Chorionic Gonadotropin (HCG)
Chorionic Gonadotropin (HCG) is a gonad-stimulating polypeptide hormone obtained from the urine of pregnant women. It is widely used in veterinary theriogenology across multiple species. **Key Clinical Uses:** * **Cattle:** Treatment of nymphomania due to cystic ovaries. * **Dogs & Cats:** HCG challenge testing to diagnose retained testicular tissue (cryptorchidism) or functional ovarian tissue (ovarian remnant syndrome). * **Horses:** Induction of ovulation and management of persistent follicles. * **Exotics:** Management of estrus in ferrets, cystic ovaries in guinea pigs, and empirical treatment for feather plucking in birds. > **Clinical Pearl:** Because HCG is a large, foreign human protein, repeated administration in veterinary patients can lead to the formation of neutralizing antibodies, which may progressively diminish its clinical efficacy over time.
Mechanism: HCG is a glycoprotein that primarily mimics the action of **luteinizing hormone (LH)**, with minor **follicle-stimulating hormone (FSH)**-like activity. * **In Males:** Binds to LH receptors on testicular interstitial (**Leydig**) cells โ stimulates differentiation and **androgen (testosterone)** production โ promotes testicular descent and spermatogenesis. * **In Females:** Binds to LH receptors on the ovary โ stimulates the **corpus luteum** to produce **progesterone** โ triggers ovulation of mature follicles. In bitches, it also induces estrogen secretion.
Dosing by species
- HCG Challenge test (Male cats or females with suspected sexual differentiation disorder) ยท 250 micrograms ยท IM ยท once ยท Take sample for resting testosterone level. Administer HCG and take a 4 hour post sample.
- HCG Challenge test (Queens to diagnose functional ovarian tissue) ยท 50-100 Units ยท IM ยท once ยท Give during apparent estrous episode. Measure progesterone level in 5-7 days. >1 ng/mL indicates functional tissue.
- Infertility, reduced libido, testis descent in male cats ยท 50-100 Units ยท IM/SC ยท repeated if necessary
- Infertility in queens due to confirmed ovulation failure ยท 100-500 Units ยท IM ยท once
- To induce ovulation in anestrus queens ยท 250 micrograms ยท IM ยท once daily for 2 days ยท 2 days ยท Give FSH-P 2 mg IM daily until estrus is observed. Give HCG on first and second day of estrus.
- After artificial insemination ยท 50-75 Units ยท IM ยท immediately after insemination; repeat in 24 hours ยท 24 hours
- Estrus management ยท 100 Units ยท IM ยท repeat in 1 week as necessary ยท Most effective 14 days after onset of estrus.
- Treatment of ovarian cysts ยท 10,000 Units deep IM or 2500-5000 Units IV. Alternatively, 500-2500 Units injected directly into the follicle. ยท IM/IV/Intrafollicular ยท once ยท May repeat in 14 days if animal's behavior or physical exam indicates a need for retreatment.
Routes of administration
Contraindications
- Androgen-dependent neoplasias (e.g., prostatic carcinoma)
- Precocious puberty
- Known hypersensitivity to HCG
- Pregnancy (FDA Category X in humans, unless specifically indicated for reproductive management)
Adverse effects
- Hypersensitivity reactions / Anaphylaxis
- Pain at the injection site
- Antibody production leading to diminished efficacy (with repeated use)
- Abortion in mares if given prior to the 35th day of pregnancy
- Gynecomastia, headache, depression, irritability, and edema (reported in humans)
Monitoring
- Testosterone levels (for HCG challenge test in males)
- Progesterone levels (for HCG challenge test in females)
- Resolution of clinical signs (e.g., cessation of estrus behavior, resolution of cystic ovaries)
- Signs of hypersensitivity or anaphylaxis post-injection
Overdose
No overdosage cases have been reported with HCG in veterinary medicine.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.