3 - Incompatibilities Flashcards
What is phenytoin used for?
- Generalized tonic-clonic seizures
- Simple/complex partial seizures
- Status epilepticus
- Tx/prevention of seizures after trauma/surgery
What is important about the administration of phenytoin?
- IV dose is 50 mg/mL and must not exceed 50 mg/min or will cause severe hypotension or cardiac arrhythmias
- Elderly and those w/ CVD, shouldn’t exceed 25 mg/min
What is the loading dose and maintenance dose of phenytoin?
- Loading = 10-15 mg/kg by slow infusion
- Maintenance = 100 mg q6-8h
What are the cosolvents used w/ phenytoin and what do they do?
- Alcohol 10% and propylene glycol 40%
- Help solubilize phenytoin; remove the free acid that phenytoin would produce at lower pH
What is used to adjust the pH of phenytoin?
NaOH to pH 12
Is slow IV infusion of phenytoin recommended? Why or why not?
- Not recommended
- Lack of solubility and precipitation
How is phenytoin administered (how is it prepared and given)?
100 mg or less is mixed in 50 mL NS and given over 5-15 min
What was the methods used for dilution of phenytoin injections?
- Add 0.5 mL NS to 5 tubes using a 1 mL syringe
- Add 0.5 mL of phenytoin to tube 1, mix, and withdraw 0.5 mL of this solution to add to tube 2
- Repeat until tube 5 will have a final volume of 1 mL
- Repeat entire process using D5W instead of NS
What are the results of the phenytoin injection test?
- Should precipitate right away in presence of D5W b/c water solubility is low and D5W takes away water for phenytoin to interact it, so will come out of water (precipitate) faster than in presence of NS
- W/ NS should take > 2 h to precipitate
Describe the mechanism of aminoglycosides
Bind 30S ribosomal subunit to cause misreading of tRNA
Which organisms are aminoglycosides effective against?
- Aerobic
- GN bacteria
What is monitored when aminoglycosides are used?
Blood levels and sCr to avoid ototoxicity and nephrotoxicity
When are aminoglycosides and beta-lactams used together?
For synergy in severe infections (ex: endocarditis caused by group D streptococcus)
Methods of AG and beta-lactams test
Mix 1 mL of reconstituted beta-lactam w/ 1 mL of AG solution
What were the results of the AG and beta-lactam test?
- Ampicillin, cefazolin and pen-G are compatible w/ AGs
- Cloxacillin is not compatible w/ gent or tobra b/c has a chlorine atom making its water solubility poor
Which “common medications” were used to test incompatibilities of commercial products?
- Phenytoin
- Lidocaine
- KCl
- Epinephrine
- Diphenhydramine
- Aminophylline
- 0.5 M HCl
- 0.5 M NaOH
What can parenteral drug incompatibilities cause?
- SEs
- Under-tx
- Occlusion
What should be referenced when determining if parenteral drugs can be mixed?
- Manufacturer
- Concentration
- Diluents
- Order of mixing
- Time frames
- Temperature
- Test methods
What can sometimes determine whether a combo is compatible or not?
Order of mixing and length of time mixing
Weak drugs (acids/bases) depend on ___ of the solution
pH
What can cause precipitation w/ weak acids/bases?
Large difference in solubility and altered pH
If there is enough ___ in a solution, precipitation may not occur even w/ pH changes
Alcohol
When does precipitation occur?
When the salt form is converted to a neutral free form by a pH change
What should be done when handling solutions of weak electrolytes?
- Add a buffer
- Keep incompatible pH solutions separate
- Dilute final solution so the concentration of drug is less than precipitation concentration of neutral free form
- Use short expiration times
When a drug is dissolved and another drug added forms a _____ w/ the first drug, precipitation can occur
Soluble salt
What determines precipitation if a drug has an organic salt w/ an unusual counter ion?
Dependent on concentration and pH
