Topical administration/Local application:

• It refers to application of drugs to body surface like skin and mucus membrane.
• Drug administered by this route generally affects the part of the body to which it is applied thus producing localized effect.
• Some drugs applied topically are absorbed from the site of application and produce systemic effects.

Skin:

• A large number of drugs are applied externally on skin to produce various pharmacological effects either in the skin or deep inside the skin. Depending on site of action, route of application could be called epicutaneous (outside the skin) or percutaneous (through skin).
• Epicutaneous application is meant for delivering active principles only to site of application to produce localized effect. It is commonly used to eradicate and to treat superficial skin disorders such as eczema, psoriasis, dermal infections, itching and photosensitization.
• Percutaneous application drugs are specially designed to cross intact skin to produce systemic effects.
• Drugs applied on skin includes; ointments, lotions, liniments, solutions, creams, powders, and gel.
• Application of drugs on skin may be done in different ways:

a. Bath:

• Immersion of body or any parts into medicated water or any other fluid medium.
• Generally given for their local effects upon the skin in cutaneous disorders.

b. Dip:

• Type of bath in which whole body is immersed for a time in medicated fluid; particularly insecticidal fluid.
• More useful in small to medium sized animals like sheep and goat.
• It ensures complete wetting of animals in medicated fluid.

c. Inunction:

• Application of semi-solid or liquid drug preparation on surface of body by rubbing or friction.
• Used for application of ointments, liniments, oils, for local action or causing absorption of active ingredient.

d. Dusting:

• Application of fine particles of solid matter on the surface of the body.
• Used in therapeutics for application of dusting powders on skin for superficial skin conditions or in body cavities for surgical conditions.

e. Spray:

• Application of drug on skin in form of mist or cloud of small flying drops produced by spray machine.
• Coat should be combed or brushed in opposite directions and spray applied to roots of fur.
• Mostly used for application of analgesics, counter-irritants and ectoparasitic ides.

f. Pour-on:

• Application of drug solution along animal’s dorsal midline behind shoulders to hip bones.
• Some drug is absorbed percutaneously and produces systemic action.
• Commonly used for control of horn flies, lice and other arthropods of cattle and sheep.

g. Spot-on:

• Similar to pour-on, but specified amount of drug solution is applied to small area on head or back.
• Commonly used in application of ectoparasiticide in almost all species.

Mucus membranes:

• Topical application of drugs on mucus membranes is routinely used for providing localized action.
• In this case, drug remains largely unabsorbed at the site of application.
• Amount of drugs absorbed through mucus membrane depends on several factors such as drug concentration, size of drug molecule, drug lipid solubility, type of formulation, mucosal contact time, pH of absorption site and venous drainage of mucosal tissues.

a. Sublingual and buccal routes:

• Sublingual refers to drug administration below the tongue and buccal refers to spread over buccal mucosa or held in mouth.
• Useful for high lipid soluble drugs and non-irritating drugs.
• Thin epithelium and rich capillary network under tongue or in buccal mucosa permit rapid drug absorption and pharmacological action.
• Drug is saved from G.I destruction from digestive enzymes and hepatic inactivation.
• Drugs formulated in form of either soft tablet (sub-lingual) or hard tablets (buccal route).

b. Rectal/per-rectal route:

• Insertion of drugs into rectum either in the form of suppository or as an enema
• Rectal suppositories contain drugs primarily used for laxative purposes.
• For providing systemic effect in condition when it is impossible or undesirable to deliver medication by mouth.

c. Intra-ocular route:

• Drugs are applied topically as drops, solutions, gel or ointment onto the conjunctiva.
• It is used almost always for their local effects in eye.

d. Intranasal route:

• Drug solution applied as nasal sprays or drops.
• It has rapid onset of action.
• Commonly used to administer decongestants for rhinorrhoea and corticosteroids for allergies.

e. Intramammary route:

• Drugs are administered into orifice of teat usually with help of teat solution.
• Commonly used in milch animals for treatment of mastitis.

f. Intravaginal route:

• Drugs are applied topically on vagina to provide local action.
• It is commonly used in female animals to treat various gynecological disorders.
• Solutions, tablets, cream, gels and suppositories area available for vaginal applications.

g. Other routes:

• Intrauterine- into the uterus
• Intraurethral- into the urethra
• Intraaural/aural- into the ear