Drugs; most common routes of administration, Absorption pattern, Advantages and disadvantages

 Routes of Drugs Administration

Oral: Variable affected by many factors

Advantages

• Safest and most common, convenient, and economical route of administration 

Disadvantages

• Limited absorption of some drugs
• Food may affect absorption
• Patient compliance is necessary
• Drug may be metabolized before systemic absorption

Example.

• Acetaminophen tablets
• Amoxicillin suspension

Sublingual: Depends on the drugs, few drugs (for example, nitroglycerin) have rapid, direct systemic absorption. Most drugs erratically or incompletely absorbed.

Advantages

• Bypasses first-pass effect
• Bypasses destruction by stomach acid
• Drug stability maintained because the pH of saliva relatively neutral
• May cause immediate pharmacological effects

Disadvantages

• Limited to certain types of drugs
• Limited to drugs that can be taken in small doses
• May lose part of the drug dose if swallowed

Example

• Nitroglycerin
• Buprenorphine

Intravenous: Absorption not required

Advantages

• Can have immediate effects
• Ideal if dosed in large volumes
• Suitable for irritating substance and complex mixtures
• Valuable in emergency situations
• Dosage titration permissible
• Ideal for high molecular weight proteins and peptide drugs

Disadvantages

• Unsuitable for oily substance
• Bolus injection may result in adverse effects
• Most substances must be slowly injected
• Strict aseptic techniques needed

Example

• Vancomycin
• Heparin

Intramuscular: Depends on drug diluents: Aqueous solution: slow and sustained 

Advantages

• Suitable if drug volume is moderate
• Suitable for oily vehicles and certain irritating substance
• Preferable to intravenous if patient must self-administer 

Disadvantages

• Affects certain lab tests (creatine kinase)
• Can be painful
• Can cause intramuscular haemorrhage (precluded during anticoagulation therapy )

Example

• Haloperidol

Subcutaneous: Depends on drug diluents, Aqueous solutions, prompt depot preparations, slow and sustained

Advantages

• Suitable for low-release drugs
• Ideal for some poorly soluble suspensions 

Disadvantages

• Pain or necrosis if drug is irritating
• Unsuitable for drugs administered in large volumes

Example

• Insulin
• Heparin

Inhalation: Systemic absorption may occur, this is not always desirable

Advantages

• Absorption is rapid, can have immediate effects
• Ideal for gases
• Effective for patient with respiratory problems
• Doses can be titrated
• Localized effect to target lungs, lower doses used compared to that with oral or parenteral administration
• Fewer systemic side effects

Disadvantages

• Most addictive route (drug can enter the brain quickly )
• Patient may have difficulty regulating dose.
• Some patients may have difficulty using inhalers

Example

• Albuterol

Topical: variable, affected skin conditions, area of skin

Advantages

• Suitable when local effect of drug is desired
• May be used for skin, eye, intra-vaginal and intranasal products
• Minimizes systemic absorption
• Easy for patient

Disadvantages

• Some systemic absorption can occur
• Unsuitable for drugs with high molecular weight or poor lipid solubility

Example

• Clotrimazole cream
• Hydrocortisone cream

Transdermal: slow and sustained

Advantages

• Bypasses the first-pass effect
• Convenient and painless
• Ideal for drugs that are lipophillic and have poor oral bioavailability
• Ideal for drugs that are quickly eliminated from the body

Disadvantages

• Some patients are allergic to patches, which can cause irritation
• Drug must be highly lipophilic
• Limited to drugs that can be taken in small daily doses

Example

• Nitroglycerin

Rectal: Erratic and variable

Advantages

• Partially bypasses first-pass effect
• Bypasses destruction by stomach acids
• Ideal if drug causes vomiting
• Ideal in patients who are vomiting or comatose

Disadvantages

• Drugs may irritate rectal mucosa
• Not a well-accepted route

Example

• Bisacodyl