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

Fluconazole: an antifungal used orally,  intravenously or vaginally to treat yeast and fungal infections. Side-effects of systemic administration include hepatotoxicity (liver damage).

• For vaginal candidiasis (vaginal thrush), a once-only oral dose is often sufficient.

Pramlintide -Amylin mimetics

Mechanism
synthetic analogue of human amylin that acts in conjunction with insulin
↓ release of glucagon
delays gastric emptying

Clinical use

type I and II DM

Opiate Antagonists

Opiate antagonists have no agonist properties. They are utilized to reverse opiate induced respiratory depression and to prevent drug abuse.

A. Naloxone

 Pure opiate antagonist , Short duration of action,  Only 1/50th as potent orally as parenterally

B. Naltrexone

Pure opiate antagonist, Long duration of action, Better oral efficacy

Clarithromycin Used to treat  pharyngitis, tonsillitis, acute maxillary

sinusitis, acute bacterial exacerbation of chronic  bronchitis,  pneumonia (especially atypical pneumonias associated with Chlamydia pneumoniae or TWAR), skin and skin structure infections, and, in HIV and AIDS patients to prevent, and to treat, disseminated Mycobacterium avium complex or MAC.

Unlike erythromycin, clarithromycin is acid-stable and can therefore be taken orally without being protected from gastric acids. It is readily absorbed, and diffused into most tissues and phagocytes.

Clarithromycin has a fairly rapid first-pass hepatic metabolism, i.e it is metabolised by the liver. However, this metabolite, 14-hydroxy clarithromycin is almost twice as active as clarithromycin.

Contraindications Clarithromycin should be used with caution if the patient has liver or kidney disease, certain heart problems (e.g., QTc prolongation or bradycardia), or a mineral imbalance (e.g., low potassium or magnesium levels).

Topical Anesthetics

Benzocaine

Benzocaine is a derivative of procaine, an ester type local anesthetic, and is poorly soluble in water and is

available only as a topical anesthetic.

-  Localized allergic reactions are sometimes encountered    

-  Overdosing is unlikely as benzocaine is poorly absorbed into the blood, which decreases the likelihood of systemic toxicity.

- The onset of surface anesthesia is rapid requiring less than one minute.

Tetracaine

- Tetracaine is an ester type local anesthetic

-  Topically applied tetracaine as opposed to benzocaine has a prolonged duration of action.

Cocaine

- Cocaine is a ester type anesthetic that is used exclusively as a topical agent.

- Cocaine is unique among topical and injectable anesthetics in that it has vasoconstrictive as well as anesthetic properties. It is used sparingly because of its abuse potential but is still used when hemostasis of mucous membranes is essential.

- Cocaine is generally available in concentrations of 2-10 % solution.

Lidocaine

- Lidocaine is an amide local anesthetic that is available in injectable and topical formulations.

- It is available in gel, viscous solution, ointment and aerosol preparations in concentrations ranging from 2-10 %.

- The onset of anesthesia is slower relative to benzocaine but, the duration is about the same.

- Absorption into the bloodstream is greater than benzocaine providing a greater risk of systemic toxicity.