Allergovet 10% Injectable Solution (Diphenhydramine HCl 100mg/ml) – Anti-Allergy & Antihistamine for Dogs, Horses, Cattle & Pigs | 50ml

What Is Allergovet 10%?

Allergovet 10% is a veterinary injectable solution containing diphenhydramine hydrochloride 100mg per ml (10% w/v). It is a first-generation H1 antihistamine for intramuscular (IM) or subcutaneous (SC) administration in multiple species including dogs, horses, cattle, sheep, goats, and pigs. The 50ml multi-dose vial delivers rapid parenteral antihistamine action in emergency and non-emergency allergic and inflammatory conditions across a broad range of farm and companion animals.

Allergovet 10% can also be applied topically to mucous membranes as a local anaesthetic — diphenhydramine has intrinsic membrane-stabilising (sodium channel blocking) properties similar to lidocaine, making it useful for mucosal anaesthesia when conventional local anaesthetics are unavailable.

How Diphenhydramine Works

Diphenhydramine is a first-generation H1-receptor antagonist. It works by competitively blocking histamine at H1 receptors throughout the body — in the skin, blood vessels, bronchial smooth muscle, and gastrointestinal tract. By occupying H1 receptors before histamine can bind, diphenhydramine prevents the cascade of allergic and inflammatory effects that histamine triggers:

• Vasodilation and capillary leak — responsible for urticaria (hives), swelling, and the hypotension of anaphylactic shock
• Bronchoconstriction — causing respiratory distress in allergic reactions and asthma
• Itch and pain sensory nerve stimulation — causing pruritus in allergic skin disease
• Increased gastrointestinal secretions — relevant in allergic gut responses

In addition to H1 blockade, diphenhydramine has significant anticholinergic (antimuscarinic) activity, which contributes to its usefulness in conditions involving smooth muscle spasm and excessive secretions — including forestomach atony in ruminants and bronchial asthma. Its CNS-depressant properties provide a mild sedative effect that can be beneficial in distressed or reactive animals.

The local anaesthetic effect arises from diphenhydramine’s ability to block sodium channels in neuronal membranes — a mechanism shared with lidocaine — making topical application to mucosae a clinically useful option.

Indications by Species

Dogs

• Urticaria (hives) — acute skin wheals following insect stings, food reactions, or drug exposure
• Allergic dermatitis and dermatoses — hypersensitivity skin reactions
• Allergic conjunctivitis — ocular signs of systemic or localised allergy
• Drug and feed allergies — including vaccine reactions
• Anaphylactic shock — as an adjunct to adrenaline (epinephrine) in the emergency management of anaphylaxis
• Insect and snake bites — to reduce histamine-mediated swelling and local reaction
• Motion sickness — diphenhydramine’s central anticholinergic activity reduces vestibular stimulation
• Pre-medication before vaccination — in animals with a known history of vaccine reactions

Horses

• Anaphylaxis and acute allergic reactions — drug reactions, insect hypersensitivity
• Laminitis acuta (aseptic diffuse pododermatitis) — diphenhydramine is used in the acute phase to reduce the inflammatory mediator cascade contributing to lamellar disruption in the hoof; not a primary treatment but part of supportive management
• Periodic ophthalmia (recurrent uveitis / moon blindness) — antihistaminic and anti-inflammatory support during acute flare-ups
• Chronic alveolar emphysema (heaves / RAO) — antihistaminic reduction of bronchospasm and airway inflammation
• Insect bite hypersensitivity (sweet itch) — acute management of urticaria and pruritus
• Transport disease / travel stress reactions — mild sedative and antihistaminic support

Cattle and Large Ruminants

• Anaphylactic shock — adjunct to adrenaline in acute anaphylaxis (e.g. following vaccine reactions, insect mass attacks)
• Drug and feed allergies — urticaria and systemic allergic responses
• Bronchial asthma — antihistaminic and anticholinergic reduction of bronchoconstriction
• Forestomach atony (rumen atony) — the anticholinergic component of diphenhydramine contributes to smooth muscle normalisation; used as adjunct support in atony cases
• Retained placenta — antihistaminic and anti-inflammatory support to reduce uterine inflammation and promote placental separation
• Insect and snake bites

Sheep and Small Ruminants

• All indications applicable to large ruminants (at lower volumes)
• Gangrenous mastitis — antihistaminic and anti-inflammatory adjunct support in treatment of gangrenous mammary infection
• Retained placenta — as for cattle

Pigs and Piglets

• Oedema disease (piglets) — caused by Shiga toxin-producing E. coli; toxin-mediated vasogenic oedema involves histamine-related vascular permeability; diphenhydramine reduces capillary leak as part of supportive management
• Allergic reactions — drug reactions, feed allergies, insect bites

Dosage

Allergovet 10% is administered intramuscularly (IM) or subcutaneously (SC). The general parenteral dose is 1–2 mg diphenhydramine HCl per kg body weight, which corresponds to 0.01–0.02 ml of the 10% solution per kg.

