Basic Principles Flashcards
What must all drug prescriptions be (9)
legible, unambiguous (e.g no range of doses), use an approved name (e.g. salbutamol not Ventolin), In capitals, without abbreviations, signed.
If drug as ‘as required’ provide indication and max frequency or total dose in 24hrs.
if antibiotic include indication and stop/review date.
Include duration if treatment not long term
Importance of P450 system
Most drugs are metabolised to inactive metabolites by the cytochrome P450 enzyme system in the liver, preventing them from having infinite effects.
However, the activity of these enzymes can be altered by drugs.
Therefore if the drug effects the P450 enzymes, it can in turn affect how quickly other drugs are metabolised, causing their effects to last longer or shorter
Enzyme inducer effect
increase P450 activity, hasten metabolism so reduce the effect (therefore patients may require increased dose)
Enzyme inhibitor effect
decrease enzyme P450 activity, slow down metabolism, increase the effect of the drug (therefore may require reduced dose)
Possible effect of erythromycin on warfarin and why
Warfarin is metabolised by the P450 enzymes. Erythromicin is an enzyme inhibitor.
Therefore warfarin is metabolised more slowly, therefore the effect is increased, which can cause a dangerous rise in INR (meaning blood is taking a long time to clot). Therefore warfarin dose should be decreased.
NOTE: be aware of this in patients with excessive anticoagulation
Common Enzyme Inducers
NOTE: enzyme inducers, metabolised quicker, drug conc decreased and therefore less effective
PC BRAS
Phenytoin
Carbamazepine
Barbiturates
Rifampicin
Alcohol (chronic excess)
Sulphonylureas
Common enzyme inhibitors
NOTE: enzyme inhibitors, metabolised slower, drug conc increased and therefore more effective
AODEVICES:
Allopurinol
Omeprazole
Disulifiram
Erythromycin
Valporate
Isoniazide
Ciprofloxacin
Ethanol (acute intoxication)
Sulphonamides
Phenytoin drug class and indication
Anticonvulsant
Prevention and treatment of seizures (tonic clonic, focal, after injury or surgery, status epilepticus)
Carbamezipine drug class and indication
Anticonvulsant
Tonic clonic seizures, trigeminal neuralgia, prophylaxis of bipolar disorder unreactive to lithium, diabetic neuropathy, adjust in alcohol withdrawal
Barbiturates Drug class, examples and indication
sedative-hypnotic
Amobarbital, Butalbital, Methohexital, Pentobarbital, Phenobarbital, Primidone
Secobarbital
Range of uses - insomnia, epilepsy (pheno, primi), tremor, neonatal withdrawal
rifampicin drug class and indication
Antibiotic, antimycobacterial (inhibit DNA-dependant RNA polymerase)
Tuberculosis, endocarditis, HiB
Sulphonylureas example, indication, mechanism
e.g gliceride, glipizide, glimepiride, tolbutamide
T2DM, second line after metformin
Stimulate release of insulin from beta cells
Allopurinol drug class and indication
Xanthine oxidase inhibitors
prophylaxis of gout/hyperuricaemia
Omeprazole drug class and indication
Proton-pump inhibitor (PPI)
H-pylori, prevention of gastric ulcers NSAID duodenal disorder, prophylaxis of NSAID treatment, GORD
Disulifiram indication
Adjunt in alcohol dependence
Erythromycin class, mechanism
macrolide antibiotic
inhibit protein synthesis, bind to 50S ribosome subunit
Valporate drug class and indication
anticonvulsant
epilepsy, migraine prophylaxis
Isoniazid class and indication
Antibiotic
Tuberculosis
Ciprofloxacin class and mechanism
Fluroquinolone antibiotic
inhibit enzyme activity to prevent cell division
bacterial eye infection, otitis externa, Resp tract infections, UTI etc
Sulphonamides mechanism, example
inhibit enzyme DHPS
‘sulpha drugs’ - sulfamethazine, sulfadiazine etc
Drug to increase before surgery and why
long term corticosteroid (e.g. prednisolone), commonly have adrenal atrophy so won’t mount an adequate ‘stress’ response to surgery, resulting in profound hypotension. similar to ‘sick day rules’ where dose should be doubled if ill, patients should have IV steroids at the induction of anaesthesia
Drugs to stop before surgery
I LACK OP
Insulin
Lithium
Anticoagulants/antiplatelets
COCP/HRT
K-sparing diuretics
Oral hypoglycaemic
Perindopril and other ACE-inhibitors
Examples of anticoagulants
apixaban, dabigatran, rivoroxaban, warfarin, heparin
Examples of anti-platelets
Acetylsalicylic acid (aspirin), clopidogrel, prasugrel, ticegralor
Examples of K-sparing diuretics
Spironolactone, Eplerenone, Amiloride, Triamterene
examples or oral hypoglycaemics
slufonylureas (glipizide, glyburide, gliclazide, glimepiride), meglitinides repaglinide and nateglinide), biguinides (metformin), thiazolidinediones (rosiglitazone, pioglitazone), DPP-4 inhibitors (Sitagliptin, lingagliptin), SGLT2 inhibitors (dapagliflozin and canagliflozin)
When to stop COCP and HRT
4 weeks before surgery
When to stop lithium
day before surgery
when to stop K-Sparing diuretics
Day of surgery
when to stop ace-inhibitors
day of surgery
When to stop anticoagulants and antiplatelets
variable (don’t need to memorise)
when to stop oral glycemic drugs and insulin
variable (don’t need to memorise)
why should metformin/oral hypoglycaemic be stopped before surgery
patients are nil by mouth, so if given metformin will cause lactic acidosis
other oral hypoglycaemic and insulin will cause hypoglycaemia unless stopped.
insulin should be delivered on a sliding scale, and glucose levels checked every hour
