Drugs Acting on the Pituitary

The pituitary gland (hypophysis) is the master endocrine organ controlling hormone secretion from target glands. Drugs acting on it are used for hormone replacement, suppression of excess hormone, or diagnostic purposes. These notes summarize the major drug classes, mechanisms, and Kenyan clinical details.

1. Classification of Pituitary Drugs

• Hypothalamic–pituitary axis regulators (e.g. GnRH analogues)

• Pituitary hormone replacements (GH, ACTH analogues)

• Hormone release inhibitors (Somatostatin analogues, Dopamine agonists)

• Posterior pituitary hormone analogues (Vasopressin, Oxytocin)

2. Growth Hormone and Related Drugs

a) Somatropin (Recombinant Human Growth Hormone)

Mechanism: Stimulates IGF-1 synthesis → promotes growth of bones, cartilage, and soft tissue.

Indications: GH deficiency, Turner’s syndrome, chronic renal failure with growth retardation.

Dose: 0.025–0.035 mg/kg/day subcutaneously.

Kenyan Trade Names: Norditropin®, Genotropin®.

Adverse Effects: Edema, arthralgia, headache, increased intracranial pressure, hyperglycemia.

Clinical Notes: Monitor growth velocity and glucose tolerance regularly.

b) Pegvisomant (GH Receptor Antagonist)

Mechanism: Blocks GH receptors → decreases IGF-1 levels.

Indication: Acromegaly refractory to surgery or somatostatin analogues.

Dose: 10–20 mg subcutaneously daily.

Trade Name: Somavert®.

Adverse Effects: Elevated liver enzymes, injection-site pain.

Clinical Notes: Monitor liver enzymes periodically.

3. Gonadotropin-Releasing Hormone (GnRH) and Related Drugs

a) GnRH Agonists (Leuprolide, Goserelin, Buserelin)

Mechanism: Continuous stimulation → downregulation of GnRH receptors → suppression of LH/FSH.

Indications: Prostate cancer, endometriosis, uterine fibroids, precocious puberty.

Dose: Leuprolide 3.75 mg IM monthly; Goserelin 3.6 mg SC monthly.

Trade Names: Zoladex®, Lucrin Depot®.

Adverse Effects: Hot flashes, bone loss, decreased libido, mood swings.

Clinical Notes: Use add-back therapy (estrogen/progestin) to minimize bone loss.

b) GnRH Antagonists (Cetrorelix, Elagolix, Degarelix)

Mechanism: Block GnRH receptors → immediate inhibition of LH/FSH release.

Indications: Endometriosis, ovarian hyperstimulation prevention, advanced prostate cancer.

Dose: Elagolix 150 mg orally daily.

Trade Names: Cetrotide®, Orilissa®, Firmagon®.

Adverse Effects: Hot flashes, headache, bone density loss.

4. Dopamine Agonists (Prolactin Inhibitors)

a) Bromocriptine

Mechanism: D2 receptor agonist → inhibits prolactin secretion.

Indications: Hyperprolactinemia, prolactinoma, galactorrhea, Parkinson’s adjunct.

Dose: 1.25–2.5 mg orally twice daily.

Trade Names: Parlodel®, Bromergon®.

Adverse Effects: Nausea, vomiting, orthostatic hypotension.

Clinical Notes: Start low and titrate to avoid hypotension.

b) Cabergoline

Mechanism: Long-acting D2 agonist → suppresses prolactin secretion.

Indications: Hyperprolactinemia, prolactinoma.

Dose: 0.25–0.5 mg twice weekly.

Trade Name: Dostinex®.

Adverse Effects: Nausea, dizziness, fatigue.

Clinical Notes: Better tolerated and more effective than bromocriptine.

5. Posterior Pituitary Hormones

a) Desmopressin (ADH Analogue)

Mechanism: V2 receptor agonist in kidney → promotes water reabsorption.

Indications: Central diabetes insipidus, nocturnal enuresis, mild hemophilia A.

Dose: 10–20 µg intranasally or 0.2 mg orally daily.

Trade Names: Minirin®, DDAVP®.

Adverse Effects: Hyponatremia, headache, nasal irritation.

Clinical Notes: Monitor serum sodium regularly.

b) Oxytocin

Mechanism: Binds uterine oxytocin receptors → stimulates uterine contractions.

Indications: Labor induction, postpartum hemorrhage prevention.

Dose: 1–5 IU IV infusion titrated to uterine response.

Trade Names: Syntocinon®.

Adverse Effects: Uterine hyperstimulation, water intoxication (rare).

Clinical Notes: Use only under medical supervision in hospital settings.

6. Summary Table

7. Kenyan Clinical Notes

• Bromocriptine and cabergoline are available in Kenyan pharmacies.
• GH therapy (Somatropin) is specialist-prescribed and expensive.
• Desmopressin widely used for nocturnal enuresis and diabetes insipidus.
• Oxytocin (Syntocinon®) is standard in Kenyan maternity units.
• Monitor side effects: blood pressure, sodium, liver enzymes, bone density.