Test 190  (Ocular pharmacology)

1. The following are true about ophthalmic drugs:

a. non-ionized drugs are more lipid soluble and 
    therefore penetrate the eye better

b. ionized drugs are more stable in tear and penetrate
    the stroma better

c. most ocular drugs are weak acid

d. making the pH of an ophthalmic drug more basic 
    will increase ocular penetration 

e. contact time with the cornea is increased by increasing
    the viscosity of the drugs

 
Answera.T   b.T  c.F   d.T  e.T
pH-determines degree of ionization of a drug (remember:
nonionized drugs will be more lipid soluble and penetrates the epithelium better which is hydrophobic, while ionized drugs  will be more stable in the tears and better penetrate stroma which is hydrophilic. Since the pH of tears is slightly alkaline(7.4) many ocular drugs are weak bases (alkaloids) existing in both their charged and uncharged forms at that pH. If the pH of the solution is made more basic then more uncharged forms of the molecule are present, increasing lipid solubility and epithelial penetration

2. Malignant hyperthermia:

a. is an autosomal recessive disorder

b. occurs with exposure to inhalation anaesthesia 

c. causes hypokalaemia

d. causes elevated serum creatinine kinase

e. should be treated with intravenous dantrolene

 

Answera.F  b.T  c.F  d.T  e.T
Malignant hyperthermia is an autosomal dominant muscular disorder-1:15000 to 50000 patients.
It occurs with exposure to succinyl choline or inhalation anaesthetics, oxidative phosphorylation becomes decoupled, causing resp/metab acidosis, hyperkalemia, hypercalcemia, tachypnea, tachycardia, hyperthermia, myoglobin release.
Preoperative screening in suspected cases include family history, elevated CPK preop, muscle biopsy and contracture tests, platelet assay-add halothane to platelets, detect decrease in pH.
The treatment involves stopping anaesthesia, dantrolene sodium-1-mg/kg IV to prevent calcium release from sarcoplasmic reticulum, the use of ice baths and correct acidosis

 
 

3. Adrenaline:
 

a. stimulates the a receptor more than b receptors

b. decreases trabecular outflow

c. increases aqueous production

d. can be used to prolong the action of local anaesthetic

e. can be added to the irrigation fluid during cataract 
    surgery to maintain pupil dilatation

 
Answer
a.T   b.F  c.T  d.F  e.F
Adrenaline-effect is mainly alpha, slight beta
The ocular effects include increased trabecular
outflow and small increase in aqueous production
Its clinical utility include anaesthetic additive to prolong action, mydriasis and treatment of glaucoma

 

. 4. Apraclonidine:

a. is an agonist of both a1 and a2 receptors

b. increases trabecular outflow

c. loses its effect on intraocular pressure control over time

d. crosses the blood brain barrier readily

e. causes eyelid retraction in patients with Horner's 
    syndrome

Answer
a.T  b.F  c.T  d.F  e.T
Apraclonidine-alpha 2 and 1 agonist.
Its clinical uses include lowering IOP by aqueous suppression-0.5% tid decreases IOP 20-28% and 
as 1% pre-YAG laser to prevent IOP spikes does
not cross blood brain barrier, very little cardiovascular side effects.
The IOP lowering effect exhibits tachyphylaxis over time
Its unwanted effects include: 
-transient dry mouth and nose
-eyelid retraction
-mydriasis
-conjunctival blanching

5. 5-fluorouracil:

a. is derived from Streptococcus caespitosis

b. is a purine analog

c. inhibit thymidylate synthetase

d. does not inhibit proliferating cells which are not 
    synthesizing DNA

e. inhibits fibroblast proliferation

 
Answer
a.F   b.F  c.T  d.T  e.T
Mitomycin C is harvested from Streptococcus caespitosis.
5-fluorouracil:
a) fluorinated pyrimidine analog inhibiting thymidylate synthetase
b) effective against cell actively synthesizing DNA in the S phase of the cell cycle (does not inhibit proliferating cells not synthesizing DNA)
c) used as an inhibitor of fibroblast proliferation intra- and postoperatively in glaucoma filtering surgery

 

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