Routes of Drug Administration 2024-2025 PDF

Routes of drug administration By Dr. Mariam Ashraf Amin Pharmacology and Toxicology department Faculty of Pharmacy 2024-2025 Onset vs. Duration of drug action There are two major ways of drug administration, enteral and parenteral. a) Enteral routes (rela...

Routes of drug administration By Dr. Mariam Ashraf Amin Pharmacology and Toxicology department Faculty of Pharmacy 2024-2025 Onset vs. Duration of drug action There are two major ways of drug administration, enteral and parenteral. a) Enteral routes (related to GIT): oral, sublingual, buccal and rectal. b) Parenteral routes (away from GIT): injections, local (topical) and inhalation  First-pass metabolism It is the metabolism of some drugs in a single passage through the liver or gut wall before reaching the systemic circulation. a) Hepatic first-pass effect: Drugs absorbed from the GIT are carried first in portal circulation to the liver where they are extensively metabolized as nitroglycerin and propranolol. b) Intestinal first-pass effect: due to intestinal mucosal metabolism e.g., isoprenaline and tyramine. - For example, large amounts of lidocaine and insulin are subjected to first-pass metabolism and therefore oral routes are not recommended with these drugs. - The first-pass effect can be avoided completely by sublingual & parenteral but partially by rectal administrations. Different first-pass metabolic effects after sublingual (nothing), after oral (Complete) and after rectal route (partial). Different routes of drug administration A. Enteral routes 1- Oral route  1- Oral route Giving a drug by mouth Advantages Disadvantages ✓ Easy χ Delayed onset of action due to slow absorption ✓ Self-administration (limits its usefulness in emergency conditions ✓ Economic that necessitate urgent & rapid treatment). ✓ Safe because overdosage toxicity could be χ Destruction of some drugs by GI fluids as in overcome by different procedures including some types of penicillins that are inactivated emesis and antidotes such as activated by gastric HCl. Enteric coating of a drug charcoal. protects it from the acidic environment. χ Exposure to first- pass metabolic effects χ Interactions with food in GIT χ Not suitable in unconscious, uncooperative, severely ill patients, & in presence of vomiting or convulsions.  Dosage forms used orally: Oral drops Syrup Suspension Capsules Tablets Effervescent sachets Special types of tablets: - Enteric coated tablet - Sustained release tablet (SR) - Colored tablet - Effervescent tablet - Chewing tablet - Lozenges 2- Sublingual route  2- Sublingual route Drugs placed under the tongue to diffuse directly into the systemic circulation Advantages Disadvantages ✓ Rapid onset, so it is suitable in emergency as Ҳ Not suitable for all drugs, only for nitrates as in acute anginal attacks and severe nitroglycerin ( for acute attack of angina) hypertension. ✓ Due to direct drainage of drugs into the and captopril (for hypertension) superior vena cava, thus by-pass first-pass metabolism in the liver and so bioavailability is high and more than oral route. ✓ Excess dose can be expelled. 3- Rectal route  3- Rectal route Advantages Disadvantages ✓ Suitable when oral ingestion is precluded as χ Not suitable in cases of diarrhea and may cause in: irritation and burning sensation. unconscious and vomiting patients. χ Inconvenient and unacceptable by most ✓ 50% of the drug by-pass liver as blood patients even children. supply of the lower half of rectum passes to systemic circulation (partial 1st pass metabolic effect). ✓ Can be given for local purposes (e.g., local anesthetics in piles) or absorbed for systemic effect (e.g., theophylline or diclofenac suppositories). ✓ Avoidance of gastric irritation by the drug.  Dosage forms used rectally: i- Suppository: used for both topical and systemic effects. ii- Enema (evacuant and used in cases of constipation or retention). Different routes of drug administration B. Parenteral routes 1- Parenteral injections  1- Parenteral injections a- Intravenous (I.V.): Advantages Disadvantages ✓ Very rapid onset, so suitable in emergency. χ More expensive, ✓ Proper dose adjustment. χ Needs aseptic conditions, ✓ Maintenance of drug in active form as no χ Difficulty of self-administration destruction in liver or by HCl, or digestive χ Painful enzymes (bioavailability 100%). χ Needs patent vein. ✓ Suitable for large volumes (as fluids, blood; IV χ Difficult to eliminate the drug if toxicity infusion). occurs. ✓ Suitable for irritant drugs (as blood vessels are χ Not suitable for suspension and oily relatively insensitive, e.g., anticancer drugs). solutions as may form thrombi or emboli. ✓ Suitable in unconscious, uncooperative patients, severely ill patients, and in presence of vomiting. ✓ Suitable when drugs are poorly absorbed orally or lose efficacy when given orally e.g. insulin.  