This study analyzed 28,956,638 prescriptions from March 21, 2007 to March 20, 2008 and 15, 610, 912 prescriptions from March 21, 2008 to December 20, 2009 from 33 different medical universities in Iran (
Tables 1 and
3).
2008-2009
| 2007-2008
| |
|---|
| NP | %SI | NP | %MI | Total NP | NP | %SI | NP | %MI | Total NP |
|---|
| 110,837 | 0.71 | 140,498 | 0.90 | 15,610,912 | 194,009 | 0.67 | 222,966 | 0.77 | 28,956,638 | All of physicians |
| 11,990 | 9.01 | 1 2,681 | 9.53 | 133,047 | 25,526 | 7.30 | 27,044 | 7.74 | 349,496 | Cardiologist |
| 60 | 0.04 | 80 | 0.06 | 137,947 | 164 | 0.06 | 217 | 0.07 | 297,314 | Dermatologist |
| 391 | 0.17 | 538 | 0.24 | 228,455 | 663 | 0.12 | 853 | 0.15 | 570,150 | ENT |
| 77,905 | 0.69 | 97,480 | 0.86 | 11,282,948 | 116,067 | 0.50 | 149,599 | 0.74 | 20,292,902 | General practitioners |
| 639 | 0.32 | 833 | 0.42 | 198,365 | 1,819 | 0.36 | 2,294 | 0.46 | 499,681 | General surgeon |
| 1,291 | 0.15 | 1,398 | 0.17 | 845,843 | 95 | 0.07 | 1180 | 0.08 | 1,450,666 | Gynecologist |
| 948 | 0.73 | 1,111 | 0.86 | 129,257 | 1,901 | 0.74 | 2149 | 0.83 | 257,951 | Infectious disease |
| 38,917 | 1.16 | 53,481 | 1.73 | 4,327,964 | 66,766 | 0.96 | 85,273 | 1.30 | 8,663,736 | All of medical specialists |
| 16,795 | 2.16 | 19,761 | 2.54 | 777,710 | 24,295 | 1.82 | 28,634 | 2.14 | 1,338,054 | Internist |
| 2,928 | 1.43 | 6,203 | 3.04 | 204,226 | 3,060 | 0.86 | 4,706 | 1.29 | 365,579 | Neurologist |
| 347 | 0.33 | 614 | 0.59 | 104,429 | 388 | 0.19 | 804 | 0.39 | 206,481 | Neurosurgeon |
| 129 | 0.05 | 165 | 0.07 | 137,947 | 395 | 0.07 | 460 | 0.09 | 535,621 | Ophthalmologist |
| 328 | 0.12 | 492 | 0.18 | 270,933 | 570 | 0.11 | 768 | 0.15 | 500,391 | Orthopedist |
| 815 | 0.11 | 1,011 | 0.13 | 774,807 | 1,862 | 0.11 | 2,158 | 0.13 | 1,695,170 | Pediatrist |
| 1,866 | 1.33 | 4,159 | 2.97 | 139,970 | 4,068 | 1.20 | 8,571 | 2.53 | 338,411 | Psychiatrist |
| 390 | 0.30 | 4,435 | 3.42 | 129,755 | 1,005 | 0.39 | 5,435 | 2.10 | 258,771 | Urologist |
A total of 20, 292, 902 prescriptions in 2007- 2008 and 11, 282, 948 prescriptions in 2008-2009 belonged to general practitioners and 8, 663,736 prescriptions in 2007-2008 and 4, 327, 964 prescriptions in 2008-2009 belonged to medical specialists. The percentage of interactions with significant clinical importance was higher in prescriptions of medical specialists and of those, cardiologists and internists ranked top on the list, while dermatologists ranked the lowest. The mean items per prescriptions (MIP) and percentage of prescriptions with more than four items per prescriptions (% > 4IP) are shown in
Table 2. MIP and % > 4IP were highest in the cardiologists, general practitioners, internists and infectious disease specialists in 2007-2008, while MIP and % > 4IP were highest among cardiologists, infectious disease specialists, internists, and neurologists in 2008-2009.
