Review of Pharmacology - 9E (2015)

General Pharmacology
• Other factors that affect duration of action of IV drugs are:
––
Clearance
––
Half Life
––
Volume of distribution which depends on lipid solubility, ionization at physiological pH, protein binding
affinity of tissues and regional blood flow.
20. Ans. (a) High first pass metabolism (Ref: KDT 7/e p16)
• The causes of low bioavailability are:
1. Reduced absorption
2. High first pass metabolism
21. Ans. (b) Phenytoin; (c) Carbamazepine (Ref: KDT 7/e p26)
• CYP3A4 cary out biotransformation of large number of drugs. The inhibition of this isoenzyme by erythromycin,
clarithromycin, ketoconazole, itraconazole etc. is responsible for important drug interactions with terfenadine, astemizole
and cisapride. Rifampicin, barbiturates and other anticonvulsants are important inducers.
22. Ans. (a) If a drug is administered rectally it follow 1st order kinetics; (b) If a drug is administered I.M. it follows zero
order kinetics; (c) If a drug is administered I.V. it follows 1 st order kinetics (Ref: KDT 7/e p30-31)
• The order of kinetics of drugs does not depend upon the route of administration. It depends upon the type of drugs.
• In case of i.v. injection bioavailability is 100%, but is frequently lower in oral ingestion.
23. Ans. (c) Phenobarbitone; (d) DDT (Ref: KDT 7/e p26)
• P-450 inducers are:
––
Phenobarbitone, rifampicin, phenytoin, chloral hydrate, phenylbutazone, griseofulvin, DDT, and chronic
alcohol ingestion.
––
Ketoconazole and cimetidine inhibit the drug metabolizing enzymes.
24. Ans. (a) Plasma protein binding; (b) Lipid solubility; (c) Degree of blood flow; (d) Age (Ref: KDT 7/e p17-18)
• Factors affecting drugs distribution:
– Lipid solubility of drugs. – Regional blood flow.
– Ionization at physiological pH. – Fat: lean body mass ratio (changes with age).
– Degree of plasma protein binding. – Disease like CHF, uremia, cirrhosis.
– Affinity for different tissues.
25. Ans. (b) I.M. administration needs sterile technique; (c) I.D. injection produces local tissue necrosis and irritation
(Ref: KDT 7/e p8-9)
• 100% bioavailability is seen in case of IV route.
• Sterile technique is needed in case of I.V. and I.M. administration.
• Irritation and local tissue necrosis is seen in case of intradermal (ID) route.
• In inhalational route, absorption of drugs takes place from vast surfaces of alveoli-so bioavailability is high and action
is very rapid. [KDT 6/e p9]
26. Ans. (a) Obesity; (c) Pregnancy; (d) Older age; (e) Neonate (Ref: KDT 7/e p17-18)
• In elderly patients, the V d
is more because of increased total body fat content and decreased plasma protein binding
of drugs.
• In paediatric patients also, there is greater volume of extracellular fluid and this provides a larger volume of distribution
of highly ionized drugs. Therefore, a larger initial dose may be required to achieve the desired blood level.
• In obese patients because of greater than normal adipose content, V d
is increased.
• In Pregnancy also blood volume increases about 30-40%. Although the total protein is increased, but plasma protein
concentration is decreased, thus altering V d
.
27. Ans. (a) Mercaptopurine; (b) Dipivefrine; (c) Enalapril (Ref: KDT 7/e p23)
General Pharmacology
Prodrug
• Enlapril
• Dipivefrine
• Mercaptopurine
Active form
• Enalaprilat
• Epinephrine
• Methylmercaptopurine
28. Ans. (a) Lignocaine; (b) Propanolol; (c) Salbutamol (Ref: KDT 7/e p27)
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