Antibacterial drugs

Drugs in this class

• Penicillinase (lactamase)-sensitive penicillins
  • Benzylpenicillin (penicillin G, parenteral)
  • Penicillin V (phenoxymethyl penicillin, oral)
• Penicillinase-resistant penicillins
  • Flucloxacillin
• Broad-spectrum penicillins
  • Ampicillin
  • Amoxicillin
  • Co-amoxiclav (amoxicillin plus clavulanic acid; Augmentin)
• Antipseudomonal penicillins
  • Piperacillin (with tazobactam; Tazocin)
  • Ticarcillin (plus clavulanic acid)

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Warfarin (Teaching Point)

Prescribing information:

See above for treatment targets and advice on starting warfarin.

• By mouth, usual daily dose in the range of 2-9 mg.
  • 0.5 mg tablets are white
  • 1 mg tablets are brown
  • 3 mg tablets are blue
  • 5 mg tablets are pink

Teaching PointTreatment of excessive anticoagulation with warfarin

• See treatment of bleeding in heparin for management of severe bleeding.
• Remember, warfarin does not usually cause bleeding but makes what would ordinarily be trivial bleeding worse. If there is bleeding, investigate the cause.
• Excessive anticoagulation is usually the result of a failure to take account of a factor that will enhance the anticoagulant effect of warfarin:
  • The patient has a severe intercurrent illness and the dose of warfarin is not reduced.
  • A drug that enhances the action of warfarin is started.
  • A drug that reduces the effect of warfarin is stopped.
  • The maintenance dose is incorrect, but the INR has not been measured.
• INR >8.0
  • No bleeding. Stop warfarin and restart at a lower dose once the INR is <5.0.
  • If the patient is at high risk of bleeding consider giving 0.5 mg vitamin K1 iv or 5 mg by mouth.
• INR 5.0-8.0
  • No bleeding. Stop warfarin and restart at a lower dose once the INR is <5.0.
• INR >0.5 units above target but <5.0
  • No bleeding. Continue warfarin at a lower dose.

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Amiodarone (Teaching Point)

Prescribing information

• Treatment by mouth
  • 200 mg 3 times daily for 1 week reduced to 200 mg twice daily for a further week.
  • Maintenance dose, usually 200 mg daily or the minimum required to control the arrhythmia.
• Treatment by intravenous infusion
  • Via a central line, 5 mg/kg over 20-120 minutes with ECG monitoring; maximum 1.2 g in 24 hours.
• Emergency treatment during cardiopulmonary resuscitation
  • VF or pulseless VT, 300 mg by intravenous injection over at least 3 minutes (pre-filled syringe).

Teaching Point

Drugs with a long half-life. Onset and offset of action.

• Amiodarone is an example of a drug with a very long half-life (about 50 days). The half-life of a drug is the time taken for the plasma concentration of the drug to fall by half, and is a measure of how quickly a drug is eliminated from the body.
• When a second dose of a drug is taken, its pharmacokinetic profile is superimposed on that of the first dose, and so on for subsequent doses. For a given dose, the pattern of plasma concentrations that results will depend upon two factors: the dosage interval and the half-life of the drug. A consequence of first-order pharmacokinetics (essentially exponential decay) is that during repeated administration, drug accumulation occurs. This is because the higher the plasma concentration is, the faster it falls. Eventually, during a dosage interval, the plasma concentration falls as fast as it rises. At this point a steady state is reached, after about four half-lives of administration, provided that the dosage interval is not excessively long. Before such a steady state has been reached one cannot say that the drug has reached its maximum effect.
• The practical consequence of this is that the maximum effect of amiodarone is not reached until about 4 half-lives have elapsed, about 200 days, unless a loading dose is given.
• It is unwise to declare that a drug is not effective until a steady state has been reached. Prematurely increasing the dose may lead to excessive accumulation and toxicity.
• In the same way as it takes a very long time for amiodarone to have its maximum effect, it takes a very long time for amiodarone to be eliminated from the body once it has been stopped. Adverse effects and drug interactions can occur weeks after amiodarone has been stopped.

Drugs with long half-lives
Bisphosphonates Amiodarone Choloroquine Hydroxychloroquine Gold salts Auranofin Sodium aurothiomalate Alfacalcidol Levothyroxine Digitoxin Phenytoin Fluoxetine Digoxin Warfarin	Years (in bone) 50 days 48 days 18 days 21 days 6 days 14 days 7 days 5 days Variable, up to 60 hours or more 48 hours 40 hours 24 hours

Amiodarone has a complex mechanism of action that is incompletely understood, but is probably mediated through effects on cardiac potassium channels.