2008-2009
| 2007-2008
| |
|---|
| % > 4IP | M.I.P | % > 4IP | M.I.P |
|---|
| 21 | 3.26 | 19 | 3.26 | All of physicians |
| 37 | 3.67 | 31 | 3.67 | Cardiologist |
| 3 | 2.06 | 4 | 2.13 | Dermatologist |
| 13 | 2.89 | 10 | 2.96 | ENT |
| 24 | 3.41 | 21 | 3.41 | General practitioners |
| 12 | 2.76 | 11 | 2.85 | General surgeon |
| 7 | 2.50 | 5 | 2.43 | Gynecologist |
| 25 | 3.42 | 15 | 3.12 | Infectious disease |
| 15 | 2.91 | 11 | 2.83 | All of medical specialists |
| 26 | 3.41 | 19 | 3.23 | Internist |
| 25 | 3.35 | 13 | 2.93 | Neurologist |
| 8 | 2.71 | 8 | 2.87 | Neurosurgeon |
| 13 | 2.89 | 2 | 2.22 | Ophthalmologist |
| 11 | 2.81 | 7 | 2.67 | Orthopedist |
| 15 | 2.98 | 11 | 2.94 | Pediatrist |
| 15 | 2.88 | 14 | 3.03 | Psychiatrist |
| 8 | 2.35 | 7 | 2.50 | Urologist |
The percentage of prescriptions with rapid onset interactions was highest among cardiologists. In contrast, the percentage of prescriptions with delayed onset interactions was the highest with psychiatrists in 2007-2008 and the highest in the neurologists in 2008-2009 (
Table 3). The list of medications in
Table 4 indicated that digoxin and diuretics were commonly associated with DDIs. The most common interacting combination prescribed was digoxin and furosmide in 2007-2008, and captopril and triamteren in 2008-2009 (
Tables 5 and
7).
2008-2009
| 2007-2008
| |
|---|
| no* | %Delayed | no* | %Rapid | no* | %Delayed | no* | %Rapid | All of physicians |
|---|
| 1,405,481 | 8.8 | 498,120 | 2.54 | 2,385,690 | 7.51 | 734,601 | 2.16 |
|---|
| 45,629 | 34.3 | 14,417 | 10.84 | 101,331 | 28.99 | 32,822 | 9.39 | Cardiologist |
| 1,382 | 1 | 105 | 0.08 | 2,870 | 0.97 | 421 | 0.14 | Dermatologist |
| 10,181 | 4.46 | 1,163 | 0.51 | 19,876 | 3.49 | 2,435 | 0.43 | ENT |
| 990,502 | 8.78 | 317,847 | 2.82 | 1,527,800 | 7.53 | 499,955 | 2.46 | General practitioners |
| 13,570 | 6.84 | 6,300 | 3.18 | 30,558 | 6.12 | 9,395 | 1.88 | General surgeon |
| 18,798 | 2.22 | 9,232 | 1.09 | 28,610 | 1.97 | 15,731 | 1.08 | Gynecologist |
| 16,007 | 12.38 | 5,233 | 4.05 | 24,622 | 9.55 | 6,184 | 2.4 | Infectious disease |
| 497,652 | 16.09 | 108,637 | 2.74 | 785,614 | 12.57 | 151,502 | 2.06 | All of medical specialists |
| 127,679 | 16.42 | 48,744 | 6.27 | 181,861 | 13.59 | 47,471 | 3.55 | Internist |
| 119,345 | 58.44 | 11,128 | 5.45 | 117,739 | 32.21 | 9,017 | 2.47 | Neurologist |
| 16,866 | 16.15 | 988 | 0.95 | 33,214 | 16.09 | 2,378 | 1.15 | Neurosurgeon |
| 8,600 | 3.4 | 497 | 0.2 | 15,165 | 2.83 | 1,183 | 0.22 | Ophthalmologist |
| 16,766 | 6.19 | 872 | 0.32 | 14,284 | 2.85 | 1,547 | 0.31 | Orthopedist |
| 18,359 | 2.37 | 3,037 | 0.39 | 36,165 | 2.13 | 6,733 | 0.4 | Pediatrist |
| 70,524 | 50.39 | 4,288 | 3.06 | 155,780 | 46.03 | 9,824 | 2.9 | Psychiatrist |
| 13,946 | 10.75 | 2,633 | 2.03 | 23,539 | 9.10 | 6,361 | 2.46 | Urologist |
| Digoxin |
| Diuretics |
| HMG CoA reductase Inhibitors |
| Allopurinol |
| ACE Is |
| Warfarin |
| Gemfibrozil |
| Haloperidol |
| Amiodarone |
| Clonidine |
| Drug 2 | Drug 1 | % | no* |
|---|
| Digoxin | Furosmide | 0.11 | 74,084 |
| Captopril | Triamterene-H | 0.09 | 67,619 |
| Gemfibrozil | Atrovastatin | 0.08 | 65,103 |
| Haloperidol | Propranolol | 0.04 | 26,789 |
| Amitriptyline | Clonidine | 0.03 | 20,666 |
| Doxycycline | Penicilline G | 0.01 | 8,526 |
| Chlorpromazine | Propranolol | 0.01 | 8,049 |
| Propranolol | Verapamil | 0.009 | 6,904 |
