Part two of the series
SYSTEMIC ROUTES: Here the drug is intended to be absorbed into the blood stream and distributed all over the body, through circulation.
The various Systemic routes include –
1. Oral – Both solid dosage forms and liquid dosage forms syrups, emulsions, mixtures can be orally administered. It is the oldest and commonest mode; safer, more convenient and noninvasive. Additionally, no assistance is needed. It is a painless route and the medicament need not be sterile.
The disadvantages of the oral route of administration include
· Cannot be used for drugs with unpalatable taste
· Drug action is slower, thus making the route unsuitable for emergencies
· Cannot be used in unconscious, uncooperative or vomiting patient.
· Some drugs are not well absorbed orally
· Some drugs may be destroyed by digestive juices or the liver(hepatic metabolism)
2. Sublingual or buccal – lipid soluble and non-irritating drugs can be administered by this route of administration. Here the tablet or pellet is placed under the tongue or crushed in the mouth and spread over the buccal mucosa. Absorption is relatively rapid. This route bypasses the liver and thus drugs with high first pass metabolism can be absorbed directly into systemic circulation.
3. Cutaneous – Here drugs are applied over the skin for slow/prolonged action. The drug should be highly lipophillic. This route of administration also bypasses the liver. The drug, in an appropriate dosage form is applied onto the skin. Absorption of the drug can be enhanced by rubbing the preparation, by using an oily base and an occlusive dressing. Transdermal therapeutic systems (TDS) are comprise of adhesive patches of various shapes and sizes, which deliver the contained drug at a constant rate into systemic circulation via the stratum comeum.
(Mote on TDS later)
4. Nasal – Many drugs are very easily absorbed across the nasal mucosa. This route of administration too has the advantage that it bypasses digestive juices and liver. However, only limited numbers of drugs have been used by this route and its use in the administration of some other peptide drugs, like insulin is being studied.
5. Inhalation – This route of administration is used for the administration of Volatile liquids and gases. e.g. general anaesthetics. The drug is absorbed from the surface of the alveoli and action is very rapid. Care has to be exercised to ensure that the drug is not irritant since irritant vapours (ether) cause inflammation of respiratory tract.
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6. Rectal – This route of administration can be used for administering certain irritant and unpleasant drugs, in the form of suppositories or retention enema systemic effect. This route is especially useful in patients are vomiting or in unconscious patients. However, it is an inconvenient and embarrassing; absorption is slower, irregular and may even be unpredictable.
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7. Parenteral – This route of administration involves injecting the drug into the body, thereby taking the drug directly into the tissue fluid or blood without having to cross the Gastointestinal Tract (GIT). This route of administration overcomes the limitations of oral administration.
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The parenteral route of administration offers several advantages such as
· It is useful even in unconscious, uncooperative or vomiting patient.
· drug action is faster
· Liver is bypassed.
· No interference by food or digestive juices
· No gastric irritation and vomiting
The disadvantages of parenteral routes include
· Invasive and painful
· requires assistance of another person
· chances of local tissue injury
· Sterilization of the preparation makes it costlier
The main parenteral routes of administration include
(i) Intravenous (i.v.)
(ii) Intramuscular (i.m.) Depot preparations (oily solutions/ aqueous suspensions) can be injected by this route.
(iii) Intradermal iniection
(iv) Subcutaneous (s.c.) – eg. Dermojet, Pellet implantation, Sialistic (nonbiodegradable) and biodegradable implants