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Section IVOther important drugsKinetics
Mannitol is minimally absorbed from the gut. Following intravenous administration
mannitol is distributed throughout the extracellular fluid space. It is freely filtered
at the glomerulus and not reabsorbed, resulting in an elimination half-life of 100
minutes. It is not metabolized to any significant extent.Carbonic anhydrase inhibitors (acetazolamide)
Acetazolamide is a weak diuretic that is more commonly used as prophylaxis against
mountain sickness. When used as eye drops it inhibits aqueous humour production
and is useful in the treatment of glaucoma.Mechanism of action
Acetazolamide inhibits (non-competitively) carbonic anhydrase, which catalyzes
the formation of H+and HCO− 3 from CO 2 and H 2 Ovia H 2 CO 3 in the proximal tubule.
As a result less H+ions are available for excretion resulting in a metabolic acidosis,
counteracting the respiratory alkalosis associated with mountain sickness.Effects
Biochemical−H+excretion is inhibited and HCO 3 −is not re-absorbed leading
to an alkaline urine. Na+and water excretion are slightly increased providing an
increased drive for K+secretion. Therefore, it produces an alkaline urine in the
presence of a hyperchloraemic acidosis.Kinetics
Acetazolamide has an oral bioavailability of more than 95%, is highly protein bound
and is excreted unchanged in the urine.