Molecular structure of cimetidine
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Tagamet

Cimetidine is a histamine H2-receptor antagonist that inhibits the production of acid in the stomach. It is largely used in the treatment of heartburn and peptic ulcers. It is marketed by GlaxoSmithKline under the trade name Tagamet®, and was approved by the Food & Drug Administration for prescriptions starting January 1, 1979. more...

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Clinical Use

History and development

Cimetidine was the prototypical histamine H2-receptor antagonist from which the later members of the class were developed. Cimetidine was the culmination of a project at Smith, Kline & French (SK&F; now GlaxoSmithKline) to develop a histamine receptor antagonist to suppress stomach acid secretion.

At the time (1964) it was known that histamine was able to stimulate the secretion of stomach acid, but also that traditional antihistamines had no effect on acid production. In the process, the SK&F scientists also proved the existence of histamine H2-receptors.

The SK&F team used a rational drug-design structure starting from the structure of histamine - the only design lead, since nothing was known of the then hypothetical H2-receptor. Hundreds of modified compounds were synthesised in an effort to develop a model of the receptor. The first breakthrough was Nα-guanylhistamine, a partial H2-receptor antagonist. From this lead the receptor model was further refined and eventually led to the development of burimamide - the first H2-receptor antagonist. Burimamide, a specific competitive antagonist at the H2-receptor 100-times more potent than Nα-guanylhistamine, proved the existence of the H2-receptor.

Burimamide was still insufficiently potent for oral administration and further modification of the structure, based on modifying the pKa of the compound, lead to the development of metiamide. Metiamide was an effective agent, however it was associated with unacceptable nephrotoxicity and agranulocytosis. It was proposed that the toxicity arose from the thiourea group, and similar guanidine-analogues were investigated until the ultimate discovery of cimetidine.

Shortcomings

Cimetidine is a known inhibitor of many isozymes of the cytochrome P450 enzyme system (specifically CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4). This inhibition forms the basis of the numerous drug interactions that occur between cimetidine and other drugs. For example, cimetidine may decrease metabolism of some drugs, such as oral contraceptives.

Adverse drug reactions were also found to be relatively common with cimetidine.

The development of longer-acting H2-receptor antagonists with reduced adverse effects such as ranitidine proved to be the downfall of cimetidine and, whilst it is still used, it is no longer amongst the more widely used H2-receptor antagonists.

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Clinical quiz
From American Family Physician, 11/1/05

Clinical Quiz questions are based on selected articles in this issue of American Family Physician. Answers appear in this issue. AFP has been reviewed by the American Academy of Family Physicians as having content acceptable for Prescribed credit. Term of approval is for one year from the beginning distribution date of January 2005. This issue has been reviewed and is acceptable for up to 5.0 Prescribed credits, of which 0.75 credit conforms to AAFP criteria for evidence-based continuing medical education (EB CME) clinical content. The amount of CME has been doubled to reflect two-for-one credit for the EB CME portion only. When reporting CME credits, AAFP members should report total Prescribed credits earned for this activity. It is not necessary for members to label credits as EB CME for reporting purposes.

The AAFP is accredited by the Accreditation Council for Continuing Medical Education to provide CME for physicians.

The AAFP designates this educational activity for a maximum of 5.0 Category 1 credits toward the American Medical Association Recognition Award (AMA/PRA). Each physician should claim only those credits that he or she actually spent in the activity.

AAFP Credit

Each copy of AFP contains a Clinical Quiz answer card. AAFP members may use this card to obtain the designated number of Prescribed credit hours for the year in which the card is postmarked.

AMA/PRA Category 1 Credit

AAFP members who satisfy the Academy's CME requirements are automatically eligible for the AMA/PRA.

Physicians who are not members of the AAFP are eligible to receive the designated number of credits in Category 1 of the AMA/PRA on completion and return of the Clinical Quiz answer card. AFP keeps a record of AMA/PRA Category 1 credits for nonmember physicians. This record will be provided on request; however, nonmembers are responsible for reporting their own Category 1 CME credits when applying for the AMA/PRA or other certificates or credentials.

For health care professionals who are not physicians and are AFP subscribers, a record of CME credit is kept by the AAFP and will be provided to you on written request. You are responsible for reporting CME credits to your professional organization.

NOTE: The full text of AFP is available online (http://www.aafp.org/afp), including each issue's issue will link you to the Clinical Quiz. Just follow the online directions to take the quiz and, if you are an AAFP member, you can submit your answers for CME credit.

Instructions

(1) Read each article, answer all questions on the quiz pages, and transfer your answers to the Clinical Quiz answer card (bound into your copy of AFP). This will help you avoid errors and permit you to check your answers against the correct answers.

(2) Mail the Clinical Quiz answer card within one year (by November 30, 2006). The bar code on the answer card contains your identification for CME credit hours.

Before beginning the test, please note: Each Clinical Quiz includes two types of questions: Type A and Type X.

Type A questions have only one correct answer and may have four or five choices. Here is a typical Type A question:

Type X questions may have one or more correct answers. They are multiple true-false questions with four options. Here is a typical Type X question:

Clinical Quiz questions are written by the associate and assistant editors of AFP.

CME Quality Survey

Please answer the following questions to help us monitor the quality of AFP's CME material on an ongoing basis. Mark your answers on this issue's quiz card. We would appreciate hearing any suggestions you have for improving the CME experience offered through AFP. See the directory on page 1635.

Answers to This Issue's Clinical Quiz

Q1. B Q2. D Q3. D Q4. C Q5. A Q6. B Q7. A Q8. D Q9. D Q10. A Q11. C Q12. B, D Q13. A, D Q14. A, C, D Q15. A, B, C, D Q16. A, B, C, D Q17. A, B, C Q18. A, B, D Q19. A, B, C

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