INTRODUCTION:

Epilepsy is one of the most common neurological disorders encountered worldwide¹. It is estimated that 50 million people worldwide have epilepsy and 80% of epilepsy cases are in developing countries². Annual incidence of epilepsy in India is approximately 27.3/100,000 per year³. Treatment with anti epileptic drugs (AEDs) is generally chronic, and may be associated with significant metabolic effects including decreased bone mass and increased fractures^4,5. Association of bone abnormalities with chronic AED therapy was described approximately four decades ago^{6, 7}.

The low bone mass associated with AED treatment is largely unrecognized, undetected, and untreated^4,5.

Enzyme inducing AEDs are the most common drugs having deleterious effects on bone health 8, but non-enzyme-inducing AEDs like valproate⁸ and newer AEDs⁹ also have adverse effect on bone metabolism.

AEDs have been identified as an independent risk factor for low bone density and osteoporosis¹⁰. Osteoporosis is characterized by low bone mass and decreased bone strength that lead to increase in fracture risk¹¹.

Although many studies have shown an increased risk of bone fractures associated with AEDs, but most of these are conducted outside India. We did not find any study conducted in India, which has included biochemical parameters of both bone formation and bone resorption. Also there are controversial data regarding the level of vitamin D and its metabolites during antiepileptic therapy. Vitamin D deficiency has not been seen in all studies, which document bone disease in patients treated with AEDs^12-14. The present study was done to know the biochemical changes in bone metabolism in patients who are on antiepileptic therapy.

MATERIAL AND METHODS:

This case-control study was conducted at a tertiary care hospital in south India in June 2010. 80 patients and 20 controls, aged 20 to 40 years were enrolled for the study. The study was approved by Institutional Ethics Committee and informed consent was taken from all the patients. The information was obtained from the patients who were on AEDs attending Neurology out patient. The detailed history from all the patients was obtained. All patients who were using AEDs for at least one year were included in the study. Patients were excluded if they had abnormal liver, renal or thyroid function tests, pregnant and lactating, premature menopause, known risk factors for decreasing bone density, like heavy cigarette smoking, diseases or medications¹⁵ known to influence calcium metabolism or bone mass.

The patients were instructed to fast overnight. Next day morning blood and urine samples were collected for analyzing bone biochemical markers. The following seven markers were measured to determine the risk of fractures namely serum calcium, serum phosphorous and 25(OH) D levels, bone formation markers - BSAP(Bone specific alkaline phosphatase) and osteocalcin, bone resorption markers - C-telopeptide and urinary hydroxyproline.

Descriptive statistical analysis has been carried out in the present study. Student t test/Chi-square test has been used to find the significance of homogeneity of study characteristics between two groups of patients. Student t test (Unpaired, two tailed) has been used to find the significance of study parameters between two groups. Data was analyzed using SPSS (version 18). The P value was interpreted as follows

+Suggestive significance 0.05<P<0.10

*Moderately significant 0.01<P<0.05

**Strongly significant P<0.01

RESULTS:

In this study, 80 cases and 20 controls were included. The baseline data of cases and controls is shown in table 1.

Table 1: Baseline characteristics of patients and controls

Characteristic	Patients (n=80)	Controls (n=20)	P-value
Age in years*	31.04±7.49	28.25±6.84	0.134
Gender (M:F)	26:54:00	12:8	0.112
BMI (kg/m²)*	24.4±3.6	25.6±3.9	0.19
Duration of therapy*	4.26±2.63	-	-
Type of seizures
Generalized	46(57.5%)	-	-
Focal	34(42.5%)	-	-

*Mean±SD; No statistically difference was seen between the groups.

The use of various AEDs and number of patients on mono/poly therapy is shown in table 2

Table 2: Use of anti epileptic drugs

Drug therapy	Number	Percentage
Monotherapy	56	70
Polytherapy	24	30
Enzyme inducing drugs	42	52.5
Non-Enzyme inducing drugs	16	20
Enzyme +Non Enzyme inducing drugs	10	12.5
New drugs	6	7.5
Enzyme inducing + new drugs	6	7.5

Most common enzyme inducing drug was carbamazepine, followed by phenytoin. Most common non enzyme inducing drug used was valproic acid, followed by ethosuximide. Most common new drug used was lamotrigine.

DISCUSSION:

Osteoporosis is a common condition with major public health and economic implications¹⁶. The findings of the present study document that AED therapy is associated with changes in bone biochemical markers which may predispose to development of osteoporosis. Bone biochemical abnormalities have been described in previous studies which include hypocalcaemia, hypophosphataemia, and elevated alkaline phosphatase^17,18. Another concern is the rapid increase in utilization of these medications for other indications like bipolar disorder.

In the present study changes in all the biochemical markers were statistically significant in cases when compared with controls (table 3). In absence of other factors such as reduced dietary intake and vitamin deficiency, these findings reflect increased bone turnover associated with AEDs. When gender comparison was done among the biochemical markers, only bone specific alkaline phaosphatase and serum phosphorus showed a statistically significant difference (table 4). It is postulated that Women with epilepsy are more vulnerable because of low bone mineral density (BMD), when compared to males¹⁹.

