Methylprednisolone
Methylprednisolone is a synthetic, intermediate-acting **glucocorticoid** that is approximately 4 to 5 times more potent than hydrocortisone and possesses negligible mineralocorticoid activity. It is utilized extensively in veterinary medicine for its potent anti-inflammatory and immunosuppressive properties. **Clinical Pearls & Formulations:** * **Methylprednisolone base:** Used in oral tablet formulations for maintenance or tapering therapy. * **Methylprednisolone acetate (Depo-Medrolยฎ):** A microcrystalline suspension for IM, intralesional, or intra-articular injection. It is slowly absorbed, providing a prolonged repository effect (weeks to months). **Note:** It can cause profound and prolonged Hypothalamic-Pituitary-Adrenal (HPA) axis suppression. * **Methylprednisolone sodium succinate (Solu-Medrolยฎ):** A highly water-soluble ester designed for rapid IV administration in acute crises (e.g., spinal cord trauma, severe allergic reactions, shock), though high-dose use in shock/trauma is increasingly controversial. While highly effective, the goal of glucocorticoid therapy is always to use the **lowest effective dose for the shortest possible duration** to minimize systemic adverse effects, particularly iatrogenic hyperadrenocorticism (Cushing's syndrome).
Mechanism: Glucocorticoids exert their effects by diffusing across cell membranes and binding to specific **cytoplasmic glucocorticoid receptors (GR)**. * **Genomic Pathway:** The receptor-ligand complex translocates to the nucleus โ binds to **glucocorticoid response elements (GREs)** on target genes โ alters gene transcription. * **Anti-inflammatory Mechanism:** They induce the synthesis of **lipocortin-1 (annexin-1)** โ inhibits **phospholipase A2** โ blocks the release of arachidonic acid from membrane phospholipids โ profoundly decreases the synthesis of pro-inflammatory **prostaglandins and leukotrienes**. * **Immunosuppressive Mechanism:** They suppress the transcription of inflammatory cytokines (e.g., IL-1, IL-2, IL-6, TNF-alpha), inhibit macrophage and neutrophil migration/function, and induce apoptosis in lymphocytes. * **Metabolic Effects:** Stimulate hepatic gluconeogenesis, promote protein catabolism, and redistribute lipid stores.
Dosing by species
- Labeled uses (Oral) ยท Cats weighing 5-15 lbs: 2 mg; Cats weighing >15 lbs: 2-4 mg; these total daily doses should be divided ยท PO ยท q6-10h ยท Divide total daily dose and give 6-10 hours apart.
- Labeled uses (Injectable) ยท up to 20 mg (average 10 mg) ยท IM ยท May repeat at weekly intervals ยท Depending on breed (size), severity of condition, and response.
- Intralesional (sub-lesional) use ยท 10-40 mg total dose ยท intralesional ยท A sufficient volume of 20 mg/mL methylprednisolone acetate is used to undermine the lesion.
- Antiinflammatory (glucocorticoid effects) ยท 200 mg ยท IM ยท repeated as necessary ยท Labeled use.
- Intra-articular use ยท 100 mg ยท IA
- Labeled uses (Oral) ยท Dogs weighing 5-15 lbs: 2 mg; Dogs weighing 15-40 lbs: 2-4 mg; Dogs weighing 40-80 lbs: 4-8 mg; these total daily doses should be divided ยท PO ยท q6-10h ยท Divide total daily dose and give 6-10 hours apart.
- Labeled uses (Injectable) ยท 2-120 mg (average 20 mg) ยท IM ยท May repeat at weekly intervals ยท Depending on breed (size), severity of condition, and response.
- Intralesional (sub-lesional) use ยท 10-40 mg total dose ยท intralesional ยท A sufficient volume of 20 mg/mL methylprednisolone acetate is used to undermine the lesion.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Systemic fungal infections (unless used for Addison's replacement)
- Viral infections
- Arrested tuberculosis
- Peptic or corneal ulcers
- Acute psychoses
- Cushingoid syndrome
- Idiopathic thrombocytopenia (for IM administration)
- Acute local infections (for intrasynovial/intratendinous use)
- Chronic systemic therapy using sustained-release injectable forms
- Pregnant animals
- Renal disease
- Diabetes mellitus
Adverse effects
- Polyuria (PU), polydipsia (PD), polyphagia (PP)
- Iatrogenic hyperadrenocorticism (Cushingoid signs) with sustained use
- HPA axis suppression
- Weight gain and lipidemias
- Dull, dry haircoat and alopecia
- Muscle wasting and weakness
- Gastrointestinal ulceration, vomiting, diarrhea, melena, hematochezia
- Elevated liver enzymes (ALP, ALT) and hepatopathy
- Pancreatitis
- Activation or worsening of diabetes mellitus (especially in cats)
- Behavioral changes (depression, lethargy, viciousness, panting)
- Extracellular hyperglycemia leading to volume expansion and potential CHF (cats)
- Hypothalamic-pituitary-adrenal (HPA) axis suppression
- Adrenal atrophy
- Weight loss (catabolic effect)
Drug interactions
- Amphotericin B ยท May cause hypokalemia; potential for CHF and cardiac enlargement ยท moderate
- Analgesics/Opiates/Local Anesthetics (epidural) ยท Combination in epidurals has caused serious CNS injuries and death
- Anticholinesterase agents (e.g., pyridostigmine) ยท May lead to profound muscle weakness in myasthenia gravis patients
- Aspirin ยท Glucocorticoids may reduce salicylate blood levels
- Barbiturates ยท May increase the metabolism of glucocorticoids and decrease blood levels
- Cyclophosphamide ยท Glucocorticoids may inhibit hepatic metabolism of cyclophosphamide
- Cyclosporine ยท May mutually inhibit hepatic metabolism, increasing blood levels of both drugs
- Potassium-depleting diuretics ยท May cause hypokalemia
- Ephedrine ยท May reduce methylprednisolone blood levels
- Estrogens ยท May potentiate the effects of methylprednisolone
- Insulin ยท Insulin requirements may increase due to glucocorticoid-induced insulin resistance ยท moderate
- Ketoconazole and Azole Antifungals ยท May decrease metabolism of glucocorticoids; ketoconazole may induce adrenal insufficiency upon withdrawal
Monitoring
- Weight, appetite, and signs of edema
- Serum and/or urine electrolytes
- Total plasma proteins, albumin
- Blood glucose
- Growth and development in young animals
- ACTH stimulation test (if iatrogenic Cushing's or Addison's is suspected)
- Clinical signs of iatrogenic hyperadrenocorticism (PU/PD, polyphagia, weight gain)
- Blood glucose levels (especially in diabetic or pre-diabetic patients)
- Serum electrolytes (specifically potassium)
- Thyroid panel (T3 and T4 may be artificially decreased)
- Signs of gastrointestinal ulceration (melena, vomiting blood)
Overdose
Short-term administration of massive doses is unlikely to cause harmful effects, though one case of acute CNS effects in a dog after accidental ingestion has been reported. If acute overdose occurs, provide supportive treatment as required. **Chronic Overdosage:** Chronic usage leads to serious adverse effects, primarily iatrogenic hyperadrenocorticism (Cushing's syndrome), characterized by profound metabolic, dermatologic, and immunosuppressive changes.
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.