Zycortal 25mg/ml (Desoxycortone Pivalate / DOCP) Prolonged-Release Injection for Dogs – Mineralocorticoid Replacement for Addison’s Disease | 4ml

What Is Zycortal?

Zycortal is a prolonged-release injectable suspension manufactured by Dechra Animal Health, containing desoxycortone pivalate (DOCP) 25mg/ml. It is used for long-term mineralocorticoid replacement therapy in dogs with primary hypoadrenocorticism (Addison’s disease) that have lost the ability to produce sufficient aldosterone from their adrenal glands.

Each 4ml vial contains 100mg desoxycortone pivalate. Zycortal is administered by subcutaneous injection approximately every 25–40 days, with the exact dose and interval adjusted to each individual dog based on clinical response and electrolyte monitoring.

Understanding Addison’s Disease — Why Zycortal Is Needed

The adrenal glands sit above the kidneys and produce two essential categories of hormones:

• Mineralocorticoids (primarily aldosterone) — regulate sodium and potassium balance, and therefore blood volume and blood pressure
• Glucocorticoids (primarily cortisol) — regulate metabolism, immune function, and the stress response

In Addison’s disease (primary hypoadrenocorticism), the adrenal cortex is destroyed — most commonly by immune-mediated attack — and production of both hormone types fails. The consequences of mineralocorticoid deficiency are particularly life-threatening:

• Without aldosterone, the kidneys cannot retain sodium — sodium is lost in the urine, followed by water, causing dangerous dehydration and low blood pressure
• Simultaneously, potassium accumulates in the blood (hyperkalaemia), disrupting cardiac muscle function and potentially causing life-threatening arrhythmias
• The combination of hyponatraemia, hyperkalaemia, hypovolaemia and cardiovascular compromise constitutes an Addisonian crisis — a medical emergency

Zycortal replaces the missing mineralocorticoid function. It does not replace glucocorticoids — most dogs with Addison’s disease also require concurrent prednisolone to address the glucocorticoid deficiency.

How Desoxycortone Pivalate (DOCP) Works

Desoxycortone pivalate is a synthetic mineralocorticoid that mimics aldosterone’s actions at the mineralocorticoid receptors in the renal tubules. It promotes:

• Sodium and chloride retention in the kidneys — retaining sodium retains water, restoring blood volume and blood pressure
• Potassium and hydrogen ion excretion — correcting the dangerous hyperkalaemia of untreated Addison’s disease

The pivalate ester formulation creates a depot effect after subcutaneous injection: the drug is slowly released from the injection site over several weeks rather than being absorbed immediately, providing prolonged activity from a single injection. Peak blood concentrations (Tmax) occur approximately 10 days after injection, and the plasma half-life is approximately 17 days. This pharmacokinetic profile allows dosing intervals of approximately 25–40 days in most dogs.

Important: Zycortal Replaces ONLY Mineralocorticoids

This is the most clinically critical point about Zycortal. It provides mineralocorticoid replacement only. Dogs with primary Addison’s disease have combined mineralocorticoid and glucocorticoid deficiency. Without glucocorticoid replacement (prednisolone or hydrocortisone), the dog will remain ill despite Zycortal treatment.

The standard management of Addison’s disease requires:

• Zycortal (DOCP) — monthly to 6-weekly subcutaneous injection for mineralocorticoid replacement
• Prednisolone — daily oral tablets for glucocorticoid replacement (typically at physiological replacement doses: 0.1–0.2mg/kg/day)

Your veterinarian will prescribe both components and adjust each based on the dog’s response and monitoring results.

Dosage and Monitoring Protocol

Initial Dose

The starting dose is 2.2mg/kg body weight administered as a single subcutaneous injection.

The 4ml vial (100mg total) provides approximately one full dose for a 45kg dog. For smaller dogs, vials can be used across multiple doses under aseptic technique if your vet advises this. Always use a graduated syringe for accurate dose measurement.

Monitoring Schedule and Dose Adjustment

The Zycortal dosing protocol is individualised based on serum Na+/K+ ratio monitoring. The normal target Na+/K+ ratio is 27–32.

Day 10 Check (Intermediate Assessment)

Approximately 10 days after the first injection (which is the time of peak drug concentration), measure the serum Na+/K+ ratio. Use these results to determine how to adjust the second dose (given on approximately Day 25):

Day 25 Check (Second Dose Assessment)

Approximately 25 days after the first injection, reassess the dog’s clinical status and Na+/K+ ratio:

• If clinically normal and Na+/K+ ratio 27–32 — administer second dose using the adjusted dose from the Day 10 table above
• If clinically normal and Na+/K+ ratio > 32 — either adjust dose (reduce) or consider extending the dosing interval
• If clinically abnormal or electrolytes outside target — reassess glucocorticoid dose and/or Zycortal dose under veterinary guidance

Long-Term Maintenance

Once the optimal dose and interval are established, they are maintained consistently. In the Zycortal clinical trial:

• Average final dose: 1.9 mg/kg (range 1.2–2.5 mg/kg)
• Average dosing interval: 38.7 days (range 20–99 days)
• Most dogs settled on an interval of 25–46 days