• Amiodarone prolongs the action potential and refractory period homogeneously throughout the heart.
• The principal ECG change is a prolongation of the QT interval.
• Amiodarone is a class III antiarrhythmic drug in the Vaughan-Williams classification.

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Flecainide

Prescribing information:

Long-term prophylaxis of supraventricular and ventricular arrhythmias (specialist use only)

• By mouth, for ventricular arrhythmias, initially 100 mg twice daily. Maximum dose 400 mg daily in exceptional cases.
• By mouth, for supraventricular arrhythmias, 50 mg twice daily, increased if required to a maximum of 300 mg daily

Flecainide can be used for the treatment of SVT and VT, but its principal use is for the termination of acute atrial fibrillation.

• It can be used in patients with Wolff-Parkinson-White syndrome.
• See adenosine for more information on treatment of SVT.

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Metoclopramide

Prescribing information:

• By mouth, intramuscular injection, or intravenous injection (over 1-2 minutes), 10 mg tds.
• High-dose metoclopramide can be used with cytotoxic chemotherapy; seek specialist advice.

Metoclopramide is metabolized by the liver. Reduce the dose in hepatic insufficiency.

• Antiemetic drugs are rarely needed for vomiting associated with pregnancy. If severe seek specialist advice. Metoclopramide is an option in such cases.
• Do not use metoclopramide in patients with gastrointestinal obstruction or haemorrhage; the actions on the stomach may be dangerous.
• Do not use metoclopramide in patients with Parkinsonian symptoms; the antidopaminergic actions can worsen these.
• Do not give metoclopramide to patients with phaeochromocytoma; it can precipitate a hypertensive crisis.
• The use of metoclopramide in patients under 20 years old is specialized

• Nausea and vomiting are symptoms, not diagnoses. Always consider the underlying cause. Long-term treatment should be of the cause, rather than with antiemetic drugs.
• Like the treatment of pain, the treatment of nausea and vomiting should be based on avoidance and prophylaxis, rather than waiting for symptoms to occur before tackling them.

Metoclopramide is used widely but is especially useful:

• For nausea owing to gastrointestinal, biliary, and liver disease; however, it should not be used if there is gastrointestinal obstruction.
• In high dosages for emesis associated with chemotherapy, but it has largely been replaced by the 5HT3 receptor antagonists for this indication.
• Consider the following factors:
  • Identify patients who are at high risk of postoperative nausea and vomiting and give them treatment early. A dose of 10 mg alone is often inadequate for postoperative nausea and vomiting.
  • Treat pain, as this is often a contributory factor.
  • Refer to the teaching point in 5HT3 receptor antagonists (p. 73) for information on the treatment of nausea and vomiting due to chemotherapy.
  • Metoclopramide is unlikely to be effective for motion sickness; this is mediated through the vestibular system.

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Treatment of obesity

1. 
   
   Obesity is increasingly common. For example, 17% of adults in the UK are classed as obese (BMI >30). The changes in metabolism associated with obesity are central to the pathophysiology of insulin resistance and type II diabetes; obesity is also an important risk factor for hypertension and coronary artery disease; and there is an increased incidence of osteoarthritis of weight-bearing joints.
   
   


2. 
   
   Medical causes of obesity (e.g. Cushing's syndrome, hypothyroidism) are rare, but should be excluded before starting treatment.
   
   



3. 
   
   Weight gain results from an imbalance between energy intake and expenditure. The only long-term solution is to reduce intake and increase energy expenditure through exercise. Diets should be low in calories, but not very low. Aim for a total daily intake of around 1000 kCal. In patients who are motivated to lose weight, drug treatments can increase the amount of weight lost as part of a diet and exercise programme. Drug treatments are ineffective if given alone, and should not be continued for long periods (see individual articles for details).
   
   


4. 
   
   Ideally, obesity should be managed by a multidisciplinary team, but in many countries such expertise and resources are scarce.
   
   


5. 
   
   NICE has advised that patients with a (e.g. BMI >30 kg/m2 should receive treatment. Patients with complications arising from obesity (obstructive apnoea, hypertension, type II diabetes) have most to gain from weight reduction and represent a priority group for treatment. Consider treatment in this group if they have a BMI >28 kg/m2.
   
   


6. 
   
   Treatment of obesity should form part of a wider assessment of a patient's lifestyle and risk factors for cardiovascular disease. Help with stopping smoking can be particularly beneficial (see p. 236).
   
