Pharmacodynamics of Drugs Acting Locally on the Skin
Session 12: Pharmacodynamics of Drugs Acting Locally on the Skin
Total Session Time: 120 minutes
Prerequisites
None
Learning Tasks
By the end of this session students are expected to be able to:
Describe mechanism of action of Drugs acting locally on the skin
Describe drug interactions associated with Drugs acting locally on the skin
Describe side effects of Drugs acting locally on the skin
Describe contraindications of Drugs acting locally on the skin
Resources Needed:
Flip charts, marker pens, and masking tape
Black/white board and chalk/whiteboard markers
Computer and LCD projector
SESSION OVERVIEW
Step
Time
Activity/
Content
Step
Time
Activity/
Content
Step
Time
Method
Content
Method
Method
1
1
05 minutes
05 minutes
Presentation
Introduction, Learning Tasks
Introduction, Learning Tasks
2
2
45 minutes
45 minutes
Presentation/
Mechanism of Action of Drugs Acting
Mechanism of Action of Drugs Acting
2
2
45 minutes
45 minutes
Buzzing
Locally on The Skin
Locally on The Skin
Buzzing
Locally on The Skin
Locally on The Skin
3
3
20 minutes
20 minutes
Presentation/
Drug Interactions Associated With Drugs
Drug Interactions Associated With Drugs
3
3
20 minutes
20 minutes
brainstorming
Acting Locally on The Skin
Acting Locally on The Skin
brainstorming
Acting Locally on The Skin
Acting Locally on The Skin
4
4
20 minutes
20 minutes
Presentation
Side Effects of Drugs Acting Locally on The
Side Effects of Drugs Acting Locally on The
4
4
20 minutes
20 minutes
Presentation
Skin
Skin
Skin
Skin
5
5
20 minutes
20 minutes
Presentation/
Contraindications of Drugs Acting Locally on
Contraindications of Drugs Acting Locally on
5
5
20 minutes
20 minutes
Brainstorming
the Skin
the Skin
Brainstorming
the Skin
the Skin
6
6
05 minutes
05 minutes
Presentation
Key Points
Key Points
7
7
05 minutes
05 minutes
Presentation
Evaluation
Evaluation
PST 05104 Pharmacology & Therapeutics 98 NTA Level 5 Semester 1 Facilitator Guide
SESSION CONTENTS
STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)
READ or ASK students to read the learning tasks and clarify
ASK students if they have any questions before continuing.
STEP 2: Mechanism of Action of Drugs Acting Locally on the Skin (45 minutes)
Activity: Buzzing (5 minutes)
ASK students to pair up and buzz on the following question for 2 minutes
What are the mechanisms of actions of drugs acting locally on the skin ?
ALLOW few pairs to respond and let other pairs add on points not mentioned
WRITE their response on the flip chart/board
CLARIFY and SUMMARIZE by using the content below
These drugs includes antibacterial/antibiotics, ant protozoans, antifungal and anti-viral The following are the mechanism of action of Anti-infective drugs
Antibacterial/antibiotics
Some widely used topical antibiotics are bacitracin, neomycin, gentamycin, mupirocin and polymyxins.
Mechanism of action of antibacterial/antibiotics is either inhibiting bacterial growth (bacteriostatic) or kills bacteria (bactericidal) or can have both actions depending on
its concentration (e.g Clindamycin and erythromycin in treatment of acne)
Aminoglycosides act by interfering bacteria protein synthesis.
Mupirocin act by inhibiting protein and RNA synthesis by binding reversibly to sub unit 50s of bacteria ribosome or disrupt synthesis of peptidoglycan layer of bacterial
cell wall. It also inhibits bacterial isoleucyl-tRNA synthetase.
Polymyxins binds to lipopolysaccharide on outer cell wall of Gram Negative Bacteria leading to permeability change in cell envelope hence leakage of cell content. Polymyxins are only active against gram negative bacteria (P. aeruginosa, E. coli, K. pneumoniae).
