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Introduction to Pharmacology Cheat Sheet by

Pharmacokinetics & Pharmodynamics
pharmacology     dentistry

Defi­nit­ions

Phar­mac­olo­gy: The study or science of drugs. Or the study of the effects of chemical substances upon living tissues.
Drug: Chemical substance. Capable of modifying a biological system. Used for the treatment, diagnosis or prevention of a condition.
Phar­mac­ody­nam­ics: Study of the biological activity a drug has on a living system. Mechanism of action. Structure- activity relati­onship of the drug.
Phar­mac­oki­net­ics: Study of the processes of absorp­tion, distri­bution, transf­orm­ation and excretion of drugs in the body in function of the time. Study of effects the body has on a drug.

Sources of Drugs

Natr­ual:
1: Insulin: Obtained from the pancreas of bovine or pigs
2: Digitalis: Extracted from species of the foxglove plant
3: Iron (ferro­us/­Sul­fate): Obtained mineral sources
Synt­het­ic:
1: Synthe­sized by chemists - Majority of today's drugs

Routes of Admini­tra­tion:

Inha­lat­ion:
Used as gas: volatile anaest­hesia
Used as an areosol: bronch­odi­altors
 

Routes of Admini­str­ation

Local routes of admist­rat­ion:
- topical
- intrat­hecal
- intra-­con­juc­tival
- vaginal
- intrad­ermal
- intra-­nasal
- intra-oral
- intra-­art­icular
Locally admini­stered drugs may result in production of systemic effects

Routes of Admini­tra­tion

Syst­emic:
Enternal Admini­str­ati­on:
- sublingual
- gastro­int­ers­inal: oral
-rectal
Pare­nteral Admini­str­ati­on:
- subcut­aneous (sc)
- intram­uscular (im)
- intrav­enous (iv)

General Principles of Drug Action:

*see picture in Powerpoint
Mech­anisms involved in passage of drugs across cell membra­nes:
1. Pharma­ceu­tical formul­ation
2. Lipid diffus­ion: A lipid-­soluble , non-el­ect­rolyte is readily absorbed. A lipid insoluble non-el­ect­rolyte is absorbed very slowly. Most drugs are weak organic substa­nces. Most drugs exist partly un-ionized and partly ionized
Most common mechanism by which drugs cross cell membranes: To enter the body, To be distri­buted To be reabsorbed
3. Aqueous Diffus­ion: Filtration through pores. Water-­soluble drugs: MW < 100 Daltons, Cross the cell membranes through the polar pores and the spaces between membranes of adjacent cells.
4. Active transp­ort: Specific carrie­r-m­ediated transport sysytem. For substances which are: Lipid insoluble to dissolve in the cell membrane and too large to flow through pores.
Features for active transport system: -Ability to workag­ainst concen­tra­tion, osmotic ,elect­rical or hydros­tatic gradiants. -Speci­ficity. -Need for energy source (usually ATP) -Site for compet­ition of drugs/­sub­sta­nces. -Saturable
5. Facill­itated Diffus­ion: Passive process. Involves a specific and saturable carrier system. More rapid than simple diffusion.
6. Pinocy­tos­is: Extrac­ellular fluid taken into a cell. The membrane develops a saccular indent­ation fillled with extrac­ellular fluid. The indent­ation is pinched off forming a vesicle or vacuole of fluid within the cell.
 

Factors of the Fate of a Drug in the Body:

Physical and Chemical profile of the drug:
1. molecular Weight. 2. Chemical stabilty. 3. Lipid solubi­lity.
Degree of ioniza­tion.

Abso­rpt­ion:

Transfer of a drug from its site of admini­str­ation to the blood stream.
Its rate & efficiency depend on the route of admini­str­ation.
Complete (100%) after IV admini­str­ation.

Factors Influe­ncing Absorption of Drugs:

1. Blood flow to the absorption site
2. Total surface area available for absorption
3. Contact time at the absorption site
4. Presence of food and gastric emptying
5. Binding of drugs to food consti­tuents

pH , pKa and Ionization of a Weak Basic Drug:

When a weak basic drug is in a medium where the pH is alka­line , it dissoc­iates into ionized and un-ionized particles. The fraction (%) of un-ionized particles is higher than the fraction of ionized particles. Therefore the absorption rate of the drug is higher. The higher the alkalinity of the medium the higher the absorption rate of a weak basic drug.
When a weak basic drug is in a medium where the pH is acidic , it dissoc­iates into ionized and un-ionized particles. The fraction (%) of un-ionized particles is lower than the fraction of ionized particles. Therefore the absorption rate of the drug is lower. The higher the acidity of the medium the lower the absorption rate of the weak basic drug.
 

Drug Distri­but­ion:

Process by which a drug leaves the blood stream and enters the inters­titium (extra­cel­lular fluid) or the cells of the tissues
Principle factors involved in drug distri­but­ion:
1.Blood flow
 
2.Capi­llary permea­bility
 
3.Degree of binding of the drug to plasma and tissue proteins

Drug Displa­cem­ent:

Warfarin and other highly bound coumar­in-type antico­gau­lants
Clofibrate Phenyl­but­azone, Ethacrynic acid, Mefenamic acid, Nalidixic acid, Oxyphe­but­azone , Chloral hydrate
Tolb­uta­mide
Phenyl­but­azone, Salicy­lates, Sulfaf­urzole

Bioa­vai­lib­ilty:

Extent of absorption ofa drug following its admini­str­ation by routes other than iv injection.
factors that infuence bioava­ili­bity:*
-First pass effect
 
-Solub­ility of drug
 
-Chemical stability
 
-Nature of drug formation

Ther­apeutic Equiva­lan­ce:

Two similar drugs that have comparable efficancy and safety.

Bioe­qui­val­ance:

Two related drugs that show comparable bioava­ilibity
Bioi­neq­uiv­ala­nt: Two related drugs with a signif­icant difference in bioava­ila­bility.

Inac­tiv­ation of Drugs:

-Drug metabolism
-Drugs are eliminated from body by 2 principle mechan­isms:
1. Liver metabolism
2. Renal excretion
> Water- soluble drugs are generally excreted unchanged by the kidney.
> Lipid- soluble drugs are not easily excreted by the kidney because they are largely reabsorbed from the proximal tube

Effects of Drug Metabo­lism:

> To form inactive metabolite from an active drug, thereby termin­ating the action of the drug. (eg. asprin, parace­tamol)
> To form an active metabolite from an inactive or less active drug. (eg. dopamine)
>To form a toxic metabolite from an initially less toxic drug. (eg. hydrox­yla­mine)

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Comments

AlbertEinstein AlbertEinstein, 15:41 18 Feb 18

Very interesting read. The ending got me messed up though :/ Also maybe a bit more character development but idk though.

Carmilaa Carmilaa, 15:51 18 Feb 18

Will take into consideration, thanks so much for the feedback. This is actually one of many Pharmacology cheatsheets so please stay tuned for more "character development" (no spoilers but I don't see this subject treating us well).

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