Routes of Drug Administration and Transport of Drugs Across ...

Routes of Drug Administration and Transport of Drugs Across ...

ROUTES OF DRUG ADMINISTRATION AND TRANSPORT OF DRUGS ACROSS CELL MEMBRANE. BY DR O.A ODUNIYI(MBBS,MSc,FMCFM) Geriatric-biased family physician/clinical pharmacologist), College of MEDICINE,UNILAG. OBJECTIVES At the end of the period of lecture, the student should be able to; List various routes of administration of drug.

Select or make a choice of route of a drug depending on clinical condition of patient. Vividly describe advantages and disadvantages of various routes of drug administration Various methods of drug transport processes across the cell membrane. INTRODUCTION To administer a drug is to make the drug accessible to the patients body where the effect is desired.The drug therefore, is desired by the therapist to elicit or manifests an effect where it is desired.

For this to occur, the drug must come in contact with the tissues of organs and cells of tissues by one way or the other, the way the drug comes in contact or is made accessible to the tissue fluids tissues, cells, extracellular and intra cellular fluids is the route of administration of drug. Choice of Route of Administration This is based on the way the drug is preferred for administration i.e. based on the drug dosage forms. Drugs are administered in various dosage forms: as solid e.g. oxtetracycline

capsule Paracetamol tablet ,Dimenhydrinate pill, as solution - codeine syrup, as suspension insulin, penicillin procaine, Aerosol beclomethesone ,Volatile liquid - halothane or nitrous oxide ,as ointments, lotions, pastes etc. Choice of Route of Administration Based on the nature of the drug, oil based, organic. Polar, non polar solvent etc. The desired bioavailability of the therapist. Desired onset of action - how fast the therapist wants to see the manifest effect of the drug. This is important, especially in life threatening conditions

or circumstances that require immediate onset of action are shock, circulatory collapse, the nature of the disease and itslocation of the disease Choice of Route of Administration Duration of action If a duration is required to be long; the drug is administered 2-4 times daily. This could be done in a depot form, as a patch on the skin, another example is treating anaplasmosis, the aqueous oxytetracycline is administered 2-3days by intramuscular,subcutaneous or intravenous

injection. The long acting oxytetracycline, which is designated for slow absorption over 4-5 days. LOCATION OF DESIRED EFFECTS OF THE DRUG Routes of drug administration: The routes of drug administration for systemic effect may be divided into two major groups: Oral (enteral) and parenteral (systemic). When the gastro-intestinal tract is by-passed by injection or introduction into the lungs (inhalation). When the drug is effect is desired locally it is administered topically, that is on

the skin. ORAL OR ENTERAL ADMINISTRATION OF DRUG Oral ingestion is the most ancient method of drug administration, another organ where the substance or drug to be administered is placed is the rectum. ( Intrarectally) The drug could be placed in the mouth, under the tongue, that is (sublinqual). The drug could be administered directly into the stomach using intragastric tube.

Advantages and disadvantages of oral route

Advantages: 1-Safe 2-Sterility is no required 3-Danger of acute drug reaction is minimal Disadvantages: 1-Ingestion of drug could cause gastric irritation. 2-Nausea 3-Vomiting (in animals like dog, pig) 4-Complexes formed with ingested drug could prevent the drug absorption 5-The drug could be destroyed by low gastric pH or by the digestive and liver enzymes before entry into the circulation.

PARENTERAL ADMINISTRATION Parenterally par means beyond enteral means intestinal. This is the route of administration of drug without crossing the intestinal mucosa. This is possible when the drug is directly into the blood or tissue fluid using syringes and needles. The most important and most frequently used parenteral routes are I.V. (intravenous route), intramuscular route and SC (subcutaneous route respectively.

OTHER LESS FREQUENT PARENTERAL ROUTES ARE:

Tissue infiltration Intra articular Intradermal Epidural Subarachnoid Intra-arterial Intrathecal

Intrathoracic Intracardiac Intramedullary Intratesticular Intralesional Subconjuctival Intramammary Advantages of Parenteral route of drug administration Bioavailability is faster and more predictable. Gastric irritation and vomiting are provoked.

