Basic principles for all prescribing

Question 1

Every drug prescription must be…

Answer 1

• Legible
• Unambiguous e.g. not a range of doses
• An approved (generic) name e.g. salbutamol not Ventolin
• IN CAPITALS
• Without abbreviations
• Signed
• Provide two instructions (if as required): indication + max frequency
• Antibiotics: indication & stop/review date
• Duration if not longer term e.g. 7-28 days

Question 2

Most drugs are metabolised to inactive metabolites by what?

Answer 2

Cytochrome P450 enzyme system in liver (prevents metabolites exerting infinite effects)

Question 3

What is an enzyme inducer

Answer 3

Increases P450 enzyme activity
Hastens metabolism of other drugs - reduces effect (patient will require more of drug)

Question 4

What is an enzyme inhibitor (Give a common example)

Answer 4

Decreases P450 enzyme activity
Increased levels of other drugs

Common example:
Erythromycin (inhibitor) can raise INR if the warfarin dose is not decreased

Question 5

How are topical drugs e.g. creams often prescribed

Answer 5

In FTUs (finger tip units)

1 FTU = line from tip of adult finger to first crease, provides enough to treat one side of both hands

Question 6

What is a general rule for prescribing for surgery

Answer 6

Most drugs should be continued during surgery (i.e. not stopped beforehand)
Risk of losing disease control&raquo_space; risk posed by drug continuation

e.g. CCBs & BBs

Question 7

Most common enzyme inducers

Answer 7

INCREASE enzyme activity - DECREASES drug concentration

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

Question 8

Most common enzyme inhibitors

Answer 8

DECREASES enzyme activity - INCREASES drug concentration

AODEVICES

• Allopurinol
• Omeprazole
• Disulfiram
• Erythromycin
• Valproate
• Isoniazid
• Ciprofloxacin
• Ethanol (acute intoxication)
• Sulphonamides

Question 9

What to consider in patients on long term corticosteroids e.g. prednisolone prior to surgery

Answer 9

These patients commonly have adrenal atrophy - unable to mount adequate physiological response, leads to HYPOTENSION if discontinued

Like ‘sick day rules’ - DOUBLE daily dose

At induction of anaesthesia - IV steroids

Question 10

Drugs to stop before surgery

Answer 10

I LACK OP

• Insulin
• Lithium
• Anticoagulants / antiplatelets
• COCP/HRT
• K sparing diuretics
• Oral hypoglycaemic
• Perindopril & other ACEis