Routes of Drug Administration

Intravenous

• No barriers to absorption since drug is put directly into the blood.
• There is a very rapid onset for drugs administered intravenously.  This can be advantagous in emergency situations, but can also be very dangerous.
• This route offers a great deal of control in respect to drug levels in the blood.
• Irritant drugs can be administer by the IV route without risking tissue injury.
• IV drug administration is expensive, inconvenient and more difficult than administration by other routes.
• Other disadvantages include the risk of fluid overload, infection, and embolism.  Some drug formulations are completely unsafe for use intravenously.

Intramuscular:

• Only the capillary wall separates the drug from the blood, so there is not a significant barrier to the drug's absorption.
• The rate of absorption varies with the drug's solubility and the blood flow at the site of injection.
• The IM route is uncomfortable and inconvenient for the patient, and if administered improperly, can lead to tissue or nerve damage.

Subcutaneous

Same characteristics as the IM route.

Oral

• Two barriers to cross: epithelial cells and capillary wall.  To cross the epithelium, drugs have to pass through the cells.

• Highly variable drug absorption influenced by many factors:  pH, drug solubility and stability, food intake, other drugs, etc.
• Easy, convenient, and inexpensive.  Safer than parenteral injection, so that oral administration is generally the preferred route.
• Some drugs would be inactivated by this route
• Inappropriate route for some patients.
• May have some GI discomfort, nausea and vomiting.
• Types of oral meds = tablets, enteric-coated, sustained-release, etc.
• Topical, Inhalational agents, Suppositories

ANTIDEPRESSANTS

Monoamine uptake inhibitors

1. Tricyclic antidepressants (TCAs)
2. Selective serotonin reuptake inhibitors (SSRIs)
3. Serotonin-norepinephrine reuptake inhibitors(SNRIs)
4. Norepinephrine reuptake inhibitor

Monoamine oxidase inhibitors (MAOIs) 

Monoamine receptor antagonists 

AUTOCOIDS

An  organic substance, such as a hormone, produced in one part of organism and transported by the blood or lymph to another part of the organism where it exerts a physiologic effect on that part.

TYPES OF AUTACOIDS:
 Amines : Histamine,5-Hydroxytryptamine.
 Lipids    : Prostaglandins, Leukotriens, Platelet activating factor.
 Peptide : Bradykinin , angiotensin. 

Carbamazepine (Tegretol): most common; for generalized tonic-clonic and all partial seizures; especially active in temporal lobe epilepsies

Mechanism: ↓ reactivation of Na channels (↑ refractory period, blocks high frequency cell firing, ↓ seizure spread)

Side effects: induces hepatic microsomal enzymes (can enhance metabolism of other drugs)

Antifungal

There are several classes of antifungal drugs.

The polyenes bind with sterols in the fungal cell wall, principally ergosterol. This causes the cell's contents to leak out and the cell dies. Human (and other animal) cells contain cholesterol rather than ergosterol so are much less suceptible.

Nystatin

Amphotericin B

Natamycin

The imidazole and triazole groups of antifungal drugs inhibit the enzyme cytochrome P450 14α-demethylase. This enzyme converts lanosterol to ergosterol, and is required in fungal cell wall synthesis. These drugs also block steroid synthesis in humans.

Imidazoles:

Miconazole

Ketoconazole

Clotrimazole

The triazoles are newer, and are less toxic and more effective:

Fluconazole

Itraconazole

Allylamines inhibit the enzyme squalene epoxidase, another enzyme required for ergosterol synthesis:

Terbinafine

Echinocandins inhibit the synthesis of glucan in the cell wall, probably via the enzyme 1,3-β glucan synthase:

Caspofungin

Micafungin

Others:

Flucytosine is an antimetabolite.

Griseofulvin binds to polymerized microtubules and inhibits fungal mitosis.

Paracetamol

Paracetamol or acetaminophen is analgesic and antipyretic drug that is used for the relief of fever, headaches, and other minor aches and pains.

paracetamol acts by reducing production of prostaglandins, which are involved in the pain and fever processes, by inhibiting the cyclooxygenase (COX)  enzyme.

Metabolism Paracetamol is metabolized primarily in the liver. At usual doses, it is quickly detoxified by combining irreversibly with the sulfhydryl group of glutathione to produce a non-toxic conjugate that is eventually excreted by the kidneys.