1- Parenteral injections b- Intramuscular (I.M.) Advantages Disadvantages ✓ As IV but IM is suitable only for moderate χ Unlike I.V., it is not suitable for anticoagulant as volume drugs, and in cases of irritant drug heparin I.M. may cause hematoma. need deep IM injection). χ Limited volume is given I.M. (4-5 ml). ✓ Very rapid absorption of drugs χ More expensive, ✓ Repository and slow release preparations χ Needs aseptic conditions, can be given I.M. Good blood flow to muscle χ No self-administration sites enhances drug uptake. χ Painful ✓ Unlike IV, it is suitable for suspensions and oily solutions.  1- Parenteral injections c- Subcutaneous (S.C.): Advantages Disadvantages ✓ Suitable for suspensions and oily solutions χ Slow onset of action. ✓ Gives prolonged duration of action. χ Not suitable for large volume and irritant drugs ✓ Rate of absorption is usually constant but (as cause severe pain and necrosis). slow to provide sustained effect. ✓ Can be used with hormones as insulin, implantable contraceptive (S.C. pellets give effect for 5-6 years). Notes: Absorption after S.C. or I.M. can be enhanced by increasing blood supply by massaging, and hot fomentation and can be reduced by decreasing blood supply via cold fomentation, or injection of vasoconstrictors as epinephrine.  1- Parenteral injections d- Intrathecal: Advantages Disadvantages ✓ Leads to high concentration in CSF and so χ Needs special precaution to avoid infection, and can be used in spinal nerve injury. treatment of CNS disorders as infection χ Difficult and needs professional physician. to inject antibiotic, in spinal anesthesia in diagnosis of some CNS disorders by withdrawing CSF samples. Injection in the subarachnoid space through one of the vertebral interspaces between the 2nd and 5th lumbar levels to avoid injury of the spinal cord which terminates in adults above the 2nd lumbar vertebras. Spinal anesthesia  1- Parenteral injections Other types of injection: Dosage forms used by parenteral injections E- Intracardiac i. Ampules (for single dose). F- Intraarterial ii. Vials (for multidose). G- Intraarticular: iii. Bottles (for I.V. infusion) The injection of drugs directly into the joint space produces a rapid and local effect, e.g., intraarticular injection of corticosteroids in rheumatoid arthritis H- Intradermal I- Intraperitoneal 2- Inhalational route  Inhalational route Advantages Disadvantages ✓ Suitable for volatile compounds, gases, and χ Not used in irritant drugs. aerosol. χ Difficult to adjust dose. ✓ Can be used for local or systemic effect. χ May need special apparatus (difficulty to use ✓ Avoid first-pass metabolism. the inhaler properly.) ✓ Rapid onset due to large area of absorbing surface (alveolar membrane). ✓ Self-administration is possible. Used for drugs that can be dispersed in an aerosol, e.g., β-adrenergic agonists in bronchial asthma (local effect) or vaporize easily e.g., gaseous and volatile anesthetics (systemic effect) Almost as rapid as iv injections. 3- Topical or local administration  Topical or local administration Advantages Disadvantages ✓ Application of drugs to the skin or mucous χ Some systemic absorption may occur membrane (of nose, throat, ear, conjunctiva, especially in presence of destruction or rectum, or vagina). inflammation of skin and if the drug is highly ✓ Provides high local concentrations with little or lipid soluble as in organophosphorus no systemic effects (but some drugs used compounds. topically to give systemic effect as in transdermal patch for angina). ✓Transdermal: application of the drug on the skin to reach the systemic circulation (Slow absorption) Examples: Nicotine patch, Nitroglycerin patch Dosage forms used locally: 1- Drops (eye, nasal, and ear drops). 3- Ointment (applied for dry skin). 2- Cream (applied for wet skin). 4- Lotion. Thank you