Prednisolone vs dexamethasone.
Corticosteroids vary along three axes at once, and students often collapse them into a single idea of strength. Glucocorticoid potency, mineralocorticoid activity and duration move independently, and this pair separates all three cleanly.
Dexamethasone is roughly six to seven times more potent as a glucocorticoid than prednisolone and has essentially no mineralocorticoid activity, so it does not cause the sodium and water retention prednisolone can. It also lasts considerably longer, which makes it less suitable for alternate-day regimens.
Prednisolone vs Dexamethasone at a glance
| Property | Prednisolone | Dexamethasone |
|---|---|---|
| Glucocorticoid potency | Moderate, 5 mg equivalent | High, 0.75 mg equivalent |
| Mineralocorticoid activity | Some | Negligible |
| Fluid retention | Possible | Uncommon |
| Biological half-life | Intermediate, 12 to 36 hours | Long, 36 to 72 hours |
| HPA suppression | Less per equivalent dose | Greater, due to duration |
| Typical use | Asthma, inflammatory disease, replacement | Cerebral oedema, croup, antiemesis |
Why potency and mineralocorticoid activity are separate axes
Glucocorticoid and mineralocorticoid effects are mediated by different receptors, and a steroid can be potent at one while inert at the other. Hydrocortisone has substantial activity at both, prednisolone has strong glucocorticoid and mild mineralocorticoid activity, and dexamethasone has powerful glucocorticoid activity with essentially none at the mineralocorticoid receptor. That is why dexamethasone is chosen where fluid retention must be avoided.
Why duration decides the regimen
A long biological half-life keeps the hypothalamic-pituitary-adrenal axis suppressed continuously, which removes the recovery window that alternate-day dosing depends on. Prednisolone, being intermediate acting, allows the axis some recovery between doses. This is why long-term maintenance tends to use shorter-acting agents even when a longer one would be more convenient.
What applies to both
Neither can be stopped abruptly after prolonged use, because suppression of ACTH causes adrenal atrophy and the patient is left unable to mount a cortisol response. Both also raise blood glucose, thin the skin, increase infection risk and reduce bone density over time. These are class effects of glucocorticoid activity and scale with equivalent dose.
Which one would the question pick?
Exams rarely ask what a drug does. They describe a patient and ask which of the two you would choose, so the scenarios below matter more than either drug monograph.
| Scenario | Pick | Why |
|---|---|---|
| Cerebral oedema | Dexamethasone | High potency with no mineralocorticoid effect to worsen oedema. |
| Asthma exacerbation | Prednisolone | Established short course with appropriate duration. |
| Heart failure or hypertension needing steroid | Dexamethasone | Avoids sodium and water retention. |
| Long-term maintenance | Prednisolone | Shorter duration permits alternate-day regimens. |
Traps that catch people on this pair
Converting on milligrams rather than potency
A milligram of dexamethasone is not a milligram of prednisolone. Conversion must use glucocorticoid equivalence.
Assuming stronger means more side effects of every kind
Dexamethasone is a more potent glucocorticoid yet causes less fluid retention, because the two effects come from different receptors.
Common questions
What is the difference between prednisolone and dexamethasone?
Dexamethasone is roughly six to seven times more potent as a glucocorticoid than prednisolone and has essentially no mineralocorticoid activity, so it does not cause the sodium and water retention prednisolone can. It also lasts considerably longer, which makes it less suitable for alternate-day regimens.
How much dexamethasone equals prednisolone?
Approximately 0.75 mg of dexamethasone is equivalent to 5 mg of prednisolone in glucocorticoid potency, making dexamethasone roughly six to seven times more potent.
Why does dexamethasone not cause fluid retention?
Fluid retention comes from mineralocorticoid activity, and dexamethasone has essentially none. Prednisolone retains mild mineralocorticoid activity and hydrocortisone has substantially more.
Why must steroids be tapered?
Prolonged exogenous steroid suppresses ACTH and causes the adrenal cortex to atrophy. Stopping abruptly leaves the patient with neither the drug nor a gland able to produce cortisol.
Go deeper on the mechanism
A comparison only sticks once the shared mechanism underneath it does, because what separates two drugs is always a variation on something they have in common.
- Endocrine pharmacology questions — test the distinction under time
- CYP450 inducers and inhibitors
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Study aid only. This page is written for learning and examination practice. It is not medical advice, not clinical decision support, and must never be used to make a decision about a real patient. Always verify against your local formulary, the product literature and a qualified pharmacist. See our medical disclaimer.
Two drugs, one property apart.
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