# Ross Vet Prep Medical Mathematics Absorption of Drugs

## 24 terms · Ross Vet Prep Medical Mathematics Absorption of Drugs

### Absorption of Drugs

The transfer of the drug from the site of administration to circulation and considered "finished" when the drug reaches the blood

### 2 Classes of Factors Affecting Drug Absorption

1. Factors related to the drug
2. Factors related to the animal

### 6 Factors of Absorption Related to the Drug

1. Molecular Size
2. Lipid Solubility
3. Degree of Ionization
4. Dissolution of Drug
5. Concentration of Drug at Absorptive Site

### Molecular Size

In hydrophilic drugs (lipid soluble drugs diffuse in the membrane), the smaller the molecular size, the faster the penetration of the drug through the pores

### Lipid Solubility

The greater the lipid solubility, the greater the diffusion

### Degree of Ionization

The higher the ratio between N/I, the faster diffusion

### Dissolution of Drug in Water

Oral absorption of liquid drugs is faster than solid drugs and the oral absorption of solid drugs depends on their rate of dissolution

1. Sublingual and inhalation have a very rapid absorption.
2. Intramuscular is slower than sublingual and inhalation
3. Subcutaneous is slower than intramuscular
4. Oral is slower than injection
5. IV is not absorption because by definition absorption is movement to the blood and IV is already in the blood

### 5 Factors of Absorption Related to the Animal

1. Blood Flow
2. Absorbing Surface Area
3. Connective Tissue
4. Species
5. Individual

### Blood Flow

Increased blood flow increases drug absorption
Blood flow itself may be modified by drugs, physiological factors and disease.

### 3 Things that Increase Blood Flow

1. Heat
2. Massage
3. Sympathetic stimulation increases blood flow to the skeletal muscles

### 4 Things that Decrease Blood Flow

1. Sympathetic stimulation decreases blood flow to the GI tract and subcutaneous sites and skin
2. Heart failure
3. Shock
4. Edema

### Main site of absorption in monogastric animals for all drugs given orally

Upper part of the small intestine because of the extensive surface area and rich blood supply

### Gastric Emptying

The movement of the drug from the stomach to the intestine. A rate limiting step that determines the rate of absorption.

### 6 Factors affecting Drug Absorption from GI tract

1. Rate of dissolution (solid drugs)
2. Activity of the gut
3. Presence of other substances
4. Blood Flow
5. Species
6. Individual

### Rate of Release of Dissolution

Liquid drugs are absorbed faster than powder which are absorbed faster than small tablets which are absorbed faster than large tablets

### Transit time

The length of time a drug stays in the system

### Less Blood Flow

Less Drug carried

### More blood flow

More blood carried

### Hypermotility of the gut/intestines

Decreases absorption

### Hypomotility of the gut/intestines

Increases absorption

Gastric emptying

### Which drugs NEED food in order to be absorbed?

those that need acidity

### For most drugs, what is the effect of food?

Decrease absorption.