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

Barbiturates, including amobarbital (Amytal), pentobarbital (Nembutal), phenobarbital (Luminal), and secobarbital (Seconal), are central nervous system depressants. They are commonly used for anesthesia and are prescribed to treat seizures.

Griseofulvin is a medicine which is used to treat fungal infections. This includes fungal infections of the nails and scalp, as well as the skin when antifungal creams have not worked. It is taken by mouth. It is prescribed in particular for an infection called scalp ringworm (also called tinea capitis)

Question 2

Enzyme inhibitors

Answer 2

= reduce P450 enzyme activity = increased levels of other drugs (less metabolised)

AO DEVICES

• Allopurinol
• Omepraxole
• Disulfiram
• Erythromycin
• Valproate
• Isoniazid- bacteriostatic used for TB
• Cirpofloxacin
• Ethanol (acute intaxication)
• Sulphonamides

+ metronidazole + cimetidine + amiodarone + imidazoles + SSRIs

Cimetidine, sold under the brand name Tagamet among others, is a histamine H₂ receptor antagonist that inhibits stomach acid production. It is mainly used in the treatment of heartburn and peptic ulcers.

Disulfiram is a drug used to support the treatment of chronic alcoholism by producing an acute sensitivity to ethanol. Disulfiram works by inhibiting the enzyme acetaldehyde dehydrogenase, causing many of the effects of a hangover to be felt immediately following alcohol consumption.

Isoniazid= abx used esp for TB

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

Druggs 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).*

Buproprion - a medication primarily used to treat major depressive disorder, seasonal affective disorder and to support smoking cessation

Question 7

Drugs metabolised by P450s!

Answer 7

Drugs Metabolised: COWEST

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