3rd-year class Practical Pharmacology 2010-2011 Lab.1 3rd-year class Practical Pharmacology 2010-2011

Routes of Drugs Administration

Enteral routes of administration 1-Swallowing 2-Sublingual (buccal) 3-Rectal

Swallowing 1-For systemic effect 2-For effect in the gut

For systemic effect Advantages: 1. Convenience 2. Acceptability

Disadvantages: 1.Absorption may be delayed, reduced or evenly enhanced after food. 2.Absorption may be slow or irregular after drugs that inhibit gut motility ( antimuscarinic,opioids,..) 3.Difference in presystemic elemination is a cause of variation in drug effect between patients.

4.Some drugs are not absorbed ( gentamycin )and some drugs are destroyed in the gut (insulin). 5.Tablets taken with too small quantity of liquid in supine position, can lodge in the esophagus with delayed absorption and may even cause ulceration(doxycyclin,KCL)especially for elderly and those with left a trial enlargement.

For effect in the gut Advantages: 1.The drug can be placed at the site of action(neomycin,antihelmethics) 2.In non-absorbed drugs the local cocentration can be higher than it would be safe in the blood.

Disadvantages: 1.The drug distribution may be uneven 2.In some diseases of the gut the whole thickness of the wall is affected and effective blood concentration may be needed(bacillary dysentry,typhoid)

2-sublingual or buccal sulcus for systemic effect Advantages Quick effect is obtained (glycerol trinitrate , nifidipine) especially if the tablet is chewed ,giving a greater surface area for solution . The effect can be terminated by spitting out the tablet .

Disadvantages: The inconvenience if use has to be frequent. Irritation of the mucous membrane. Excessive salivation which promote swallowing ,so losing the advantages of bypassing presystemic elimination .

3- rectal administration A-for systemic effect B-for local effect

A-for systemic effect (suppositories or solution ) Advantages A drug that is irritant to the stomach can be given by suppository (aminophylline,indomethacin) The route is suitable in vomitting ,migraine,morning sickness or when the patient cannot swallow. When cooperation is lacking (sedation in children).

Disadvantages: Psychological :the patient may be embarrassed or may like the route too much . Rectal inflammation may occur with repeated use. Absorption may be unreliable (especially if rectum is full of feces).

B-for local effect e.g. in proctitis or colitis

Parenteral routes of administration Intravenous (bolus or infusion) Advantages: It gives swift, effective and highly predictable blood concentration . It allows rapid modification of dose ,i.e. immediate cessation of administration is possible if unwanted effects occur during administration. The route is suitable for administration of drags that are not absorbed from the gut or too irritant to be given by other routes (anti cancer).

Disadvantages Local venous thrombosis is liable to occur with prolonged infusion and with bolus doses of irritant formulations .(diazepam , micro particulate components of infusion fluids) Infection of intravenous catheter and the small thrombi on its tip are risky during prolonged infusions . Plasma concentrations may rise at such a rate that normal mechanisms of distribution and elimination are outpaced. So, hazard if a drug is given too quickly.

2-intramuscular injection Advantages: Reliable route. Depot preparations (penicillin, neuroleptics ) can be used at monthly or longer intervals. Suitable for irritant drugs. Absorption is more rapid than following subcutaneous injection ( soluble preparations are absorbed in 10-30 min. ) Disadvantages : The route is not acceptable for self-administration. It may be painful . If any adverse effect may occur to a depot formulation , it can not be removed.

3-subcutaneous injection Advantages : Reliable route . Acceptable for self – administration . Disadvantages : Poor absorption in peripheral circulatory failure . Repeated injections at one site may cause lipoatrophy , resulting in erratic absorption .

4-inhalation A-as a gas : volatile anaesthetics . B-as an aerosol : these are particles dispersed in a gas , the particles are small enough to remain in suspension for a long time instead of sedimenting rapidly under gravity . These particles may be liquid (fog) or solid (smoke) e.g. salbutamol . C-as a powder : sodium cromoglycate .

Advantages: 1-Can be rapidly taken up or eliminated giving the close control that has marked the use of this route in general anesthesia. 2-Self administration is practicable. 3-Aerosol&powder provide high local concentration for action on bronchi, minimizing systemic effect. 4-Aerosol can be used for systemic effect (ergotamine in migraine).

Disadvantages: 1-Special apparatus is needed. 2-Drug must be non-irritant if the patient is concious. 3-Obstructed bronchi may cause therapy to fail (mucus plug).

5-Topical application 1-For local effect 2-For systemic effect

For local effect Advantages: (skin ,eye ,lung ,anal canal ,vagina) Provision of high local concentration without systemic effects.

Disadvantages: 1-Absorption can occur, especially when there is tissue destruction so that systemic effects result. 2-Occular administration of β- adrenoceptor blocker may cause systemic effect(1st-pass elimination is bypassed) and such eye drops are contraindicated to patients with asthma or COAD.

For systemic effect Transdermal delivery system (TDS) release drug through a rate controlling membrane into the skin and so into the systemic circulation. Fluctuations in plasma concentrations associated with other routes are largely avoided, as is 1st-pass elimination in the liver. Examples: GTN in angina and ERT in post-menapause can be given as sticking plaster to skin or as an ointment.