Chapter 1: Basic principles of prescribing

Question 1

Enzyme inducers

Answer 1

increase P450 enzyme activity = reduced levels of other drugs

PC BRAS

• Phenytoin
• Carbamezapine
• Barbituates
• Rifampicin
• Alcohol (chronic excess)
• Sulphonylureas

+ smoking + griseofulvin

Question 2

Enzyme inhibitors

Answer 2

= reduce P450 enzyme activity = increased levels of other drugs

AO DEVICES

• Allopurinol
• Omepraxole
• Disulfiram
• Erythromycin
• Valproate
• Isoniazid
• Cirpofloxacin
• Ethanol (acute intaxication)
• Sulphonamides

+ metronidazole + cimetidine + amiodarone + imidazoles + SSRIs

Question 3

Drugs that would be DETRIMENTAL intraoperatively if discontinued

Answer 3

Calcium Channel Blockers

Beta Blockers

Which therefore must be continued

Question 4

Drugs which must be INCREASED during surgery

Answer 4

Long-term corticosteroids e.g. prednisolone, as adrenal atrophy so can’t mount adequate physiological stress response to surgery. (As with doubling of steroids with sick-day rules) During induction of anaesthesia, patients should be given IV steroids.

Question 5

Drugs to STOP before surgery

Answer 5

I LAACK OP

• Insulin: Variable, sliding scale
• Lithium: day before
• Anticoagulants (warfarin/heparin incl prophylactic dose): variable, occasionally continue
• Antiplatelets (aspirin, clopidogrel, dipyrifamole): variable, occasionally continue
• COCP/HRT: 4 weeks before
• K+-sparing diuretics: day of surgery
• Oral hypoglycaemics: patient NBM, metformin continue (unless risk of lactic acidosis e.g. contrast dyes)
• Perinodopril (and other ACEi): day of surgery

Question 6

Drugs that worsen seizure control in patients with epilepsy:

Answer 6

The following drugs may worsen seizure control in patients with epilepsy:

• mefenamic acid
• methylphenidate (used in ADHD)
• alcohol, cocaine, amphetamines
• ciprofloxacin, levofloxacin
• aminophylline, theophylline
• bupropion

*Some medications such as benzodiazepines, baclofen and hydroxyzine may provoke seizures whilst they are being withdrawn.

Other medications may worsen seizure control by interfering with the metabolism of anti-epileptic drugs (i.e. P450 inducers/inhibitors).*

Question 7

Drugs metabolised by P450s!

Answer 7

Drugs Metabolised: COWEST

• Ciclosporin
• OCP
• Warfarin
• Epileptic: phenytoin, carbamazepine
• Statins
• Theophyline