Zoletil 100 / Zoletil 50 (Tiletamine + Zolazepam) Injectable Anaesthetic for Dogs & Cats – Virbac

What Is Zoletil?

Zoletil is a veterinary injectable anaesthetic manufactured by Virbac, combining two complementary active ingredients in a fixed-ratio lyophilised powder: tiletamine hydrochloride (a dissociative anaesthetic) and zolazepam hydrochloride (a benzodiazepine tranquilliser). Together they produce balanced general anaesthesia — surgical depth anaesthesia with muscle relaxation, analgesia, and sedation — without the need for inhalant equipment.

Zoletil is available in two concentrations: Zoletil 100 and Zoletil 50. It is licensed for use in dogs and cats and is also widely used in zoo and wildlife medicine for exotic and wild animal restraint.

Zoletil 100 vs Zoletil 50 — What Is the Difference?

Both Zoletil 100 and Zoletil 50 contain tiletamine and zolazepam in an equal 1:1 ratio. The difference is in the concentration after reconstitution with the 5 ml sterile water diluent supplied:

Zoletil 50 allows for more precise dosing in smaller animals where the lower concentration makes accurate volume measurement easier. Zoletil 100 is preferable for larger dogs and high-dose protocols where injecting smaller volumes is advantageous.

How Zoletil Works

Tiletamine — Dissociative Anaesthetic

Tiletamine is an NMDA (N-methyl-D-aspartate) receptor antagonist, pharmacologically similar to ketamine. It produces dissociative anaesthesia — a state where the animal is unaware of its environment and insensitive to pain, while protective reflexes (pharyngeal, laryngeal, cough) and muscle tone remain largely intact. Tiletamine provides strong superficial analgesia and moderate visceral analgesia. It does not suppress the respiratory centre at therapeutic doses. The eyes remain open during anaesthesia, and some animals may exhibit athetoid movements (slow, involuntary limb movements) — this is a normal feature of dissociative anaesthesia and should not be interpreted as inadequate anaesthesia depth; do not give additional Zoletil to stop it.

Zolazepam — Benzodiazepine Tranquilliser

Zolazepam is a benzodiazepine that enhances tiletamine’s CNS depression by inhibiting subcortical brain areas. It provides anxiolysis, sedation, and striated muscle relaxation, and critically, prevents tiletamine-induced convulsions. Zolazepam accelerates and smooths recovery from anaesthesia and improves the quality of muscle relaxation. Its elimination half-life differs between species: in dogs zolazepam is eliminated more rapidly than tiletamine (contributing to a rougher recovery), while in cats tiletamine is cleared faster (resulting in a smoother recovery).

Indications

• Sole anaesthetic for short-duration diagnostic procedures, examinations, minor surgery, imaging, wound care, and sample collection in dogs and cats
• Induction agent prior to maintenance with inhalant anaesthesia (isoflurane, sevoflurane) for longer procedures
• Chemical restraint for fractious, aggressive, or unmanageable animals where safe handling is not otherwise possible
• Wild and exotic animal capture — widely used in zoo and wildlife medicine for a broad range of species

Reconstitution Instructions

Zoletil is supplied as lyophilised powder in a sealed glass vial with a separate vial of sterile water for injection (5 ml). The solution must be prepared before use:

1. Remove the flip-off cap from both vials
2. Wipe the rubber stoppers of both vials with an alcohol swab
3. Draw up all 5 ml of sterile water using an aseptic technique
4. Inject the 5 ml of water into the powder vial
5. Gently swirl (do not shake vigorously) until the powder is fully dissolved
6. The reconstituted solution should be clear to slightly yellow — do not use if cloudy or particulate matter is present

Use the reconstituted solution immediately or store as below.

Dosage Table

All doses are expressed in mg/kg of body weight. Zoletil is administered by intramuscular (IM) or intravenous (IV) injection. Give IM injections deep into large muscle groups. For IV use, administer slowly.

Atropine Premedication

To control salivation, administer atropine sulfate subcutaneously 15 minutes before Zoletil:

• Dogs: 0.1 mg/kg SC, 15 minutes before Zoletil
• Cats: 0.05 mg/kg SC, 15 minutes before Zoletil

Top-Up Dosing

Zoletil has no cumulative effect and may be re-dosed if the procedure extends beyond the initial anaesthesia period. Additional doses must not exceed 1/3 to 1/2 of the initial dose. The maximum total dose (initial + all top-up doses combined) must not exceed:

• Dogs: 30 mg/kg total
• Cats: 72 mg/kg total

Duration and Recovery

• Surgical anaesthesia duration: 20–60 minutes depending on dose and species
• Analgesia persists longer than surgical anaesthesia depth
• Recovery is gradual and calm: 2–6 hours to full normal behaviour
• Keep the animal in a quiet, dimly lit, warm area during recovery — noise and bright light can disturb recovery quality
• Recovery may be prolonged in obese, old, or overdosed animals
• In cats: recovery tends to be smooth (tiletamine is cleared faster than zolazepam)
• In dogs: recovery can be rougher (zolazepam is cleared faster than tiletamine, leaving residual tiletamine effects)

Contraindications — Do Not Use Zoletil In:

• Animals with severe cardiac or pulmonary (respiratory) dysfunction
• Animals with pancreatic disease
• Pregnant animals at any stage of pregnancy — Zoletil crosses the placental barrier and causes respiratory depression in neonates
• Animals requiring Caesarean section
• Cats with renal insufficiency — tiletamine is renally excreted; impaired kidneys prolong anaesthesia dangerously
• Animals with hypertension
• Very young, very old, or severely debilitated animals — use with caution; reduce dose and monitor closely

Drug Interactions — Critical Warnings

Side Effects

• Hypersalivation — most common; managed with atropine premedication
• Athetoid movements (slow involuntary limb movements) — normal feature of dissociative anaesthesia; do not give additional Zoletil to stop these
• Apnoea (temporary breathing pause) may occur at high doses — ensure airway management is available
• Hyperthermia or hypothermia — monitor body temperature, especially in cats and small dogs with large body surface-to-mass ratio; supplemental heat may be required
• Pulmonary oedema — reported in cats; observe closely for dyspnoea, lethargy, anorexia, or unusual behaviour post-anaesthesia
• Vocalisation and excitement during induction or recovery — minimise external stimulation

Overdose — Signs and Emergency Management

Early signs of overdose include: loss of cranial and spinal reflexes, respiratory depression, cardiovascular depression (from doses above 20 mg/kg), CNS depression, and loss of protective airway reflexes.

Management is supportive: maintain airway, provide assisted ventilation with oxygen, and monitor cardiovascular status. Doxapram (5.5 mg/kg IV) has antagonistic activity against the tiletamine-zolazepam combination, increasing heart rate, respiratory rate, and reducing arousal time. There is no specific complete reversal agent for the tiletamine component.

Storage & Shelf Life

• Store unopened vials at +5°C to +20°C, away from light and moisture
• Shelf life unopened: 2 years from date of manufacture
• Reconstituted solution: use within 24 hours at room temperature or within 8 days if refrigerated at 4°C in the dark
• Do not freeze the reconstituted solution

Frequently Asked Questions

What is the difference between Zoletil 100 and Zoletil 50?

Both contain tiletamine and zolazepam in a 1:1 ratio, but Zoletil 100 has twice the concentration after reconstitution (100mg/ml total vs 50mg/ml total). Zoletil 100 is preferred for larger dogs and wildlife where small injection volumes are important. Zoletil 50 is more practical for cats and small dogs where the lower concentration allows for more precise volume measurement at small doses.

Can Zoletil be used as the only anaesthetic?

Yes. Zoletil is designed for use as a sole anaesthetic for short procedures (20–60 minutes) in dogs and cats. It can also be used as an induction agent followed by maintenance with an inhalant anaesthetic (isoflurane, sevoflurane) for longer surgeries.

How long does Zoletil anaesthesia last?

Surgical anaesthesia typically lasts 20–60 minutes depending on the dose. Analgesia persists beyond the anaesthesia period. Full recovery to normal behaviour takes 2–6 hours. Keep the animal in a quiet, warm, dark space during recovery to avoid disturbing the recovery quality.

Can I use acepromazine before Zoletil?

No — this combination is contraindicated. Phenothiazines such as acepromazine combined with Zoletil can cause severe cardiac and respiratory depression, hypotension, and hypothermia. Pulmonary oedema has been reported in cats. Use atropine (not acepromazine) for premedication to control salivation.

Can Zoletil be used in pregnant dogs or cats?

No. Zoletil is contraindicated at any stage of pregnancy and must not be used for Caesarean sections. Tiletamine and zolazepam cross the placental barrier and cause respiratory depression in newborns.

How long can reconstituted Zoletil be stored?

Reconstituted Zoletil solution can be stored for 8 days in a refrigerator at 4°C in a dark place, or for 24 hours at room temperature. Discard any unused solution after these periods.

What do I do if my animal is not waking up from Zoletil?

Prolonged recovery can occur with overdose, high doses, obesity, old age, or renal impairment (especially in cats). Keep the animal warm, maintain a clear airway, and monitor breathing and heart rate. Doxapram (5.5 mg/kg IV) can be administered to increase respiratory and heart rate and shorten arousal time. Contact your veterinarian immediately.

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