In shock or anaphylaxis: Doses may be doubled. In life-threatening anaphylaxis, diphenhydramine is given as an adjunct to adrenaline (epinephrine) — never as a substitute. Administer adrenaline first in anaphylactic shock; Allergovet provides secondary antihistaminic support.

Topical / mucosal anaesthesia: Apply the 10% solution (undiluted) as drops directly onto the mucosal surface. Onset of local anaesthetic effect is typically within 2–5 minutes.

Route and Frequency of Administration

• IM (intramuscular) — preferred route for rapid systemic action
• SC (subcutaneous) — acceptable; slightly slower onset than IM
• Topical — applied to mucosae for local anaesthesia only
• Repeat administration as directed by your veterinarian, typically every 8–12 hours depending on severity and response

Withdrawal Periods

Very short withdrawal periods make Allergovet 10% practical for use in productive farm animals where rapid return to slaughter or milking eligibility is important.

Contraindications

• Known hypersensitivity to diphenhydramine or other antihistamines
• Use with caution in animals with glaucoma — anticholinergic effects may raise intraocular pressure
• Use with caution in animals with prostatic enlargement — anticholinergic effects may worsen urinary retention
• Use with caution in cardiovascular disease — may cause tachycardia at higher doses
• Avoid in pregnant animals unless benefit clearly outweighs risk — safety in pregnancy not fully established
• Do not use as the sole treatment in anaphylactic shock — adrenaline must be administered first

Drug Interactions

• CNS depressants (sedatives, tranquillisers, barbiturates, anaesthetics): additive CNS depression — use with caution and reduce doses accordingly
• Anticholinergic drugs (atropine, butylscopolamine): additive anticholinergic effects — increased risk of ileus, urinary retention, dry mouth, tachycardia
• Epinephrine / adrenaline: diphenhydramine is a useful adjunct in anaphylaxis management alongside adrenaline
• Heparin: diphenhydramine may antagonise heparin activity

Side Effects

• Sedation / CNS depression — most common; animals may appear drowsy or dull for several hours after injection; generally resolves without intervention
• Dry mouth (xerostomia) — anticholinergic effect; evident as reduced salivation
• Hyposthenuria — reduced urine concentrating ability (reduced urine specific gravity); transient
• Tachycardia — anticholinergic effect at higher doses
• Urinary retention — particularly in males; monitor in dogs after injection
• Paradoxical excitation — rare; occasionally seen in cats and some individuals of other species

Storage

• Store between 15–30°C, protected from light
• Keep in the original vial; do not transfer to other containers
• Once broached, use under appropriate aseptic conditions; observe standard multi-dose vial hygiene
• Keep out of reach of children

Frequently Asked Questions

Can Allergovet 10% be used in cats?

The official label targets ruminants, pigs, dogs, and horses. Diphenhydramine can be used in cats but with extra caution — cats are more sensitive to anticholinergic effects and can occasionally show paradoxical CNS excitation rather than sedation. If using in cats, always consult a veterinarian for appropriate dosing, as the dose is lower and the margin for adverse effects is narrower than in dogs.

Is Allergovet 10% the same as Benadryl?

The active ingredient is the same — diphenhydramine hydrochloride — but Allergovet 10% is a veterinary injectable formulation at 100mg/ml, designed for IM and SC injection in large and small animals. Human Benadryl products are formulated for oral use in humans at much lower concentrations. Never use human Benadryl formulations as injectable solutions in animals.

Can Allergovet replace adrenaline in anaphylactic shock?

No. In life-threatening anaphylaxis, adrenaline (epinephrine) is the first-line emergency treatment and must be given immediately. Allergovet 10% is used as an adjunct — it blocks ongoing histamine-mediated effects after adrenaline has been administered. Diphenhydramine alone is not fast enough or potent enough to reverse severe anaphylaxis.

How quickly does Allergovet 10% work?

Following IM injection, peak blood levels are reached within 30–60 minutes. Clinical improvement in acute allergic reactions (reduction in urticaria, itch, and swelling) is typically visible within 30 minutes to 1 hour. The sedative effect may be evident even sooner. Duration of action is typically 4–8 hours.

Why is Allergovet used for laminitis in horses?

Acute laminitis involves a complex inflammatory cascade including histamine release and vascular disruption in the hoof lamellae. Diphenhydramine is used as part of supportive management to reduce the histamine-mediated vascular component of the inflammatory process. It is not a primary treatment for laminitis — it supports a broader management protocol that should include veterinary assessment, NSAIDs, dietary restriction, and appropriate shoeing/support.

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