Adjusting for Ongoing Clinical Signs

Administration

1. Shake the vial carefully to resuspend before use — Zycortal is a suspension that settles
2. Administer by subcutaneous injection (not intramuscular or intravenous)
3. Use an appropriately graduated syringe for accuracy — this is especially critical for small dogs where volumes are very small
4. Do not mix Zycortal with other veterinary medicinal products in the same syringe
5. Administer at room temperature — allow the vial to equilibrate from refrigerator temperature before injecting

Addisonian Crisis — Emergency Guidance

An Addisonian crisis is a life-threatening emergency. A dog in Addisonian crisis must NOT receive Zycortal as the first treatment. Before Zycortal is started, a dog with severe hypovolaemia, dehydration, pre-renal azotaemia, and cardiovascular compromise requires:

1. Emergency IV fluid therapy with isotonic saline — to restore sodium, blood volume, and perfusion
2. Emergency glucocorticoid injection (dexamethasone or hydrocortisone IV) — for stress and shock management
3. Cardiac monitoring — hyperkalaemia causes potentially fatal arrhythmias
4. Emergency stabilisation at a veterinary clinic before starting long-term management with Zycortal

If your dog is acutely unwell — collapsed, severely depressed, vomiting, unable to stand — this is a veterinary emergency. Do not attempt to give Zycortal at home. Seek emergency veterinary care immediately.

Stress Dosing Protocol

Dogs with Addison’s disease cannot produce extra cortisol in response to stress (surgery, illness, travel, trauma). Before any anticipated stressful event:

• Temporarily increase the prednisolone dose (typically 2–3× the maintenance dose) starting the day before the stressor and continuing for 1–3 days
• If the dog is vomiting and cannot take oral prednisolone, injectable dexamethasone may be needed — keep a pre-loaded syringe available if your vet advises this
• Zycortal dosing interval adjustments are generally not required for short-term stressors, but should be discussed with your veterinarian for major events (e.g., surgery)

Contraindications

• Hypersensitivity to desoxycortone pivalate or any excipient (chlorocresol)
• Use with caution in dogs with congestive heart failure — sodium retention worsens fluid overload
• Use with caution in severe renal disease — altered electrolyte handling
• Use with caution in primary hepatic insufficiency
• Use with caution in oedema of any cause
• Safety not established in pregnant or lactating bitches

Drug Interactions

Side Effects

• Polydipsia and polyuria (very common) — increased thirst and urination; usually indicates appropriate mineralocorticoid activity or mild over-replacement; assess Na+/K+ ratio if excessive
• Common: unusual urination patterns, lethargy, alopecia (hair loss), dyspnoea, vomiting, reduced appetite, reduced activity, depression, diarrhoea, polyphagia, tremors, fatigue, urinary tract infections
• Uncommon: injection site pain and swelling
• Rare: pancreatic disorders (may be exacerbated by concurrent glucocorticoid use)

Storage

⚠️ Refrigerate: Store at 2°C – 8°C (36°F – 46°F). Do not freeze.

• Keep in original packaging, protected from light
• Allow the vial to reach room temperature before injection
• Shake gently before use to resuspend
• Once opened, note date of first use and follow your veterinarian’s guidance on shelf life of the broached vial
• Keep out of reach of children

Zycortal vs Fludrocortisone — Two Options for Mineralocorticoid Replacement

Frequently Asked Questions

Does my dog need prednisolone as well as Zycortal?

Yes — almost certainly. Zycortal only replaces mineralocorticoid function. The adrenal cortex in dogs with primary Addison’s disease also fails to produce glucocorticoids (cortisol). Without prednisolone (or another glucocorticoid) to replace this, dogs remain unwell despite Zycortal treatment. Most Addison’s dogs are managed with both Zycortal every 25–40 days AND daily prednisolone at physiological doses. Discuss the combined management plan with your veterinarian.

How do I know if the Zycortal dose is correct?

By monitoring the serum sodium/potassium (Na+/K+) ratio. A ratio of 27–32 is the target. Your vet will check this at Day 10 and Day 25 initially to adjust the dose. Once stable, electrolytes are typically checked every 3–6 months. Clinical signs — particularly excessive thirst/urination or returning weakness — should prompt an earlier check.

What happens if I miss or delay a Zycortal injection?

The mineralocorticoid effect of the previous dose gradually wanes. The dog may begin showing signs of mineralocorticoid deficiency: lethargy, reduced appetite, vomiting, weakness, and in severe cases collapse (Addisonian crisis). If a dose is delayed, contact your veterinarian — do not simply give the next scheduled dose without electrolyte assessment, as the dog may need emergency treatment.

Can I give Zycortal at home, or must it be at the clinic?

Zycortal is a subcutaneous injection. Some veterinarians teach owners to administer it at home once the technique and dose have been established. However, the associated electrolyte monitoring (blood tests) must be conducted at the veterinary clinic. Discuss home administration with your vet.

How many doses does the 4ml vial provide?

It depends entirely on your dog’s weight. At the initial dose of 2.2mg/kg: a 10kg dog needs 0.88ml (about 4.5 doses per vial); a 20kg dog needs 1.76ml (about 2.3 doses per vial); a 40kg dog needs 3.52ml (about 1 full dose per vial). For most medium-to-large dogs, one vial per injection visit is practical. See the dosage table above for your dog’s weight.

Related products: Prednisolone 5mg Tablets – Glucocorticoid for Addison’s disease co-management