How are drugs absorbed in the body

1. DRUG
ABSORPTION
IT IS THE RATE AND COMPLETENESS WITH
WHICH THE DRUG ENTERS THE BODY FROM
THE SITE OF ADMINISTRATION OR THE
PASSAGE OF A DRUG FROM ITS SITE OF
ADMINISTRATION INTO THE PLASMA.
FACTORS:
-DRUG PHYSICAL AND CHEMICAL
PROPERTIES (e.g. DRUG SOLUBILITY IN
WATER AND LIPIDS AS A SUSPENTION OR AS
SOLID IMPLANTS).
AMNA MEDANI, 2015

2. -ROUTE OF DRUG ADMINISTRATION(e.g.I/V ROUTE IS
RAPID AND AT THE SAME TIME IT CAN BE IRRITANT).
-THE AMOUNT AND CONDITION OF CONNECTIVE
TISSUE AT THE SITE OF S/C AND I/M INJECTIONS.
-THE AREA OF ABSORPING SURFACE TO WHICH THE
DRUG IS EXPOSED(e.g. LARGE INTESTINAL AND
PULMONARY EPITHELIUM).
AMNA MEDANI, 2015

3. -THE RATE OF CAPILLARY FLOW (e.g.TRAUMA AT THE
INJECTION SITE MAY DECREASE THE RATE OF
CAPILLARY FLOW).
-THE ACTIVITY OF STOMACH CAN GREATLY
INFLUENCE THE RATE OF ABSORPTION (e.g.WHEN
EMPTY AND THE DRUG IS GIVEN IN LARGE
QUANTITIES).
-THE REMOVAL OF CALCIUM IONS (e.g.BY A
CHELATING AGENT) FROM THE INTESTINES CAN
AFFECT ABSORPTION.
AMNA MEDANI, 2015

4. -PERMEATION THROUGH SKIN VARIES IN
DIFFERENT AREAS (e.g.THE UNDER ARM IS A GOOD
ABSORPING AREA ,WHERE AS THE DAMAGED SKIN
MAY ALLOW FOREIGN SUBSTANCES MORE READILY
AMNA MEDANI, 2015

5. ABSORPTION WITH REGARD TO
ROUTE:-SUBLIGUAL ADMINISTRATION:
-USEFUL WHEN A RAPID RESPONSE IS REQUIRED
AND THE DRUG IS UNSTABLE AT THE GASTRIC pH
OR IS RAPIDLY METABOLISED BY THE LIVER (e.g.
GLYCEROL TRINITRATE AND ISOPRENALINE). THEY
PASS INTO THE BLOOD WITHOUT ENTERING THE
LIVER (DRUGS CAN ESCAPE THE FIRST PASS
EFFECT . HIGH MOLECULAR WEIGHT DRUGS ARE
NOT ABSORPED BY THIS ROUTE e.g. INSULIN AND
PEPTIDES.
AMNA MEDANI, 2015

6. -ORAL ROUTE:
-USEFUL FOR THE MAJORITY OF DRUGS:
-STOMACH ABSORPT ION : ABSORPTION USUALLY HAPPEN AFTER THE
DRUG PASSES THE PYLORIC SPHINCTER (e.g.ALCOHOL AND ASPRIN).
- INTESTINAL ABSORPTION:
I / BY PASSIVE DEFUSION:
-STONG BASES WITH pK 10 OR HIGHER(e.g. MUSCLE RELAXANT
TUBOCURINES ARE GIVEN I/V AND HYPOTENSIVE GUANETHIDINE AND
SUXAMETHONIUM ARE GIVEN ORALLY) AND STRONG ACIDS WITH pK 3
AND LESS ARE FULLY IONIZED AND HENCE , POORLY ABSORPED.
-OTHER HIGHLY POLAR MOLECULES(e.g.AMINOGLYCOSIDES
ANTIBIOTICS) ARE POORLY ABSORPED AND HENCE, GIVEN ORALLY TO
STERILIZE THE GUT WITHOUT CAUSING A SYSTEMIC EFFECT.
II/BY CARRIER MEDIATION(e.g. LEVODPA IS TAKEN BY THE CARRIER
SYSTEM THAT TRANSPORTS PHENYLALANINE,
FLUOROURACIL”CYTOTOXIC” IS TRANSPORTED BY THE SYSTEM THAT
CARRIES NATURAL PYRIMIDINE, IRON IS ABSORPED IN ASSOCIATION
WITH TRANSFERRIN AND CALCIUM IS ABSORPED BY MEANS OF
VITAMIN- D-DEPENDANT CARRIER SYSTEM.
AMNA MEDANI, 2015

