General Pharmacology

Route of Drug Administration

Medical Networking Introduction

A route of administration is the path by which a drug, fluid, poison or other substance is brought into contact with the body.

No single method of drug administration is ideal for all drugs in all circumstances Factors governing choice of route -

Drug related factors: Patient related factors  Condition of the patient  Physical and Chemical  Site of desired action properties  Effect of digestive juice,  Compared first pass metabolism bioavailability for  Urgency for response different routes  Accuracy of dosing Route of administration

Enteral Topical Parenteral (Oral Ingestion) (Other then Enteral)

Oral Route Beyond Intestine (Tab., Cap. Syr.)

Sublingual Rectal Inhalation Intra- Intra- Intra- muscular peritoneal medullary Buccal Sub-cutaneous Nasal Intra- Intra- Transdermal venous articular Oral Administration

 Both solid dosage forms (powders, tablets, capsules, spansules, dragees, moulded tablets) and liquid dosage forms (elixirs, syrups, emulsions, mixtures) can be given orally.

 Absorption mainly takes place from the intestine. Oral Administration of Drugs

ADVANTAGES DISADVANTAGES  Action of drugs is slower and thus not suitable for  Safe emergencies.  Convenient  Unpleasant drugs (chloramphenicol) are difficult to administer.  Economical  May cause nausea and vomiting  Cannot be used for unconscious/ vomiting patient.  Usually good absorption  Absorption of drugs may be variable and erratic  No need for sterilization certain drugs are not absorbed (streptomycin).  Others are destroyed by digestive juices (penicillin G, insulin) or in liver (GTN, testosterone, lidocaine). Rectal Administration of Drugs

 Drugs that are administered rectally as a suppository.  Can serve as local as well as systemic route of administration of drugs.  Unreliable absorption  Preferable in patients who are vomiting, post- operative, difficult to establish intravenous access (child having seizures). Rectal Administration of Drugs

ADVANTAGES DISADVANTAGES

 Used in children  Inconvenient  Little or no first pass effect  Absorption is slow and  Used in vomiting or erratic unconscious  Irritation or inflammation  Higher concentrations of rectal mucosa can occur rapidly achieved Sublingual andBuccal Administration of Drugs

 When rapid response is required  Drug unstable at gastric pH  Drug rapidly metabolised by the liver  Absorbed drugs directly reach systemic circulation, bypassing portal circulation, hence escapes first pass metabolism. Sublingual and Buccal Administration of Drugs

ADVANTAGES DISADVANTAGES

 Drug absorption is quick  Unpalatable & bitter  Quick termination drugs  First-pass avoided  Irritation of oral mucosa  Can be self administered  Large quantities not given  Economical  Few drugs are absorbed Parenteral Route of DrugAdministration

A) Intradermal

B) Subcutaneous (SC)

C) Intramuscular (IM)

D) Intravascular (IV) Intravenous Administration of Drugs

 Fastest route of administration of drugs  Peak concentration reaching tissues depends on rate of administration  Bolus dosing  Infusion dosing Intravenous Administration of Drugs

ADVANTAGES DISADVANTAGES • Most common route for drugs not • May induce hemolysis or cause absorbed orally. other adverse reactions by the • Avoids first-pass metabolism; too-rapid delivery of high absorption bypassed concentrations of drug. • Permits a rapid effect and a maximal • Thrombophlebitis of vein and degree of control over the circulating necrosis of adjoining tissue if levels of the drug. Titration of dose extravasation occurs. with response. • Large quantities can be given Intramuscular and Subcutaenous Administration of Drugs

 Large skeletal muscle are used for intra- muscular administration.

 Subcutaenous Administration: drug is deposited in loose subcutaneous tissue.

 Faster absorption than oral administration. Intramuscular Administration of Drugs

ADVANTAGES DISADVANTAGES  Only up to 5ml drug given  Absorption reasonably uniform  Local pain and abscess, infection  Rapid onset of action  Expensive  Mild irritants can be given  Nerve damage  First pass avoided, Gastric factors avoided  Local hematoma can occur in anticoagulant treated pt. Subcutaenous Administration of Drugs

ADVANTAGES DISADVANTAGES

 Less blood supply: slow absorption  Should be avoided in shock  Depot preparation can be patient used  Only small volume can be  Risk associated with injected intravascular injection avoided Transdermal Route of Drug Administration  Achieves systemic effects by application of drugs to the skin  Rate of absorption determined by drug factors and site of application  Slow effect (prolonged drug action)  First pass effect avoided  Absorption- increase by oily base, occlusive dressing, rubbing preparation Local Route of Drug Administration Local Application: Application to Epithelial Surface Cutaneous Administration: Usually absorption poor over intact skin. Advantages: • Steady rate of drug delivery • Presystemic metabolism avoided

Disadvantages: • Only applicable for Lipid soluble drugs • Relatively Expensive Different Formulations of TopicalPreparation

Lotion Paste

Shake Lotion

Cream/ Ointment/ Emulsion Local Application: Applicationto Epithelial Surface  Eye/Ear Drops:  Eye Drops: Absorption through conjunctival sac epithelium  Ear Drops: Absorption through epithelial lining of External ear  Sterile; require aseptic handling  Desirable for local effects: lacks systemic reactions. Administration By Inhalation

 Systemic Administration of drugs • Large surface area and large blood flow: rapid exchange of drugs, possible to adjust plasma levels rapidly • Nasal Sprays  Local Administration of drugs Intrathecal Administration of Drugs

 Injection into sub- arachnoid space  Minimises systemic adverse effects Intravitreal Administration of Drugs

 An intravitreal injection is a procedure to place a medication directly into the space in the back of the eye called the vitreous cavity, which is filled with a jelly-like fluid called the vitreous humor gel.

 Ranibizumab for wet age-related macular degeneration. Topical Therapy:

Advantages Disadvantages

Delivery onto the target organ at Time consuming an optimal concentration

Depends largely on patient’s Rapid onset of action compliance and patience

Systemic effects are less More expensive