Table 3: Comparison of study parameters between case and controls

Study parameters	Controls	Cases	Pvalue
Serum calcium (mg/dl)	9.94±0.48	8.67±1.09	<0.001**
Serum Phosphorous (mg/dl)	3.59±0.27	3.24±0.45	<0.001**
BSAP (U/L)	11.11±2.76	16.04±4.49	<0.001**
25 (OH) D levels (ng/ml)	34.10±4.68	28.79±9.51	0.018*
Osteocalcin (ng/ml)	7.94±1.82	11.62±4.51	<0.001**
C-Telopeptide (pg/ml)	352.78±36.73	473.19±41.23	<0.001**
Urine Hydroxyproline (mg/24hr)	26.95±5.97	38.29±15.28	<0.001**

BSAP= Bone specific alkaline phosphatase; * Moderately significant; ** Strongly significant; All the biochemical parameters were statistically significant in cases when compared with the controls.

We did not find any recent studies which have documented the gender differences in bone biochemical markers. In a study 12, patients on AEDs had accelerated bone turnover with elevated markers of bone formation and bone resorption. However, only the women showed biochemical signs of vitamin D deficiency. In the same study¹² decreased urinary deoxypyridinoline levels were seen in male patients receiving multiple AEDs but not in women or with use of single AED.

Gender wise comparison of bone biochemical markers is shown in table 4.

Table 4: Comparison of study parameters between gender in cases

Study parameters	Male	Female	P value
Serum calcium (mg/dl)	8.41±1.14	8.79±1.05	0.155
Serum Phosphorous (mg/dl)	3.10±0.54	3.29±0.38	0.072⁺
BSAP (U/L)	19.02±4.17	14.76±4.01	<0.001**
25 (OH) D levels (ng/ml)	30.07±11.26	28.25±8.71	0.437
Osteocalcin (ng/ml)	11.60±4.58	11.20±4.46	0.205
C-Telopeptide (pg/ml)	489.92±48.02	466.39±43.04	0.366
Urine Hydroxyproline (mg/24hr)	42.29±15.05	36.57±15.18	0.126

BSAP= Bone specific alkaline phosphatase + Suggestive significance, ** Strongly significant P<0.01; All the biochemical parameters were not statistically significant except for serum phosphorus and BSAP.

Biochemical markers were compared between patients on monotherapy and polytherapy (table 5). There was a statistically significant difference between serum calcium and phosphorus levels, C-telopeptide levels in the polytherapy group. This is in accordance with the other studies which have has shown polytherapy is associated with a higher risk of bone metabolism abnormalities than is monotherapy. Polypharmacy also has been identified as a risk factor for low bone mass in adult patients^20-22.

The AEDs most commonly associated with altered bone metabolism and decreased bone density are inducers of the cytochrome P450 enzyme system, including phenytoin, carbamazepine, primidone and phenobarbital^11,12,16,17. In the present study, most commonly prescribed drugs were enzyme inducing (52.5%), and the most common enzyme inducing drug prescribed was carbamazepine followed by phenytoin. But we did not find out the exact relationship between the individual drug or drug group on bone biochemical markers.

Table 5 shows the comparison of biochemical markers between monotherapy and polytherapy patients.

Table 5: Comparison of study parameters between Mono and poly therapy in cases

Study parameters	Monotherapy	Polytherapy	P value
Serum calcium (mg/dl)	8.81±1.18	8.34±0.72	0.076⁺
Serum Phosphorous (mg/dl)	3.31±0.46	3.07±0.38	0.029*
BSAP (U/L)	15.94±4.31	16.26±4.97	0.769
25 (OH) D levels (ng/ml)	30.27±10.28	25.35±6.34	0.033
Osteocalcin (ng/ml)	11.43±4.59	12.07±4.39	0.565
C-Telopeptide (pg/ml)	456.91±43.05	513.12±49.89	0.021*
Urine Hydroxyproline (mg/24hr)	36.71±15.69	41.96±13.89	0.161

BSAP= Bone specific alkaline phosphatase

+ Suggestive significance, * Moderately significant ; Serum calcium and phosphorus, C-Telopeptide levels had statistically significant difference, all other parameters were not statistically significant.

Controversy exists regarding interpretation of biochemical markers of bone metabolism, some authors opine that elevated bone turnover markers are associated with an increased risk of fracture, independently of BMD²³. While other authors opine that “monitoring of these markers demonstrated a rapid response to treatment, compared to the standard BMD measurement These biochemical markers can be used as a supplementary evidence for a more severe disorder of BMD”^{24, 25}. Their utility in clinical practice is unclear, but can be used for monitoring excessive bone remodeling and response to treatment. Biochemical markers can also be used for early detection of bone changes because biochemical differences are observed as early as three months, whereas radiological changes are seen between one and three years²⁶.

The strength of the present study is we have evaluated the normal minerals (calcium and phosphorus) along with markers of both bone formation and resorption, which is done in very few studies in India.

LIMITATIONS OF THE STUDY:

The present study has certain limitations, it was a case controlled study with a small sample size, we did not evaluate the individual drugs causing biochemical changes and bone mineral density. Future studies should be prospective longitudinal studies with large sample size and should measure biochemical markers before and after initiation of therapy.

CONCLUSION:

Antiepileptic drugs appear to have negative influence on bone metabolism, there was a significant association between AED use and change in biochemical markers, which may increase the risk of fracture. AED therapy may be a modifiable factor in bone heath. Identifying an individual AED which causes change in biochemical markers of bone metabolism may prevent risk of fracture. Further multicentre prospective studies are needed to know the association of AED and altered bone metabolism, especially in presence of risk factors that also may contribute to the disease. Physicians should consider a monitoring schedule for patients on antiepileptics, especially if they have other risk factors that contribute to bone disease.

ACKNOWLEDGEMENT:

We authors thank the participants of the study.

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Received on 14.09.2013 Modified on 10.10.2013

Research J. Pharm. and Tech. 6(11): November 2013; Page 1237-1239