7. FACTORS AFFECTING INTESTINAL ABSORPTION:
-GIT MOTILITY IS REDUCED BY DISEASE AND DRUGS
LIKE MUSCURINIC RECEPTOR BLOCKERS AND
HENCE,REDDUCE THE ENTRIC ABSORPTION
.EXCESSIVE MOTILITY OF THE GUT BY A DRUG LIKE
METOCLOPRAMIDE MAY ALSO REDUCE
ABSORPTION.A DRUG TAKEN AFTER A MEAL IS
OFTEN SLOWLY ABSORPED AS ITS PROGRESS TO
THE INTESTINE IS DELAYED.
-SPLANCHNIC BLOOD FLOW (TO VISCERA AND
INTERNAL ORGANS) IS REDUCED IN
HYPOVOLAEMIC STATES LEADING TO DECREASED
ABSORPTION(e.g. ADRENORECEPTOR BLOCKING
DRUGS LIKE PROPRANOLOL EVEN IF TAKEN AFTER
A MEAL).
AMNA MEDANI, 2015

8. -PARTICLE SIZE AND FORMULATION(e.g. PHENACETIN
ALTHOUGH RAPIDLY METABOLIZED ,SLOW
ABSORPTION MAY REDUCE THE PLASMA PEAK AND
DIGOXIN IF TAKEN IN A LARGE PARTICLE SIZE A WEAK
PLASMA CONCENTRATION WILL BE ABTAINED, i.e. A
SMALL DIFFERENCE IN PHARMACEUTICAL
FORMULATION CAN MAKE A LARGE DIFFERENCE IN
THE EXTENT OF ABSORPTION. AS WELL,
FORMULATIONS LIKE CAPSULES MAY DELAY
ABSORPTION OR TABLETS MAY HAVE A RESISTANT
COATING TO GIVE THE SAME EFFECT. TO OBTAIN
SUSTAINED ABSORPTION A MIXTURE OF SLOW AND
FAST RELEASE PARTICLES ARE OBTAINED IN THE
SAME CAPSULE.
- CHEMICALLY THE DRUG STATUS IN THE INTESTINE
MAY AFFECT ABSORPTION (e.g. TETRACYCLINE BOUND
TO CALCIUM IONS AND CALCIUM RICH FOOD MAY
PREVENT ITS ABSORPTION AND LIQUID PARAFFIN MAY
RETARD THE ABSORPTION OF LIPOPHILIC
SUBSTANCES LIKE VITAMIN-K).
AMNA MEDANI, 2015

9. BIOAVAILABILITY: IS THE OVERALL PROPORTION
OF THE DRUG THAT PASSES INTO THE SYSTEMIC
CIRCULATION AFTER ORAL ADMINISTRATION
TAKING INTO ACCOUNT BOTH ABSORPTION AND
LOCAL METABOLITE DEGRADATION.IT IS
INDIVIDUAL-SPECIFIC AND TIME-IGNORING.
AMNA MEDANI, 2015

10. III/RECTAL ADMINISTRATION:
IT IS USED FOR LOCAL DRUGS (e.g. ANTI-
INFLAMMATORY DRUGS IN ULCERATIVE COLITIS)
OR SYSTEMIC DRUGS BY-PASSING THE LIVER
ENTRAL ROUTE(e.g.PROGESTERONE AND
TESTESTERONE) OR AVOIDING GASTRIC
IRRITATION(e.g.ANTI-INFALMMATORY DRUGS) OR
AVOIDING VOMITING.
AMNA MEDANI, 2015