Parenteral routes could be used in unconscious, uncooperative and vomiting patient. There are no chances of interference by food or digestive enzymes. Liver enzymes are by-passed. It essential sometimes in the absorption of the active form of the drug. Disadvantages of parenteral routes

It is generally more risky The preparation must be sterile The technique is intensive and painful. Drug administered by all routes except intraarterial might still be eliminated by first pass elimination in liver prior to distribution to the rest of the body. INTRAVENOUS ROUTE: The drug is injected slowly, sometimes it could

be infused rapidly as bodies. This method provides accurate, reliable dosage of drug directly into the circulation. It means that the biovailability of drug is 100% when administered intravenously. Advantages of intravenous route This route is often used in drug administration in life threatening situations. The drug would have rapid onset of action. Irritating and non-isotonic solutions can be administered intravenously, since the intima

of the vein are insensitive. Disadvantages of intravenous route The drugs administered by this method have short duration of action. Thrombophlebitis of veins Necrosis of adjoining tissue. Severe adverse effect especially when organs such as liver, heart, brain are involved in toxicity. INTRAMUSCULAR

The drug is injected deep in the belly of a large skeletal muscle. The muscles that are usually used are detoid, triceps, Gluteus,. Maximus, rectus, femurs depending on the species of animal. The muscle is less richly supplied with sensory nerves, hence injecting a drug 1M is less painful. Advantages of intramuscular route It is convenient route in administering drugs in animals that are difficult to restrain.

It is used in administering aqueous or oleaginous suspensions or solutions. Muscles are highly vascularized thus, the drug could be absorbed haematogenously or through the lymphatic fluid. Disadvantages of intramuscular route Disadvantages Intramuscular injection into fascia might lead to erratic absorption of the drug. There is a possibility of improper deposition of drug preparation in nerves, fats, blood vessels

or between muscle bundles in connective sheaths. SUBCUTANEOUS The drug is deposited in the loose subcutaneous tissue that is richly supplied with nerves but less vascular. The rate of absorption is slower than the intramuscular route. Advantages and disadvantages of subcutaneous route

Advantages: It is a good route of administration especially in skin infections. It is relatively safer than I.M. and I.V. Absorption is slower thus, it is a good route of a prolonged effect is to be achieved. Disadvantages: If the drug is irritating it might cause the sloughing off of the skin epitheral tissue. Other forms of subcutaneous route include; pellet implantation and dermoject.

Pellet implantation The drug dosage form of the drug is in solid pellet and is implanted subcutaneously suing a trochar and cannula under the skin. Dermoject: In this method, needle is not used, rather a high velocity jet of drug solution is projected from a microfine orifice of gun-like implement. The solution passes through the superficial layer of the skin and gets deposited in the subcutaneously. This method is used in Mass innoculation. INTRA-ARTERIAL ROUTE Drugs and diagnostic agents are administered via this route. The

diagnostic media e.g. (Contrast media in angiography) is injected directly into the artery. This is also of great use in treatment of limb malignancies. Advantages: - The first pass and cleansing effects are by-passed. - Bioavailability is 100%. - It is of great clinical value in administering anticancer drugs for example, in limb malignancies, the drug is administered into the brachial artery or femoral artery. Disadvantages: - Intra arterial injection requires great and expertise - If the drug is of adverse effect there might be great danger.

INTRAPERITONEAL The peritoneum possess a cavity that offers a large absorptive area for drugs. The perioneum is highly vascularized. This route is used in laboratory animals administration and large animal practice for administration of large volumes of fluid. The injection is made via the sub-lumbar fossa. Disadvantages: - Irritating compounds may produce peritonitis or adhesion. INTRATHECAL

This is a route of administration of drug in which the effects of the drug is desired in the C.N.S. The blood brain barrier and the blood-cerebrospinal fluid barrier often slow the entrance of drug into the C. N. S. The drug will be accessible to the meninges and cerebrospinal axis. The injection made in the lumbar area or in the cisterna magna. These routes are primarily for diagnostic procedures (e.g. Myelography) and treatment of meningoencephelitis. Local anaesthetics are sometimes administered intrathecally to produce region or spinal anaethesia.

