Chorionic Gonadotropin (HCG)
Chemistry - A gonad-stimulating polypeptide secreted by the placenta, chorionic gonadotropin is obtained from the urine of pregnant women. It occurs as a white or practically white, amorphous, lyophilized powder. It is soluble in water and practically insoluble in alcohol. One International Unit of HCG is equal to one USP unit. There are at least 1500 USP Units per mg.
Chorionic gonadotropin has many synonyms, including human chorionic gonadotropin , HCG , hCG , CG , chorionic gonadotrophin , pregnancy-urine hormone , and PU .
Storage/Stability/Compatibility - Chorionic gonadotropin powder for injection should be stored at room temperature (15-30°C) and protected from light. After reconstitution, the resultant solution is stable for 30-90 days (depending on the product) when stored at 2-15°C.
Pharmacology - HCG mimics quite closely the effects of luteinizing hormone (LH), but also has some FSH-like activity. In males, HCG can stimulate the differentiation of, and androgen production by, testicular interstitial (Leydig) cells. It may also stimulate testicular descent when no anatomical abnormality is present.
In females, HCG will stimulate the corpus luteum to produce progesterone, and can induce ovulation (possibly also in patients with cystic ovaries). In the bitch, HCG will induce estrogen secretion.
Uses/Indications - The veterinary product’s labeled indication is for “parenteral use in cows for the treatment of nymphomania (frequent or constant heat) due to cystic ovaries.” It has been used for other purposes in several species, refer to the Dosage section for more information.
Pharmacokinetics - HCG is destroyed in the GI tract after oral administration, so it must be given parenterally. After IM injection, peak plasma levels occur in about 6 hours. HCG is distributed primarily to the ovaries in females and to the testes in males, but some may also be distributed to the proximal tubules in the renal cortex.
HCG is eliminated from the blood in biphasic manner. The initial elimination half-life is about 11 hours and the terminal half-life is approximately 23 hours.
Contraindications/Precautions - In humans, HCG is contraindicated in patients with prostatic carcinoma or other androgen-dependent neoplasias, precocious puberty or having a previous hypersensitivity reaction to HCG. No labeled contraindications for veterinary patients were noted, but the above human contraindications should be used as guidelines. Antibody production to this hormone has been reported after repetitive use, resulting in diminished effect.
Adverse Effects/Warnings - Potentially, hypersensitivity reactions are possible with this agent. HCG may cause abortion in mares prior to the 35th day of pregnancy, perhaps due to increased estrogen levels. No other reported adverse reactions were noted for veterinary patients.
In humans, HCG has caused pain at the injection site, gynecomastia, headache, depression, irritability and edema.
Overdosage - No overdosage cases have been reported with HCG.
Drug Interactions - No interactions have apparently been reported with HCG.
a) Foal: 1000 Units injected twice weekly for 4-6 weeks (McDonald 1988) (Note: Many clinicians believe that medical treatment is unwarranted and that surgery should be performed.)
To induce ovulation in early estrus when one, large dominant follicle that is palpable with a diameter >35 mm is present:
a) HCG: 2000 - 3000 IU IV (preferable to treat mare 6 hours before mating) (Hopkins 1987)
For treatment of persistent follicles during the early transition period:
a) 1000 - 5000 IU (results are variable). (Van Camp 1986)
To hasten ovulation and reduce variability of estrus after prostaglandin synchronization:
a) HCG: 1500 - 3300 IU 5-6 days after the second prostaglandin treatment or on the first or second day of estrus. (Bristol 1986)
To induce ovulation after estrus has commenced:
a) 2500 - 4000 IU IM or SQ; ovulation generally occurs in 24-48 hours (Roberts 1986b)
Dosage Forms/Preparations/FDA Approval Status/Withholding Times - All HCG products are prescription (Rx).
Chorionic Gonadotropin (HCG) Powder for Injection 5,000 Units per vial with 10 ml of diluent to make 500 Units/ml
Chorionic Gonadotropin (HCG) Powder for Injection 10,000 Units per vial with 10 ml of diluent to make 1000 Units/ml
Chorionic Gonadotropin (HCG) Powder for Injection 20,000 Units per vial with 10 ml of diluent to make 2000 Units/ml
There are several products available with a variety of trade names, as well as many generically labeled products. Two commonly known products are A.P.L® (Wyeth-Ayerst) and Follutein® (Squibb). Veterinary-Approved Products are known to be available from Solvay (Follutein®) and LyphoMed (generically labeled). There are chorionic gonadotropin products approved for use in dairy cattle and beef cattle. There are no withdrawal times for either milk or meat.
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