11. IV/APPLICATION TO EPITHELIAL SURFACES :
A/CUTANEOUS ADMINISTRATION: ALTHOUGH
MOST DRUG BEING WEAKLY LIPID-SOLUBLE , ARE
POORLY ABSORPED FROM AN UN-BROKEN SKIN ,A
NUMBER OF ORGANOPHOSPHATE INSECTICIDES
MAY CAUSE POISONING THROUH SKIN.
AMNA MEDANI, 2015

12. B/ TRANSDERMAL: USED IN STICK-ON PLASTERS
APPLIED ON AN AREA OF THIN SKIN(e.g.
GLYCERYLTRINITRATE(ANGINA),
FENTANYL(ANALGESIC),HYOSCINE(SEA
SICKNESS),
CLONIDINE(ANTIHYPERTENSIVE),OESTROGENS
AND ANDROGENS) TO PRODUCE A STEADY RATE
OF DELIVARY.THIS APPLIES TO RELITIVELY LIPID-
SOLUBLE DRUGS AND IS EXPENSIVE .
AMNA MEDANI, 2015

13. C/NASAL SPRAYS:THESE ARE USED TO REPEATED
INJECTIONS AND GIT DESTRUCTION (e.g.
VASOPRESSIN PEPTIDE IS RELATED TO THE
PITUTARY HORMONE).
AMNA MEDANI, 2015

14. D/ EYE DROPS:THESE ARE ABSORPED THOUGH
CONJECTIVAL SAC DUE TO THEIR ADEQUATE
LIPID SOLUBILITY(e.g .PHYSOSTIGMINE”A
TERTIARY AMINE” OR DYFLOS “AN UN CHARGED
ANTICHOLINESTERASE” CAN TREAT GLOUCOMA
BETTER THAN A QUATERNARY COMPOUND LIKE
NEOSTIGMINE). SYSTEMIC EFFECT AFTER
ABSORPTION MAY INCLUDE SIDE EFFECTS
.PASSAGE INTO THE NASOLACRIMAL DUCT MAY
CAUSE ABSORPTION OR SWALLOWING OF THE
DRUG.
AMNA MEDANI, 2015

15. V/ ADMINISTRATION BY INHALATION:
THESE DRUGS ARE ADMINISTERED AND
ELEMINATED VIA LUNGS WHERE THE LARGE
ABSORPING AREA AND THE BLOOD FLOW RAPIDLY
ADJUST THE DRUG PLASMA
CONCENTRATION(e.g.ANAESTHETIC DRUGS ).
I/DRUGS USED TO AFFECT THE LUNG (e.g.
ISOPRENALINE OR
SALBUTAMOL”BRONCHODILATORS” TO A ACHIEVE A
HIGH CONCENTRATION IN THE LUNG THAN IN
OTHER ORGANS.THESE DRUGS MAY REACH THE
SYSTEMIC CIRCULATION LEADING TO SIDE
EFFECTS(e.g. HYPOTENTION AND CONVULTION IN
CASE OF LOCAL ANAESTHETIC SPRAYED INTO THE
BRONCHIAL TREE IN PREPARATIONS FOR
BRONCHOSCOPY).
AMNA MEDANI, 2015

16. II/CROMOGLYCATE “AN ANTI-ASTHMA DRUG” IS
GIVEN BY INHALATION.IT IS WATER INSOLUBLE AND
IS INHALED AS A DRY POWDER DISPERSED AS A
FINE CLOUD BY AN INHALER.
III/ ENDOTRACHEAL ADMINISTRATION IS USED IN
CARDIAC EMERGENCIES FOR RAPID ACCESS TO
THE HAERT VIA PULMONARY VIENS(e.g. ATROPINE
AND ADRENALINE 10-20 ML VIA ENDOTRACHEAL
TUBE).
AMNA MEDANI, 2015

