Drug excretion

Published on 23/06/2015 by admin

Filed under Complementary Medicine

Last modified 23/06/2015

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Chapter 18 Drug excretion

Chapter contents

Kidneys 133
Bile 136
Lungs 136
Saliva, tears and perspiration 136
Breast milk 136

Drug excretion can occur by several means:

• via the kidneys
• in the bile
• through the lungs
• in saliva, tears, perspiration
• in breast milk.

Kidneys

• The greatest proportion of drug excretion occurs through the kidneys.
• The liver makes most drugs and remedies water soluble for removal via the kidneys (see Figure 17.1, p. 131).
• One-fifth of the plasma reaching the kidney glomerulus is filtered through the pores in the glomerular cell membrane. The rest passes through the blood vessels around the renal tubules (Figure 18.1).
• Substances with a low molecular weight and not bound to plasma proteins can easily pass through the cell membranes into the tubules.
• Active secretion against a concentration gradient also takes place in the tubules.
image

Figure 18.1 A nephron: the functional unit of the kidney.

The factors affecting the rate at which the drug or remedy is excreted by the kidneys are:

• kidney disease
• pH of urine
• change in renal blood flow
• concentration of drug or remedy in plasma
• its molecular weight.

Kidney Disease

Useful complexes such as plasma proteins (see Chapter 16 ‘How do drugs get into cells?’, p. 126) can be lost, increasing the amount of unbound remedy in the body, with resulting toxicity. Other compounds may be lost in the urine as the reuptake is reduced.

pH of Urine

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