   


7. 
   
   Many patients are desperate to lose weight but find it difficult to modify their lifestyle; these patients are particularly vulnerable to those offering miracle treatments. Many of these contain amphetamines, diuretics, and thyroid hormones. They have no place in the treatment of obesity and can cause significant harm.
   
   


8. 
   
   Fenfluramine, dexfenfluramine, and phenteramine are centrally-acting appetite suppressants structurally related to amphetamines. They have been withdrawn because they can cause pulmonary hypertension.
   
   


9. 
   
   Bulk-forming supplements (e.g. methylcellulose) are unlikely to cause harm, but there is little evidence that they are effective.
   
   

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Colestyramine and colestipol

Prescribing information:

Colestyramine

• For lipid reduction or diarrhoea: introduce gradually over 3-4 weeks. Maintenance dosage usually 12-24 g daily in water (or another suitable liquid) in single or up to 4 divided doses.
  • Up to 36 g daily can be used if necessary
• For pruritus: 4-8 g daily in water (or other suitable liquid).

Colestipol

• For lipid reduction: 5 g 1-2 times daily in liquid, increased if necessary at intervals of 1-2 months to a maximum of 30 g daily (in single or 2 divided doses).

These drugs cause constipation in 50% of patients.

• Nausea and heartburn are common.
• These drugs will reduce absorption of the vitamins A, D, E, and K; prolonged treatment can cause deficiency. Give vitamin A, D, and K supplements to those taking long-term treatment.
• These drugs rarely cause a hypochloraemic acidosis.

Advise the patient not to take any other drugs either 1 hour before or 4-6 hours after taking these drugs.

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Cholic acids

Prescribing information

• Ursodeoxycholic acid is given as an example.
  • Dissolution of gallstones, 8-12 mg/kg daily as a single dose at bedtime or in 2 divided doses. Treat for up to 2 years, and continue for 3-4 months after stones dissolve.
  • Primary biliary cirrhosis, 10-15 mg/kg daily in 2-4 divided doses.

Drugs in this class

• Ursodeoxycholic acid
• Chenodeoxycholic acid

Treatment of cholesterol gallstones (not other types of gallstone): Ursodeoxycholic acid is used in the treatment of primary biliary cirrhosis and primary sclerosing cholangitis. These are unlicensed, specialist uses.

Cholic acids can worsen liver impairment in those with existing disease: Cholic acids can worsen peptic ulcer and symptoms from ileal disease; avoid in these patients. The manufacturer advises that these drugs should not be used in pregnancy, although there is no evidence of harm.

Gallstones

• These drugs will act only on cholesterol gallstones (which are radiotranslucent).
• Laparoscopic cholecystectomy is the treatment of choice for symptomatic gallstone disease.
• If the patient is unsuitable for surgery, consider treatment with the cholic acids.
  • Treatment can be for up to 2 years.
  • Stop the treatment 3 months after the stone has disappeared.
  • A repeat ultrasound examination should be performed 4-12 weeks after the stone has disappeared to confirm this.
  • The recurrence rate is high once treatment has stopped; it is estimated to be 25% after 1 year and 50% by 5 years.

• These drugs will act only on cholesterol gallstones (which are radiotranslucent).
• Laparoscopic cholecystectomy is the treatment of choice for symptomatic gallstone disease.
• If the patient is unsuitable for surgery, consider treatment with the cholic acids.
  • Treatment can be for up to 2 years.
  • Stop the treatment 3 months after the stone has disappeared.
  • A repeat ultrasound examination should be performed 4-12 weeks after the stone has disappeared to confirm this.
  • The recurrence rate is high once treatment has stopped; it is estimated to be 25% after 1 year and 50% by 5 years.

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Mesalazine and related compounds (aminosalicylates)

Aminosalicylates

• Sulfasalazine
• Mesalazine
• Balsalazide
• Olsalazine

Prescribing information: Sulfasalazine

• Tablets and enteric-coated tablets, 500 mg per tablet.
• For an acute attack the usual dose is 1-2 g 4 times daily until control is achieved; this may require concomitant corticosteroids. The maintenance dose is usually 500 mg 4 times daily.
• Suppositories for rectal treatment. Usual dose 0.5-1 g morning and night.
• Enema for distal colonic disease. Usual dose 3 g at night, retained for at least 1 hour.