| Amiodaron | Digoxin | 0.008 | 6,417 |
| Azithromycine | Atrovastatin | 0.007 | 5,727 |
| %Incidence per total of prescriptions | drug categories |
|---|
| 85 | Cardiovascular |
| 74 | Anti hypertensive |
| 24.78 | ACEI s |
| 34.44 | Antiarrhythmic |
| 22.63 | Digitalis |
| 30.08 | CNS drugs |
| 4 | Diuretics |
| 1 | Macrolides |
| 1 | Tetracyclins |
| 1 | Penicillins |
| Documentation | Total of prescriptions | no 2* | no 1* | Onset | Significance | Severity | Drug 2 | Drug 1 |
|---|
| probable | 74,084 | 29,901 | 44,183 | Delayed | 1 | Major | Furosemide | Digoxin |
| probable | 64,063 | 24,406 | 39,657 | Delayed | 1 | Major | Triamterene | Captopril |
| suspected | 65,083 | 29,543 | 35,540 | Delayed | 1 | Major | Atorvastatin | Gemfibrozil |
| probable | 59,640 | 27,962 | 31,678 | Delayed | 1 | Major | Triamterene | Enalapril |
| possible | 39,497 | 14,650 | 24,847 | Rapid | 4 | Major | Codeine | Cimetidine |
| suspected | 38,075 | 14,369 | 23,706 | Delayed | 1 | Major | Lovastatin | Gemfibrozil |
| possible | 26,789 | 11,679 | 15,110 | Rapid | 4 | Major | Propranolol | Haloperidol |
| unlikely | 25,205 | 11,198 | 14,007 | Delayed | 5 | Major | Hydrochlorothiazide | Allopurinol |
| probable | 21,706 | 7,919 | 13,787 | Delayed | 1 | Major | Spironolactone | Captopril |
| probable | 20,666 | 9,040 | 11,626 | Rapid | 1 | Major | Clonidine | Amitriptyline |
| probable | 11,586 | 4,703 | 6,883 | Delayed | 1 | Major | Hydrochlorothiazide | Digoxin |
| possible | 9,756 | 3,729 | 6,027 | Rapid | 4 | Major | Fluoxetine | Metoclopramide |
| suspected | 8,526 | 2,906 | 5,620 | Delayed | 1 | Major | Penicillin G | Doxycycline |
| probable | 8,326 | 3,237 | 5,089 | Delayed | 1 | Major | Spironolactone | Enalapril |
| probable | 8,049 | 3,008 | 5,041 | Delayed | 1 | Major | Propranolol | Chlorpromazine |
| suspected | 7,365 | 2,621 | 4,744 | Delayed | 1 | Major | Simvastatin | Gemfibrozil |
| probable | 6,904 | 2,509 | 4,395 | Rapid | 1 | Major | Verapamil | Propranolol |
| probable | 6,417 | 2,372 | 4,045 | Delayed | 1 | Major | Digoxin | Amiodarone |
| probable | 7,818 | 4,004 | 3,814 | Delayed | 1 | Major | Atorvastatin | Azithromycin |
| suspected | 5,991 | 2,396 | 3,595 | Delayed | 1 | Major | Nortriptyline | Cisapride |
| suspected | 6,717 | 3,488 | 3,229 | Delayed | 1 | Major | Sulfasalazine | Methotrexate |
| possible | 4,651 | 1,548 | 3,103 | Rapid | 4 | Major | Trazodone | Fluoxetine |
| suspected | 4,596 | 1,656 | 2,940 | Delayed | 2 | Major | Warfarin | Penicillin G |
| possible | 4,219 | 1,427 | 2,792 | Delayed | 4 | Major | Captopril | Allopurinol |
| probable | 4,620 | 1,913 | 2,707 | Delayed | 1 | Major | Lovastatin | Azithromycin |
| probable | 4,107 | 1,448 | 2,659 | Rapid | 1 | Major | Verapamil | Atenolol |
| possible | 5,395 | 2,764 | 2,631 | Rapid | 4 | Major | Omeprazole | Methotrexate |
| suspected | 7,266 | 4,929 | 2,237 | Delayed | 1 | Major | Naproxen | Methotrexate |
| suspected | 3,352 | 1,239 | 2,113 | Delayed | 1 | Major | Trifluoperazine | Cisapride |
| suspected | 3,510 | 1,410 | 2,100 | Delayed | 1 | Major | Propranolol | Clonidine |
| established | 3,471 | 1,450 | 2,021 | Delayed | 1 | Major | Warfarin | Aspirin |
Our findings also revealed the most alarming DDIs in prescriptions from March 21, 2007 to December 20, 2009 with significant clinical importance by incidence per 100 prescriptions as shown in
