1. Clinical Overview
Testosterone is the primary endogenous androgen, a steroid hormone synthesized from cholesterol in the Leydig cells of the testes (95%), and to a lesser extent in the adrenal cortex and ovaries. In the Indian market, 100mg is a common strength for intramuscular injection (as esters like enanthate or cypionate) and transdermal gel sachets. It is used for androgen replacement therapy in males with hypogonadism. It exerts profound anabolic (tissue-building) and androgenic (masculinizing) effects by binding to and activating the androgen receptor.
| Onset | Duration | Bioavailability |
|---|---|---|
| Intramuscular (esterified): 24-72 hours for symptomatic improvement. Transdermal Gel: Serum levels rise within 30 minutes, steady-state in 2-3 days. | Intramuscular Testosterone Enanthate/Cypionate (100mg): 2-4 weeks. Transdermal Gel: Requires daily application. | Oral (unmodified): Very low (<10%) due to extensive first-pass metabolism. Intramuscular: ~100%. Transdermal Gel: ~10-15% of applied dose. |
2. Mechanism of Action
Testosterone diffuses into target cells and is either reduced to its more potent metabolite, 5α-dihydrotestosterone (DHT) by 5α-reductase (in tissues like prostate, skin), or aromatized to estradiol (in adipose tissue, brain). Testosterone or DHT binds to the intracellular androgen receptor (AR) in the cytoplasm. The hormone-receptor complex dimerizes, translocates to the nucleus, binds to specific DNA sequences (Androgen Response Elements), and regulates the transcription of target genes, leading to protein synthesis and cellular effects.
3. Indications & Uses
- Male Hypogonadism (Primary and Hypogonadotropic)
- Delayed Puberty in Males (with clear endocrine deficiency)
4. Dosage & Administration
Adult Dosage: Male Hypogonadism: IM (Enanthate/Cypionate): 50mg to 400mg every 2 to 4 weeks. A common regimen is 100mg to 250mg every 2-3 weeks. Transdermal Gel (1% or 2%): 50mg to 100mg applied once daily. Dose MUST be individualized based on serum testosterone levels, clinical response, and tolerability.
Administration: IM Injection: Deep intramuscular into gluteal or thigh muscle. Rotate sites. Use proper aseptic technique. Transdermal Gel: Apply to clean, dry, intact skin on shoulders, upper arms, or abdomen. Wash hands after application. Allow to dry. Avoid skin-to-skin contact with others, especially women and children, for several hours. Do not apply to genital area.
5. Side Effects
Common side effects may include:
- Injection site pain/reactions
- Acne or oily skin
- Increased frequency of erections
- Gynecomastia (breast tenderness/enlargement)
- Headache
- Fluid retention/edema
- Increased hematocrit/hemoglobin
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Warfarin | Testosterone may potentiate anticoagulant effect, increasing INR and bleeding risk. | Major |
| Insulin, Oral Hypoglycemics | Testosterone may alter insulin sensitivity; dose adjustment may be needed. | Moderate |
| Corticosteroids (e.g., Prednisolone) | Increased risk of severe edema due to synergistic mineralocorticoid effect. | Moderate |
| Cyclosporine, Tacrolimus | Testosterone may inhibit CYP3A4, increasing levels of these drugs and risk of toxicity. | Moderate |
| Prostate cancer drugs (e.g., GnRH agonists) | Antagonistic effect; contraindicated. | Major |
| ACTH or Adrenal Steroids | Increased risk of edema and acne. | Moderate |
7. Patient Counselling
- DO have regular blood tests (Testosterone, CBC, PSA, Lipids, LFTs) as advised by your doctor.
- DO report any chest pain, shortness of breath, leg swelling/pain, or signs of stroke immediately.
- DO wash hands thoroughly after applying gel and cover application sites with clothing.
- DO inform all your doctors and surgeons that you are on testosterone therapy.
- DON'T share your medication with anyone, especially athletes or bodybuilders.
- DON'T change your dose or dosing schedule without consulting your doctor.
- DON'T apply testosterone gel to broken skin or allow others to contact the application site.
8. Toxicology & Storage
Overdose: Symptoms are an extension of adverse effects: Severe nausea/vomiting, priapism, aggressive behavior ('roid rage'), significant fluid retention leading to heart failure, severe hypercalcemia (in immobilized patients or cancer), hepatotoxicity, and profound polycythemia increasing thrombotic risk.
Storage: Store at controlled room temperature (15°C to 30°C). Protect from light and moisture. Do not freeze. Keep IM vials/ampoules and gel sachets in their original packaging, out of reach of children and pets. Do not puncture or burn used gel sachets. Dispose of used needles/syringes in a sharps container.