Salazopyrin

• Tablets and enteric-coated tablets. Contain 500 mg per tablet.
• Suspension. Contains 250 mg sulfasalazine per 5 mL.
• Suppository. Contains 500 mg sulfasalazine per suppository.
• Retention enema. Contains 3 g sulfasalazine per enema.

Prescribing information: Mesalazine

Asacol

• Tablets contain mesalazine 400 mg. Dose is 6 tablets daily in divided doses for an acute attack. Titrate to between 3 and 6 tablets daily for maintenance of remission.
• Foam enema. Delivers mesalazine 1 g. Used for acute attacks. One dose per day for rectosigmoid disease, increased to two doses for disease affecting the descending colon.
• Suppositories. Available as 250 mg and 500 mg doses. Dose is 750-1500 mg daily in divided doses, last dose taken at bedtime.

Pentasa

• Modified-release tablets contain mesalazine 500 mg. Dose is up to 4 g in divided doses to control an acute attack. Maintenance dose is usually 1.5 g daily, in divided doses.
  • Do not chew the tablets; doing so will destroy the modified-release system.
• Modified-release granules contain mesalazine 1 g per sachet. Dose is 4 g in divided doses to control an acute attack. Maintenance dose is usually 2 g daily, in divided doses.
  • Do not chew the granules; doing so will destroy the modified-release system.
• Retention enema contains mesalazine 1 g. Dose is 1 g at bedtime.
• Suppositories contain mesalazine 1 g. Dose is one suppository at bedtime for an acute attack. Maintenance dose is usually one suppository daily.

Salofalk

• Tablets contain mesalazine 250 mg. Dose is 6 tablets daily in 3 divided doses. Maintenance titrated to between 3 and 6 tablets in divided doses.
• Suppositories contain mesalazine 500 mg. Dose for an acute attack is 1-2 suppositories given 2-3 times per day according to response.
• Enemas contain mesalazine 2 g. Dose is 1 enema at bedtime for control of acute attack or for maintenance.

Prescribing information: Balsalazide

• Capsules contain balsalazide 750 mg. Dose for an acute attack is 2.25 g 3 times daily until remission occurs or for up to maximum of 12 weeks.
• Maintenance dose is 1.5 g twice daily, adjusted according to response (maximum 6 g daily).

Prescribing information: Olsalazine

• Dose for an acute attack, 1 g daily in divided doses after meals, increased if necessary over 1 week to a maximum of 3 g daily (maximum single dose 1 g).
• Maintenance dose, 500 mg twice daily after meals.

The active ingredient of all of these drugs is 5-aminosalicylic acid. The mechanism of its action in inflammatory bowel disease is not fully understood, although it may act by altering cytokine function. However, what is important is that the drug is delivered to the site of action, usually the large bowel or distal ileum. Each of the drugs in this class does this in a different way after oral administration.

Mesalazine formulations. Modified-release formulations provide delivery of 5-aminosalicylic acid to the large bowel.

Olsalazine is a dimer of 5-aminosalicylic acid; it is cleaved in the lower bowel to release 5-aminosalicylic acid.

Balsalazide is mesalazine attached by an diazo bond to a carrier molecule. This bond is cleaved in the colon to release active mesalazine.

Sulfasalazine is 5-aminosalicylate coupled to a carrier sulfapyridine molecule. This drug has different properties from the others in the class and is the subject of a separate article.

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Loperamide (Immodium)

Opioid receptor agonist

Binds to opioid receptors in the gut wall, reducing peristalsis.Also increases anal tone.

Prescribing information:

Acute diarrhoea

• 4 mg initially, followed by 2 mg after each loose stool for up to 5 days; usual dose 6-8 mg daily.
• Maximum dose 16 mg daily.

Chronic diarrhoea in adults

• Initially 4-8 mg daily in divided doses, subsequently adjusted according to response and given in two divided doses for maintenance.
• Maximum dose 16 mg daily.

Alternative antimotility drugs

• Codeine
• Morphine
• Co-phenotrope
• Bile salt sequestrants (e.g. colestyramine, aluminium hydroxide) for patients who have had an ileal resection or who have ileal disease.

