposal of the hazardous wastes.
Plunge dips must be managed properly and the pesticide maintained at the concentration recommended by the manufacturer. In the case of sheep, mechanical stripping results from the fleece acting as a sieve toward the active ingredient, with the degree of filtration being primarily determined by particle size.
Chemical stripping is due to the preferential absorption of pesticide by the fleece. Reinforcement refers to the addition of undiluted chemical product to the dip without the addition of water, whereas topping-up refers to the addition of water and undiluted chemical product to the dip vat to return the volume to the starting level. Proper dip management also minimizes contamination of the dip with organic matter. Hand spraying generally results in uneven coverage of animals and is considered an inefficient method of application.
By comparison, recirculating and nonrecirculating spray races facilitate whole body spraying and wet cattle to the skin. The situation with sheep is different—the very short contact time in a spray race limits the uptake of insecticide, which means the fleece seldom becomes saturated. Because of this, spray races should be used as an adjunct to shower or plunge dipping of sheep. Shower dips are less labor intensive than plunge dips and are cheaper to operate. A typical shower dip consists of a sump containing the dip wash, a pump, and a showering pen constructed with a concrete floor and fitted with rotating and fixed nozzles.
There are two types of shower dips: a conventional shower dip in which the sump volume is periodically maintained by adding fresh dip wash, and a constant replenishment shower dip in which a small-volume sump is continually filled from a large-volume supply tank to maintain dip levels. Proper dip management requires attention to the factors described above for plunge dipping. In addition, all equipment must be functioning properly for the fleece to become saturated.
Sheep should not be dipped by either the plunge or shower method until shearing wounds have healed to avoid clostridial infections or caseous lymphadenitis caused by Corynebacterium pseudotuberculosis. Moreover, the correct use of bacteriostats is recommended to prevent post-dipping lameness caused by Erysipelothrix insidiosa.
Insecticidal collars are plasticized polymer resins impregnated with an active ingredient. Collars for the control of ticks and fleas on dogs and cats release the active ingredient as a vapor, a dust, or a liquid, depending on the physicochemical properties of the chemical. Volatile liquid insecticides such as dichlorvos or naled are used in vapor-release collars. The insecticide distributes through the collar matrix as a vapor before being released. Powdered insecticides such as phosmet, stirofos, carbaryl, and propoxur are used in dust-release collars.
Translocation of the active ingredient within the collar matrix leads to deposits forming at the surface; distribution of the insecticide to the animal depends on the animal's physical activity.
Nonvolatile liquid insecticides such as chlorfenvinphos or diazinon are used in liquid-release collars. The active ingredient distributes as a liquid in the collar matrix and to the surface, where it is released. Two types of insecticide-releasing ear tags to control flies on cattle are available. One is constructed from a polymer that provides structural support and acts as a release rate-controlling matrix. The other is a membrane-based ear tag that consists of an insecticidal reservoir with a relatively impermeable backing on one side and a rate-controlling membrane on the other.
Back rubbers typically consist of burlap supported across lanes, gateways, or areas where cattle congregate. Back rubbers are charged by soaking thoroughly in oil-containing pesticide, typically a synthetic pyrethroid, an organophosphate, or a combination of the two. Dust bags facilitate the self-treatment of cattle to control flies and lice. They are constructed of an inner porous bag containing the active ingredient, which is commonly a synthetic pyrethroid or an organophosphate, and an outer weatherproof skirt.
Dust bags are hung in lanes or gateways so that passing cattle brush against them and receive a topical application of pesticide. Inhalational anesthetics are critical in management of anesthesia. Currently, enflurane, halothane, isoflurane, methoxyflurane, and nitrous oxide are the most commonly used inhaled anesthetic agents. These agents are usually delivered to animals in a carrier gas that includes oxygen, using an anesthetic machine fitted with one or more vaporizers and a patient breathing circuit.
Inhalational therapy of airway disease is used to deliver high concentrations of drugs to the lungs while avoiding or minimizing systemic adverse effects. To be delivered into the airways, a drug must be presented as an aerosol, either as solid particles or liquid droplets in air. Particle or droplet size largely determines the extent to which the drug penetrates the alveoli. Particles too small or too large for optimal delivery into alveolar sacs are either exhaled or deposited on larger bronchial airways.
Compared with delivery by the oral or parenteral routes, the onset of pharmacologic action of inhaled agents is faster and the doses administered smaller, thereby reducing the potential incidence of adverse systemic effects. The delivery systems used for inhalational therapy of airway disease in animals are nebulizers and metered-dose inhalers. In the poultry industry, inhalation of aerosolized vaccines is a common way to immunize flocks of birds.
From developing new therapies that treat and prevent disease to helping people in need, we are committed to improving health and well-being around the world. The Veterinary Manual was first published in as a service to the community. The legacy of this great resource continues in the online and mobile app versions today. This site complies with the HONcode standard for trustworthy health information: verify here.
Common Veterinary Topics. Videos Figures Images Quizzes. Oral Route of Administration and Dosage Forms. Oral Modified-release Delivery Systems for Ruminants. Capreomycin is an antibiotic used to treat tuberculosis. It is eliminated mainly by The subcutaneous tissue is also considered. The PBPK model diagram is shown in the figure provided. Additionally, you may account for the following processes in your simulations:.
The intramuscular IM drug delivery model represents the site of injection as a single compartment. Within this compartment, drug can be bound, and local clearance can take place. Drug can also be transported into the lymph or systemic circulation.
GastroPlus now provides two intramuscular IM dosage forms, both of which assume that drug is injected into the muscle tissue. One of these is an immediate release IR dosage form, with the other treated as controlled release CR.
The skin barrier function of full-term newborn babies is nearly the same as in older children and adults. However, the barrier function in premature babies is markedly impaired. The surface area of a baby is proportionally much greater than that of an adult.
Organs such as the liver, kidneys, blood and central nervous system are not fully developed. This means topically applied medications can be more likely to result in side effects and toxicity. Like oral medicines, some topical medications may be unsafe during pregnancy and lactation. These include:. Medications are classified according to their risk.
The FDA classification system is often used. Pregnancy categories used in New Zealand follow. Drugs which have been taken by a large number of pregnant women and women of childbearing age without any proven increase in the frequency of malformations or other direct or indirect harmful effects on the fetus having been observed.
Drugs that have been taken by only a limited number of pregnant women and women of childbearing age, without an increase in the frequency of malformation or other direct or indirect harmful effects on the human fetus having been observed.
Studies in animals[1] have not shown evidence of an increased occurrence of fetal damage. Category B2Drugs that have been taken by only a limited number of pregnant women and women of childbearing age, without an increase in the frequency of malformation or other direct or indirect harmful effects on the human fetus having been observed.
Studies in animals[1] are inadequate or may be lacking, but available data show no evidence of an increased occurrence of fetal damage. Studies in animals[1] have shown evidence of an increased occurrence of fetal damage, the significance of which is considered uncertain in humans. Drugs that, owing to their pharmacological effects, have caused or may be suspected of causing harmful effects on the human fetus or neonate without causing malformations.
These effects may be reversible. Drugs that have caused or are suspected to have caused or may be expected to cause an increased incidence of human fetal malformations or irreversible damage.
These drugs may also have adverse pharmacological effects. Drugs that have such a high risk of causing permanent damage to the fetus that they should not be used in pregnancy or when there is a possibility of pregnancy. See smartphone apps to check your skin. Books about skin diseases Books about the skin Dermatology Made Easy book.
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