Simple Pharmanotes

 Absorption of drugs by Non per Oral Route.

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• Movement of the unchanged form of drug molecules from site of administration to systemic circulation is called absorption.

• Non-per oral absorption indicates drug administration routes other than the oral route, which bypasses the GIT & enters the systemic circulation.

• Some of the non-oral absorptions are discussed here:

1. Buccal-Sublingual Administration:

• Buccal Route : 

• The medication is placed b/w cheek & the gum. 

• They are absorbed by passive diffusion.

• Sublingual Route: 

• The drug is placed under the tongue & allowed to dissolve. 

• They are absorbed by carrier-mediated transport.

• Advantages -

1. Rapid absorption.

2. No first-pass hepatic Metabolism.

3. No degradation of drugs.

• Disadvantages

1. limited mucosal surface area

2. Concern for taste & discomfort of the medication.

• Factors to be Considered:

1. Lipophilicity of drugs.

2. Salivary secretion.

3. pH of the saliva.

4. Binding of the drug to the oral mucosa

5. Thickness of oral mucosa epithelium.

• Examples:

1. Antianginals: nitrites & nitrates.

2. Antihypertensives: nifedipine.

3. Bronchodilators: Fenoterol.

4. Steroids estradiol

5. Peptides: Oxytocin.

2) Rectal Route:

• The rectum is the ending portion of the large intestine, approximately 15 cm long, from the colon to the anal sphincters. 

• It can be used as a drug delivery route for both local and systemic effects.

• Drugs are absorbed majorly by passive diffusion.

• Advantages:

• Rapid absorption.

• Bypasses portal circulation and hence has no first pass effect.

• Disadvantages:

• Not comfortable.

• Irritant drugs can not be given.

• Irregular absorption.

• Factors to be considered:

• Presence of fecal material.

• Drug irritation.

• pH of rectal fluid which is almost 8.

• Limited surface area of rectum.

3) Vaginal Route:

• It is not commonly used but has the advantages of bypassing the first-pass effect and can serve as an effective method for local and systemic therapy.

• Most of the time it is intended for local action to treat bacterial or fungal infections. 

• Drugs are absorbed majorly by passive diffusion.

• Advantages:

• Easy administration.

• Action can be controlled easily.

• Can bypass portal circulation and hence has no first pass effect.

• Disadvantages:

• Not comfortable.

• Irritant drugs can not be given.

• Irregular absorption.

• Factors to be considered:

• Vaginal secretions.

• Bacterial metabolism.

• pH of lumen fluid which is acidic around 4-5.

• Examples:

• Steroids: Progesterone:

• Antimicrobial: Metronidazole.

• Antifungal: Fluconazole.

4) Intranasal Route:

• Drugs administered in the nasal cavity get absorbed rapidly directly into the systemic circulation.

• The drugs given by this route can even bypass the BBB, and hence the route is gaining popularity for CNS targeting drugs.

• Drugs are mainly absorbed by passive diffusion and pore transfer techniques.

• Advantages:

• Rapid absorption.

• Can bypass BBB.

• Disadvantages:

• Irritant drugs can not be given.

• Nasal secretions.

• Factors to be considered:

• Needs more lipophilic drugs.

• Lower molecular size.

• Nasal secretions and their pH.

• Pathological conditions.

• Examples:

• Antihistamines: Phenylpropanolamine.

• Corticosteroids: Budesonide.

• Analgesics: Fantanyl.

5) Intraocular Route:

• Administration of a drug within the eye. 

• Intraocular drugs are almost always used for their local effects.

• Drugs are absorbed mainly by passive diffusion.

• Advantages:

• Both lipophilic as well as hydrophilic drugs can be absorbed.

• pH of lacrimal fluids plays an important role in the absorption of weak electrolytes.

• Disadvantages:

• Irritant drugs can not be given.

• Lower Dose.

• Limited surface area.

• Lacrimal secretions.

• Administration of the correct amount is difficult.

• Factors to be considered:

• pH of lacrimal fluids.

• Dose of the drug.

• Irritability of the drug.

• Blinking of eyes.

• Viscosity of the drug and dosage form.

• Examples:

• Mydriatics: Atropin.

• Miotics: Pilocarpine.

• Antibiotics: Ciprofloxacin.

• Corticosteroids: Betamethasone.

6) Topical Route: 

• The skin is the largest organ of the human body.

• Many of the time the drugs are applied on the skin for local effects, the  mode is termed the Topical route.

• When the drugs are applied on the skin for the systemic effects the mode is called percutaneous or transdermal route.

• The main barrier for drug absorption is “Stratum corneum”.

• The drugs are absorbed by passive diffusion.

• Liniments, lotions, ointments, creams etc are conventional dosage forms while transdermal patches, implants are modern dosage forms used for this route of administration.

• Advantages:

• Easy application.

• Lack of gastric hostility, first pass effect.

• Reduced dosing frequency: Increased patient compliance.

• Disadvantages:

• Some drugs may cause skin irritation.

• Improper absorption of certain drugs.

• May cause inconvenience to the patients.

• Factors to be considered:

• Skin condition.

• Environmental factors.

• Application procedure.

• Composition of vehicle used in dosage form.

• Examples:

• Diclofenac diethylammonium, 

• Nitroglycerine, 

• Lignocaine.

7) Pulmonary Route:

• Drugs are administered by inhalation for local as well as systemic effects; they are absorbed through the vast and highly vascularised surface area of alveoli.

• Drug absorption takes place by passive diffusion (lipophilic drugs) and pore transport (hydrophilic drugs).

• Advantages:

• Rapid absorption.

• Rapid onset of action.

• Local effect on the respiratory system.

• Bypasses first pass metabolism.

• Disadvantages:

• Some drugs may cause irritation.

• Some vehicles are known to stimulate respiratory secretions.

• Action being rapid can not be controlled easily.

• Factors to be considered:

• Particle size of the drug.

• Effects of drug and propeller on mucus thickness, mucociliary clearance.

• Properties of propeller used.

8) Intra Subcutaneous Route:

• Drug is injected into subcutaneous tissue present below the skin.

• Shows complete absorption as blood supply is comparatively good.

• Generally, absorption of drugs from a s.c. site is slower than that from i.m. sites due to poor perfusion than in muscles.

• However the absorption from this route can be enhanced by addition of a vasodilator.

• Drugs are absorbed by passive diffusion.

• Advantages:

• Rapid onset of action.

• No first pass effect and GI metabolism.

• Disadvantages:

• Lower doses required 1-4 ml.

• Irritant drugs can not be administered.

• Examples:

• Adrenaline.

• Insulin.

• Heparin.

• Morphine.

9) Intramuscular Route:

• DRugs are injected inside the muscular mass from where they get absorbed.

• The absorption takes place by many mechanisms like: Passive diffusion, Pore transport, Endocytosis.

• Absorption of drugs from i.m. sites are relatively rapid but much slower in comparison to i.v. injections.

• Advantages:

• Large volumes can be administered.

• Irritant drugs can also be administered.

• Can serve as a depot.

• Disadvantages:

• Painful.

• May cause damage to nerves.

• Factors to be Considered:

• Vascularity of the injection site.

• Lipid solubility and ionization of drugs.

• Molecular size of the drug.

• Volume of injection and drug concentration.

• pH, composition and viscosity of the injection vehicle.

• Examples:

• Penicillin G.

• Progesterone.

Commonly Asked Questions:

1. Discuss Buccal route and sublingual route as a route of drug administration.

2. Discuss the factors to be considered while using intramuscular route of administration.

3. Wite a note on factors affecting drug absorption through Non per Oral Routes.