Table 5.
The study of DDIs in the present population showed that the highest DDIs with clinical importance were the antihypertensive drugs such as beta blockers, calcium channel blockers followed by ACE-Is (
Table 6).
Based on these results, the increase in DDIs in the prescriptions occurs when number of items per prescription increased, which led to a rise in the index of DDIs with clinical significance.
This study revealed that with the increase of percentage in prescriptions with more than four items per prescription in the years 2008-2009, as compared to 2007-2008 (
Figure 1), significant major DDIs in the prescriptions of all physicians, general practitioners, and medical specialists in 14 different fields significantly increased. (
Figure 2) This was clearly visible in the prescriptions of cardiologists, internists, General practitioners, infectious disease specialists and neurologists who had a greater number of items per prescription.
The percentage of prescriptions with more than four items per prescription in the years 2008-2009 as compared to 2007-2008
Major drug interactions in the prescriptions of all physicians in the years 2008-2009 as compared to 2007-2008
Polypharmacy is an important factor which leads to DDIs; however, the more the number of items per prescriptions, the more the likelihood of DDI’s occurance. Straubhaar
et al. (
25) reported in a study at the University Hospital Basel that hospitalization of patients with heart failure resulted in an increase in the number of drugs prescribed per patient and, thereby, also in the number of potentially interacting drug combinations per patient. During the hospital stay, close medical monitoring combined with continuous nursing and therapeutic care is generally guaranteed, but this may profoundly change after discharge. The elderly generally have several concurrent diseases (
26) and consequently, the number of drugs used to treat them is greater, and the greater the number of drugs, the higher the possibility of DDIs. Malone
et al. (
27), using the prescription database of a North American insurance company with 46 million clients, carried out a retrospective study of the prevalence of 25 clinically relevant interactions. They found that their clients of 70 years or more made up to 7.1% of the total population, but they suffered from 44.8% of all DDIs.
In three past studies on primary care, the rates of potential DDIs for patients receiving two or more drugs were 24.3%, 29.5%, and 42.0%, respectively (
28,
39). Another study reported 2.2% of prescriptions with adverse interacting drugs in relation to all prescriptions (
30,
31).
In another study, all drug pairs concurrently prescribed to 9481 adults aged 50 to 75 years were evaluated in a health-screening examination. More than 52% of the patients received a combination therapy of drug pairs and 881 (6.4%) were identified as interacting. Of these 881 interactions, 132 (15.0%) were of major severity and 101 of 132 (76.5%) were considered manageable. Only 31 (23.5%) of 132 major interactions (3.5% of all interacting pairs) offered no management options and should thus have been avoided (
32). The results of this study and past studies, especially on DDIs in Iran when compared to the present, showed that its percentage is rising and continues to pose problems (
33-
36).