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Drugs with names beginning co-

Drugs that have names beginning with co- are mixtures of two different drugs. The theoretical advantage of this is that two synergistic drugs are combined in a single tablet to aid compliance. However, this advantage is often outweighed by the disadvantage of giving two drugs with different actions when one would be sufficient. See misoprostol article (p. 31) for more information on combination formulations. The Table below shows a few examples:

Formulation	Component drugs	Potential advantages	Potential disadvantages
Co-codamol	Paracetamol Codeine	Opioid/paracetamol synergy.	Opioid can cause confusion
Co-amilofruse	Furosemide Amiloride	Potassium-sparing actions of amiloride.	Amiloride not always required, especially in those also taking ACE inhibitors.
Co-fluampicil	Ampicillin Flucloxacillin	Broader antibacterial spectrum.	Wider spectrum rarely required. May encourage bacterial resistance if used inappropriately.
Co-tenidone	Atenolol Chlorthalidone	Single tablet for the treatment of hypertension.	Two drugs are not always required. Not suitable for dose titration.
Co-careldopa	Carbidopa L-dopa	Peripheral dopa decarboxylase inhibitor (carbidopa) reduces adverse effects from the peripheral conversion of L-dopa to dopamine.

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Misoprostol

Prescribing information:

Benign gastric and duodenal ulceration and NSAID-associated ulceration

• By mouth, 800 micrograms daily (in 2-4 divided doses) with breakfast (or main meals) and at bedtime; treatment should be continued for at least 4 weeks and can be continued for up to 8 weeks if required.

Prophylaxis of NSAID-induced gastric and duodenal ulceration

• By mouth, 200 micrograms 2-4 times daily (depending on the perceived risk of bleeding in that patient), taken with the NSAID.

Synthetic prostaglandin analogue

• Reduces the volume and proteolytic actionof gastric juice.
• Also increases bicarbonate and mucus secretion.
• See prostaglandins section (p. 450) for more information.

Risk factors for NSAID-induced gastric ulceration

• Linear increase in risk with increasing age (especially over 65 years).
• History of peptic ulceration.
• Debilitated patients.
• Long-term treatment with maximal doses of NSAIDs.
• Concomitant treatment with drugs that can cause bleeding.

Treatment and prevention of benign gastric and duodenal ulcers.

• Its most common use is as prophylaxis against gastric ulceration in those at risk who need to continue taking NSAIDs.

• Unlicensed use to induce a medical abortion and to induce labour.

• Misoprostol increases uterine tone and can induce abortion. It is contraindicated in women who are pregnant or planning pregnancy.
• The manufacturers advise against use in all women of childbearing age, unless they are fully aware of the risks.
• Misoprostol has the potential to cause hypotension, although this is not commonly seen in practice. Consider alternatives for those in whom hypotension can precipitate severe complications (e.g. cerebrovascular and cardiovascular disease).
• No dosage reduction is usually required in renal or hepatic insufficiency.

Combination formulations: Advantages and disadvantages

A combination formulation contains two or, rarely, three drugs of different types. Many combination products are available, but they are only acceptable or even preferable when the following minimum criteria are met:

• When the frequency of administration of the two drugs is the same
• When the fixed doses in the combination product are therapeutically and optimally effective in most cases (i.e. when it is not necessary to alter the dose of one drug independently of the other)
  • It is the second criterion that is the most difficult to achieve in clinical practice. For example, patients may require different dosages of an NSAID over time, but the dose of misoprostol does not need to change. A new prescription of the combination product will be required each time the dose of NSAID is changed; this is expensive and may be confusing for the patient.

Nevertheless, combination products do have a number of potential advantages:

Potential Advantages	Examples
Antituberculosis drugs (rifampicin + isoniazid) Ferrous sulfate and folic acid (pregnancy)	Improved compliance
Triple vaccine (diphtheria, tetanus, pertussis) Combined insulins (e.g. Mixtard®)	Ease of administration
Amoxicillin + clavulanic acid (co-amoxiclav)* Combined oral contraceptive (oestrogen + progestogen)	Synergistic or additive effects
Levodopa + decarboxylase inhibitors (Parkinson's disease)	Reduced adverse effects
*Even so, co-amoxiclav is often given as combination tablets plus extra amoxicillin in separate tablets.

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Proton pump inhibitors (PPIs)

Prescribing information:

Omeprazole

• Ulcer healing, by mouth: 20 mg daily.
• Maintenance dose, by mouth: 10“20 mg daily (see notes above).
• Reflux oesophagitis, by mouth: 20“40 mg daily.
• Also available in an intravenous formulation.

Esomeprazole

• Reflux oesophagitis, by mouth: 40 mg daily.

Lansoprazole

• Ulcer healing, by mouth: 30 mg daily.
• Maintenance dose, by mouth: 15“30 mg daily (see notes above).
• Reflux oesophagitis, by mouth: 30 mg daily.

