Drug Administration

Introduction

The absorption pattern of drugs differs considerably between individual drug substances, as well as between the different administration routes.

A medication administration route is often classified by the location at which the drug is administered, such as oral or intravenous.

  • The choices of routes in which the medication is given depends not only on the convenience and compliance, but also on the drug's pharmacokinetics and pharmacodynamic.

The right route of administration and dosage form is selected to maximise outcome of treatment. To illustrate,

  • 32 years old epileptic male with fever and infection on nasogastric feeds, prescribed with phenytoin 300 mg daily. Which dose form do you choose (capsules, suspensions or injections) and why?
  • 48 years old patient with osteomyelitis, microbiological culture positive for the bacteria Methicillin Resistant Staphylococcus Aureus (MRSA). Which dose form do you choose (IV or oral) and why?
  • 4 years old boy diagnosed with bronchitis requiring salbutamol for relief of airway spasm. Which dose form do you choose (inhaler, nebuliser or oral) and why?



Pharmacokinetics

All drugs irrespective of their delivery route remain foreign to the human body, and distribution, metabolic and elimination processes commence immediately following drug absorption until the drug is eliminated from the body via the urine, faeces, saliva, skin or lungs in unchanged or metabolized form.

Pathway of A Drug Following Administration

Dosage forms may vary in time of onset of therapeutic effects.

Time of Onset of Different Dosage Forms



Advantages and Disadvantages

Advantages and Disadvantages of Various Dosage Formulations



Contraindications

An oral medication route is contraindicated for patients who cannot tolerate oral drugs, such as those who have altered mental status or have nausea or vomiting that hinder them from safely ingesting the drug orally.

A rectal route is contraindicated in patients with active rectal bleeding or diarrhoea or after a recent rectal or bowel surgery.

An intramuscular route is contraindicated in an active infection or inflammation at the site of drug administration, myopathies, muscular atrophy, thrombocytopenia, or coagulopathy.

A subcutaneous route of medication is contraindicated in an actively infectious or inflamed site. Doses that require to be injected more than 1.5 ml at once should be avoided. Subcutaneous injection volumes larger than 2 ml are associated with adverse effects, such as pain and leakage at the injection site.

An intranasal medication is contraindicated in patients with nasal trauma, anatomic obstruction, presence of a foreign body, or copious mucous or bleeding.

Similarly, an inhaled medication is contraindicated in patients with airflow obstruction.



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