Testosterone
**Testosterone** is the principal endogenous androgenic steroid. In veterinary medicine, the use of injectable testosterone esters is primarily limited to specific hormonal and reproductive applications. - **Small Animals**: Primarily used for the treatment of **testosterone-responsive urinary incontinence** in neutered male dogs and cats. It has also been used rarely to treat specific bilateral alopecia (dermatitis) in neutered male dogs. - **Large Animals**: Used in bovine medicine to produce an **estrus-detector (teaser) animal** from cull cows, heifers, or steers. - **Clinical Note**: Its efficacy for increasing libido or treating infertility/hypogonadism in domestic animals has generally been disappointing. - **Regulatory**: Testosterone products are **controlled substances (C-III)** due to their anabolic steroid classification.
Mecanismo: Testosterone is highly lipophilic and diffuses across target cell membranes. In many tissues, it is converted by **5-alpha-reductase** → **dihydrotestosterone (DHT)**. Both testosterone and DHT bind to intracellular **androgen receptors** → the receptor complex translocates to the nucleus → binds to DNA hormone response elements → modulates gene transcription. - **Urethral Tone**: Helps maintain normal urethral muscle tone and mucosal integrity in neutered males. - **Anabolic Effects**: Increases protein anabolism and decreases catabolism → retention of nitrogen, sodium, potassium, and phosphorus. - **Erythropoiesis**: Stimulates **erythropoietic stimulating factor (erythropoietin)** → increases red blood cell production. - **Endocrine Feedback**: Large exogenous doses exert negative feedback on the pituitary gland → inhibits **luteinizing hormone (LH)** and **follicle-stimulating hormone (FSH)** → inhibits spermatogenesis.
Dosificación por especie
- Infertility or reduced libido · 0.1-1 mg every other day or every third day for 3-5 injections IM or SC. Not indicated for testis descent. · IM/SC · every other day or every third day · 3-5 injections · Using either testosterone cypionate or propionate
- Testosterone-responsive urinary incontinence (may be used with phenylpropanolamine) in males · Testosterone propionate 5-10 mg IM as needed. · IM · as needed
- To produce an estrus-detector (teaser) animal (cull cows, heifers, steers) · Testosterone propionate 200 mg IM on day 1 and on days 4-9. On day 10, give 1 gram IM and attach a chinball marker and put with the breeding herd. To maintain the teaser give 1 gram booster every 10-14 days. · IM · varies
- To produce an estrus-detector (teaser) animal (cull cows, heifers, steers) · Alternatively, initially give testosterone enanthate 0.5 gram IM and 1.5 gram SC (divided in two separate locations). After 4 days attach chinball marker and put in with breeding herd. To maintain, give 0.5-0.75 gram SC every 10-14 days. · IM/SC · varies
- Testosterone-responsive urinary incontinence (may be used with phenylpropanolamine) in males · Testosterone propionate: approximately 2 mg/kg IM or SC 3 times per week. Testosterone cypionate: 200 mg IM once per month · IM/SC · 3 times per week / once per month
- Testosterone-responsive urinary incontinence · Testosterone propionate: 2.2 mg/kg IM q2-3 days. Testosterone cypionate: 2.2 mg/kg IM once per month · IM · q2-3 days / once per month
Vías de administración
Contraindicaciones
- Known hypersensitivity to the drug
- Prostate carcinoma
- Pregnancy (FDA Category X / Papich Class D)
Efectos adversos
- Perianal adenomas
- Perineal hernias
- Prostatic disorders (enlargement)
- Behavior changes (aggression)
- Polycythemia (at high doses)
- Oligospermia or infertility (in intact males with chronic use)
Interacciones farmacológicas
- Corticosteroids · May enhance the edema associated with ACTH or adrenal steroid therapy
- Insulin / Oral Antidiabetic Agents · Testosterone may decrease serum glucose levels
- Propranolol · Testosterone cypionate may increase propranolol clearance
- Warfarin · Testosterone may increase anticoagulant effects
Monitorización
- Clinical efficacy (resolution of incontinence, estrus detection behavior)
- Adverse effects (prostatic enlargement, aggression, perineal hernias)
- Hematocrit/PCV (for polycythemia with chronic use)
Sobredosis
No specific acute toxicity information is available. - **Chronic Overdose**: High dosages or chronic usage may result in oligospermia or infertility in intact males due to negative feedback on LH/FSH. - **Other Effects**: Polycythemia (excessive red blood cells) has been reported in humans receiving high dosages. - **Treatment**: Discontinue therapy and provide supportive care. Monitor hematocrit and prostatic size.
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