Читать книгу Clinical Pharmacology and Therapeutics - Группа авторов - Страница 36

Three processes are implicated in renal excretion of drugs:

1 Glomerular filtration: This is the most common route of renal elimination. The free drug is cleared by filtration and the protein‐bound drug remains in the circulation where some of it dissociates to restore equilibrium.

2 Active secretion in the proximal tubule: Both weak acids and weak bases have specific secretory sites in proximal tubular cells. Penicillins are eliminated by this route, as is about 60% of procainamide.

3 Passive reabsorption in the distal tubule: This occurs only with un‐ionised, i.e. lipid‐soluble, drugs. Urine pH determines whether or not weak acids and bases are reabsorbed, which in turn determines the degree of ionisation.

If renal function is impaired, for example, by disease or old age, then the clearance of drugs that normally undergo renal excretion is decreased. This is discussed in more detail later in this section.