Prescribing

Question 1

Basic principles

Answer 1

• Legible
• Unambiguous (e.g. not a range of doses, such as 30–60 mg codeine which is a common error and entirely your fault if a patient is overdosed within your prescribed dosage range)
• An approved (generic) name, e.g. salbutamol not Ventolin® (See Box 1.1).
• IN CAPITALS
• Without abbreviations
• Signed (even when practising or in an exam, sign and make up a bleep number in order to get into this habit)
• If a drug is to be used ‘as required’ provide two instructions: (1) indication and (2) a maximum frequency (e.g. twice daily) or total dose in 24 hours (e.g. 1 g)
• If an antibiotic is being prescribed include the indication and stop/review date
• Include duration if the treatment is not long term (e.g. antibiotics) or if it is in a GP setting (e.g. 7 or 28 days).

Question 2

use of trade names

Answer 2

There are a small number of exceptions when trade names should be used; one of the most important reflects the various preparations of tacrolimus (used for preventing the rejection of transplanted organs). The BNF states that trade names should be used for prescribing because switching between brands can result in toxicity (if relative levels increase) or rejection (if relative levels decrease).

You will often see the brand name Tazocin® written instead of piperacillin with tazobactam – this is done for simplicity but is not acceptable, particularly because it masks the fact that the drug contains penicillin that is made obvious by the ‘cillin’ in piperacillin.

Question 3

Enzyme inducers MOA and examples

Answer 3

↑ Enzyme Activity→↓ Drug Concentration

PC BRAS: Phenytoin, Carbamazepine, Barbiturates, Rifampicin, Alcohol (chronic excess), Sulphonylureas

OR

SCRAP GP:
* Sulphonylureas
* Carbamazepine
* Rifampicin
* Alcohol
* Phenytoin

• Griseofluvin
• Phenobarbitone

Question 4

enzyme inhibitors MOA and examples

Answer 4

↓ Enzyme Activity→ ↑ Drug Concentration

AODEVICES: Allopurinol, Omeprazole, Disulfiram, Erythromycin, Valproate, Isoniazid, Ciprofloxacin, Ethanol (acute intoxication), Sulphonamides

OR

SICK FACES:
* Sodium Valporate
* Isoniazide
* Cimetidine
* Ketoconazole

• Fluclonazole
• Alcohol + grape fruit juice
• Chloramphenicol
• Erythromycin
• Sulfonamides

Question 5

sick day rules and steroids

Answer 5

double dose

surgery - give IV steroids during induction of anaesthesia

Question 6

drugs to stop before surgery and when

Answer 6

I LACK OP: Insulin, Lithium, Anticoagulants/antiplatelets, COCP/HRT, K-sparing diuretics, Oral hypoglycaemics, Perindopril and other ACE-inhibitors.

†Patients are ‘nil by mouth’ before surgery, thus metformin should be stopped because it will cause lactic acidosis. The other oral hypoglycaemics and insulin will cause hypoglycaemia unless stopped. In all cases, a sliding scale should be started instead where hourly blood glucose monitoring adjusts the hourly dose of insulin given to provide much tighter control.

Question 7

diabetic drugs and surgery

Answer 7

omit:
metformin:
* od/bd: continue as notmal
* tds: stop lunchtime dose

Sulphonylureas:
* omit morning dose

SGLT2-inhibitors:
* omit on day of surgery

Rest:
* take as normal