In primary health care, 9-70% of patients are reported to be exposed to drugs with the risk of a drug interaction, with 1-23% of major significance (
37-
42). A French study reports an incidence of 27 per 10,000 prescriptions with contraindicated DDIs in an ambulatory outpatient population (
43). During hospital admission, the number of DDIs per patient increased with potential clinically relevant DDIs occurring in 1 out of 70 prescriptions (
44-
47). In another study, 22 potential DDIs of clinical relevance and 65 of ‘possible’ clinical relevance per 100 outpatients per year were recorded. Reported incidences in outpatients ranged from 9.2% to 70.3% for DDIs of any severity and from 1.2% to 23.3% for those considered of major significance (
31,
1,
48-
51).
In addition, Chen
et al. (
52) found an incidence of 1.9 per 1000 patient (95% confidence interval 1.5, 2.3) of prescribed potentially hazardous/contraindicated DDIs. They identified multiple possible causes (
e.g., lack of knowledge of the DDIs or of the patient medication history) and system failures (
e.g., incomplete medication records, lack of communication between primary and secondary care or between the prescriber and the patient) for the dispensing of contraindicated drug combinations.
Unfortunately, there are little supportive data on the incidence of potential DDIs in other large ambulatory populations. Few published studies have determined such errors exclusively, with most aggregating various types of potential medication errors.
Quite frequently, the determination of medication errors found in studies has been part of a planned intervention that might include medication selection or dosage assessment (
53-
55), laboratory monitoring (
54-
56), or inappropriate prescribing (
56,
59). Moreover, most studies on medication errors have involved interventions in hospitalized or with institutionalized patients, but not with outpatients (
54,
56,
60-
64). In the year 1988, Dumbro
et al. (
28) reported that out of the total number of DDIs they had discovered, 17% were of great significance, while in our study, we found major DDIs with significant clinical importance as shown in
Table 2. Comparing general practitioners and medical specialists, it is evident that from March 21, 2007 to December 20, 2009, more alarming DDIs were found in the prescriptions of medical specialists (
Figure 3). The same observation was made when we compared the prescriptions resulting in major DDIs of clinical importance (
Figure 4). It seems that medical specialists deal more with potent drugs with a low therapeutic index that might be a cause of more DDIs in their prescriptions.
Major drug interactions with significant clinical importance in the prescriptions of general and specialist practitioners
Major drug interactions with significant clinical importance in the prescriptions of all physicians in the years 2008-2009 as compared to 2007-2008
Abundance of drug categories in the DDIs
The results of our study also revealed that the most common drugs associated with major interactions of significant clinical importance were those prescribed by cardiologists. Previous studies have also shown that prescriptions of cardiologists had the highest rate of DDIs (
65). With regard to the interactions detected, other studies without intervention by pharmacists found more DDIs in the fields of cardiology (27.9%), hematology (23.4%), neurology (2.7%), psychiatry (5.3%), and gastroenterology (5.1%). In addition, 151 DDIs were detected during the three-month follow-up period. The interactions found most frequently were: digoxin-furosemide, furosemid-corticoid, AAS-low molecular weight heparin, amiodarone-furosemide, omeprazole-diazepam, phenytoin-corticoid and AAS-oral antidiabetics (
65,
66), while in our study, we found that the most common interacting combination prescribed were: digoxin-furosmide, captopril-plustriamteren, gemfibrozil-atorvastatin, enalapril-triamteren, cimetidine-codeine, gemfibrozil-lovastatin, and haloperidol-propranolol.
Shivo
et al. (
67) in the year 2000 carried out a study in Finland that showed harmful interactions between over the counter (OTC) drugs (especially NSAIDs and analgesics) and prescription drugs. This shows that DDIs do not solely occur with prescription drugs, but food and other OTC drugs purchased and consumed by patients also play a role and could sometimes be responsible for treatment failure.