Pantoprazole

• Ulcer healing, by mouth: 40 mg daily.
• Maintenance dose, by mouth: 20“40 mg daily (see notes above).
• Reflux oesophagitis, by mouth: 20“40 mg daily.

Rabeprazole

• Ulcer healing, by mouth: 20 mg daily.
• Maintenance dose, by mouth: 10“20 mg daily (see notes above).
• Reflux oesophagitis, by mouth: 10“20 mg daily.

These drugs bind irreversibly to the H+/K+-ATPase, located in the secretory cannaliculae of parietal cells. The drug must be absorbed into the body to do this; it does not act directly from the stomach lumen. It also requires an acid environment to be activated; this provides a negative feedback mechanism”inhibition of acid production reduces the activation of the PPI. The H+/K+-ATPase is the final common pathway of gastric acid secretion, so these drugs are powerful antacids. See H2 antagonists section (p. 24) for details of acid secretion.

Drugs in this class

• Omeprazole
• Esomeprazole
• Rabeprazole
• Pantoprazole
• Lansoprazole

When suppression of gastric acid is required.

• Healing of gastric and duodenal ulcers.
• Reflux oesophagitis.
• Eradication of Helicobacter pylori infection, in combination with antibacterial drugs (see teaching point below).
• Treatment of Zollinger“Ellison syndrome.
• High-dose intravenous omeprazole has been used as adjunctive treatment in patients with high-risk bleeding duodenal ulcer (unlicensed indication).

Treatment:

• Some patients report that they cannot swallow tablets because they do not wish to take the drug, or because they are worried about adverse effects of the drug.
• Identify whether difficulty swallowing tablets is in fact a symptom of a more general swallowing problem. Causes include:
  • Oesophageal strictures (benign and malignant)
  • Stroke
  • Muscle weakness (e.g. myasthenia gravis)
• Some patients may have problems because they do not take tablets with water; this is potentially hazardous. Tablets can stick to the oesophageal muscoa and cause ulceration; this has been a particular problem with bisphosphonate drugs, which should be taken with a full glass of water.
• Some patients find gelatin capsules more difficult to swallow than tablets; a change of formulation may solve the problem.
• A modified-release formulation may mean that the drug needs to be given less often.
  • Some drugs (e.g. alendronate) are available in a formulation that can be given once weekly.
• There are several options for patients with persistent problems in swallowing tablets:
  • Prescribe an elixir or melt formulation.
  • Some capsules can be opened and the contents suspended in yoghurt or fruit juice (e.g. Lansoprazole, Zomorph®). Warn the patient not to chew the granules.
  • Discuss with a pharmacist whether a specially prepared suspension or elixir can be produced.
  • Parenteral administration is an option but is rarely ideal, although subcutaneous administration may be suitable.

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Histamine H2 receptor antagonists

Prescribing information:

Famotidine

• Ulcer healing, by mouth: 40 mg at night.
• Maintenance dose, by mouth: 20 mg at night.
• Reflux oesophagitis, by mouth: 20“40 mg bd.

Nizatidine

• Ulcer healing, by mouth: 150 mg bd or 300 mg at night.
• Maintenance dose, by mouth: 150 mg at night.

• Reflux oesophagitis, by mouth: 150“300 mg bd.
• Also available in parenteral formulations (see note below).

Ranitidine

• Ulcer healing, by mouth: 150 mg bd or 300 mg at night.
• Maintenance dose, by mouth: 150 mg at night.
• Reflux oesophagitis: 150“300 mg bd.
• Also available in parenteral formulations (see note below).
• Parenteral use of these drugs is usually limited to prophylaxis against stress ulceration on the ICU.
• The usual dose of ranitidine for this indication is 50 mg tds; this should be reduced to 25 mg tds in severe renal insufficiency.

The principal effect of these drugs is inhibition of histamine-driven production of stomach acid. Gastric acid is produced through three major pathways (see teaching point below). One of these is stimulated by histamine. These drugs are effective antacid drugs but, because they act on only one of the pathways, they are not able to suppress gastric acid secretion completely, even at high dosages.

Drugs in this class

• Cimetidine
• Famotidine
• Nizatidine
• Ranitidine
• Ranitidine bismuth citrate

Safety

• Beware of prolonged treatment with these drugs without a diagnosis; they can mask the symptoms of gastric malignancy.

Efficacy

• Efficacy is usually judged by symptom relief.
• If ineffective reconsider the diagnosis.
• If the diagnosis is reflux oesophagitis, a proton pump inhibitor may be preferable.

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