Concept of Prodrug – This book covers the entire syllabus of “Pharmacology” prescribed by BNMC- for diploma in nursing science & midwifery students. We tried to accommodate the latest information and topics. This book is an examination set up according to the teachers’ lectures and examination questions.
At the end of the book, previous questions are given. We hope in touch with the book students’ knowledge will be upgraded and flourish. The unique way of presentation may make your reading of the book a pleasurable experience.
Concept of Prodrug
It is an inactive form of a drug, which is converted to an active form after metabolism.
Uses of Prodrug (advantages)
1. To improve bioavailability: Parkinsonism is due to deficiency of dopamine. Dopamine itself cannot be used since it does not cross the BBB. So it is given in the form of a prodrug, levodopa.
Levodopa crosses the BBB and is then converted into dopamine
2. To prolong the duration of action: Phenothiazines have a short duration of action, whereas esters of phenothiazine (fluphenazine) have a longer duration of action.
3. To improve the taste: Clindamycin has a bitter taste, so clindamycin palmitate suspension has been developed for paediatric use to improve the taste.
4. To provide site-specific drug delivery
First Pass (Presystemic) Metabolism
First Pass (Presystemic) Metabolism
This refers to metabolism of a drug during its passage from the site of absorption into the systemic circulation.
➤ All orally administered drugs are exposed to drug metabolizing enzymes in the intestinal wall and liver (where they first reach through the portal vein).
➤ Presystemic metabolism in the gut and liver can be avoided by administering the drug through sublingual, transdermal or parenteral routes
➤ However, limited presystemic metabolism can occur in the skin (transdermally administered drug) and in lungs (for drug reaching venous blood through any route). The extent of first pass metabolism differs for different drugs and is an important determinant of oral bioavailability.
Attributes of drugs with high first pass metabolism:
Attributes of drugs with high first pass metabolism:
1. Oral dose is considerably higher than sublingual or parenteral dose.
2. There is marked individual variation in the oral dose due to differences in the extent of first pass metabolism.
3. Oral bioavailability is apparently increased in patients with severe liver disease.
4. Oral bioavailability of a drug is increased if another drug competing with it in first pass metabolism is given concurrently, e.g. chlorpromazine and propranolol.
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