The intravenous route:
Advantages of IV:
- Delivered immediately and with rapid and predictable onset of effect
- Administration of precise quantities is possible
- Bypasses the first pass metabolism of the GI tract
- Available to use when enteral route is not available (e.g., NBM, nausea or
vomiting, GI tract unavailable due to illness or surgery, lowered
consciousness or altered neurology affecting the safety of swallowing and
increased risk of aspiration)
Absorption and distribution:
- Medicines administered via the oral route are absorbed across the GI
membrane in the small intestine and transported via the venous system to the
liver.
- The hepatic portal vein delivers absorbed drug to the liver where metabolism
can begin. The bioavailability (how much of a drug is available to exert an
effect) varies drug to drug and patient to patient.
Metabolism:
- Drugs extensively metabolised by the liver after GI absorption are referred to
as having a ‘high fast pass effect’. This can lead to little drug being left to have
an effect on the body.
- IV administration bypasses the GI system, allowing a bioavailability of 100%.
- Metabolism occurs to enable drugs to be excreted by the body.
- If drugs are metabolised via the same pathway in the liver you can expect
them to interact or have an effect on each other.
Advantages of IV:
- Delivered immediately and with rapid and predictable onset of effect
- Administration of precise quantities is possible
- Bypasses the first pass metabolism of the GI tract
- Available to use when enteral route is not available (e.g., NBM, nausea or
vomiting, GI tract unavailable due to illness or surgery, lowered
consciousness or altered neurology affecting the safety of swallowing and
increased risk of aspiration)
Absorption and distribution:
- Medicines administered via the oral route are absorbed across the GI
membrane in the small intestine and transported via the venous system to the
liver.
- The hepatic portal vein delivers absorbed drug to the liver where metabolism
can begin. The bioavailability (how much of a drug is available to exert an
effect) varies drug to drug and patient to patient.
Metabolism:
- Drugs extensively metabolised by the liver after GI absorption are referred to
as having a ‘high fast pass effect’. This can lead to little drug being left to have
an effect on the body.
- IV administration bypasses the GI system, allowing a bioavailability of 100%.
- Metabolism occurs to enable drugs to be excreted by the body.
- If drugs are metabolised via the same pathway in the liver you can expect
them to interact or have an effect on each other.