Antifungal
Antifungal drugs may be fungicidal (able to destroy fungi) or fungistatic (able to slow or retard the multiplication of fungi)
PST 05104 Pharmacology & Therapeutics 99 NTA Level 5 Semester 1 Facilitator Guide
Azoles (Ketoconazole, Clotrimazole and miconazole nitrate) acts by inhibits the biosynthesis of plasma membrane by preventing synthesis of ergosterol and other steroids which results to damage of fungal cell wall membranes and loss of essential
intracellular elements.
Terbinafine Hydrochloride: binds with squalene epoxidase enzyme and hinders biosynthetic pathway of ergosterone and results to growth and it is associated with high intracellular squalene concentrations which interfere with fungal membrane function and cell wall synthesis causes death of fungi.
Antiviral
Commonly agents are: acyclovir, famciclovir and valacyclovir
Acyclovir works by lowering the ability of the herpes virus to multiply, it acts as specific inhibitor of herpesvirus DNA polymerase (HSV), type 1 and 2 and varicella
zoster virus.
This selectivity is due to the ability of these viruses to code for a viral thymidine kinase capable of phosphorylating acyclovir to monophosphate (this capability is absent in uninfected cells)
Ant protozoans
Mechanism of action of ant protozoans differ significantly with drug to drug e.g Paramomycin (antibacteria drug but also it is antiprotozoal agent) interfere with metabolic processes (glycolysis and fatty acid oxidation) or by interfering with reproduction and larval physiology or interfering with muscular physiology of parasites (e,g in treatment of leishmaniasis).
Corticosteroids:
Used for their Antinflammatory action
Details on glucocorticosteroids is found on pharmacology of Antinflammatory drugs
STEP 3: Drug Interactions Associated with Drugs Acting Locally on the Skin (20 minutes)
Activity: Brainstorming (5 minutes)
Ask students to brainstorm on the following question:
What are drug interactions associated with drugs acting locally on the skin?
ALLOW few students to respond
WRITE their responses on the flip chart/ board
CLARIFY and SUMMARISE by using the content below
PST 05104 Pharmacology & Therapeutics 100 NTA Level 5 Semester 1 Facilitator Guide
Most of drugs for treating skin infection do not show significant drug interactions because
of minimal systemic absorption of these drugs hence systemic drug interactions are unlikely.
Drug interactions can result only when the skin barrier is destroyed hence systemic absorption.
Antibiotics/antibacterial
o For example oral metronidazole has been reported to potentiate the anticoagulant effect of warfarin and coumarin anticoagulants resulting in a prolongation of prothrombin but the effect of topical metronidazole on prothrombin time is unknown.
Antifungal
o Miconazole when co administered with warfarin it may increase the anticoagulant
effect of the warfarin by inhibiting hepatic microsomal cytochrome p-450 enzyme.
o Amphotericin B fungistatic activity is antagonised by azoles antifungal when applied simultaneously
o Amphotericin B decreases the effects of miconazole.
STEP 4: Side Effects of Drugs Acting Locally on Skin (20 minutes)
Antibacterial/antibiotics (side effects already mentioned in NTA Level 4)
In addition, the following are side effects which are rarely reported
o Prolonged use of mupirocin and other topical antibacterial can cause microscopic organisms, such as bacteria or fungi, to overgrow and also they may cause diarrhoea due to infection. They should be only used as recommended.
o Clindamycin may cause diarrhoea, dizziness, headache, contact dermatitis, maculopapular rash, erythema, endometriosis, menstrual disorder, inflammatory swelling, abdominal cramps and GIT disturbance
Antifungal
Amphotericin B is well tolerated but only occasionally causes local irritation of the skin and it may cause temporary yellow staining of the skin especially when the cream vehicle is used
Antiviral
Rarely reported side effects of topical antiviral are; dry lips, desquamation, dryness of skin, cracked lips, burning skin, flakiness of skin
STEP 5: Contraindications of Drugs Acting Locally on Skin (10 minutes)
Activity: Brainstorming (5 minutes)
Ask students to brainstorm on the following question:
What are the contraindications of Drugs acting locally on skin? ALLOW few students to respond?
