MANNITOL

1) Action

• Osmotic diuretic

2) Mechanism

• Filtered into tubular fluid —> not easily reabsorbed by tubules —> increase in osmotically active substances in tubules —> increase osmotic pressure prevents water reabsorption —> diuresis

3) Indications

• Promotion of diuresis, in the prevention &/or treatment of the oliguric phase of ARF before irreversible renal failure becomes established

• Promotion of renal excretion of toxic substances

• Reduction of cerebral oedema

4) Effects on organs—side effects

• As mannitol is rapidly distributed in the ECF & extract water from the cells —> hyponatremia & expansion of extracellular compartment

• Protects renal function by increasing renal blood flow, increasing GFR and reducing injury after ischaemia [by scavenging free oxygen radicals]

5) Toxic effects/ precautions with administration

• Disturbances in electrolyte & water balance

6) Contraindications

• Well established anuria due to severe renal disease

• Intracerebral bleeding

7) Reversal, antagonism or antidote

8) Loading dose, maintenance dose, frequency & method of administration

• 20% w/v 500ml

• 50—100 g IV to prevent oliguria during cardiac surgery

9) Drug’s metabolism—Drug’s excretion—Half life (pharmacokinetics)

• Almost inert metabolically

• Remains confined in extracellular space

• 80% of a 100mg dose will appear in urine in 3 hours