DAMS - LAST LOOK: Pharmacology

LAST LOOK Pharmacology LAST LOOK Pharmacology Largest Medical Education Institute in the Country Published by Delhi Academy of Medical Sciences (P) Ltd.HEAD OFFICE Delhi Academy of Medical Sciences (P.) Ltd. 4-B, Grovers Chamber, Pusa Road, Near Karol Bagh Metro Station, New Delhi-110 005 Phone : 011-4009 4009
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Different names for drugs:

Name of drug	Refers to
	Chemical name	Structure of the drug (Acetyl salicylic acid)
	Generic name	Non-proprietary name of the drug (Aspirin)
	Brand / Trade name	Proprietary name (Aspirin)

Definitions: 1. ORPHAN DRUGS:-used for diagnosis/treatment/prevention of a rare disease or condition(Fomepizole, digibind, liothironine) 2. Essential drugs- Drugs that meet health needs of the majority of population, it should be affordable by all people and it should be available in all time, most of the essential drugs prepared as single compound. The first 'Model List of Essential Drugs' was brought out by the WHO in - 1977 Current Model List of Essential Drugs - th (2017): 433 drugs Current national list of essential medicines in India contains - 376 drugs 3. Pharmacovigilance: monitoring of adverse drug reactions 1.2: PHARMACOKINETICS Definition: study of drug movement, in, through and out of the body. Includes - (Mnemonic: ADME) Absorption Distribution Metabolism Excretion Note: Some scientists prefer to include dissolution of drugs also in pharmacokinetics (DADME)A. ABSORPTION: The two major factor that responsible for drug absorption include lipid solubility and Non-Ionisation Lipid solubility is calculated by pK value.

HENDERSON HESSELBACH EQUATION-pKa = pH +log( ionized A-)/( un ionized HA) pKA = pH means what is the inference?- 50% of drug is in the ionized form & 50% non ionized form Most common site of drug absorption: Upper duodenum (because intestine has large surface area and thin mucosa than stomach) All drugs absorption- Small intestine > Stomach Conversely, Alkalinisation of urine is done for excretion of acidic drugs Acidification of urine can be done for excretion of basic drugs, but not practically advised due to increased risk of renal stone formation.

E.g. of acidic drugs	E.g. of basic drugs
Sulfonamides	Morphine
Barbiturates	Atropine
NSAIDs	Amphetamines
Penicillin V	Ephedrine
Chloroquine
Polymyxin B
Vancomycin

DRUG TRANSPORT- Simple passive diffusion(no need of energy or carrier) Facilitated passive diffusion(carrier dependent, no need of energy). E.g 5-FU Active transport (energy and carrier dependent) E.g. E.g. E.g.

Proteins Most common method of drug absorption: Simple diffusion Simple diffusion is quantified using: Fick's law Fick's law: R = (C x A x P) / T, where R = Rate of simple diffusion across a membrane C = Concentration gradient across the membrane A = Surface area available for diffusion P = Permeability coefficient of the drug (indicates its lipophilicity) T = Thickness of the membrane Bioavailability(F): Percentage of administered drug that enters the systemic circulation in unchanged form Expressed as fraction or percentage (It has no units) Route with maximum bioavailability - Intravenous (100% or 1 as entire drug is administered directly into systemic circulation) Formula of Biavavilability: Froute = AUCroute / AUCIV Fig 1 : Plasma concentration versus time curve of a drug after a single dose C max- Maximum plasma concentration T MAX- rate of absorption AUC- extent of absorption Bioequivalent: Compariso of bioavailability of 2 brands of same medicine. Permissible variation is 80-125% Except with phenytoin: Never change the brands Factors decreasing oral bioavailability of drugs: 1. Decreased oral absorption 2. High first pass metabolism

Food decreases absorption of	Food increases absorption of
Ampicillin	Carbamazepine
Captopril	Griseofulvin (fatty food)
Digoxin	Lithium
Isoniazid	Lumefantrine
Levodopa	Nitrofurantoin
Rifampicin	Riboflavin
Tetracycline	Fibrates
Erlotinib

2. High first pass metabolism

High first pass metabolism
Not given orally	Given orally in high doses
Hydrocortisone	Propranolol
Isoprenaline	Alprenolol
Lignocaine	Salbutamol
Testosterone	Verapamil Nitroglycerine Morphine Pethidine Methyltestosterone Propoxyfene

O ne-liners: Route with highest first pass metabolism - Oral Most common site of first pass metabolism on oral administration - LiverRectally given drug absorbed through External hemorrhoidal vein mean - no first metabolismSublingual and Buccal administration also bypass first pass metabolism B.DISTRIBUTION Volume of distribution (Vd):Formula - Dose administered / Immediate plasma concentration Expressed in litres or litres/kg body weight Indicates - Extent of tissue penetration of drugNext page