WRITE their responses on the flip chart/ board
CLARIFY and SUMMARISE by using the content below
PST 05104 Pharmacology & Therapeutics 101 NTA Level 5 Semester 1 Facilitator Guide
Topical anti-infective drugs
Antibiotics
o These medications should not be used if the patient is allergic to any ingredients of the medications.
Antifungal
o They are contraindicated in patients with known hypersensitivity to the contents of the drugs
o Miconazole cream is contraindicated during the pregnancy because small amounts of these drugs may be absorbed from the vagina, the drug is used during the first trimester only when essential.
Antiviral
o Acyclovir is contraindicated in patients who have developed acyclovir hypersensitivity or valacyclovir hypersensitivity.
o Because of similar chemical structures and possible cross-sensitivity, acyclovir should not be used in patients with famciclovir hypersensitivity, ganciclovir hypersensitivity, penciclovir hypersensitivity, or valganciclovir hypersensitivity.
o Pregnancy
Topical acyclovir products are classified as pregnancy risk category B. No complete or well-controlled pregnancy studies have been performed in humans.
o Breast-feeding
Exposure of the infant after maternal use of topical administration of acyclovir is minimal, provided the treatment area does not involve the breast. Women who have active herpetic lesions on or near the breast should avoid nursing until the lesions have completely resolved.
o Ophthalmic administration
Acyclovir cream and ointment products are for external topical use only. Avoid ophthalmic administration or use inside the mouth or nose.
PST 05104 Pharmacology & Therapeutics 102 NTA Level 5 Semester 1 Facilitator Guide
STEP 6: Key Points (5 minutes)
Clotrimazole and miconazole are common medicines in treatment of superficial fungal infections
Amphotericin B should not applied together with azoles
Long term use of topical antibacterial drugs should be avoided
Most of topical preparations do not have drug interactions due to minimal systemic absorption
Patient history is very important before dispensing any topical preparation to the patient
STEP 7: Evaluation (5 minutes)
What are the indications of acyclovir cream?
What is the mechanism of action of topical antifungals?
What is the mechanism of terbinafine hydrochloride?
PST 05104 Pharmacology & Therapeutics 103 NTA Level 5 Semester 1 Facilitator Guide
References
Katzung, B. G. (2018). Basic and clinical pharmacology. New York: Mcgraw Hill Education.
Santos, R. R., Rang, H. P., Dale, M. M., Ritter, J. M., & Flower, R. J. (2007). Rang & Dale Farmacologia. Rio de Janeiro: Elsevier.
Tripathi, K. (2018). Essentials of Medical Pharmacology. Place of publication not identified:
Jaypee Brothers Medical P.
Ministry of Health and Social Welfare. (2013). Standard Treatment Guidelines & National Essential Medicines List Tanzania Mainland (4th ed.). Dar es salaam, Tanzania government printers.
Sally S.R, Jeanne C.S. (2000). Introductory Clinical Pharmacology (6th ed) New York, Lippincott Williams and Wilkins.
School of Pharmaceutical sciences. (2011).Tanzania Pharmaceutical Handbook (2nd ed.).
Dar es Salaam, ARDHI University press.
The Royal Pharmaceutical Society of Great Britain. (2007). Martindale, the Extra Pharmacopoeia (5TH ed). London, pharmaceutical press.
The Royal Pharmaceutical Society of Great Britain. 2009. British National Formulary (59th ed). London, BMJ Group and RPS Publishing.
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PST 05104 Pharmacology & Therapeutics 104 NTA Level 5 Semester 1 Facilitator Guide
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