Intrademal and intra-articular Intrademal: the drug is injected into the skin raising a bleb. This route is used in diagnosis of tuberculosis (tuberculin testing in human) and (allergen sensitivity testing). Intra-articular: Intra-articular injection of antiinflammatory preparation (e.g. steroids) may be justified in some forms of lameness due to acute inflammation or trauma e.g. (swollen bursa or tendon sheath) Other routes of drug injection include intra-medullary, which is used for blood transfusion directly into the bone marrow. This is done in neonates when other is difficult.

Pulmonary Route (Inhalation) Gases, volatile liquids, and aerosols (fine droplets ion air). Some drugs such as ventolin are administered using a nebulizer or inhalers. Anaesthesia such as halothane, sevoflurane are vaporized and made to be atomized by a process atomization This is delivered into the respiratory passages with the aid of anaesthetic machine or vapourizer. The vapourised anaesthesia is inhaled to cause anaesthesia and thus is eliciting its effect. DRUG TRANSPORT PROCESSES

Principal mechanisms of transport of drug molecules across the cell membrane are : Principal mechanisms of transport of drug molecules across the cell membrane are 1. Passive diffusion 2. Carrier mediated transport (a) Active transport (b) Facilitated transport 3. Vesicular transport (a) Pinocytosis (b) Phagocytosis 4. Pore transport 5. Ion pair formation

PASSIVE TRANSPORT PASSIVE TRANSPORT Passive diffusion is the process by which molecules spontaneously diffuse from a region of higher concentration to a region of lower concentration. This process is passive because no external energy is expended. Mathematical expression Passive diffusion is best expressed by Ficks first law of diffusion which can be expressed mathematically

CARRIER MEDIATED TRANSPORT: CARRIER MEDIATED TRANSPORT Some polar molecules cross the membrane more readily than can be predicted from their concentration gradient and partition coefficient values. This suggests the presence of some specialized transport mechanisms without which many essential water-soluble nutrients like monosaccharides , amino acids and vitamins will be poorly absorbed. The mechanism is thought to involve a component of the membrane called as the carrier that binds reversibly or noncovalently with the solute molecules to be transported.

Characteristics of Carrier Mediated Transport: Active Transport: Active Transport The drug is transported from a region of lower concentration to a region of higher concentration, i.e. against the concentration gradient Endogeneous substances that are transported actively include Sodium (Na+), potassium (K+), calcium ( Ca ++), iron (Fe+ +) in ionic state; certain amino acids and vitamins like niacin, pyridoxine and ascorbic acid .

Facilitated diffusion: Facilitated diffusion Facilitated diffusion is also a carrier mediated transport system but it moves along a concentration gradient ( i.e from higher to lower concentration) and hence it does not require any energy. Acetylcholine (ligand) binds to certain synaptic membrane and opens Na+ channels and initiate a nerve impulse. Gamma amino butyric acid (GABA) binds to GABAA receptors and the chloride channel opens. This inhibits the creation of a nerve impulse.

VESICULAR TRANSPORT: VESICULAR TRANSPORT Vesicular transport is the process of engulfing particles or dissolved materials by the cell . Vesicular transport ------- a ) Pinocytosis b) Phagocytosis Vesicular transport is the proposed process for the absorption of orally administered Sabin polio vaccine and large proteins. Transport of proteins, polypeptides like insulin from insulin producing cells of the pancreas into the extracellular space.

PORE TRANSPORT: PORE TRANSPORT Very small molecules (such as urea, water, and sugars) are able to rapidly cross cell membranes as if the membrane contains channels or pores. A certain type of protein called transport protein may form an open channel across the lipid membrane of the cell. Drug permeation through aqueous pores is used to explain the renal excretion of drugs and the uptake of drugs into the liver. ION PAIR FORMATION:

ION PAIR FORMATION Strong electrolyte drugs are highly ionized or charged molecules, such as quaternary nitrogen compounds with extreme pKa values. When ionized drugs is linked up with an oppositely charged ion, an ion pair is formed in which the overall charge of the pair is neutral. This neutral drug-complex diffuses more easily across the membrane . Examples: Propranolol , a basic drug, forms an ion pair with oleic acid. Quinine forms an ion pair with hexylsalicylate

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