17. VI/ ADMINISTRATION BY INJECTION:
A/ I/V ROUTE: IS THE FASTEST AND THE MOST
CERTAIN AFTER REACHING THE LUNGS AND THEN
THE CIRCULATION. THIS IS AFFECTED BY THE RATE
OF INJECTION WHICH SHOULD BE CAUTIOUSLY
SLOW,USED USUALLY IN HOSPITAL PATIENTS(e.g.
LIGNOCAINE”ANTI-DYSRYTHMIC” ,HEPARIN,CERTAIN
ANAESTHTICS,ERGOMETRINE AND DIAZEPAM).
AMNA MEDANI, 2015

18. B/ S/C AND I/M ROUTES:
THESE ROUTES ARE FASTER THAN THE ORAL ROUTE
,BUT THEIR RATE OF ABSORPTION DEPENDS ON THE
SITE OF INJECTION AND THE PHYSIOLOGICAL
FACTORS(e.g. THE BLOOD FLOW).THE S/C INJECTION
RESULTS IN AN ABSORPTION RATE HIGHER THAN
THAT OF THE I/M INJECTION. IN BOTH ROUTES, THE
DIFFUSTION THROUGH TISSUE CAN BE INCREASED
BY HYLURONIDASE ENZYME”INTRACELLULAR MATRIX
BREAKING ENZYME”.APPLICATION OF HEAT OR
MASSAGE MAY INCREASE THE RATE OF REMOVAL OF
THE DRUG BY THE LOCAL BLOOD FLOW”CRITICAL IN
PATIENTS WITH PERIPHERAL CIRCULATORY
FAILURE”(e.g. MORPHINE IN TRAUMATIC PATIENTS).
AMNA MEDANI, 2015

19. METHODS FOR DELAYING ABSORPTION:
DRUG ABSORPTION MAY BE DELAYED EITHER TO
REDUCE ITS SYSTEMIC ACTION IN ORDER TO
LOCALIZE ITS EFFECT OR TO ELONGATE ITS TIME OF
ABSORPTION BY:
I/ THE ADDITTION OF ADRENALINE OR
NORADRENALINE TO A LOCAL ANAESTHETIC
REDUCES ITS ABSORPTION, PROLONGS ITS ACTION
AND REDUCES ITS BLOOD TOXICITY.
AMNA MEDANI, 2015

20. II/THE PRODUCTION OF LOCAL ANAETHESIA TO A
WHOLE LIMB (e.g. TO RESET A FRACTURE) BY
APPLICATION OF AN ARTERIAL PRESSURE CUFF TO
ARREST BLOOD FLOW ,THEN I/V INJECTION OF AN
ANAESTHETIC BELOW THE CUFF . THIS WILL WORK
UNTILL THE CUFF IS RELEASED.
III/ADMINISTRATION OF SLOW RELEASE DRUGS
“POORLY SOLUBLE SALTS AND ESTER OR COMPLEX
IN AQUEOUS SUSPENTIONS OR OILY SOLUTIONS”(e.g.
PROCAINE PEICILLIN ,OESTRADIOL,DEOXYCARTONE
AND TESTOSTERONE).
AMNA MEDANI, 2015

21. IV/CHANGE OF THE PHYSICAL PROPERTIES LIKE pH
CHANGE (e.g.INSULIN ZINC SUSPENTIONS OF
IMMEDIATE AND SUSTAINED RELSEASE.
V/STERIOD HORMONES ARE IMPLANTED S/C AS
SOLID PELLETS TO ACHIEVE CONTINUIOUS
ABSORPTION AT A RATE PROPORTIONAL TO THE
SURFACE AREA OF THE IMPLANT (e.g.
DEOXYCORTONE ACETATE IN THE TREATMENT OF
ADDISON,S DISEASE, TESTOSTERONE AND
OESTRADIOL).
AMNA MEDANI, 2015

22. INTRATHECAL INJECTION:
THIS IS USED BY INJECTING INTO THE
SUBARACHNOID SPACE VIA A LUMBER PUNCTURE
FOR ADMINISTRATION OF SOME ANTIBIOTICS IN
MENINGITIS AND FOR LOCAL ANATHESIA.
AMNA MEDANI, 2015