Altrenogest: veterinary dose and monograph

At a glance

Drug class

Veterinary drug

Also known as

Regumate, Matrix, Allyl trenbolone

Species with doses

Dogs, Horses and Pigs

General dose range

0.044 mg/kg PO q24h — check the species tables for the indication

Routes

PO

Last reviewed

1 October 2026

Indications

• Suppression of oestrus / behavioural control in performance mares
• Synchronisation and management of the mare's oestrous cycle for breeding
• Maintenance of pregnancy in mares with confirmed luteal insufficiency
• Oestrus synchronisation in gilts (swine, Matrix)

Altrenogest dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• Luteal insufficiency / pre-term labour: Plumb’s p.58: 0.088 mg/kg once daily when tocolytics fail (Davidson 2006); equine product 2 mL per 100 lb daily (Purswell). Stop 2–3 days before the expected whelping date; exogenous progestagen can predispose to pyometra. Avoid the first trimester.

Horses

• Oestrus suppression / cycle management: Papich 5e and Plumb’s p.58 (Regu-Mate label): 0.044 mg/kg (1 mL per 110 lb) PO once daily for 15 days, on the tongue or on grain; long-term oestrus suppression 0.044 mg/kg daily. Wear gloves — absorbed through skin; pregnant women must not handle.
• Maintenance of pregnancy (luteal insufficiency): Plumb’s p.58: 0.088 mg/kg PO once daily (Dascanio); 0.044 mg/kg once daily until day 60–120 or to term (McCue 2003); placentitis 22–44 mg per mare daily (Valla). Confirm luteal insufficiency.

Pigs

• Oestrus synchronisation (gilts): Papich 5e p25: 6.8 mL (15 mg altrenogest) per gilt once daily for 14 consecutive days, top-dressed on part of the daily feed. Gilts must observe the label slaughter withdrawal.

Contraindications

Known or suspected uterine infection/pyometra (progestins worsen it). Pregnant or potentially pregnant HUMAN handlers must not contact the product. Hypersensitivity. Use in food animals only per label (swine product). Avoid in mares with progesterone-responsive tumours.

Species-specific warnings

Horses: Avoid in mares with uterine infection (progestins worsen pyometra/endometritis). The product is a human reproductive hazard — handle with gloves.

Adverse effects

• Generally well tolerated in the mare at label dose
• Progestin effects (uterine — risk of worsening infection)
• Human exposure effects (menstrual disruption) — the key safety concern

Drug interactions

• Prostaglandins (PGF2α): opposing reproductive effects (progestin maintains, prostaglandin lyses CL)
• No major small-molecule pharmacokinetic interactions of note

Pregnancy and lactation

Used to MAINTAIN pregnancy in mares with luteal insufficiency; do not use to mask an inevitable abortion. The dominant safety issue is HUMAN handler exposure (pregnant/child-bearing-age women must avoid skin contact).

Monitoring

• Oestrus behaviour / cycle status (efficacy)
• Pregnancy status when used for maintenance (ultrasound; confirm ongoing viability)
• Uterine health (avoid in infection)
• Handler safety compliance (gloves; pregnant staff excluded)

Toxicity and overdose

Very well tolerated in target species at label doses. The principal "toxicity" concern is accidental HUMAN absorption (transdermal), which can disrupt the menstrual cycle and is contraindicated in pregnancy — hence mandatory gloves and careful handling.

Management: In animals: supportive; no specific antidote required. Human exposure: wash skin thoroughly with soap and water immediately and seek medical advice (especially if pregnant). Reinforce protective handling.

Clinical pearls

• The standard oral progestin for suppressing oestrus/behaviour in performance mares — effect reverses within days of stopping
• Also maintains pregnancy in luteal-insufficient mares — but confirm the indication; don't use it to prop up a doomed pregnancy or mask uterine infection
• HANDLER SAFETY is paramount: it absorbs through skin and disrupts human menstrual cycles — gloves are mandatory and pregnant/child-bearing-age women must not handle it
• In swine (Matrix), it synchronises gilt oestrus when fed for ~14–18 days

Mechanism of action

A synthetic progestogen that binds progesterone receptors and exerts negative feedback on the hypothalamic–pituitary axis, suppressing GnRH/LH and thereby preventing follicular development and oestrus. By mimicking luteal progesterone it also maintains uterine quiescence and supports pregnancy in mares lacking adequate endogenous progesterone. On withdrawal, the axis is released and oestrus resumes.

Formulations and products

• Oral solution 2.2 mg/mL (0.22 %, Regumate)
• Oral solution 4 mg/mL (0.4 %, Matrix — swine)
• Regumate (MSD Animal Health) — 2.2 mg/mL (0.22 %) oral solution, Oral solution
• Matrix (MSD Animal Health) — 4 mg/mL (0.4 %) oral solution, Oral solution

Storage

Oral solution: 15–30 °C, protect from light; handle with impermeable gloves; keep away from women of child-bearing potential.

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

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Frequently asked questions