Biochemistry /Pharm Y2S2 - Biopharmaceutics
Pharm Y2S2 - Biopharmaceutics
This deck covers key concepts in biopharmaceutics, focusing on drug absorption, metabolism, and pharmacokinetics, particularly in pediatric patients.
Define absolute bioavailability.
Fraction of a drug that enters the systemic circulation.
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Key Terms
Term
Definition
Define absolute bioavailability.
Fraction of a drug that enters the systemic circulation.
What are the benefits of injectables?
Rapid response Patient may be unconscious Drug cannot be removed in vomiting Good where drugs have limited oral bioavailability
Which layer of the skin is the most impermeable and hardest to penetrate?
Stratum corneum
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What is the dermis?
Thick layer of tissue below the skin that is perfused by capillaries from deeper layer of arteries/veins in the hypodermis
What is the stratum corneum?
Outer layer of dead cellular material
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What is the general transit time of the GIT?
12-36 hours
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| Term | Definition |
|---|---|
Define absolute bioavailability. | Fraction of a drug that enters the systemic circulation. |
What are the benefits of injectables? | Rapid response Patient may be unconscious Drug cannot be removed in vomiting Good where drugs have limited oral bioavailability |
Which layer of the skin is the most impermeable and hardest to penetrate? | Stratum corneum |
What is the dermis? | Thick layer of tissue below the skin that is perfused by capillaries from deeper layer of arteries/veins in the hypodermis |
What is the stratum corneum? | Outer layer of dead cellular material |
What is the general transit time of the GIT? | 12-36 hours |
What are the two sites of first pass metabolism? | Liver Intestinal wall |
Describe the features of the stomach leading to minimal absorption. | Tight junctions between cells limit paracellular transport Epithelial surface is smooth with low surface area |
Describe the features of the small intestine leading to maximal absorption. | Transit time is 3-4 hours Large surface area Highly perfused with 25% of cardiac output |
What is the splanchnic circulation? | Intestinal veins flow into portal vein Blood rich in materials is filtered through hepatic sinusoids |
What is the transit time of the colon? | 2-48 hours depending on frequency of defication |
Is there anything that affects transit time of the small intestine? | Independent of fed/fasted state |
What is the volume of the stomach? | 50mL fasted >1000mL fed |
What properties of neonatal GIT affects drug absorption/bioavailability? | Reduced acid secretion may increase bioavailability of acid labile drugs and increase solubility of acidic drugs |
List the age ranges of paediatrics. | Neonate 0-27 days Infant 1-23 months Child 2-11 years Adolescent 12-18 years |
How does the expression of metabolising enzymes in the gut wall differ in paediatrics? | CYP3A expressed in 50% of children under 6 months |
How does the expression of metabolising enzymes in the liver differ in paediatrics? | CYPs generally present from birth, reaching adult levels by 2-5 years UGTs reach adult levels anytime from 2 years |
What are the physiological changes that occur in children that can alter absorption and pharmacokinetics? | saliva production gastric pH and emptying rate intestinal transit, SA and motility drug metabolising enzymes drug efflux transporters |
What is the general trend of pH along GIT as you get older? | pH decreases |
What effect does transit time have on paediatric formulations? | Irregular intestinal motility leads to variable transit times which can be a problem for controlled release formulations |
How is metabolism affected in paediatric patients? | Children have a larger liver size and hepatic blood flow per body weight so there is more 1st pass metabolism and increased clearance |
What is formulation bridging? | Assessing the rate and extent of absorption from one formulation vs. another |